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Currently, thermosyphons are used to cool such devices as power amplifiers of radio frequency systems, data center hardware, LED light sources, etc. One of the important factors affecting the efficiency of such cooling systems is the orientation of the thermosyphons in space. This paper is dedicated to research and visualization of vaporization events in two-phase thermosyphons, primarily focusing on investigating and visualizing the influence of orientation in space on vaporization. The studies were performed for100% fill ratio. Vaporization was video recorded at 240 frames per second, whereupon the obtained footage was converted into image sequence. The analysis of the obtained materials has shown that at intensive boiling for tilt angle range of 5—45°, a part of the working fluid is always outside the evaporator. When the angle is decreased, the portion of the working fluid outside the evaporator increases. Moreover, for the 5° tilt angle, the evaporator can be completely drained at certain time intervals. It is proposed that the thermal resistance at low heat flux values for smaller tilt angles can be lower than for vertical orientation because of thin liquid films. Evaporation is more effective in thin liquid films than in large volumes. This prompts the conclusion that smaller angles will allow obtaining lower thermal resistance for the same filling ratio. On the other hand, maximum heat transfer ability decreases dramatically for the angle range of 0—10°. The obtained results can be used in further studies to analyze and explain the aspects of heat transfer in two-phase thermosyphons with a short evaporator.

Modern continuous lighting systems use powerful high-performance LEDs as light sources and an important task is to begin using alternative renewable energy sources for their power supply (including during the day). The simplest of the renewable energy sources is photovoltaic solar energy converter. However, solar photovoltaic generation depends significantly on many factors - geographical location, time of day, state of the atmosphere, time of year and the like. In addition, photovoltaic generation depends on the weather conditions and cloudiness, which makes it unstable and prone to change drastically (by an order of magnitude) during daylight hours. Therefore, an important element of the power system based on renewable energy sources is the system of accumulation of generated energy. The method of power stabilization using supercapacitors for systems with a significant change in power generation in the electrical power system is analyzed. The paper offers design principles of the power supply systems for powerful LEDs with supercapacitor energy storage devices intended to make the use of energy from sources with variable generation more efficient. The systems with supercapacitor-based drives, which allow to ensure stable operation of the lighting system when the power supply from an alternative source is absent or reduced, provide high safety and reliability, and have a significantly longer service life than battery-based energy storage systems.

Using LED technologies to create a comfortable light environment for human life and work can help reduce electricity consumption while maintaining, and usually improving, the energy and spectral parameters of lighting systems. At the same time, LED lighting systems for residential and industrial buildings are usually powered by electricity generated mainly by thermal power plants. Such plants mostly use fossil fuels and their combustion leads to environmental pollution. The article proposes the concept of a lighting system, which allows improving the ecology by reducing the energy consumption of lighting systems through the use of renewable energy sources. The proposed operation algorithm of the system for power supply control of LED light sources allows selecting the most appropriate energy sources in real time, thus making it possible to increase the luminous efficiency of the lamp by at least 20% when using industrial element base. This design can help to move away from traditional energy storage systems (batteries), which significantly increases the service life of such systems, their reliability and environmental safety. Placing photovoltaic converters in close proximity to the consumer (on the roofs and facades of buildings) ensures a decrease in ohmic losses and creates favorable conditions for using solar energy to light residential and industrial premises with LED lamps, which can significantly increase the economic and energy efficiency of such systems.

LED light sources, and powerful multichip light sources in particular, are currently widely used for lighting household and industrial premises. With an increase in power, the amount of heat increases as well, which leads to an increase in the temperature of semiconductor crystals and, accordingly, to a decrease in the reliability of LEDs and a change in their photometric characteristics. Therefore, when developing the design of LED lighting devices, special attention is paid to thermal management. Since the early 2000s, heat pipes have been widely used to efficiently remove heat from powerful electronic components. They do not require power for moving the working fluid and are most suitable for use in LED luminaires. In this study, the authors carry out a computer simulation of a cooling system based on heat pipes, which is then used to design and test a powerful compact LED lamp with a thermal load of up to 100 W. Heat pipes with a length of 150 mm are used to remove heat from the LED light source to the heat exchanger rings located concentrically around it. The heat exchanger rings are cooled by natural convection of the ambient air. The results of computer modeling of the temperature field of the developed cooling system show that at a power of the LED light source of 140.7 W, the temperature of the LED matrix case is 60.5В°C, and the experimentally measured temperature is 61.3В°C. The experimentally determined thermal power of the LED matrix is 91.5 W. The p-n junction temperature is 79.6В°C. The total thermal resistance of the cooling system is 0.453В°C/W. The obtained results indicate the effectiveness of the developed design.

The paper presents the results on numerical simulation of the temperature field of a cold plate type liquid heat exchanger for a multichannel transmitter/receiver module. Each side of the cold plate carries 8 local microwave fuel elements with a heat dissipation capacity of 11 W each and one block with low-power electronic elements (total power of all elements — 50 W), installed symmetrically on both sides. The total heat dissipation capacity is 276 W. The cold plate is cooled by pumping a liquid heat carrier (Antifreeze A 65) through a curved cooling channel of rectangular cross-section made inside the liquid heat exchanger. The study was conducted at a working fluid flow rate of 2, 4, 6, 8 and 10 l/min. Numerical simulation allowed obtaining the temperature distribution of the mounting surfaces of the cold plate and determining the values of the working fluid flow rate, which provide effective cooling of the mounting surfaces. It is shown that at a flow rate of 4 l/min, the temperature values at the installation sites of local microwave elements do not exceed 64°C. The total thermal resistance of the cooling system based on a liquid heat exchanger is from 0.063 to 0.028°C/W with a flow rate from 2 to 10 l/min, respectively.

The problem of climate change poses a challenge for humanity: it is necessary to reduce harmful emissions into the atmosphere, caused mainly by the burning of coal in thermal power plants. Partially, this problem can be solved by the use of energy-saving devices and equipment, including the replacement of traditional light sources with more efficient LEDs. This, however, causes the problem of ensuring normal thermal modes of the LEDs, since the more powerfull the LED is, the more heat is released in their semiconductor crystals, which leads to an increase in the temperature of the crystals and a decrease in the reliability of the device. This problem becomes especially urgent when using powerful multi-chip LED light sources, the so-called SOB matrices, whose power even now exceeds 500 W. This article presents a new design of a powerful LED lamp for indoor illumination of rooms with low ceilings. The heat from the LED is transferred via heat pipes to the heat exchanger rings looped around the light source. The heat exchanger rings are cooled by the natural convection of the surrounding air (at an ambient air temperature of 20°C). Computer simulation allowed evaluating the ability of the proposed cooling system to provide a normal thermal mode of the LED light source. The results on the computer simulations of the temperature field of light source's cooling system showed that when the LED power is 300 W, the temperature of the light source's base at the point where it is connected to the light source does not exceed 67.6°C. When the contact zone is covered with a 0.1 mm layer of heat-conducting paste (Arctic Silver 5 type) with a thermal conductivity coefficient of 8.7 W/(m·°C), the temperature of the LED case reaches 70°C. If the thermal resistance of the LED light source is 0.1°C/W, then the temperature of its semiconductor crystals will be 100°C, well below the allowable temperature value of 150°C. The total thermal resistance of the cooling system is 0.159°C/W.

Frequency multipliers are used in electronic devices to generate spectrally pure sinusoidal signals in the frequency range from a few to tens of GHz. The multipliers are used to multiply the frequency of highly stable but more low-frequency devices with the subsequent extraction of the necessary harmonics from the frequency spectrum of the received microwave range. The frequencies selected after multiplication (set) have significantly higher energy, spectral and range characteristics, which allows them to be used as local oscillators and synthesizers in receiving and transmitting systems. The authors of this paper theoretically substantiate and practically demonstrate the possibility of an unconventional implementation of a microstrip multiplier of the microwave range based on a directional traveling wave filter. The proposed implementation does not require the use of active semiconductor elements. The well-known circuit and technological principles for the creation of microstrip microwave multipliers are considered in the paper. The features, problems and shortcomings arising from their implementation are analyzed. The effectiveness of using the balanced circuit for frequency multiplication is confirmed. A list of mandatory requirements and conditions necessary for the implementation of the microwave multipliers is given. It is demonstrated that the features of the microstrip travelling-wave filter are identical to the conditions and requirements for the implementation of balanced multipliers. It is shown and substantiated how an unconventional implementation of a passive microwave multiplier is possible due to the electromagnetic interaction of the input and output nodes of such a filter with an annular travelling-wave resonator. Using the example of modifying a block diagram of a directional filter into a multiplier circuit, the possibility of creating a microwave doubler is confirmed by separating a given frequency from the frequency spectrum of a traveling-wave ring resonator.

The paper describes features of the design and manufacturing technology of a volumetric detachable heat flow imitator designed for the study of thermal characteristics and for carrying out thermal tests of heat pipes of cooling systems for electronic equipment. The authors use thin alumina ceramic plates with deposited with diamond-like films as heating elements of the imitator. Experimental results are presented on the surface temperature of heating elements and the temperature drop between the heating elements and the heat pipe in the region of the input heat flux values from 5 to 25 W. The use of the proposed heat flow imitator allows speeding up the process of research and testing of heat pipes.

The results of an experimental study of the thermal resistance of an aluminum gravitational heat pipe with isobutane (R600a) as a working fluid under conditions of heat removal of natural air convection are presented. Comparison of the thermal resistance of an aluminum gravitational heat pipe with a threaded capillary structure and the thermal resistance of an aluminum thermosyphon of the same size, having a smooth surface of the body in the evaporation zone, is given. It is shown that in the range of values of the input heat flux from 5 to 50 W the thermal resistance of the gravitational heat pipe is substantially lower than the thermal resistance of the thermosiphon. The studies were conducted both without the use of additional radiators in the condensation zone of heat transfer devices, and with the use of one, two and three radiators.

Aluminium and copper heat pipes with grooved and metal fibrous capillary structure are high effective heat transfer devices. They are used in different cooling systems of electronic equipment like a LED modules, microprocessors, receive-transmit modules and so on. However thus heat pipes have heat transfer limitations. There are few types of this limitations: hydraulic limitation, boiling limitation, liquid entrainment by vapor flow and sonic limitation. There is necessity to know which one of these limitations is determinant for heat pipe due to design process. At a present article calculations of maximum heat transfer ability represented. All these calculations were made for LED cooling by using heat pipes with grooved and metal fibrous capillary structures. Pentane, acetone, isobutane and water were used as a coolants. It was shown that the main operation limit for axial grooved heat pipe, which determinate maximum heat transfer ability due to inclination angle for location of cooling zone higher than evaporation zone case, is entrainment limit for pentane and acetone coolants. Nevertheless, for isobutane coolant the main limitation is a boiling limit. However, for heat pipes with metal fibrous capillary structure the main limitation is a capillary limit. This limitation was a determinant for all calculated coolants: water, pentane and acetone. For high porosity range of capillary structure, capillary limit transfer to sonic limit for heat pipes with water, that means that the vapor velocity increases to sonic velocity and can't grow any more. Due to this, coolant cant in a needed quantity infill condensation zone and the last one drained. For heat pipes with acetone and pentane, capillary limit transfer to boiling limit. All calculations were made for vapor temperature equal to 50°C, and for porosity range from 30% to 90%.

Given article presents the results of an experimental comparison of three radiators which are: pressed radiator made of aluminum plate (basic variant), radiator made of copper wire, and copper/water pulsating heat pipe. The radiators are intended to take off heat from the LED module with the power capacity of 10,55 W. It is established that under natural convection all three radiators can keep temperature level of the circuit board module less than 64 C that lies within the operating range. In comparison with basic variant the use of the copper wire radiator allows lowering of the temperature in the LED module center on 3.9 C, and the same value for the pulsating heat pipe is 7.1 C.

New energy-saving technologies for lighting is a promising trend in lighting technology. To this end, during the recent decade, have been actively developed and implemented lighting units based on LED modules. Reliability of such devices is largely dependent on the ensuring of cooling of the LEDs. Heat pipes are being used with ever increasing frequency for increasing an efficiency of cooling of powerful LEDs within a lightening device. Results of experimental modeling of thermal characteristics of two aluminum heat pipes with grooved capillary structure and ammonia used as a heat transfer agent, designed for application as a heat transfer elements in designs of powerful LED lightening device with forced air cooling are presented in this paper. It is shown that for the heat flux range of 50 to 100 W and for incident flow speed in the range of 0.8 to 2.1 m/s the temperature in the heating zone of the heat pipe falls into the range of 31.0 to 52.5 °C. In this case the temperature difference along the heat pipe is between 0.9…1.7 °C, when a minimal value of the fed heat flux is 50 W, and 1.7…3.1°C, when a maximum value of the heat flux is 100 W. The value of heat transfer resistance of the heat pipes was in the range of 0.012 to 0.044 °C/W. The key factors influencing the thermal characteristics of the heat pipes are: the value of the fed heat flux, the speed of cooling air flux, heat pipe inclination angle with respect to the horizon. By using five such heat pipes within the powerful LED lightning device it is possible to achieve an elimination of the total heat flux from LED modules up to 500 W. At an efficiency factor of LEDs of about 75% this is equivalent to intake power 665 W. Taking into account that luminous efficiency of modern LEDs is about 10 times as high as those of incandescent lamps, proposed lightning device will produce a luminous flux which is equivalent to the luminous flux of a lightening device with incandescent lamps with a power of 6650 W, so that this will allow reducing an input power of the lightening device by 5985 W.

Considered in this paper are the parameters and characteristics of the developed highly efficient electronic control systems for powerful LED modules (drivers), built on the basis of a single-stage flyback converter with a nominal power close to 200 W. The results of experimental tests show that, at the nominal load, the minimum efficiency of the developed driver reaches 88.2% with the power factor above 0.97 and the coefficient of total harmonic current distortion close to 23.4%. With the maximum value of the efficiency factor of the developed system 90.3% and the supply voltage 240 V, the power factor is higher than 0.99, and the total harmonic current distortion is 3.6%. The values of current harmonics of the driver do not exceed the maximum allowable values defined by the current standards. Used driver construction topology enabled to reduce the cost of the final product due to the unification of the component base, which increases the availability and manufacturability of the design. The use of a modern element base made it possible to ensure the deviation of the output current from the set one by no more than 1% over the whole range of the operating voltage of the supply (180...250 V), which allows using the developed driver in intelligent lighting systems and lighting systems with a combined power supply. [ABSTRACT FROM AUTHOR]

LED development is accompanied by the need to ensure a constructive solution for the thermal conditions problem. For this purpose one can use pulsating heat pipes (PHP), that operate more efficiently after the start of heat carrier boiling. This article describes the physical representation and formula that allows determining the boiling point, which is a lower bound of the PHP effective operating range. It is shown that the main factors influencing the required heat flow are driving capillary pressure and velocity of the vapor bubble. The formula was obtained for the closed PHP made of the copper with water as a heat carrier. Information about this heat flux can be used for further design of cooling systems for heat-sensitive elements, such as LED for promising lighting devices.

Thermal characteristics of multichannel slot-hole heat exchanger with the developed surface of heat exchange inside the opened-cycle water cooling system are experimentally investigated. Graphic dependences of average value of temperature of the simulator of a heat current and temperatures of the heat exchanger base are presented on tapped-off power. Dependences of tapped-off power and hydraulic losses on the of water consumption are given. It is shown, that use of developed slot-hole heat exchanger provides higher values of tapped-off power as compared to well-known two-channel slot-hole heat exchanger: at the temperature of heat-generating component simulator of +60°С the tapped-off power increases with 307 up to 750 W. Recommendations on increase of adaptability of slot-hole heat exchanger manufacturing are given. Heat exchanger is suitable for application in microprocessors and others heat-generating components and electronic equipment units cooling.

The principal technical characteristics of scientific and technical production, created according to the 2003—2011 years Government industry development program in the field of microelectronics, are expounded.

The thermal performances of a designed double-channel slot-hole water aluminium heat exchanger for a powerful electronic component and water copper heat exchanger, available in the market, Titan in a composition both made system of water cooling, and unlocked are explored experimentally. The pictorial dependences of tapped power on medial value of temperature of the simulator of a heat flow are given. Is shown, that the slot-hole heat exchanger allows to obtain higher values of tapped power at identical temperature of the simulator. At temperature of the simulator of a heat-generating component +60°C with in the made system of cooling the tapped power is incremented with 112 up to 172 W, and in unlocked - with 234 up to 307,4 W.

The paper proposes a new method for determining the optimal peak wavelengths of quasi-monochromatic LEDs, when they are combined with white broadband high-power LEDs in lighting systems with tunable correlated color temperature (CCT). Simulation of the resulting radiation spectrum was used to demonstrate the possibility to use the developed method in LED lighting systems with tunable parameters of the synthesized light. The study enables to determine the peak wavelengths of quasi-monochromatic LEDs (474 and 600 nm), which, when being combined with a basic white LED (Cree CMA 2550), allow controlling the widest CCT range. Quasi-monochromatic LEDs with particular optimal spectral parameters allow adjusting CCT within the range from 3098 up to 6712 K, while maintaining a high color rendering index (higher than 80) over the most part (3098 to 5600 K) of the regulation range. [ABSTRACT FROM AUTHOR]

Considered in this paper are development and creation of high-power LED luminaires with high light efficiency and color rendering index (CRI). As light sources, there used are 6 powerful LED COB (Chip-on-Board) modules CreeCXA 2550, the radiation of which contains quasi-chromatic peaks in the spectral range 600...650 nm. It allows to provide CRI values higher than 92. Features of the improved compact construction of the luminaire with indicated COB modules have been presented. To ensure normal thermal regimes of LED COB modules, a small cooling system based on heat pipes has been created, the optimal dimensions of the structural elements of which have been determined by computer simulation. The results of modeling and experimental studies have shown that the developed and manufactured passive cooling system of LED COB modules provides operation temperature modes (up to 85 °C) of light-emitting crystals at the total electric power of COB modules up to 290 W and allows using the luminaires of this type in the systems of continuous artificial illumination with combined power supply. The efficiency of the developed cooling system at some angles to the horizon expands the scope of applying the illumination device. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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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 °C, 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 °C. The offered cooling system based on heat pipes is capable to provide the thermal resistance 0.131 °C/W when scattering the thermal power 500 W under the maximum temperature of LED source crystal 135.5 °C. Recommendations for application of the developed cooling system have been formulated. [ABSTRACT FROM AUTHOR]

Discussed in the article is the possibility to create a wall-mounted LED luminaire with a built-in cooling system for a volumetric LED module put in the enclosed volume of the diffuser. The use of aluminum heat pipe with a threaded capillary structure has been proposed for cooling high-power LEDs of the volumetric module in the luminaire design. It has been shown that the use of heat pipe with a simple capillary structure allows the heat flux from the LED module to be efficiently transferred outside the light diffusing area to the decorative radiator located on the top of the lamp and to disperse it into the surrounding air. The proposed design of the wall lamp with heat pipe allows to increase the luminous flux and durability of the luminaire. [ABSTRACT FROM AUTHOR]