Liquid-adjustment evaporator with zeotropic mixtures: Principle, design and statistical analysis

Zeotropic mixture has advantages of environmentally-friendly, safe and flexible thermal properties, its featured temperature glide during phase change can match the temperature variations of heat sources, enhancing the system thermodynamic performance. It has been considered as a promising alternative candidate. However, the heat transfer coefficient of zeotropic mixture generally worse than that of its pure composition, and its nonlinear temperature-enthalpy relationship also leads to extra irreversible losses. To overcome these issues, liquid-adjustment is implemented to improve heat transfer capacity and reduce irreversible losses. Firstly, the principles of liquid-adjustment for zeotropic mixture is introduced and illustrated. Secondly, a conceptual design of liquid-adjustment evaporator with counter flow for zeotropic mixture and water is proposed. Thirdly, the optimized scheme is selected and compared to the conventional evaporator. The liquid-adjustment evaporator has a 9.72 % increased heat transfer capacity and a 22.4 % reduced total exergy resistance. Meanwhile, its local heat transfer coefficients can be significantly increased by 111 % and exergy resistance decreased by 52.5 % after the first separation. Finally, statistical analysis is carried out to reveal the interactions and insights of the parameters. It is found that the vapor quality is the main influential factor in both heat transfer coefficient and local slope of T-Q curve.