Comparison of thermal characteristics of three modifications of gravity heat pipe with threaded evaporator at different inclination angles

Abstract

In this paper, the thermal characteristics of three modifications of a gravity heat pipe with a threaded evaporator (cylindrical, semi-flattened, and flattened) under natural convection conditions are experimentally investigated. That is considered to be of practical interest for the use in energy-efficient passive cooling systems of electronics for various purposes (LED lighting devices, batteries of electric vehicles, transmission modules of radars, etc.). The length of the gravity heat pipe was 230 mm, the primary diameter was 12 mm, the thickness of the flattened sections was 5.5 mm, and the working fluid was Freon 141b. The input power was varied from 5 W to 50 W (in 5 W increments) at tilt angles of 0°, 15°, 30°, 45°, 60°, and 90°. This paper presents the analysis of the flattening effect on various parameters, including the temperature in the heating zone, temperature distribution along the length of the gravity heat pipe, thermal resistance, and effective thermal conductivity. It is established that the semi-flattened heat pipe exhibits the best thermal characteristics. Moreover, this study reveals the influence of the orientation of the flattened part of the gravity heat pipe relative to the horizontal plane (parallel or perpendicular to it) on its thermal characteristics. The results obtained indicate the prospects of using semi-flattened and flattened gravitational heat pipes with a threaded evaporator in passive air-cooling systems for electronics with input power values up to 50 W, for example, in passive cooling systems for LED devices, power amplifiers for transmitting modules, etc.