Innovative design of heat dissipation structure for LED street lamp based on AD and TRIZ

Transcription

1 Innovative design of heat dissipation structure for LED street lamp based on AD and TRIZ R.Ma,L.Liu&T.Yu Shanghai Key Lab of Intelligent Manufacturing and Robotics, School of Mechatronic Engineering and Automation, Shanghai University, China Abstract To solve the problems of low heat dissipation, low reliability, and complex structure of a light-emitting diode (LED) street lamp, we study the integration theory of axiomatic design (AD) and Teoriya Resheniya Izobreatatelskikh Zadatch (TRIZ), and the FloEFD simulation model. We have established an integrated design model on the basis of AD and TRIZ and applied to the design of heat dissipation structure of an LED street lamp. We also analyze the function of the heat dissipation structure, as well as determine the design conflict, and solve it. Then, we obtain a new type of a heat dissipation structure for LED street lamps and adopt the thermal simulation of FloEFD to verify the rationality of the heat dissipation structure. It can improve the performance and reliability of LED street lamps. Keywords: AD, TRIZ, LED street lamp, heat dissipation structure, innovative design. 1 Introduction Light-emitting diode (LED) lamps are a new generation of lighting products with the following characteristics: high efficiency, long life, simple structure, small volume, light weight, rapid response, good seismic performance, and full color spectrum. They have introduced a new field of lighting technology in the traditional lighting industry and provided a new direction for designing energy-saving lighting. In many applications of LED products, LED street lamp is a very promising application. Owing to the complex environment of outdoor lighting, many factors affect the reliability of LED street lamps; the junction temperature of an LED chip has a great influence on the life, reliability, and failure mode of an LED [1]. When an LED is connected to the power supply, the temperature of the positive negative doi: /iwama150191

2 160 Advanced Manufacturing and Automation V junction raises. Once a certain threshold is reached, it affects LED color, luminous flux and voltage, etc. At the same time, the high temperature can also cause the thermal expansion of the packaging material, which leads to the failure of the LED, so the heat dissipation design of LED street lamps is very important [2]. The traditional method has not been able to solve the technical problems considering the heat dissipation in the process of the LED street lamps design. In this paper, we use axiomatic design (AD) and Teoriya Resheniya Izobreatatelskikh Zadatch (TRIZ) to guide the design and design a heat dissipation structure of LED street lamp, which is beautiful and good in heat dissipation. Finally, we achieve the objectives of reducing the junction temperature of lamps, as well as prolonging their service life and improving their reliability. 2 Integrated design model based on AD and TRIZ 2.1 Integration theory of AD and TRIZ Axiomatic design is a structural design method proposed by Professor Nam P. Suh of Massachusetts Institute of Technology in the 1980s [3]. Axiomatic design includes functional independence axiom and minimum information axiom. Independence axiom maintains independence between functional requirements. It is the basis for judging whether a design is reasonable. It is used to analyze the relationship between functional requirements and design parameters. This relationship can be expressed as a design matrix A (Fig. 1): {FR s } = A {DP s }, (1) Figure 1: Three forms of design matrix. When the design matrix A is a diagonal matrix, the design is a noncoupling design. When the design matrix A is an upper triangular matrix or a lower triangular matrix, the design is a quasicoupling design. If the design matrix A is a general matrix, a variation in the design parameters has a mutual effect on the two functional requirements. It does not satisfy the requirements of the independence axiom. There may be design conflict; further analysis will determine whether there is a conflict. Axiomatic design can help designers judge the rationality of a design, but it does not provide the right method for a correct design. Researchers, such as R. A. Shirwaiker, G. E. Okudan, and Tan Runhua proposed the use of TRIZ to solve the conflict problem in the process of AD analysis [4, 5]. TRIZ is the solution to

3 Advanced Manufacturing and Automation V 161 the problem of invention. It is based on summarizing a large number of patents and innovation, summed up the tool that to solve specific conflicts in the design process. It consists of 40 inventive principles and a separation principle, 39 general parameters and a conflict matrix, the evolution law of a technology system, etc. The aim is to solve conflicts in design and obtain innovative solutions. 2.2 Thermal simulation based on FloEFD FloEFD is a general fluid heat transfer analysis software [6] mainly used for thermal simulation of LED lamps, as well as for determining whether the junction temperature of an LED chip is within the scope of regulation and determining whether the design of a heat dissipation structure is reasonable. The main steps in thermal simulation of lamps are as follows: (1) Establishing the model of LED lamps and importing into the FloEFD software (2) Creating an LED lamp project and setting the relevant parameter properties including unit, analysis type, gravity direction, fluid type, solid material, and mesh (3) Examining the model and setting the boundary condition (4) Adding material properties to each component of an LED lamp, adding contact resistance on the contact surface of lamp parts, establishing the double resistance model to replace a chip as the heat source, and setting the target of the components Finally, the temperature distribution of an LED lamp can be obtained by postprocessing. And we can determine whether the junction temperature of a chip is reasonable. 2.3 Integrated design model based on AD and TRIZ By comparing the TRIZ and AD theory, we find that each has its own advantages. Designing a heat dissipation structure for an LED street lamp involves the optimization and integration of two theories and combining with FloEFD thermal simulation. Then, we build the integrated design model of a heat dissipation structure for the LED street lamp on the basis of AD and TRIZ (Fig. 2). The integrated design model mainly includes the following steps: (1) Establishing the function-structural model for the heat dissipation structure of the LED street lamp on the basis of the characteristics of the heat dissipation structure and user s requirements. (2) Determining the coupling of the design matrix and rearranging the design matrix. If the design matrix is a diagonal or a triangular matrix, it is a noncoupling design On the basis of the independence axiom, the design can be accepted for the next step or rejected. (3) Using TRIZ s correlation tool to continue conflict resolution, the innovative principle solution of the heat dissipation structure is obtained to determine

4 162 Advanced Manufacturing and Automation V Figure 2: Integrated design model of heat dissipation structure based on AD and TRIZ. the integrated design model of the heat dissipation structure for the LED street lamp. (4) Establishing the model of the heat dissipation structure of the LED street lamp and then carrying out thermal simulation based on FloEFD to determine whether the junction temperature of the LED chip is within a reasonable range. (5) Determining, on the basis of the simulation results of FloEFD, whether design requirements are met. If they are not meet, TRIZ s correlation tool is used to carry out the conflict resolution again. And the structure model is established for simulation. Otherwise, the next step is followed.

5 Advanced Manufacturing and Automation V 163 (6) Determining the scheme of the heat dissipation structure on the basis of thermal simulation based on FloEFD. Finally, a high reliability of the heat dissipation structure of the LED street lamp is obtained. 3 Innovative design of heat dissipation structure for LED street lamp based on AD and TRIZ 3.1 User requirements analysis As temperature greatly influences luminous flux, color, and reliability of lamps, it requires LED street lamp working continuously. This research on heat dissipation of LED street lamps, natural convection is mainly adopted; the parameters of fin shape, thickness, fin pitch, etc. mainly depend on the experience of engineers, as effective methods for determining these factors are lacking. The structure of the fin and heat sink, which are parts of the lamp, will affect the appearance of the lamp. The purpose of this paper is to design a new type of heat dissipation structure on the basis of a 400 W LED street lamp and control the junction temperature of the LED chip within 85 C. The street lamp has the following requirements: good thermal performance, high reliability, beautiful appearance, simple structure, easy to manufacture, low cost. 3.2 Analysis of heat dissipation structure of LED street lamp based on AD First, user requirements need to be summarized: FR 0, which is an LED street lamp that can work continuously and have a beautiful appearance. The corresponding design parameter is summarized as DP 0, which is the heat dissipation structure of the lamp. Function decomposition is FR 0 ; FR 1 is the reasonable structure of heat dissipation; FR 2 is simple and beautiful appearance of the lamp; and FR 3 is light weight. We introduce some user demands as constraints on the design parameters of the heat dissipation structure, namely C 1 : good performance in heat dissipation, C 2 : low cost of lamp, C 3 : high reliability of lamp, C 4 : convenient maintenance of lamp, C 5 : beautiful appearance of lamp, and C 5 : simple structure of heat dissipation. Depending on the functional requirements FR 1, FR 2, FR 3, and their corresponding constraints of C 1, C 2, C 3, C 4, C 5, C 6, the design parameters are obtained under the condition of the constraints. They are DP 1 : convection cooling of fin, DP 2 : surface appearance of lamp, and DP 3 : overall structure shape of lamp. Through analysis, it is found that design parameters that affect the functional requirement FR 1 are DP 1 and DP 2 ; design parameters that affect the functional requirement FR 2 are DP 1, DP 2, and DP 3 ; and design parameters that affect the functional requirement FR 3 are DP 1 and DP 3. The design matrix is obtained on the basis of the application of the independence axiom: FR DP 1 FR 2 = DP 2. (2) FR DP 3

6 164 Advanced Manufacturing and Automation V In the matrix, 1 represents the two correlation, 0 means the two is not relevant, in the following process the symbol meaning is the same. Equation (2) shows that the design matrix is a general matrix, which does not satisfy the independence axiom. The design is coupled with the need for further decomposition of the function: (1) FR 1 is decomposed into FR 11, the heat generated by an LED chip that is rapidly transmitted to the fins, and FR 12, the quantity of heat emitted into the atmosphere from the fins. The corresponding design parameters are DP 11, the shape of the radiating fin, and DP 12, the heat convection channel for a lamp. The formation of the design matrix is: [ FR11 FR 12 ] = [ ][ DP11 DP 12 ]. (3) (2) FR 2 is the simple and beautiful appearance of a lamp. We have no special structure on the surface, in line with the aesthetic requirements of people. So there is no need for further decomposition. (3) FR 1 is decomposed into FR 31, and FR 32. The corresponding design parameters are DP 31, the connected structure between the heat dissipation structure and the power cavity. The formation of the design matrix is: [ FR31 FR 32 ] = [ ][ DP31 DP 32 ]. (4) According to design matrixes (3) and (4), it can be known whether the design matrix is a diagonal matrix, satisfying the independence axiom. Through the zigzag mapping transformation, we obtain the hierarchy model of a function and the hierarchy model of a design parameter, that is a function-structural model of the heat dissipation structure (Fig. 3). Through the analysis of the model, we find that there is a conflict between light and heat, as well as between the structure and the heat. To optimize the design of an LED street lamp, we must solve these conflicts and optimize the design parameters of the coupling. 3.3 Solution of design conflict and principle solution based on TRIZ Axiomatic design has advantages in determining the design of lamps, but it cannot solve the conflict problem in the design process [7]. According to design matrix (2), this design is a quasicoupling design, which can be accepted by the independence axiom. But if the heat generated by an LED chip cannot be passed to the fins for heat dissipation, and the heat from the fins cannot be effectively

7 Advanced Manufacturing and Automation V 165 Figure 3: Function-structural model of heat dissipation structure for LED street lamp. released into the atmosphere, it directly affects the normal operation of an LED street lamp. Through the analysis of design constraints, it is found that this is actually a technical conflict. By TRIZ, we convert the above functional requirements into TRIZ standard parameters, checking the following table [8]: FR 11 : the heat generated by an LED chip, which is rapidly transmitted to the fins, which can be converted into standard parameter 12: showing the shape. FR 12 : the quantity of heat emitted into the atmosphere from the fins, which can be converted into standard parameter 6: the area of the stationary object. To improve the above two characteristics, which will lead a decrease in the following characteristics: standard parameter 8: for the volume of stationary object; standard parameter 32: for manufacturability. According to TRIZ standard parameters, with checking table [8], the available conflict matrix is shown in Table 1.

8 166 Advanced Manufacturing and Automation V Improved Characteristics Table 1: Local table of TRIZ conflict matrix. Deterioration characteristics Volume of stationary object... Manufacturability Area of stationary object... 40, 16 Shape 14, 4, 15, , 32, 17, 28 Combined with the actual situation of an LED street lamp, inventive principles that we can use are the inventive principle 1: segmentation. And through analysis, we can know that the thermal performance of the structure of an LED street lamp will be promoted, which will lead the fins increasing heat dissipation. But the weight of the structure will be also increased. This is actually a physical conflict, and we can use the principle of separation of space, the corresponding inventive principles being 1, 2, 3, 4, 7, 3, 17, 24, 26, 30. Combined with the actual situation of an LED street lamp, the inventive principle that we can use is the inventive principle 24: mediator. According to research, 80% of innovation is based on existing technology innovation [9]. So it is very important to study the heat dissipation structure of a typical LED street lamp. An LED street lamp uses the integrated design of shell and the heat dissipation structure; the driving power is placed inside. The power cavity and the heat dissipation structure are integrated. The structural model of the whole lamp is shown in Fig. 4. Figure 4: Structural model of whole lamp: 1 shell, 2 LED chip, and 3 glass. An improved LED street lamp is still used in the integrated design of a shell and the heat dissipation structure. According to the inventive principle 1: segmentation, the original cavity, which places LED chips, is divided into two parts to prevent the heat generated by LED chips from being highly concentrated. According to the inventive principle 24: mediator, four pieces of a heat pipe are symmetrically arranged at the two ends of the heat dissipation structure, which allows the heat generated by LED chips in the two regions to be transmitted rapidly to the fins for heat dissipation. At the same time, as the structure of the

9 Advanced Manufacturing and Automation V 167 whole lamp is made of ADC12, thermal-radiation ability is low. According to the conflict matrix, the thermal radiation ability of the street lamp can be improved. According to the guidance of the innovation principle of TRIZ, we reestablish the structural model of the LED street lamp (Fig. 5). Figure 5: Improved structure model of the whole lamp: 1 shell, 2 heat pipe, 3 radiation material layer, and 4 power cavity. 4 Thermal simulation and verification of LED street lamp based on FloEFD The selected light source was OSRAM LCW CQAR.PC; the power of each lamp bead was 2 W. In thermal simulation, the double thermal resistance model was used to replace the light source of an LED and predict the junction temperature of the LED chip. It considered all packages containing two parallel components (shell and knot) with a high-conductivity material. It needed to define two thermal resistance: junction shell thermal resistance (R jc ) and junction board thermal resistance (R jb ), using these thermal resistance values to calculate the thermal conduction through the package [10]. The double thermal resistance model is shown in Fig. 6. Related parameter settings were as follows. Through the specification of OS- RAM LCW CQAR.PC, we obtained the value of R jc as 3.8 K/W; the default setting of R jb was 190 K/W. The ambient temperature was 30 C, and the total power of the LED street lamp was 400 W. According to 37% of the electro-optic conversion efficiency, heat generated by LED chips was 252 W. Each light source module was replaced by a double thermal resistance model. We added contact resistance on the contact surface of lamp parts. The metal layer material of printed circuit board board was Al6061, and the material of the heat dissipation structure was ADC12. The effective thermal resistance of the heat pipe was 0.3 K/W, and the radiation coefficient was The thermal simulation result of the LED street lamp is shown in Fig. 7. The thermal simulation result of the improved LED street lamp is shown in Fig. 8. From the results of thermal simulation, we knew that the junction temperature of the LED chip was C before an improvement in the lamp structure, and

10 168 Advanced Manufacturing and Automation V Figure 6: Double thermal resistance model. Figure 7: Thermal simulation result of LED street lamp. the junction temperature of the LED chip was C after an improvement in the lamp structure. The junction temperature of the LED chip that affected the performance of the LED street lamp was controlled within 85 C. The structure of heat dissipation was reasonable, and it could ensure the normal operation of the LED street lamp. 5 Conclusion In the design process of the heat dissipation structure of an LED street lamp, using the integration theory of AD and TRIZ, as well as the FloEFD simulation model, we establish the integrated design model of the heat dissipation structure

11 Advanced Manufacturing and Automation V 169 Figure 8: Thermal simulation result of improved LED street lamp. of an LED street lamp based on AD and TRIZ. Meanwhile, we analyze the design task and functional requirements of the heat dissipation structure and establish a function-structural model of the heat dissipation structure of the LED street lamp, clearing the design conflict of the lamp. And then, we establish the conflict matrix of the heat dissipation structure of the lamp by using TRIZ, as well as the application of the principle of separation, combined with the actual situation of the LED street lamp, resolving the design conflict of the lamp. So the innovative scheme of the heat dissipation structure for an LED street lamp is obtained. Finally, thermal simulation based on FloEFD is used to verify the rationality of the heat dissipation. It shows that the heat dissipation structure can improve the reliability of an LED street lamp. Acknowledgments This work was supported by the National High Technology Research and Development Program of China (863 Program): 2013AA03A112, as well as the Absorption of Imported Technology and Innovative Project of Shanghai City: 15XI The authors are grateful for the financial support. References [1] Shailesh, K.R., C.P. Kurian, and S.G. Kini, Junction temperature measurement of a LED street light using forward voltage method. International Conference on IEEE Advances in Electronics, Computers and Communications (ICAECC), October 2014, Bangalore, pp. 1 6, [2] Xin Tong, The structural research and optimizational design on the radiator of LED lamps, Jilin University, Changchun, pp. 1 2, [3] Li-bin Zhang, Wei-min Shi, Guan-jun Bao, Fang Xu, and Hong-wu Zhan, General design process model based on axiomatic design Journal of Mechanical Engineering, 46(23), pp , 2010.

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