Thermal performance characteristics of a wraparound loop heat pipe (WLHP) charged with R134A

Abstract

An experimental investigation of the performance of a wraparound loop heat pipe (WLHP) charged with R134a is reported in this paper. The copper WLHP has a two-pass evaporator section and a two-pass condenser section, each pass is 330 mm in length with an inner tube diameter of 11.2 mm. The considered configuration is similar to that used to build industrial heat exchangers, which are used for heat recovery in energy efficient air handling units. R134a is chosen as the WLHP working fluid as it is widely used. A variable output electrical heater was used to heat the evaporator section with the condenser section being cooled using a 2-pass shell and tube heat exchanger, equipped with 7 baffles to enforce coolant (water) cross flow around the condenser tubes. An average heat pipe thermal resistance expression, based on the experimental data, is introduced and used to characterise the thermal performance for the WLHP under the considered experimental conditions. The nature of the heat transfer processes and the working fluid path within the heat pipe are analysed under various operational conditions and areas of enhancement for this type of heat pipes are identified. An average value for the WLHP overall effective thermal resistances as low as 0.048 °C/W is reported.