Effect of Inlet Flow Angle on Performance of Multilouvered Fin Heat Exchangers

摘要

The effect of inlet flow angles on flat tube multilouvered fin heat exchangers is studied. Five inlet flow angles, α= +- 25, +- 45 and 0 degrees are employed with respect to the face of the heat exchanger. One louver angle θ = 25 degrees, and three fin pitches, F_p =1.0, 1.5 and 2.0 are considered. There is a strong correlation between the response of the flow efficiency and heat transfer coefficient to inlet flow angle. Positive flow angles, which are in the same direction as the louver angle, have to undergo a smaller rotation to be aligned with louver directed flow in the bank, and exhibit better performance characteristics than negative inlet flow angles. The first-order effect of inlet flow angles is to reduce the effective mass flow rate and Reynolds number through the heat exchanger. For positive flow angles and small fin pitches, the heat transfer coefficient correlates well with the effective Reynolds number {Re_(eff) = Re(cosα)}. However, this is not the case when flow angles are negative and the fin pitch increases. Under these conditions, the Nusselt number deviates considerably from the effective Reynolds number analogy, with a subsequent loss in heat transfer capability. For large negative inlet flow angles (α = -45), the heat transfer coefficient drops as much as 50% for a fin pitch F_p = 2.