Electrohydrodynamic (EHD) enhancement of shell-side phase-change heat transfer of alternate refrigerants

Experimental studies were performed to address the applicability of EHD enhancement technique on the shell-side phase-change heat transfer processes of particular interest to the refrigeration and HVAC industries, including (1) the EHD-assisted pool boiling, (2) the EHD-assisted external condensation, and (3) the EHD-induced spray-film evaporation. Each heat transfer process was studied parametrically to identify the optimal operating conditions and the heat transfer surface/electrode configuration for implementation of the EHD technique. Very attractive heat transfer enhancements were obtained for all the three EHD-enhanced heat transfer processes studied. The required EHD power consumptions in all cases were almost negligible when compared to the heat exchanger capacity.;Visualization studies were conducted to better understand the EHD phenomena associated with phase-change heat transfer processes. It was concluded that the electro-convection and the increased evaporation were the major contributions to the enhancement of boiling heat transfer. The underlying mechanism for the enhancement of condensation was based on effective liquid extraction and dispersion phenomena, which reduced the film thickness on the heat transfer surface, leading to substantially higher heat transfer coefficients.;Empirical correlations were also developed for the EHD-assisted external condensation and the EHD-induced spray-film evaporation on a vertical smooth tube and a vertical flat plate, respectively. The predictions from these correlations agreed well with the experimental results. These correlations were also employed in a cycle simulation program to quantify the performance of a vapor compression cycle that was equipped with EHD-enhanced heat exchangers. Results indicate that the use of EHD technology leads to significant improvement in COP of the system and/or reduction in heat exchanger size.