Experimental investigation of the effect of inclination angle on convection-driven melting of phase change material in a rectangular enclosure Babak Kamkari a,⇑ , Hossein Shokouhmand a , Frank Bruno b a School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran 14395-515, Iran b Barbara Hardy Institute, University of South Australia, Mawson Lakes, SA 5095, Australia article info Article history: Received 17 September 2013 Received in revised form 23 December 2013 Accepted 3 January 2014 Available online 28 January 2014 Keywords: Phase change material Natural convection Heat transfer enhancement Thermal storage Inclination angle Melting abstract This paper investigates the dynamic thermal behavior of phase change material (PCM) melting in a rect- angular enclosure at various inclination angles. Lauric acid as a PCM with high Prandtl number (Pr  100) is used. The enclosure is heated isothermally from one side while the other walls are thermally insulated. Experiments were performed with hot wall temperatures of 55, 60 and 70 °C ð3:6  10 8 6 Ra 6 8:3  10 8 Þ for different inclination angles of 0°, 45° and 90°. Image processing of melt photographs along with recorded temperatures were used to calculate the melt fractions, Nusselt numbers and the local interfa- cial heat transfer rates at the solid–liquid interface. Qualitative time-dependent natural convection flow structures were deduced indirectly from the instantaneous shape of the solid–liquid interface which were confirmed by quantitative data from temperature measurements. The results reveal that the enclo- sure inclination has a significant effect on the formation of natural convection currents and consequently on the heat transfer rate and melting time of the PCM. As the inclination angle is decreased from 90° to 0°, the convection currents in the enclosure increases and chaotic flow structures appear. When melting commences in the horizontally inclined enclosure, the solid–liquid interface line becomes wavy which implies the formation of Benard convection cells in the liquid PCM. For the same hot wall temperatures, a decrease in inclination angle leads to a considerable enhancement in energy transport from the hot wall of the enclosure to the PCM. It is found that the heat transfer enhancement ratio for the horizontal enclo- sure is more than two times higher than that of the vertical enclosure. Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction Solid–liquid phase change problems in relation to phase change materials (PCMs) have been of growing interest in recent decades. PCMs are attractive as they are capable of absorbing and releasing a considerable amount of energy at a nearly constant temperature during the melting and solidification processes. They can be incor- porated into various thermal systems where their latent heat is uti- lized for thermal storage purposes or heat rejection. There is a wide range of applications for PCMs such as solar thermal systems [1,2], desalination [3], heat recovery [4], buildings [5,6], refrigeration [7], thermal management of electronics [8,9], spacecrafts [10,11], and smart textile [12]. In order to maximize the thermal performance of systems using PCMs, a better understanding of the thermal behavior of the PCM is required. Over the past decades, several investigations have been performed to study the role of natural convection on the melting heat transfer and morphology of the so- lid–liquid interface. These studies are classified into two groups based on the Prandtl number of the PCM employed in the investi- gation; low Prandtl number (Pr < 1) and high Prandtl number ðPr P 1Þ PCMs. Metallic PCMs have a high thermal conductivity and are catego- rized as low Prandtl number PCMs. One of the first studies in this field was conducted by Gau and Viskanta [13]. The role of the natural convection on the solid–liquid interface motion of pure gallium (Pr  0.021) was studied during melting from below and solidification from above in a rectangular enclosure. Different nat- ural convection flow regimes were identified and it was found that the turbulent natural convection within the liquid PCM consider- ably distorts the solid–liquid interface and increases the melting rate. They also reported similar findings when they commenced melting a lipowitz eutectic from the bottom in a rectangular cavity (Pr  0.067) [14]. In another experimental work by the same inves- tigators [15], the influence of natural convection on the melting heat transfer during phase change of gallium on a vertical wall was studied. Despite the high thermal conductivity of metallic 0017-9310/$ - see front matter Ó 2014 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ijheatmasstransfer.2014.01.014 ⇑ Corresponding author. Tel.: +98 9124034778; fax: +98 2188013029. E-mail addresses: kamkari@ut.ac.ir (B. Kamkari), hshokoh@ut.ac.ir (H. Shokouhmand), frank.bruno@unisa.edu.au (F. Bruno). International Journal of Heat and Mass Transfer 72 (2014) 186–200 Contents lists available at ScienceDirect International Journal of Heat and Mass Transfer journal homepage: www.elsevier.com/locate/ijhmt