Performance comparison of different total heat exchangers applied for waste heat recovery

Abstract

The total heat exchanger plays an important role in waste heat recovery systems, which can transfer total heat between flue gas and air. In this study, quantitative comparison of two total heat exchangers (double spray towers and an enthalpy wheel) has been investigated, and the main causes of the performance difference are analyzed. Experimental results show that the enthalpy wheel has a superior performance compared with the double spray towers. The enthalpy wheel achieves a higher total heat efficiency of 88.4%, which helps to enhance the waste heat recovery efficiency of a boiler. There are mainly three reasons: (1) the enthalpy wheel has a considerable NTU for its large specific surface area; (2) the flow rate mismatch in spray towers makes heat transfer effect deteriorate; (3) the maximal heat exchange efficiency of double spray tower is lower than that of enthalpy wheel because of the constant heat capacity of spray water. The specific heat capacity of air changes during heat and mass transfer process. Desiccant material in the enthalpy wheel works as a media with a variable heat capacity, matching with the flue gas or air better.