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
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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
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.
Reference: www.fantester.com
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.
Reference: www.fantester.com
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.
Reference: www.fantester.com
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
Q = 60 x A x V
where,
Q = Air Flow Rate (m3/min)
A = Nozzle Sectional Area (m2)
V = Average Flow Velocity through nozzle (m2/sec)
V= ( 2 g Pn / r)1/2
where,
g = gravitational acceleration 9.8 m/s2
Pn = Differential Pressure
r = Specific Gravity of Air (1.2 kg/M3 at 20oC, 1atm)
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 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
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
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
Typical Performance Curve
Reference: www.fantester.com
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 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
Typical System Resistance
Curve
Reference: www.fantester.com
Theoretical Operating Point
Theoretical operating point
• Superimpose Performance curve on
Impedance Curve.
• Intersection of the two curves represents
theoretical operating point of the fan.
Reference: www.fantester.com
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:
*Tcomponent = Tambient + Pcomponent x Rthermal
where,
Tcomponent = Case temperature of component
Tambient = Ambient temperature upstream of the heat sink
Pcomponent = Power dissipation of component
Rthermal = Thermal Resistance
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!