Flow Boiling in Confined Spaces under Spatially and Temporally Varying Heat Flux Conditions

Flow boiling heat transfer has great potential for heating and cooling purposes in various applications due to its high heat transfer rate and uniform surface temperature. However, challenges such as dry-out, flow instabilities, and limited understanding of the underlying physical phenomena remain. Most research has focused on uniform and constant heat flux conditions, but many real-world applications are characterized by temporally and/or spatially varying heat flux conditions. This study presents a new experimental setup designed to evaluate the impact of these non-constant and non-uniform heat flux conditions on the heat transfer to low global warming potential refrigerants in different flow regimes. The setup's calibration and validation are detailed using R1233zd(E). Experimentally obtained Nusselt numbers for single phase liquid convective heat transfer were within a 10% error margin of the Gnielinski correlation and the intended flow regimes can successfully be reached. Further validation is required to investigate the effects of parameters like flow rate, pressure, and temperature before conducting two-phase flow tests, as well as time-varying and non-uniform heat flux tests. The final goal is to develop heat transfer correlations that capture the effect of the non-constant and non-uniform heat flux conditions. Those correlations could then be used in the development of cooling systems.