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Convective heat exchange within a compact heat exchanger

Convective heat exchange within a compact heat exchanger. EGEE 520 Instructor: Dr. Derek Elsworth Student: Ana Nedeljkovic-Davidovic 2005. 1. Introduction. Characterised mainly by a high heat transfer area per unit volume; Optimization between heat exchange and pressure drop;

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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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