Array type high power LED lamp thermal analysis (Figure)

With the rapid development of petroleum, chemical, electric power, medicine, railway, shipbuilding and other industries, the demand for lighting power is increasing. The promotion and application of high-power LED lighting energy-saving technology in these industries will produce immeasurable social benefits and economy. benefit. Since the above-mentioned industrial lighting places are often in special conditions that are flammable and explosive, special requirements are placed on the thermal control and explosion-proof performance of lighting fixtures and equipment using these places. 'LED is a semiconductor component that converts electrical energy into visible light. It changes the principle of the three primary colors of incandescent tungsten light and energy-saving lamps. It uses electric field illumination and is a cold light source. When the semiconductor device PN junction is in the 45 state, the theoretical lifetime can reach 100,000 hours. However, due to the current technical stage of LED chip development, only 10% ~ 30% of the electrical energy can be converted into light energy, and the rest of the energy will be stored on the chip in the form of thermal energy, and the LED light efficiency is inversely proportional to the temperature of the Ding. For every 10 increase in temperature, it will result in a 5% to 8% light decay and a serious consequence of halving life. Since the heat generated by the LED is mainly dissipated into the air by means of heat conduction and heat exchange, the heat dissipation device of the LED lamp is rationally optimized, the internal flow field of the lamp is improved, the temperature of the LED lamp surface and the chip temperature are effectively reduced, and the stability is improved. And the service life has become a subject of research by many scholars. Su Da et al. studied the influence of packaging technology on the heat dissipation performance of high-power LED lamps. Yu Binhai et al. studied the thermal resistance of LED lamps and discussed their effects on heat dissipation. Zhang Xinbiao et al discussed the effects of heat sink fin thickness, height, spacing, and number on the heat dissipation of LED lamps. Qi Jun et al. carried out flow field analysis on the structural geometric factors affecting the heat dissipation performance of LED lamps, and carried out parameter optimization design. In this paper, the effects of heat dissipation on the heat dissipation of the lamp body are studied, and the relevant optimization parameters are obtained.

Based on the previous finite element simulation analysis, this paper further discusses the heat dissipation structure, lamp body material, load and boundary conditions of the luminaire, and improves the numerical analysis model of the array type high-power explosion-proof LED heat dissipation structure, and calculates the indoor closed environment. The temperature field, temperature gradient and heat flux density of the lamp are used to obtain the temperature of the chip and the surface of the lamp body. Then, according to the numerical analysis of the model parameters, the sample is trial-produced, and the sample is sent to the National Explosion-proof Electrical Product Quality Supervision and Inspection Center for temperature test; Finally, the simulation results and temperature test data are compared and analyzed.

1LED heat dissipation structure numerical simulation 1.1 lamp body structure The appearance of the lamp body used in this paper is composed of a lamp housing and a lamp cover. The inside is equipped with a heat absorption plate, an aluminum substrate and 60 1W standard LED chips, and the lamp housing and heat absorption. Various types of heat dissipating fins are arranged on the disc to increase the heat exchange area with the air to improve the heat dissipation effect of the lamp. The specific model is as shown, where (c) and (d) are internal perspective views to show the structural model of the internal chip and the heat absorbing disk.

The outer diameter is 247mm, the thickness is 12mm, and the bottom end is 6mm; the outer diameter of the large cylinder is 267mm, the inner diameter is 247mm, the height is 63mm; the upper part of the lamp housing is cone, the inner diameter of the lower end is 218mm, the inner diameter of the upper end is 208mm, the thickness is 5mm; The thickness of the sheet is 5mm, 6 pieces are symmetrically distributed, and the spacing is 10mm. The thickness of the large cylindrical ring in the lower part of the lamp housing is 5mm, the height is 60mm, and the symmetrical distribution is 30. The angle between the fins is 8°, 25°, 27° and 73 respectively. °; inner aluminum substrate thickness 2mm, outer diameter 200mm; heat absorption plate total height 30mm, the lower part is combined with the aluminum substrate, the ring direction is combined with the lamp shell, the upper part is hollowed out 25mm to place the heat sink, the height is 8mm, wherein the inner ring of the large ring Each has 30 fins with a thickness of 2mm. The inner ring of the small ring is evenly distributed with 10 fins, and the thickness is 3.5mm. The inner diameter of the arc that separates the fins is 10mm, 72mm, and the thickness is 2mm. This model is omitted. The plastic part of the LED package, the lens, the substrate, the thin wire, etc. have an effect on the heat dissipation of the lamp body. In fact, it has been shown that changing the packing material of different packages has little effect on the reduction of the thermal conductivity temperature, even if the thermal conductivity of the encapsulating material reaches 7 W/m K, compared to the material using a thermal conductivity of only 0.25 W/m K. The temperature of the chip is not much lower, and the temperature of the aluminum substrate is only decreased by 2.271 ft. Secondly, the heat sink and the aluminum substrate, the aluminum substrate and the heat absorbing plate are thermally conductive through the silica gel, and the components are very tightly combined. Generally, the thickness of the silica gel is on the order of micrometers, for the convenience of analysis, The effect of silica gel can be ignored. At the same time, in the establishment of the finite element model, in order to facilitate the meshing, the rounded corners, holes and some local features that have little effect on the results are ignored.

1.2 Through the simulation analysis of the previous stage, the lamp body materials discussed the changes of the surface temperature of the chip and the lamp body when the lamp body is made of stainless steel, cast iron, aluminum alloy, copper, silver, diamond and other materials. Because stainless steel and cast iron have relatively low thermal conductivity, the maximum temperature of the chip exceeds the thermal design threshold of the chip by 95 ft. While copper, silver and diamond are satisfied, the cost is too high, and it is not easy to add it. The model adopts the lamp body material as aluminum alloy ADC12, the thermal conductivity is 237W/m4, the lamp cover is tempered glass, and the thermal conductivity is 300W/mK. 1.3 The calorific value of the chip is well known. With the increase of the input power of the LED, the brightness of the lamp It will also increase proportionally, but since the efficiency of LED is far below 100%, only a small amount of electrical energy can be converted into light energy, and about 70% of the energy converted into thermal energy causes the junction temperature of the chip to rise. To this end, this paper uses 60 arrays of 1W standard LED chips on an aluminum substrate in an array of 6, 12, 18 and 24 chips in diameter. While increasing the power of the lamp, the chip is cooled and the junction temperature of the chip is lowered. In this model, the calorific value of the chip is 85% of the input power, which is 0.85W, the nominal size is 1mmx1mmx1mm, and the heating rate is 0.85W/mm3. At the same time, in order to simulate the chip, the thermal conductivity of the chip is taken as a larger value.

1.4 Environmental parameters The heat transfer path of the lamp is chip, aluminum substrate, heat absorption plate, lamp body, then the lamp body exchanges heat with the surrounding air to dissipate the heat, thereby reducing the junction temperature of the lamp. However, the calculation of the heat exchange between the lamp body and the air is difficult to give a more accurate calculation result, and it is also prone to error when used. According to the past, it is generally recommended to use some empirical data. The empirical formula for the air convection coefficient is as follows: h represents the air convection coefficient; v represents the air flow rate.

However, the heat exchange coefficient of air is about 5W/m2-k under convection, and the heat exchange coefficient with air under forced convection with air flow rate of 3m/s is about 15W/m2k. Considering the test, the lamp is placed in the test chamber. The indoor heat exchange coefficient is taken as 5W/m2k, and the heat exchange coefficient of the internal cavity of the lamp is 2.5W/m2k. The ambient temperature of the lamp is the same as the ambient temperature in the test chamber during the test. For 50 1.5 simulation analysis, the simulation calculation was carried out with ANSYS software. According to the above, the finite element model of array type explosion-proof LED lamp was established, and the material parameters of chip, lamp body and tempered glass cover were defined. The sol-id90 unit was selected and the model was networked. Divided into the grid, finally applied the chip's heat rate and environmental boundary conditions, the steady-state temperature field calculation, the simulation results of the array type explosion-proof LED lamp, including the temperature field, temperature gradient and heat flux density of the lamp, as shown, (d), and both are internal perspectives.

The heat is effectively diverted and passed to the air without the junction temperature of the chip exceeding 95, which ensures the service life of the lamp. It can be seen from the fixed point that the highest temperature of the lamp appears at the chip, the size is 76.8, the lowest temperature appears at the top of the lamp housing, the size is 69.7, and the temperature difference is 7.1. By observing the overall temperature cloud image, the temperature field of the lamp is basically the same. It can be seen that the characteristics of the chip are mainly that the aluminum alloy with good thermal conductivity is selected for the lamp body material, so that the temperature distribution of the lamp body is relatively small, and the relative temperature difference is not large. Secondly, the heat dissipating fins are arranged reasonably, including the lamp housing. The fins on the top and the lower ring of the lamp housing, as well as the heat dissipating fins of the internal heat absorbing plate, increase the heat exchange area between the lamp body and the air, so that the temperature of the lamp body can be transmitted to the air, reducing the lamp body and the chip. Absolute temperature. In addition, it can be seen that the maximum temperature outside the lamp housing is closer to the heat absorbing plate, the size is 72.1, the temperature at the top of the casing is 69.7, and the temperature of the tempered glass cover is 70.6. 2 Temperature test in order to verify the finite element simulation calculation Reasonability, and further understanding of the heat dissipation mechanism of the explosion-proof LED lamp, the temperature test of the above-mentioned explosion-proof LED lamp. Approximately 1:1 ratio sample preparation was performed on the above-mentioned explosion-proof LED lamp simulation model using modern Gadding technology, as shown. The explosion-proof lamp is composed of an explosion-proof main body of cast aluminum alloy and an increased safety type junction box. The two are connected by wires and are sealed, and the arrangement of the main body casing, the lamp cover, the heat absorbing plate, the aluminum substrate and the chip are arranged. The finite element model is designed to have a junction box added to the upper part of the housing, the internal cavity to place the terminal block, and the remaining parts to add small holes and circular chamfers.

The temperature test of the sample is carried out at the National Quality Supervision and Inspection Center for Explosion-proof Electrical Products. The test is a complete machine test. The sample is placed in a test chamber of 50 and continuously operated until the temperature is stable. Finally, a representative temperature value of the surface of the lamp housing is measured. The test results are compared with the temperature values ​​of the simulation results, as shown in Table 1.

Table 1 Test test temperature and simulation analysis results Comparison of project environment / shell surface maximum temperature / junction box temperature / transparent part temperature / chip temperature / simulation 50, closed temperature test 50, sealed untested Considering test equipment, test environment, limited Simplification of the metamodel (junction box, hole, chamfer, simplification of silica gel) and negligence of contact thermal resistance (contact thermal resistance between the heat sink and lamp housing, lamp cover and lamp housing), test and simulation There is a certain error in the results of the simulation. From the qualitative point of view, the increase in the contact resistance and the simplification of the silica gel will result in a more uneven temperature difference between the measured values; the increase in the heat dissipation area such as the junction box and the hole will result in a lower measured surface temperature; the heat exchange coefficient of different materials is difficult. Accurate determination also brings some errors; the comparison of temperature tests and simulation results also reflects the trend of these qualitative analysis. Considering the quantitative calculation, the maximum error of several temperature comparisons is 3.6, the error rate is 5.4%; the minimum error is 0.6, the error rate is 0.8%, and the error is relatively small. The simulation can basically accurately reflect the temperature distribution of the product, thus Further help enterprises to improve and optimize the heat dissipation structure of the product, reduce the chip temperature, meet customer needs, and improve product quality and performance.

3 Conclusions This paper uses ANSYS simulation software to simulate the array high-power explosion-proof LED lamps. Considering that the luminaire will be applied to petroleum and chemical fields, it puts forward higher requirements for the heat dissipation of the luminaire. This paper has made a detailed examination from the heat dissipation design of the luminaire structure, the selection of the lamp body material, the heat generation of the chip and the reasonable definition of environmental parameters. Discussion and analysis to facilitate the simulation results closer to the actual, while more effectively reducing the junction temperature of the chip. Then through the simulation calculation, the temperature distribution, temperature gradient and heat flux density of the luminaire are obtained. Finally, the luminaire was sampled and tested for temperature of the whole machine. The representative temperature values ​​of the surface of the luminaire were measured to verify the simulation results. From the comparison of the two, the simulation results can reflect the temperature distribution of the sample more accurately, and it also shows that the explosion-proof lamps have better heat dissipation effect and can meet the heat dissipation requirements of petroleum and chemical sites.

(Continued on page 44) Condition 2) The maximum compressive stress (and VonMises stress) of the main chord of the boom is 265 MPa and 269 MPa, respectively, slightly higher than the allowable stress of Q345B of 257.5 MPa. At a pressure of 1100 Pa, the maximum compressive stress (VonMises equivalent stress) also reaches 256.534 MPa. From a safety point of view, the strength of the upper and lower chords of the tower crane and the main string of the tower body is slightly insufficient, and the stress can be exceeded or close. The parts with the allowable stress are suitably reinforced (select a larger section or use a stiffener to weld).

3.2 Tower stiffness The relationship between the horizontal static displacement generated by the tower crane at the junction with the boom (the joint between the boom and the rotating column) and the free height H of the tower is recommended: In this analysis, H = ( Continued from page 7)

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Smelting - adding materials in a furnace in a certain order to melt them into alloys of uniform chemical composition.

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