MAPUA INSTITUTE OF TECHNOLOGY

Muralla St. Intramuros, Manila

School of Mechanical Engineering and Manufacturing Engineering

Experiment Number 9 AIR FLOW MEASUREMENT

8 JEREMIAS, John Karlo B. Date of Performance: September 10, 2015

ME139L / A3 Date of Submission: September 17, 2015

Group 1

Engr. Teodulo A. Valle Instructor

GRADE

TABLE OF CONTENTS

PAGE

OBJECTIVES 1

THEORIES AND HYPOTHESIS 1

LIST OF APPARATUS 2

PROCEDURES 3

SET-UP OF APPARATUS 4

FINAL DATA SHEET 5

SAMPLE COMPUTATION 6

TEST DATA ANALYSIS 7

DISCUSSION 8

QUESTION AND ANSWERS 13

CONCLUSION 14

RECOMMENDATION 15

REFERENCES 16

PRELIMINARY DATA SHEET 17

EXP 9: AIR FLOW MEASUREMENT

1

EXPERIMENT NO. 9

Air Flow Measurement

OBJECTIVES

To understand the theory behind volumetric air flow

To learn the operation of anemometer

To measure of the air flow of ventilation shafts

To quantify the difference of result between analog and digital anemometer

THEORY AND HYPOTHESIS

Generally, the measurement of fluid flow is of great importance in many industrial

processes, some examples including air flow in the ventilating ducts of a coal mine, the

flow rate of water in a condenser at a power station, the flow rate of liquids in chemical

processes, the control and monitoring of the fuel, lubricating and cooling fluids of ships

and aircraft engines, and so on. Fluid flow is one of the most difficult industrial

measurements to carry out, since flow behavior depends on many variables concerning

the physical properties of a fluid. There are many fluid flow measuring instruments

generally flow meters, which can measure the flow rate of fluids in terms of mass (kg/s),

volume (m3/s) and velocity (m/s). To measure the air velocity and pressure, Anemometers

are used.

Anemometer is an instrument used for measuring wind speed. This is used in

meteorology, mines, tunnels, and ventilation systems; in aircraft testing and other

experimental work. There are three types of anemometer: The cup anemometer, propeller

type and hot wire.

Flow velocity is a vector quantity used to

describe the motion of a fluid. It can be easily

determined for laminar flow but complex to determine

for turbulent flow. In case of anemometer

measurement, it is desirable to measure air at laminar

flow. Laminar and Turbulent flow

EXP 9: AIR FLOW MEASUREMENT

2

In addition to flow velocity, volumetric flow rate is an important quantity in fluid

dynamics analysis. Volumetric flow is defined as the volume of fluid that passes through

a given surface per unit time. Mathematically, volumetric flow rate is the derivative of the

volume of fluid that passes through a given surface with respect to time; in SI units this is

expressed as meters cubed per second. Volumetric flow rate is related to the flow velocity

vector as the surface integral with respect to the surface in question. If the surface area

in question is a flat, plane cross-section, the surface integral reduces as shown in

Equation 2, where A is the surface area of the surface in question and v is the flow velocity

of the fluid.

LIST OF APPARATUS

1. Digital Anemometer – An

electronic air flow measuring tool

used to directly gauge the air flow

velocity.

Mathematical Expression of Volumetric Flowrate Q

EXP 9: AIR FLOW MEASUREMENT

3

2. Analog Anemometer – Used to

measure the linear distance travel

by a constant air flow velocity. To

get the velocity, one must use time

measuring devices such as

stopwatch.

3. Stopwatch – Used to measure the

range of time from when the device is

activated and stopped.

4. Steel rule/steel tape - A steel

rule is a simple measuring

instrument that is used for

measuring distances and ruling

straight lines.

PROCEDURE

A. Digital Anemometer

1. Measure the area where air flow is.

2. Place the propeller of the anemometer where the air flow is maximum.

Generally, on a laminar air flow, this occurs at the center.

3. Record the output shown by the anemometer.

B. Analog Anemometer

1. Measure the area where air flow is.

EXP 9: AIR FLOW MEASUREMENT

4

2. Place the propeller of the anemometer where the air flow is maximum.

Generally, on a laminar flow, this occurs at the center.

3. Turn the anemometer on. At the same time, start the stop watch.

4. Measure air flow for at least one minute.

5. To get air velocity, divide the recorded data by the anemometer by the time

elapsed by the measurement.

SET-UP OF APPARATUS

A. Analog Anemometer

The propeller of the anemometer will be placed

perpendicular to the area where the air flow moves.

After that, the device is turned on and the dial

rotates. For one minute, the distance travelled by

the wind will be measured and to get the average

velocity, the time it took to get the measured value

will the divisor for the total distance travelled.

B. Digital Anemometer

Unlike the analog anemometer, the measurement of the

air flow velocity using the digital anemometer happens

simultaneously. One does not require the use of

stopwatch for this part of the experiment. When using this

device, the anemometer must be placed perpendicularly

to the cross sectional area of the shaft for accurate

reading.

Measurement of Air flow

Velocity through digital

anemometer

Measurement of Air flow Velocity

through analog anemometer

EXP 9: AIR FLOW MEASUREMENT

5

FINAL DATA SHEET

ANEMOMETER

PLACE AREA

(m2)

ANALOG DIGITAL

%

DIFFERENCE V

(m/s)

Vave

(m/s)

Vol.

Flow

(m3/s)

V (m/s) Vol. Flow

(m3/s)

HVAC

ROOM

LOWER

AIRCON

0.033

2.9

2.83 0.093 2.7 0.089 4.4 2.75

2.83

HVAC

ROOM

OVERHEAD

0.1

1.66

1.53 0.153 1.4 0.14 8.87 1.5

1.42

FACULTY 0.0396

6.7

6.57 0.26 6.4 0.253 2.73 6.5

6.5

EXP 9: AIR FLOW MEASUREMENT

6

SAMPLE COMPUTATION

HVAC ROOM LOWER AIRCON

o Area

o Vave

o Volumetric Flow Rate

o % Difference

𝐴𝑟𝑒𝑎 = 𝑙𝑤 = (0.15𝑚)(0.22𝑚) = 0.033 𝑚2

𝑉𝑎𝑣𝑒 =∑ 𝑉

𝑛=

(2.9 + 2.75 + 2.83)

3= 2.83 𝑚/𝑠

𝑄 = 𝐴𝑉 = (0.033𝑚2)(2.83𝑚

𝑠) = 0.093 𝑚3/𝑠

% 𝐷𝑖𝑓𝑓 =𝑉1 − 𝑉2

𝑉1 + 𝑉22

𝑥 100% =0.093 − 0.089

0.093 + 0.0892

𝑥 100% = 4.4%

EXP 9: AIR FLOW MEASUREMENT

7

TEST DATA ANALYSIS

During the experiment,

when measuring the air flow

velocity, it was made sure

that when using the analog

anemometer, there would be

three trials since the values

one can obtain using the

said device can be affected

by human error such as misplacement of the device and misreading of the dial. After that,

the average of the velocities will be the one to be compared to the results yielded from

using the digital anemometer. It was noticed that on all the places, the results given by

the analog anemometer is higher compared to the digital one. Though this has no

conclusive reason, this yielded to a much higher volumetric flow rate of air.

PLACE ANALOG DIGITAL

% Diff V Vol V Vol

HVAC ROOM

LOWER

AIRCON

2.83 0.093 2.7 0.089 4.4

HVAC ROOM

OVERHEAD 1.53 0.153 1.4 0.14 8.87

FACULTY 6.57 0.26 6.4 0.253 2.73

Results Summary

EXP 9: AIR FLOW MEASUREMENT

8

DISCUSSION

AIR AS FLUID

In physics, a fluid is a substance that continually deforms (flows) under an

applied shear stress. Fluids are a subset of the phases of matter and include

liquids, gases, plasmas and, to some extent, plastic solids. Fluids can be defined

as substances that have zero shear modulus or in simpler terms a fluid is a

substance which cannot resist any shear force applied to it.

Although the term "fluid" includes both the liquid and gas phases, in

common usage, "fluid" is often used as a synonym for "liquid", with no implication

that gas could also be present. For example, "brake fluid" is hydraulic oil and will

not perform its required incompressible function if there is gas in it. This colloquial

usage of the term is also common in medicine and in nutrition ("take plenty of

fluids").

Liquids form a free surface (that is, a surface not created by the container)

while gases do not. The distinction between solids and fluid is not entirely obvious.

The distinction is made by evaluating the viscosity of the substance. Silly Putty can

be considered to behave like a solid or a fluid, depending on the time period over

which it is observed. It is best described as a viscoelastic fluid. There are many

examples of substances proving difficult to classify. A particularly interesting one

is pitch, as demonstrated in the pitch drop experiment currently running at the

University of Queensland.

FLUID FLOW

A conduit is any pipe, tube, or duct that is completely filled with a flowing

fluid. Examples include a pipeline transporting liquefied natural gas, a

microchannel transporting hydrogen in a fuel cell, and a duct transporting air for

heating of a building. A pipe that is partially filled with a flowing fluid, for example

a drainage pipe, is classified as an open-channel flow.

CLASSIFYING FLUID FLOW

Laminar Flow and Turbulent Flow

Flow in a conduit is classified as being either laminar or turbulent,

depending on the magnitude of the Reynolds number. The original research

involved visualizing flow in a glass tube as shown in Fig. 10.2a. Reynolds

(1) in the 1880s injected dye into the center of the tube and observed the

following:

EXP 9: AIR FLOW MEASUREMENT

9

When the velocity was low, the streak of dye flowed down the tube with

little expansion, as shown in Fig. 10.2b. However, if the water in the tank

was disturbed, the streak would shift about in the tube.

If velocity was increased, at some point in the tube, the dye would all at

once mix with the water as shown in Fig. 10.2c.

When the dye exhibited rapid mixing (Fig. 10.2c), illumination with an

electric spark revealed eddies in the mixed fluid as shown in Fig. 10.2d.

The flow regimes shown in Fig. 10.2 are laminar flow (Fig. 10.2b) and

turbulent flow (Figs. I 0.2c and 10.2d). Reynolds showed that the onset of

turbulence was related to a 'TT-group that is now called the Reynolds

number (Re = p VD/JJ.) in honor of Reynolds' pioneering work. The

Reynolds number is often written as Re0 , where the subscript "D" denotes

that diameter is used in the formula. This subscript is called a length sea/e.

indicating the length scale for Reynolds number is good practice because

muliple values are used.

Reynolds discovered that if

the fluid in the upstream

reservoir was not completely

still or if the pipe had some

vibrations, then the change

from laminar to turbulent flow

occurred at Ren - 2100.

However, if conditions were

ideal, it was possible to reach a much higher Reynolds number before the

flow became turbulent. Reynolds also found that, when going from high

velocity to low velocity, the change back to laminar flow occurred at Ren -

2000. Based on Reynolds' experiments, engineers use guidelines to

establish whether or not flow in a conduit will be laminar or turbulent. The

guidelines are as follows:

EXP 9: AIR FLOW MEASUREMENT

10

Volumetric Flow Rate

In physics and engineering, in particular fluid dynamics and hydrometry, the

volumetric flow rate, (also known as volume flow rate, rate of fluid flow or volume

velocity) is the volume of fluid which passes per unit time; usually represented by

the symbol Q. The SI unit is m3/s (cubic metres per second). Another unit used is

sccm (standard cubic centimeters per minute).

In US Customary Units and British Imperial Units, volumetric flow rate is

often expressed as ft3/s (cubic feet per second) or gallons per minute (either U.S.

or imperial definitions).

Volumetric flow rate should not be confused with volumetric flux, as defined

by Darcy's law and represented by the symbol q, with units of m3/(m2·s), that is,

m·s−1. The integration of a flux over an area gives the volumetric flow rate.

Fundamental Definition

Volumetric flow rate is defined by the limit:

i.e., the flow of volume of fluid V

through a surface per unit time t.

Since this is only the time derivative of volume, a scalar quantity, the

volumetric flow rate is also a scalar quantity. The change in volume is the

amount that flows after crossing the boundary for some time duration, not

simply the initial amount of volume at the boundary minus the final amount

at the boundary, since the change in volume flowing through the area would

be zero for steady flow.

Volumetric flow rate can also be defined by:

Reynolds number guidelines

EXP 9: AIR FLOW MEASUREMENT

11

where:

= flow velocity

= cross-sectional vector area/surface

MEASURING AIR FLOW VELOCITY

Anemometers are meteorological devices sed to measure wind speeds and can

commonly be found in weather stations. They get their name from the Greek word for

wind; anemos. Not only instruments used in meteorology but also in aerodynamics

instruments that take airspeed measurements are described as anemometers. The first

known description of an anemometer is said to be around 1450. Measurements of wind

can be taken in two different forms, the speed of the wind and the pressure. However,

there is a connection between these two. Anemometers can be divided into two different

classes, measuring the speed of the wind or the pressure. As there is a connection

between wind speed and pressure, an anemometer measuring the speed for example

would still be able to provide information on the pressure of the wind. There are several

different designs of anemometers that exist in the industry today, each using different

methods to measure the speed or pressure of the wind.

Types of Anemometers

1. Cup Anemometers

Also known as rotational anemometers, cup anemometers are the simplest

types of anemometers and have been around for a very long time. The

make up of these meters consists of a vertical central pole and four

horizontal arms at the top that have a cup attached to each of them. As wind

presses against these cups, the arms at the top rotate around the central

pole. The speed of the rotation would determine the speed of the wind. The

speed of the wind is usually observed through digital readouts in these

anemometers. Researchers, meteorologists and many educational

institutions worldwide make use of these anemometers for commercial or

research activities. Not only for commercial, but one can make their own

EXP 9: AIR FLOW MEASUREMENT

12

anemometer for their own personal use. For these meters, the speed of the

wind can be calculated by multiplying the revolutions the cups make in a

minute with the circumference that the cups create. This method would

provide a rough estimate of the speed of the wind. A disadvantage of these

meters is that they are prone to friction. As the cups rotate around their axis,

they encounter friction which could affect the accuracy of the readings.

2. Windmill Anemometers

These anemometers, just like the cup anemometers, measure the velocity

of the wind. They are also able to determine the direction of the wind as

they have a propeller that is attached to the front of the device with a tail

section behind, on the same axis as the propeller on a central pole. As wind

presses against the propeller, it spins it and the faster the propeller spins,

the faster is the velocity of the windmill anemometer. The windmill

anemometer adopts that shape of a windmill, hence its name. The windmill

anemometer has to be parallel to the direction of the wind in order for it to

function properly and provide accurate results. The turning effect of the

propeller causes the mechanism in the anemometer to be able to calculate

the speed of the wind.

3. Ultrasonic

Ultrasonic, as its name would suggest, involves sonic pulses to measure

the velocity of the wind. The device sends sonic pulses across a path to

sensors located across which are able to sense the incoming pulses. As the

movement of wind is able to disrupt sonic pulses, the disruption is used to

determine the speed of the wind. These anemometers are able to provide

very accurate measurements of wind data. They also do not involve any

moving parts and thus are able to detect very minimal changes in the speed

of the wind. They usually make use of four sensors that are arranged in a

square pattern to be able to get accurate results.

EXP 9: AIR FLOW MEASUREMENT

13

QUESTION AND ANSWERS:

1. Define Volumetric Flow.

In physics and engineering, in particular fluid dynamics and hydrometry, the

volumetric flow rate, (also known as volume flow rate, rate of fluid flow or volume

velocity) is the volume of fluid which passes per unit time; usually represented by

the symbol Q. The SI unit is m3/s (cubic metres per second). Another unit used is

sccm (standard cubic centimeters per minute).

2. Why is it much harder to record air velocity at turbulent flow as compared to

laminar flow?

In theory, laminar flow of fluid indicates that the mass of fluid moving on as

stream flows in a uniform velocity. The turbulent flow on the other hand, is much

more complex, that is, each fluid particle has its own path function and varies in

velocity. Therefore, constant air flow velocity does not apply for turbulent flow.

3. Why does one must consider the normal velocity of flow at a surface area when

measuring volumetric flow rate?

The formula for volumetric flow is the dot product of the Area and velocity

function of the fluid. In general, when using the dot product operator, both vectors

being multiplied must be perpendicular with one another, if not, the cosine function

will be used. Due to this, when measuring the volumetric flow rate, the component

of the velocity that is perpendicular to the stream area is used.

4. Give some applications of anemometers.

Anemometers are commonly used on weather stations for predicting

weather patterns. In engineering, this apparatus can be used to predict air motion

for ventilation. Aside from that, on systems that use propellers such as wind

turbine, anemometers can be used to determine whether the place where such

system will be placed is feasible enough.

EXP 9: AIR FLOW MEASUREMENT

14

CONCLUSION

On the experiment, the group is given 4 specific objectives and these are: 1. To

understand the theory behind volumetric air flow; 2. To learn the operation of

anemometer; 3. To measure of the air flow of ventilation shafts; 4. To quantify the

difference of result between analog and digital anemometer.

During the course of the activity, each members of the group were able to

understand the theory behind the experiment. The air flow velocity component to be used

on the calculation must be perpendicular to the area due to the nature of the equation for

volumetric flow. Also, they were able to use each type of anemometer with small

percentage difference between each values obtained.

It was noticed that on all shafts where air flow velocity is measured, the results

found using the analog anemometer is higher compared to the ones generated from the

digital one. Due to this, the volumetric flow is also higher.

EXP 9: AIR FLOW MEASUREMENT

15

RECOMMENDATION

The experiment used two types of anemometer. These are the analog

anemometer and digital anemometer. Both types have the same operation, that is, to

measure the air flow through a propeller, which makes use of the direct air flow of the

shaft. To further understand the concept behind flow rate, more types of anemometer can

be found useful. Some example include the hot-wire anemometer which makes use of

the temperature difference due to convection to measure air flow.

EXP 9: AIR FLOW MEASUREMENT

16

REFERENCES

http://www.princeton.edu/~asmits/Bicycle_web/transition.html

https://en.wikipedia.org/wiki/Volumetric_flow_rate

https://en.wikibooks.org/wiki/Fluid_Mechanics_Applications/A13:_Anemometers_

and_their_Applications

http://www.britannica.com/technology/anemometer

EXP 9: AIR FLOW MEASUREMENT

17

PRELIMINARY DATA SHEET