Low Latent Heat Research Articles

Effect of phase change materials on the short-term thermal storage in the solar receiver of dish-micro gas turbine systems: A numerical analysis

• Solar receiver with short-term thermal storage for Dish-Micro Gas Turbine system. • Effect of suitable PCMs on the output parameters of PCM integrated solar receiver. • Detailed numerical analysis using CFD methods. • Steady state parametric analysis for the effect of important parameters of PCM. • Detailed transient analysis for thermal storage behavior of the solar receiver. The solar dish-micro gas turbine system is a new alternative to the existing technologies for small-scale power production (<100 kW) in rural off-grid areas. In these solar-only systems, the short-term thermal energy storage in the solar receiver reduces the effect of natural fluctuations of the solar flux and ensures the stable working fluid (WF) temperature to the gas turbine. It improves the system performance and stability of the small gas turbine. In this context, a concept of Phase Change Material (PCM) integrated solar receiver was presented by authors in previous studies, where the receiver was filled with high-temperature PCM and WF (air) tubes were immersed in it. The PCM stores heat during charging phase and releases heat during the solar breakdown. The selection of PCMs for this receiver is a challenging task due to the high operating temperature ( T m > 1000 K). This study deals with the analysis of the impact of main parameters of the PCM on the performance of the solar receiver and detailed thermal analysis of the component using selected suitable PCMs. The 3D numerical analysis has been performed using Ansys Fluent R2. Moreover, the optical analysis has been carried out by ray tracing using SolTrace. The results of Soltrace are input to the Ansys Fluent and solar radiations are made to impinged on the cavity of the solar receiver. Steady-state parametric analysis has been performed considering the effect of latent heat of fusion, thermal conductivity, and the specific heat of the PCM on the outlet parameters of the receiver. The results showed a significant effect of these parameters on the heat storage of the solar receiver and the solidification/melting rate of PCM. The latent heat has major effect on the thermal storage in the PCM while thermal conductivity has high impact on the solidification/melting rate of the PCM. The transient simulations have been performed for the detailed melting/solidification behavior of the receiver using four metallic PCMs including MgSi, AlSb, NiSi, and Mg 2 Si. AlSb is characterized with comparatively lower latent heat and high thermal conductivity and showed quick solidification in discharging phase. Mg 2 Si has high melting temperature and a low thermal conductivity as compared to the other selected PCMs and thus has a comparatively slow solidification rate than AlSb and MgSi. The results show a good behavior of the component short term (15–20 min) thermal energy storage and stabilization of WF (air) temperature above 1000 K during this period.

Evaluation of the Effect of Low Soil Temperature Stress on the Land Surface Energy Fluxes Simulation in the Site and Global Offline Experiments

AbstractThe root water uptake (RWU) rate of plants is influenced by various environmental factors. Low soil temperature stress can reduce RWU rate by inhibiting the growth of plant roots and increasing the hydraulic resistance of water transport among the soil‐plant‐atmosphere continuum. Given that low soil temperature stress is not accounted for in current land surface models (LSMs); in this study, we introduce three functions to represent low soil temperature stress, and modify the RWU scheme of the Common Land Model to quantify the role of low soil temperature stress on water and energy exchange between land and atmosphere. The simulated water and energy fluxes are evaluated using both in situ and global observational data sets. The results from in situ simulations show that ignoring effects of low soil temperature stress, latent, and sensible heat fluxes in spring are overestimated and underestimated, respectively, with the root mean square error up to 40 W/m2. By incorporating the low soil temperature stress functions into the RWU scheme, nearly 40% of the simulated errors are reduced. The global simulated results also highlight the importance of accounting for low soil temperature stress on increasing the accuracy of the modeled latent heat flux over high latitude areas. While uncertainties from related physical processes and parameters warrant further investigations, our results indicate that consideration of low soil temperature stress significantly affects water and energy transport from land to atmosphere by restricting RWU rate, emphasizing the need to integrate it in LSMs to increase the model reliability, especially over cold regions.

Can Land Surface Models Capture the Observed Soil Moisture Control of Water and Carbon Fluxes in Temperate‐To‐Boreal Forests?

AbstractThe reservoir of soil water is exchanged with the atmosphere through evaporative processes, which are mediated via vegetation through transpiration. Carbon uptake is closely coupled to transpiration, and most process‐based models link transpiration and photosynthesis explicitly. Here, we evaluate the simulation of water and carbon fluxes in forested areas of North America using point‐based simulations of the Community Land Model version 5 (CLM5) with Soil Moisture Active/Passive (SMAP) satellite derived soil moisture measurements and in situ measurements at eight Fluxnet and two United States Climate Research Network (CRN) sites. Compared to observations, there is a broad site‐to‐site variability in simulated soil moisture, with some sites exhibiting wet biases and others dry biases. The bias sign does not depend on ecosystem or other environmental drivers such as radiation and temperature. Compared to Fluxnet latent heat (LH) and gross primary production (GPP) flux tower observations, simulated LH flux biases at deciduous broadleaf forests are linked with soil moisture biases, and the model captures the observed seasonal cycle and parabolic seasonal relationship with soil moisture. The parabolic shape is driven by high soil moisture and low LH fluxes in June, peak LH and drier soil conditions in July, followed by further soil moisture drawdown in August. GPP is underestimated at most sites, and the model exhibits a linear relationship between soil moisture and GPP. Because the photosynthesis parameterizations are similar in most Earth system models, further model development that incorporates observations and observed relationships is needed to accurately capture the GPP‐soil moisture relationship.

Urban Heat Island associated with Land Use/Land Cover and climate variations in Melbourne, Australia

Urbanization is known as one of the most prominent global problems that alter the atmosphere and land surface properties. The intensity of Urban Heat Island (UHI) associated with surface temperature and component attributes were assessed using the Community Land Model (CLM). The variations of UHI with Land Use/Land Cover (LULC) and climate variations were also investigated to provide a link among urbanization, surface energy balance interactions, and extreme hydroclimatic events which are drought (‘big dry’ and ‘angry summer’) and heavy rainfall (‘big wet’) in Melbourne, Australia. Generally, UHI demonstrated a uniform increasing trend with an ∼1.20 ± 0.20 °C increment, along with urbanization expansion of +14.93 % from 2001 to 2014. Furthermore, urban area showed positive contribution to UHI based on Land Contribution Index (LCI). High surface temperatures also resulted in higher sensible heat flux (Qh) and lower latent heat flux (Qle). During the multiple extreme climate events, the UHI biophysical drivers were majorly related to the convection reduction during ‘big dry’ (2001−2009), surface evaporative cooling during ‘big wet’ (2010−2011), and heat storage release during ‘angry summer’ (2012–2013). Overall, this analysis demonstrated correlation of UHI intensity and its component attributes with urban expansion, which was associated with LULC and climate variations in Melbourne.

THE EFFECT OF EXPANDED GRAPHITE ON THE CHARGING TIME OF STEARIC ACID PHASE CHANGE MATERIAL IN A HOT WATER TANK

The present work is to investigate the thermal conductivity of the phase change material (PCM) of stearic acid (SA) by using the supporting material of expanded graphite (EG). The EG is used with the mass ratio of 10%, 15% and 20%. SA is commercial grade and the EG is formed by thermal method using natural graphite powder and crystalline zinc nitrate. The composite materials of (SA/10% EG, SA/15% EG and SA/20% EG) are prepared by direct impregnation method. Thermal conductivity of pure SA and composite PCMs are investigated by laboratory apparatus of heat transfer base unit TD1002. The thermal conductivity of the SA/10%EG composite PCM has been improved to 0.64 W/mK from that of SA (0.28 W/mK) with the percentage enhancement of 129%. To verify the morphology of the materials, scanning electron microscopy (SEM) analysis is utilized. The results show that the EG is formed in multilayers with pores in which stearic acid is well absorbed. The charging characteristics of pure SA, SA/10% EG and SA/15% EG for low temperature latent heat storage (LHS) system are studied experimentally. The system is applied for domestic water heating. The PCM is filled in a 33 mm diameter cylindrical copper tube and placed in hot water storage tank. The water is filled in tank from the top section through the distributor to uniform entry. The phase change phenomena of the PCMs are measured by inserting thermocouples at two layers of PCM tube. The result shows that the melting time decreases with the increasing mass ratio of expanded graphite in composite PCM. Although the melting time of both layers are nearly the same at the experiment of composite PCMs, the lower layer takes longer time than upper layer for pure PCM. The charging time is decreased by 67% for SA/10%EG and 79% for SA/15% EG composite PCM from that value of pure SA.

Numerical investigation of the CHF in a vertical round tube and a single rod channel based on the eulerian two-fluid model

The critical heat flux (CHF) is essential to the operational safety of nuclear power plants (NPP), and it plays a vital role in the thermal-hydraulic and structural design of a fuel assembly. In this study, the commercial computational fluid dynamics package STAR-CCM+ was used to predict the departure from the nucleate boiling (DNB) phenomenon. Based on the Eulerian two-fluid model and the extended Rensselaer Polytechnic Institute (RPI) wall boiling model combined with the Weisman-Pei bubble crowding model, the DNB phenomenon was investigated for two coolants (water and R134a) with different geometric structures and working conditions. The results demonstrated that one set of Eulerian two-fluid models could accurately predict the CHF within a certain range of working conditions. The CHF value calculated in this study show good agreement with the experimental measured CHF data, which indicated that the Eulerian two-fluid model had a good application prospect for CHF prediction. The observed mean error was less than 10%. The results of this study may contribute to an advanced boiling model development for CHF prediction in complex geometric structures such as fuel assembly. In addition, these results demonstrated that it was feasible to use the refrigerant R134a, which had a low critical pressure and low latent heat of vaporization, as the modeling fluid to replace water, which had a high latent heat of vaporization and a high critical pressure in the experimental study.

Performance Evaluation of an Adsorption Heat Pump System Using MSC-30/R1234yf Pair with the Impact of Thermal Masses

In this study, we evaluated the performance of low Global Warming Potential (GWP) refrigerant R1234yf on the activated carbon (MSC-30) for adsorption heating applications. The adsorption isotherms of MSC-30/R1234yf were measured using a constant-volume–variable-pressure (CVVP) method from very low relative pressure to the practical operating ranges. The data were fitted with several isotherm models using non-linear curve fitting. An improved equilibrium model was employed to investigate the influence of dead thermal masses, i.e., the heat exchanger assembly and the non-adsorbing part of the adsorbent. The model employed the model for the isosteric heat of adsorption where the adsorbed phase volume was accounted for. The performance of the heat pump was compared with MSC-30/R134a pair using the data from the literature. The analysis covered the desorption temperature ranging from 60 °C to 90 °C, with the evaporation temperature at 5 °C and the adsorption temperature and condensation temperature set to 30 °C. It was observed that the adsorption isotherms of R1234yf on MSC-30 were relatively lower than those of R134a by approximately 12%. The coefficient of performance (COP) of the selected pair was found to vary from 0.03 to 0.35 depending on the heat source temperature. We demonstrated that due to lower latent heat, MSC-30/R1234yf pair exhibits slightly lower cycle performance compared to the MSC-30/R134a pair. However, the widespread adaptation of environmentally friendly R1234yf in automobile heat pump systems may call for the implementation of adsorption systems such as the direct hybridization using a single refrigerant. The isotherm and performance data presented in this work will be essential for such applications.

Isopropyl palmitate integrated with plasterboard for low temperature latent heat thermal energy storage

In recent years, the latent heat thermal energy storage using phase change materials (PCMs) has become a hot topic; it has attracted much attention in the utilization of renewable energy sources to improve the energy efficiency of buildings. Isopropyl palmitate (ISOP) with phase transition temperature of 10°C to 13°C and heat of fusion of ~113 J/g was selected to be used as a PCM in building applications. ISOP, 15%, was mixed with plasterboard (PB) as a building material in two techniques, immersion and direct incorporation, in order to retain the ISOP into the porous structure of PB. Scanning electron microscope (SEM) demonstrated that the layer structure of the PB particles was uniformly absorbed by ISOP. Phase transition temperature of ISOP in both techniques determined using differential scanning calorimeter (DSC) is still similar to that of ISOP accompanied with much reduction in the latent heat, particularly in the direct incorporation technique. TCA 300 thermal conductivity analyzer addressed that the thermal conductivity of the PB has been slightly increased with the addition of ISOP. The stored thermal energy performance in a small test room is experimentally investigated. These results indicated that applying ISOP to the south wall of the testing room had the potential to reduce the fluctuation of the indoor air temperature. The effect of ISOP on the mechanical properties of PB has been investigated in the flexural mode using three-point bending test. Moreover, the fire risk of ISOP has been assessed using cone calorimetric. The results confirmed that the novel composite ISOP has a significant opportunity in building applications for thermal energy storage.

Form‐stable phase‐change materials supported by 1‐octadecylamine‐modified montmorillonite for latent heat storage

Form-stable phase-change materials (FSPCMs) are of great significance for relieving the contradiction of energy supply and demand. Unfortunately, the practical application of FSPCMs is severely compromised by their intrinsic drawbacks including lower latent heat storage (LHS) capacities, inferior interfacial compatibility, and cycling durability. Herein, we have provided a group of novel FSPCMs with higher LHS capacities, using paraffin as the LHS materials, which tightly intertwines with the 1-octadecylamine-modified montmorillonite (C18-MMT) under the capillary action as well as induced dipole force due to its n-alkyl chains compatibility. The obtained composite FSPCMs not only exhibit high melting enthalpies (137.56 J/g) but also demonstrate enhanced shape stability and thermal stability. In addition, the composites also render an impressive long-term thermal cycling capability and structure stability even after 100 thermal cycling durability tests, which are believed to have great potential for application in the thermal management of green energy-saving buildings.

Experimental investigation on diesel engine through n-Butanol blend biodiesel

N-Butanol may be considered as the future replacement to ethanol due to its lower latent heat of vaporization, low level of impurities and higher heating value than diesel. These properties motivated researchers to perform the experiments in this field in the search of alternative fuels. In the current work an experimental investigation on single-cylinder four stroke diesel engine charged up with n–Butanol blends and pure diesel were used to predict the performance parameter without modification in the engine. In this experimental investigation, N-Butanol was added to diesel with known percentages to enhance the performance of a diesel engine. The blends of n- Butanol biodiesel and diesel fuel were mixed as in the percentage of 95% diesel with 5% n-Butanol as B5, 90% diesel with 10% n-Butanol as B10, 85% diesel with 15% n-Butanol as B15 and 80% diesel with 20% n-Butanol as B20 respectively. Results showed that when the percentage of the blend of n-butanol blend increased to 20% at 16 kg load then Brake thermal efficiency were increased to 30.33% and Brake specific fuel consumption were deceased 16.7% at 16 kg load simultaneously. The results of the experimental study can be further utilized to carry out a similar investigation with various blends of Biodiesel.

Engineering biochar with multiwalled carbon nanotube for efficient phase change material encapsulation and thermal energy storage

Currently, numerous efforts are being made to develop shape-stabilized composite phase change materials (PCMs) to respond to unbalanced renewable energy storage systems. In this study, we engineered hybrid materials based on commercially available and environmentally friendly biochar derived from bamboo and multiwalled carbon nanotubes (CNTs) via a one-step hydrothermal method. The organic liquid n-dodecane was used as the energy storage material. The hybrid material provides favorable morphological and interconnected framework structures for PCM encapsulation and energy storage capacity in the composite PCMs. The PCM loading capacity of biochar, biochar-CNT, and CNTs reached 51.3%, 70.6%, and 83.2% with latent heat of 93.4 ± 1.1, 127.3 ± 1.1, and 152.3 ± 1.3 J/g, respectively. The integration of CNTs with biochar positively affected the latent heat storage capacity of the composite PCMs compared with that of the composite PCMs without CNTs. The pristine biochar exhibited a low PCM loading ratio and latent heat compared with biochar-CNTs and CNTs, presumably due to the limited pore space and strong intermolecular interaction between the reactive functional groups and PCM. Meanwhile, the obtained composite PCMs exhibited outstanding shape and thermal stabilities and chemical compatibilities. This synthesis strategy is expected to create a platform for fabricating biochar-based multifunctional PCMs for desired applications.

THE EVALUATION OF THE INFLUENCE OF LAND SURFACE TEMPERATURE IN ENERGY BALANCE ESTIMATED BY S-SEBI MODEL

Abstract. Evapotranspiration (ET) is one of the least understood components of the hydrological cycle. Its application is varied, from agricultural, ecological and hydrological monitoring, to control of the evolution of climate change. The goal of this work was to analyze the influence that uncertainties in the estimate of Land Surface Temperature (LST) can cause on ET estimates by S-SEBI model in Pampa Biome area. The results indicate that the daily evapotranspiration is higher when the pixel LST is lower, which also shows the influence of land use on the variability of ET. They also demonstrated the importance of LST's accuracy in the selection of the driest and wettest pixels in applying S-SEBI model, because when there are uncertainties in estimates of LST, the errors in the estimates of the energy components multiply. The Pampa Biome native grass crops have lower Latent Heat Flux (LET) than other land uses, with higher values of LET during the spring-summer period when compared to autumn-winter.

Effect of Si Addition on Flow Behavior in Al-Mg and Al-Mg-Si Molten Alloys

This study investigates the fluidity change of Al-Mg binary alloys with the addition of Si and examines the factors that determine flow length in these binary and ternary alloys. Fluidity tests for Al-6Mg-xSi (all compositions in mass percent; x = 0, 3, 5, or 7) alloys were carried out using a spiral-type steel mold. The results show a decrease in both the rate of oxidation and the freezing range, as well as an increase in the heat of fusion of Al-Mg-Si ternary alloys with increasing Si content. Nevertheless, at constant superheating of 60 °C, a lower fluidity was achieved in ternary alloys of ≤ 5 pct Si content than in Al-6Mg alloy. However, further increase to 7 pct Si content yielded a flow length 25 pct higher than for Al-6Mg alloy. Further superheating above the liquidus temperature resulted in increased flow length for Al-Mg-Si ternary alloys, with a flow length increase of about 1 cm per 5 °C temperature increase. Instead of solidification range, Tα–Te range (the temperature difference between the start of the pro-eutectic α-Al phase (Tα) and eutectic phases (Te)), was used in this study, as it was found to be a more suitable criterion for predicting flow length for Al-Mg-Si ternary alloys. The key variables for predicting flow length were found to differ based on alloy composition. In the ternary alloys, total heat content and (Tα–Te) range were found to be the most influential factors driving flow behavior, while the poor fluidity of Al-6Mg binary alloys was found to be driven primarily by high oxidation tendency and low latent heat of fusion.

Comparative experimental investigation on the effects of heavy alcohols- safflower biodiesel blends on combustion, performance and emissions in a power generator diesel engine

The experimental works carried out in this article evaluates the potential of using heavy alcohol and safflower biodiesel as the blended fuel mixtures without making any modifications in the tests diesel engine. For this purpose, volumetrically 20% of Propanol, Pentanol, Butanol, and Octanol were blended with safflower biodiesel fuel and they were named as PR20, PE20, BU20, and OC20, respectively. The performance, combustion, and emission data were found out at the same conditions of constant engine speed and various loads and compared with pure biodiesel (B100) and diesel fuel(ULSD). In the experiments, a four-cylinder, water-cooled diesel engine that was loaded by an electrical power generator was used for the tests. The addition of alcohol causes an increase in fuel consumption due to a decrease in lower thermal performance. The use of heavy alcohols in diesel engine in specific quantities by mixing with biodiesel significantly increases engine brake thermal efficiency. Negative effects of low cetane number and high latent heat of vaporization that may decrease ignition delay and decrease cylinder pressure while increase peak heat release was considered to be compensated by the better mixing properties and atomization of alcohol blended biodiesel thus eventually improve the combustion. Alcohol addition to biodiesel fuel can be accepted as a useful application to increase brake thermal efficiency and reduce nitrogen oxide (NOx), carbon monoxide (CO), and hydrocarbon (HC) emissions by reducing the density and viscosity.

How an urban parameterization affects a high‐resolution global climate simulation

The impact of urban areas on the global and regional climate has been assessed using the global Conformal Cubic Atmospheric Model (CCAM) including an urban canyon parameterization at a global resolution of 50 km. Simulations were produced with and without urban areas to assess urban impacts for the historical period 1980–2000. Two different land cover and urban datasets (one based on IGBP‐DIS, the other on MODIS) were tested. In addition, simulations were performed for the end of the 21st century with the RCP8.5 scenario. Evaluation of the historical climate simulations indicates realistic local urban effects, such as higher daily minimum air temperatures (tasmin), higher sensible heat flux and lower latent heat flux at urban grid cells. In regions with large fractions of urban areas, some regional changes are also noted. In addition, there are significant regional effects far away from the main urban areas, which are similar in magnitude to the effects of the different non‐urban land cover input datasets. Under the projected warming at the end of the 21st century (with no land cover change), there is a decrease in anthropogenic heating, primarily during wintertime. There is a slightly smaller increase in daily maximum temperature and a slightly larger increase in tasmin in urban areas compared to rural areas. This leads to a smaller increase in the diurnal temperature range within urban areas. The tasmin changes also imply an increase in the urban heat island effect for larger cities. The results of this sensitivity study show that there is a detectable impact of urban areas on high‐resolution global climate simulations. Consequently, there is a need to include urban areas in global simulations, as well as in studies of land‐use change.

Impacts of trehalose and l-proline on the thermodynamic nonequilibrium phase change and thermal properties of normal saline

Understanding the phase change behavior and thermal properties of cryoprotective agents (CPAs) in biological solutions is essential for enhancing the success of cryopreservation and biobanking. In this study, the phase change behavior and thermal properties of normal saline added with trehalose or l-proline were investigated using differential scanning calorimeter (DSC) and cryomicroscope during freezing and warming. The addition of trehalose or l-proline can eliminate the eutectic formation in normal saline. Trehalose had significantly lower latent heat release than l-proline does at a high concentration of 1 M (P < 0.05), while unfrozen water content of trehalose is significantly lower than that of l-proline at all the concentrations (P < 0.05). It was also found that addition of 0.2 M, 0.3 M and 1 M trehalose can achieve partial vitrification in normal saline and that the glass transition temperature rises along with the increase in concentrations of trehalose. However, no vitrification was observed in normal saline with l-proline at any concentrations. Besides, rates of ice crystal growth in normal saline added with trehalose are slower than those in normal saline with l-proline at the same concentrations. These results suggest that both trehalose and l-proline can act as CPAs by avoiding eutectic formation and inhibiting ice formation in normal saline for cell cryopreservation. It could be useful for CPA selection and designing in the future.

Validation of Spring Wheat Responses to Elevated CO2, Irrigation, and Nitrogen Fertilization in the Community Land Model 4.5

AbstractThe Community Land Model (CLM) started to incorporate crop growth models since version 4.0 in 2012. Since then, the crop model in CLM has been evolved remarkably, but some of the key crop growth responses to environmental conditions (such as the elevated CO2) have not been well validated. Here, we set up single point simulations with CLM (version 4.5) and validated spring wheat growth response against the Maricopa spring wheat Free Air CO2 Enrichment (FACE) experiment that consisted of multiyear paired treatments to understand the growth response to elevated CO2, irrigation, nitrogen fertilization, and their interactions. Overall, CLM showed too positive growth response to elevated CO2 but insufficient growth response to irrigation. The overestimated growth response to elevated CO2 may be due to ignoring factors (e.g., leaf traits) that will limit crop growth under elevated CO2. The insufficient response to irrigation is due to CLM simulating lower latent heat flux during April and May, which resulted in higher soil moisture. In response to nitrogen fertilization, CLM underestimated leaf area index increase but overestimated grain yield increase. In terms of energy fluxes, CLM showed decreased latent heat flux in response to elevated CO2 but increased latent heat flux in response to nitrogen fertilization, but the response magnitude was much smaller than the observations. Based on these validations, we summarized further model developments for CLM to better simulate crop growth process.

Preparation and characterizations of a novel temperature-tuned phase change material based on sodium acetate trihydrate for improved performance of heat pump systems

Application of latent heat thermal energy storage unit is regarded as an effective method to improve the coefficient of performance of hot water heat pump systems (HWHPS). With consideration of energy efficiency and domestic hot water usage, phase change materials with a melting temperature range of 45–48 °C are suitable for practical applications. The most commonly used PCMs, paraffin-based materials, are costly and have low latent heat density, which restrains their applications. This study therefore aims to prepare a novel sodium acetate trihydrate based composite PCM with suitable phase change temperature and cost-effectiveness for HWHPs. A series of SAT-based composites with varying mass fraction of potassium chloride (KCl), urea, disodium phosphate dodecahydrate (DSP) and carboxyl methyl cellulose (CMC) were prepared. Their thermophysical properties and stability were investigated by freezing-melting cycling tests, differential scanning calorimetry (DSC) and X-ray powder diffraction (XRD). The experimental results indicated that the optimized SAT-based CPCM with 8 wt% KCl, 3 wt% urea, 6 wt% CMC and 1.5 wt% DSP displayed a favorable phase change temperature of 47.8 °C and a higher latent heat of 242.0 kJ/kg. Meanwhile, the results demonstrated that it has extraordinary thermal cycling performance, negligible vibration in phase change temperature and latent heat, and good stability in chemical properties.

A novel form stable PCM based bio composite material for solar thermal energy storage applications

• Development of PCM-water hyacinth biochar based form stable thermal energy storage material. • The thermophysical properties and thermal stability of the proposed composite material has been analysed and discussed. • Negligible leakage has been reported at 6:4 ratios (PCM: biochar). • The composite has good thermal conductivity and latent heat of fusion. • The developed material is suitable for solar energy applications. Phase change materials found to be a promising solution in the field of thermal energy storage. However, the low thermal conductivity and form stability over cycles of charging and discharging of PCM are challenges to address. In the proposed study, a novel and low cost biochar-PCM hybrid latent heat energy storage material have been developed and tested. The biochar is prepared from aquatic invasive weed plants by using a batch type pyrolyser. The characteristics and properties of the novel energy storage material have been evaluated using various experimental and analytical methods. The methods include Brunauer, Emmett and Teller (BET), Scanning electron microscope (SEM), X-ray powder diffraction (XRD), Differential Scanning Calorimetry (DSC), Thermogravimetric analysis (TGA), Fourier-transform infrared spectroscopy (FT–IR) and thermal conductivity tester. The study also put forward the optimized proportion of biochar and PCM in hybrid thermal energy storage material. The new material shows superior thermal conductivity over pure PCM as well as better stability due to the high carbon content and porosity of the developed biochar. Simple Impregnation method has been used to prepare form stable composite material which has good thermal and structural stability. The best mixing ratio (PCM: biochar) is found to be 6:4 (wt/wt%) with minimum leakage of PCM from the composite. The sample prepared through this method yield all the desirable properties as compared to other developed samples. The chemical properties of the composite remain the same as the pure PCM, which confirms no chemical interaction between the PCM and biochar. The heat of fusion is calculated to be 179.4 J/g. The thermal conductivity of the PCM is enhanced up to 13.82 times with the addition of water hyacinth biochar as a supporting matrix. The addition of aluminum metal powder further increases the thermal conductivity by 17.27 times higher than that of PCM alone.

In situ one-step construction of monolithic silica aerogel-based composite phase change materials for thermal protection

Currently, numerous studies are devoted to the pursuit of thermal conductivity enhancement of phase change materials (PCMs). On the contrary, few researches are reported to reduce the thermal conductivity of PCMs. Generally, the PCMs with reduced thermal conductivity have great potential in thermal protection application. Herein, we propose a novel in situ one-step strategy to facilely prepare monolithic silica aerogel-based composite PCMs. The silica aerogels possess low thermal conductivity and are used to encapsulate PCMs to prepare composite PCMs, such as polyethylene glycol (PEG) or octadecanol. Compare with PEG2000@silica aerogel, the resulting monolithic octadecanol@silica aerogel have low thermal conductivity (0.12 W m−1 K−1), high latent heat (127.73 J/g), large compressive strength (11 MPa), good hydrophobicity (contact angle 124°) and superior thermal cycling stability. This monolithic silica aerogel-based composite PCMs could prolong heat preservation duration due to the synergistic effect between low thermal conductivity and high latent heat of composite PCMs, showing potential promise for direct application to the thermal insulation and thermal protection device. More importantly, this in situ one-step synthesis strategy is universal for different types of PCMs.