Heat pipe efficiency enhancement with refrigerant–nanoparticles mixtures Paisarn Naphon * , Dithapong Thongkum, Pichai Assadamongkol Thermo-Fluid and Heat Transfer Enhancement Laboratory (TFHT), Department of Mechanical Engineering, Faculty of Engineering, Srinakharinwirot University, 63 Rangsit-Nakhornnayok Rd., Ongkharak, Nakhorn-Nayok 26120, Thailand article info Article history: Received 25 February 2008 Accepted 20 September 2008 Available online 28 November 2008 Keywords: Heat pipe Nanofluids Efficiency enhancement abstract In the present study, the enhancement of heat pipe efficiency with refrigerant–nanoparticles mixtures is presented. The heat pipe is fabricated from the straight copper tube with the outer diameter and length of 15, 600 mm, respectively. The refrigerant (R11) is used as a base working fluid while the nanoparticles used in the present study are the titanium nanoparticles with diameter of 21 nm. The mixtures of refrig- erant and nanoparticles are prepared using an ultrasonic homogenizer. Effects of the charge amount of working fluid, heat pipe tilt angle on the efficiency of heat pipe are considered. For the used pure refrig- erant as working fluid, the heat pipe at the tilt angle of 60°, working fluid charge amount of 50% gives the highest efficiency. At the optimum condition for the pure refrigerant, the heat pipe with 0.1% nanoparti- cles concentration gives efficiency 1.40 times higher than that with pure refrigerant. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction An advanced electronic devices employing high speed and high level of heat generation have to be small in size, light-weight. However, the level and reliability of heat rejection efficiency lar- gely require for these devices. Heat pipe technology has been used in a wide variety of applications in the heat transfer devices. Lin et al. [1] experimentally investigated a study of two-phase flow and heat transfer of R141b in a small tube. Lin et al. [2] developed the high performance miniature heat pipes for cooling of high heat flux electronics. Esen [3] experimentally studied a solar cooking system using vacuum-tube collectors with heat pipes using a refrigerant as working fluid. Song et al. [4] studied the heat transfer performance of axial rotating heat pipes under steady state. Effects of rotational speed, working fluid loading, and heat pipe geometry on the heat transfer performance were considered. Xuan et al. [5] measured the performance of a flat plate heat pipe under different heat fluxes, orientations and amount of the working fluid. Effects of charge amount of the working fluid, thickness of the sintered layer, and orientation of the heat pipe on the performance were dis- cussed. Vasiliev [6,7] applied the micro and miniature heat pipes in modern heat exchangers for cooling electronic components. Huang et al. [8,9] used a heat pipe in the solar-assisted heat pump water heater system. Lin et al. [10] presented a design method by using CFD simulation of the dehumidification process with heat pipe heat exchangers. Liu et al. [11] developed a looped separate heat pipe as waste heat recovery facility for the air-conditioning exhaust system. Effects of the length of the evaporator, vapor tem- perature, and power throughout on the critical values of the upper and lower boundaries were considered. Vlassov et al. [12] investi- gated the optimal mass characteristics for a heat pipe radiator assembly for space application. Recently, Dussadee et al. [13] developed an aeration–thermosyphon heat pipe for controlling paddy temperature in a paddy bulk silo. The most frequently used coolants in the heat transfer devices study are air, water, and fluoro-chemicals. However, the heat transfer capability is limited by the working fluid transport proper- ties. One of the methods for the heat transfer enhancement is the application of additives to the working fluids to change the fluid transport properties and flow features. Therefore, in order to fur- ther enhance thermal performance of heat pipe, the use of nanofl- uids is proposed. Xuan and Li [14] presented a procedure for preparing a nanofluid. Xue [15,16] considered the interface effect between the solid particles and the base fluid in nanofluids. The theoretical results on the effective thermal conductivity of nano- tube/oil nanofluid and Al 2 O 3 /water nanofluid were in good agree- ment with the experimental data. Roy et al. [17] numerically investigated on the laminar flow and heat transfer of nanofluid in a radial flow cooling system. Tsai et al. [18] considered effect of structural character of gold nanoparticles in nanofluid on heat pipe thermal performance Maiga et al. [19] experimentally studied the heat transfer behaviours of water–cAl 2 O 3 and ethylene glycol– cAl 2 O 3 nanofluids in a uniformly heated tube. Wen and Ding [20] experimentally studied on the convective heat transfer of nanofl- uids in a copper tube. Zhou [21] experimentally investigated on the heat transfer characteristics of copper nanofluids with and without acoustic cavitation. Bang and Chang [22] studied the boil- ing heat transfer characteristics of water with nanoparticles sus- pended. Effects of different volume concentrations of alumina 0196-8904/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.enconman.2008.09.045 * Corresponding author. Tel.: +663 7322625x2065; fax: +663 7322609. E-mail address: paisarnn@swu.ac.th (P. Naphon). Energy Conversion and Management 50 (2009) 772–776 Contents lists available at ScienceDirect Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman