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Convective heat exchange within a compact heat exchanger

This study delves into convective heat exchange in compact heat exchangers, focusing on optimization between heat transfer and pressure drop. Analytical expressions and governing equations are used to model temperature distribution and validate results. Parametric studies and analysis of the Nusselt number demonstrate the impact of velocity and wall temperature on heat transfer coefficients. The importance of determining local heat transfer coefficients for precise calculations is highlighted. Conducted in 2005 by Ana Nedeljkovic-Davidovic under the guidance of Dr. Derek Elsworth.

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Convective heat exchange within a compact heat exchanger

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  1. Convectiveheat exchange within a compact heat exchanger EGEE 520 Instructor: Dr. Derek Elsworth Student: Ana Nedeljkovic-Davidovic 2005

  2. 1.Introduction • Characterised mainly by a high heat transfer area per unit volume; • Optimization between heat exchange and pressure drop; • Parallel flow compact heat exchangers d=2[mm]

  3. 2.1Governing Equations • Analytical expression describing parabolic velocity distribution u=16Umax(y-y0) (y1-y) (x-x0) (x1-x0) / [(y1-y0)2(x1-x0)2] • Energy balance equation • Boundary condition Twall=500[K] T inlet=300[K]; Convective flow-outlet;

  4. 2.2Solution using FEMLABTemperature distribution • Air: • k=0.0505 (w/m K) • c= 1529 (J/kg K) • ρ= 0.8824 (kg/m3) • Velocity: • U max = 2.2 (m/s) • Twall=500[K] • Tinlet=300[K] • Aluminum: • k=155 (w/m K) • c= 895 (J/kg K) • ρ= 2730 (kg/m3)

  5. 3.1Validation FEMLAB results: ∫T2dA=0.001528 [Km2]; ∫WdA=3.168e-6 [m/s m2] Mass and heat flow rate: Average heat transfer coefficient: a=89.21 [W/m2K] Average value of the Nusselt number: Nu= aD/k=3.18 Thermally fully developed flow with constant wall temperature Nu=2.976 ( A.F. Mills, 1999, Heat transfer)

  6. 3.2 Validation • Re= 68 <2300 • Tm=400[K] • Thermally developing, hydraulically developed flow for Re <2300 and constant wall temperature (Housen)

  7. 4. Parametric study

  8. 5.Section of the heat exchanger

  9. 6. Conclusion • Average value of the Nusselt number Nu= aD/k=3.18 • Convective heat transfer coefficient increases with an increase in velocity and with an increase in wall temperature • To calculate more precise value of a and Nu , local heat transfer coefficient is necessary to be determined.

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