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This paper deals with the investigations on the thermal performance of a vertically oriented closed loop pulsating heat pipe (VCLPHP), both experimentally and by the use of dimensionless numbers. The working fluids used are acetone, ethanol, methanol and heptane. The VCLPHP consists of copper capillary tubes bent into five turns. The tube’s inner and outer diameters are 2 mm and 3 mm, respectively, and are made of copper. The lengths of the evaporator, adiabatic and condenser sections are 50 mm, 90 mm and 70 mm, respectively. A constant fill ratio and a constant heat input of 60% and 80W, respectively, were used for the experimental investigations. The evaporator section was heated by means of a strip heater with a heating capacity of 400W. The condenser was cooled by circulating water. The experimental results showed that acetone is a better performer as compared to other fluids in terms of low thermal resistance and high heat transfer coefficient. Heptane showed the lowest thermal performance among all fluids. Ethanol and methanol showed average performance. The dimensional analysis was carried out using Kutateladze number, Prandtl number, Karman number, Bond number and Jacob number. Ethanol which showed an average performance in experimental investigations displayed the best thermal performance in terms of Prandtl number. With respect to Bond number, Karman number and Jacob number, acetone showed the best thermal performance. Heptane showed average thermal performance for all dimensionless numbers. Since the thermal performance of acetone both experimentally and by dimensional analysis was better than other working fluids, it may be considered as a suitable working fluid for application in PHP.

Thermal performance of a vertical closed loop pulsating heat pipe and analysis using dimensionless numbers