Volumetric Enthalpy Research Articles

Study of phase equilibria in a two-component system diphenyloxide <i>- n -</i> nonadecane

Using the Schroeder, UNIFAC and UNIFAC Dortmund methods, the fusibility diagram of the diphenyloxide – n –nonadecane system was calculated and it was shown that it belongs to the eutectic type. Individual substances and their mixtures were studied experimentally using a differential scanning microcalorimeter. On the DTA heating curve of the eutectic alloy, two endo-effects are noted, corresponding to the polymorphic transition of n–nonadecane and the melting of the eutectic. A comparison of the eutectic coordinates calculated by these methods with experimental data is presented. For a eutectic alloy, the specific enthalpy of fusion, molar values of entropy and enthalpy of fusion, volumetric specific enthalpy of fusion and density for standard conditions are calculated. The eutectic mixture can be recommended for use as a coolant, as well as the working fluid of a heat accumulator.

X-ray computed tomography analysis of calcium chloride hexahydrate solidification

Latent Thermal Energy Storages (LTESs) are receiving increasing interest, since they offer many advantages to the field of Thermal Energy Storages (TESs), such as a nearly isothermal solid–liquid phase transition and a high energy storage density. To boost the transition towards a climate-neutral future, a lot of work is surely needed on Phase Change Materials (PCMs) which are used inside LTESs. Salt hydrates, a particular class of PCMs, are very attractive in terms of cost and volumetric latent enthalpy but present drawbacks that still limit their effective deployment in real applications, such as supercooling and phase separation (or segregation). The current work assesses the suitability of X-ray Computed Tomography (XCT) as a novel technique in the field of LTESs to study the solidification of phase-change materials. In this study, calcium chloride hexahydrate (CaCl2·6H2O) is chosen as a representative PCM and the results derived are shown to be repeatable. For the first time, the direct measurement of the volumetric liquid fraction is correlated to temperature measurements allowing for the visualisation of supercooling and the validation of an enthalpy-porosity numerical model, which could be useful in the design of LTES. XCT methodology offers unmatchable features as compared to the other method to measure the volumetric liquid fraction. Given its accuracy and the rigorous protocol, it can be considered as a benchmark for new liquid fraction measurement technologies but it also permits to study how the different PCMs melt and solidify, giving new insights on the mechanisms at the basis of the most crucial challenges, among those: subcooling, segregation, and metastable phase change.

Latent Thermal Energy Storage System for Heat Recovery between 120 and 150 °C: Material Stability and Corrosion

Thermal energy represents more than half of the energy needs of European industry, but is still misspent in processes as waste heat, mostly between 100 and 200 °C. Waste heat recovery and reuse provide carbon-free heat and reduce production costs. The industrial sector is seeking affordable and rugged solutions that should adapt the heat recovery to heat demand. This study aims to identify suitable latent heat materials to reach that objective: the selected candidates should show good thermal performance that remains stable after aging and, in addition, be at a reasonable price. This paper details the selection process and aging results for two promising phase change materials (PCMs): adipic and sebacic acid. They showed, respectively, melting temperatures around 150 °C and 130 °C, degradation temperatures (mass lost higher than 1%) above 180 °C, and volumetric enthalpy of 95 and 75 kWh·m−3. They are both compatible with the stainless steel 316L while their operating temperature does not exceed 15 °C above the melting temperature, but they do not comply with the industrial recommendation for long-term use in contact with the steel P265GH (corrosion speed > 0.2 mm·year−1).

Mechanical and thermo-physical properties of heat and energy storage backfill based on MicroPCMs

Combining backfill mining with geothermal resource exploitation, geothermal extraction is achieved by using heat and energy storage functional backfill to achieve a win-win situation of mineral and geothermal co-mining. In this study, MicroPCMs were partially substituted for tailings to prepare phase change backfill material. The influence of different MicroPCMs contents (0, 5, 10, 15, 20 wt%) on the mechanical and thermophysical properties of backfill was investigated to determine the optimal MicroPCMs contents. The results showed that with the increase of MicroPCMs content, the strength exhibited a cliff-like drop at 5% followed by a gradual decline, as confirmed by the XTDIC full-field strain deformation measurement and analysis system. The thermal conductivity and thermal diffusivity decreased with the increase of MicroPCMs content, while the volumetric specific heat capacity and enthalpy showed an increasing trend. SEM scanning results indicated that MicroPCMs would fracture under mechanical action, and the fracture proportion increased with the increase in MicroPCMs content. The recommended MicroPCMs content was around 15 wt%, where the compressive strength, volumetric specific heat capacity, and enthalpy reached 5.2 MPa, 1.6 MJ/(m3·K) and 6.16 J/g, respectively. This study provides valuable insights into the influence of MicroPCMs on the strength and thermal properties of backfill materials.

PHASE EQUILIBRIUM IN TWO-COMPONENT SYSTEMS: DIPHENYL – N-GENEICOSAN AND DIPHENYL – N-TRICOSAN

The melting curves of the diphenyl – n-geneucosane and diphenyl – n-tricosane systems were calculated using the Schroeder equation and using the UNIFAC and UNIFAC Dortmund methods. The results obtained by calculation methods showed that both systems are eutectic. The use of a differential scanning microcalorimeter made it possible to experimentally confirm the presence of phase equilibrium in these alloys. Experimentally, for each system, individual substances and compositions within each of the studied systems were studied. Based on the data obtained, phase diagrams were constructed for two systems diphenyl – n-geneucosane and diphenyl – n-tricosane. In each system, at temperatures of 29.94 °C and 40.6 °C, polymorphic transformations are observed for n-geneicosane and n-tricosane, respectively, which coincide with the literature data. The UNIFAC Dortmund method for both systems showed the smallest deviation of the composition of the eutectic alloy from the experimental data at relatively close calculated values of the melting temperature of the eutectic with the UNIFAC method. These methods can be used to preliminary estimate the coordinates of eutectics in organic systems before planning an experiment. Calculations were made of the specific enthalpy of melting, molar values of entropy and enthalpy of melting, volumetric specific enthalpy of melting and density under standard conditions for each eutectic composition. The study of the fusibility of diphenyl – n-heneicosane and diphenyl – n-tricosane systems is important for understanding its physical properties and possibilities of application in various technological processes. Eutectic mixtures can be used as coolants and heat-storing substances. Eutectic melts of diphenyl – n-heneicosane and diphenyl – n-tricosane systems are safe to use.

PHASE EQUILIBRIUM STATES IN A TWO-COMPONENT DIPHENYL-n-NONADECANE SYSTEM

The melting curves of the diphenyl-n-nonadecane system were calculated using the Schroeder equation and using the UNIFAC and UNIFAC Dortmund methods. The calculation results showed that the diphenyl-n-nonadecane system is eutectic. The compositions experimentally studied by the method of differential thermal analysis and calculated by the indicated methods are not eutectic. Individual substances and 9 compositions within the studied system were experimentally studied using a differential scanning calorimeter. Based on the data obtained, a phase diagram was constructed, including one single-phase field above the liquidus curve and 4 two-phase fields – α-n-C19H40+(Ph)2, β-n-C19H40+(Ph)2, L+n-C19H40, L+(Ph)2. The predominant branch of the liquidus curve belongs to the more refractory component, diphenyl. In the solidus at a temperature of 18.7 °C, a polymorphic transformation α-n-C19H40 ⇆ β-n-C19H40 is noted, which coincides with the literature temperature data. The heating DTA curve of the eutectic alloy showed two endoeffects corresponding to the polymorphic transition of n-nonadecane and the melting of the eutectic. The calculation of the eutectic coordinates by the UNIFAC Dortmund method showed the smallest deviation in the composition of the eutectic alloy from the experimental data. For an alloy of eutectic composition, the specific enthalpy of melting, the molar values of the entropy and enthalpy of melting, the volumetric specific enthalpy of melting, and the density for standard conditions are determined. This two-component system was studied by low-temperature differential thermal analysis. The eutectic melt can be used in industry as a heat carrier. Also, the eutectic composition of the diphenyl-n-nonadecane system under study can be used as a working fluid of a heat accumulator. For citation: Kazakova A.I., Yakovlev I.G., Garkushin I.K. Phase equilibrium states in a two-component diphenyl-n-nonadecane system. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2023. V. 66. N 6. P. 46-53. DOI: 10.6060/ivkkt.20236606.6733.

Alternating one-phase and two-phase crystallization mechanisms in octahedral patchy colloids.

Colloidal systems possess unique features to investigate the governing principles behind liquid-to-solid transitions. The phase diagram and crystallization landscape of colloidal particles can be finely tuned by the range, number, and angular distribution of attractive interactions between the constituent particles. In this work, we present a computational study of colloidal patchy particles with high-symmetry bonding-six patches displaying octahedral symmetry-that can crystallize into distinct competing ordered phases: a cubic simple (CS) lattice, a body-centered cubic phase, and two face-centered cubic solids (orientationally ordered and disordered). We investigate the underlying mechanisms by which these competing crystals emerge from a disordered fluid at different pressures. Strikingly, we identify instances where the structure of the crystalline embryo corresponds to the stable solid, while in others, it corresponds to a metastable crystal whose nucleation is enabled by its lower interfacial free energy with the liquid. Moreover, we find the exceptional phenomenon that, due to a subtle balance between volumetric enthalpy and interfacial free energy, the CS phase nucleates via crystalline cubic nuclei rather than through spherical clusters, as the majority of crystal solids in nature. Finally, by examining growth beyond the nucleation stage, we uncover a series of alternating one-phase and two-phase crystallization mechanisms depending on whether or not the same phase that nucleates keeps growing. Taken together, we show that an octahedral distribution of attractive sites in colloidal particles results in an extremely rich crystallization landscape where subtle differences in pressure crucially determine the crystallizing polymorph.

Research on the novel Al–W alloy powder with high volumetric combustion enthalpy

Abstract Al–xW alloy powder (x = 10, 20, 30, 40, 50 wt.%) was prepared by thermite reduction method and gas atomization method. The phase identification, surface morphology, spatial phase structure, oxidation behavior and combustion performance of the alloy powder were investigated by XRD, SEM/EDS, DSC, DTA/TG and oxygen bomb tests, respectively. The results show that among Al–xW alloy powder, Al–20W alloy powder has the largest volumetric combustion enthalpy measured in an oxygen bomb calorimeter (83,440 ± 790 J/cm3), which is superior to pure Al powder. Al–20W alloy powder has good sphericity and exhibits a special spatial phase structure, in which the metastable Al/W intermetallic compound is distributed in the pure Al matrix. In the process of stabilization, metastable phase transforms into the stable Al12W and release energy. The study of thermal oxidation behavior shows that Al–20W alloy powder has excellent thermal oxidation activity and oxidation completeness in air. Al–20W alloy powder is almost completely oxidized in air at 1500 °C, and only Al2O3 is detected in the oxidation product. The oxidation product particles of Al–20W alloy powder at 1500 °C are in the shape of a hollow shell. The combustion of Al–20W alloy powder produces a large amount of gaseous combustion product WO3, which is beneficial to increase the pressure inside the solid-propellant rocket engine. In summary, Al–W alloy powder has excellent application prospects in the field of energetic materials such as solid propellants and explosives.

Design method for heating towers used in vapor-compression heat pump systems

Given that they are highly efficient in summer and frost-free in winter, heating tower heat pumps are evolving rapidly. However, lack of an appropriate design method of heating towers is complicating the design process and causing a mismatch between cooling and heating conditions. To address this problem, this study develops a total heat transfer model taking enthalpy difference as the driving force, then experiments are carried out to test the volumetric enthalpy transfer coefficients. Based on the model and the coefficients, a novel design method is proposed based on curves of required and available transfer units, involving four steps, namely: 1) determination of design conditions, 2) calculating tower thermal performance, 3) sizing x-y section of packing, 4) determination of air flow rate and packing size. Finally, a performance comparison and matching degree analysis of the designed tower are presented. The results show that the proposed design method is simple and clear by avoiding trial-and-error. The designed tower saves considerable power consumption of the tower fans and pumps and achieves good matching degree between its heating and cooling capacities by setting reasonable approaches and ranges. The model, the coefficients and the design method can be used accurately by researchers/designers.

3D finite element enthalpy method for analysis of phytosanitary treatment of wood by microwave

Circulations of some wood products are identified as one of the causes that have facilitated the introduction of pathogens and insects in several countries of the world. This biological invasion has caused the destruction of plant species, causing significant economic and ecological losses for many regions of the world. To this end, the World Trade Organization (WTO) has established, through the International Plant Protection Convention (IPPC), the “ISPM 15” standard on the use of microwaves for phytosanitary treatment. The goal of this work is to quantify numerically the minimum time required for the phytosanitary treatment of three Eastern Canadian wood species, trembling aspen (Populus tremuloides Michx.), white birch (Betula papyrifera) and sugar maple (Acer saccharum). The nonlinear heat conduction problem is solved using three-dimensional volumetric specific enthalpy based on finite element analysis. The incident microwaves are supposed plane wave. The dielectric and thermophysical properties are a function of temperature, moisture content and structural orientation. It is worth noting that these investigations were performed at the frequency of 2466 MHz, temperatures from − 20 to 60 °C, and moisture content of 131%. This study focused on a sample cube of wood 22 mm thick and a pallet (100 mm × 50 mm × 22 mm).

Preparation, Microstructure and Thermal Property of ZrAl3/Al Composite Fuels

AbstractZrAl3/Al composite fuels (Al‐xZr, x=10, 20, 30, 40, 50, 53 wt.%) were prepared by the non‐consumable arc‐melting technique and close‐coupled gas‐atomization. In order to study the effects of the zirconium content and the oxygen partial pressure on the thermal properties of composite fuels, X‐ray diffraction, scanning electron microscopy, TG‐DTA and DSC were used to characterize the composite fuels, respectively. The result shows that the addition of zirconium leads to the formation of a special structure inside the powder, promoting the oxidation of ZrAl3/Al composite fuels. Besides, non‐selective oxidation of ZrAl3 played an important role in promoting the oxidation process. The oxygen bomb experiment was conducted to evaluate the combustion performance of ZrAl3/Al composite fuels. Oxygen bomb experiments show that the gravimetric combustion enthalpy of the composite fuels decreases linearly with the increase of zirconium content, and increases with the increase of oxygen partial pressure. However, the volumetric combustion enthalpy decreases first and then increases with the increase of zirconium content, and shows a general upward trend when the partial pressure of oxygen reaches 2.5 MPa or more. The pressure curve indicates that the Al‐53Zr composite fuels have the maximum pressure propagation rate (dP/dt)max (which characterizes the maximum flame propagation rate and higher energy releasing rates) in the prepared series of composite fuels. The study demonstrates a complete combustion of ZrAl3/Al composite fuels under high pressure. ZrAl3/Al composite fuels could be considered as a very promising energetic additive in the field of new‐energetic material.

Thermodynamics of Deep Supercritical Geothermal Systems

The study of water is very important in science and for many industrial applications, such as steam turbines, high pressure devices and supercritical cycles. In aquifers, hydrocarbon reservoirs, geothermal systems and atmosphere-ocean interactions, water is one of the most important fluids in action. Specifically, geothermal reservoirs contain water in a wide thermodynamic range. The temperature gradient between the core and the surface of the Earth results from a continuous flow of natural heat, embracing all kind of thermal energy resources that can be classified in terms of their profoundness, going from shallow depths (102 m), to medium depths (103 m), and to even deeper depths (104 m), reaching the immense temperatures of molten rocks. Warm aquifers below oil reservoirs, hot dry rock, submarine reservoirs, and engineered geothermal reservoirs are examples of profound geothermal systems. The fluids in very deep reservoirs can be at supercritical thermodynamic conditions, at more than 400°C and pressures larger than 220 bar, having higher fluid density, more volumetric enthalpy and heat available. They could provide twenty times as much power, per unit fluid volume, as the normal geothermal fluids used today. During the span of human life, deep geothermal energy represents practically an infinite potential. The aim of this paper is to provide a computational description of water thermodynamics at supercritical conditions showing the power it represents. The water properties are defined in terms of the Helmholtz potential or free energy, and are calculated for single phase, liquid, vapor and supercritical, as functions of density or pressure, and temperature. These properties are internal energy, enthalpy, entropy, specific isochoric heat, specific isobaric heat, compressibility, bulk modulus, Joule coefficient, speed of sound, thermal expansivity and thermal diffusivity.

Self-Propagating Heat Synthetic Reactivity of Fine Aluminum Particles via Spontaneously Coated Nickel Layer

Aluminum powders are known to provide outstanding volumetric exothermic enthalpy energy during thermal oxidation. However, the amount of energy released tends to be limited by the dense surface oxide (Al2O3) layer of the powder. Hence, a prerequisite for improving the reactivity of passivated Al particles is to remove the Al2O3 film from the surface. Considering that the self-propagating high-temperature synthesis (SHS) reaction of Ni and Al can generate additional exothermic heat in Al powder, Ni can be considered as a promising alternative to the surface oxide layer. Here, we report oxide-layer-free fine Al particles with a characteristic Ni/Al interface, where a Ni layer replaces the Al2O3 film. The microstructure of the synthesized powder consists of a 200-nm-thick Ni layer homogeneously coated on the Al surface, which has nanosized craters caused by the geometrical removal of Al2O3. Thermal analysis and in-situ heating transmission electron microscopy (TEM) results clearly show that active interdiffusion of atoms through the Ni/Al interface results in the formation of intermetallic compounds to provide additional exothermic energy, compared to the result for simply mixing Ni and Al powders. Hence, these findings provide new routes for the design and application of reactive metallic particles using the SHS reaction.

Uncertainty Analysis of Melting and Resolidification of Gold Film Irradiated by Nano- to Femtosecond Lasers Using Stochastic Method

A sample-based stochastic model is presented to investigate the effects of uncertainties of various input parameters, including laser fluence, laser pulse duration, thermal conductivity constants for electron, and electron–lattice coupling factor, on solid–liquid phase change of gold film under nano- to femtosecond laser irradiation. Rapid melting and resolidification of a free-standing gold film subject to nano- to femtosecond laser are simulated using a two-temperature model incorporated with the interfacial tracking method. The interfacial velocity and temperature are obtained by solving the energy equation in terms of volumetric enthalpy for control volume (CV). The convergence of variance (COV) is used to characterize the variability of the input parameters, and the interquartile range (IQR) is used to calculate the uncertainty of the output parameters. The IQR analysis shows that the laser fluence and the electron–lattice coupling factor have the strongest influences on the interfacial location, velocity, and temperatures.

A finite element model of thermal evolution in laser micro sintering

Laser micro sintering (LMS) is a promising technique for micro-additive manufacturing. During LMS of metallic powder, the material property variation and the heat input energy profile are important to understand physical phenomena involved. This paper presents a finite element temperature distribution profile in LMS of nickel powder on 304 stainless steel substrate. The simulation considered the transition of powder-to-dense sub-model which involves effective thermal conductivity, volumetric enthalpy, and absorptance change; and a moving volumetric Gaussian distribution heat source sub-model. It is found that, for a specified cross section, the mechanism of preheating the nickel powder changes for the heat source from previous laser-irradiated substrate region to molten nickel as the laser beam approaches, while the center of molten pool slice is slightly shifted toward the reverse direction of laser scanning when the laser moves away due to the thermal accumulation effect. Simulated sintered widths showed very good agreement with experimental measurement, and relative prediction errors are below 16 % within the process window.

Determination of the eutectic concentration between Mn(NO3)2·6H2O and NaNO3 using the DSC peak sharpness method

While inorganic eutectic phase change materials (PCM) present the advantage of a high volumetric melting enthalpy and a high thermal stability under repeated heating/cooling cycles, there is a lack of known materials in the temperature range of 20–24 °C, interesting for building applications. The DSC peak sharpness method is employed to determine the eutectic concentration between Mn(NO3)2·6H2O and NaNO3, which is 96.5 mass% Mn(NO3)2·6H2O and 3.5 mass% NaNO3. Thereby, the DSC peak sharpness method is demonstrated to yield the same result independently of the two chosen heating/cooling rates of 0.5 and 2 K min−1. The eutectic PCM has an onset temperature of 22.1 °C and a melting enthalpy of (126 ± 6) J g−1. Even though the same eutectic concentration is obtained for both heating/cooling rates, the heating/cooling rate of 0.5 K min−1 reveals that the melting peak of Mn(NO3)2·6H2O is composed of two overlapping melting peaks. The second melting peak supposedly corresponds to the eutectic between Mn(NO3)2·6H2O and Mn(NO3)2·4H2O, which melts at a slightly lower temperature than Mn(NO3)2·6H2O (difference of −0.6 °C). This assumption is in accordance with the water content of the purchased Mn(NO3)2·6H2O measured via Karl Fischer titration being (0.66 ± 0.2) mass% too low.

Passivation and Stabilization of Aluminum Nanoparticles for Energetic Materials

In aircraft applications, fuel is used not only as a propellant but also as a coolant and improving both the thermal conductivity and combustion enthalpy of the fuel is beneficial in these applications. These properties can be enhanced by dispersing aluminum nanoparticles into the fuel; however, the nanoparticles require stabilization from agglomeration and passivation from oxidation in order for these benefits to be realized in aircraft applications. To provide this passivation and stabilization, aluminum nanoparticles were encapsulated with a coating by the plasma enhanced chemical vapor deposition (PE‐CVD) method from toluene precursors. The thermal conductivity, combustion and ignition properties, and stability of the nanoparticles dispersed in RP‐2 fuel were subsequently evaluated. In addition, the effect of dispersing aluminum nanoparticles in RP‐2 fuel on the erosion rate of fuel nozzles was evaluated. The dispersion of PE‐CVD coated aluminum nanoparticles at a concentration of 3.0% by volume exhibited a 17.7% and 0.9% increase in thermal conductivity and volumetric enthalpy of combustion, respectively, compared to the baseline RP‐2 fuel. Additionally, particle size analysis (PSA) of the PE‐CVD coated aluminum nanofuel exhibited retention of particle size over a five‐month storage period and erosion testing of a 1 mm stainless steel nozzle exhibited a negligible 1% change in discharge coefficient after 100 hours of testing.

3D numerical analysis of the thermal effect and dielectric anisotropy on thawing frozen wood using microwave energy

This paper addresses the thawing of frozen wood by microwave. The effect of thermal and dielectric anisotropy on thawing wood is considered. The nonlinear heat conduction problem involving phase changes such as wood freezing is solved using three-dimensional volumetric specific enthalpy based on finite-element analysis. The dielectric and thermophysical properties are a function of temperature, moisture content and structural orientation. The specific volumetric enthalpy approach is validated by analytical, numerical and experimental testing. Finally, we studied the thermal effect and dielectric anisotropy on thawing frozen sugar maple wood (Acer saccharum) at 2466 MHz.

Investigation of pinacone hexahydrate as phase change material for thermal energy storage around 45 °C

Phase change materials (PCM) with a transition temperature around 45°C can be used in various applications, e.g. as intermediate storages for heat pumps in space heating systems, for the thermal protection of battery systems or to increase the efficiency of dishwashers by preheating water. At that temperature level, typical PCMs are either salt hydrates or organic materials like paraffins and fatty acids. Salt hydrates usually provide higher volumetric enthalpy changes, whereas for organic PCMs, corrosion is generally less problematic. Organic hydrates combine the advantages of salt hydrates and organic PCMs. For the diol pinacone, the existence of a hexahydrate with a melting temperature around 45°C and a high melting enthalpy of about 300J/g was reported in literature. To investigate the applicability of pinacone hexahydrate as a PCM, we conducted a detailed calorimetric characterisation of its phase change. DSC and T-History measurements were performed to determine the enthalpy curves for melting and crystallisation. We measured an enthalpy change of (340±17)J/g ((332±17)kJ/l) between 32°C and 47°C, which is a suitable operating temperature range. In addition, enthalpy changes within 15K around the phase change of PCMs with similar melting temperatures (docosane, lauric acid, zinc nitrate tetrahydrate) were measured and confirmed the promising properties of pinacone hexahydrate for compact thermal energy storage.

3D Numerical Simulation of Thawing Frozen Wood Using Microwave Energy: Frequency Effect on the Applicability of the Beer–Lambert Law

In this article, the frequency effect on the applicability of Beer–Lambert's law for thawing frozen wood using the microwave energy was analyzed. To this end, we use Maxwell's equations to determine the absorbed power and characterize the critical slab thickness L crit of three Canadian eastern wood species: trembling aspen (Populus tremuloides Michx), yellow birch (Betula alleghaniensis), and sugar maple (Acer saccharum). The critical thickness L crit above which the Beer–Lambert law is valid is estimated as a hyperbolic function in the frequency domain: L crit = m/f n (f is the frequency of microwave radiation; m and n are adjustment constants). The nonlinear heat conduction problem involving phase changes such as wood freezing is solved by a three-dimensional volumetric specific enthalpy-based finite element method. The dielectric and thermophysical properties are functions of temperature and moisture content. The specific volumetric enthalpy approach is validated by experimental testing. For instance, we studied the frequency effect on the thawing of frozen trembling aspen wood.