진동형 히트파이프를 이용한 LED 방폭등의 방열 기술 연구

Abstract

Recent global issues, including environmental problem of carbon dioxide induced global warming and high oil price, have led to a strong demand for high efficiency energy systems for the industries to continue to grow. In lighting industry, the high-efficiency LEDs (Light Emitting Diodes) are expected to replace the conventional lighting systems. Insufficient dissipation of the heat produced in the LEDs (typically ~90% of the power consumed) could cause a reduction of the LED lifetime as well as the luminance. Therefore, the first thing to consider for the LED lighting system is to develop an efficient cooling system.

In this study, an efficient cooling system for the imposed thermal boundary conditions of explosion-proof LED lightings was investigated. An explosion-proof lighting is a sealed lamp that can be used safely in a flammable environment of various industrial sites where a risk of flammable gas explosion exists. The purpose of this study is to develop a cooling system of explosion-proof LED lightings that can provide an efficient cooling as well as to use them free of installation alignment angle.

To achieve these goals, a special technology, Pulsating Heat Pipes (PHP), was applied to this cooling system. A PHP, one class of heat pipes, is made of bent capillary tubes and charged with a working fluid in a part of the internal volume. When a sufficient temperature difference exists between the heating part and the cooling part of the device, a pulsating two-phase flow of vapor and liquid slugs is induced by the vapor pressure difference corresponding to the temperature difference. Evaporation and condensation inside the capillary tube reduces substantially the thermal resistance between the heating and cooling parts.

Two experiments were conducted to develop an optimum design of the PHP for the boundary conditions of explosion-proof LED lightings. The first experimental PHP was made of copper tubes of internal diameter of 2.1 mm and the number of tube turns was 8. Five working fluids of ethanol, FC-72, water, acetone, and R-123 were chosen for comparison. The experimental results showed that an optimum range of charging ratio (liquid fluid volume to total volume) exists for high cooling performance

50% for most of the fluids.

The second experimental PHP with an increased number of turns from 8 to 26 was made of copper tubes of same diameter. The effects of the PHP alignment angle (top heated or bottom heated) and the PHP types (looped or unlooped) were investigated for three working fluids of FC-72, water, and R-123. Optimum design requirements for the cooling of an explosion-proof LED lighting were established based on the results of the two experiments. These optimum design requirements include: i) a minimum number of tube turns for a PHP operable in top heat mode, ii) the use of R-123 as working fluid with 50 % charging ratio, and iii) an unlooped type PHP.

These design requirements were applied to the design and construction of a cooling system for a 30 W explosion-proof LED lighting. The performance test of this cooling system showed an efficient cooling. With the progress achieved so far, the cooling system of an explosion-proof LED lighting developed in this study will be able to find many industrial applications.