| Enhancement of external condensation heat transfer for refrigerants is of a great value and importance especially in the case of tube bundle configuration. Significant enhancements have been achieved in recent years with passively enhanced tubes. Further augmentation, most likely, will have to be achieved actively. Electrohydrodynamics (EHD) phenomena show a great potential for significantly enhancing the heat transfer in two-phase systems.; This research investigates, theoretically and experimentally, the behavior and effects of longitudinal EHD induction pumping of a micro film of liquid along a horizontal single tube during condensation, with regards to flow management and heat transfer. The refrigerant R123 is used as working fluid. The controlled flow management on a single tube is expected to translate in an increased thermal performance in tube-bundle configuration, since the negative flooding effect would be minimized.; More fundamental understanding on the EHD induction pumping of a stratified liquid/vapor medium is gained by extending a theoretical model to four different electrode configurations. Corresponding numerical solutions and a parametrical study is carried out. Also, the effect of heat transfer across the liquid film is investigated numerically. Furthermore, the gravity effect on the EHD induction pumping of a thin liquid film axially along a horizontal tube is explored theoretically, using a simplified analytical model. Corresponding stability issues are addressed.; A corresponding experimental apparatus has been specifically designed and constructed for this research, using R123 as working fluid. Electrode configurations with electrodes placed in the liquid film are used. An extensive study of heat flux, voltage and frequency effects is carried out with an electrode geometry of small wavelength (6mm). Three heat fluxes representative of HVAC&R applications are chosen: 15, 25, and 45 kW/m2, corresponding to average film thickness of 50–100 μm. Voltages of 1–3 kV and frequencies of 0–60 Hz are applied. Mean outside heat transfer coefficient and corresponding flow rate measurements are presented for these operating conditions. Also, an electrode configuration including partitions forcing the axially pumped liquid to drain at selected locations is tested. Finally, electrical power requirements associated with the application of the electric field to induce a pumping motion are addressed. |
