Experimental Verification of Expedited Freezing of Nanoparticle-Enhanced Phase Change Materials (NEPCM)

2011 ◽  
Author(s):  
Liwu Fan ◽  
J. M. Khodadadi
Keyword(s):  
Thermal Conductivity ◽  
Phase Change ◽  
Phase Change Materials ◽  
Freezing Process ◽  
Freezing Front ◽  
One Dimensional ◽  
Unidirectional Freezing ◽  
Finite Slab ◽  
The One ◽  
Pure Cyclohexane

Highly-conductive nano-sized particles are dispersed into phase change materials (PCM) to improve their effective thermal conductivity, thus leading to suspensions that are referred to as nanoparticle-enhanced PCM (NEPCM). In order to assess the extent of expedited phase change due to the enhanced thermal conductivity, the one-dimensional unidirectional freezing process of NEPCM in a finite slab was investigated experimentally. Thermocouple readings were recorded at several equally-spaced locations along the freezing direction in order to monitor the progress of the freezing front. As an example, cyclohexane (C6H12) and copper oxide (CuO) nanoparticles were chosen to develop the NEPCM with three different volume fractions (0.5, 1.0, and 2.0 vol%). It was shown that the freezing rate for the 0.5 vol% NEPCM is considerably raised as compared to pure cyclohexane. However, further increase of the fraction of nanoparticles to 1.0 and 2.0 vol% did not linearly expedite freezing. Significant sedimentation of nanoparticles was observed for the 2.0 vol% NEPCM. Additionally, in this case the undesirable supercooling phenomenon was enhanced, which suppresses the growth rate of the solidified NEPCM.

A Theoretical and Experimental Investigation of Unidirectional Freezing of Nanoparticle-Enhanced Phase Change Materials

2012 ◽  
Vol 134 (9) ◽  
Author(s):  
Liwu Fan ◽  
J. M. Khodadadi
Keyword(s):  
Thermal Conductivity ◽  
Experimental Investigation ◽  
Phase Change ◽  
Phase Change Materials ◽  
Solid Phase ◽  
Experimental Setup ◽  
Cold Plate ◽  
Numerical Predictions ◽  
Unidirectional Freezing ◽  
Measured Thermal Conductivity

Highly-conductive nanostructures may be dispersed into phase change materials (PCM) to improve their effective thermal conductivity, thus leading to colloidal systems that are referred to as nanostructure-enhanced PCM (NePCM). Results of a theoretical and experimental investigation on freezing of NePCM in comparison to the base PCM are presented. A one-dimensional Stefan model was developed to study the unidirectional freezing of NePCM in a finite slab. Only the thermal energy equation was considered and the presence of static dispersed nanoparticles was modeled using effective media relations. A combination of analytical and integral methods was used to solve this moving boundary problem. The elapsed time to form a given thickness of frozen layer was therefore predicted numerically. A cooled-from-bottom unidirectional freezing experimental setup was designed, constructed, and tested. Thermocouple readings were recorded at several equally spaced locations along the freezing direction in order to monitor the progress of the freezing front. As an example, cyclohexane (C6H12) and copper oxide (CuO) nanoparticles were chosen to prepare the NePCM samples. The effective thermophysical and transport properties of these samples for various particle loadings (0.5/3.8, 1/7.5, and 2/14.7 vol. %/wt. %) were determined using the mixture and Maxwell models. Due to utilization of the Maxwell model for thermal conductivity of both phases, the numerical predictions showed that the freezing time is shortened linearly with increasing particle loading, whereas nonmonotonic expediting was observed experimentally. The maximum expediting was found to be nearly 8.23% for the 0.5 vol. % sample. In the absence of a nanoparticle transport model, the mismatch of the cold plate boundary conditions, lack of accurate thermophysical properties, especially in the solid phase of NePCM samples and precipitation issues with 2 vol. % samples were addressed by improving the experimental setup. Through adopting a copper cold plate, utilizing measured thermal conductivity data for both phases and using 1, 2, and 4 wt. % samples, good agreement between the experimental and numerical results were realized. Specifically, adoption of measured thermal conductivity values for the solid phase in the Stefan model that were originally underestimated proved to be a major cause of harmony between the experiments and predictions.

Optimization of thermal conductivity in composites loaded with the solid-solid phase-change materials

2018 ◽  
Vol 25 (6) ◽  
pp. 1157-1165
Author(s):  
Taoufik Mnasri ◽  
Adel Abbessi ◽  
Rached Ben Younes ◽  
Atef Mazioud
Keyword(s):  
Thermal Conductivity ◽  
Phase Change ◽  
Phase Change Materials ◽  
Solid Phase ◽  
Spherical Inclusions ◽  
First Case ◽  
The Matrix ◽  
Composite Conductivity ◽  
First Time

AbstractThis work focuses on identifying the thermal conductivity of composites loaded with phase-change materials (PCMs). Three configurations are studied: (1) the PCMs are divided into identical spherical inclusions arranged in one plane, (2) the PCMs are inserted into the matrix as a plate on the level of the same plane of arrangement, and (3) the PCMs are divided into identical spherical inclusions arranged periodically in the whole matrix. The percentage PCM/matrix is fixed for all cases. A comparison among the various situations is made for the first time, thus providing a new idea on how to insert PCMs into composite matrices. The results show that the composite conductivity is the most important consideration in the first case, precisely when the arrangement plane is parallel with the flux and diagonal to the entry face. In the present work, we are interested in exploring the solid-solid PCMs. The PCM polyurethane and a wood matrix are particularly studied.

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