Energy balance in a piston-cylinder system

Tonny

Hi, I am simulating the behaviour of oscillating flow and heat transfer in a piston-cylinder system using CFX-11.0. The 2-D axisymmetric model includes a moving boundary and isothermal boundary conditions are applied. My problem is that the energy balance of a whole cycle can't be reached while temperature and pressure seem to get to a steady state. In a simple piston-cylinder system, the net PV work during a cycle should be equal to the neat heat in and out of the system as the system gets to a steady state. In my cases, the net heat is nearly 2~9 times larger than the net PV work. It is noted that the net PV work is calculated by integrating PdV over a cycle and the net heat is calculated by integrating the heat flux over whole boundary area using CFX-post function and time period. I had simulated the MIT single space experiments using CFX. The results of pressure agree well with the experimental data, but the net loss is a few times larger than the net PV work over a cycle.

Any help will be highly appreciated.

Best regards

Taotao