Start-up from the frozen state of two-phase thermosyphons

Abstract

In a cold region, ethylene glycol or propylene glycol aqueous solution is usually used as a working fluid of thermosyphons, because if pure water is used as a working fluid, the thermosyphon tube breaks due to the volume expansion of ice when water freezes into ice. If a non-freeze working fluid is required, for example, under the environmental temperature of −20 °C, around 37 mass% ethylene glycol aqueous solution must be used. Usually, two-phase heat transfer coefficients of binary mixtures become lower than pure liquid. As the concentration of ethylene glycol increases, the freezing point lowers, and then the heat transfer coefficient also lowers. Therefore, if the small concentration of ethylene glycol is used, the degradation in heat transfer may be small. In the present study, 1–40 mass% ethylene glycol aqueous solutions were prepared, and they were poured into glass test tubes, respectively. These glass test tubes were immersed in ethanol of −20 °C to −40 °C, which were cooled down by a refrigerator. Consequently, the test tube with pure water was cracked and broken, but the other test tubes were not broken even in the case of 1 mass% concentration. Since the above fact was found, the start-up experiment from the frozen state of the two-phase thermosyphon was carried out using 1 and 2 mass% ethylene glycol aqueous solutions as the working fluid. As a result, it was revealed that these thermosyphons started up smoothly without any troubles.