Analysis and Design of a Paraffin/Graphite Composite PCM Integrated in a Thermal Storage Unit

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
R. Pokhrel ◽  
J. E. González ◽  
T. Hight ◽  
T. Adalsteinsson
Keyword(s):  
Phase Transition ◽  
Thermal Conductivity ◽  
Transition Temperature ◽  
Energy Storage ◽  
Phase Change ◽  
Specific Heat ◽  
Latent Heat ◽  
Phase Transition Temperature ◽  
Thermal Storage ◽  
Melting And Solidification

The addition of latent heat storage systems in solar thermal applications has several benefits including volume reduction in storage tanks and maintaining the temperature range of the thermal storage. A phase change material (PCM) provides high energy storage density at a constant temperature corresponding to its phase transition temperature. In this paper, a high temperature PCM (melting temperature of 80°C) made of a composite of paraffin and graphite was tested to determine its thermal properties. Tests were conducted with a differential scanning calorimeter and allowed the determination of the melting and solidification characteristics, latent heat, specific heat at melting and solidification, and thermal conductivity of the composite. The results of the study showed an increase in thermal conductivity by a factor of 4 when the mass fraction of the graphite in the composite was increased to 16.5%. The specific heat of the composite PCM (CPCM) decreased as the thermal conductivity increased, while the latent heat remained the same as the PCM component. In addition, the phase transition temperature was not influenced by the addition of expanded graphite. To explore the feasibility of the CPCM for practical applications, a numerical solution of the phase change transition of a small cylinder was derived. Finally, a numerical simulation and the experimental results for a known volume of CPCM indicated a reduction in solidification time by a factor of 6. The numerical analysis was further explored to indicate the optimum operating Biot number for maximum efficiency of the composite PCM thermal energy storage.

Analysis and Design of a Paraffin/Graphite Composite PCM Integrated in a Thermal Storage Unit

2008 ◽  
Author(s):  
R. Pokhrel ◽  
J. E. Gonza´lez ◽  
T. Hight ◽  
T. Adalsteinsson
Keyword(s):  
Phase Transition ◽  
Thermal Conductivity ◽  
Transition Temperature ◽  
Phase Change ◽  
Specific Heat ◽  
Latent Heat ◽  
Phase Transition Temperature ◽  
Thermal Storage ◽  
High Energy ◽  
Melting And Solidification

The addition of latent heat storage systems in solar thermal applications has several benefits including volume reduction of storage tanks and maintaining the temperature range of the thermal storage. A Phase change material (PCM) provides high energy storage density at a constant temperature corresponding to its phase transition temperature. In this paper, a high temperature PCM (melting temperature 80°C) made of a composite of paraffin and graphite was tested to determine its thermal properties. Tests were conducted with a differential scanning calorimeter (DSC) and allowed the determination of the melting and solidification characteristics, latent heat, specific heat at melting and solidification, and thermal conductivity of the composite. The results of the study showed an increase in thermal conductivity by a factor of 4 when the mass fraction of the graphite in the composite was increased to 16.5%. The specific heat of the composite PCM (i.e., CPCM) decreased as the thermal conductivity increased, while the latent heat remained the same as the PCM component. In addition, the phase transition temperature was not influenced by the addition of expanded graphite. To explore the feasibility of the CPCM for practical applications, a numerical solution of the phase change transition of a small cylinder was derived. Finally, based on the properties obtained in DSC, a numerical simulation for a known volume of CPCM in a water tank was produced and indicated a reduction in solidification time by a factor of six.

Experimental Characterization of the Thermal Diffusivity of Paraffin Phase Change Material Embedded With Herringbone Style Graphite Nanofibers

2012 ◽  
Author(s):  
Ronald J. Warzoha ◽  
Anthony Rao ◽  
Rebecca Weigand ◽  
Amy S. Fleischer
Keyword(s):  
Thermal Conductivity ◽  
Energy Storage ◽  
Thermal Diffusivity ◽  
Phase Change ◽  
Specific Heat ◽  
Latent Heat ◽  
Thermal Energy ◽  
Thermal Energy Storage ◽  
Melt Temperature ◽  
Graphite Nanofibers

Phase change materials (PCMs) are promising candidates for thermal energy storage due to their intrinsically high values of latent heat. However, PCMs are unable to effectively utilize all of their energy storage capacities due to their poor thermophysical properties. In this study, the effect of graphite nanofibers (diameter = 2 to 1000 nm, length = 100μm) on the bulk thermal properties of paraffin PCM (Tmelt = 56 °C) is investigated. Material properties including effective thermal conductivity, specific heat, latent heat, melt temperature and thermal diffusivity are measured using a Differential Scanning Calorimeter (DSC) and comparative reference bar apparatus. Results suggest that the addition of nanostructures not only increases thermal conductivity by up to 180%, but also reduces the specific heat capacity and density of nano-enhanced paraffin, leading to improved thermal diffusivity and thus greater utilization of its latent heat for transient thermal energy storage.

Study on the Microstructure and Storage Heat Performance of Mg-25Al-15Zn-xCu Alloys

2015 ◽  
Vol 1120-1121 ◽  
pp. 1104-1108
Author(s):  
Hong Yan Wen ◽  
Xiao Ming Fan ◽  
Xiao Min Cheng
Keyword(s):  
Phase Transition ◽  
Transition Temperature ◽  
Phase Change ◽  
Latent Heat ◽  
Phase Transition Temperature ◽  
X Ray Diffraction ◽  
Scanning Calorimetry ◽  
Optical Microstructure ◽  
Solid Solution Matrix ◽  
And Storage

With the help of optical microstructure(OM), X-ray diffraction(XRD) and differential scanning calorimetry(DSC), the microstructure and storage heat performance of Mg-based phase change thermal storage alloys were investigated.The results show that the microstructure of Mg-25Al-15Zn-xCu (x=0, 2%, 8% and 14%, respectivly) alloys are mainly composed of primary crystal α (Mg) solid solution matrix, β-Mg17Al12, CuZn, MgAl2Cu and Mg32(Al,Zn)49 phases. The phase transition temperature of Mg-25Al-15Zn and Mg-25Al-15Zn-8Cu alloys ​​are 412.1 °C and 405.9 °C respectively; and phase change latent heat values of that were 175.4 J/g and 209.3 J/g. The addition of Cu led to the formation of new phase, reducing the phase transition temperature and increasing the value of phase change latent heat.

Preparation of Expanded Perlite-Based Binary Eutectic Composite of Phase Change Heat Storage Materials

2011 ◽  
Vol 383-390 ◽  
pp. 2889-2893
Author(s):  
Bao Yun Zhang ◽  
Chang Mei Jiao ◽  
Peng Wang ◽  
Long Jiang ◽  
Bao Hua Ji ◽  
...  
Keyword(s):  
Phase Transition ◽  
Transition Temperature ◽  
Phase Change ◽  
Latent Heat ◽  
Phase Transition Temperature ◽  
Phase Change Materials ◽  
Vacuum Impregnation ◽  
Expanded Perlite ◽  
Good Thermal Stability ◽  
Binary Eutectic

The binary eutectic of lauric acid-stearic acid / expanded perlite composite phase change materials (PCM) was prepared using the method of vacuum impregnation. The structures and properties of this composite PCM were characterized by FT-IR, SEM, DSC and TG analysis. The results showed that the binary eutectic of fatty acid had been composed with porous skeleton expanded perlite completely in a physical method, the phase transition temperature of composite PCM was about 33.0 °C and latent heat was 131.3 J/g. it had a good thermal stability after 100 times of recycling and gave the phase transition temperature 33.5 °C and the latent heat of 128.1 J/g respectively.

Effect of Latent Heat to Solidification Process of Phase Change Material

2012 ◽  
Vol 174-177 ◽  
pp. 1214-1218
Author(s):  
Jin Feng Mao ◽  
Wei Hua Li ◽  
Yong Li ◽  
Bo Wang ◽  
Dong Dong Lou ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Phase Transition ◽  
Transition Temperature ◽  
Phase Change ◽  
Latent Heat ◽  
Phase Transition Temperature ◽  
Initial Temperature ◽  
Heat Storage ◽  
Theoretical Models ◽  
Storage Unit

The heat transfer characteristics of heat storage unit are analyzed by many researchers from both theoretical and experimental in solidification heat release. Most theoretical models define the initial temperature of the phase change materials is equal to the phase transition temperature, in fact, thermal storage unit in the application, its initial temperature is not equal to the phase transition temperature. Many theoretical models have not considered the impact of latent heat of solidification. In this paper, homemade inorganic hydrated salt material is used as heat storage media, packaging with a cylindrical container. The phase change heat transfer process was analyzed both from theoretical and experimental. The effect of initial temperature and the latent heat of the heat transfer material were both considered.

scholarly journals Variation of thermal conductivity of DPPC lipid bilayer membranes around the phase transition temperature

2017 ◽  
Vol 14 (130) ◽  
pp. 20170127 ◽  
Author(s):  
Sina Youssefian ◽  
Nima Rahbar ◽  
Christopher R. Lambert ◽  
Steven Van Dessel
Keyword(s):  
Phase Transition ◽  
Thermal Conductivity ◽  
Thermal Properties ◽  
Transition Temperature ◽  
Lipid Bilayer ◽  
Lipid Bilayers ◽  
Phase Transition Temperature ◽  
Temperature Gradients ◽  
Phase Behaviour ◽  
Gel Phase

Given their amphiphilic nature and chemical structure, phospholipids exhibit a strong thermotropic and lyotropic phase behaviour in an aqueous environment. Around the phase transition temperature, phospholipids transform from a gel-like state to a fluid crystalline structure. In this transition, many key characteristics of the lipid bilayers such as structure and thermal properties alter. In this study, we employed atomistic simulation techniques to study the structure and underlying mechanisms of heat transfer in dipalmitoylphosphatidylcholine (DPPC) lipid bilayers around the fluid–gel phase transformation. To investigate this phenomenon, we performed non-equilibrium molecular dynamics simulations for a range of different temperature gradients. The results show that the thermal properties of the DPPC bilayer are highly dependent on the temperature gradient. Higher temperature gradients cause an increase in the thermal conductivity of the DPPC lipid bilayer. We also found that the thermal conductivity of DPPC is lowest at the transition temperature whereby one lipid leaflet is in the gel phase and the other is in the liquid crystalline phase. This is essentially related to a growth in thermal resistance between the two leaflets of lipid at the transition temperature. These results provide significant new insights into developing new thermal insulation for engineering applications.

Latent Heat Storage: Container Geometry, Enhancement Techniques, and Applications—A Review

2019 ◽  
Vol 141 (5) ◽  
Author(s):  
S. Arunachalam
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Energy Storage ◽  
Phase Change ◽  
Latent Heat ◽  
Thermal Energy ◽  
Heat Exchangers ◽  
Phase Change Materials ◽  
Heat Storage ◽  
Low Thermal Conductivity

Energy storage helps in waste management, environmental protection, saving of fossil fuels, cost effectiveness, and sustainable growth. Phase change material (PCM) is a substance which undergoes simultaneous melting and solidification at certain temperature and pressure and can thereby absorb and release thermal energy. Phase change materials are also called thermal batteries which have the ability to store large amount of heat at fixed temperature. Effective integration of the latent heat thermal energy storage system with solar thermal collectors depends on heat storage materials and heat exchangers. The practical limitation of the latent heat thermal energy system for successful implementation in various applications is mainly from its low thermal conductivity. Low thermal conductivity leads to low heat transfer coefficient, and thereby, the phase change process is prolonged which signifies the requirement of heat transfer enhancement techniques. Typically, for salt hydrates and organic PCMs, the thermal conductivity range varies between 0.4–0.7 W/m K and 0.15–0.3 W/m K which increases the thermal resistance within phase change materials during operation, seriously affecting efficiency and thermal response. This paper reviews the different geometry of commercial heat exchangers that can be used to address the problem of low thermal conductivity, like use of fins, additives with high thermal conductivity materials like metal strips, microencapsulated PCM, composite PCM, porous metals, porous metal foam matrix, carbon nanofibers and nanotubes, etc. Finally, different solar thermal applications and potential PCMs for low-temperature thermal energy storage were also discussed.

Composite phase change materials improve the photo-thermal effects of cotton fabrics

2020 ◽  
pp. 004051752097561
Author(s):  
Wei Zhang ◽  
Shang Hao ◽  
Jiali Weng ◽  
Yibo Zhang ◽  
Jiming Yao ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Surface Temperature ◽  
Ambient Temperature ◽  
Phase Change ◽  
Latent Heat ◽  
Thermal Effects ◽  
Phase Change Materials ◽  
Thermal Storage ◽  
Cotton Fabrics ◽  
Composite Phase Change Materials

We report on the impregnation-based preparation of composite phase change materials (CPCMs) with thermal storage properties, using paraffin wax and multi-walled carbon nanotubes (MWCNTs). We coated the CPCMs on the fabric by scraper coating, then evaluated their shape stability, latent heat, thermal conductivity, thermal storage stability and photo-thermal effects. Results show that CPCMs with 10% acid-oxidized MWCNTs introduce only a small phase leakage when heated at 50℃ for 900 s; their latent heat energy reduces by 16.5%, while their thermal conductivity increases by 131.9% compared to pure paraffin. When exposed to sunlight at an ambient temperature of 12.5℃, the cotton fabrics coated with CPCMs record a 12.8℃ higher surface temperature than the pristine fabric, while their heat dissipation is delayed by 120–180 s. The fabric surface temperature increases to twice the ambient temperature during daytime. Overall, these findings indicate that the coated fabric has excellent thermal stability, affirming its potential as photo-thermal functional material.

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