Study, Optimisation and Numerical Simulation of Natural Convection around the Radial Heat Sink

1. INTRODUCTION

The application of fins or plates in heat exchanger is to dissipate heat from internal to external environment. This property of the plate attracts the researchers and analysts because the plate has various applications in the field of heat exchangers, boiling water, steam funnels, heaters, coolers, electrical conveyors, electronic devices, etc. These researches always focused on enhancing of intensity and productivity on the economical path. As all the studies always concentrated on designing a part considering minimum weight and minimum balance is critically required. For increasing the heat transfer capacity blades are broadened in order to achieve a better heat transfer in various devices. So while designing it is considered that, a heat sink is located at appropriate distance and has minimum contact with other parts in a constrained convection and regular constrained working conditions. In order to increase heat capacity, some gadgets are used for increasing the heat transfer in a constrained. There are different shapes of blade are available, but due to straight ness of rectangular blades, are extensively used in assembling. Characteristic convection from a square with blades may well be utilized to reenact wide assortment of planning applications even as offer higher understanding into more and more complicated frameworks of heat transfer, for example electric devices, heat exchangers, refrigerators etc. Cooling of a hardware device with fine heat sinks is a usual practice due to its easy assembling and applying process and high unwavering quality. Constrained clusters on vertical and even faces are used in the various construction applications, in order to dissipate heat to outer environment. For The best method for the improvement of heat transfer capacity of any device can be achieved by using the balanced components and the utilization of whole surface area of device. In the various studies, huge amount of balances are used for the small heat sink in gas as working abject. Balancing a plate is an old one technique for reducing heat sink. Now the spiral balancing design of heat sink is in use. And this works with the combination of roundabout plate with various blades layered on the plates. And the plates are joined by the various types of fitments like mechanical, cement, welding, binding, and brazing.

In various fluids different type of heat transfer phenomenon is seen which the result of heat transfer operations. Various fluids undergo different heat exchange phenomenon to exchange their heat via surrounding, liquid to liquid heat exchange, solid to liquid heat exchange and vice versa. This phenomenon of heat transfer perceives due to some of mechanical changes in the body or some thermodynamical changes. These all changes of heat transfer or we can say energy transfer depends on the factors like temperature of body, motion, and external and internal environmental conditions etc. So, the exchange of temperature due to difference between the two sources or medium is called heat transfer.

Heat transfer can be achieved by three different modes;

• CONDUCTION • RADIATION • CONVECTION

different temperatures. The heat of the warmer object will travels towards the cooler object, and it will continue until the temperature of both objects will become same. And this is performed by the help of collision of molecules.

Basically, radiations are the emitting from the object in the form of electromagnetic waves and travel from one object to other, and this performed without any physical contact between the two objects.

Convection is the transfer of molecules movement within the fluid like gases, liquids etc. Convection cannot take place in the solids because of the movement of molecules is not possible. Simple example of convection is, when the water is boiled, as we are transferring heat from the bottom layer of water it transfer heat to the upper layers by convection.

Kim et al, [1] in the present study CFD analysis has been carried out to find the efficiency of the system having extended surfaces as fins. For the complete study a chamber having the fin structure is designed to perform an analytical study on it. For the analytical study different no. of fins, Rayleigh number is defined to have the desired solution from the overall study. Rayleigh number is calculated using the Nusselt no. and further calculations were carried out. In the study heat transfer phenomenon in the chamber having plate fins and extended fins were simulated to have desired results. Overall from chamber having plate fins showed better results as compared to other designs used for the simulation. The result showed that it shows around 36% higher performance as compared to extended surfaces designs. Kim et al, [2], in the present study author presented his work on cooling of LED light where different researches are still prevailing to improve its overall performance. In the current work a hollow fin heat sink and a round heat sink is utilised for the simulation purpose. From the study various parameters such as heat transfer, temperature and velocity were identified to provide a suitable conclusion from the study. In this work air is circulated in the heat sink to find its effectiveness for further cooling. From the study a slant shape heat sink best results with for convection. Such studies are based on forced convection phenomenon. In complete analytical work Rayleigh number ranging from the values 300000-1000000 was selected with different fin numbers ranging

Lee et al [3], In the present investigation, a heat sink of LED lighting was enhanced regarding its fin-tallness profile to acquire solid cooling execution for high-control LED lighting applications. In this, convection and radiation heat transfer is modelled and tested in order to approve its numerical design. For the result depiction and optimum value consideration Pareto procedure was utilised. From the study the results of radiant heat transfer and convection were obtained. From the study overall 45% efficiency of fin was improved to provide efficient solution in LED Performance. This performance of fins can eradicate various heat based problems seen at the time of working. This study was conducted analytically using CFD as the base operation for the simulation for the meshing ICEM surf was utilised. Lee et al [4], in this author explained about the heat sink performance used as heat transferring device used in various application. Heat sink has high application in electrical devices were electrical systems are maintained in their desired temperature using the heat sink cooling proficiency. For finding the efficiency of overall system in the present work convection and radiation is utilised where air with certain velocity is passed in the chamber or enclosure where heat sink is placed, When the air gets in contact with these extended surfaces which are made of materials having high thermal conductivity gets cooled with their interaction. In the current work Length of the fin is varied to have more surface area for the contact of heat sink. As a result high efficiency is seen in the present work. For the CFD analysis a model is created using the modelling software and further the geometry is used for the heat transfer simulation. During the complete working various operations were performed on the heat sink such as name selection, meshing and pre-processing of boundary conditions etc. results from the study showed the improvement of 12.3% whereas the mass is increased by 20%. Wange et al [5], in the present study an experimental and an analytical study has been performed on this heat sink. From the study results of heat transfer coefficient were estimated to find the efficiency of overall heat sink device. Results obtained from the experimental study were validated with the results of numerical study performed using different fluid flow software‘s. Heat sink having large surface contact area showed better results as compared to the heat sink having less surface area of contact. The study was based on the forced convection procedure where air was used as the parameter for the judgment and different contours of temperature, velocity and pressure were obtained to compare the results of experimental and analytical based simulation. Further from the study it is Hwan et al [6], in present study, the experimental and numerical investigation of natural convection in radial heat storage sink, which have a horizontal circular base and rectangular fins. The flow pattern of chimney, i.e., Air enters from outside and then it is passes from fins after heating and then flow from the inner region of the heat sink. In this, parameters on the basis of three different geometries (fins, fin length, and number of fins) and a parameter without any add (Heat flux) on the thermal resistance and average heat transfer for the heat sink. And also correlation is used to predict average Nusselt for radial heat sink. And it is resulted that from the study, thermal resistance decreased and the heat transfer coefficient increased in proportion to heat flux applied to heat sink.

1. To study the effect of holes, slots on the radial heat sink fins and understanding the possibility of reduction of mass in the radial heat sink for same thermal performance. 2. To study the effect of orientation of the radial heat sink. 3. To study the effects of interrupted fins, understanding the aftermath of the distribution of mass.

1. Selection of base model for the further study. 2. Modelling of geometry using the selected parameters. 3. Name selection on different components and domains used. 4. Meshing of overall system. 5. Result simulation of heat sink. 6. Result evaluation on behalf of heat transfer, temperature and velocity etc.

Seung-hwan yu, Kwan-soo Lee, Se-jin Yook [6] studied the effect of fin length, height, number of fins on a single operating parameter heat flux. Numerical simulation was conducted on Ansys

The model in Fig 4.2 shows the heat sink with its domain generated in solid works 2016 and exported as .STEP file to the Ansys fluent 15. Boolean operation of subtracting base from domain was done. Assigned solid to the base and fluid to the domain.

The procedure used in this numerical analysis is validated with available numerical analysis. A rectangular plate heat sink analysis carried out by [6] (Ref)‘s model is created using CAD software with

Radial heat sink with holes 4mm 8mm 12mm was studies for 800W/m2 was studied. And the results were tabulated

Figure 16: Velocity vector of 12mm hole heal sink

It can be seen from the Fig 5.14 that as the hole size increases the difference between the ambient and average temperature also increases. Thermal resistance also increasing. So making a hole for an optimized fin will not yield any additional benefit. Fig 5.15 shows the thermal resistance for different sized hole.

From the above table when compared to the reference model the IA3 base temperature is increased for increase in orientation angle. So IA3 performs better when kept in horizontally. But for reference model the base temperature increased till it the installation angle 60o. At 60o it has a minimum base temperature and again at 90 degree the base temperature has increased slightly.

The thermal performance and fluid flow of three dimensional radial heat sink is studied using Finite volume method. The heat sink orientation for natural convection was analysed. By visualizing the numerical analysis data, we observed airflow cooling air entering from outside was heated as it passed between the fins, and then rose from the inner region of heat sink. Studies were performed to compare the effects of the Holes, Slot, Interrupted, Redistribution fin mass and orientation on the thermal resistance and the heat transfer coefficient. The Holes, slot, interruption increased, the thermal resistance and heat transfer coefficient generally decreased. However, after redistributing the interrupted fin mass heat transfer increased, obtained an effective low heat sink temperature and found more even heat distribution at the base of the heat sink when compared to the reference model. The thermal resistance decreased and the heat transfer coefficient increased in proportion to the heat flux applied to the heat sink base. Based on the analysis the fin with 2mm cut redistributed mass is a better model when compared with the reference model. It can be seen that from the analysis both mass reduction and thermal performance enhancement cannot be done simultaneously.

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M.Tech Scholar, Thermal Engineering, SRK University, India