Jet impingement heat transfer enhancement for the GPU-3 Stirling engine

In support of the Department of Energy's Stirling Engine Highway Vehicle Systems Program, this investigation demonstrated the benefits resulting from enhanced combustion-gas-side heat transfer using jet impingement in the GPU-3 Stirling engine. A computer model of the combustion-gas-side heat transfer was developed to predict the effects of a jet impingement system and the possible range of improvements available. A low temperature (315/sup 0/C) pretest was run on the GPU-3 heater head to verify the jet impingement model and to improve the correlation coefficients in the model. Utilizing the pretest data in the updated model, a high temperature silicon carbide jet impingement heat transfer system was designed and fabricated. The system model predicted that at the theoretical maximum limit, jet impingement enhanced heat transfer can: (1) reduce the flame temperature by 275/sup 0/C, (2) reduce the exhaust temperature by 110/sup 0/C, and (3) increase the overall heat into the working fluid by 10%, all for an increase in required pumping power of less than 0.5% of the engine power output. Initial tests on the GPU-3 Stirling engine at NASA-Lewis demonstrated that the jet impingement system increased the engine output power and efficiency by 5% to 8% with no measurable increase inmore » pumping power. The overall heat transfer coefficient was increased by 65% for the maximum power point of the tests. Preliminary cost estimates indicate that addition of jet impingement to the system will cost less than $50/unit on a production basis. On the basis of improved engine performance for minimal additional cost, jet impingement is an attractive addition to the design of advanced Stirling engines.« less