ผลของความเร่งหนีศูนย์กลางและสารทำงานที่มีต่อขีดจำกัดสมรรถนะของท่อความร้อนชนิดสั่นวงรอบแบบหมุน

Abstract

This research was studied for determine the reason on occurrence of the critical state of the rotating closed-loop pulsating heat pipe (RCLPHP) and to identify the effect of the centrifugal acceleration, working fluid, evaporation length and the meandering turn numbers to the critical heat flux (Q̇ crit) of the RCLPHP. Therefore, there are 4 dependent variables in this experiment. The quantitative experiment was performed by using the RCLPHP constructed from a 1.78 mm diameter copper capillary tube, which was bent into three different number of meandering turns: 11, 22 and 33 turn. The length of evaporator section and the length of the condenser section of heat pipe are equal. The evaporator section length was adjusted to two values, 50 mm and 100 mm. The working fluid were R123, ethanol and water. The filling ratio of the working fluid was 50% by volume of the RCLPHP. Additionally, the centrifugal acceleration of the RCLPHP was varied within 0.5g, 1g, 5g, and 10g, where g is the Earth's gravity. The experiment found that when the RCLPHP was reach into the critical state, the working fluid inside the heat pipe was dry-out and unable to transfer the heat from the evaporator sections to the condenser section. The critical state of the RCLPHP can be observed from 3 thermal characteristics as follows: the temperature of condenser section was decreased, the difference temperature between the evaporator section and condenser section was increased and the thermal resistance was increased when compared with the previous value of the heat input to the evaporator section. In the experiment involving the effect of dependent variables to the critical state of the RCLPHP, it was found that when the centrifugal acceleration was increased from 0.5g, 1g, 5g by 10g, the critical thermal density of the heat pipe was decreased. When the latent heat of the working fluid was increased from 160 kJ/kg to 904 kJ/kg and 2,260 kJ/kg, the critical heat flux of the RCLPHP was increased. Increasing the length of the evaporator section of the RCLPHP from 50 mm to 100 mm, the critical heat flux of the heat pipe was decrease. Regarding the number of meandering turns, it was found that when the number of meanderings turns of the heat pipe with the evaporator section length of 50 mm is increased from 11 to 22 and 33 turns, the critical heat flux was decreased. In contrast, the heat pipe with the evaporator section length of 100 mm found that when the number of turns was increased from 11 to 22 turns, the critical heat flux was increased and when the number of turns was increased from 22 to 33 turns, the critical heat flux was decreased. The results of this research led to the creation of a correlation for predicting the thermal performance limit of the RCLPHP. The correlation for calculate the performance limt of the RLPHP is Kumax=1.83 x 1020 Fr12.996Ka0.137Bo-0.056Ja-0.212Pr0.545 LeDi-13.316 LtLe-0.051. The correlation can be used to calculate the critical heat flux of heat pipes for design of the RCLPHP that can be installed on a rotating device or machine without operating into critical state.