Experimental correlations and CFD model of a non-tubular heater for a Stirling solar engine micro-cogeneration unit

Highlights: • Revised correlations of C_f and N_st agree satisfactorily with 183 experimental data. • A validated CFD model provides tables and figures for the heater wall temperature. • Semi-empirical procedure for engine analysis is completed with the heater CFD model. • Brake power of 562 W at 888 rpm is predicted for air at 6.9 bar and heater at 600 °C. • 23.7% of brake efficiency is estimated for the engine with non-tubular heater. -- Abstract: A non-tubular heat exchanger for use in a Stirling solar engine micro-CHP unit is being developed by the University of Oviedo and the technological research centre IK4-Tekniker Foundation. In this article, the correlations for the friction factor and Stanton number previously obtained under steady flow conditions are revised and the corresponding experimental data are used to validate a CFD model of the heater. The CFD model enables the estimation of variables whose measurement is practically unviable, as is the case for the spatial distribution of wall and gas temperatures. The conceptual importance of the heater wall temperature for the analysis and design of Stirling engines is highlighted, and some limitations that are inherent in the non-tubular geometry are observed. The CFD model provides a basis for the analysis of engine operation and for subsequent geometric optimization of the heater. To evaluate the engine power and efficiency forecasts under nominal operating conditions, the CFD model is used to complement the analysis procedure based on experimental data from benchmark engines with very different geometries and operating variables. The results predict that the engine will be able to exceed the targets set in the preliminary design stage.