Decrement in heat transfer effectiveness due to solid heat conduction for a counter-current spiral heat exchanger

A new approach employing the 3-D printing technique for manufacturing a counter-current spiral heat exchanger is proposed. The heat exchanger has a thick wall, which could affect its heat transfer performance. Given this characteristic, the decrement in heat transfer effectiveness (Δɛ/ɛ) of the heat exchanger operated at balanced/unbalanced-flow condition and equal/unequal numbers of transfer units on hot-flow and cold-flow sides is numerically solved and graphically presented. The optimum Biot number, resulting from a trade-off between the spiral-direction heat conduction and the radial-direction solid-wall thermal resistance, is verified to be in the range of 10−4-10−2. The Δɛ/ɛ value at the optimum Biot number nears zero. At a balanced-flow operation, the maximum possible Δɛ/ɛ values of the heat exchanger for gas-to-gas, liquid-to-liquid and gas-to-liquid waste heat recovery applications are evaluated. It is found that a proper selection of the wall material for the heat exchanger can largely reduce the effect of solid-wall heat conduction on the heat transfer effectiveness.