Heat Transfer for Louvered Fin

Heat Transfer for Louvered Fin - Heat and Mass Transfer...

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Heat and Mass Transfer An experimental investigation of heat transfer and flow friction characteristics of louvered fin surfaces by the modified single blow technique K. C. Leong, K. C. Toh Abstract This paper describes the development of an experimental facility to determine the heat transfer and flow friction characteristics of heat exchange surfaces by the modified single blow technique and the application of this transient technique to evaluate the performance characteristics of louvered fin heat exchangers. The reli- ability of implementing the modified single blow technique on the developed test facility is borne out by the good agreement in the heat transfer and flow friction data for the parallel plate test core when compared with theoretical and empirical correlations available in the literature. Per- formance evaluation of two louvered fin surfaces used mainly for cooling of large land and marine based elec- trical power generator sets is carried out and compared with similar louvered fin surfaces available in the litera- ture. On the basis of dimensionless area and power factors, it was found that the flat fin is slightly superior in overall performance than its corrugated counterpart for low Reynolds numbers. Both surfaces are however inferior in performance when compared with the flat fin surface of Achaichia and Cowell and the corrugated fin surface of Davenport. Use of the j/f ratio as an approximate figure of merit led to an inaccurate assessment of the performance of the louvered fin heat exchanger surfaces evaluated in this study. List of symbols A c exchanger minimum free-flow area (m 2 ) A fr exchanger frontal area (m 2 ) A s total exchanger surface area (m 2 ) C specific heat (J/kg ± K) D h hydraulic diameter, 4 A c L = A s (m) G mass velocity, _ m = q o A fr (kg/m 2 ± s) h convective heat transfer coefficient (W/m 2 ± K) k thermal conductivity (W/m ± K) K c ; K e entrance and exit pressure loss coefficients L length of test core (m) M s mass of solid (kg) _ m mass flow rate (kg/s) P pressure (N/m 2 ) p fan power (W) q heat transfer rate (W) T temperature (K) v fr frontal velocity (m/s) h time (s) s i time constant of inlet fluid temperature response (s) q m mean fluid density (kg/m 3 ) q o porosity of solid matrix D P pressure drop across test core (N/m 2 ) Dimensionless groups f Fanning friction factor j Colburn- j factor, St-Pr 2 = 3 NTU number of heat transfer units, hA s = _ m f C f Nu Nusselt number, hD h = k f Pr Prandtl number, l C f = k f Re Reynolds number, GD h = l St Stanton number, h = GC f T ² f Dimensionless fluid temperature, ³ T f ´ T i µ = ³ T fm ´ T i µ T ² s Dimensionless solid temperature, ³ T s ´ T i µ = ³ T fm ´ T i µ x ² Dimensionless length variable, x = L k Longitudinal heat conduction parameter of solid material, k y A fr q o = ³ _ m f C f L µ h ² Dimensionless time, _ m f C f h = M s C s s ² i Dimensionless time constant, _ m f C f s i = M s C s Subscripts av average value ex experimental values f fluid (air) fm final steady-state value i initial value or orifice plate
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Heat Transfer for Louvered Fin - Heat and Mass Transfer...

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