| dc.description.abstract | Due to the gradually popularized of the communication satellite and cold chain transportation applications, low-temperature heat pipes are increasing it importance drastically in the past years. Most of those applications are in the temperature range of -20 to -40 oC. However, very few researches have been conducted within this temperature range. This study provided an experimental measurement of heat transfer performance of heat pipes operating at temperatures near -40 oC. Using three different sintered copper heat pipes with outside diameters of 8mm, 10mm, and 12 mm and using refrigerant R-32, R-134a, and R-245fa as working fluid were tested.
Based on the experimental results, the thermal resistance of refrigerant R-32 is best, followed by refrigerant R-134a, while refrigerant R-245fa performs the worst. The possible reason is that refrigerant R-32 has best property of saturated vapor pressure gradient, liquid thermal conductivity, and liquid transport parameter compared to refrigerant R-134a and refrigerant R-245fa.
The overall thermal resistance of the diameter of 12mm heat pipe is lower than that of the diameter of 10mm heat pipe in both refrigerant R-245fa and R-134a heat pipes. The reason is the larger diameter heat pipe, the heat transfer area of the liquid-vapor interface in the evaporating and condensing sections increases, leading to a decrease in the liquid-vapor interface thermal resistance and thus reducing the overall thermal resistance of the heat pipe. However, in the R-32 refrigerant heat pipe, the diameter of 12mm heat pipe has a thicker wick than the diameter of 10mm heat pipe. This results in an increase in the thermal resistance with the fluid-wick interface. The thickness of the wick has a more significant impact on the thermal resistance, causing the diameter of 10mm heat pipe has lower thermal resistance than the diameter of 12mm heat pipe in refrigerant R-32 heat pipes. | en_US |