Air Flow Bench

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Air Flow Bench

• Presented By
• Saket Karajgikar Nikhil Lakhkar
• Advisor Prof. Dereje Agonafer

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Air Flow Experimental Bench
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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

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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
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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.

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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
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Applications of Air Flow Bench

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

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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)
• where,
• g gravitational acceleration 9.8 m/s2
• Pn Differential Pressure
• r Specific Gravity of Air (1.2 kg/M3 at
  20oC, 1atm)

V ( 2 g Pn / r)1/2
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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

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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

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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

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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

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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

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Typical Performance Curve
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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

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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

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Typical System Resistance Curve
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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
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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

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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
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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
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Thank You!