analysis and improvements of a flow calibration system

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Analysis and Improvements of a Flow Calibration System Mechanical Engineering Programme

Bachelor Project-Report

VIA University College Denmark

Author: Javier I. Camacho (164649)

Supervisor:Klaus Gnter Bahner

Date: 12/12/2014Number of Characters:105665

2014


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Javier I. CamachoAnalysis and Improvements of a Flow Calibration System

Mechanical Engineering Programme

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Table of Content

Executive Summary ...................................................................................................... 10

1 Introduction ............................................................................................................ 13

1.1 Relevant Definitions .................... ..................... ....................... ............. 13

1.2 Specification of Purpose ..................... ..................... ...................... ....... 17

1.3 Problem Formulation ...................... ...................... ..................... ........... 18

1.4 Delimitations ........................................................................................ 19

2

General Aspects of the Flow Calibration System ............................................... 21

2.1 Measurement Method ...................... ..................... ..................... ........... 21

2.2 Process Work Flow Chart of the Calibration System ...................... ....... 22

2.3 Phase I (Sample Preparation) ....................... ..................... .................. 23

2.4 Phase II (Flow Generation) ..................... ..................... ...................... ... 29

2.5 Actual Flow Generation Methods .......................................................... 32

2.6 Fluid Flow Generation (by Syringe Pump) .................... ..................... ... 32

2.7 Fluid Flow Generation (by Compressed Air) ........ ....................... .......... 34

3 Performance Analysis of the Degasification Process ........................................ 36

3.1 Quantification of the Degasification Process ................... ...................... 36

3.2 Expected Vacuum Pump Performance ................. ..................... ........... 38

3.3 Vacuum Pump Performance Test ......................... ...................... .......... 39

3.4 Sample Tank Strength Analysis ..................... ..................... .................. 40

3.5 Conclusions of the Degasification Process System ..................... .......... 43

4 Analysis of the Fluid Flow Generation Methods ................................................. 45

4.1 Purpose ............................................................................................... 45

4.2 Flow Generation by Syringe Pump ............ ..................... ...................... 47


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4.3 Flow Generation by Compressed Air ..... ....................... ..................... ... 56

4.4 Resume of Actual Flow Generation Methods ..................................... ... 65

5 Flow Rate Stability Analysis ................................................................................. 68

5.1 Short Term Stability Analysis ...................... ..................... ..................... 69

5.2 Long Term Flow Stability Analysis .................... ...................... .............. 80

6 Ideas Generation .................................................................................................... 88

6.1 Idea Generation Criteria ...................................... ....................... .......... 88

6.2 Ideas Generation Process ................................... ....................... .......... 90

6.3 Ideas Selection Process ...................................... ....................... .......... 95

6.4 Improvements in Fluid Flow Calibration System.............. ...................... 96

6.5 Expected Short Term Stability of the Fluid Flow ..................... ............ 102

6.6 Expected Long Term Stabilityof the Fluid Flow .................... ............ 103

6.7 Economics ......................................................................................... 104

7 Conclusions .......................................................................................................... 106

7.1 Actual System Performance ................................ ............................... 106

7.2 Improvements in the Actual System ...................... ...................... ........ 108

8 Appendices ........................................................................................................... 109

8.1 Appx. Section I (Introduction) ............................................................. 109

8.2 Appx. Section II(General Aspects Calibration System) ........................ 109

8.3 Appx.Section III(Analysis of the Degasif ication) .................................. 109

8.4 Appx. Section IV(Analysis of the Flow Generation Method) ................ 109

8.5 Appx. Section V (Flow Rate Stability Analysis) ................................... 109

8.6 Appx.Section VI(Improvements Calibration System) ........................... 109


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9 Sources, References and Literature ................................................................... 110


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Table of Figures and Tables

Figure 1(Metrological Traceability Chain)(O'Connor 2014) ............................................ 14

Figure 2(Smart Intravenous Infusion Pump) (Rothschild 2014) ...................................... 15

Figure 3 Fluke IDA 5 plus (DUT)(Fluke ) ........................................................................ 16

Figure 4Project Objective Tree ...................................................................................... 17

Figure 5Problem Formulation ........................................................................................ 18

Figure 6 Calibration Traceability ..................................................................................... 21

Figure 7 Process Work Flow Chart of the System.(Microsoft 2013) ............................... 22

Figure 8 Degasification System ...................................................................................... 24

Figure 9 Effect of Air dissolved in Water Density at Different Temperatures ................. 26

Figure 10 Gas Bubble Trapped in a tube ........................................................................ 26

Figure 11Vacuum Pump (Busch) .................................................................................... 27

Figure 12 On-Off Valve(Swagelok ) ................................................................................ 28

Figure 13 Sample Fluid Tank .......................................................................................... 28

Figure 14 (3-Way) Valves(Swagelok ) ............................................................................ 28

Figure 15 Fluid Flow Pattern ........................................................................................... 29

Figure 16 Regimens of Fluid Flow (White ) .................................................................... 31

Figure 17 Laminar Flow (White )..................................................................................... 31

Figure 18 Turbulent Flow (White ) .................................................................................. 31

Figure 19 Fluid Flow Generation (by Syringe Pump) ................................................. 32

Figure 20 Syringe Pump (World Precision Instrument ) ................................................. 33

Figure 21 Scale (Sartorius ) ............................................................................................ 33

Figure 22 Needles Gauge ............................................................................................... 33

Figure 23 Flow Generation(by Compressed air) ............................................................ 34

Figure 24 Gases Dissolved in Water (at 101.325 kPa) ................................................... 37

Figure 25 Gases Dissolved in Water (at 23.4mbar) ........................................................ 37

Figure 26 Gases Dissolved in Water .............................................................................. 39

Figure 27 Tank Model (Autodesk 2015) .......................................................................... 40

Figure 28 Sample Tank Top ........................................................................................... 40

Figure 29 Sample Tank Knobs ....................................................................................... 42

Figure 30 Sample Tank Fitting ........................................................................................ 42

Figure 31 Molded Knobs ................................................................................................ 42

Figure 32 Air Inlet Fitting ................................................................................................ 42

Figure 33 Data Scatter Plot (15mL/hr) (Mathworks 2014) .............................................. 47
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Figure 34 Non-Linear Regression and Residuals Plot. (Mathworks 2014) ..................... 48

Figure 35 Residual Plot(15mL/hr) ................................................................................... 49

Figure 36 Residual Periodrogram (15mL/hr) .................................................................. 49

Figure 37 Residuals Histogram(15mL/hr) ....................................................................... 49

Figure 38 Normal Curve Fitting Plot (15mL/hr) .............................................................. 50

Figure 39 Density Plot Histogram(15mL/hr) .................................................................. 50

Figure 40 Syringe Pump Flow Behaviour ....................................................................... 51

Figure 41 Fluid Flow Stability [15mL/hr] ......................................................................... 52

Figure 42 Raising Time Analysis [15mL/hr] .................................................................... 53

Figure 43 Flow Generation(by Syringe Pump) ................................................................ 53

Figure 44 Scatter Plot (60mL/hr) .................................................................................... 56

Figure 45 Linear Regression Plot (60mL/hr) ................................................................... 57

Figure 46 Residual Plot (60mL/hr) .................................................................................. 59

Figure 48 Normal Curve Fitting Residuals (60mL/hr) ..................................................... 59

Figure 48 Normal Curve Fitting (60mL/hr) ...................................................................... 60

Figure 49 Density Plot (60mL/hr) .................................................................................. 60

Figure 50 Flow Generation System (by Air) .................................................................... 61

Figure 51 Regasification Diagram................................................................................... 61

Figure 52 Total Concentration in Water in Function on Depth (PTC 2011) .................... 63

Figure 53 Flow Rate Stability Approach ......................................................................... 68

Figure 54 TUR 1:1{{ Bennett.K}} ..................................................................................... 69

Figure 55 TUR 4:1{{ Bennett.K}} ..................................................................................... 69

Figure 56 TUR 10:1{{ Bennett.K}} ................................................................................... 69

Figure 57 Estimation of Maximum Fluctuations ............................................................. 70

Figure 58 Maximu Fluctuations vs % Uncertainty ........................................................... 71

Figure 59 Pressure Drop Diagram .................................................................................. 72

Figure 60 DTU Mode #1.................................................................................................. 73

Figure 61 DTU Mode #2.................................................................................................. 73

Figure 62 Short Term Stability Approach Diagram ......................................................... 74

Figure 63 Long Term Flow Stability (System Diagram) .................................................. 80

Figure 64 Calibration Time Approach ............................................................................. 81

Figure 65 Water Column Effect Diagram ........................................................................ 82

Figure 66 Water Column Effect Calculation Approach ................................................... 83

Figure 68 Water Column Effect Resume ........................................................................ 85

Figure 68 Factor tha Affect Vacuum Degasification ....................................................... 88

Figure 69 Flow Generation Alternatives Diagram ........................................................... 91
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Figure 70 Flow Control Alternative Diagram ................................................................... 91

Figure 71 Piston Pump Working Principle (Car-May) ..................................................... 92

Figure 72 Car May Piston Pump Module (Car-May) ....................................................... 92

Figure 73 Piston Pump Flow Stability(Car-May) ............................................................ 92

Figure 74 Pressure Controller (ElveFlow OB1 Mk3) ....................................................... 94

Figure 75 Pressure Controller Pressure Stability ........................................................... 94

Figure 76 Pressure Controller(Pressure Profiles) ........................................................... 94

Figure 77 Vacuum Pump nXDS6i Edwards .................................................................... 95

Figure 78 Pressure Controller (OB1 Mk3) ...................................................................... 95

Figure 79 Improvements System Diagram...................................................................... 96

Figure 80 Improvements Degasification System ............................................................ 97

Figure 81 Vacuum Pump ................................................................................................ 98

Figure 82 3-way Valve (NW25) ....................................................................................... 98

Figure 83 Exhaust Silencer ............................................................................................. 98

Figure 84 NW25 Adapter ................................................................................................ 98

Figure 85 Clamp NW25................................................................................................... 98

Figure 86 Hose (1/2 in) ................................................................................................... 98

Figure 87 NW25 Hose Adapter ....................................................................................... 98

Figure 88 Centering Ring ................................................................................................ 98

Figure 89 Improvements in Flow Generation System .................................................... 99

Figure 90 Pressure Controller OB1 MkIII(Elveflow ) ..................................................... 100

Figure 91 Pressure Source Connections(Elveflow ) ..................................................... 100

Figure 92 Gas Cylinder ................................................................................................. 100

Figure 93 Mechanical Pressure Regulator .................................................................... 100

Figure 94 Reducing Adapter(Swagelok ) ...................................................................... 100

Figure 95 Reducer(Swagelok ) ..................................................................................... 100

Figure 96 PFA Tubing(Swagelok ) ................................................................................ 100

Figure 97 Male Luer-Lock ............................................................................................. 100

Figure 99 Expected Short Term Fluid Flow Stability ..................................................... 102

Figure 99 Pressure Controller Pressure Profile (Elveflow ) .......................................... 103

Figure 100 Cost Estimated of the Improvements.......................................................... 104
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Acknowledgements

I would like to express my gratitude to my supervisor, Mr. Klaus Gnter Bahner,

for his excellent guidance, patience, and providing me the tools to improve many

skills during this project for my future professional life.

I would like to thank DTI (Danish Technological Institute) to give me the opportunity

to work in this project.

Many thanks to the companies ElveFlow and Car-May to provide relevant

information and guidelines about their products.

I also would to thank to my friend and colleague Stiina who helped me to improve

some technical skills.

I would never have been able to finish my project without the help and support of

my family from Denmark and Uruguay.

Finally, I would like to thank my girlfriend Helena. She was always there cheering

me up and stood by me through the good times and bad.


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Analysis and Improvements of a Flow Calibration System

Mechanical Engineering Bachelor Project

When you can measure what you are speaking about and express it

in numbers, you know something about it; but when you cannot

express it in numbers, your knowledge is of a meagre and

unsatisfactory kind. It may be the beginning of knowledge, but you

have scarcely, in your thoughts, advanced to the stage of science.

(William Thomson, 1st Baron Kelvin, GCVO, OM, PC, PRS, 26 June 1824 17

December 1907; A.K.A. Lord Kelvin).

Executive Summary

The report, in the sections I and II, is a detailed description of the general aspects

of the flow calibration system and a specification of the main purpose of the

components that is incorporated in the system. This information is necessary in

order to present the scenario of the project, and to lay foundations for further

decisions.

In order to solve and understand the two main problems of the system, which are

the presence of gas bubble and the fluid flow rate stability (from 1mL/hr to 6L/hr),

an investigation of the actual performance is described in the sections III, IV, V.

The results of this analysis shows that there is a problem in the actual performance

of the vacuum pump that affect the level of the degasification which increase the

probability of gas bubbles formation. Furthermore, traces of oil were found in the

sample fluid tank.

The analysis of the behaviour of the flow rate for the two different flow generation

methods that are in use (syringe pump/Compressed air), suggests that the flow

rate stability of both systems is affected by different parameters but they have a

common point which is the needle gauge dimension. The selection of the needle

gauge for the different flow rates contribute to the flow rate stability. From the

calculation can be assumed that this is directly related to the pressure drop at the

needle. The lower pressure drop at the needle means more sensibility of thesystem to small changes in pressure.


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The data analysed from the syringe pump method to generate flow at the specific

flow rate of 15 mL/hr, shows that the pump contributes to the flow rate stability

with a sinusoidal effect, due to the mechanical principle (rotating spindle) that is

incorporated in the pump to generate the flow. The results from the data analysed

from the compressed air method to generate flow at the specific flow rate of 60

mL/hr, shows a completely different behaviour, the flow rate has a decreasing

linear tendency. The causes of this effect could be attributed to the water column

effect and the lack of pressure control of the mechanical pressure regulator due to

the low flow. In this particular case the water column effect can be rejected from

the equation considering the small amount of pressure change that the small

dispensed volume generates, but cannot be extrapolated to the rest of the flow

rate range and also depend of the needle gauge selection.

The last section of the analysis is focused on the determination of a suitable flow

rate stability. The maximum instantaneous fluctuation is assumed at 0.3% of the

average reading.

The section VI describes the suggested changes in the system in order to improve

the actual performance. The main improvement in the degasification process isthe dry vacuum pump. This pump allow to achieve a vacuum level of 23.4mbar

that is considered the required vacuum level to satisfy the adequate fluid sample

degasification level. The fact that the pump is not operating with oil eliminates the

potential source of contamination of the fluid sample and reduces the cost of

maintenance and oil disposal. The improvement in the flow generation system is

the incorporation of a pressure controller with an expected pressure stability

performance below 0.3% of the average reading. The advantages of this controller

are that it compensates the long term stability by creating a custom pressure profile

and possibility of future improvements. The final estimated budget exceeds in

24.2% the initial expected amount of 50000 kr, but is considered justified by the

improvements in the actual system and the potential of future development.


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Section I

Introduction


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1 Introduction

Measurements are part of our daily life and play a very important role in it.

Metrology is the science of measurements and the National Metrology Institutes

around the world make sure that the used measurement confidence is fit for the

specific purpose.

The calibration of fluid flow measurement devices is a key procedure used to

ensure accurate measurement.

An example of devices that are required to be calibrated is infusion pumps in which

the amount of substances administered in health treatments need to be undercontrol. That reveals the importance of the quality of the calibration reference

system.

1.1 Relevant Definitions

In the initial stage of the project, a literature study is performed with the main

purpose to get new knowledge and try to understand the concepts behind

calibration and the terminology. The concepts that are considered relevant and the

formal definitions of the medical device involved, are defined in the following

section.

Calibration

Calibration is the process of comparing a measuring instrument against an

authoritative reference (Standard Reference Instrument or Procedure) to identify

any bias or systematic error in the readings.

Generally, a calibration will be performed by repeating the process of comparison

at a representative selection of points across the measurement range (usually the

range is divided in 10 equals intervals, but this will depend on the application of

the instrument and the specific measurement interval).


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Importance of Calibration

The primary reason for calibrating is based on the fact that even the best

measuring instruments cannot maintain absolute stability, in other words, they driftand lose their ability to give accurate measurements.

Environmental conditions, elapsed time and type of application can all affect the

stability of an instrument. Even instruments of the same manufacturer, type and

range can show varying performance. One unit can be found to have a good

stability, while another performs differently.

Other good reasons for calibration are:

To maintain the credibility of measurements

To maintain the quality of process instruments at a good-as-new level

ISO9001, other quality systems and regulations.(Raimo 2012)

Metrological Traceability

According to the International Organization for Standardization publicat ion entitled

International Vocabulary of Metrology- Basic and General Terms in Metrology:

Metrological traceability is a property of a measurement result whereby the resultcan be related to a reference through a documented unbroken chain of

calibrations, each contributing to the measurement uncertainty.(BIPM 2008)

Figure 1(Metrological Traceability Chain)(O'Connor 2014)


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Medical Devices with a measuring function (Class I)

Medical Devices with a measuring function must be designed and manufactured

in such a way as to provide sufficient accuracy and stability within appropriatelimits of accuracy and taking account of the intended purpose of the device. The

limits of accuracy must be indicated by the manufacturer. (European Commission

1993, Public Health European Commission 2014)

Infusion Pump

An infusion pump is defined as

a medical device with

measuring functions and with

specific quality control

requirements that need to be

fulfilled. The fluid flow meter

incorporated in the infusion

pump is not a direct device

involved in the fluid flow meter

calibration system, but it is

placed at the end of the metrological traceability chain.

Since the system is used to calibrate medical devices, the quality control of the

process is important because the lack of this can lead to serious injuries or even

death (e.g. administration of drugs, like anaesthesia)

An external infusion pump is a medical device used to deliver fluids into a patients

body in a controlled manner. There are many different types of infusion pumps,

which are used for a variety of purposes and in a variety of environments. Infusion

pumps may be capable of delivering fluids in large or small amounts, and may be

used to deliver nutrients or medications such as insulin or other hormones,

antibiotics, chemotherapy drugs, and pain relievers. Some infusion pumps are

designed mainly for stationary use at a patients bedside. Others, called

ambulatory infusion pumps, are designed to be portable or wearable. (U.S.

Department of Health and Human Services 2014)

Figure 2(Smart Intravenous Infusion Pump) (Rothschild 2014)


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Hospital Working Reference

The calibration of the fluid flow meter that is incorporated in the infusion pump is

performed by comparing the measurement against the Hospital WorkingReference (DUT (Device Under Test)). The Hospital Working Reference, or a

precision flow meter, are the devices that is required to be calibrated to the

Standard Reference System.

Example of hospital working reference (DUT) and technical specifications:

Fluke IDA 5 plus

Technique: Calculated by measuring a volume over time

Range: 0.1 ml/h to 1500 ml/h (2600 ml/h is shown)

Accuracy: 1 % of reading 1LSD for flows of 16 ml/hr to 200 ml/hr for

volumes over20 ml; otherwise, 2 % of reading 1 LSD after delivery of 10

ml.Accuracy 1500 ml/hr not specified.

Figure 3 Fluke IDA 5 plus (DUT)(Fluke )

Information about the hospital working reference in the Appx. Section I (Introduction)


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1.3 Problem Formulation

Figure 5Problem Formulation

1.3.1 Degasification Process System

In order to achieve a suitable degasification to avoid the presence of gas bubbles

and ensures the fluid sample quality, the system should fulfil certain requirements.

Regarding this point some sub problems arose:

Which are the requirements that the vacuum pump needs to fulfil?

What is the actual vacuum pump performance compared to the expected?

Is the actual vacuum pump the most suitable for the water degasification

in calibration purpose?

1.3.2 Fluid Flow Generation Process

The stability of the generated fluid flow is important in order to eliminate or reduce

the potential source of error that can contribute in the final uncertainty result of the

measurement procedure, so this approach leads to a few questions:

What is the actual performance of the two different methods that are used

for the fluid flow generation?

Why are two different methods required to achieve the entire fluid flow

range?

Why does the fluid flow have a tendency to drop?

Which are the sources of fluctuations?

How is the flow rate in the actual configuration regulated?


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1.4 Delimitations

1.4.1 Improvements in the Fluid Flow Generation System

Considering the wide flow rate range from 1 mL/hr (16.67L/min) to 6L/hr

(100mL/min) and the difficulty that this involve, the option of splitting the flow

rate range is acceptable, if it is not possible to combine the entire flow range in

one integrated system.

The expected performance of the system regarding the specifications

requirements will be based in the calculations and in the suggested

improvements.

The project budget for the possible improvements is estimated in 50.000 kr.


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Section II

General Aspects of the Flow Calibration System


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2 General Aspects of the Flow Calibration System

2.1 Measurement Method

Figure 6 Calibration Traceability

The calibration of the Working Reference of the Hospital to the Standard

Reference is performed by an Indirect Measurement Method of the volumetric fluid

flow rate. The term indirectly refers to the fact that the volumetric fluid flow rate is

the result of mathematical operations and corrections of the measurand

(mass/time) and not a direct measurement of the volumetric flow rate.

This method is called Gravimetric/Weighing, which is the weighing of the mass

of water in a period of time with a precision scale. The volumetric flow rate is

calculated based on the results of the mass as a function of time, considering the

contribution of all the parameters that affect this measurement.

It is possible to see the list of these parameters and how the calculation of the

uncertainty is performed in the uncertainty budget example. (CMD, DTI 2013).

(See Appx. Section II (General Aspects Calibration System))

Importance of the Gravimetric/Weighing Method

The Gravimetric/Weighing Method, is the factor that introduces the metrological

traceability in the measurement procedure, considering that the precision scales

are calibrated to a mass authority reference.

Furthermore, this mass authority reference also has traceability to a higher level

(Lower Measurement Uncertainty Level) in the metrological traceability chain.


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2.2 Process Work Flow Chart of the Calibration System

Figure 7 Process Work Flow Chart of the System.(Microsoft 2013)

This part of the section is intended to describe the system and find the answers of

the following questions:

How does this system work?

Why is it important to have degasification?

What is the physics involved in the degasification process?

What type of fluid flow pattern is the system dealing with?

The calibration process is implemented through two main phases or steps:

Phase I (Sample Preparation)

Phase II (Flow Generation & Measurement Process)


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2.3 Phase I (Sample Preparation)

In order to perform a calibration and fulfil the specific quality requirements for a

calibration laboratory ((ISO 2005) (ANSI 2013)), several steps and specific

laboratory working conditions need to be satisfied.

Laboratory Working Conditions

A laboratory is a controlled environment, which means that among other things it

should be free of dust sources and have no direct sunlight.

The temperature and relative humidity are controlled to keep them within a

specified range. The atmospheric air pressure is constantly monitored in order to

calculate the buoyancy effect in the mass measurement and to evaluate its

contribution in the final result (see table 1). (See Appx. Section II (General Aspects

Calibration System)( DTI Uncertainty Budget Example))

Laboratory Working Conditions

Air Temperature Range: 19-23 CUncertainty:

0.3C

Gradient and change over

1 hour:1C (worst case)

Air Relative Humidity Range: 20-70 %rh Uncertainty: 5%rhGradient and change over

1 hour:5% (worst case)

Air PressureRange: 970 - 1060

mbar

Uncertainty: 1

mbar

Gradient and change over

1 hour:1mbar (worst

case)

Table 1(Laboratory Working Conditions) (CMD, DTI 2013)

Water Supply

The fluid sample is tap water. The water is introduced into the fluid sample

container (or sample reservoir) by the means of a beaker. The procedure of

supplying the water into the sample container is by pressure difference between

the beaker (atmospheric pressure) and the reservoir tank (vacuum).


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Temperature Stabilization

The temperature stabilization procedure consists in waiting the required time in

which the fluid sample (tap water) will reach the equilibrium temperature regardingthe laboratory condition. The time of this stabilization process will depend on the

temperature difference between the water from the tap and the laboratory

conditions. This stabilization is important considering that the temperature of the

sample will affect the density of the water.

Degasification

There are many procedures to

achieve water degasification, in

this case it is performed by

vacuum degasification process.

The procedure is to lower the

boiling of the liquid by lowering the

pressure above the liquid. That

pressure reduction is achieved by

using a rotary vane vacuum pump

(BuschPB0004).

This method compared to for

example heating the water until

the boiling point, has the

advantages that the fluid

temperature is maintained almost

constant, assuming there is no

heat transfer from the vacuum

process compared to the heating

process.Figure 8 Degasification System


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Importance of Degasification

Water Density Change Effect

The standard properties for water are typically referred for pure water. In real

situations like in the laboratory the water is in contact with atmospheric air.

Therefore, the influence of the dissolved air on the properties of water are relevant

in order to ensure the accuracy of the measurement process. (Harvey.A, Kaplan.S

& Burnett.J 2005, Friend.D, Harvey.A 2004).The effect of the change in density

due to the dissolved air and temperature can be corrected by an equation showed

in the figure 9. (Harris 2012)

Figure 9 Effect of Air dissolved in Water Density at Different TemperaturesGas Bubble Formation

The gas bubble formation

increases the importance of the

degasification. It is necessary to

avoid the presence of air

bubbles that stick to the surface of the tube submerged at the measurement beaker

placed on the scale (CMD, DTI 2013). The gas bubbles can cause flowdisturbances and pressure fluctuations, resulting in flow rate instability (IDEX

Health & Science 2014a). Another important effect of the presence of gas bubbles

in the measurement system is that these bubbles act as capacitance producing an

increment in the time responds in the fluid flow generation.(Plecis.A, Velv.G &

Bertholle.F).The degasification is a key procedure in order to eliminate or minimize

the risk of gas bubble formation as the formation of these is a potential source of

error during a calibration procedure. The above figure shows a gas bubble trapped

in a micro-tube.

994

996

998

1000

1002

0 5 10 15 20 25 30

Water Density[kg/m^3] vs Temperature[C]

Air-Free Water [kg/m^3] Air-Saturated Water [kg/m^3]

Figure 10 Gas Bubble Trapped in a tube


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Components of the Actual Degasification System

In order to understand how the system works and how the different components

interact in the process, it is necessary to know which these components are andthe working principle of the most relevant ones.

Vacuum Pump Operation Principle

The vacuum pump is the core

equipment in the degasification

process. The working principles

of the vacuum pump is a rotary

vane. (Busch) In the vacuum

pump the following parameters

are of special interest:

Ultimate vacuum pressure.

Nominal displacement.

Fluid (oil) that is used as sealant and coolant.

These parameters are important in order to perform further analysis about the

actual performance of the vacuum pump. (See Appx. Section II (General Aspects

Calibration System) (Vacuum Pump Data Sheet))

The ultimate vacuum pressure is 2 mbar (PUltiimate) (See Annex III Technical

Information Data Sheets), and the recommended maximum vacuum pressure is

about 1/10 of the ultimate pressure (20mbar) due to the fact that at higher vacuum

level the nominal displacement (4m3

/hr) and the performance of the pumpdecrease exponentially. (Pfeiffer 2014)(Vanatta.C.M 1965, Umrath 1998).

The fact that the vacuum pump is working in contact with oil makes it relevant to

take into account for any possible oil contamination of the fluid sample due to the

back stream of the oil.

Figure 11Vacuum Pump (Busch)


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Degasification System Operation

The sample fluid tank is previously filled with water tap. Normally the amount of

water in the tank is about 75% of the total capacity which about 3.2L, leavingapproximately 1L of free volume. This volume is occupied by atmospheric air, and

this is the volume that the vacuum pump should be able to evacuate.

The operation is performed by closing the Switching (3-Way) Valve (to isolate the

system from exterior) placed at the top of the tank, and open the On-Off (2-Way)

Valve placed at the bottom in order to connect the system to the inlet of the pump.

The pump is working for about 10 min. After that the pump is switched off manually

and the On-Off (2-Way) Valve is closed in order to avoid oil from the pump to enter.

Figure 12 On-Off Valve(Swagelok )

Figure 13 Sample Fluid TankFigure 14 (3-Way) Valves(Swagelok )

(See Appx. Section II (General Aspects Calibration System) (Sample Reservoir)

(Valves and Fittings))


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2.4 Phase II (Flow Generation)

Importance of Fluid Flow Stability

Regarding the stability of the fluid flow, this can be divided into two categories: the

long term stability (average flow rate) and short term stability (instantaneous flow

rate). The relevance of the fluid flow stability in function of time is that lack of

stability can be assumed as a potential source of errors that requires to be under

controlled conditions to ensure accurate measurement results.

Unfortunately, it is not possible to give reliable expected values about the effect of

the fluid flow stability (long term and short term) in the final measurement

uncertainty result. This requires a complex analysis of all the parameters that

contribute in the measurement process (uncertainty analysis) in order to calculate

the expected effect of the flow stability in the measurement results.

Assumed Applicable Theory Fluid Dynamics

Considering the fluid flow theory that would be applicable to this problem in order

to analyse the system, it is required to look at the conditions of the system

regarding the following parameters:

Flow Characteristics

Fluid Properties

Relationship between length and diameter of the tube

Based on the classification of fluid flow,

different parameters are considered; Time

(flow change in function of time), Space

(the change in cross sectional area in the

system), Flow Pattern (Turbulent or

Laminar (the fluid pattern is smooth and

regular with no turbulences)).

It is assumed that ideally the generated fluid flow should be steady-uniform-

laminar,at leastin the portion of the system where the DUT is placed and at the

end of the system where the precision scale is placed and the tube is considered

Figure 15 Fluid Flow Pattern


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In the Hagen-Poiseuille Law, the assumptions that are necessary to consider in

order to be applicable are:

The flow is laminar (no turbulences Reynolds Numbers < 2100), The fluid is incompressible.

Newtonian Fluid (constant viscosity regardless the stress placed on it).

Figure 16 Regimens of Fluid Flow (White )

Figure 17 Laminar Flow (White ) Figure 18 Turbulent Flow (White )

The laminar flow could show some natural disturbances which are damped rapidly.

The increment of the Reynolds Number (Re) causes instability of the laminar flow,

which first passed for the transition region. If the Re is large enough the flow will

fluctuate continually, until the complete turbulent fluid flow pattern is developed.

Another important concept to keep on mind is the continuity principle, basically

that state that (there is no loss of mass (no leaks or fluid absorption in the system)):

= = = =

Considering that this is the first time that one works with this very specific topics,

the previous part about the theoretical applicable principles, in the degasification

and the fluid flow generation, can be under discussion, regarding if the actual

conditions met 100% the assumption from the theory.


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2.5 Actual Flow Generation Methods

Considering the actual system, the range of flow generation is from 0.73L/hr to

6L/hr, and the fluid flow generation is performed by two methods:

Fluid Flow Generation (by Syringe Pump)

Fluid Flow Generation (by Compressed Air)

2.6 Fluid Flow Generation (by Syringe Pump)

Figure 19 Fluid Flow Generation (by Syringe Pump)

The diagrams shown for the different methods are simplified in order to make the

picture more understandable (the components from the degasification process

were removed).The syringe pump flow generator accomplish the task with a

stepper motor which rotates a spindle screw and generates a linear displacement

of the syringe plunger, producing the outflow of the sample fluid.

The fluid flow range of the syringe pump is between 0.73L/hr (with a syringe of

1mL) to 1257mL/hr (with a syringe of 60mL), and the flow rate is regulated by a

speed controller incorporated in the pump.

Regarding the flow range, a suitable selection of the syringe size and needle

gauge is required in order to achieve the desirable output from the system.


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The main components of the system are:

Syringe pump (which requires different syringe size for different flow rate)

Reservoir sample tank (the same as where the degasification is performed), Needles gauge that provide fluid resistance with different diameters.

Scale (there are three different scales depending on the flow rate

measured).

Scale#1 (Sartorius Mod 6.6S Max.Capacity:10g Resolution:1g)

Scale#2 (A&D Mod Fx300iWP Max. Capacity 320g Resolution:0.001g)

Scale#3 (A&D Mod Fx300iWP Max. Capacity 3200g Resolution:0.01g)

DUT (Hospital Reference, Precision Flow meter)

Figure 20 Syringe Pump (World Precision Instrument )

Figure 21 Scale (Sartorius )

Figure 22 Needles Gauge

(See Appx. Section II (General Aspects Calibration System) (Needles Gauge)

(Scale) (System Setup Diagrams) (Syringe Pump Data Sheet))


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2.7 Fluid Flow Generation (by Compressed Air)

Figure 23 Flow Generation(by Compressed air)

This method of flow generation is performed by creating a difference in pressure

between inlet and outlet tube, and with this flow generation method it is expected

to cover the complete range (1mL/hr to 6L/hr). The source of air pressure is themain supply line of compressed air at 7 0.5 bar.

The regulation method that is used is a manual operation of a flow regulator valve

(Swagelok) and a pressure regulator valve (Parker-Porter). This regulation

scheme also requires a suitable selection of needle gauge at the end of the outlet

to build up flow resistance and to achieve the proper regulation of the flow rate.

(See Appx. Section II (General Aspects Calibration System) (System Setup

Diagrams))


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Section IIIAnalysis of the Degasification System


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3 Performance Analysis of the Degasification Process

Purpose

The analysis of the actual system performance is a key procedure to find the strong

and weak points in the actual design configuration. The results will be helpful to

identify any problem that should be avoided or minimized in the improvements of

the fluid flow calibration system.

3.1 Quantification of the Degasification Process

Dissolved Gases in the Water at Different Pressures

The main purpose of this calculation is to find the level of gasses dissolved in water

at different pressure in order to establish reference points regarding degasification

level at the equilibrium state. The concentration of dissolved gases (solute) in the

water (solvent) is calculated at the atmospheric pressure (at 101.325 kPa) and at

the water vapour pressure (23.4mbar) (assuming this is the lowest concentration

level), at the temperature of 20 C.

Henrys Law Conditions

Molecules are in dynamic equilibrium state.

No gases at high pressure.

There is no chemical reaction between the solute (Gases in the air) and the

solvent (Water) (solute and solvent are chemically inert).

Assumptions

Henry's Law Conditions are met.

Isothermal/Isobaric Process (Constant Temperature/Pressure).

Air mixture is considered ideal gas in order to simplify the calculations.

In the sake of simplify ing the calculations the air is assumed to be dry air.

Air Composition N2(78.103%),O2(20.940%), Ar (0.917%), CO2 (0.04%)


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Results

The calculation results shows that the estimated lowest concentration of dissolved

gases in water is placed at the water vapour pressure (23.4mbar at 20 C),

because at this pressure the water will start to boil at the given temperature and

the partial pressure of each gas that compose the air is very low.

The reduction in concentration of the gasses dissolved in water is in the order of

97.69% at equilibrium state at 23.4 mbar. The concentration of gases dissolved in

water at this pressure is very small compared to the initial concentration at

atmospheric pressure. Therefore, the concentration of gases dissolved in the

water can be approximated to be zero and considered the ideal level.

Total Gases Dissolved: 25.922 mg/L of Water

Figure 24 Gases Dissolved in Water (at 101.325 kPa)

Total Gases Dissolved: 0.598 mg/L of Water

Figure 25 Gases Dissolved in Water (at 23.4mbar)


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3.2 Expected Vacuum Pump Performance

The purpose of this calculation is to find the expected time (Pump-Down Time) to

reach the water vapour pressure, at the same condition that the test of the vacuum

pump was performed. In this case to get an idea of the expected performance, the

calculation is carried out without considering the losses of the system (pipes

dimensions, valves) and tolerance of the pump (10% for air at 20C) that can

reduce the actual performance of the pump. The vacuum pressure that is assumed

the lowest required, is the water vapour pressure (23.4mbar at 20 C), based on

quantification of the amount of gases dissolved in water at different pressures

shown in the previous calculation. The conditions that is considered the expected

performance of the vacuum pump are:

Room Temperature 20 C

Volume to evacuate 0.938 L (free surface volume) Vacuum Pump Intake Pressure 23.4 mbar Vacuum Pump Discharge Pressure 101.325 kPa Vacuum Pump Displacement:4m3/hr

= ()

(Vanatta.C.M 1965)(Pfeiffer 2014)

Results

The final result of the expected Ideal pump down time is approximately 3.3s, of

course this value will be higher in a real situation due to all the losses of the

system. The pump displacement tolerances of 10% for air at 20C, together with

the system resistance and condensation of the water vapour inside the pump are

the major parameters that can affect the performance of the pump. (Pfeiffer

2014)(Vanatta.C.M 1965, Umrath 1998) (See Appx.Section III(Analysis of the

Degasification)


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3.3 Vacuum Pump Performance Test

The test of vacuum level achieved by the pump was performed in the laboratory,

at the condition of 20 [C] and pressure 101.325 [kPa]. The vacuum generated

was measured with a digital vacuum meter, with resolution of 0.001bar.

Results

The vacuum pressure value after

approximately 10 min was 76.25 mbar,

which shows that the pump does not

perform as it is expected.

Another test was performed, in order to

check if the problem was in the pump

as assumed, the digital vacuum was

connected just directly to the pump to

avoid any potential leak that could also be another source of performance

reduction. The vacuum meter shows the same vacuum level (76.25 mbar) as

before but immediately after being connected to the pump.

Now, there is more evidences that the pump does not work properly, but one more

test was performed to check if there is any problem in the reservoir tank. In this

case the test was to connect the tank to a better vacuum pump system. The

vacuum achieve was much better (26.25 mbar) and faster, approximately 3min.

The vacuum pump is not equipped with a gas ballast system that allow to

counteract the accumulation of water vapour condensation from the process. Theaccumulation of this condensation could lead to a reduction of the pump

performance. Furthermore, as trace of oil was found it in the fluid sample reservoir,

it is required to check the compressed air filter system before it is possible to

achieve a conclusion about the origin of the oil. This is based in the fact that

compressed air is used as a flow generator method and the air is in direct contact

with the fluid sample. The actual degasification level (at 76.25mbar) at equilibrium

state is approximately 3.2 times greater than the expected at 23.4 mbar. (See

Appx.Section III(Analysis of the Degasif ication)

Figure 26 Gases Dissolved in Water


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3.4 Sample Tank Strength Analysis

The sample tank is subjected to an external and

internal pressure. The regulation for this type of

pressure vessel is the following: 2000 No. 128 the

Pressure Systems Safety Regulations

2000(page.10). 6.Pressure systems excepted

from all regulations: Any pressure system or part

thereof which: (a) is the subject of a research

experiment; or (b) Comprises temporary

apparatus being used in a research experiment

(Department of Trade and Industry) (Health and

Safety )

Even though there are exceptions from the

regulations in the present system, it does not

mean that the tank should not be safe to operate.

The absence of information about the dimension

and material used in the construction of the tankand the lack of any label indicating the working

pressure, makes it necessary to perform an

estimation of the minimum wall thickness of the

tank and the material. The fittings and steel road

assembly that are incorporated in the tank are also

considered important regarding the strength of the

tank to ensure safe operation.

It is necessary to consider the potential risk of

implosion and explosion at the working pressure values of pressure 2 bar and

vacuum max.23.4mbar (rough vacuum). The visual inspection lead in the

assumption that the material of the main cylinder tank could be PC (polycarbonate)

or PMMA (polymetacrylate) with at least 5mm of thickness. The relationship

between the assumed thickness (5mm) and the measured outer diameter of the

tank (110 mm) allows to treat the tank as Thin-Walled Pressure Vessel (r/t 10).

Figure 27 Tank Model (Autodesk 2015)

Figure 28 Sample Tank Top


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Results

The calculations end up in the following results:

Thin-Walled Pressure Vessel (r/t 10)

Material Pressure Minimum Thickness Assumed Thickness SF

PC 2 bar 0.15mm 5 mm 33

PC 5 bar 0.38mm 5mm 13

PC 7 bar 0.53mm 5mm 9.4

PMMA 2 bar 0.16mm 5mm 31

PMMA 5 bar 0.40mm 5mm 12.5

PMMA 7 bar 0.56mm 5mm 8.9

Table 2 Pressure vs Minimum Tickness

The expected minimum thickness for the actual working conditions (2bar) is

0.16mm. Even if the tank is pressurized at 5 bar (maximum main supply) the

minimum thickness is 0.40mm. (Gere.M, Goodno.J 2009)

The assumed thickness of 5mm is 12.5 times bigger than the required minimum

thickness in the worst case at 5bar and the material PMMA (lower mechanical

properties). Even if the assumed 5mm thickness is wrong and the actual is 3mm,

the safety factor is bigger than 5 (for PMMA at 7bar, worse case) which is still in

the acceptable range between 5 and 8 for avoiding life threatening situations. (See

Appx.Section III(Analysis of the Degasif ication)


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Fittings and Rods Axially Loaded

Figure 29 Sample Tank Knobs Figure 30 Sample Tank Fitting

Figure 31 Molded Knobs Figure 32 Air Inlet Fitting

Fittings

The fitting (pipe connexions) incorporated in the sample tank are under axial load

(worse case) of 66 N and 92N at the internal pressure of 5 bar and 7 bar

respectively.

Moulding Plastic Knobs

The calculation is performed considering that the moulding plastic knob is the

weakest part in the steel rod assembly. The plastic moulding knobs at the end of

the stainless steel rods are subjected to 392 N of tensile force at the internal

pressure of 2bar. The calculated minimum number of knobs is 2.28, which is lower

than the actual number of knobs (4). At the internal pressure of 5bar the knobs are

subjected to a tensile force of 981 N and the minimum number of knobs is 6 which

is higher than the actual. This will require other types of knobs or steel nuts, as

example could be the aluminium start knobs (DIN 6335). (See Appx.Section

III(Analysis of the Degasification)


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3.5 Conclusions of the Degasification Process System

[1]. The lowest concentration of dissolved gases in water is estimated at the

water vapour pressure (23.4mbar at 20 C). The water vapour pressure of

23.4 mbar at 20 C can be considered as the vacuum level reference for a

suitable degasification level.

[2]. The exclusion of any potential leak in the system and the result of the

vacuum pump test, with maximum vacuum level of 76.25 mbar after more

than 5 min, allows to conclude that the vacuum pump shows poor

performance. A recommendation of another type of pump that can handle

water vapour at the pressure of 23.4mbar should be considered.

[3]. Trace of oil was found it in the fluid sample reservoir, but in this case it is

not possible to conclusively assume that the oil comes only from the pump.

It is required to check the compressed air filter system. This is based in the

fact that compressed air is used as a flow generator method and the air is

in direct contact with the fluid sample.

[4]. It is possible to conclude that at 2 bar internal pressure and at 23.4mbar of

vacuum, the sample tank reservoir can operate under safety conditions. The

pipe fittings and the rod assembly do not represent a risk. The incorporation

of a label that indicate the working pressure of the tank could be a good

practice.

[5]. It is necessary to mention that if the tank is required to operate at higher

pressure of 2 bar up to 7 bar, it is recommended to replace the moulding

plastic knobs by stainless steel nuts (M6) or an aluminium star knobs (DIN

6335), in order to operate under safety conditions.


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Section IV

Analysis of the Flow Generation Methods


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4 Analysis of the Fluid Flow Generation Methods

4.1 Purpose

The main purpose of this analysis is to determine and describe the actual

behaviour of the fluid flow rate for the two different methods of flow generation in

order to identify any potential source of systematic error:

Syringe Pump

Compressed Air

Background Theory

The analysis of the actual behaviour of the fluid flow rate, is performed by a

statistical analysis of the data gathered in test at 15mL/hr by syringe pump method

and at 60mL/hr by compressed air method. The characteristics that are relevant to

know about the flow are: relative position of the flow rate in function of time by

finding the centrality (mean value) and measure of variability or dispersion

(standard deviation, range).

Before this analysis is performed, it is necessary to prepare the data in order toget reliable results by removing the outlier data points.

The outlier rejection criteria is based in function of what is known about the

measurement process. For example, in the extreme data values (initial and final

data points of the measurement process) it is expected that the flow is

inconsistence considering the time required to achieve the expected flow value.

Another important graphic tool is the histogram (frequency distribut ion) which

shows the frequency occurrence of the flow data points in different intervals in

which the data is grouped (bins). From these histograms it is possible to determine

the probability distribution of the data and formulate a hypothesis about the

possible parameters that are causing the behaviour.

This analysis will be complemented by a regression analysis (Linear and non-

Linear Regressions) in order to determine an equation that describe the data, and

analyse that residual in order to identify any systematic error.


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Linear Regression Model

Coefficient of Determination (R2)

This is a value between 0 and 1, and is useful under the assumption of a linear

model fitting. This is because for linear models the sum of the squared errors is

always added up.

+= =

The values close to 1 or 100% means the model closely resembles the data.

Non-Linear Regression Model

In the case of non-linear regression models:

+

In order to evaluate the goodness of fit of the model, it is required to use the

standard error of the regression, in this case it should be as small as is possible in

order to have a good fit.

Residuals Analysis

In order to detect the potential presence of systematic errors, the residuals should

be randomly distributed (to avoid systematic errors), and need to be normal

distributed with a mean value of 0.

(Kirkwood.B, Sterne 2003)(Montgomery, Runger 2014)(Bates.D, and Watts.D )


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4.2 Flow Generation by Syringe Pump

4.2.1 Flow Rate Data Analysis 15[mL/hr]

Scatter Plot of the Original Data [15mL/hr (0.004mL/s)]

Figure 33 Data Scatter Plot (15mL/hr) (Mathworks 2014)

Outliers Rejection Criteria

The sample size of this data is 12.000 points (20 min of calibration at 10 Hz sample

rate). The rejection criteria in this case is based on the big sample size and theextreme values. (15mL/hr initial and 0 ml/hr as a final value).

Descriptive Statistical Analysis of Fluid Flow Rate [15ml/hr]

Nominal Value Mean(x) n(Sample Size) SD CI (95%)

15 mL/hr 14.09 mL/hr 9655 0.55mL/hr 0.011 mL/hr

Table 3 Statistical Data (15mL/hr)

95% = 1 . 9 6 =14.091.960.55

9655 =14.090.011

= 14.101 / = 14.079 /


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Non-Linear Regression Analysis (15[mL/hr])

The non-linear regression analysis is performed by modelling a two terms Fourier

series. The selection of the Fourier series is based in the sinusoidal behaviour ofthe flow rate. The two terms are chosen instead ofhigher terms, based on that an

increment in the terms does not reflect a relevant reduction in the standard error

value, but shows an increment in the complexity of the model. ((See Appx. Section

IV)(Flow Rate Data Analysis 15[mL/hr](by syringe pump).

It is expected that this equation can be used as a descriptive model of the fluid

flow behaviour in order to find any systematic pattern in the analysis of the

residuals. The model give as a result:

General model Fourier Equation

= + + + +

Coefficients (with 95% confidence bounds)

a0 0.003919 (0.003918, 0.00392) a1 -0.0001996 (-0.000201, -0.0001981)

b1 4.46e-06 (3.018e-06, 5.902e-06) a2 -1.402e-05 (-1.547e-05, -1.257e-05)

b2 -3.923e-05 (-4.07e-05, -3.776e-05) 0.02902 (0.029, 0.02905)

Table 4Fourier Series Coeficients(Mathworks 2014)

Non-Linear Regression Plot

Figure 34 Non-Linear Regression and Residuals Plot. (Mathworks 2014)

Results

This non-linear regression model (two terms Fourier series) can be considered as

a good representation of the data based on the standard error value of 1.4% of the

reading data values.


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Residual Analysis

Residual Plot

Figure 35 Residual Plot(15mL/hr)

Residual Periodogram Plot

Figure 36 Residual Periodrogram (15mL/hr)

Histogram of Residuals

Figure 37 Residuals Histogram(15mL/hr)

Results

The residual plot and a randomness analysis (See Appx. Section IV Flow Rate

Data Analysis 15[mLhr])(StatPoint Technologies 2013)) shows that the residuals

are not randomly distributed. It is assumed that one of the probable causes that

produce this systematic error could be the high pressure drop in the needle which

generates high flow velocity and turbulences. It is difficult to determine or identify

only one source of this systematic error, due to the generated broad band of the

noise. Based on the normality test the residuals are not normal distributed and the

mean value is not 0. The histogram of the residuals shows that there is enough

evidences to consider that the residuals are not normally distributed.


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Histograms and Normal Fitting Plots of Fluid Flow Rate [15ml/hr]

Figure 38 Normal Curve Fitting Plot (15mL/hr)

Figure 39 Density Plot Histogram(15mL/hr)

Results

The normality test ((See Appx. Section IV (Analysis of the Flow Generation

Method)( Flow Rate Data Analysis 15[mL/hr](by syringe pump))), shows that there

are strong evidences that the sample data is not normal distributed. It is shown

also in the histogram fitting plot that the data is not normal distributed, but is

symmetric with respect to the mean value. Considering this symmetry, and based

on the previous observed sinusoidal behaviour, it is possible to assume that the X-

Factor or parameter that is the major contributor to the process and produce the

non-normality of the probability distribution, is the syringe pump spindle rotation.


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Short Term Flow Rate Stability [15mL/hr]

Figure 41 Fluid Flow Stability [15mL/hr]

Nom.Value

Mean SDFlow

VariationMax.

FluctuationSTDError

95% CI

15.00 14.09 0.55 3.88% 9.67 % 0.0056 0.011Units[mL/hr]

Table 6 Data Analysis Table (15mL/hr)

The graph shows the fluid flow rate in percentage (at nominal value 15mL/hr) with

respect to the mean value. In the data table the maximum fluctuations are

highlighted (9.67% with respect to the mean value). This percentage of fluctuation

values will be useful in order to quantify and compare the actual fluctuations with

respect to the improvements in the fluid flow calibration system.

The accuracy of the syringe pump was calculated in base of the difference between

the assumed nominal value (15mL/hr) and the actual mean value (14.09mL/hr)

given as a result 6.1% of accuracy. This seems too high considering that the

manufacture claims 1% of accuracy.


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Raise Time Analysis

Figure 42 Raising Time Analysis [15mL/hr]

Results

The data starts to be recorded at about 14

s. After approximately 40 s, the input flow

rate signal starts to appear in the plot with

random fluctuations. At about 55s the flow

is observed with raising stable behaviour

until about 80s, where 90% of the final

mean value is reached.

The raise time is about 7.5% of the total

calibration time of approximately 20 min.

This parameter is assumed to be directly

affected by the fluid flow resistance and the

syringe size (if the syringe volume is too

high with respect to the precision of the

syringe pump motor, there will be a delay ofthe motor before it starts to move).

If the fluid flow resistance is too high with respect to the desirable flow rate, the

pressure required to reach this flow rate will be higher and of course this pressure

is not reached instantaneous due to the deformation of all the components. That

will lead to an increment of the raising time. (Plecis.A, Velv.G & Bertholle.F )

Figure 43 Flow Generation(by Syringe Pump)


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The fluid flow resistance is deduced from Hagen-Poiseuille Law:

=

= 8

The flow resistance depends on the length and radius of the pipes, and the

viscosity of the fluid. In the system, one of the major contributors to the fluid flow

resistance that also affect the raise time is the dimensions of the needle gauge,

based on the small inner diameter range (from 150m up to 794m). Another

possible explanation of the high raise time is presence of air bubbles in the system.

It is possible to assume that the 7.5% raise time with respect to the 20 min

calibration time is due to the fluid flow resistance in the system and the potential

presence of gas bubbles caused by the poor vacuum pump performance that has

been shown.

4.2.2 Conclusions of the Flow Generation by Syringe Pump

[1]. The source of the sinusoidal oscillations in the f low rate behaviour is

conclusively mechanical, due to the rotations of the stepper motor.

[2]. The visibility of this effect is assumed as affected by the syringe dimensions

but it is not possible to conclude anything about the level of contribution; this

is based on that not all the evidences are present, like the syringe size used

in the procedure to collect the data and also the needle gauge dimensions.

[3]. The reduction of the syringe size increase flow stability but decrease the

available volume capacity, which in this case (calibration purpose) is

undesirable considering the calibration time. This specific problem should

be considered in the improvements of the calibration system.

[4]. The fluid flow generated by the syringe at 15mL/hr, show that the maximum

fluid flow fluctuations are 9.67% with respect to the mean value.

It is not possible to conclude that the syringe pump performs in the

mentioned fluctuation range because of the missing information about the

syringe size.

[5]. It is possible to assume that the 7.5 %( 80s to reach the 90% of the f inal

mean value) of raise time with respect the 20 min calibration is caused bythe fluid flow resistance in the system. Regarding the fact that there is no


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evidence about the dimensions of the selected needle and syringe, it is not

possible to conclude that the cause of this raise time is the needle and the

syringe size. This fluid flow resistance is an important parameter to take into

account in the improvements of fluid flow generation system.

Another probable cause could be the presence of gas bubbles during the

initial phase of the calibration and if this is the cause, the source of this

effect is considered to be the poor vacuum pump performance.

The major difficulty will be to find the equilibrium between rise time and flow

stability. Higher fluid resistance offer a stable flow but the price is the low

responsiveness of the system, and the system is limited by the maximum

capacity of the scales.

[6]. It is noticed that one of the major advantages of this system is that the flow

is regulated by a controller incorporated inside of the pump.

This will have an effect in reduction of the time that the system requires to

achieve the desirable flow value, compared with the manual regulation. A

disadvantage could be the restricted or limited volume capacity and the fluid

flow range compared with the expected performance of fluid flow generator

by air pressure.[7]. The mechanical method to generate a continuous flow should be considered

as a potential method with the appropriate compensation of the fluctuation

generated by the method.


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Linear Regression Analysis [60mL/hr (0.017mL/s)]

Figure 45 Linear Regression Plot (60mL/hr)

In order to determine a suitable model that can be used as a descriptive model of

the behaviour a linear regression model is decided to be used. This is based on

the clear decreasing linear tendency of the fluid flow rate.

Regression Model was performed and this model gives as a result:

General model Linear Regression Equation

= +

Coefficients (with 95% confidence bounds)

a0 0.01634 (0.01634, 0.01635) a1 -1.853e-06 (-1.867e-06, -1.839e-06)

Results

This linear regression model can be considered a good representation of the data

analysis and improvements of a flow calibration system

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