Effect of flow rate and flow pattern of hot water on Overall Heat Transfer Coefficient for Double Pipe Heat Exchanger

Abstract

A double-pipe multi-pass heat exchanger with necessary accessories was designed, developed, and evaluated for heat transfer performance. The performance of the heat exchanger for heating chilled water was evaluated in terms of rate of heat transfer, terminal temperature, effectiveness, and U-values by varying the flow rate of hot water at 5, 10, 15, 20, and 25 lpm, while keeping the flow rate of the medium to be heated in the inner pipe at 1.0 lpm. The maximum temperature rise was observed in the first pass of the heat exchanger at all flow rates of hot water in both flow patterns. The actual U-values of the heat exchanger ranged from 390.08 to 483.92 W/m² K and from 386.21 to 437.90 W/m² K using hot water from the solar thermal system in counter-current and co-current flow, respectively. It was observed that the actual U-value increased as the flow rate of the service fluid increased up to 20 lpm in both flow patterns. The actual U-values and effectiveness of the heat exchanger were found to be higher in the case of counter-current flow than in the co-current flow pattern at all flow rates studied. The regression equations obtained by correlating the flow rate of hot water with the actual U-values were y = 305.1x⁰·¹⁴⁷ (R = 0.9146) and y = 338.6x⁰·⁰⁰¹⁷ (R = 0.9913) for counter-current and co-current flow patterns, respectively.