Optimal Design of Crossflow Heat Exchangers,"

Introduction Air-to-air heat exchangers are becoming more popular in HVAC applications, in process heat recovery and drying applications in the paper, food, steel and chemical industries, and in regenerative gas turbine systems. These exchangers can be configured as heat-pipe heat exchangers, rotating regenerators, plate recuperators, and plate-fin and tube-fin type heat exchangers Crossflow heat exchangers show inferior performance when compared to rotary heat exchangers. For equal overall heat transfer conductance and equal capacitance rates of the fluid streams, the effectiveness of the crossflow heat exchanger is consistently lower than the effectiveness of a well-operated rotary heat exchanger. Although the latter type heat exchanger is operated with counterflow of the fluid streams, the modeling equations for both types of exchangers are similar and, for infinite transfer coefficients, the performance of both exchangers is the same, neglecting flow leaks and carry-over effects in the rotary exchanger. This reduced performance of the cross-flow recuperator must result from the fact that the heat transfer surface within the exchanger is not used effectively. This effect thus points towards a nonoptimal design of conventional crossflow heat exchangers. The design procedures for compact crossflow heat exchangers are well established These existing rating and sizing procedures use the results obtained from the theoretical and elaborate experimental work on compact heat exchanger surface