(Drs. Said Abdel-Khalik and Sheldon Jeter, co-advisors)
"Electrohydrodynamic Enhancement of Convection and Boiling Heat Transfer in a Shell-and-Tube Heat Exchanger"
This thesis investigates the electrohydrodynamic (EHD) enhancement of heat transfer in a shell-and-tube heat exchanger filled with refrigerant R-134a. Electrohydrodynamics actively increases heat transfer rates in dielectric media through its impact on vapor bubble dynamics and liquid motion.
The experimental set-up consists of a 2” OD, 35” long, copper, shell-and-tube heat exchanger filled with 1,1,1,2-tetraflouroethane (R-134a) on the shell side. The shell side of the heat exchanger is a part of a natural circulation loop with a shell-and-tube condenser, a riser, and a downcomer. The condenser is placed at the highest elevation in the loop to assure continuous steady state operation of the R-134a circuit. Constant temperature baths control tube-side water temperatures in the evaporator and condenser. A hexagonal array of electrodes parallel to the length of the evaporator tube is submerged within the R-134a. A regulated high voltage DC module creates an electrostatic field with a potential of up to thirty kilovolts. The heat transfer rate in the evaporator is determined by measuring the water flow rate and temperature change. Experiments are conducted at different condenser water inlet temperatures, evaporator water inlet temperatures, and applied electric field potential. The effect of the applied electric field on the heat transfer rate for both convection and boiling conditions has been quantified. Results from EHD research of the type conducted in this investigation may beneficially reduce the size and/or the temperature difference requirements for heat exchangers under both terrestrial and micro-gravity conditions.