Experimental and numerical study on the flow topology of finned heat sinks with tip clearance

Abstract

Keywords:An experimental and numerical study is presented that focuses on the flow topology in finned heat sinks with tip Heat sink clearances. As it is well known, the use of tip clearances has, normally, a global beneficial effect. Typically, heat Tip clearance transfer may degrade (a negative effect) by a somewhat small percentage while pressure drop may decrease (a Heat transfer versus pressure drop positive effect) by a substantial amount. In this context, the important question from an R&D standpoint is to understand the flow topology so that the actual design of the tip clearance optimizes the balance between heat transfer and pressure drop. In this study, a 3D numerical method is validated, first, comparing with the Particle Image Velocimetry based experimental results obtained in the actual setup in isothermal conditions. Then, the flow solver thus validated is used in a series of thermal cases in which both the tip clearance height and Reynolds number are varied so as to clarify the flow topology. In particular, it has been found that the behavior of both heat transfer and pressure drop cannot be explained in view, only, of flow development and thermal development aspects. This is so because the Nusselt versus Graetz curves that have been generated do not collapse into a single fit; instead, they collapse into several families that are governed by the tip clearance parameter. Distinct heat transfer rates have been observed for the different fin walls. The transfer rate of the side walls is nearly three times larger than that of the bottom walls, and this suggests the optimum place to locate the heat sources in a practical engineering application. Nomenclature list Latin symbolsA w C Cp cs

Impact of Channels Aspect Ratio on the Heat Transfer in Finned Heat Sinks with Tip Clearance

“…The inlet velocity conditions were validated by conducting isothermal experiments in devices with W = 10 mm for the different TR and comparing the measured velocities (using Particle Images velocimetry PIV techniques) with the computational results. Details of the experimental setup and validation are described in [12]. For all the device walls, a non-slip condition for the velocity and zero normal pressure gradient was used.…”

“…Giri and Das [11] made a computational study where they considered a shrouded rectangular fin array, varying clearance spacing, fin spacing and Reynolds number. Sastre et al [12] studied a squared-channel fin configuration with tip clearance both experimentally and numerically. They reached the conclusion that heat transfer was greatly reduced by the presence of the tip clearance, suggesting that small tip clearances, which are able to significantly reduce the pressure drop, are more convenient to keep a good heat transfer performance.…”

“…However, the actual quantification of these effects seems to be very dependent on the studied problem, somewhat contradictory and not studied yet in detail in the presence of tip clearance. In this context, the objective of the present study consists on conducting three dimensional numerical simulations of a simplified general heat sink configuration with tip clearance (similar to [12]) with straight fins of different aspect ratios, to determine the flow topology and thermal performance for different flow conditions. The main novelty of the work that is being presented is that the effect of tip clearance geometry is quantified by means of performing a systematic parameter analysis.…”

Natural convection with water-copper nanofluid around a finned vertical cylindrical electronic component

“…Reyes et al (2011) studied experimentally a fin-based micro-heat sink with tip clearance and found that for certain optimum configurations heat transfer degraded by a factor of 20% while pressure related to pumping power decreased by about 500%. Sastre et al (2018) performed a detailed experimental and numerical study on the flow topology around the tip clearance of fins used in a mockup heat sink. The emphasis was focused on the three-dimensional flow structures that appear in the tip clearance area.…”