lab 5 airflow measurement (fan characteristics)

NORTH CAROLINA AGRICULTURAL AND TECHNICAL STATE UNIVERSITY

CIVIL, ARCHITECTURAL AND ENVIRONMENTAL ENGINEERING CAEE 363 Engineering Fluid Mechanics & Hydraulics Lab

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Pump/Fan Characteristics: Airflow Measurement

Objectives

Investigate “affinity law” characteristics of a laboratory controlled fan by measuring airflow

through the fan for volumetric flow rate or discharge (Q), pressure difference or head created by

fan speed (P), and power consumed (Power). Specifically, the objectives are to

a. develop a relationship between Q and P, and

b. develop a relationship between Q and Power.

Commonly used units in airflow measurements are: cubic feet per minute, CFM, for discharge;

Pascal, pa, for pressure; and watt, W, for power.

Apparatus

This experimental setup consists of

a. Calibrated Fan for airflow

b. Digital Pressure and Flow Gage

c. Power consumption measurement unit

Figure: (a) calibrated fan unit, and (b) Digital Pressure and Flow Gage (DG 700)

Introduction and Theoretical Concept

The affinity laws are used in hydraulics and HVAC system to express the relationship between

several variables involved in pump or fan performances (such as head or pressure, volumetric

flow rate or discharge, shaft speed, and power). They apply to pumps, fans, and hydraulic

turbines.



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The affinity laws are useful as they allow prediction of the head discharge characteristic of a

pump or fan from a known characteristic measured at a different speed or impeller diameter. The

only requirement is that the two pumps or fans are dynamically similar, that is the ratios of the

fluid forced are the same.

Pump/Fan affinity laws:

(1)

Or, P = K1 Q2 (2)

Or, P = K2 Q3 (3)

Where, Q: volumetric flow rate

N: shaft operational speed

H or P: pressure of head developed by the pump/fan

Power: Shaft power

K1 and K2: proportionality constant

Notice the proportionality characteristics in above equations. For example,

Flow or discharge produced is proportional to the motor speed, so if we want to double

the flow then we must double the motor speed.

Pressure produced is proportional to the motor speed/discharge squared. If the motor

speed is doubled, then the pressure produced will be 22 = 4 times greater.

Power required is proportional to the motor speed/discharge cubed. If want to double the

speed, the power required will be 23 = 8 times greater.

Procedure

1) Connect “calibrated airflow fan”, “digital pressure flow gage”, and “power monitoring

device”

2) Start the fan and keep it at one speed level measure flow rate (CFM), pressure created

(W), and power consumed (Power)

3) Repeat above measurements for different speeds of the fan



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Results Calculation and Analysis

1) Plot P vs. Q and Power vs. Q from experimental data and derive a relationship by

plotting a smooth curve (power curve) through data points and find R-squared values

2) Obtain proportionality constants K1 and K2 from plotted curves in step 1

3) Do calculations of actual P and Power for given Q using above equations 2 and 3 for

given K

4) Compare your theoretical results (calculated in step 3) with experimental results (data

collected in the experiment)

5) Discuss your results

6) Conduct and error analysis of your results (here you can plot errors with respect to Q to

see the error propagation for different value of Q)

Data Collection

Readings Flow (CFM) Pressure (Pa) Power (W)

1

2

3

4

5

6



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Lab Report: Write a scientific lab report

Cover Page: Include course name and number, the lab title, the student team members, and the

date the lab is submitted (5 points)

Introduction: A description of the experiment and background theory (5 points)

Objectives: Provide a paragraph that describes the objective or purpose of the lab (5 points)

Hypothesis: What hypothesis is this lab attempting to prove or disprove? (5 points)

Equipment: Provide a description (make and model) of the equipment used to collect the data

(5 points)

Procedure: Provide a detailed description of the procedure followed. A sketch might be

helpful (5 points)

Data: Provide a table of the data collected (5 points)

Analysis: Describe how the data were analyzed. Show your calculations (10 points)

Conclusion: Discuss whether the hypothesis proved or disproved (5 points)

Discussion: Discuss whether the experiment produced the expected results. What were the

expected results based on the theory? If the experimental results did or did not

agree with the theoretical expectations, explain why? (10 points)

lab 5 airflow measurement (fan characteristics)

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