• Energy Research

Using the method of computer modelling, considered in this paper is optimization of a passive air system design for cooling the powerful LED luminaire based on heat pipes and cooling rings. Thermal and mass characteristics of the cooling system have been studied for various design parameters: distance between rings, thickness of ring materials and thermal loads. It has been shown that, to provide a minimal case temperature of LED source, the optimal distance between cooling rings should be 6 mm, but in this case the mass of cooling system is not least. To reduce the luminaire mass, it is reasonable to choose the distance between the cooling rings equal to 8 mm. Then the temperature of light source increases by only 1.8 °С, or by 2.2%, while the mass of cooling system reduces by 1357 g, or by 20.5%. At the same time, lowering the ring thickness from 2 down to 0.8 mm can in addition reduce this mass by 2700 g, or by 48.6%. However, when doing so the temperature of LED source case is increased by 5.9 °С. The offered cooling system based on heat pipes is capable to provide the thermal resistance 0.131 С/W when scattering the thermal power 500 W under the maximum temperature of LED source crystal 135.5 С. Recommendations for application of the developed cooling system have been formulated.

The use of LEDs for plant lighting (phytolighting) provides a more energy- efficient alternative to traditional lighting methods. Combination of LEDs with different spectral composition and the possibility to change the composition of resulting radiation in a single lighting device allows one to improve the efficiency of phytolighting systems and optimize them for different conditions of plant growth and development. In this work, we have investigated quasi-monochromatic LEDs specialized for efficient phytolighting and efficient white LEDs with different CRI. Being based on the research, the most effective LEDs for building phytolighting systems have been identified, and their optimal ratio with red quasi-monochromatic LEDs for building phytolighting systems in rooms with a constant presence of people (greenhouses, winter gardens, etc) has been determined.

Abstract To increase the compactness of a LED luminaire, in this work it has been suggested to use 8 radial thermal pipes as a heat sink from a COB (Chip-on-Board) matrix to the heat-transfer surface, while the latter should be rings of heat exchanger located concentrically around the light source. These rings are cooled utilizing natural convection of ambient air. The used computer modelling enabled us to evaluate the possibility of the suggested cooling system to provide the normal thermal regime for a power COB matrix. It has been shown that for the power 500 W, as the LED light source, provided that all electric power is converted into thermal power, the temperature of the luminaire base frame in the place of contact with the light source does not exceed 85.5 °C. When using the heat-conducting paste of Arctic Silver 5 type with the thermal conductivity of 8.7 W/(m·°C) in the contact zone and the paste layer thickness 0.1·10-3 m, it corresponds to the temperature of the LED light source case 89.5 °C. With account of the thermal resistance inherent to the COB matrix, the temperature of its semiconductor crystals reaches 139.5 °C, which does not exceed the acceptable value of operation temperature for these crystals 140 °C. At lower values (from 50 to 80%) of the consumed electric power, which is converted into thermal energy, depending on the type of COB, the value of the working temperature of the semiconductor crystal is from 112.5 to 128.7 °C.

Abstract This work is for the first time an experimental study of thermal characteristics of an copper gravity heat pipe (thermosyrhon) with an outer diameter of 12 mm and a length of 230 mm with a threaded evaporator and freon R141b as working fluid under natural convection. The study demonstrates how a change in power input in the range from 5 W to 70 W (with a 5 W step) at natural convection affects such thermal characteristics of the gravity heat pipe (GPH) as temperature in evaporator section, temperature distribution along the length of the GPH, total thermal resistance, thermal resistance in evaporation and condensation sections, and heat transfer coefficients in evaporation and condensation sections. Also studied is the influence of tilt angle of the GPH changing from 0 to 90° (with a 15° step) on its thermal characteristics. The coefficient of convective heat exchange between the heat sink and air at different values of heat flux and tilt angle is determined experimentally. The obtained research results indicate that the GPH with a threaded evaporator can be effectively used in natural air cooling systems for electronic equipment with high heat flux values, for example, LED devices, power amplifiers of T/R modules, etc.

There has been developed, manufactured, and researched by numerical and experimental methods an operating sample of a typical construction of a cooling system of electronic heat-loaded modules of dual application, which can be used in devices of both special and civil purposes. The main idea of organizing an effective cooling is to provide heat transfer from a heat-loaded module, located in conditions where it is impossible to provide the thermal regime necessary for trouble-free operation, to an area where it is possible to organize the dissipation of the transported heat flow through free convection. A gravity-assisted heat pipe with a threaded capillary structure was used as a heat transfer device. As heat-loaded modules there were used powerful volumetric electronic modules made in the form of a prism with flat side faces, on which powerful semiconductor electronic components were installed. Due to application of a highly efficient closed evaporation-condensation cycle of heat transfer occurred in heat pipes, it became possible to increase the power of the electronic module in almost two times while keeping its temperature within the specified limits., graphical dependences of the temperature of semiconductor electronic components on the consumed electric power in the range from 13 to 36 W were obtained by using a calculation method. The experimental data were compared with those obtained due to the calculation.

Abstract In this paper, for the first time, a novel design of pulsating heat pipe (PHP) with one evaporator and two condensers located on both sides of the evaporator at an angle to the horizon was proposed, manufactured, and experimentally investigated for the purpose of use in cooling systems for electronic devices operating in a tilted position. The PHP body is made of a copper capillary tube with an inner diameter of 1.5 mm. The working fluid is methanol. The number of turns is 4. The heating zone dimensions are 60 mm × 36 mm, and the cooling zone dimensions are 200 mm × 35 mm. The РНР condensers were cooled by aluminum radiators blown by two fans with an air flowrate of 5.2 m3 h–1. The launch of the РНР began with a power of 30 W at all positive tilt angles and in a horizontal position. The dependences of the temperature in the heating and cooling zones and the PHP thermal resistance both on the power input (from 30 W to 200 W) and on the orientation in space (at tilt angles of 0 deg, 15 deg, 30 deg, 60 deg, 90 deg) were obtained. It is shown that when the evaporator is located below the condensers, the РНР works stably. Moreover, in the power range from 120 W to 200 W, the tilt angle practically does not affect the thermal resistance of the PHP. A comparison of the thermal resistance of the developed РНР with known РНРs filled with methanol showed the high efficiency of the developed РНР: at power input from 120 W to 200 W, the thermal resistance was from 0.2 °С W–1 to 0.18 °С W–1. The developed РНР design is promising for use in air cooling systems, for instance, of radar transmit/receive modules and high-power LED lighting systems.

Developed in this work are the principles for creation of a system to control and governing the energy efficiency of solar panels providing power supply for LED luminaires. Realization of these principles allows the most efficient using the electric power generated by solar panels, to save in a real-time scale the data about system functions as well as provide a complex analysis of these data. Optimization of using the electric energy generated by solar panels will enable to determine the maximum possible power in each specific moment and to automatically tune its consumption. The complex data obtained with this system can be further used for not only statistical fixation of the produced and consumed electric energy in fact but also for prediction of the energy amount that will be generated by these solar panels in future. The analysis of results will enable to optimize the area of solar panels and more exactly determine parameters of electronic components both for illumination systems and designing solar photoelectric stations of various purposes.