An Investigation On Thermodynamic Performance Of Single-pressure Heat Recovery Steam Generator

The process of energy transfer and conversion is widely used in the field of industries. It is important to understand the basic rules of energy transfer processes for controlling and improving the processes.Energy is conservative in its transfer and conversion process, while exergy is non-conservative for the irreversibility in its transfer process. Thus, the exergy must have its particular rules. It is of great theoretical significance and practical value to study the rules of exergy transfer and conversion. But there is a lack of the research of exergy transfer on heat recovery steam generator.This paper is based on"The first and the second thermodynamic laws". In considering the flow friction or not, the exergy transfer characteristics is investigated in a single-pressure heat recovery steam generator which operating above the surrounding temperature. Exergy transfer effectiveness and heat transfer effectiveness are firstly derived and their equations have been provided. The effects of heat transfer unit number and the ratio of heat capacities of the cold fluid to the hot fluid on heat transfer processes and exergy transfer processes of heat recovery steam generator are discussed systemically. In addition, contraste the exergy transfer effectiveness for zero pressure drop and that for a finite pressure drop. Meanwhile, exergy transfer effectiveness is compared with heat transfer effectiveness.It is found that: the heat transfer effectiveness is always larger than the exergy transfer effectiveness under the same conditions for a single-pressure heat recovery steam generator which is composed of economizer, evaporator and superheater; and the exergy transfer effectiveness for zero pressure drop is also always higher than that for a finite pressure drop under the same conditions. Furthermore, when heat transfer unit number and the ratio of heat capacities of the cold fluid to the hot fluid of heat recovery steam generator are varied, the exergy transfer effectiveness and the heat transfer effectiveness present different characteristics.