A study of heat transfer between the walls and gas inside the cylinder of a reciprocating compressor.

摘要

A numerical model of the flow and heat transfer inside the cylinder of a reciprocating compressor is used to analyze the heat transfer between the wall and the gas. A control volume finite-difference technique is used in conjunction with the SIMPLER algorithm to solve the ensemble averaged equations for conservation of mass, momentum and energy. Turbulence closure is obtained with a version of the k-;The numerical model is tested by computing the flow and heat transfer in a Helium-filled gas spring operating over a wide range of speeds, and comparing the numerical results with recent measurements by other researchers. At low speeds the flow is laminar and hysteresis loss is controlled by conduction. At higher speeds the flow is turbulent and the roll up of a corner vortex between the piston and the cylinder wall is observed. For both high and low speeds a significant phase difference occurs between the heat transfer at the gas-wall interface, and the difference between the bulk gas temperature and the cylinder wall temperature. Overall, the predictions of hysteresis loss are in very good agreement with the experiments, except for the highest speed tested (1000 RPM) where the magnitude of the hysteresis loss is small.;The numerical model is used to simulate a single-cylinder reciprocating compressor operating at 1750 RPM, using Refrigerant 12 as the working fluid. Results of the compressor simulations show that the flow field inside the cylinder is dominated by a large vortex driven by the jet of gas from the suction port. This vortex thoroughly mixes the gas so that the temperature field is relatively uniform, except for steep gradients near the walls. Parameter studies show that completely eliminating the heat transfer results in slight performance gains: a 1 percent increase in mass flow rate, and a 1.6 percent decrease in work input per unit mass. Large reductions in cylinder wall temperature have the same effect as eliminating the heat transfer. Design changes that affect the suction jet do not significantly change the heat transfer between the walls and the gas.