Three aspects in this paper, the high power LED heat sink
Beside this year when the scene, many bosses complain the business is bad, are seeking simple product breakthrough. Is always as a side dish as firms invest heavily industrial lighting, floated to the surface at the beginning of this year and concern for you.
Now that is required is simple, the structure is too complex suite is difficult to your boss. Shape with different color in the radiator is small at the UFO radiator seems to stand out from the suite, a show down at least can see dozens of UFO type Highbay.
As is known to all, there are three ways to heat transfer, conduction, convection and radiation. We are more than this one has a special feature the radiator of product structure and simple to talk about the high power LED heat sink on the design and application, there may be room to improve.
A transmission, first to see.
Because this kind of lamps and lanterns is generally itself is not direct contact with the surrounding buildings, solid so conduction and not directly to the heat generated by the light source and power supply "loose" to the surrounding environment, but still very important, because it is to take away heat from the light source and light source of the most direct way. Early design of high power radiator often ignores this, improve radiator fins area blindly, ignoring the heat didn't spread to fins. So this kind of radiator fins temperature is very low, if the cooling effect is remarkable, but a little bit careful some customers can find light spot temperature is very high, did not have the effect of the radiator should be.
We can from the basic formula of heat conduction further to see how to ensure the heat transfer efficiency of the radiator.
Phi lambda - A * (dt/dx)
Lambda as the coefficient of thermal conductivity;
A, for the contact area.
DT/dx to temperature gradient, which can be a brief understanding for temperature difference;
Let's look at the shape of the back to UFO Highbay radiator. The material for the die casting aluminum, brand mostly ADC12. The coefficient of thermal conductivity of 96 w/mK, not particularly outstanding. But due to the limit of the die casting technology of sectional area is larger, fin so won't produce bigger problems. Plus is a integrated structure, in the process of the heat conduction only aluminum plate with a radiator thermal contact resistance (light internal thermal resistance and light and thermal resistance is different between the aluminum substrate, temporarily not discuss here), and the contact area is quite large, can be said to be don't need to worry about heat conduction problem.
But there are a few problems if not handled properly can cause big problems.
One is the contact surface roughness. UFO type radiator size is larger, and the product internal stress and thermal deformation of the die casting technology is larger, if you can't do a good job after annealing and processing, can cause a little bit of deformation aluminum plate and significantly reduce the contact area between the radiator, it will do have a great impact on thermal conductivity.
The second stage is the choice and use heat conduction medium. Thermal conductive medium is our commonly used is the official name of the "thermal conductive paste, often in the lamps and lanterns of BOM cost proportion is very small, many enterprises just as well with a little bit. In fact, heat conduction medium selection and use for heat dissipation of lamps and lanterns has a great influence. Contact even processed, flat under a magnifying glass is still not enough. Thermal conductive medium is a good way to fill the gap between the contact surface. Because of the low coefficient of thermal conductivity of air is to the outrageous, only 0.024 W/mK, so failed to direct contact with or without filling the position of the heat conduction medium almost for thermal insulation.
Although many enterprises are filled with heat conduction medium between the contact surface, but because most of the heat conduction medium itself liquidity is poorer, simply apply thermal conductive paste by manpower or a mechanical connection pressure effect is not good. And common the coefficient of thermal conductivity of thermal conductive medium is only 1 w/mK, much lower than the coefficient of thermal conductivity of aluminous material itself, so the heat conduction medium in the case of ensure fill gaps is the thinner the better. Ideal situation is to choose more than 1.8 W/mK heat-conducting medium and using the stencil to guarantee the uniformity and thickness, can give full play to the efficacy of radiator itself.
Second, then the convection.
Convection is the most main way of heat dissipation of radiator. Most researchers tend to be concerned about the problem of convection in the area of ignoring the influence of convection several other factors. We still consider this problem through decomposition of formula.
Phi hA (Ts - T up)
H as the convection coefficient, more complex;
For A convection area;
For the object, and the temperature of the environment temperature;
A don't need to say more, most of the designers at design time will take into account the area is larger, the better. Can be big fins not only increased the assembly, the production difficulty, but also increase the cost. So how the fins area is suitable? Believe that this is the difficult problem that every designer has a headache.
Because of the convective heat transfer is often accounts for more than 80% of the heat dissipation of lamps and lanterns, the problem requires comprehensive considerations.
Convection coefficient involves a lot of details, such as fluid properties, flow velocity, fins on the surface of the shape, size, and the relative position and so on and so on. LED lamps and lanterns of heat dissipation mostly natural convection (i.e., no fan, etc in the case of forced air flow), how to improve convection coefficient under the condition of reasonable, in the eyes of many designers became a kind of "metaphysics", often by a considerable number of computer aided numerical simulation to achieve better effect. Where space is limited, don't discuss, personally, I summarized some experience can be summarized as follows: "less, more rough, try to change the flow state".
Fewer obstacles, to try not to stop movement of airflow, provide a bottom-up flow channel, so as to improve the flow of the gas efficiency. Such as shown in the header of the UFO type radiator, opened more holes in edge that gas can directly from the lower through the fins, is the rise of temperature of the heat sink can be reduced effectively.
More rough, is the rough surface processing. Now more manufacturer in pursuit of beauty and easily surface treatment, chose a smooth surface, it is wrong. Gas and liquid, the solid surface has the adhesion, smooth surface makes it hard for gas flow close to the solid part of the position of gas for heat exchange with the outside world and exchange, this is bad for heat dissipation. When reaches a certain value of surface roughness of the radiator of the heat dissipation efficiency will be significantly increase.
Try to change the flow state it is relatively difficult to explain. Simply put, you can refer to a cigarette in a windless environment produced by the flue gas, it is easy to observe just left the location of the cigarette smoke is soaring, and reached a certain height after flue gas mess up suddenly, become cluttered.
This is actually a layer flow turbulence transition process. You can be understood as a gas in the process of laminar flow is relatively orderly moving in one direction, like in the sight of the peak of high speed. In turbulent flow in the process of gas due to the disturbance, or too fast, thus become chaotic, as in the high speed in the presence of a car accident we bypass, jostled each other. Obviously, under the condition of turbulent flow and no longer distinguish between inside and outside, in the form of a relatively chaos, can more effectively to let the airflow close to fins with outer air exchange. This shift is a good way to improve the thermal efficiency. The common means of change of gas flow state has a hole on the fins, grain production or manufacturing cylinder type lamps and lanterns of forced air flow speed, etc.
Natural need not wordy, and temperature difference can achieve good thermal conductivity, nature is a good way to ensure the radiator and the temperature of the gas is enough big, thus increasing the heat transfer.
Based on the above discussion, we can see the UFO type radiator some defects:
1, so the heat exchange area is insufficient. Is limited by the die casting technology, UFO type radiator is difficult to have a higher height of fins, it is hard to further enhance the density of fins, this led to the UFO radiator cooling area is insufficient.
2. Unable to change the gas flow state. Also subject to the conditions of technology, this kind of radiator fins surface is very difficult to make complex grain or open hole, and short makes gas heating accelerated the height of the fins is insufficient, so difficult to change the flow of the gas.
3. The surface is not rough. Has been analyzed above, you don't go into here.
Three, finally see the radiation heat transfer.
The heat transfer process of radiation heat transfer in LED lamps and lanterns is often can have up to 5% or so, the influence of surface roughness and it mainly depends on the color of the radiator. Friends as long as remember black rough surface can have close to the theoretical value of the radiation efficiency, there are a variety of products on the market are so-called can significantly improve radiation in thermal efficiency, but it's even up 20% of the radiation efficiency, also can only less than 1% overall ascension, please consider itself.
Above all, we can see the UFO radiator of favor by market still has a large room to improve in some ways. Fact is also like this paper deduces the conclusion, UFO type radiator shell the highest temperature is often more than 75 degrees, and aluminum plate solder joint temperature according to the manufacturers of component selection ranged from 80-80 degrees, it does not guarantee the life of the product very well. Manufacturer if you can according to the suggestion on the UFO type radiator made some processing, believe to be able to make a more stable product, to a certain extent after all lamps and lanterns of industrial change trouble, cost is various, stability compared with price has more important significance.
----------Archled Technology Co.,Limited