The response surface method is applied to design the heat exchanger with decreasing tube diameter

for the traditional design methods are not suitable for the optimization of the performance and cost of heat exchanger simultaneously. The method fits the relationship among the tube length

fin pitch

performance and cost of heat exchanger into a quadratic continuous function that can be solved directly. The accuracy of the method is verified by applying it to the optimization of 7mm tube heat exchanger

the deviation from the experimental data is 0.3%. Using the method for the optimization of 9.52mm tube heat exchanger into 5mm tube heat exchanger

the cost and refrigeration charge of designed heat exchanger decrease by 28% and 39.8%

respectively

while the performance is unchanged.