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

• A heat transfer model for a spiral heat exchanger was developed.
• The heat transfer model includes both radial and stream-wise solid heat conductions.
• Optimal values for both number of transfer units and Biot number (Bi) were found.
• The effect of solid heat conduction on the effectiveness is small for 0.01 < Bi < 0.1.

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.