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Calculation of the mean convective heat transfer coefficient kc for the air-side heat transfer of heat exchangers with flat tubes and several fin geometries.

Functions kc_flatTube and kc_flatTube_KC

There are basically three differences:

• The function kc_flatTube is using kc_flatTube_KC but offers additional output variables like e.g. Reynolds number or Nusselt number and failure status (an output of 1 means that the function is not valid for the inputs).
• Generally the function kc_flatTube_KC is numerically best used for the calculation of the mean convective heat transfer coefficient kc at known mass flow rate.
• You can perform an inverse calculation from kc_flatTube_KC, where an unknown mass flow rate is calculated out of a given mean convective heat transfer coefficient kc

Restriction

• According to the kind of fin geometry the calculation is valid in a range of Re from 100 to 5000.
• medium = air

Geometry

Calculation

The mean convective heat transfer coefficient kc for heat exchanger is calculated through the corresponding Coulburn factor j:

j = f(geometry, Re)

with the resulting mean convective heat transfer coefficient kc

kc =  j * Re_L_p * Pr^(1/3) * lambda / L_p (Louver fin)

or

kc =  j * Re_D_h * Pr^(1/3) * lambda / D_h (Rectangular offset strip fin)

with

D_h	as hydraulic diameter [m],
kc	as mean convective heat transfer coefficient [W/(m2K)],
lambda	as heat conductivity of fluid [W/(mK)],
L_p	as louver pitch [m],
Nu_D_h = kc*D_h/lambda	as mean Nusselt number based on hydraulic diameter [-],
Nu_L_p = kc*L_p/lambda	as mean Nusselt number based on louver pitch [-],
Pr = eta*cp/lambda	as Prandtl number [-],
Re_D_h = rho*v*D_h/eta	as Reynolds number based on hydraulic diameter [-],
Re_L_p = rho*v*L_p/eta	as Reynolds number based on louver pitch [-],

Verification

The mean Nusselt number Nu representing the mean convective heat transfer coefficient kc is shown below for different fin geometries at similar dimensions.

References

Y.-J. CHANG and C.-C. WANG:

A generalized heat transfer correlation for louver fin geometry. In International Journal of Heat and Mass Transfer, volume 40, No. 3, pages 533-544, 1997.

Y.-J. CHANG and C.-C. WANG:

Air Side Performance of Brazed Aluminium Heat Exchangers. In Journal of Enhanced Heat Transfer, volume 3, No. 1, pages 15-28, 1996.

R.-M. Manglik, A.-E. Bergles:

Heat Transfer and Pressure Drop Correlations for the Rectangular Offset Strip Fin Compact Heat Exchanger. In Experimental Thermal and Fluid Science, volume 10, pages 171-180, 1995.