Closed-loop oscillating heat-pipe with check valves (CLOHP/CVs) air-preheater for reducing relative humidity in drying systems

A CLOHP/CV air-preheater has been used for recovering the waste heat from the drying cycle. The CLOHP/CV heat-exchanger consisted of copper tubes 3.58 m long and internal diameter 0.002 m. The evaporator and condenser sections were 0.19 m long, the adiabatic sections 0.08 m long, the hot air velocity was 0.5, 0.75 or 1.0 m/s with the hot air temperature 50, 60 or 70 °C, and the relative humidity was 100%. The working fluid was R134a with a filling ratio of 50%. The hot-air temperature increased from 50 to 70 °C; the heat-transfer rate increased slightly. The velocity increase from 0.5 0.75, to 1.0 m/s led to the heat-transfer rate slightly decreasing. The velocity increase from 0.5 to 1 m/s led to a slight decrease in effectiveness. As the hot-air temperature increases from 50 to 70 °C, the effectiveness slightly increased; and the relative humidity was reduced to the range 54–72% from 89% to 100%. The CLOHP/CV air-preheater can reduce the relative humidity and achieve energy thrift.