Experimental and Numerical Characterisation of a Non-Tubular Stirling Engine Heater for Biomass Applications

In the current context of environmental deterioration and rising energy costs, systems based on Stirling engines are interesting not only because of their proven efficiency and very low noise level, but also because of their ability to use renewable energies. Micro-CHP units based on Stirling engines fuelled by both solar energy and biomass can reduce CO2 emissions on a household scale, but the second option avoids problems usually related to the intermittency of solar energy. This paper describes the geometry and experimental characterisation of a new non-tubular heater design that is potentially interesting for biomass applications, and its analysis by means of a CFD model. The CFD model provides valuable information, under engine operating conditions, on the temperature distributions in the walls and the working gas, as well as the pressure and velocity of the gas particles, which are operating variables that are almost impossible to measure in practice. The new heater can be coupled to the Stirling engine of a previously developed micro-CHP unit for solar energy conversion, which has another non-tubular heater. The heat transfer rates achieved with both non-tubular heaters are compared with each other and with the values of the SOLO V160 engine heater, which consists of a tube bundle. The results show that the micro-CHP Stirling unit would develop more indicated power with the biomass heater than with the solar heater, providing information for future improvements of the indicated efficiency.