Effect of channel angle of pin-fin heat sink on heat transfer performance using water based graphene nanoplatelets nanofluids Hafiz Muhammad Ali ⇑ , Waqas Arshad Department of Mechanical Engineering, University of Engineering and Technology, Taxila 47050, Pakistan article info Article history: Received 26 November 2015 Received in revised form 16 August 2016 Accepted 16 August 2016 Available online 25 August 2016 Keywords: Minichannel Graphene nanoplatelets Convective heat transfer coefficient Electronics cooling Angle of channel abstract This study reports an experimental work to examine the angle effect of pin fin heat sink channel in terms of convective heat transfer coefficient, log mean temperature difference and thermal resistance using water based graphene nanoplatelets (GNPs) nanofluids in a flow rate range of 0.25–0.75 LPM. Three heat sinks having channel angles, measured from positive x-axis, 22.5 degree, 45 degree and 90 degree are used. The volumetric concentration of GNPs particles is 9.5% and these particles consist of overlapped two-dimensional graphene layers. All heat sinks are fabricated with copper substrate, which is main- tained at uniform heat flux during experimentation. Heat sink with 22.5 degree channel angle shows bet- ter thermal performance as compared to other tested heat sinks. For the same flow rate, 22.5 degree heat sink shows lowest convective thermal resistance as compared to other tested heat sinks. Ó 2016 Elsevier Ltd. All rights reserved. 1. Introduction Due to ever increasing heat generation by electronics products, different cooling techniques are being adopted for safety consider- ation. With technological development, heat flux generated by electronic chips has reached to more than 100 W/cm 2 [1]. As a result, failure risk of electronic devices has also increased. Conse- quently, there was a need of an ideal cooling method to remove this excessive heat for proper functioning of electronic products. Air cooling methods have become insufficient for high heat removal aptitude. Due to air cooling methods limitations, research- er’s attention was moved to ideal liquid cooling techniques. At the beginning, water was used as coolant. Although, water gave better results; however, it showed limitations of heat removal. Hence, there was a need of a liquid that has better thermal properties than water. Nanofluids, containing dispersed nanoparticles, have recently showed promising results for thermal applications. These nanoparticles have size in the range of 1–100 nm. The other popular approach adopted by researchers was the modification of the heat sink geometry with a perspective to achieve a better fluid-geometry interaction. Subsequently, minichannels and ultimately microchannels which has hydraulic diameter ranging 10–1000 lm were introduced. Recently, research on micro level has attracted interest due to rapid growth in elec- tronics industry, which needs higher heat transfer rates through a compacted area. First time in 1981, Tuckerman and Pease [2] used microchan- nels for thermal management of microprocessor, where higher sur- face area was available for heat transfer. They investigated performance of silicon made microchannels using water as coolant. Although heat transfer performance was increased with higher surface area, however, a great increase in pressure drop by using microchannels was also reported. Their investigation gave new direction to researchers. Particularly, after the discovery of nanofluids by Choi and Eastman [3] in 1995, the applications of microchannels further increased. After this innovation, Kandlikar and co-workers performed series of investigation on microchan- nels using liquid as coolant. They found 4–10-fold increase in heat transfer enhancement using liquid as compared to heat transfer enhancement by air. They reported possibility of heat removal up to 1000 W/cm 2 with enhanced microchannels [4–6]. Sohel et al. [7] experimentally showed that by the increase of volumetric concentration of Al 2 O 3 /H 2 O nanofluids from 0.1% to 0.25%, thermal effectiveness increased at all flow rates. However, they found that thermal effectiveness was not necessarily increased with the increase of flow rate. They found 18% convec- tive heat transfer coefficient enhancement by using 0.25% concen- trated Al 2 O 3 /H 2 O nanofluids as compared to distilled water. Liquid impingement cooling is also very useful technique in terms of heat transfer enhancement. Naphon and Wongwises [8] used this technique to lower the base temperature, and found sig- nificant temperature reduction than conventional cooling systems. They observed that the velocity was one of the dominant factors in heat transfer rate. Heat transfer enhancement was increased with a decrease in inlet diameter of the nozzle. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2016.08.061 0017-9310/Ó 2016 Elsevier Ltd. All rights reserved. ⇑ Corresponding author. E-mail address: h.m.ali@uettaxila.edu.pk (H.M. Ali). International Journal of Heat and Mass Transfer 106 (2017) 465–472 Contents lists available at ScienceDirect International Journal of Heat and Mass Transfer journal homepage: www.elsevier.com/locate/ijhmt