Raju R.Yenare et al Int. Journal of Engineering Research and Applications www.ijera.com ISSN : 2248-9622, Vol. 4, Issue 3( Version 1), March 2014, pp.239-243 www.ijera.com 239 | Page Experimental Study for Heat Transfer Enhancement Due To Surface Roughness at Laminar Flow Raju R.Yenare, Prof Kundlik V.Mali. Department of Mechanical Engineering Sinhgad College of Engineering, Pune Department of Mechanical Engineering Sinhgad College of Engineering, Pune Abstract An investigation was conducted to determine whether dimples on a heat sink fin can increase heat transfer for laminar airflows. This was accomplished by performing experimental studies using two different types of dimples: 1) circular (spherical) dimples, and 2) oval (elliptical) dimples. Dimples were placed on both sides of a aluminium plate with a relative pitch of S/D=1.21 and relative depth of δ/D=0.16 (e.g., circular dimples). For oval dimples, similar ratios with the same total depth and circular-edge-to-edge distance as the circular dimples were used. For those configurations the average heat transfer coefficient, pressure drop, thermal performance and Nusselt number ratio were determined experimentally. For circular and oval dimples, heat transfer enhancements (relative to a flat plate) were observed for Reynolds number range from 600 to 2000 (Reynolds number based on channel height). Also the results are validated analytically for Nusselt number and friction factor for plain vertical plate. This experiment was undertaken to provide the needed experimental data that fill the gap for the use of dimples for laminar flow conditions. Specifically, this investigation was conducted to determine whether or not the use of dimples can enhance heat transfer characteristics for heat sink applications. Dimples enhanced heat transfer from its surface for laminar air flows while the pressure drop was equivalent or smaller than that of the flat surface. These surfaces do indeed enhance thermal performance without the penalty associated with higher pressure drops. I. INTRODUCTION The importance of heat transfer enhancement has gained greater significance in such areas as microelectronic cooling, especially in central processing units, macro and micro scale heat exchangers, gas turbine internal airfoil cooling, fuel elements of nuclear power plants, and bio medical devices. A tremendous amount of effort has been devoted to developing new methods to increase heat transfer from fined surface to the surrounding flowing fluid. Rib tabulator, an array of pin fins, and dimples have been employed for this purpose. In case of the electronics industry, due to the demand for smaller and more powerful products, power densities of electronic components have increased. The maximum temperature of the component is one of the main factors that control the reliability of electronic products. Thermal management has always been one of the main issues in the electronics industry, and its importance will grow in coming decades. The use of heat sinks is the most common application for thermal management in electronic packaging. Heat sink performance can be evaluated by several factors: material, surface area, flatness of contact surfaces, configuration, and fan requirements. Aluminum is the most common material because of its high conductivity (205W/mK), low cost, low weight, and easiness with respect to manufacturability. Copper is also used for heat sinks because of very high conductivity (400W/mK), but its disadvantages include high weight, high price, and fewer choices as far as production methods. To combine the advantages of aluminum and copper, heat sinks can be made of aluminum and copper bonded together. To improve performance, heat sinks should be designed to have a large surface area since heat transfer takes place at the surface. In addition, flatness of the contact surface is very important because a nominally flat contact area reduces the thermal interface resistance between the heat sink and heat source. A heat sink must be designed to allow the cooling fluid to reach all cooling fins and to allow good heat transfer from the heat source to the fins. Heat sink performance also depends on the type of fluid moving device used because airflow rates have a direct influence on its enhancement characteristics. To obtain higher performance from a heat sink, more space, less weight, and lower cost are necessary. Thus, efforts to obtain more optimized designs for heat sinks are needed to achieve high thermal performance. One method to increase the convective heat transfer is to manage the growth of the thermal boundary layer. The thermal boundary layer can be made thinner or partially broken by flow disturbance. RESEARCH ARTICLE OPEN ACCESS