1. Air Flow Bench Presented By:
Saket Karajgikar & Nikhil Lakhkar
Advisor: Prof. Dereje Agonafer
3. Air flow bench Configuration
4. 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
5. Experimental Bench Contd
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.
6. Experimental Bench Contd
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.
7. Experimental Bench Contd
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.
8. Applications of Air Flow Bench Air Flow Bench is used for:
To calculate the Air Flow Rate
Fan Performance Curve Measurement
9. Air Flow Rate
Q = Air Flow Rate (m3/min)
A = Nozzle Sectional Area (m2)
V = Average Flow Velocity through nozzle (m2/sec)
g = gravitational acceleration 9.8 m/s2
Pn = Differential Pressure
r = Specific Gravity of Air (1.2 kg/M3 at 20oC, 1atm)
10. 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
11. 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
12. Fan Performance Testing Experimental 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
13. Fan Performance Testing Experimental 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
14. Fan Performance Testing Experimental 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
15. Typical Performance Curve
16. 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
17. System Impedance Testing Experimental 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
18. Typical System Resistance Curve
19. Theoretical Operating Point Superimpose Performance curve on Impedance Curve.
Intersection of the two curves represents theoretical operating point of the fan.
20. 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
21. 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:
Tcomponent = Case temperature of component
Tambient = Ambient temperature upstream of the heat sink
Pcomponent = Power dissipation of component
Rthermal = Thermal Resistance
22. Calculation of thermal resistance (Contd..) *Graph of Thermal Resistance Vs. Approach velocity is plotted
23. Thank You!