Convective heat exchange within a compact heat exchanger

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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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### Convectiveheat 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;
• Parallel flow compact heat exchangers

d=2[mm]

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;

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)
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:

Thermally fully developed flow with constant wall temperature

Nu=2.976

( A.F. Mills, 1999, Heat transfer)

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

(Housen)

6. Conclusion
• Average value of the Nusselt number