Heat transfer performance of Pulsating Heat Pipe with Hydrofluoroolefin

Pulsating heat pipes (PHP) are increasingly attracting attention for their potential to downsize electronic devices to be designed. Unlike conventional heat pipes, PHP maintains high heat transfer performance despite having a smaller diameter, and have a smaller dependence on heating orientation. In this study, hydrofluoroolefins (HFO) are selected as an environmentally-friendly and non-flammable working fluid for PHP. The flat-plate PHP is made of aluminum alloy, and its dimensions are a length of 222 mm, a width of 55 mm, and a thickness of 3 mm. It is prepared the channel, which is 1.2 mm × 1.2 mm square, 22 turns, and closed-end serpentine. The working fluids are R1233zd(E) and R1336mzz(Z) as HFO, and the other is R245fa as one of conventional hydrofluorocarbon (HFC). The filling ratio of each working fluid is approximately 50 %. The flat-plate PHP is set vertically, heated in the top heating orientation, and measured the equivalent thermal conductivity. When the cooling temperature is 40 °C, the equivalent thermal conductivity with R1233zd(E) and R1336mzz(Z) are between 2500 and 4000 W/(m･K), and higher than that of R245fa. When the cooling temperature is −5 °C and the heat transport rate is less than 100 W, the equivalent thermal conductivity with all working fluids are equivalent, and R1233zd(E) and R1336mzz(Z) have larger temperature dependence than R245fa. The maximum heat transport rate with R1233zd(E) is the highest, and around 190 W. When the cooling temperature is 40 °C, the maximum heat transport rate with R1336mzz(Z) is 150W, and higher than that with R245fa (104W). From the above results, we have concluded that PHP with R1233zd(E) and R1336mzz(Z) have higher heat transport performance than that with R245fa, and R1233zd(E) and R1336mzz(Z) may replace as the working fluid for PHP, instead of conventional R245fa.