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ME 379 Final Presentation
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Pressure Drop Across A Louvered-Fin Heat ExchangerAnthony DelRicciNathan GentitMatthew Zeld
Problem Statement
The pressure drop across an array of nozzles is known and is used to calculate the volumetric flow rate of air through a wind tunnel. With this calculated volumetric flow rate and known geometrical properties of the louvered-fin heat exchanger, the loss coefficients, friction factor, and ultimately, the pressure drop across the louvered-fin heat exchanger can be estimated.
Thermal Fluids Principle• Pressure drop across
heat exchanger• Friction factor• Entrance/exit losses• Fluid properties• Fluid velocity• Heat exchanger dimensions
• Fluid velocity• Volumetric flow rate• Heat exchanger dimensions
• Volumetric flow rate• Wind tunnel with
nozzle array (ASHRAE standard)• Expansion factor• Discharge coefficient
of nozzles• Pressure drop across
nozzles• Nozzle dimensions• Tunnel dimension• Fluid properties
THEORY
Determining Volumetric Flow Rate (ASHRAE Standards)
• (1)
Figure 1. Example inlet chamber setup for multiple nozzles in a chamber
Determining Volumetric Flow Rate (ASHRAE Standards)
• (2)• Expansion factor
• (3)• Nozzle throat pressure to nozzle entrance pressure ratio
• (4)• Nozzle throat diameter to wind tunnel diameter ratio
Determining Volumetric Flow Rate (ASHRAE Standards)
• (5)
• Discharge coefficient of each nozzle
• (6)• Reynolds number through the nozzle array
Determining Velocity Through the Heat Exchanger• Function of volumetric flow rate and heat exchanger
dimensions• (7)
• : free-flow area
Figure 2. Theory for calculating the velocity through the heat exchanger
Pressure Drop Across Heat Exchanger• Standard equation for pressure drop across a compact heat
exchanger• (8)
Entrance effect Flowacceleration
Corefriction
Exit effect
Figure 3. Schematic of pressure variation of flow through a heat exchanger
Pressure Drop Across Heat Exchanger• (9)• Exchanger flow stream mass velocity
• : Exchanger total heat transfer area• Fin and tube surface area in contact with flowing air
• : Exchanger free-flow area• Total frontal area minus frontal area of tubes and fins
• (10)• Contraction ratio (= projected frontal area)
Pressure Drop Across Heat Exchanger• and : Entrance and exit
loss coefficient• Contraction ratio• Reynolds number
• (11)• : louver pitch• : dynamic viscosity
• For exchangers with frequent fin interruptions, use R = ∞ curve.
Figure 4. Finding loss coefficients [1]
Pressure Drop Across Heat Exchanger• Friction factor correlation for many types of compact heat
exchangers by Chang and Wang.• “Can correlate 85% of the present friction data with 10%
uncertainty.”
• (12)• : total airside surface area to external tube surface area ratio• : louver surface area to total airside surface area ratio
EXPERIMENTALAPPARATUS
Experimental Apparatus
• Blower• Wind tunnel• Nozzle array
• Housing duct• Condenser (heat exchanger)• Differential pressure gages• 1 : before and after nozzle array• 2 : before heat exchanger and atm
Experimental Setup
Figure 5. Blower side of the test setup
Experimental Setup
Figure 6. Heat exchanger side of the test setup
Experimental Setup
Figure 7. Nozzle array
Experimental Setup
Figure 8. Heat exchanger inside of housing duct, facing direction of flow
Experimental Setup
Gage used to measure nozzle array
pressure drop
Pressure tap in front of heat
exchanger
Figure 9. Pressure gage setup
Figure 10. Pressure gage setup
Heat Exchanger Dimensions• Width = 715 mm• Height = 433 mm• Depth = 12 mm• Tube height = 1.40 mm• Tube spacing = 5.63 mm
Figure 11. Schematic of heat exchanger tubes and fins
Heat Exchanger Dimensions• Fin pitch = 89 fins/dm• Fin thickness = 0.06 mm• Louver pitch = 0.850 mm
• E = 6.298• El = 0.4182
Figure 12. Schematic of heat exchanger louvers
Heat Exchanger Dimensions
Figure 13. Louver profiles
Figure 14. Picture of fins and louvers
EXPERIMENTALPROCEDURE
Experimental Procedure
• 1. Connect duct to wind tunnel• 2. Turn blower on low power setting• 3. Record pressure drop across nozzle array• 4. Record pressure drop across heat exchanger• 5. Repeat for two more blower settings• (moderate and high)
• 6. Turn off blower• 7. The remainder of the experiment is data calculation
*Read safety guidelines before performing experiment.
DISCUSSION OF RESULTS
Experimental Data
Table 1. Experimental pressure drop data
Theoretical Calculations• Using highest blower speed as a sample
• Looking at the graph:
Theoretical Calculations• Using highest blower speed as a sample
• Repeat for all flow rates
Discussion of Results
Figure 15. Theoretical and experimental pressure drops across heat exchanger
Discussion of Results• Error lies within the friction factor correlation• “Can correlate 85% of the present friction data with 10% uncertainty.”
• Rearrange Eq. 8 to solve for friction factor necessary to match theoretical pressure drop
Discussion of Results• Friction factor: function of Reynolds number
Figure 16. Calculated friction factor and necessary friction factor versus Reynolds number
Discussion of Results• Curve-fit necessary friction factors• Keeping same equation form• Reynolds number exponent changes• Heat exchanger components stay constant• Leading coefficient changes
Uncertainties• Pressure gages (± 2%)• Nozzle array: carried out through all equations• Heat exchanger: on Figure 15 experimental data points
• Friction factor (± 10%)• Cited as uncertainty in source• Overall largest contributor to uncertainty
CONCLUSION
Conclusion• Found volumetric flow rate in a wind tunnel• Using nozzle array• ASHRAE Handbook standards
• Determine pressure drop across a heat exchanger• Use existing empirical calculations• Compare calculations to experimental results
• Difference between experiment and theory was large• Derived new empirical formula for friction factor
QUESTIONS?