Modeling and Testing

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We use atomic-level simulations to study thermal transport mechanisms in NePCM, focusing on modeling of heat transfer in suspensions of nanoparticles (nanofluids), paraffin base nanocomposites, and solid-solid/solid-liquid interfaces.

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Study of the regulation mechanisms of heat conductance of composite phase change materials due to carbon-based nanostructured fillers

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The enhanced thermal conductivity of solid nanoparticle suspensions used as phase change materials (NePCM), referred to as nano-enhanced PCM, was investigated using experimental and numerical methods using FLUENT. As for the experimental part, at the early stage, eicosane (C20H42), were selected as the base PCM. Copper oxide (CuO) nanoparticles, stabilized by sodium oleate acid (SOA), were used as the nano-structured thermal conductivity enhancers. Thermal conductivity measurements were performed using the transient plane source (TPS) technique for the NePCM samples for different methods of solidification. The dependence of thermal conductivity on both temperature and the loading of CuO nanoparticles were investigated. Beside this, structural characterization of the solid disk samples will be performed to study the effect of solidification scheme on the final crystalline structure as well as to acclaim that the particles are well-dispersed within the matrix according to the assuption. Using pre-fabricated cold plates, with the availability of a pair of eicosane-CuO solid composites, an iso-thermal stage set-up for holding the two samples while sandwiching the delicate TPS sensor during the tests was designed and fabricated. The resulted thermal conductivity values will also be compared against the Maxwell theory.

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Abstract:

The enhanced thermal conductivity of solid nanoparticle suspensions used as phase change materials (NePCM), referred to as nano-enhanced PCM, was investigated using experimental and numerical methods using FLUENT. As for the experimental part, at the early stage, eicosane (C20H42), were selected as the base PCM. Copper oxide (CuO) nanoparticles, stabilized by sodium oleate acid (SOA), were used as the nano-structured thermal conductivity enhancers. Thermal conductivity measurements were performed using the transient plane source (TPS) technique for the NePCM samples for different methods of solidification. The dependence of thermal conductivity on both temperature and the loading of CuO nanoparticles were investigated. Beside this, structural characterization of the solid disk samples will be performed to study the effect of solidification scheme on the final crystalline structure as well as to acclaim that the particles are well-dispersed within the matrix according to the assuption. Using pre-fabricated cold plates, with the availability of a pair of eicosane-CuO solid composites, an iso-thermal stage set-up for holding the two samples while sandwiching the delicate TPS sensor during the tests was designed and fabricated. The resulted thermal conductivity values will also be compared against the Maxwell theory.

Relevant Data:

Abstract:

The enhanced thermal conductivity of solid nanoparticle suspensions used as phase change materials (NePCM), referred to as nano-enhanced PCM, was investigated using experimental and numerical methods using FLUENT. As for the experimental part, at the early stage, eicosane (C20H42), were selected as the base PCM. Copper oxide (CuO) nanoparticles, stabilized by sodium oleate acid (SOA), were used as the nano-structured thermal conductivity enhancers. Thermal conductivity measurements were performed using the transient plane source (TPS) technique for the NePCM samples for different methods of solidification. The dependence of thermal conductivity on both temperature and the loading of CuO nanoparticles were investigated. Beside this, structural characterization of the solid disk samples will be performed to study the effect of solidification scheme on the final crystalline structure as well as to acclaim that the particles are well-dispersed within the matrix according to the assuption. Using pre-fabricated cold plates, with the availability of a pair of eicosane-CuO solid composites, an iso-thermal stage set-up for holding the two samples while sandwiching the delicate TPS sensor during the tests was designed and fabricated. The resulted thermal conductivity values will also be compared against the Maxwell theory.

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Abstract:

Producing thermal energy storage (TES) composites of phase change materials (PCM) and Nanostructure-enhanced phase change materials (NePCM) is a proven method of thermal conductivity enhancement. TES composites consist of a highly-conductive, highly-porous structure impregnated with PCM/NePCM. Fabrication of TES composites involves penetration of PCM/NePCM in liquid state into porous structures known as infiltration phenomenon. Due to the scale of the pores in porous structures (such as graphite and metal foams) the infiltration happens as a result of different driving forces, e.g. gravity, pressure gradient, dynamic pressure, and interfacial forces. These competing driving forces cause different phenomena during the infiltration of wetting and non-wetting liquids which lead to diverse behaviors of liquid interface and lead to formation of void in pore level. In this research project, the infiltration of wetting and non-wetting liquids into porous structures was investigated numerically in pore level and considered experimentally on samples of graphite foam. The transient evolution of liquid interface was investigated numerically during the liquid penetration into the pores of a porous structure. Pressure gradient, gravity and interfacial forces (surface tension and contact angle), were considered to be the driving forces of the infiltration. Liquid interface shape, position and velocity were investigated during the infiltration for different combinations of driving forces and contact angles. During the infiltration of wetting liquids temporary and permanent pinning of the interface was observed /investigated as well as wicking flow through the pores and infiltration time/pressure behavior was extracted. The interface behavior and infiltration time was studied for the case of non-wetting liquids as well. The interface shape and contact angle in non-wetting liquids can lead to entrapment of air inside the pore, e.g. void formation. The utilized numerical approach is based on a multiphase flow analysis considering the penetration of liquid into the pore and escape of air from the pore. Thus, Volume-of-Fluid (VOF) method was used for direct simulation of flow in representative elementary volume (REV) of a porous structure. The proposed numerical method is capable of tracking the evolution of liquid front and predicting the formation of void inside the pore based on the fluids properties and flow conditions. The volume and distribution (shape) of the void was predicted for infiltration of non-wetting liquids using a two-dimensional model. The numerical results of were validated against the numerical results of the coupled VOF level-set method, known to be more accurate in tracking the interface. The predicted time-evolving liquid interfaces from two methods were compared and found to be in good agreement. Moreover, the numerical results of liquid penetration length and time during the wicking flow through a pore and a network of series pores were verified against the experimental results of unidirectional horizontal infiltration performed on the same structure of graphite foam infiltrated with liquid cyclohexane. The numerical and experimental results were found to be in good agreement.

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Microencapsulated paraffin wax (a MicroEncapsulated Phase Change Material or MEPCM) was used to enhance the thermal storage capacity of gypsum tiles. Multiple configurations with varying amounts and positions of PCM where tested in order to determine the optimal combination of parameters that would yield the best thermal performance improvement compared to a non-enhanced gypsum tile. Four tiles of different compositions were made to serve as analogues for common sheetrock or drywall building material. The first tile was pure gypsum plaster with no PCM enhancement. The second tile contained 10% PCM by total weight evenly dispersed throughout the plaster matrix. The third contained 20% PCM by total weight also evenly dispersed. The fourth tile consisted of two layers. The first layer was pure gypsum plaster, and the second contained 10% PCM by total weight. Both layers were of uniform height, and together made a single tile of the same thickness as the other samples. A small control volume with an internal heating source was used to simulate hot, outdoor conditions while the conditioned lab space simulated the occupied area of a residential or business structure. Each tile was fitted onto one side of the control volume and subjected to a temperature gradient of approximately 22 to 37˚C. The double-layered tile was tested twice with each side facing the heat source and the conditioned space. Surface and ambient temperature measurements were taken as each sample was allowed to warm steadily until reaching a steady state. The temperature measurements from each sample were then compared to see what effect the PCM enhancement had on the gypsum tiles’ thermal performance.

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We use continuum based models to study the solidification process of colloidal suspensions. The effect of the particle size and its thermophysical properties on the evolution of the solid-liquid interface will be investigated in detail for different NEPCM suspensions.

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