High Latent Heat Capacity Research Articles

Thermal performance evaluation of bischofite at pilot plant scale

Abstract The selection of the proper thermal energy storage (TES) material for an application is crucial. On the one hand, these materials should have suitable thermal properties for the operational temperatures range of the systems they are planned to work for, such as thermal stability, high latent heat and high heat capacity. On the other hand, they should be available on the market and at low price. Besides, researchers have to bear in mind the importance of testing TES materials not only at laboratory scale but also at higher scale, since it has been demonstrated that some thermal characteristics are volume-dependant. In the present study, bischofite, a by-product obtained from the non-metallic industry in the North of Chile with desired thermal properties for mid-temperature applications (around 100 °C), has been studied. A first analysis was performed in terms of comparing the thermal properties and cost of bischofite with other material previously studied as TES materials in order to evaluate its potential in both latent and sensible phases. Afterwards, a second analysis was experimentally performed in terms of testing bischofite at large-scale (204 kg) in a pilot plant facility. The experimental procedure consisted on several charging processes within two different temperatures ranges: from 50 °C to 80 °C and from 80 °C to 120 °C in order to study the behavior of the material in the sensible solid phase and latent phase respectively. The temperature profiles, the power given by the HTF, the energy balance in the storage system and the accumulation energy rate of the bischofite were analyzed. Results of both analysis showed that bischofite has potential as TES material for mid-temperature applications.

Ultrasonic synthesis and characterization of polystyrene/n-dotriacontane composite nanoencapsulated phase change material for thermal energy storage

In this paper, polystyrene(PS)/n-dotriacontane(Dot) composite nanoencapsulated phase change material (NEPCM) for thermal energy storage was synthesized by a facile and time-saving ultrasonically initiated miniemulsion polymerization method. The influences of ultrasonic factors including ultrasonic power output, time and temperature, the ratio of composite emulsifiers composed by sodium dodecyl sulfate (SDS) and poly-(ethylene glycol) monooctylphenyl ether (OP-10), as well as the Dot/styrene ratio on the z-average particle size, conversion, encapsulation efficiency and the phase change enthalpy of NEPCM were systematically investigated. The morphology, chemical structure and thermal performance of NEPCM were characterized by particle size analyzer, transmission electron microscope (TEM), Fourier transform infrared (FT-IR), X-ray diffractometer (XRD), differential scanning calorimetry (DSC) and thermogravimetric analysis (TG), respectively. The results showed that the ultrasonic technique can be successfully applied for the synthesis of PS/Dot NEPCM with high conversion (95.02%) and excellent encapsulation efficiency (61.23%) in a relatively short reaction time (35min). The synthesized composite nanocapsules with uniform spherical core/shell structure and z-average particle size of 168.2nm, had a high latent heat capacity (Tm 70.9°C, 174.8J/g) and good thermal stability, which indicates that it has great potential for the thermal energy storage.

Thermal Energy Storage Properties of Hybrid Nanocomposite – Embedded Phase Change Material for Sustainable Buildings

The thermal properties of the new copper–titania hybrid nanocomposite embedded organic ester phase change material (HNPCM) were analyzed experimentally. The surface functionalized hybrid nanocomposite (HyNC) embedded into the PCM has effectively created the densely packed network of thermal interfaces in the PCM matrix layers. The experimental results suggest that, the incorporation of the HyNC has enabled the HNPCM to exhibit improved thermal conductivity (0.347 W/m K), congruent phase transition temperature (freezing: 33.53ᵒC, melting: 35.32 ᵒC), high latent heat capacity (freezing: 109.05 kJ/kg, melting: 109.14 kJ/kg) and considerable reduction in (freezing time: 21.2%, melting time: 29.2%). The improved thermal properties being achieved facilitate the HNPCM to be considered as a viable thermal storage material for high performance and sustainable building cooling and heating applications.

Preparation, thermal and rheological properties of hybrid nanocomposite phase change material for thermal energy storage

This paper presents the experimental investigation on the thermal properties and viscosity of the new organic ester phase change material embedded with the silver–titania hybrid nanocomposite (HyNPCM) with the mass proportions ranging from 0.1% to 1.5%. The HyNPCM embedded with the surface functionalized hybrid nanocomposite exhibited improved thermal conductivity from 0.286W/mK to 0.538W/mK, congruent phase change temperature (6.8°C), high latent heat capacity (90.81kJ/kg), substantial reduction in the supercooling degree (1.82°C), thermal stability (191°C) and chemical stability, while compared to the pure PCM. Experimental results reveal that, the freezing and the melting times of the HyNPCM were reduced by 23.9% and 8.5% respectively, when compared to the pure PCM. The increased mass proportion of HyNC resulted in the increased viscosity up to 3.89%, which suggests the existence of relative dependencies between the thermal properties and the viscosity of the HyNPCM. In total, the improved thermal properties and the heat storage potential of the HyNPCM has facilitated them to be considered as a viable candidate for the cool thermal energy storage applications in buildings without sacrificing energy efficiency.

Study on thermal storage properties of hybrid nanocomposite-dibasic ester as phase change material

The present work reports the experimental investigation on the thermal storage properties of the new organic dibasic ester phase change material incorporated with the silver-titania hybrid nanocomposite (HiNPCM) with mass proportions ranging from 0.08% to 1.0%. The change in thermal properties and viscosity of PCM due to incorporation of hybrid nanocomposite (HyNC) were signified. The Fourier Transform Infrared (FTIR) spectra confirmed the physical interaction of HyNC with PCM and ensured chemical stability of HiNPCM. The improved thermal conductivity (58.4%), congruent phase change temperature (9.69°C), high latent heat capacity (162.2kJ/kg), considerable reduction in supercooling degree (14.1%), thermal stability (270°C), phase transition enhancement (freezing: 20.47%, melting: 21.43%), reduction in (freezing time: 29.9%, melting time: 9.17%) and increased viscosity (2.56%) of HiNPCM were attributed to the embedded surface functionalized HyNC. In total, with the improved thermal storage properties, the HiNPCM can be considered as a potential candidate for the cool thermal storage applications in buildings.

Preparation and thermal energy storage properties of building material-based composites as novel form-stable PCMs

In this study, ten kinds of composite phase change materials (PCMs) were prepared by impregnation of xylitol penta palmitate (XPP) and xylitol penta stearate (XPS) esters into gypsum, cement, diatomite, perlite and vermiculite via vacuum adsorption method. The form-stable composite PCMs were characterized by using SEM and FT-IR, DSC and TG analysis techniques. The maximum impregnation ratio of both XPP and XPS into gypsum, cement, perlite, diatomite, and vermiculite were found to be 22, 17, 67, 48 and 42wt%, respectively. The DSC results showed that the melting temperatures and latent heat capacities of the composite PCMs varied from 20°C to 35°C and from 38J/g to 126J/g. TG investigations revealed that the composite PCMs had excellent thermal durability above their working temperature ranges. The thermal cycling test also exhibited that the composite PCMs had good thermal reliability and chemical stability. In addition, thermal conductivities of the composite PCMs were increased by addition of EG in mass fraction of 10%. All of the conclusions indicated that among the prepared composite PCMs, especially perlite and diatomite based-PCMs are potential candidates for energy storage applications such as solar heating and cooling in buildings since they had relatively higher latent heat capacity.

PW based phase change nanocomposites containing γ-Al2O3

Phase change nanocomposites were prepared by dispersing γ-Al2O3 nanoparticles into melting paraffin wax (PW). Intensive sonication was used to make well dispersed and homogeneous composites. Differential scanning calorimetric (DSC) and transient short-hot-wire (SHW) method were employed to measure the thermal properties of the composites. The composites decreased the latent heat thermal energy storage capacity, Ls, and melting point, Tm, compared with those of the PW. Interestingly, the composites with low mass fraction of the nanoparticles, have higher latent heat capacity than the calculated latent heat capacity value. The thermal conductivity of the nanocomposites was enhanced and increased with the mass fraction of Al2O3 in both liquid state and solid state.

Thermal Characteristics of Paraffin/Expanded Perlite Composite for Latent Heat Thermal Energy Storage

This study focuses on the preparation and thermal properties of paraffin/expanded perlite composite as novel form-stable phase change material for latent heat thermal energy storage by vacuum impregnation method. The paraffin could be absorbed in pores of expanded perlite as much as 55 wt% without melted phase change material seepage from the composite and this mixture was described as form-stable composite phase change material. The melting and freezing temperatures and latent heats of form-stable composite phase change material were measured using differential scanning calorimetry analysis. The thermal cycling test indicated that the form-stable composite phase change material had good thermal reliability in terms of the changes in thermal properties after 5,000 thermal cycling. Thermal conductivity of the form-stable composite phase change material was increased by about 46% by adding 5 wt% expanded graphite. The results indicated that the prepared form-stable paraffin/expanded perlite/expanded graphite composite phase change material has a great potential for latent heat thermal energy storage systems solar passive heating purposes due to suitable phase change temperature, high latent heat capacity, good thermal reliability, and thermal conductivity.

Study on the efficiency of effective thermal conductivities on melting characteristics of latent heat storage capsules

Improvement of the thermal conductivity of a phase change materials (PCM) is one effective technique to reduce phase change time in latent heat storage technology. Thermal conductivity is improved by saturating porous metals with phase change materials. The influence of effective thermal conductivity on melting time is studied by analyzing melting characteristics of a heat storage circular capsule in which porous metal saturated with PCM is inserted. Numerical and approximate analyses were made under conditions where there are uniform or non-uniform heat transfer coefficients around the cylindrical surface. Four PCMs (H 2O, octadecane, Li 2CO 3, NaCl) and three metals (copper, aluminum and carbon steel) were selected as specific materials. Porosities of the metals were restricted to be larger than 0.9 in order to keep high capacity of latent heat storage. Results show that considerable reduction in melting time was obtained, especially for low conductivity PCMs and for high heat transfer coefficient. Melting time obtained by approximate analysis agrees well with numerical analysis. A trial estimation of optimum porosity is made balancing the desirable conditions of high latent heat capacity and reduction of melting time. Optimum porosity decreases with increase in heat transfer coefficient.

Carbon balance of the continuous permafrost zone of Russia

An increase in the atmospheric concentration of CO, is prolected to cause climate warming. Warming of the permafrost environment could change the balance between carbon accumulation and decomposition processes and substantially disrupt the equilibrium of the carbon cycle. Warming may accelerate the rate of decomposition, which is limited by low temperatures, and thaw deeper layers of formerly frozen organic soils, making them available for decomposition. At the same time, productivity of vegetation may increase in response to warming. The continuous permafrost zone occupies approximately 40% of Russian territory, and 5 % of the land surface area of the world. Disruption of the carbon cycle within the permafrost zone in Russia could have a profound effect on the global terrestrial carbon cycle. To evaluate changes in the carbon cycle within the permafrost environment of Russia, it is necessary to quantify the present carbon pools and fluxes Once the carbon balance is established under the present clunate, potential disruptions under a warming climate can be identlfied. A framework to assess the carbon balance for the continuous permafrost zone of Russia was created. Under the present climate, the phytomass (live vegetation, aboveand below-ground) carbon pool was 17.0 Gt (10' t). The mortmass (coarse woody debris) carbon pool was 16.1 Gt. The litter carbon pool was 6.4 Gt C and the soil carbon pool including peatlands was 139.4 Gt. Live vegetation and plant detritus (mortmass and litter) taken together were approximately one-third of the soil carbon pool. The rate of carbon turnover was 1.58 Gt yr-l and the rate of humus formation was 0.083 Gt C yr-'. The phytomass carbon pool of the permafrost zone was 19 % of the former Soviet Union (FSU) phytomass pool and 3 % of the world biomass carbon pool. The permafrost zone accumulated a significant amount of aboveand below-ground plant detritus (mortmass and litter). Climate warming may cause forest migration to the north and increase net carbon accumulation in shrubby tundra ecosystems and ecosystems on soils of low permeabhty, compensating for possible carbon losses from tussock tundra. Shrubby tundra formations and gleylc soils occupy approximately one-half of the area of the Russian tundra biome. The degradation of permafrost would not directly affect the rate of carbon emissions from mineral soils and peatlands. The present depth of the active layer (i.e. layer of seasonal freezing and thawing) in mineral soils exceeds the depth of the organic horizons. In peatlands, thawing of the active layer could cause an additional mass of organic matter to become available for decomposition. However, thawing of the active layer in peatlands may not be this extensive because of the low thermal conductivity and high latent heat capacity of peat.