Inward Solidification Heat Transfer of Nano-Enhanced Phase Change Materials in a Spherical Capsule: An Experimental Study

2017 ◽  
Vol 140 (2) ◽  
Author(s):  
Zi-Qin Zhu ◽  
Min-Jie Liu ◽  
Nan Hu ◽  
Yuan-Kai Huang ◽  
Li-Wu Fan ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Phase Change ◽  
Phase Change Materials ◽  
Classical Problem ◽  
Solidification Time ◽  
Graphite Nanoplatelets ◽  
Practical Applications ◽  
Retrieval Rate ◽  
Microscale Transport ◽  
Spherical Capsule

The classical problem of inward solidification heat transfer inside a spherical capsule, with an application to thermal energy storage (TES), was revisited in the presence of nano-enhanced phase change materials (NePCM). The model NePCM samples were prepared by dispersing graphite nanoplatelets (GNPs) into 1-tetradecanol (C14H30O) at loadings up to 3.0 wt %. The transient phase change, energy retrieval, and heat transfer rates during solidification of the various NePCM samples were measured quantitatively using a volume-shrinkage-based indirect method. The data reduction and analysis were carried out under single-component, homogeneous assumption of the NePCM samples without considering the microscale transport phenomena of GNPs. It was shown that the total solidification time becomes monotonously shorter with increasing the loading of GNPs, in accordance with the increased effective thermal conductivity. The maximum relative acceleration of solidification was found to be more than 50% for the most concentrated sample, which seems to be appreciable for practical applications. In addition to enhanced heat conduction, the possible effects due to the elimination of supercooling and viscosity growth were elucidated. The heat retrieval rate was also shown to be increased monotonously with raising the loading of GNPs, although the heat storage capacity is sacrificed. Despite the remarkable acceleration of the solidification time, the use of a high loading (e.g., 3.0 wt %) was demonstrated to be possibly uneconomical because of the marginal gain in heat retrieval rate. Finally, correlations for the transient variations of the melt fraction and surface-averaged Nusselt number were proposed.

Heat Transfer During Constrained Melting of Nano-Enhanced Phase Change Materials in a Spherical Capsule: An Experimental Study

2016 ◽  
Vol 138 (12) ◽  
Author(s):  
Li-Wu Fan ◽  
Zi-Qin Zhu ◽  
Min-Jie Liu ◽  
Can-Ling Xu ◽  
Yi Zeng ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Natural Convection ◽  
Phase Change ◽  
Phase Change Materials ◽  
Classical Problem ◽  
Dominant Mode ◽  
Graphite Nanosheets ◽  
Melting Experiments ◽  
Spherical Capsule

The classical problem of constrained melting heat transfer of a phase change material (PCM) inside a spherical capsule was revisited experimentally in the presence of nanoscale thermal conductivity fillers. The model nano-enhanced PCM (NePCM) samples were prepared by dispersing self-synthesized graphite nanosheets (GNSs) into 1-dodecanol at various loadings up to 1% by mass. The melting experiments were carried out using an indirect method by measuring the instantaneous volume expansion upon melting. The data analysis was performed based on the homogeneous, single-component assumption for NePCM with modified thermophysical properties. It was shown that the introduction of nanofillers increases the effective thermal conductivity of NePCM, in accompaniment with an undesirable rise in viscosity. The dramatic viscosity growth, up to over 100-fold at the highest loading, deteriorates significantly the intensity of natural convection, which was identified as the dominant mode of heat transfer during constrained melting. The loss in natural convection was found to overweigh the decent enhancement in heat conduction, thus resulting in decelerated melting in the presence of nanofillers. Except for the case with the lowest heating boundary temperature, a monotonous slowing trend of melting was observed with increasing the loading.

An Experimental Study of Inward Solidification of Nano-Enhanced Phase Change Materials (NePCM) Inside a Spherical Capsule

2016 ◽  
Author(s):  
Min-Jie Liu ◽  
Zi-Qin Zhu ◽  
Li-Wu Fan ◽  
Zi-Tao Yu
Keyword(s):  
Thermal Conductivity ◽  
Phase Change ◽  
Phase Change Materials ◽  
Classical Problem ◽  
Transient Phase ◽  
Graphite Nanoplatelets ◽  
The Matrix ◽  
Thermally Conductive ◽  
Spherical Capsule ◽  
Enhanced Thermal Conductivity

Nano-enhanced phase change materials (PCM), referred to as NePCM, have been proposed by doping highly thermally-conductive nanofillers into matrix PCM to prepare composites that have enhanced thermal conductivity. The classical problem of inward solidification of PCM inside a spherical capsule, with applications to thermal energy storage, was revisited in the presence of nanofillers. In this work, the model NePCM samples were prepared with 1-tetradecanol (C14H30O) possessing a nominal melting point of 37 °C as the matrix PCM. Graphite nanoplatelets (GNPs) were synthesized and utilized as the nanofillers at loadings up to 1% by weight. The transient phase change and heat transfer during solidification were characterized by means of an indirect method that is based on the knowledge of transient volume shrinkage of the PCM. The experimental results showed that the total solidification time becomes shorter with increasing the loading of GNPs, in accordance to the increased effective thermal conductivity of the NePCM samples.

A Novel Indirect Visualization Method for Studying the Melting Heat Transfer of Nano-Enhanced Phase Change Materials Using Thermochromic Liquid Crystal Thermography

2020 ◽  
Vol 142 (4) ◽  
Author(s):  
Nan Hu ◽  
Zi-Rui Li ◽  
Run-Hui Zhang ◽  
Li-Wu Fan
Keyword(s):  
Heat Transfer ◽  
Liquid Crystal ◽  
Phase Change ◽  
Phase Change Materials ◽  
Phase Interface ◽  
Classical Problem ◽  
Dominant Mode ◽  
Thermochromic Liquid Crystal ◽  
Melting Heat ◽  
Melting Heat Transfer

Abstract In order to give more sights into the melting (and solidification) heat transfer processes of nano-enhanced phase change material (NePCM) with invisible phase interfaces, a novel indirect method for tracking the phase interface by thermochromic liquid crystal (TLC) thermography is proposed. As an example case to demonstrate the applicability of the proposed method, the classical problem of melting heat transfer in a differentially heated rectangular cavity was revisited in the presence of NePCM of various loadings. A narrowband TLC was selected and calibrated carefully to build the hue–temperature relationship prior to being applied in the melting experiments. For validation purpose, the case of an unloaded NePCM, with a clear visible phase interface, was tested via combined direct and indirect observations. It was shown that this TLC method can easily and accurately capture the dynamic motions of the phase interface during melting. Based on the shape evolutions of the phase interface, it was concluded that for the NePCM sample with a higher loading (and hence a much greater viscosity), heat conduction becomes the dominant mode of heat transfer during melting as a result of the significantly deteriorated natural convection effect. This gives an intuitive confirmation of the hypothesis made in previous studies that were conducted using volume-average-based indirect methods.

Natural Convection in an Enclosure With Blend of Micro Encapsulated Phase Change Materials

2013 ◽  
Author(s):  
Yasmin Khakpour ◽  
Jamal Seyed-Yagoobi
Keyword(s):  
Heat Transfer ◽  
Thermal Expansion ◽  
Natural Convection ◽  
Phase Change ◽  
Latent Heat ◽  
Phase Change Materials ◽  
Numerical Study ◽  
Pure Water ◽  
Operating Conditions ◽  
Effective Density

This numerical study investigates the effect of using a blend of micro-encapsulated phase change materials (MEPCMs) on the heat transfer characteristics of a liquid in a rectangular enclosure driven by natural convection. A comparison has been made between the cases of using single component MEPCM slurry and a blend of two-component MEPCM slurry. The natural convection is generated by the temperature difference between two vertical walls of the enclosure maintained at constant temperatures. Each of the two phase change materials store latent heat at a specific range of temperatures. During phase change of the PCM, the effective density of the slurry varies. This results in thermal expansion and hence a buoyancy driven flow. The effects of MEPCM concentration in the slurry and changes in the operating conditions such as the wall temperatures compared to that of pure water have been studied. The MEPCM latent heat and the increased volumetric thermal expansion coefficient during phase change of the MEPCM play a major role in this heat transfer augmentation.

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