Performance Analysis of Water Recovery Heat Exchanger with Novel Design Methodology

There are many models in the literature for heat and mass transfer of vapor condensation in the presence of a non-condensable gas, but most models require the evaluation of three different heat transfer coefficients and input parameters that are usually unknowns and experimentally measured. In this paper, a condensing heat exchanger (CHE) with a new application was introduced for a turbofan aircraft to recover both heat and water and a novel methodology for the design of a CHE that evaluates directly the total heat transfer coefficient for the gas mixture was presented. Such a methodology locates the onset of condensation and does not require any experimental measurements. An air-cooled CHE was divided into 50 sections and the principles of thermodynamics, energy balance, and heat transfer were applied to evaluate the temperatures, properties, length of each section, and the local air and total gas heat transfer coefficients. The results showed that enhancing the overall heat transfer coefficient and reducing the CHE weight could be achieved with a less total pressure drop for the gas and airflows by increasing the air mass velocity at the same mass flow rates of the gas and air when compared with raising the gas velocity at the same mass flow rates of the gas and air.