Local boiling heat transfer and pressure drop in smooth horizontal tube for geothermal facilities

•Measurements of local evaporation heat transfer and pressure drop.•Experiments are conducted respecting the geothermal facilities application.•The new correlation are proposed for local evaporation heat transfer.•Two-phase flow structures for tested refrigerant mass fluxes are investigated.•The proposed correlation well predicts the experimental data of local pressure drop.

Improving the energy efficiency of thermal machines is a key point which ensures a strong advancement in solving problems related to energy consumption and environmental protection. Our study concerns an energy characterization and optimization of geothermal heat pumps heat exchangers for industrial and residential applications. As part of this study, experimental analysis of the boiling of the R134a is carried out in a smooth horizontal tube external diameter 7.94 mm and 1 m of length. The refrigerant Reynolds number ranges from 4200 to 9820. This paper presents a detailed description of the experimental device, instrumentation of the test section and analysis of results. The influence of refrigerant inlet Reynolds number on the dry-out phenomenon is determined, and flow map is presented. Based on the experimental data, correlations are proposed to predict the heat transfer coefficient and frictional pressure drop.