Novel Hydronic Heat Exchanger for Ice Thawing Applications

In progressive freeze concentration (PFC), a solution is phase-separated into solid ice and liquid concentrate fractions to achieve separation of certain compounds of interest by migrating all the compounds into the liquid phase, leaving the solid fraction free of any solutes. PFC is advantageous in water purification over conventional distillation by consuming considerably less energy during the phase change. However, the thawing of ice that follows usually requires more energy than PFC itself and this negates the energy efficiency benefits of PFC in the first place. Therefore, this paper introduces a novel method of using water as a heating medium (hydronic) to thaw ice that used only 7.9 % of the energy required for conventional electric resistance heating. A heat exchanger (HEX) using only room-temperature water was found to be able to thaw ice at a reasonable rate, higher efficiency and achieve overall heat transfer coefficient of 422 W/m2·°C. Shape of HEX coil and temperature setting of the electric heater were investigated for responses like electrical energy consumption and ice thawing rate. The M-shaped HEX coil with three bends increased ice thawing rate and consumed less electrical energy compared to S-shaped HEX coil with only two bends due to rate of heat transfer improvement induced by turbulence inside curved sections of the HEX coil. Increasing the temperature setting of the electric heater increased ice thawing rate but maintained the same total electrical energy consumption. Room temperature water is an energy-efficient method to thaw ice compared to electric resistance heating.