Heat current method for analysis and optimization of a refrigeration system for aircraft environmental control system

Abstract

Optimization of refrigeration system for aircraft environmental control system (ECS) benefits the whole aircraft performance significantly. However, due to the complex dehumidification process, the heat transfer and heat-work conversion processes in the system, numerous intermediate variables in the system model aggravate the nonlinear and multivariate properties of the governing equations. Taking the typical two-wheel high-pressure de-water ECS as an example, this contribution introduces the heat current method to model the refrigeration system, which reveals the system topology and heat transfer and heat-work conversion characteristics simultaneously. Analogous to electrical circuit, the governing equations of whole system are obtained according to the circuit principle. Furthermore, a comparison is conducted to clarify the differences between the traditional energy flow method based on Sankey diagram and the heat current method. Next, taking the minimum takeoff gross weight as the objective, using the Lagrange multiplier method directly solves this nonlinear optimization and offers the optimal structural and operating parameters of the system. The optimized results show that the cruise flight hour has little impact on the optimal design variables, while the cabin heat load has an approximately linear relationship with the optimal design variables. Finally, when only the cabin temperature changes, the node temperatures are almost constant, which can be taken as a criterion for the design of each component.