Thermal design of a high temperature bayonet tube heat exchanger with inner and outer fins

In this paper, a new metallic high temperature bayonet tube heat exchanger with inner and outer fins is proposed. The prime motivation for the presented study is to design a heat exchanger used in the ultra high temperature environment, such as Externally Fired Combined Cycle and syngas production processes. Previous research has shown that bayonet-element is a suitable structure in such a cruel condition, but the heat transfer efficiency is not high. Therefore, in order to improve the heat transfer performance and reduce the cost, a new bayonet tube heat exchanger with fins being employed outside and inside outer tubes of bayonet-elements has been proposed and designed. An improved Log-Mean Temperature Difference method is used for the thermal design process. Meanwhile, two other identical structure heat exchanger are designed for comparison: the one made of only one material, the other without fins. These designs are performed under identical mass flow, inlet temperature, operating pressure, specified allowable fractions of total pressure drop and geometrical size except for fins or materials. The results indicate that the new type heat exchanger has a great potential to increase the heat transfer performance and reduce the cost.