Experimental performance of R134a filled thermosyphon heat pipe heat exchanger using plain and rifled tubes

Abstract

Heat pipe technology becomes popular in waste heat recovery applications and in heating, ventilation and air conditioning (HVAC) systems in recent years, especially in increasing the dehumidification efficiency and cooling capacity of the cooling coil especially in warm-climate countries. An experimental study was carried out on air-to-air thermosyphon heat pipe heat exchanger (THPHE) filled with R134a as the working fluid and a fill ratio of 60% of the evaporator volume. Two configurations were tested; plain and grooved (rifled) inner surface THPHE. For each THPHE module, the lengths of the evaporator and condenser sections were 300 mm and the central adiabatic section was 100 mm. There were 6 rows of 48 copper tubes with 12 mm outside diameter. Aluminum wavy plate fins were fixed between the tubes to increase the heat transfer area. A test rig was set up to study the thermal performance of the THPHE, different sets of experiments were carried out by varying the heat load as well as the mass flow rate inlet to evaporator section of the heat exchanger; the two THPHEs were examined under low temperature (30-60ᴼC) operating conditions. Four evaporator section air face velocities namely, 1, 1.5, 2, and 2.5 m/s were tested while ambient air flowed through condenser section with air face velocity controlled at 1.5 m/s. The results shows that the THPHE effectiveness values are shown to vary with the evaporator inlet temperature and mass flow rates. Also, the inner grooved THPHE showed a significant effect on increasing the thermal performance of the heat exchanger as compared with the plain inner surface THPHE.