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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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convective heat exchange within a compact heat exchanger

Convectiveheat exchange within a compact heat exchanger

EGEE 520

Instructor: Dr. Derek Elsworth

Student: Ana Nedeljkovic-Davidovic

2005

1 introduction
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 1 governing equations
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 2 solution using femlab temperature distribution
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 1 validation
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)

3 2 validation
3.2 Validation
  • Re= 68 <2300
  • Tm=400[K]
  • Thermally developing, hydraulically developed flow for Re <2300 and constant wall temperature

(Housen)

6 conclusion
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.