Investigation on cyclic degradation of thermophysical properties of paraffin wax as a phase change material and their impact on heat storage performance

Thermo-physical property study of the Phase Change Material (PCM) is necessary to build an efficient latent heat thermal energy storage system (LHTESS). The stability of thermophysical property due to repeated thermal cycling is an essential factor that has to be studied to find a promising latent heat storage material with a long-duration lifetime. Void formation during the solidification process in thermal cycling is an unwanted property in the PCM. This study concentrates on the void formation due to repeated thermal cycling and its impact on thermo-physical property degradation of paraffin wax. Paraffin wax with the melting temperature in the range of 58oC to 62oC is selected as PCM. Whereas Al2O3 and CuO nanoparticles of 20-40 nm size are selected as nanoparticle additive for this study. The nano-PCM composite and hybrid nano-PCM composite samples are prepared by mixing 5 wt% of Al2O3, 5 wt% of CuO and 2.5 wt% Al2O3+2.5 wt% CuO nanoparticles with paraffin wax by bottom heating and natural cooling at ambient temperature. Samples are made to undergo 1, 50, 100, 150, and 200 thermal cycles. Morphology of the samples is studied using a Scanning Electron Microscope (SEM). The thermal properties are analysed by Differential Scanning Calorimeter (DSC). Thermal Gravimetric Analyser (TGA) is used to analyse the thermal stability and reliability. Thermal conductivity is measured using KD2 Pro thermal properties analyser. Viscosity and density is also measured using Rheometer Kinexus Lab+ and Archimedes principle to observe the impact of void formation during solidification shrinkage. Void formation in samples is quantified with help of ImageJ software. Results have revealed that nanoparticles addition has reduced the void variation by 16.8% in the hybrid-PCM composite (2.5 wt% Al2O3+2.5 wt% Cuo-PCM) after 200 thermal cycles. The void ratio is fluctuated with the thermal cycle in all the samples and has an inverse relation with all the thermophysical properties measured. The percentage of void ratio variation after C200 compared to C1 in hybrid-PCM is -16.7%,which is the least value calculated among all the samples. CuO nanoparticle addition has shown 23.3%, 23.2% and 22.25% increment in latent heat of melting, solidification and peak degradation temperature, respectively. Hybrid–PCM has shown an improvement in thermal conductivity, viscosity and density by 5.43%, 9.58% and 4.07%, respectively. Peak degradation temperature value has increased by 13.4%, 22.25% and 6.43% compared to PCM by addition of Al2O3, CuO and hybrid nanoparticles, respectively. Compared to other samples, hybrid-PCM is more stable and has shown consistency in all the thermophysical properties throughout all the thermal cycles. Paraffin wax with 2.5 wt% Al2O3+2.5 wt% CuO nanoparticles is found to be a better energy storage material in LHTESS. An addition of surfactant is recommended to improve the stability of nanoparticle distribution in nanoparticle-PCM composites. Thermophysical property improvement and stability achievement in paraffin wax by the incorporation of 2.5 wt% Al2O3+2.5 wt% CuO nanoparticles have contributed to eliminating the limitations in the life span of paraffin wax usage in thermal energy storage applications

Transient Modelling of Heat Loading of Phase Change Material for Energy Storage

As the development of solar energy is getting advance from time to time, the solar concentration technology also get the similar attention from the researchers all around the globe. This technology concentrate a large amount of energy into main spot. To collect all the available energy harvest from the solar panel, a thermal energy storage is required to convert the heat energy to one of the purpose such as electrical energy. With the idea of energy storage application that can be narrow down to commercial application such as cooking stove. Using latent heat type energy storage seem to be appropriate with the usage of phase change material (PCM) that can release and absorb heat energy at nearly constant temperature by changing its state. Sodium nitrate (NaNO3) and potassium nitrate (KNO3) was selected to use as PCM in this project. This project focus on the heat loading process and the melting process of the PCM in the energy storage using a computer simulation. The model of the energy storage was create as solid three dimensional modelling using computer aided software and the geometry size of it depend on how much it can apply to boil 1kg of water in cooking application. The material of the tank will use a standard stainless steel and pure copper as heat exchanger tube. With the XCELTHERM MK1 as the heat transfer fluid flow through the PCM medium in the tank, an analysis was performed using ANSYS FLUENT simulation software in a transient state. The simulation run on different value of velocity but kept controlled under laminar state only, then the relationship of velocity and heat distribution was studied. The melting process of the PCM also has been analyzed in this project

The effect of thermal cyclic variation on the thermophysical property degradation of paraffin as a phase changing energy storage material

Thermophysical properties of phase change material (PCM) and their thermal stability over their lifetime are necessary to be understood to build an efficient latent heat storage system. This study aims to investigate the degradation in thermophysical properties of a phase change material (paraffin wax) because of repeated thermal cycling. The samples were prepared by heating the PCM using bottom heat source and cooled at ambient temperature. This process was repeated over the period of 200 cycles. The thermal conductivity, thermal properties (stability and void formation) and the density of the samples were investigated. The voids formation has a significant effect on the thermophysical property degradation. Differential scanning calorimeter (DSC) results showed 25.17% decline in the latent heat capacity and 33.72% drop in peak degradation temperature from cycle 1–200. The sample mass was reduced by 33.72% at 600 °C after 200 cycles. In addition, after 200 cycles the thermal conductivity increased by 12% hence, repeated thermal cycling showed a significant increment in its thermal conductivity. This result indicates the potential of paraffin wax as a heat storage material in Latent heat thermal energy storage system. The decline in the percentage of property and stability is very low after 200 cycles compared to previous studies

Transient modelling of heat loading of phase change material for energy storage

As the development of solar energy is getting advance from time to time, the concentration solar technology also get the similar attention from the researchers all around the globe. This technology concentrate a large amount of energy into main spot. To collect all the available energy harvest from the solar panel, a thermal energy storage is required to convert the heat energy to one of the purpose such as electrical energy. With the idea of energy storage application that can be narrow down to commercial application such as cooking stove. Using latent heat type energy storage seem to be appropriate with the usage of phase change material (PCM) that can release and absorb heat energy at nearly constant temperature by changing its state. Sodium nitrate (NaNO3) and potassium nitrate (KNO3) was selected to use as PCM in this project. This paper focus on the heat loading process and the melting process of the PCM in the energy storage using a computer simulation. The model of the energy storage was created as solid three dimensional modelling using computer aided software and the geometry size of it depend on how much it can apply to boil 1 kg of water in cooking application. The materials used in the tank, heat exchanger and the heat transfer fluid are stainless steel, copper and XCELTHERM MK1, respectively. The analysis was performed using a commercial simulation software in a transient state. The simulation run on different value of velocity but kept controlled under laminar state only, then the relationship of velocity and heat distribution was studied and the melting process of the PCM also has been analyzed. On the effect of heat transfer fluid velocity, the higher the velocity resulted in higher the rate of heat transfer. The comparison between the melting percentages of the PCMs under test conditions show that NaNO3 melts quite faster than KNO3

Transient modelling of heat loading of phase change material for energy storage

As the development of solar energy is getting advance from time to time, the concentration solar technology also get the similar attention from the researchers all around the globe. This technology concentrate a large amount of energy into main spot. To collect all the available energy harvest from the solar panel, a thermal energy storage is required to convert the heat energy to one of the purpose such as electrical energy. With the idea of energy storage application that can be narrow down to commercial application such as cooking stove. Using latent heat type energy storage seem to be appropriate with the usage of phase change material (PCM) that can release and absorb heat energy at nearly constant temperature by changing its state. Sodium nitrate (NaNO3) and potassium nitrate (KNO3) was selected to use as PCM in this project. This paper focus on the heat loading process and the melting process of the PCM in the energy storage using a computer simulation. The model of the energy storage was created as solid three dimensional modelling using computer aided software and the geometry size of it depend on how much it can apply to boil 1 kg of water in cooking application. The materials used in the tank, heat exchanger and the heat transfer fluid are stainless steel, copper and XCELTHERM MK1, respectively. The analysis was performed using a commercial simulation software in a transient state. The simulation run on different value of velocity but kept controlled under laminar state only, then the relationship of velocity and heat distribution was studied and the melting process of the PCM also has been analyzed. On the effect of heat transfer fluid velocity, the higher the velocity resulted in higher the rate of heat transfer. The comparison between the melting percentages of the PCMs under test conditions show that NaNO3 melts quite faster than KNO3

Corrosion Effect of Phase Change Materials in Solar Thermal Energy Storage Application

The thermal energy storage (TES) system using phase change materials (PCMs) has been studied since past three decades. PCMs are widely used in heat storage applications due to their high storage density, as well as the wide range of melting and solidifying temperatures. Nevertheless, the main disadvantage of PCMs, especially salt hydrates, is their corrosive behavior with container materials. PCMs are normally encapsulated in containers, hence the compatibility of the container materials with PCM plays an important role. As such, this paper summarizes the investigations made on the corrosion behavior of PCM in various applications, besides suggesting ways to reduce (or rectify) the effect for long term successful energy storage. Moreover, PCM-storage material interaction in the latent heat TES system is important as the issue of corrosion affects the life of the container, as well as the performance of TES. The compatibility of the most commonly used PCMs with several major container materials was reviewed and it was revealed that stainless steel has emerged as the most compatible storage container material among others. On the other hand, aluminum was found to be corrosive when it is used with salt hydrates. Nonetheless, some contradictory articles are reported that several salt hydrates demonstrated compatibility with container materials. Corrosion causes thinning of cross sectional area of materials, making it brittle thus leading to an easy collapse. This situation is even more critical mainly in large scale concentrating solar thermal power plants. Hence, with the fact that there are currently large scale power plants employing TES under operation and under construction; issues pertaining to PCM-storage material compatibility should be properly and accurately addressed. Therefore, more research work is recommended in the area of finding new eutectics and less corrosive container material(s)

Effect of loading temperature on thermophysical properties of paraffin wax as PCM for thermal energy storage

Phase change materials (PCMs) have been widely used in Thermal Energy Storage (TES) system as a storage medium. The thermal and physical properties of PCMs can be affected by heat loading temperature. In this study, four samples were exposed to four different heating temperatures at 65°C, 75°C, 85°C, and 100°C for ten number of thermal cycles. Heating is done by using an oven at the same time the samples are allowed to cool freely at room temperature. Melting temperature, latent heat capacity, void ratio, thermal stability, thermal conductivity and density were measured using Differential scanning calorimetry (DSC), Scanning electron microscope (SEM), Thermogravimetric analysis (TGA), KD2 Pro and water displacement method, respectively. Results obtained from the DSC test has shown that the sample with 100°C loading temperature has the lowest phase change enthalpy among the other samples. The effect of high-temperature loading reduces the overall latent heat capacity of PCM more than 50% compared to that of 65°C sample. This reduction significantly affects the overall performance of the thermal energy storage system. The sample of 100°C loading temperature showed the highest thermal conductivity among the other samples which is 0.26667 W/mK. This result reveals that the increase in temperature of heat loading will increase the thermal conductivity of PCMs. Closer the temperature of heat loading towards the transition temperature, higher the thermal stability. Thus, the sample of 65oC loading temperature has higher stability compared to the sample of 100oC loading temperature. Density and void ratio shows the same trend as the heat loading temperature increases. However, based on the results from SEM, the void ratio does not show any significant effect on thermal and physical properties. The sample of 100oC heat loading temperature has high thermal conductivity but has a high melting temperature, low density, low latent heat capacity and low stability. Paraffin wax of 65oC heat loading temperature has all the superior characteristics as a thermal energy storage material