Geometry and nanoparticle loading effects on the bio-based nano-PCM filled cylindrical thermal energy storage system

•Melting process of bio-based nano-PCM is investigated inside cylindrical geometry.•CuO nanoparticles are dispersed in coconut oil PCM to prepare the nano-PCM.•Thermal conductivity of nano-PCM is improved by 7.5% for wt.% = 1.•Melt fraction (MF) of nano-PCM is improved by 15% for wt.% = 0.0218.•MF is calculated using interface tracking from digital images with maximum uncertainty of ±6.7%. Dispersing highly conductive nanoparticles into a Phase Change Material (PCM) is one the effective methods to increase thermal conductivity and decrease the required time for phase change in thermal energy storage systems. The current work reports an experimental effort to investigate the detailed melting process of a nano-PCM inside a Cylindrical Thermal Energy Storage (C-TES) system. The experimental setup consists of two vertical C-TES systems and a constant temperature bath. One of the C-TES systems is filled with a bio-based pure PCM (coconut oil) and the second one is filled with a nano-PCM (CuO nanoparticles dispersed in coconut oil PCM). The objective of this study is to investigate the effects of (i) height of the PCM, (ii) temperature of the hot wall, and (iii) weight fractions of nanoparticles on the melting of nano-PCM. The thermophysical properties of nano-PCM are measured and reported in this paper. Digital images of melting front and temperatures at selected locations are captured at three pre-selected boundary temperatures and four weight fractions of nanoparticles and presented. Image processing of photographs along with numerical integration is used to calculate melt fraction. To facilitate a better comparison of melting pattern between bio-based PCM and nano-PCM, solid–liquid interface is presented on the XY plots. Results show that at the beginning of the melting process, pure PCM and nano-PCM behave almost the same, however, with an ongoing heating process, nano-PCMs melt faster than pure PCM. The height of the PCM and hot wall temperature affect the melting pattern and melting time, respectively. An extensive analysis is reported as well to show how to calculate the uncertainty associated with image based melt fraction calculation.