Local Heat Transfer Characteristics of Louvered Plate Fin Surfaces

The heat transfer characteristics in 27 kinds of 15:1 scale models of multi-louvered fin heat exchanger, which is now used for automotive industries, have been investigated experimentally in the range of Reynolds number between 100 and 1800, louver pitch to fin pitch ratio, Lp/Fp = 0.3-0.9, and louver angle, θ = 20°-40°. Thermofoil heaters were used to heat louvered fins, and the local average Nusselt number for each louver in the array was obtained at constant wall temperature conditions. Also, thermal wake effect was investigated through comparison of the result that was obtained by heating only a single louver at a time and the result from heating all louvers simultaneously. A correlation was developed to predict the heat transfer characteristics. Generally, the heat transfer characteristics of the multi-louvered fins are similar to those of laminar heat transfer on a flat plate. As the Reynolds number, the louver to fin pitch ratio (Lp/Fp), and louver angle (θ) increase, the average Nusselt number increases, but the variation of average Nusselt number as a function of the louver angle is smaller than that as a function of the louver to fin pitch ratio. In the case of Lp/Fp = 0.3, the average Nusselt number of the third louver is especially lower than the others regardless of the change of louver angle. It may be that this geometry promotes the condition that induces the flow structure such as recirculation flow and flow separation.