Analysis of Stirling Engine Heater Head with Liquid NaK for Heat Transportation

摘要

Free-piston Stirling engine has been extensively studied due to its high efficiency and fuel flexibility.As a kind of external combustion engine,heat transfer at the hot end has a great influence on the engine efficiency.In order to gain higher efficiency and configuration flexibility,a heater head structure with NaK liquid metal for heat transportation was numerically investigated based on the 1 kWe class Stirling engine in our lab.Firstly,through theoretical calculation,it was found that the heat conduction through the stainless steel wall causes a major temperature difference for heat transfer in heater head of the original configuration.With the concept studied here,the heat transfer temperature difference could be much reduced.Secondly,flow velocity and temperature fields were obtained to investigate the non-uniformities of flow and heat transfer in NaK passages.In order to suppress these non-uniformities which influence the engine performance,a dual opposed NaK outlet manifolds design was selected.Meanwhile,a finite element analysis was also performed to investigate the internal stress to check the structural strength of the heater head.The results show that this heater head design can effectively reduce the heat transfer temperature difference without sacrificing the structural strength.The study provides us a useful reference for designing liquid metal heat exchanger for free piston Stirling engines in the future.