Experimental Analysis on Thermal Performance of a Pulsating Heat Pipe Using Mixed Working Fluid of Dowtherm J and R-141b

Abstract

In this study, PHP thermal performance was evaluated by the use of mixed refrigerant of Dowtherm J and R-141b. The major aim is to enhance thermal performance and start up process of pulsating heat pipe (PHP), and measure the heat transfer coefficient of mixed working fluid Dowtherm J and R-141b and pure Dowtherm J. This paper introduces the results of the effect of working fluid on thermal performance of Pulsating Heat Pipe (PHP) for medium temperature range. The serpentine type of PHP was fabricated with copper tube outside diameter (O.D 12.7mm) and inner diameter (I.D 9.7mm). The working fluid employed was Dowtherm J and also Startup procedures in PHP filled with Dowtherm J and R-141b mixture was examined. The working fluid R-141b was soluble in Dowtherm J and the mixture was homogeneous. The composition of this mixture is 99.5% Dowtherm J and 0.5% R-141b, 99% Dowtherm J and 1% R-141b and 98% Dowtherm J and 2% R-141b respectively. The working fluid Dowtherm J and R-141b mixture were carried out by varying R-141b Percentage volume within the range from (0.5~2%vol.). However, increased proportion of R-141b in the mixture also increases saturation vapor pressure which is not desirable for heat pipe operation. In the case of R-141b (0.5%vol.), PHP operation was stable. It was observed at temperature below 100℃, R-141b was boiling with increased nucleation site, and the average temperature difference between the evaporator and condenser section was 47.5℃ in the case of PHP filled with Dowtherm J and R-141b (0.5%vol.), and 89.4℃ for single Dowtherm J. The result shows that temperature difference in the case of single Dowtherm J is twice that of the mixture of Dowtherm J and R-141b.