The optimal design of cooling radiators for led lamps is a critical element of energy-saving lighting technology, since overheating of light-emitting diodes leads to a rapid decrease in the light flux, change in color, and a sharp reduction in the service life of illuminators. Light-emitting diodes production technologies are rapidly improving and over the past 10 years we have seen a shift in production paradigms from power LED to SMD and then to COB. Following these changes, radiator designs for light-emitting diode arrays are also being transformed. But, nevertheless, the problem of designing efficient cooling systems and radiators is still relevant.
The market for radiators for led lighting systems is actively developing. New companies, new design and production principles, new materials and design approaches are emerging. Cooling systems for led lamps are becoming less material-intensive, more efficient and reliable, and their size and cost are reduced. Below we will review the main trends in this market and the work of “Metal-Composite” and “HeatLab” companies in promoting advanced solutions and approaches in this area to the Russian market.
Passive radiators and cooling systems
Passive cooling devices using the principles of natural air convection are traditional and most common in the field of led lighting systems. The most popular and inexpensive radiators are produced by extrusion methods from aluminum alloys.
Their efficiency is quite high, the principles of use and installation are quite simple, which together with a relatively low cost has led to their mass distribution.
However, the material consumption and efficiency of these systems leave much to be desired. Led lighting is becoming ubiquitous and there is no doubt that in the near future this will be the main type of lighting. Therefore, radiator designs should provide relative freedom in choosing possible design solutions when placing them in the working and living space. Here is just one typical example. “MechaTronix” has tested the cooling efficiency of two radiators in an inclined position: the extruded Modul LED 9980 (Ø 99mm, h 80mm, thermal resistance at a strictly vertical position of 1.02 °C/W) and the injection-molded needle LPF11180-ZHE(Ø 111mm, h 80mm, thermal resistance at a strictly vertical position of 1.07 °C/W). When tilted, the needle radiator retains its thermal resistance at the same level, whereas when tilted 50°, the extruded radiator loses more than 20% in cooling efficiency and when the angle increases to 90°, its efficiency decreases by half (see Fig. following). In General, given the material consumption, needle radiators are significantly more efficient radiators compared to the obtained extrusion methods.
The injection molding method provides incomparably greater freedom of choice when developing the design of radiators and elements of cooling systems for LED lamps. The composition and structure of alloys in parts made by injection molding provide higher values of thermal conductivity. Given all these advantages, it can be argued that the injection molding method allows you to obtain significantly more efficient and less material-intensive radiators for LED lighting (see examples in Fig. following).
The use of natural gas and passive radiators makes it possible to develop reliable, maintenance-free and control-free heat removal systems. However, their weight and size make you think about alternative solutions.
The market for passive cooling systems and radiators for LED lighting is growing and actively developing. Along with such well – established manufacturers as “MechaTronix”, “CREE”, “LG innotek”, “Osram” there are new companies-such as “Xicato”, “Mingfa Teech”, “NingboHongyang”, which are trying to offer new solutions, lower prices and explore new market niches. There is no doubt that this process will only gain momentum and soon we will see new players in this market and solutions offered to them.
Active radiators
Despite the fact that passive cooling systems now provide a fairly effective cooling of illuminators with a total light flux of up to 4500 lumens at acceptable overall weight indicators, active cooling systems are quickly implemented where light flows of more than 10,000 lumens are needed. For illuminators providing light streams of more than 10,000 lumens, the passive cooling systems that suit them become either too large, or too heavy and too expensive. With the growth of power and light flow, installation systems of such illuminators also become more cumbersome, difficult to install and maintain, and their reliability and service life come to the fore. All this leads to the fact that a good design and application of the fan in cooling systems saves significant money in the cost of production, installation and maintenance of the active cooling system.
What are active radiators for led lighting? In fact, these are radiators with mechanical drives attached to them, providing forced ventilation. With an increase in the air flow rate between the surfaces and the radiator fins, heat exchange is strongly intensified, and the thermal resistance of such systems will significantly fall, providing equivalent cooling at significantly lower overall weight indicators. At the same time, the energy consumption of the entire system, including the mechanical drive, increases slightly, usually by no more than 10%.
Active radiators with fans are widely distributed. Here are some examples.
Industry has learned to produce fans for cooling systems of LED lamps, which provide a service life of tens of thousands of hours in different climatic conditions and at sufficiently high levels of dust and air pollution. But, nevertheless, the fan is a mechanical kinematic system that has bearings, rubbing pairs and wearable working surfaces. All this imposes certain restrictions, and manufacturers of active cooling systems continue to search for alternative ways to provide forced cooling using other physical principles and approaches. One of the approaches that have become widespread is the use of flexible, bi-morphic oscillating plates on piezoelectric drives to create pulsating air flows. Such devices were used even earlier in cooling systems and high-power heat-generating semiconductor devices. One of the pioneers who mastered the production of such devices is the Japanese company “Murata”. More powerful devices were introduced to the market a couple of years ago by “General Electric”. And now drives on plate oscillating circuits with piezo-actuators are also used for cooling the radiators of light-emitting diodes (see Fig. following).
The manufacturer guarantees the service life of such piezo actuators for more than 20 years. The devices operate from a voltage source of 5V or 12V and provide cooling of a light-emitting diode lighting source with a power of up to 110 W. Their power consumption is several times lower compared to fans. The noise generated during their operation is also significantly lower.
For. Fig below is an example of a cooling system with such piezo drives from “Nuventix” - R150-170. This system is based on the manufacturer's claims it provides a 30% reduction in energy consumption compared to metal-halide illuminators with the same light flux, it is also 40% smaller and 60% lighter compared to led lighting systems with passive radiators. The Nuventix R150-170 has another innovation: it uses heat pipes to distribute heat flow more efficiently.
The trend with the use of heat pipes in led lighting systems has emerged not so long ago and is currently actively developing. This is primarily due to the growing power of led sources and the struggle to improve the efficiency of cooling systems. For example, the company “1-AST” based in the United States, successfully promotes solutions for the use of active radiators with heat pipes for cooling led sources. The use of heat pipes in radiators opens up very large opportunities associated with the use of remote radiators, with the use of surrounding structural elements for this purpose, with the use of nearby ventilation and air conditioning channels, liquid and gas pipelines, etc. The figures below show illustrations showing a decrease in temperature under the led source by 8 °C when used in the construction of a heat pipe radiator, as well as the possibility of using a remote radiator and transporting heat flow through a heat pipe.
Another interesting and promising approach in cooling systems of led lamps is the use of ion wind. Creating a wall-mounted air flow, stimulated by high voltage, allows tens of percent to intensify the cooling process, with low energy costs. In some cases, for LED sources of low and medium power, the use of ion wind is enough to significantly reduce the mass and size characteristics of radiators. These solutions are very attractive for maintenance-free systems with a guaranteed long service life, since such flow generation devices do not contain moving parts subject to wear and will certainly be able to provide long times works. The figures below show diagrams and photos of experimental devices that use the effect of ion wind to cool the radiator.
Among the latest trends in the development of cooling systems for high-power LED lamps, we can note the use of steam chambers, heat pipes, graphite heat conductors in the bases of radiators and the use of open-pore foam metals. Of course, as the efficiency and power of led sources increases, so will the requirements for the efficiency and mass-dimensional parameters of LED lighting cooling systems. And this requires constant development and improvement of both production methods and design methods.
“Metal-Composite” company entered the market of led radiators in 2016 and mastered the production of several types of radiators for LED lamps. The company has a modern high-performance robotic complex of injection molding, its own machine park and painting equipment, which allows to carry out a full cycle of production, assembly and packaging of finished products.
“HeatLab” company is a partner company of the “Metal – Composite” production company and carries out development in the field of design of passive and active heat sink systems. “HeatLab” has at its disposal metallographic, chemical laboratories, a laboratory for physical measurements, and a powder production site. In 2016, “HeatLab” acquired a workstation and specialized licensed SOFTWARE (COMSOL Multiphysics) for calculating and modeling heat removal and heat transfer processes in complex technical systems. The company's assets include developed high-heat-conducting composite materials for special purposes, prototypes of unique devices using high-heat-conducting composite materials. “HeatLab” has started to fulfill the first orders for third-party customers to model and optimize heat removal processes in real power electronics devices and cooling systems. In 2017, “HeatLab” plans to design new types of passive and active radiators with solid-state high-heat composite heat conductors, with heat pipes, metal foams, flexible heat conductors with vibration isolation, design of technical devices that perform the functions of heat exchange and utilization of heat flows, obtaining prototypes of technical devices in the field of cooling and electricity generation.
“Metal-Composite” and “HeatLab” companies consider the market of led radiators and cooling systems as extremely promising and capacious. We aim to strengthen our presence in this market and have all the necessary prerequisites for this. The goal of our companies is to bring the most advanced, innovative solutions in the field of heat removal and cooling to the Russian market of led lamps and provide Russian manufacturers and developers with the best designs and products that allow them to compete on an equal footing with the world's leading manufacturers of led lighting systems.
