Medium Temperature Heat Research Articles

Activation of the process of layer combustion of bitter coal with iron nitrate and waste of metal rolling production

The influence of metal-rolling production waste and iron nitrate on the characteristics of the process of layer combustion of coal is investigated. As a solid fuel, coal of the T grade was used. Metal scale and iron nitrate were introduced into the fuel by mechanical mixing. According to XRD data, phases of iron oxides Fe3O4 and manganese Mn3O4 were identified in the metal scale. The characteristics of the combustion process of the studied samples were studied using high-speed video with the use of a combustion chamber at a heating medium temperature of 700°C. Combustion Also, the process of activated layer combustion coal was scaled using a solid fuel boiler unit. It has been experimentally established that the use of metal scale and iron nitrate leads to an increase in the reactivity of the fuel, as evidenced by a decrease in the ignition delay time. Due to the intensification of the combustion process, the fuel underburning and the concentration of CO formed in the composition of gas-phase combustion products were reduced.

Thermal Conductivity Enhancement of Doped Magnesium Hydroxide for Medium-Temperature Heat Storage: A Molecular Dynamics Approach and Experimental Validation.

Magnesium hydroxide, Mg(OH)2, is recognized as a promising material for medium-temperature heat storage, but its low thermal conductivity limits its full potential application. In this study, thermal enhancement of a developed magnesium hydroxide-potassium nitrate (Mg(OH)2-KNO3) material was carried out with aluminum oxide (Al2O3) nanomaterials. The theoretical results obtained through a molecular dynamics (MD) simulation approach showed an enhancement of about 12.9% in thermal conductivity with an optimal 15 wt% of Al2O3. There was also close agreement with the experimental results within an error of ≤10%, thus confirming the reliability of the theoretical approach and the potential of the developed Mg(OH)2-KNO3 as a medium heat storage material. Further investigation is, however, encouraged to establish the long-term recyclability of the material towards achieving a more efficient energy storage process.

Future Parabolic Trough Collector Absorber Coating Development and Service Lifetime Estimation

This work presents a study on the optical and mechanical degradation of parabolic trough collector absorber coatings produced through the spray coating application technique of in-house developed paint. The main aim of this investigation is to prepare, cure, load, and analyze the absorber coating on the substrate under conditions that mimic the on-field thermal properties. This research incorporates predicted isothermal and cyclic loads for parabolic trough systems as stresses. Biweekly inspections of loaded, identical samples monitored the degradation process. We further used the cascade of data from optical, oxide-thickening, crack length, and pull-off force measurements in mathematical modelling to predict the service life of the parabolic trough collector. The results collected and used in modelling suggested that cyclic load in combination with iso-thermal load is responsible for coating fatigue, influencing the solar absorber optical values and resulting in lower energy transformation efficiency. Finally, easy-to-apply coatings made out of spinel-structured black pigment and durable binder could serve as a low-cost absorber coating replacement for a new generation of parabolic trough collectors, making it possible to harvest solar energy to provide medium-temperature heat to decarbonize future food, tobacco, and paint production industrial processes.

Comparison of entransy loss analysis and the first law of thermodynamics in the optimization of organic Rankine cycle coupled with parabolic trough collector

Due to the numerous environmental issues associated with fossil fuel power plants, using solar energy to generate electricity is a viable alternative. The organic Rankine cycle (ORC) is a thermodynamic process used to convert low- and medium-temperature heat sources into electricity, often utilizing organic fluids as the working medium. Entransy is a relatively new concept that many readers may not be familiar with. Moreover, entransy loss (Ġloss) is derived from the entransy concept, which quantifies the inefficiency in transferring thermal energy through a system. In this study, (Ġloss) is used for the first time when designing an ORC cycle coupled with parabolic trough collectors. The entransy loss relations were driven with assumption that the heat capacity is a function of temperature. A genetic algorithm is a search heuristic inspired by natural selection. It is used to find optimal or near-optimal solutions to complex problems by evolving a population of candidate solutions. Two scenarios utilized the genetic algorithm in MATLAB to optimize the system (scenario 1: maximizing the output power and scenario 2: maximizing the Ġloss). In addition, the optimization parameters included turbine inlet temperature (Ttur), boiler pressure (Pboil), condenser pressure (Pcond), and the temperature of the collector fluid at the boiler outlet (Thf,out). This optimization was performed for the temperature of the collector fluid at the boiler inlet (Thf,in) in the range 310–400 °C at 10 °C intervals with four working fluids (i.e., toluene, cyclohexane, MM, and water). The land area and the beam solar radiation were considered to be 100 hectares and 800 W/m2, respectively. The results indicated that according to scenario one, at temperatures of 310–320 °C, the maximum power was obtained for the case of toluene fluid with values 59.8 and 63.5 MW. For the collector fluid temperature from 330 to 400 °C, water had the most optimal power with values ranging from 66.2 to 88.2 MW. Furthermore, toluene exhibited superiority to two other organic fluids in the 330–400 °C temperature range after water, with net power values ranged between 65.7 and 76.3 MW. The results indicated that the maximum entransy loss does not correspond to the maximum output power because the application preconditions of the entransy loss concept are not all satisfied. Across all working fluids and Thf,in, scenario 2 resulted in lower optimal output power, cycle efficiency, and system efficiency compared to scenario 1.

Estimation of preheating time for building intermittent heating subject to changes in outdoor temperature and solar radiation

Intermittent heating is to maintain indoor temperature of buildings in winter within a comfort range only during occupancy periods. Buildings have thermal inertia causing slow increments of indoor temperature, so that a preheating time is required to start heating in advance of occupancy periods. In this paper, a new method is presented to determine preheating time for building intermittent heating subject to changes in outdoor temperature and solar radiation. First, a dynamic model is developed to describe relations between indoor temperature as an output and three inputs including the heating medium temperature, outdoor temperature, and solar radiation. The dynamic model with modeling uncertainties is identified from input-output historical data. Second, the identified model is used to predict indoor temperature under future data of three inputs, and optimal preheating times are determined with a certain probability to ensure successful preheating. The experimental examples show that the dynamic model accurately describes the indoor temperature changes, and the preheating times from the proposed method are more accurate than four existing methods.

Experimental investigation on thermodynamic performance of a copper foam-based cascaded latent heat storage tubes

Cascaded latent heat storage (CLHS) systems offer an effective means for energy storage from moderate to medium and low temperature heat sources (100-200℃). In this study, a three-stage shell-and-tube cascaded latent heat storage system was designed and fabricated. Three types of paraffin wax with distinct melting points were employed as phase change materials (PCMs), and foam copper was utilized to enhance heat transfer. By adjusting the inlet temperature and flow rate of heat transfer fluid (HTF), the thermodynamic performance of each LHS stage and the entire system under different operating conditions were investigated. Exergy analysis, entransy analysis, and sensitivity analysis were employed to study the primary influential factors on system performance and the impact weights of diverse operating conditions. Experimental results highlighted the crucial significance of maintaining consistency in the physical parameters of PCMs across different stages in the CLHS system for its thermodynamic performance. The high thermal conductivity and low latent heat of PCM#2 in the second stage result in substantial energy losses during the heat storage process, reducing the efficiency of energy cascaded utilization within the system. With an increase in the HTF inlet temperature and flow rate, the energy storage capacity and rate increase, while the energy storage efficiency exhibits a decreasing trend. Moreover, the effect of varying inlet temperature on the energy storage efficiency is much smaller compared to that of inlet flow rate. This study emphasizes that heat dissipation is a critical factor affecting the thermodynamic performance of the cascaded latent heat storage system. For CLHS systems targeting high-temperature and high-flow rate heat sources, enhancing insulation is crucial for ensuring the sustained high-efficiency operation.

Thermoeconomic Analysis of a Solar-Assisted Industrial Process Heating System

Thermal energy in the industrial sector for process heating applications in the range of 50 to 250°C consumes about 35% of the global fossil fuel. Cascaded solar thermal systems are promising solutions to meet clean and uninterrupted thermal energy supply for industrial process heating. Well-engineered cascaded arrangement of solar thermal collector (STC) and photovoltaic thermal (PVT) collector can attain an average solar fraction of more than 50%. In the present research, a solar-assisted process heating system, wherein a STC integrated in series with PVT, has been designed to produce low- to medium-temperature heat at higher solar fractions. Herein, thermal performance and economic viability of this novel system have been investigated and analyzed methodically. In the present research, a comprehensive TRNSYS simulation model is developed and validated experimentally. Results show that PVT integrated with heat pipe evacuated tube collector (PVT-HPETC) and PVT integrated with flat plate collector (PVT-FPC) system can generate thermal energy as high as 1625 and 1420 W with a thermal efficiency of 81 and 77% and exergy efficiency of 13.22 and 12.72%. Levelized cost of heat (LCOH) for PVT-HPETC at process heat temperatures of 60, 70, and 80°C is 0.214, 0.208, and 0.201 MYR/kWh, respectively. It is worth to note that LCOH is less than the existing cost of heat generation which proves that these systems are economically feasible.

Isothermal (vapor ＋ liquid) equilibrium measurements and correlation of the binary mixture 3,3,3-trifluoropropene (R1243zf) ＋ isobutane (R600a) at temperatures from [formula omitted] to [formula omitted] K

The restrictions set by the F-gas Regulation and the Kigali Amendment to the Montreal Protocol have pushed an extensive research into alternatives for fluorinated greenhouse gases in air conditioning and refrigeration. Hydrofluoroolefins (HFOs) are emerging as promising substitutes for hydrofluorocarbons (HFCs) and hydrochlorofluorocarbons (HCFCs) in HVAC and refrigeration. Amongst these, R1243zf raised interests as low-GWP substitutes for R134a. The pursuit of low GWP refrigerants has also led to the examination of hydrocarbons (HCs), like propane (R290) and isobutane (R600a), due to their efficiency, low charge, and affordability, despite their flammability. The mixtures of R1243zf and isobutane could be of interest for medium temperature heat pump applications. Moreover, blending HFOs with HCs usually leads to azeotropic mixtures. While HCs benefit of a wide range of data and reliable Equations of State (EoS), HFOs, and in particular their mixtures, lack comprehensive information. This study reports vapor–liquid equilibrium (VLE) measurements for the 3,3,3-trifluoropropene (R1243zf) + isobutane (R600a) binary system in the temperature range between 283.15 K and 323.15 K. The measurements have been carried out by means of a vapor-recirculation apparatus combined with gas-chromatographic analysis. This work reports 53 experimental data with an expanded uncertainty (k=2) of 0.003 mol mol−1. The reported data, along with the data available in the literature, have been used to developed two new mixture models based on the Helmholtz free energy EoS, both leading to a significant improvement in the VLE prediction, with RMSE values lower than 0.005 mol mol−1 for both the liquid and the vapor phase composition.

Effect of preparation method of pyrolysis liquid mixed with coal on its ignition and combustion characteristics

Relevance. The need to develop technological solutions to increase the competitiveness of pyrolysis processing of various wastes. Combustion of pyrolysis liquid in a mixture with coal is one of these solutions, which makes it possible to stabilize the properties of the obtained fuel and use in standard energy equipment. Aim. To determine the influence of the method of preparing a mixture of pyrolysis liquid and low-grade coal on its ignition and combustion characteristics, as well as on composition of the released gas-phase products, depending on the temperature of heating medium and concentration of the additive. Methods. Pyrolysis and oxidation characteristics were studied using thermogravimetric analysis, and formal kinetic constants were calculated using the Coates–Radfern method. Samples of mixed fuels were prepared by the methods of homogeneous mixing and surface wetting of pyrolysis liquid of rubber processing and low-grade coal. Ignition and combustion characteristics were determined using an experimental stand, and composition of gas-phase combustion products was determined using once-through gas analyzer. Results. The authors have determined the features of pyrolysis and oxidation of the pyrolysis liquid as well as the values of formal kinetics constants, indicating the physical nature of the factors that defining the rate of these processes. It was found that at 600 °C the ignition of the studied mixtures weakly depended on concentration of the additive, while at 700 and 800 °C the dependence was linear, and the differences between the samples prepared using different methods were insignificant. For samples obtained by the method of surface wetting, combustion of the additive occurred in the gas phase near the surface of the sample. For the samples obtained by the method of uniform mixing, it occurred predominantly in the bulk of the backfill. This led to more intense and complete coal combustion in these compositions due to more uniform releasing of heat and initiation of coal particles. The concentration curves of the NO, CO and CO2 release demonstrated, that behavior of the fuel mixture components was additive in terms of released gas-phase combustion products, as well as the absence of significant nonlinear effects over the entire studied range of temperatures and additive concentrations.

Studies on the thermal cycle performance of solar thermal power generation under different heat sources

Solar thermal power generation is an important way to solve the future power demand, and some countries have entered the commercial application stage. According to the heat source temperatures provided by different solar thermal collector systems, different thermodynamic cycle modes of power generation systems were proposed so that the appropriate thermal cycle modes and working mediums at different heat source temperatures were obtained. The results show that, under a low-temperature heat source, in an organic Rankine cycle with R600 as the working medium, the cycle efficiency is 13.40% when the temperature of the turbine inlet is 100°C and the pressure is 1.5 MPa; the cycle thermal efficiency is 12.00% when the temperature of turbine inlet is 90°C. Under the conditions of medium temperature heat source, in the Rankine cycle with regenerative heat and R141b as a working medium, the efficiency is about 26.59% when the temperature of the turbine inlet is 220°C and the pressure is 3.0 MPa. Under the conditions of a high-temperature heat source, in the reheat extraction steam Rankine cycle, the theoretical cycle efficiency can reach 34.32% when the temperature of the turbine inlet is 380°C, the pressure is 8 MPa, and the condensation temperature is 41.5°C. The studies can provide a fundamental basis for the design of solar thermal power generation systems with different heat source conditions.

Experimental study of erythritol – SiO2 phase change nanocapsules for medium temperature thermal storage

Erythritol holds significant potential for medium-temperature solar energy heat utilization. However, its phase change process is susceptible to issues such as leakage, and adhesion to the container. Nanoencapsulation is considered an effective method to mitigate these challenges. Until now, progress in erythritol nanocapsulation with excellent phase change properties has been limited. This study is dedicated to improving the phase change properties of erythritol nanoencapsulation. The authors innovatively synthesized erythritol nanocapsules with a silica shell using the Sol-gel method at ambient temperature. The nanocapsules were characterized to validate the encapsulation effect and to uncover the mechanism through which thermal cycling affects the thermal storage performance of nanocapsules. The results show that the nanocapsules are mostly fabricated at 46–70 nm in diameter, have a melting enthalpy of 294.3 J/g, and a thermal storage efficiency of 78.3 %. Continuous thermal cycling leads to aging degradation of erythritol and damage to the shell layer of the nanocapsules. These factors are the primary reasons for the reduction in the phase change enthalpy of nanocapsules. The nanocapsules studied in this research have broad applications in solar medium-temperature heat utilization, waste heat recovery, and various other fields.

Evaporation rates of water droplets with soluble and insoluble additives

The relevance. Caused by a wide practical use of water with typical soluble and insoluble additives in the following technologies. They are: thermal and fire purification of liquids, polydisperse fire extinguishing, combustion of waste-derived slurry fuels, cleaning of heat-loaded surfaces, creation of heat agents based on combustion products. Any change in liquid component composition leads to a change in its thermophysical properties, heating rates and phase transformations. So far, there is not enough experimental data on evaporation rates of water droplets with typical soluble and insoluble additives. The aim. Experimental determination of evaporation rate of water droplets with typical additives under various heating methods. The methods. To register sizes of moving droplets, optical registration methods based on a high-speed video camera were used. To register the temperature of combustion products, a measuring complex, consisting of an NI 9219 board and four chromel-alumel fast-response thermocouples, was used. The authors used four methods of droplet heating: in the flow of combustion products with the dominance of convective heat transfer, in a tubular muffle furnace with the dominance of radiative heat transfer, on a solid surface with the dominance of conductive heat transfer, and in a flame with the dominance of mixed (convective and radiative) heat transfer. The results. The authors have determined the ranges of change in evaporation rates of water droplets with typical (soluble and insoluble) additives for various heating methods with the dominance of convective, radiative, and conductive heat transfer. The effect of an additive type and concentration, heating method and heating medium temperature on of droplet evaporation characteristics was established.

Versatile closed-cell SiC/C foam for microwave absorption under medium temperature, icing and mechanical conditions

Microwave-absorbing materials (MAMs) for applications such as aircraft protective layers and ship side panels often need to take into account the actual working conditions. Conventional MAMs are often difficult to take into account special functional requirements such as mechanics, high temperature, de-icing, etc. Therefore, there is an urgent need to develop MAMs with harsh environmental adaptability and multifunctional requirements.Here, we utilize SiO2 microspheres and phenolic resin to prepare precursor foams, and through calcination, we have prepared closed-cell SiC/C foam composites with both microwave absorption properties, mechanical properties and thermal properties. The effective absorption bandwidth (EAB) of the samples is up to 6.9 GHz at a thickness of 7.3 mm, which can satisfy the perfect coverage of the C-band, and can be further broadened by structural design. The samples can satisfy the full coverage of the X-band at 200 °C. The samples have loaded properties, and the maximum compressive strength of the samples is up to 10.5 mm. The samples are loaded with a maximum compression strength of 8 MPa, support repeated medium-temperature heating, and maintain a compression performance of 5.7 MPa after heating. The samples have good thermal conductivity and Joule thermal properties, and the surface temperature can be rapidly increased under the condition of applying a heat source or applying a low pressure to cope with the cold and humid working conditions. The composites in this paper are simple to prepare and have the potential for mass production.

Preparation and thermal properties of a novel ternary molten salt/expanded graphite thermal storage material

In thermal energy storage, the use of phase change materials (PCM) is a very efficient energy storage method. In the field of medium temperature thermal storage, nitrate PCM have always been a research hotspot, but their relatively high melting point and relatively low latent heat of phase change severely limit their application in thermal energy storage. In this paper, LiNO3 and NaCl with higher latent heat value were selected to improve the thermal properties of nitrate. A novel ternary mixed molten salt of NaNO3-LiNO3-NaCl with high latent heat was prepared and studied. NaNO3-LiNO3-NaCl/EG composite phase change material (CPCM) was prepared by selecting expanded graphite (EG) with a large thermal conductivity as the carrier adsorption material for molten salt. The thermophysical properties, thermal stability, and heat transfer ability of PCM and CPCM were tested. The composition and microstructure of the materials were also characterized. The experimental results showed that compared with pure NaNO3, the phase change temperature of NaNO3-LiNO3-NaCl was reduced by 45.3 °C, and the latent heat of phase change was increased by 59.4 J/g. NaNO3, LiNO3, NaCl and EG had good compatibility, without chemical reaction between them. From the microscopic morphology of the composite material, it can be seen that the PCM was uniformly dispersed into the porous structure of EG without agglomeration. The ternary new molten salt had higher thermal decomposition temperature and better thermal stability. When the addition ratio of EG was 20 %, the thermal conductivity of the ternary molten salt increased from 1.350 to 5.017 W/m·K. EG greatly improved the heat transfer capacity of PCM. And the PCM added with EG still had a high latent heat of phase change. The results show that NaNO3-LiNO3-NaCl/EG has broad application prospects in the field of medium and high temperature heat storage.

Techno-Economic Assessment of CO2-Based Power to Heat to Power Systems for Industrial Applications

Abstract The industrial sector is a major source of wealth, producing about one-quarter of the global gross product. However, industry is also a major emitter of CO2 and it represents a key challenge toward achieving the worldwide CO2 emission reduction targets. Nowadays, about 22% of the overall energy demand is heating for the industrial sector, generating about 40% of the global CO2 emissions. Additionally, 30% of the final energy demand of the industrial sector is electricity. Solutions to decarbonize the industrial sector are needed. This work presents the techno-economic assessment of four different molten salts-based power-to-heat-to-heat and power solutions aiming at decarbonizing the industrial sector, requiring medium temperature heat. The systems are studied under different electric markets. Dispatch strategies and system sizing are identified to ensure optimal techno-economic performance. The main performance indicators investigated are the levelized cost of heat and electricity (LCoH and LCoE), the operational expenditure, and the attainable savings with respect to alternative business as usual solutions. The results highlight that the proposed system can be cost-competitive, particularly in markets characterized by low electricity prices and high daily price fluctuations, such as Finland. In these locations, LCoE as low as 100 €/MWh and LCoH lower than 55 €/MWh can be attained by the base system configuration. The introduction of high temperature heat pumps can provide further LCoH reduction of about 50%. This study sets the ground for further power-to-heat-to-heat and power techno-economic investigations addressing different industrial sectors and identifies main system design strategies.

Waste incineration and heat recovery hybridized with low-focus fresnel lens solar collectors for sustainable multi-generation; A thorough techno-economic-environmental analysis and optimization

Biomass, including municipal solid waste, and solar energy are two of the inevitable sources for future decarbonized energy systems. Fresnel lens thermal collectors using cheap micro-structured foils is an interesting emerging medium-temperature solar thermal design that might be of high practical value, provided that its fluctuating output is managed. This study proposes a hybrid solar-waste solution using this type of collector for multi-generation via an Organic Rankine Cycle. The cycle is specially designed for supplying low-grade heat, power, and industrial heat (which is a very critical sector to be decarbonized) taking advantage of the generated stable solar-waste medium-temperature heat at zero emission level. To achieve this optimal design, the article conducts a thorough energy-exergy-economic-environment (4E) analysis of the system and employs the non-dominated sorting genetic algorithm (NSGA II) for the optimizations. A benchmarking analysis is also conducted to show the importance of industrial heat supply in this cycle. The results show that this hybridization, owing to the cheap and flexible heat delivery of the waste incinerator as well as the low cost of the solar collectors, is very effective for efficient and cheap multi-generation. Especially for industrial heat supply, the competitive levelized cost of energy (LCOE) of 23.96 €/MWh is obtained, which is way lower than today's achievable costs in the industry.

Synthesis and Characterization of Doped Magnesium Hydroxide for Medium Heat Storage Application.

The amount of waste heat generated annually in the UK exceeds the total annual electricity demand. Hence, it is crucial to effectively harness all available sources of waste heat based on their varying temperatures. Through suitable technologies, a substantial portion of this waste heat has the potential to be recovered for reutilization. Thermochemical energy storage (TCES) provides the best opportunities to recover waste heat at various temperatures for long-term storage and application. The potential of TCES with magnesium hydroxide, Mg(OH)2, has been established, but it has a relatively high dehydration temperature, thus limiting its potential for medium-temperature heat storage applications, which account for a vast proportion of industrial waste heat. To this end, samples of doped Mg(OH)2 with varying proportions (5, 10, 15, and 20 wt%) of potassium nitrate (KNO3) have been developed and characterized for evaluation. The results showed that the Mg(OH)2 sample with 5 wt% KNO3 achieved the best outcome and was able to lower the dehydration temperature of the pure Mg(OH)2 from about 317 °C to 293 °C with an increase in the energy storage capacity from 1246 J/g to 1317 J/g. It also showed a monodisperse surface topology and thermal stability in the non-isothermal test conducted on the sample and therefore appears to have the potential for medium heat storage applications ranging from 293 °C to 400 °C.

Optimized core design and shield analysis of a medium temperature heat pipe cooled reactor

Medium Temperature heat pipe cooled Reactor (MTR) is a new reactor concept proposed by Li et al. in (2022). Low enriched uranium zirconium hydride fuel and mercury heat pipe are introduced in MTR. The unique advantages of MTR have been verified (Li et al., 2022) and it is considered as a potential candidate for energy supply in decentralized markets. In this work, an optimized MTR core design is proposed with detailed neutronic analysis and evaluation on mercury heat pipe, reflector and control rod arrangement, further increasing the economic efficiency and mobility of MTR. Heat transfer limit of the improved heat pipe model is further increased, contributing to a great reduction on core volume. Reflector material and thickness are analyzed in detail for mass minimization. Core physics characteristics are analyzed for four control rod arrangement schemes. The control mechanism is further simplified with only 9 control rods involved in the normal regulation of the core. Core lifetime is far more than 10 years. High inherent safety of the core is ensured. Besides, preliminary design of the shielding system is also carried out. A shieling layer of 60 cm LiH and 20 cm Pb can reduce the total dose to less than 40 % of the design limits. The total mass of the optimized core is greatly reduced and its specific power is increased by 60 % compared with that of the previous design.

Expanded Vermiculite/D-Mannitol as Shape-Stable Phase Change Material for Medium Temperature Heat Storage.

Aiming to promote the application of D-mannitol in the field of phase change thermal storage, obstacles, including low thermal storage efficiency and high supercooling, should be properly disposed of. The adoption of adaptable and low-cost supporting materials to make shape-stable phase change materials (ss-PCMs) affordable is a primary solution to solve the above shortcomings. In this study, high-performance ss-PCM for effective medium-temperature heat storage was prepared using expanded vermiculite as the support for D-mannitol preservation. Among the three candidates that treated the raw vermiculite by dilute acid, calcination, and microwave heating, the calcinated expanded vermiculite (CV) was characterized as the most suitable one. After impregnating D-mannitol into the CV carrier by vacuum, a melting enthalpy of 205.1 J/g and a crystallization enthalpy of 174.1 J/g were achieved by the as-received CV/D-mannitol ss-PCM. Additionally, the supercooling of the ss-PCM was reduced to 45.6 °C. The novel CV/D-mannitol ss-PCM also exhibited excellent reusability and stability. All the findings indicate that the abundant and inexpensive CV exhibited great potential as the supporting material for D-mannitol-based ss-PCMs, which allow effective waste heat recovery and temperature regulation.

Phase transition characteristics and supercooling suppression of erythritol with organic salts as nucleating agents

The main aim of this paper is to mitigate the supercooling of erythritol using organic salts as nucleating agents. The pure erythritol exhibits significant volume effects and a strong supercooling tendency. When the aspect ratio of the ET is small, a metastable phase transition plateau at 105 °C can be observed, and then, the metastable crystal slowly transforms into a stable crystal. Experimental results reveal that calcium pimelate (CaPi) has a positive influence on the supercooling elimination of erythritol. The 1 % CaPi/erythritol composite phase change material (CPCM) melts at 118 °C and solidifies at 109 °C with the latent heat of 344.86 J/g and 281.8 J/g, respectively. Due to the improved crystallization kinetics, the supercooling phenomenon measured by T-history method is basically eliminated. The melting heat is >300 J/g and the change of phase change temperature is less after 50 cycles. In order to simulate the real environment, the CPCM cools down by room temperature in air, and the chemical stability is good. The thermal conductivity of 1 % CaPi/ET increases by 23.2 %. In total, the CaPi/erythritol CPCM is a new candidate to be used in waste heat recovery, solar energy medium temperature heat collection and other fields.