Pursue the scientific development of LED lighting - cooling will no longer be a problem

Due to its energy saving, environmental protection and long life, LED lighting is recognized as the next lighting technology and will replace various existing lighting technologies. LED is a cold light source, afraid of heat, there are 80% of the electrical energy into heat, there must be cooling measures, although LED lighting technology has been a leap forward, there are reports of light up to 200lm per watt, but LED cooling is LED lighting It is a headache, but it has not yet been solved effectively. It has become a roadblock to the popularization of LED lighting.

The biggest problem that hinders the popularization of LED lighting applications is the high price of LED lamps. Although upstream LED chip companies divide most of their profits and have significant price reductions, it is necessary to effectively allocate the entire social resources to the entire LED lighting industry chain, effectively reducing The cost is easy to buy and install by ordinary people. The standardization of LED lighting modules is the only way to go, just like existing lighting (incandescent, fluorescent, energy-saving). The obstacle to the standardization of LED lighting modules is the existence of heat dissipation problems.

Heat dissipation is part of heat transfer. The study of heat transfer by humans has been a hundred years old. In the 60s to 70s of last century, it was the peak period of people's research on heat transfer, and the main driving force was the demand of humans for the development of aerospace. In that era, many outstanding talents gathered in the field of heat transfer technology. Many heat transfer researchers became celebrities. Afterwards, people’s enthusiasm for heat transfer research has been gradually reduced. At present, there are very few professionals in heat transfer science and technology. Heat transfer science and technology are very mature. Just like mature fruits, they fall to the ground and are covered by leaves. They are not seen by people nowadays. As a result, when the electronics industry, mainly computers, suddenly increase their CPU heat, People did not remove the leaves on the ground, picked up those ripe fruits, and transplanted human mature heat transfer knowledge into the electronics industry. Instead, we started from scratch to create a lot of new terms: "active heat dissipation", "passive cooling", "heat sinking", etc. I don't know what it means. English "Sink" is also a very rare term in heat transfer technology and technology.

For the heat dissipation of LED lamps, the industry currently lacks a clear research result for each heat transfer process in the entire heat transfer process, and analyzes the convective (natural) heat transfer from the LED junctions to the air and heat sink surfaces in each process. The ratio of the heat transfer temperature difference (ie thermal resistance), which process is the largest temperature difference, that is the main contradiction, as well as the factors affecting each heat transfer process, how to reduce the thermal resistance of the technical direction, especially the heat resistance of the largest heat transfer The process, the technical direction to reduce its thermal resistance is more important. Even with the results of these studies, it must be known to structural engineers because heat transfer is ultimately achieved through structures.

From the perspective of heat transfer technology and technology, LED heat dissipation is not complicated, it only involves a very small part of heat transfer - heat conduction and convection heat transfer (mainly air natural convection heat transfer), in which heat conduction and heat transfer can be used Off-the-shelf heat transfer computer software is very accurate solution, such as analyzing the temperature distribution (heat transfer process) within the LED package chip; analyzing the internal temperature distribution from the LED chip to the heat dissipation ribs. However, special attention should be paid to the fact that for convective heat transfer, where air flow is involved, it must pass a large number of experimental studies, and calculations using computer software have only academic significance and have no practical engineering significance because the error is too large. The company is keen to promote such software.

The reasons that lead to the simple problem of LED heat dissipation are complicated: knowledge faults, personnel with mature heat transfer knowledge participate in the study of LED heat dissipation, and lack of professional LED heat-dissipation research institutions, giving the industry a clear and correct guiding ideology. There are a lot of seminars, but there is less academic atmosphere and more commercial taste. At present, many professional heat-dissipation technicians working in the industry are transferred from the aspect of computer heat dissipation, naturally bring common technical and commercial activities in that area. For example, heat pipe technology is widely applied to high-power LED lighting (such as In streetlights, new business opportunities have been created for heat pipe manufacturers that originally served computer chip radiators. There are even proposals for the use of a reflux heat pipe. If the heat dissipation of the LED lamp is like using a normal heat pipe like killing a chicken, then the use of a reflow heat pipe is like killing a chicken. One company in Taiwan has invented a liquid immersion cooling technology. This invention, which lacks basic knowledge of convective heat transfer, has also won a gold medal in the International Invention Exhibition. There are also similar companies in the country, and have a certain reputation, the development of LED liquid cooling technology, said that has applied for more than 30 patents. These inventors, inspired by the car radiator, do not know why the automotive engine uses water (liquid) cooling technology, and the role of water in the cooling process.

This article proposes a standardized LED lighting module technology program, the heat sink is classified as a component of the lamp, the wick formed by the LED core and thermal conductive core, will be designed and manufactured into a series of standards, the use of conical cylindrical thermal core, effective solution The problem of heat conduction between the wick (heat conducting core) and the heat sink (lamp) enables the wick and the lamp to be easily disassembled and assembled. The structure is very simple and the construction cost is low. It is a road to standardization of the module, and it is considered that the constant current drive Power Supply More reasonable.

Natural convection cooling, no mechanical movement, high reliability, low cost, naturally preferred by LED lights. This article will expound the principle of natural convection heat dissipation, maximum heat dissipation, and the concept of optimal design; discusses the best application structure of LED light fins - solar heat sinks, proposes convection hoods, and uses the chimney effect to enhance heat dissipation. After a large number of experiments and analysis, the results of optimization and enhancement have been achieved, and the level of heat dissipation per watt is less than 4 grams. The cost of heat dissipation is significantly reduced, and the cost of heat dissipation will no longer be taken into consideration. In short, LED heat dissipation It is not difficult and will no longer be a problem. (This article does not cover the heat transfer within the LED package, which will be elaborated in the next article and propose an effective solution.)