Thermal Investigation of the Green Revolution Energy Converter : A study on the heat transfer within the GREC in regards of temperature distribution and heat rate

Abstract: To reduce emissions, new technological solutions can be of use. One technology which is currently being developed is the Green Revolution Energy Converter, GREC. GREC is an engine with the aim to produce electricity from temperature gradients.  This project is part of a greater project that is divided in two with different focus areas. These two projects aim to deliver a specification of the next step of the prototype, called: Lab Model v3, which is expected to be built in spring 2023. The aim of this report is to contribute with new knowledge about the heat transfer on the hot section of the GREC model. The goal is to design the heat block and conductive fin, HB and CF, to deliver high amount of heat to a volume of air which is called the work generating volume, WGV. This includes evaluating two different heat transfer techniques which in this report are called None Pipe Heat Transfer, NPHT, and Pipe Heat Transfer, PHT. The temperature distribution within the CF and the HB, as well as the heat transfer to the WGV are analyzed.  This analysis is performed for different radii and thicknesses of the CF and HB, different flow rates of the heat carrier in the PHT case, and for different heat source temperatures to see if the two models are applicable in real life applications. The real life application for the NPHT model is a fuel cell vehicle and for the PHT model a district heating system.  To obtain the result, ANSYS Workbench is used to create the model of GREC and MATLAB is used to calculate heat transfer coefficient and pressure losses. Furthermore, an iterative method using COMSOL Multiphysics and ANSYS Workbench was necessary to obtain temperatures of the CF, HB and WGV. The chosen method for this study comes with several uncertainties. However the trends seen in the results can still be considered credible, but exact numbers and other detailed conclusions should be avoided.  For the NPHT model, a large model in terms of radius and thickness, results in the highest total heat rate. This is due to the combination of a large CF and heat source area. The NPHT model with smallest radius and largest thickness results in the most even temperature distribution for the NPHT cases.  The PHT model presents a more even temperature distribution on the surface of the CF than the NPHT model. The largest heat rate from the different configurations derived from the PHT model is approximately three times larger than the heat rate derived from the NPHT model with the same dimensions. Moreover, a higher flow rate on the water in the pipes of the PHT model, does not affect the heat rate or temperature distribution on the CF. Therefore, a lower flow rate could be applied to save pump power. Another conclusion to this project is that the PHT model could be applicable in a district heating system with 80 ◦C, since the heat transfer coefficient values do not differ much between 80 ◦C and 100 ◦C. The NPHT model might also be applicable in a real life application. In that case, the size of CF plays a larger role than the temperature of the heat source in terms of the possible heat rate output. A final conclusion is that size, type of heat source and design of the GREC plays a vital role in terms of temperature distribution on CF and heat rate to WGV. The GREC has the potential to be applicable in real life applications in regards of heat transfer solutions.