Tube and fin geometry alternatives for the design of absorption-heat-pump heat exchangers

The present study investigates the possibility of using highly compact, flat-tube/multilouver fin heat exchangers as replacements for conventional round-tube hydronic fluid-to-air heat exchangers used in space-conditioning applications. The advantages of these novel heat exchangers such as smaller frontal obstruction to air flow compared to round tubes (drag and fan power reduction), larger heat transfer coefficients due to the interrupted multilouver fins, and larger surface areas per unit volume can benefit absorption space-conditioning systems. A comparison of the performance of this new geometry versus conventional round-tube heat exchangers was performed through the quantification of the decrease in heat exchanger mass for equivalent heat duties. Within the limitations of the available heat transfer and friction factor correlations, round-tube heat exchangers with flat,wavy, louvered and annular fins, and flat-tube heat exchangers with multilouver fins were designed to meet typical absorption cycle design conditions. The effect of design variables such as parallel/serpentine flow arrangements of tubes, fin densities, core depth, and other parameters on heat transfer performance and tube-and air-side pressure drops was investigated. It was shown that hat-tube heat exchangers can transfer equivalent heat duties while meeting pressure drop constraints with a significant reduction in the overall mass and size.