LED is a new type of semiconductor solid-state light source with significant advantages such as low power consumption and long life. Therefore, the use of LED semiconductor lighting has been recognized as an important way to save energy and protect the environment in the face of increasing global energy shortages and increasing environmental pressures [1].
Studies have shown that [1], high-power LED electro-optical conversion efficiency is about 20%, the remaining 80% is converted into thermal energy, because the chip size is only 1 mm × 1 mm ~ 2. 15 mm × 2. 15 mm, resulting in chip power The density is very large. Unlike traditional lighting devices, white LEDs do not contain infrared in the luminescence spectrum, so their heat cannot be released by radiation. For a single LED, if the heat is concentrated in a small chip and cannot be effectively dissipated, It is easy to cause the temperature of the chip to rise, which causes non-uniform distribution of thermal stress, chip luminous efficiency and phosphor lasing efficiency. Mao Defeng et al. [2], when the junction temperature exceeds 80 °C, LED lifetime, luminous flux The output and other parameters are rapidly reduced. Chen Wei et al. [3], using micro-jet cooling, the LED input power is 9. 3 W, the junction temperature is 54. 3 ° C. Ma Wei et al. The temperature of the substrate is 33. 1 ° C. The temperature of the substrate is 33. 1 ° C.
This paper aims to propose a heat dissipation substrate-heat pipe cooling system for 80 W high-power LED under ambient temperature of 22 °C and natural convection cooling, so that the junction temperature is effectively controlled below 75 °C. The structure is because the internal working fluid of the system works within a certain range of pressure and the filling amount is reasonable, so that the concentrated heat can be spread quickly and evenly, and the heat flux density of the substrate exceeds 4 to 5 W/cm2. On this basis, the research The effect of LED input power and heat sink tilt angle on junction temperature and illuminance.
1 experimental system
1. 1 Experimental device and experimental method
The experimental setup is shown in Figure 1. The experimental system is divided into three parts: LED heat dissipation system, measurement system and data acquisition system. LED heat dissipation system: LED light source a (model V-GY70P70N8024BW, rated power 80 W) through two-way voltage regulator The steady current power supply b (model DH1718E(G), maximum output voltage 35 V, maximum output current 10 A) is supplied with power; the heat sink substrate c (also called the heat extractor) is attached to the back of the LED light source, and the heat derived from the heat dissipation substrate c passes. The heat pipe radiator d is transmitted to the environment. Measurement system: In order to facilitate the measurement and effectively display the heat dissipation substrate—the uniform temperature characteristics of the heat pipe cooling system, the system has 15 T-type thermocouples e. 1 along the working fluid flow direction. The thermocouple measures the center temperature of the heat sink substrate. The thermocouples 2 and 3 measure the temperature of the plane of the heat sink substrate diagonally. The thermocouples 4 and 14 measure the condenser outlet and inlet temperature respectively. The 5 and 13 thermocouples measure the evaporation separately. Inlet and outlet temperatures, thermocouples 6 to 12 are evenly and symmetrically placed at different locations of the radiator copper tube to measure the temperature of the radiator, and thermocouple No. 15 measures the junction temperature of the LED. During the experiment When the measured temperature value is less than ± 0.1 °C within 10 min, the heat dissipation system can be considered to enter a stable condition. Data acquisition system: The temperature signal is transmitted to the computer g through the Agilent 34970A data collector f, to the thermocouple e The measured temperature is monitored and analyzed in real time. At the same time, the uniformity of the surface temperature distribution of the radiator is monitored by the Fluke Ti55 portable infrared thermal imager. The illumination of the LED light source is measured by the TES-1330A illuminometer. The illuminance meter is perpendicular to the LED light source. The distance is 1. 2 m.