Heat Transfer Characteristics Of Gravity Heat Pipe With Self-Rewetting Fluid

Gravity heat pipe is a highly efficient heat transfer element which is widely applied to all kinds of heat transfer application fields in industry because of its simple structure, convenience in manufacturing and processing, low cost in production. With the increasing national attention on energy and environment issues, it has been increasingly important to focus the enhancement of performance in gravity heat pipe researches. The author has grasped the current research status by reviewing the literatures concerned and classified the heat transfer technologies as applying highly efficient working fluids, modifying the inner surface, and inserting inner pipe in the gravity heat pipe. Currently applying highly efficient working fluids has been the hot spot in researches. Since self-rewetting fluid is recently introduced as the highly efficient working fluid, researches conducted on it are fewer and insufficient. Thus, this paper selects the self-rewetting fluid as the gravity heat pipe’s working fluid and studies the heat transfer characteristics of the heat pipe.This paper chooses the gravity heat pipe with self-rewetting fluid as the research subject. The fundamental heat transfer characteristics of the gravity heat pipe are studied by changing the experimental parameters. The characteristics of heat transfer enhancement of the gravity heat pipe at regular and small inclination angles are acquired by the experiment in contrast with gravity heat pipe with water. The main research work and conclusions are as follows:1. The current status of heat transfer research enhancement of gravity heat pipe are reviewed by reading relevant literature and the gravity heat pipe’s basic heat transfer theory as well as the mechanism of heat transfer enhancement of self-rewetting fluid are grasped.2. The gravity heat pipe manufacturing and experimental platform set-up are accomplished. Gravity heat pipes with two different working fluids are fabricated. The experimental platform used by the paper is set up. The heat pipe performance test scheme and experimental data processing method are determined.3. The fundamental heat transfer characteristics of the gravity heat pipe with self-rewetting fluid are experimentally investigated. Conclusions are drawn as follows: with the increase of input power, inclination angle, and filling ratio, the thermal resistance of the gravity heat pipe always increases first, and then decrease. The optimum inclination angle decreases with the increase of input power. The optimum filling ratio acquired by the experiment is 180% of the heat pipe evaporator volume.4. The characteristics of heat transfer enhancement of the gravity heat pipe with self-rewetting fluid are experimentally investigated. Conclusions are drawn as follows: self-rewetting fluid can reduce the start-up time of gravity heat pipe but meanwhile increases its start-up temperature. With the increase of input power, the start-up time and start-up temperature gradually approaches those of gravity heat pipe with water. At the horizontal position, self-rewetting fluid deceases thermal resistance and increases the heat transfer limit of gravity heat pipe, and thus significantly improves the performance of gravity heat pipe. At vertical position, self-rewetting fluid is found to deteriorate the gravity heat pipe’s performance.5. The characteristics of heat transfer enhancement of the gravity heat pipe with self-rewetting fluid at small inclination angles are experimentally investigated. Conclusions are drawn as follows:gravity heat pipe with self-rewetting fluid shows higher operational temperature, axial temperature difference and thermal resistance but also shows significantly increased heat transfer limit, self-rewetting fluid proves to have certain advantages in contrast with water at small inclination angles.6. The characteristics of combined heat transfer enhancement of gravity heat pipe with self-rewetting fluid and with internal thread structure are experimentally investigated. Conclusions are drawn as follows:the effect of the combined enhancement can decrease the operating temperature, reduce the thermal resistance, and increase the heat transfer coefficient of the heat pipe.