Latent Heat Of Phase Transition Research Articles

Thermal reliability and corrosion characteristics of an organic phase change materials for solar space heating applications

The increasing interest in solar thermal energy storage necessitates the identification of new latent heat based phase change materials (PCMs). Testing the reliability and corrosion of newly identified PCMs upon repeated thermal charging and discharging cycles helps to evaluate the long term feasibility of latent heat storage system. Phenyl acetic acid (PAA) is an organic PCM with phase transition temperature of 75–80 °C and latent heat of 152 J/g. In this present work the thermal reliability on thermo-physical properties and corrosive nature of phenyl acetic acid is studied for 2000 accelerated thermal cycles. The experimental result shows that phase transition temperature and latent heat of fusion of PCM varies only ±1–3% and also has less corrosive nature to aluminium and stainless steel than copper metal containers throughout the thermal cycles. This study also comprises of experimental investigation on thermal performance of solar air heater (SAH) with built-in latent heat thermal energy storage. The solar air heater with PCM has outlet air temperature higher than ambient by 2–13 °C for 2.5 h and 1–8 °C for 2 h after solar hours at the mass flow rate of 30 and 45 kg/hr.m2 respectively. Therefore the newly identified phenyl acetic acid is a promising PCM for solar space heating applications due to good heat storage properties, long term thermal reliability and less corrosive nature.

Preparation and Thermal Features of Composite Paraffin Room Temperature Phase Change Mortar

Abstract To enhance the thermal storage capacity of building envelopes and reduce the energy consumption associated with construction, a composite paraffin room temperature phase change ceramisite for a building envelope was developed. Based on a single factor test method, 52# paraffin and liquid paraffin were heated and melted together to prepare the composite phase change material, which was infiltrated into the ceramisite by vacuum adsorption. The ceramisite adsorbed with paraffin was encapsulated using acrylic emulsion, epoxy resin, or cement paste. The sand in the traditional ceramisite was replaced with the phase change ceramisite to prepare the phase change energy storage mortar for the building application. Using mercury porosimetry, differential scanning calorimetry, and thermal conductivity detection, the phase transition temperature, phase transition latent heat, encapsulation effectiveness, adsorption rate, coefficient of thermal conductivity, and specific heat capacity of the mortar were measured for the phase change ceramisite. The results indicated the following: the phase transition temperature of the composite paraffin could accommodate the range of indoor and outdoor thermal environments (18°C–35°C); a large amount of paraffin could be adsorbed into the ceramisite interior by vacuum adsorption, with the adsorption rate being higher than 58 %; with incorporation of the phase change ceramisite, the coefficient of thermal conductivity of the mortar gradually decreased and the specific heat capacity gradually increased; and when the ceramisite ratio reached 50 %, the coefficient of thermal conductivity decreased by 51.47 % and the specific heat capacity increased by 80.6 %, indicating favorable heat storage performance.

Preparation and thermophysical properties of graphene nanoplatelets-octadecane phase change composite materials

<sec> Latent heat storage mainly uses the latent heat of phase change material (PCM) to realize thermal energy storage and utilization, which is the most important thermal energy storage method at present. However, most of PCMs have the disadvantage of low thermal conductivity, which greatly restricts the thermal response rate and system efficiency of the thermal energy storage system. With the development of nanotechnology, it is expected to improve the thermal conductivity of traditional PCMs by adding high thermal conductivity nanoparticles. In this paper, a novel two-dimensional carbon nanomaterial, graphene is selected as an additive for PCM.</sec><sec> In this paper, graphene nanoplatelets-octadecane phase change composite materials are prepared with a two-step method and the mass fractions of graphene nanoplatelets are 0%, 0.5%, 1%, 1.5%, and 2%. Their microstructures, morphologies and thermophysical properties are characterized by scanning electron microscopy (SEM), infrared spectroscopy (IR), differential scanning calorimetry (DSC), and thermal conductivity analysis. The effects of the addition quantity of graphene nanoplatelets on the phase transition temperature, enthalpy, specific heat capacity, thermal conductivity and thermal stability of the composite PCM are compared. The experimental results show that the dispersion stability of the graphene nanoplatelets in the composite system is greatly improved by the addition of dispersant, and the system does not produce obvious agglomeration nor sedimentation after multiple phase transformation cycles. The graphene nanoplatelets still maintain good lamellar structure and homogeneous dispersion in the n-octadecane matrix, and no chemical reaction occurs in the composite process. Comparing with the n-octadecane, the melting point of the composite phase change material decreases slightly, and the freezing point increases slightly. With the increase of graphene nanoplatelets, the latent heat value of graphene nanoplatelets-octadecane composite phase change material decreases gradually. For the composite phase change material with 2.0 wt.% graphene nanoplatelets, the melting enthalpy and solidified enthalpy are reduced by 6.01% and 7.35%, respectively. When the mass fractions of graphene nanoplatelets are 0.5%, 1%, 1.5%, and 2%, the thermal conductivity values of phase change composite materials are nearly 32.4%, 77.4%, 83.1%, and 89.4% higher than the thermal conductivity value of pure octadecane, respectively. Comparing with the significant increase in thermal conductivity, the addition of graphene nanoplatelets has little effect on the phase transition temperature and latent heat of PCM, and still exhibits the good heat storage performance. </sec>

The Provision of Conditions for the Formation of a High-Quality Weld During Butt Welding of Polyethylene Pipes at Low Ambient Temperature

Welding of polyethylene (PE) pipes for gas pipelines is recommended to be performed at ambient air (AA) temperature from minus 15 to plus 45 °C. The present work proposes a mathematical model of the thermal process for butt-welding of PE pipes, which takes into account the latent heat of phase transitions in the temperature range. Correspondence of the model to the real thermal process is confirmed by comparing the experimental and calculated temperatures. At a temperature from the permissible temperature range in the heat affected zone (HAZ), a cooling rate is provided in the optimum interval, which ensures the formation of the structure of the welded material that provide sufficient strength. Thus, for welding PE pipes at AA temperatures below the normative it is sufficient to establish the cooling rate in the optimum interval in the HAZ while maintaining the other technological parameters of welding. Mathematical modelling shows that the necessary cooling rate in the HAZ is obtained by preheating the ends of the welded pipes to the permissible temperature along the outreach length equal to the fivefold thickness of the pipe, melting in regular mode and cooling the welded joint in the heat-insulating structure of the calculated size.

Fabrication of Dodecanol/Diatomite Shape-Stabilized PCM and Its Utilization in Interior Plaster

A novel shape-stabilized phase change material (PCM) is prepared as an energy-efficient solution aimed at the improvement of thermal stability of building materials. Dodecanol having a suitable temperature interval of phase transition and high latent heat is selected as the PCM medium. Diatomite powder used as the PCM core material is impregnated by dodecanol using the vacuum impregnation method. The particle size distribution of the prepared PCM is analyzed at first to find the possible agglomeration of particles. A detailed characterization of mutual material compatibility is performed by scanning electron microscopy and Fourier transform infrared spectroscopy. The melting and solidification temperatures of the developed PCM are found at 23.3 °C and 21.2 °C, respectively; the measurement of corresponding latent heats shows 71.4 J·g−1 and 72.6 J·g−1. The incorporation of the novel PCM into cement–lime plaster does not significantly affect its phase change behavior and confirms its good potential for applications in building practice.

Experimental study on random heat transfer of phase change heat storage device

In the study of the heat conduction of phase change materials, due to the inherent properties, the deviation of the measured data and the processing technology of the phase change material, the uncertainty of the parameters of the material properties and geometric properties of the phase change materials exist inevitably. But at the present stage, there are very few experimental researches content of uncertain heat transfer in phase change thermal storage devices. The purpose of this paper is to study the uncertain heat transfer process of phase change heat transfer experimentally. The influence of latent heat of phase transition on the heat transfer process is mainly analyzed. The latent heat of different phase transitions is transformed into internal heat sources, and simulated by electric heating. The thermal response of phase-change heat transfer is analyzed by constructing the electric heating quantity under different probability distribution and uncertainty. The experimental results show that when the uncertainty is the same as 1/7, the difference of the standard deviation between two mean values (560 W and 630 W) is not large. The standard deviation and the mean correlation of the experimental values are not significant under the same uncertainty.

Effect of Heating Rate on Latent Heat of Fusion of Waxy Crystals in Crude Oil

Crude-oil transportation requires a study of the latent heat of phase transitions and the melting parameters of solid paraffin in the oil. The latent heat of fusion and the effect of the heating rate on melting were measured for Daqing oilfield waxy oil using differential scanning calorimetry. The peak melting ranges of the waxes were determined. The results showed that the total latent heats at heating rate 5°C/min from —20°C to the end of melting were 3035 and 39.26 J/g for two crude-oil samples. The latent heat maximum temperatures were 24.5 and 25.5°C The maximum latent heat for both samples was attained at heating rate 1°C/min. The relative deviation for the other heating rates was less than 3%. It was shown that the heating rate affected the position of the latent heat peak. The peak temperature shifted from 24 to 28°C for one sample and from 25.5 to 28.0°C for the other as the heating rate increased from I to 15°C/min. The results of the present work could be useful for further research on the paraffin precipitation mechanism during transportation of crude oil.

MAGNETIC FIELD INFLUENCE ON THE CRYSTALLIZATION OF ALUMINIUM MELTS

Conscious management of metal crystallization processes in order to obtain a defined ingot microstructure is provided by using various physical fields. These fields affect the melt and change its internal state, and therefore its crystallization kinetics. The paper describes the thermodynamics and kinetics of aluminum crystallization when the melt is treated with magnetic field. A quite simple experimental setup is created to allow studying the magnetic field effect on molten aluminum or other metals and alloys. It consists of several main components: (1) electrical furnace; (2) water-cooled copper crucible combined with an electromagnetic coil; (3) mechanical device for rapid movement of the aluminum melt crucible; (4) system for melt temperature monitoring and control and (5) electronics for data recording and processing. It is experimentally proved that magnetic field changes the melt-crystal phase equilibrium temperature, latent heat of phase transition and temperature of melt supercooling at crystallization. It is shown that changes in these parameters reduce the radius of critical nuclei and increases the speed of their origin. Temperature-time relationship are obtained for the crystallization process. It is experimentally proved that aluminum melt treatment with magnetic field reduces the time of crystallization. The analysis of aluminum samples obtained under the influence of magnetic field has shown that their structure has more fine grains compared with untreated samples.

Energy Demand Reduction in Nearly Zero-Energy Buildings by Highly Efficient Aluminium Foam Heat Exchangers

The capability periodically to store and release the latent heat of phase transition during melting and solidification of Phase Change Materials (PCMs) has been currently the main subject of interest with regard to cost reduction efforts for cooling, heating of interiors and Domestic Hot Water (DHW) necessary for the operation and maintenance of adequate thermal comfort in new modern as well as old renovated residential buildings. The main principle of PCMs facilities to reduce significantly the energy consumption in the building industry of the future is based on the ability of thermo-active heat exchangers to absorb and later to dissipate into the surroundings excessive heat which can be easily obtained from renewable sources (e.g. solar energy, geothermal heat, etc.) directly in a building or in its immediate vicinity. Smart interior tiling and furnishing systems can provide high energy efficiency by stabilizing the room temperature at a level ensuring sufficient thermal comfort basically governed by the thermal conductivity and heat exchange area between ceiling (respectively also wall and floor if necessary) heat exchangers (radiators) and the heat storage medium in the form of PCMs. Unfortunately, most conventional building materials, e.g. aerated concrete, bricks, gypsum, ceramic tiles, etc. are particularly characterized by very low thermal conductivity, which disadvantages them to be used for these purposes. However, highly porous metallic material such as aluminium foam prepared by powder metallurgy [10, 11] is on the contrary excellently heat conductive, which predisposes it to be used for light-weight design of supporting structure of very energy efficient indoor as well as outdoor thermo-active heat exchangers for building industry of the future. This contribution points to the possibility to apply aluminium foam for both the novel innovative roofing system to cover pitched roofs and the interior ceiling panels, with the minimum energy demands for maintaining the sufficient thermal comfort in future nearly Zero-Energy Buildings (nZEBs).

A fully coupled thermo-hydro-mechanical model including the determination of coupling parameters for freezing rock

The freeze-thaw damage of rock is mainly induced by cycling loading of pore ice pressure and thermal stress under coupled thermo-hydro-mechanical (THM) condition at low temperature. The accuracy and correctness of coupled T-H-M model for freezing rock are controlled by critical parameters including unfrozen water content, ice pressure, permeability, and the equivalent thermal conductivity. The difference of THM coupling process between freezing rock and freezing soil is the evolution rule of those critical parameters, which change drastically with freezing temperature. The permeability is related to the unfrozen water content and high enough to be considered at the temperature above −5 °C. Combining numerical experiment with mixture theory, the equivalent thermal conductivity of freezing rock is also studied which is proved to be well expressed by exponential weighted mean model. Then the governing equations for THM coupling of freezing rock under low temperature are deduced based on energy conservation law, mass conservation law and the principle of static equilibrium considering water/ice phase transition. Those equations include the effects of seepage velocity and latent heat of phase transition on heat transfer, the influences of segragation potential and volume strain on water flow, and the impacts of temperature and pore water/ice pressure on frost heaving strain. Compared with a famous coupled THM laboratory test conducted by Neaupane and Yamabe, the proposed THM model has a good prediction of heat conductivity and frost heaving strain for freezing rock.

Micro/nanolithography of transparent thin films through laser-induced release of phase-transition latent-heat

Large-area micro/nanolithography of transparent thin films is critical for metasurface-based optical elements, where the feature size of micro/nanostructures is generally required to be submicrometer or even nanoscale. In this work, micro/nanolith`ography through laser-induced release of phase-transition latent-heat is proposed. AgInSbTe and ZnS-SiO2 are chosen as light absorption layer and transparent thin film layer, respectively. The theoretical simulation reveals that the release of phase-transition latent-heat of AgInSbTe can heat the ZnS-SiO2 thin film to above the temperature of structural change and form micro/nanopatterns, and the thermal threshold effect of AgInSbTe thin film can confine the pattern to submicrometer or even nanoscale. The micro/nanopatterns on ZnS-SiO2 thin films can be further etched into micro/nanostructures in hydrofluoric acid solution. Using a GaN-diode-based direct laser writing lithography system, the minimum lithographic linewidth can experimentally be as low as 120 nm, which is only about 1/7 the writing spot size. The edge of obtained lithographic structure is steep and the surface is also smooth, and arbitrary lithographic structures have also been fabricated. The laser-induced release of phase-transition latent-heat is a good pathway to micro/nanolithography of transparent thin films, and has potential application in the fabrication of metasurface-based optical element.

Design and performance evaluation of a multilayer fixed-bed binder-free desiccant dehumidifier for hybrid air-conditioning systems: Part II – Theoretical analysis

The interdependent physics involved in the transport, adsorption, and thermal phenomena within desiccant-based dehumidifiers makes the construction of theoretical models essential to investigate intrinsic mechanisms. In Part II of this series, a computational model is established that increases an understanding of transient mass and heat transfer phenomena in a multilayer fixed-bed binder-free desiccant dehumidifier (MFBDD). A two-dimensional (2D) model incorporating the principles of momentum, mass and heat conservation is constructed. A modification of Darcy’s law is employed to evaluate the frictional resistance due to the presence of Micro Sphere Gel (M. S. Gel) beads in the desiccant bed. In the study, the moisture adsorption characteristics of M. S. Gel are theoretically described by employing a Linear Driving Force (LDF) model and a modified Langmuir-Sips model (based on the local relative humidity RH) owing to the unique sigmoid-shape of its adsorption isotherm at various temperature levels. The energy conservation is considered to estimate phase transition latent heat because of the moisture adsorption and heat loss to surroundings through the metal frames at different process air conditions. The validity of the model is tested by comparing the theoretical predictions with experimental observations. The results indicate that the predicted adsorbed water within the MFBDD, dehumidification capacity, temperature increase, and pressure decrease based on the simulation are in quantitative agreement with the experimental results obtained in Part I. The experimentally observed transient translocation of maximum temperature inside the M. S. Gel bed is theoretically reproduced and analyzed.

Modelling for performance prediction of highly insulated buildings with different types of thermal mass

Thermal performances of two phase change materials (PCM) in the Toronto's Net-Zero Energy House are compared and contrasted with commonly available forms of thermal mass. TRNSYS simulations show that the use of thermal mass was found to contribute to energy savings of 10–15% when different types of thermal mass were mixed into the building envelope. The results exhibit that the performance of a novel solid-solid phase PCMs, recently developed by researchers at Dalhousie University and known as DalHSM-1, could be comparable to a commercially available PCM from BASF (Micronal) in the heating mode. The cooling mode performance revealed that DalHSM-1 provided lower energy savings when compared to Micronal, due to a lower phase transition temperature and latent heat. The impact of thermal mass on the occupant comfort was also investigated by considering the total number of hours where the temperature exceeded the heating set point of 21°C. The results showed that the total number of hours where the temperature exceeded 21°C could be reduced significantly with different types of thermal mass, thus contributing considerably to the comfort of the occupants.

On a phase transition for semitransparent materials in terms of the Stefan problem

The paper deals with justification of the formula for the latent heat of phase transition of the first kind, taking into account superheating and subcooling of the formed two-phase system, in application to the solution of Stefan problem in semitransparent materials.

ОБ УЧЕТЕ НЕЛИНЕЙНЫХ И СВЯЗАННЫХ ЭФФЕКТОВ ТЕПЛОВОЙ ЗАДАЧИ И ФАЗОВЫХ ПЕРЕХОДОВ ПРИ МОДЕЛИРОВАНИИ ТЕХНОЛОГИИ КОНТАКТНОГО ТЕРМОСИЛОВОГО ПОВЕРХНОСТНОГО УПРОЧНЕНИЯ МЕТАЛЛИЧЕСКИХ СПЛАВОВ

The article considers the problem setting of the coupled thermal-structural problem arising in the process of modelling the surface hardening using electromechanical treatment (EMT). A mathematical model is presented with respect to forming the structure of metallic alloys with EMT based on a joint analysis of the calculated data on the dynamics of temperature fields and continuous cooling transformation diagramby using the Ti6Al2V titanium alloy as an example. Kinetics of the martensitic transition during EMT is described using Koistinen-Marburger equation. An algorithm of solving the thermal problem based on the finite element method in the weak Galerkin form is given. The calculated area is approximated by Zienkiewicz type infinite elements. Based on a series of computational experiments, the influence of the magnitude of the time step on the accuracy of the problem solution was investigated. The significance of the considered coupled and nonlinear effects which are specific for high-speed high-temperature thermal processes are analyzed, e.g. the change of the thermophysical properties of the metal, latent heat of phase transitions, thermal radiation and dependence between the metal physical properties and temperature. Two methods are used to consider the effects aiming to solve the thermo-structural problems: a totally coupled non-linear problem using the direct iteration method of Picard in a combination with the relaxation formulae for the convergence acceleration; the quasilinear solution when the values of the nonlinear terms are calculated on the basis of the temperature distribution obtained in the previous time step. Based on the series of numerical experiments, we analyzed the unsteady temperature fields, as well as the distribution of structural domains after EMT in the titanium pseudo-alpha-alloys.

The evaluation of heat capacity and choice of materials for short-term storage of diurnal solar heat surplus in passive solar heating systems

The results of numerical studies aimed to evaluate the heat capacity of short-term phase change heat accumulators applied in passive solar heating systems (PSHS) with a three-layer energy active translucent enclosure (TE) are presented. An example is given of calculation of specific (per unit of TE surface area) weight of heat accumulator using dimethyl sulfoxide, (СН3)2SO, with melting temperature 18.6°C and latent heat of phase transition 173 kJ/kg, as the heat storage agent.

Bulk Crystallization of Supercooled Metal Films

The overwhelming majority of modern materials are knowingly produced by crystallization from melts. Leaving apart powder metallurgy and some other technologies, the mainstream is melting and homogenizing a charge followed by its transition to a solid state. In this case, technologies based on a method of ultrafast hardening from a liquid state, the key point of which is putting a substance into a deep metastable state with a further intense phase transition, are of particular importance. This allows producing amorphous, nanocrystalline, bioactive, and other promising materials widely used in modern industry and technologies, microelectronics, medicine, etc. In particular, they can be used as durable anti-corrosion coatings. Since the quality and physicochemical properties of these materials depend directly on their morphology, the skill in controlling this morphology is an effective way of producing materials with specified functional characteristics. This requires the ability to describe in detail the kinetics of phase transitions at all stages of the process. Like any other first-order phase transitions, crystallization occurs via fluctuation-induced nucleation and growth of centers of a new phase. Hence, the overall kinetics of such a process is determined by nucleation and the growth rate of nuclei. These quantities are related to a set of various thermodynamic and kinetic parameters that are important under specific conditions and primarily to a degree of metastability of the parent phase. The main problem here is finding the time dependence of the fraction of the crystalline phase and the size distribution of the nuclei. The kinetic theory of fluctuation-induced nucleation and crystal growth is elaborated pretty well, whereas the thermophysical aspects of this problem are poorly investigated. In particular, the effect of heat release at the phase transition on the rate of the process is insufficiently studied. Theoretical analysis of phase transition shows that for the most cases the process can be divided into two particular stages. The first one is the nucleation stage. The majority of new phase nuclei form during this particular stage. Nonlinear nature of nucleation expressed in strong dependence of nucleation rate from the degree of metastability. At the beginning of this stage the process is conditioned by the factors producing metastability, though the stage ends due to reduction in the degree of metastability. This reduction results from the transition of a portion of material from metastable phase to stable phase accompanied by release of latent heat of phase transition. Typically the portion of the new phase is relatively small at the moment of the end of nucleation stage. This is due to the fact that formation of even small portion of a new phase is enough for significant reduction in nucleation rate. The main part of initial phase transits to stable state during the subsequent growth of crystals already formed during nucleation stage. In studying the phase transition the nucleation stage attracts great interest, but it is a problem of great complexity. It involves thermodynamics of small systems, nucleation kinetics, knowing the growth mechanism in a wide range of parameters, correct accounting for effect that assembly of crystals has on metastability, etc. Combined with account for the factors producing metastability it all leads to challenging, nonlinear mathematical problem described by the system of integro-differential equations. At this time the complete solution of this problem is yet to be found. In current work nonequilibrium theory of bulk crystallization of melts rapidly quenched to deeply supercooled state is developed. This theory correctly takes into account the heat release due to phase transition. It is achieved by using the real temperature fields formed around crystals in kinetic equations. Limits of validity of theories using heat release obtained from global heat balance are estimated. Proposed theory allows to describe accurately the kinetics of crystal nucleation and growth in metastable liquid and to determine the microstructure of solidified material. Particular attention was paid to the mechanism of crystal growth in highly nonequilibrium conditions and with account taken of the shrinkage during solidification. The problem of solidification of a thin layer of metal melt brought into contact with a massive cold substrate is developed. Based on the amorphization conditions formulated, the thickness of the amorphous sublayer formed near substrate is determined. The suggested model of bulk crystallization of melt makes it possible to find the morphology of the solidified layer. The work is supported by RFBR (grant #15-08-04474).

Numerical simulation of temperature field distribution for laser sintering graphene reinforced nickel matrix nanocomposites

Transient temperature field distribution is important for quality control of laser sintering graphene (Gr) reinforced nickel matrix (Ni-Gr) nanocomposites and the optimization of sintering parameters. To date, it is difficult to measure the temperature field directly. Thus, numerical simulation was utilized to study the distribution and evolution of temperature field. Finite element models were employed to simulate the sintering process of Ni-Gr coatings on AISI 4140 steel. The temperature distribution, the depth of the melting pool, the width of metallurgical bonding and the parameter optimizing method for laser sintering were investigated. In order to verify simulation results, single-track experiments were performed with the same laser sintering parameters as simulation. Simulated results reveal that convection and radiation heat transfer, and the latent heat of phase transition play a major role in the sintering process. Simulation output is consistent with experiments under the same processing parameters. Based on simulation results, substrate melting depth, metallurgical bonding width and thermal accumulation effects can be predicted. Thus, according to these guidelines, the optimal laser sintering parameters can be decided.

Effect of water content on the phase transition temperature, latent heat and water uptake of PEG polymers acting as endothermal-hydroscopic materials

Both hydroscopic materials and phase change materials represent popular research topics. This paper proposes PEG polymers as endothermal-hydroscopic materials adjusting the temperature and humidity of an environment. A homogeneous PEG mixture with different water contents is prepared via a mutual diffusion methodology in a high-temperature environment. The as-prepared mixture is characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and isothermal adsorption. The XRD and SEM results indicate that the crystallinity decreases as the moisture content increases, and the primary particles disappear. According to the DSC results, both the phase transition temperature and latent heat exhibit a negative linear relationship with the water content. Isothermal adsorption curves indicate that water molecules uniformly dispersed in the polymer can optimize its microstructure, providing a mass transfer channel for water vapour. Additionally, PEG2000 exhibits the best endothermal-hydroscopic performance. The PEG2000 phase transition temperature and latent heat decrease by 6.7 °C and 28.9 J g−1, respectively, when a 10 % liquid is added to the polymer. The D-value (change value) is clearly lower than those of PEG4000 (10.9 °C and 36.9 J g−1) and PEG8000 (10.1 °C and 55.2 J g−1). In addition, the PEG2000 water uptake is 198 g kg−1 for 6 h.

ChemInform Abstract: Entropic Phase Transitions and Accompanying Anomalous Thermodynamics of Matter

Thermodynamic consequences of subdivision for all first-order phase transitions (PT) into enthalpy- and entropy-driven ones (H-PT and S-PT), proposed previously [arXiv:1403.8053], are under discussions. Key-value for proposed discrimination is main benefit (decreasing) in enthalpy or (nega)entropy in spontaneous phase decomposition, i.e. the sign of latent heat of PT and consequent slope of its P(T)-dependence. The main driving mechanism for many isostructural S-PT is the decay (delocalization) of some kind of bound complexes, e.g. atoms, molecules etc. Thermodynamic features of H-PT and S-PT differ significantly. Entropic PT are always the part of more general thermodynamic anomaly—domain where great number of usually positive second cross derivatives (e.g. Gruneisen parameter, thermal pressure coefficient etc.) became negative simultaneously. This domain is restricted (in the case of isostructural S-PT) by remarkable bound, where all mentioned second derivatives are equal to zero. Isostructural S-PT has more complicated topology of stable, metastable and unstable states and their boundaries—binodals and spinodals in comparison with ordinary enthalpic PTs. Two new thermodynamic objects accompany isostructural S-PT: (i) appearance of third (additional) region of metastable states with positive compressibility, isolated from the regions of stable states; (ii) appearance of new additional spinodal, topped with a new singular point, separating metastable and unstable states. These additional spinodal and singular point obey to relation (∂P/∂V)T = ∞. All thermodynamic anomalies of entropic PTs correspond to conclusive and transparent geometrical feature of such PTs: multilayered structure of thermodynamic surfaces for temperature, entropy and internal energy as pressure- density functions U(P, V), S(P, V) and T(P, V).