Effect of solid heat conduction on heat transfer performance of a spiral heat exchanger

The effect of radial and spiral-direction heat conduction in the solid partition between hot and cold streams on the effectiveness of a spiral heat exchanger was numerically studied for the balanced flow condition. The heat exchanger was represented by Archimedes spirals. A maximum effectiveness was found as the number of transfer units (NTU) becomes large. The NTU value at the maximum effectiveness increases as the number of turns increases. The spiral-direction heat conduction causes the effectiveness to decrease as the Biot number (Bi) based on the partition's thermal conductivity decreases, while the radial-direction heat conduction increases the effectiveness. A competition of the two different heat transfer-phenomena results in an optimal Bi value to maximize the effectiveness. The result also shows that the effect of solid heat conduction on the effectiveness is small for 0.01 < Bi < 0.1. (C) 2014 Elsevier Ltd. All rights reserved.