THERMAL MODELING AND MANUFACTURING OF HEAT SINK FOR COOLING CPU

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1 International Journal of Mechanical Engineering and Technology (IJMET) Volume 8, Issue 9, September 2017, pp , Article ID: IJMET_08_09_054 Available online at ISSN Print: and ISSN Online: IAEME Publication Scopus Indexed THERMAL MODELING AND MANUFACTURING OF HEAT SINK FOR COOLING CPU M. Prashanth Reddy, C. Labesh kumar and T. Vanaja Assistant Professor, Department of Mechanical Engineering, Institute of Aeronautical Engineering, Dundigal, Hyderabad, India VVSH Prasad Professor, Department of Mechanical Engineering, Institute of Aeronautical Engineering, Dundigal, Hyderabad, India Dr. K Ashok Reddy Professor, Department of Mechanical Engineering, MLR Institute of Technology, Hyderabad, India ABSTRACT The development of the digital computer and its usage day by day is rapidly increasing. But the reliability of electronic components is getting affected critically by the temperature at which the junction operates. As operating power and speed increases, and as the designers are forced to reduce overall systems dimensions, the problems of extracting heat and controlling temperature becomes crucial. A heat sink is a passive heat exchanger that transfers the heat generated by an electronic or a mechanical device to a fluid medium, often air or a liquid coolant. Modern electronic devices are becoming more compact in size so the heat sink must be developed for such device. The study of heat sink is an important field for the last decade. The reason is mainly the possibilities of reducing the size, weight and cost as compared to current designs. The continual development of faster desktop computers being sold at lower prices into the market place has demanded that thermal management engineers develop and optimize thermal management devices that not only perform better, but are at the same or lower cost than previous generations. An overview of different types of heat sinks is provided. Modelling of heat sink and the development of overall model is described. Keywords: Design, Development, Manufacturing, heat sink. Cite this Article: M. Prashanth Reddy, C. Labesh kumar and T. Vanaja, VVSH Prasad and Dr. K Ashok Reddy, Thermal Modeling and Manufacturing of Heat Sink for Cooling Cpu, International Journal of Mechanical Engineering and Technology 8(9), 2017, pp editor@iaeme.com

2 Thermal Modeling and Manufacturing of Heat Sink For Cooling Cpu 1. INTRODUCTION A heat sink (also commonly spelled heat sink) is a passive heat exchanger that transfers the heat generated by an electronic or a mechanical device to a fluid medium, often air or a liquid coolant, where it is dissipated away from the device, thereby allowing regulation of the device's temperature at optimal levels. With the increase in heat dissipation from microelectronic devices and the reduction in overall form factors, it became an essential practice to optimize heat-sink designs with least trade-offs in material and manufacturing costs. Increasing power dissipation and mounting density of electronic equipment are requiring more effective thermal enhancement to cool the chip and system. One of the commonly used methods for the effective thermal enhancement is to use heat sink. Rapid development in packaging technology allows portable electronics to gain faster processing speed and enhanced capabilities. However, thermal management in the portable electronics environment is becoming increasingly difficult due to high heat load and dimensional constraints. Proper selection of fans and fin pitch in the heat sink is crucial to ensure the thermal design of the system is optimized. Advancements in semiconductor technology have led to the significant increase in power densities encountered in microelectronic equipment. As the amount of heat that needs to be dissipated from electronic devices constantly increases, the thermal management becomes a more and more important element of electronic product design. Both the performance reliability and life expectancy of electronics equipment are inversely related to the component temperature of the equipment. Therefore, long life and reliable performance of a component may be achieved by effectively controlling the device. Operating temperature within the limits set by the device design engineers. A study of heat sink fin technologies has given in formation towards important design criteria for practical cooling of electronic components. Significant work has been carried out by various researchers in the thermal analysis of heat sink design simulation model is validated by comparing the results with the experimental data, and sample cases are presented with discussions on the parametric behaviour and optimization of bidirectional heat sinks with the heaters placed symmetrically. Fourier s law of heat conduction states that if temperature gradient is present in a body, then the heat will transfer from a high-temperature region to allow- temperature region. And, this can be achieved in three different ways, such as convention, radiation and conduction. Figure 1 Heat Sink Principle Whenever two objects with different temperature come in contact with each other, conduction occurs causing the fast-moving molecules of the high-heat object to collide with the slow-moving molecules of the cooler objects, and thus, transfers thermal energy to the cooler object, and this is termed as thermal conductivity. Similarly, heat sink transfers the heat or thermal energy from a high-temperature component to a low-temperature medium like air, water, oil, etc. Usually air is used as a low-temperature medium; and, if water is used as medium, then it is termed as cold plates editor@iaeme.com

3 M. Prashanth Reddy, C. Labesh kumar and T. Vanaja, VVSH Prasad and Dr. K Ashok Reddy 2. DESIGN OF HEAT SINK The following are the various important parameters in selecting a heat sink. 1. Thermal resistance 2. Airflow 3. Volumetric resistance 4. Fin density 5. Fin spacing 6. Width 7. Length A list of design constraints for a heat sink may include parameters, such as 1. Induced approach flow velocity 2. Available pressure drop 3. Cross sectional geometry of incoming flow 4. Amount of required heat dissipation 5. Maximum heat sink temperature 6. Ambient fluid temperature 7. Maximum size of the heat sink 8. Orientation with respect to the gravity 9. Appearance and cost 3. DESIGN CALCULATION Given data Chip size = 38 mm 38 mm Q = 35 W Velocity of air flow = 4 m/s Boundary conditions Base expose to constant heat of 30W Sides of base are not adiabatic Sides and tops of fins are exposed to convective heat transfer to surrounding atmosphere at 298K Heat sink is solid Aluminium. Calculation of heat transfer coefficient h Area of Base = 38mm 38mm, Surface temperature, T s = 110 o C Ambient temperature, T = 25 o C, Mean film temperature, T f = (T S+ T /2 At 65 o c, for air ν = m 2 /s P r = C p = w/mk Reynolds number Re L = u L/ = / = Nusselts number Nu = (Re x ) 0.5 (Pr) editor@iaeme.com

4 Thermal Modeling and Manufacturing of Heat Sink For Cooling Cpu = ( ) 0.5 (0.694) 1/3 = Nu = (h L)/k = h (0.02)/ Heat transfer co-efficient h = w/m 2 k Surface temperature of heat sink Heat transfer Q = ka T/L Q = 35 W, k = 21 wm/k A = 38mm 38mm T1= 110 OC 35= (110-T2)/ ( ) T2 = OC 4. HEAT TRANSFER THROUGH FINS Governing equation of finite length fin without insulated tip Q = (hpka) T (sinhml+(h/mk coshml)/(coshml+(h/mk sinhml) = ( ) 85 sinh (0.23+ (0.01 cosh0.23)/ (cosh0.23+ (0.01 sinh0.23) Q = 2.04 W Total heat transfer rate by 40 fins Q = = 81.6 W Heat Sink Data S NO Description Heat Sink 1 Size 78mm 78mm 2 No of Fins 40mm 3 Fin Length 20mm 4 Fin Thickness 2mm 5 Fin Spacing 1.8mm 6 Heat Sink Thickness 20mm Figure 2 Design of heat sink in CATIA editor@iaeme.com

5 M. Prashanth Reddy, C. Labesh kumar and T. Vanaja, VVSH Prasad and Dr. K Ashok Reddy 5. ANALYSIS OF HEAT SINK USING ANSYS SOFTWARE The purpose of a finite element analysis is to model the behavior of a structure under a system of loads. In order to do so, all influencing factors must be considered and determined whether their effects are considerable or negligible on the final result. Many software are used for this purpose ansys, pro-e, uni-graphics, NISA, MSC, NASTRAN etc. The ANSYS program is self contained general purpose finite element program developed and maintained by swanson analysis systems Inc. The program contains many, all internal and all for main purpose of achieving a solution to an engineering problem by Finite Element Method. ANSYS provides a complete solution to design problems. It consists of powerful design capabilities like full parametric solid modelling, design optimization and auto meshing, which gives engineers full control over their analysis. First select the steady state analysis in the ANSYS software. Set the engineering data > material > aluminium > thermal conductivity. Geometry > import image > heatsink.igs > enter Set the units to millimetre > generate Model > double click Units > mm > mesh > sizing > 2.5mm > generate Steady state thermal > heat flow > 35w > select bottom face > apply Steady state thermal > convection > select the bottom faces of fin > film coefficient > magnitude > apply Steady state thermal > convection > select the faces of fin > film coefficient > magnitude > apply Solve > insert > temperature > select body > apply Solve > insert > directional heat flux > select body > apply Solve > insert > het flux > select body > apply Solve > insert > temperature probe > select the tip of the fin > apply Press solve option Solution is generated. Figure 3 Temperature Distribution editor@iaeme.com

6 Thermal Modeling and Manufacturing of Heat Sink For Cooling Cpu Figure 4 Total Heat Flux Figure 5 Directional Heat Flux 6. MACHINING PROCESS It is an advanced machining process primarily used for hard and difficult metals which are difficult to machine with the traditional techniques. Only electrically conducting materials are machined by this process. The EDM process is best suited for making intricate cavities and contours which would be difficult to produce with normal machines like grinders, end- mills or other cutting tools. Metals such as hardened tool-steels, carbides, titanium, inconel and kovar are easily machined through EDM. EDM is a thermal process which makes use of spark discharges to erode the material from workpiece surface. The cavity formed in EDM is a replica of the tool shape used as the erosions occur in the confined area. Since spark discharges occur in EDM, it is also called as "spark machining". The material removal takes place in EDM through a rapid series of electrical discharges. These discharges pass between the electrode and the workpiece being machined. The fine chips of material removed from the workpiece gets flushed away by the continuous flowing di-electric fluid. The repetitive discharge creates a set of successively deeper craters in the work piece until the final shape is produced editor@iaeme.com

7 M. Prashanth Reddy, C. Labesh kumar and T. Vanaja, VVSH Prasad and Dr. K Ashok Reddy Figure 6 Final Heat Sink after manufacturing 7. RESULTS AND DISCUSSIONS The proposed Heat sink design is suitable for the Intel core i7 processor which has been proved by our calculations. 1. Number of fins increased to 40 fins 2. Compact in size 3. Simple in construction 4. Enhanced heat transfer rate Considering the actual physics to the CATIA generated model in ANSYS, the total heat flux, temperature distribution, directional heat flux has been evaluated. S. No Description Theoretical calculations ANSYS results 01 Base temp 110 ºC 110 ºC 02 Fin tip temp 107 ºC 105 ºC 8. CONCLUSION The heat sink temperature difference results have been compared with an experimental result to find out best heat sink designs, and it shows the good correlation. The fin profiles the base plate thickness was investigated for enhancing the heat dissipation rate from CPU. Some thermal improvements as well as space reduction and material savings were attained. Eventually it is possible to finish up with a new heat sink design which has better thermal performance and uses less material. As the number of fins was increased, the total heat transfer rate also increases i.e. the number of fins is directly proportional to the Total heat transfer rate. REFERENCE [1] X. Luo, R. Hu, T. Guo, X. Zhu, W. Chen, Z. Mao, S. Liu, Low thermal resistance LED lightsource with vapor chamber coupled fin heat sink, IEEE 2010 Electronic Components andtechnology Conference, Paris, Las Vegas, 2010 (doi: /ECTC ). [2] M. Arika, C. Beckerb, S. Weaverb, J. Petroskic, Thermal management of LEDs: package tosystem, Third International Conference on Solid State Lighting SPIE, Bellingham, WA, 2004,Vol (doi: / ). [3] Y. G.-Ying, Z. X. Ping, H. S.-Hong, H. W-Wen, G. T.-Tai, Thermal simulation andoptimization design on a high power LED spot lamp, Optoelectronics Letters 7 (2) (2011) (doi: /s ) editor@iaeme.com

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