air flow bench

Air Flow Bench

Presented By:

Saket Karajgikar & Nikhil Lakhkar

Advisor: Prof. Dereje Agonafer

Air Flow Experimental Bench

Reference: www.fantester.com

Air flow bench Configuration


Experimental Bench Contd…

• The chambers are designed in accordance with AMCA 210-99/ASHRAE 51-1999 and have been sized for convenient flow ranges

• The chamber diameter is determined by the size of the axial flow fan to be tested and the maximum flow range desired

• Lower flow ranges may be achieved by utilizing smaller nozzles in the nozzle array


• They are positioned on the plate so that they may be used in parallel to achieve higher flow ranges.

• Stoppers are provided to block off nozzles not in use and are easily removed for different ranges of testing.


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• The chamber has flow straightening screens installed upstream and downstream of the nozzle array.

• The screens break up turbulence in the air stream and provide a uniform flow approaching the nozzle array.



• The flow through the chamber is controlled with a sliding gate valve called a blast gate.

• By opening the blast gate, the flow is varied through the chamber to provide test data from shut off (no flow) to free delivery (no back pressure) for fan performance evaluation.


Applications of Air Flow Bench

• Air Flow Bench is used for:– To calculate the Air Flow Rate– Fan Performance Curve Measurement– Thermal Resistance

Air Flow Rate

where,

Q = Air Flow Rate (m3/min)

A = Nozzle Sectional Area (m2)

V = Average Flow Velocity through nozzle (m2/sec)

where,

g = gravitational acceleration 9.8 m/s2

Pn = Differential Pressure

r = Specific Gravity of Air (1.2 kg/M3 at 20oC, 1atm)

Q = 60 x A x V

V= ( 2 g Pn / r)1/2

Fan Performance Curve

• A fan performance curve characterizes the ability of the fan to drive air against a flow resistance

• It is plotted as static pressure drop in inches of water gauge pressure (iwg) against air flow in cubic feet per minute (cfm)

• The measurement starts with the air flow chamber blocked so no flow occurs (i.e. 0 cfm) and proceeds with greater and greater flow rates until the static pressure has dropped to zero representing the "free delivery" condition

Fan Performance Testing

• The purpose of this test is to determine the aerodynamic characteristics of the fan under test

• Data is taken from no flow (shut off) to free flow (free delivery)

• Curve is plot using these data points

Fan Performance TestingExperimental Set-up

• Nozzle is selected based on required flow range• Nozzles should always point downstream• Fan to be tested is mounted on the front plate of

the chamber• Fan should be sealed adequately to prevent

leakage

Fan Performance TestingExperimental Procedure

• First data point is considered at no flow or shut off condition

• At this point differential pressure is zero• Start the counter blower at low speed• Slowly open the blast gate until 0.1 inches

w.g. is measured for the differential pressure• Allow the fan to stabilize and record the data

Fan Performance TestingExperimental Procedure (Contd…)

• Record the data points for different Blast gate opening

• As the experiment proceeds, differential pressure increases and static pressure decreases

• Continue taking data points till free delivery is reached (I.e zero static pressure)

• Shut off the counter blower and plot the data• Data points fully define the fan performance

curve

Typical Performance Curve


System Impedance Testing

• Purpose for this test is to determine the pressure required to move the appropriate amount of volume flow through the system

• For the impedance test, the air is forced through the unit to be tested and the pressure drops are measured for various flow points

System Impedance TestingExperimental Procedure

• Open the blast gate completely• Start the counter blower and blow air through the

unit to be tested• The first data point should be a minimum of 0.1

inches w.g. differential pressure• Take 5 to 6 data by increasing the counter

blower speed

Typical System Resistance Curve


Theoretical Operating Point

• Superimpose Performance curve on Impedance Curve.

• Intersection of the two curves represents theoretical operating point of the fan.

Theoretical operating point


Thermal Resistance

• With the evolution of the personal computer, the cooling of high power components has moved to the forefront of system design

• Over the years the power dissipation in the PC s microprocessor has been increasing steadily

• For this reason, the use of heat sinks in computers has become more common

• By measuring thermal resistance as a function of free stream velocity, thermal designers can predict the performance of heat sinks in their system and predict the temperature of components

Calculation of thermal resistance

• The airflow chamber is used as the air source for the system

• For a given volume of air drawn through the system temperatures are measured

• Thermal resistance is calculated by:

where, Tcomponent = Case temperature of component Tambient = Ambient temperature upstream of the heat sink Pcomponent = Power dissipation of component Rthermal = Thermal Resistance

*Tcomponent = Tambient + Pcomponent x Rthermal

Calculation of thermal resistance (Contd..)

• *Graph of Thermal Resistance Vs. Approach velocity is plotted

* Reference: “Standardizing heat sink characterization for forced convection” by Christian Belady

Thank You!

air flow bench

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