A Space-Time Dual Decoupling Simulation Method for Performance Analysis of Engine Exhaust Waste Heat Heat Pipe-Assisted Phase Change Energy Storage Systems

To address the high computational cost of full-domain transient simulations of heat pipe-assisted phase change energy storage systems for vehicle engine exhaust waste heat recovery, this paper proposes a space-time dual decoupling method. Dimensional analysis reveals significant time-scale disparities between the fast and slow sub-domains of the system, on the basis of which the full-domain transient model is sequentially decoupled into a steady-state calibration of the fast sub-domain and a transient evolution of the slow sub-domain. Multiple steady-state calculations are first performed to calibrate an explicit mapping between the recovered heat power and the wall temperature; this mapping is then imposed as a time-varying heat-flux boundary condition to drive the independent transient evolution of the heat storage process. The results show that the fast sub-domain reaches a quasi-steady state within 20 s, with the energy balance deviation decreasing from 38.5% to below 5%. The predicted heat pipe wall temperatures and recovered heat powers agree closely with those of the traditional full-domain transient method, with maximum relative errors of 1.2% and 5.54%, respectively, while the total computational time is reduced from 4364.54 h to 147.99 h, corresponding to an approximately 29.5-fold improvement in efficiency.