Dynamic Behavior of a Free-Piston Stirling Engine Driven Heat Pump With Magnetic Coupling

A new low-cost design for a free-piston Stirling engi ne driven heat pump is presented. The new approach uses a linear-acting magnetic coupling to transfer engine power across a hermetic shell. Camp l i ance in the coupling affects the performance and stability of the system, especially with regard to matchin g the engine dynamics to the compressor load. This paper first describes test results that were obtained with the Mark I diaphragm-coupled heat pump. Engine efficiencies exceeded 25% based on fuel higher heating value and heat pump COP was greater than .95 at the 95° ambient, 3-ton point. Following the description of Mark I test resu lts, the Mark II compressor design is presented. INTRODUCTION A residential-sized Stirling engine driven refrigerant compressor with attractive performance has been successfully developed at MT I. This work was performed under joint funding from the Gas Research Institute and DOE through a subcontract to Oak Ridge National Laboratory. Continuing design and de velopment of a market prototype model, the Mark II, is progressing under contract to ODE. The Mark I heat-actuated heat pump (HAHP) includes an oil-filled transmiss ion pressurized to 60 Bar. Chevron seal packs are used to seal two penetrations of the shafts that drive the compressor pistons, and two contoured steel diaphragms are used as flexible boundaries to contain the oil. Figure 1 shows a drawing of an adva nced Mark I HAHP that would function essentially the same as the laboratory model. Reference 1 describes that machine in detail and also describes the basic principle s of a free-piston Stirling engine.