Apparent Specific Heat Research Articles

Mathematical modeling of apparent specific heat capacity of channel catfish with different microwave heating time

AbstractChannel catfish fillets with different microwave heating times were evaluated by differential scanning calorimetry and low‐field nuclear magnetic resonance to build suitable modeling of apparent specific heat capacity (Cp) ranging from −60 to 90°C (except the obvious phase change region from −20 to 20°C). The content of bound water (Wb), immobilized water (Wi), and free water (Wf) were weighted and calculated. According to non‐linear fitting of experimental data, the obtained empirical equation of Cp, temperature (T), Wb, Wi, and Wf of samples was:. The equation was in good correlation (R2 > 0.95) with the experiment data and could provide a basis for improvement of processing parameters.

Some problems related to thermophysical properties of selected barrel steels

The paper discusses selected issues related to the thermophysical properties of selected barrel steels, which the authors have been dealing with over the last few years, i.e. 38HMJ (1.8509), 30HN2MFA, X37CrMoV5-l hot-work tool steel (1.2343), DUPLEX (1.4462) and MARAGING 350 (1.6355). In some of them, i.e. in the X37CrMoV5-1 hot work tool steel, 38HMJ, 30HN2MFA, a ferrite-austenite phase transition occurs, which causes shrinkage of the material. During a series of shots, multiple shrinkage of material degrades the barrel channel and deteriorates the ballistic parameters of the cannon barrel. Another problem concerns the apparent specific heat that we get from the DSC measurement and the dependence of the specific heat on temperature in the form that we use for the numerical simulations. The point is that the phase transition effect should not be taken into account twice, i.e. in the thermal diffusivity characteristics and in the specific heat characteristics. For all selected steels the thermophysical properties, i.e. thermal diffusivity, thermal conductivity, specific heat and thermal expansion, were obtained in a wide range of temperature, so they can be used as input data for numerical simulations.

Fluorinated graphene and its catalytic performance for AP pyrolysis: the promotion of F doping

We reported an experimental and theoretical study on the promotion role of F doping in the improved catalytic performance of fluorinated graphene(F-GO) for ammonium perchlorate (AP) pyrolysis. F-GO was prepared by using graphite oxide (GO) as carbon sources and CF3COOH as fluorinating agent. Compared with other samples, the F-GO-180 with the highest F doping amounts, more C-F semi-ionic and C-F covalent bond amounts exhibit superior catalytic performance, as 10 wt% of catalyst added in AP, the exothermic peak temperature proceeded in just one step was even lower than the HTD peak temperature for pure AP and the released apparent specific heat of the thermal decomposition of AP catalyzed by F-GO-180 is 4261.2 J/g, which is almost sevenfold of that of pure AP (603.5 J/g). The doping of F atoms in graphene increased surface defects and the content of C-F semi-ionic and C-F covalent bond amounts of F-GO, which provided more active sites during the thermal decomposition of AP. The molecular simulation calculation results further confirmed that the F doping could react with the defect structure of graphene to form more C-F semi-ionic and C-F covalent bond, which could act as catalytic active sites and facilitate the electron transfer ability of the graphene to promote the formation of free radicals in the reaction.

Self-assembly of MXene-decorated stearic acid/ionic liquid phase change material emulsion for effective photo-thermal conversion and storage

As a typical latent functionally thermal fluid with large energy storage capacity and good liquidity, phase change material emulsion (PCME) plays a broad and important role in solar energy utilization. However, the high-temperature instability and supercooling problems of PCME limit its practical application. The ionic liquid (IL)-based PCME allows for the possibility of being used as a heat transfer fluid (HTF) under more extreme temperature conditions. In this work, stearic acid (SA)/IL PCME, prepared by one-step self-assembly of MXene nanosheets at the SA/IL interface, can effectively absorb and convert solar energy into thermal energy. Furthermore, MXene-decorated SA/IL PCMEs have good high-temperature stability, little supercooling degree (0.9–3.1 °C), and large energy storage capacity. The maximum apparent specific heat capacity and average absorbance of the MXene-decorated SA/IL PCME are 4.5 and 303.1 times higher than those of IL, respectively. Under 2 sun irradiation, the 0.05–20 wt% MXene-decorated SA/IL PCME achieves high photo-thermal conversion efficiencies (91.3% at 68.9 °C, 39.4% at 115.1 °C) due to its large energy storage capacity and excellent optical absorption property. The simple interfacial self-assembly provides a promising strategy to prepare high-performance SA/IL PCME used as a novel HTF for medium-temperature solar energy utilization systems.

Fast differential scanning calorimetry to mimic additive manufacturing processing: specific heat capacity analysis of aluminium alloys

Eutectic AlSi12, commonly used in casting and in additive manufacturing, is investigated with Fast Differential Scanning Calorimetry to determine the impact of different cooling rates from the liquid state upon the apparent specific heat capacity on subsequent heating. A heat flow correction strategy is developed and refined for the reliable and precise measurement of sample heat flow using chip sensors and assessed by the evaluation of results on pure (99.999%) aluminium. That strategy is then applied to the study of the AlSi12 eutectic alloy, and rate-dependent perturbations in the measured apparent specific heat capacity are discussed in terms of Si supersaturation and precipitation. Several cooling rates were implemented from − 100 to − 30,000 K s−1, and subsequent heating ranged from + 1000 to + 30,000 K s−1. After rapid cooling, a drop in AlSi12 apparent specific heat capacity is found on heating above ~ 400 °C; even at rates of + 10,000 K s−1, a result which has high relevance in metal additive manufacturing where similarly fast temperature cycles are involved. The Literature data, temperature modulated DSC and CALPHAD simulations on the heat capacity of AlSi12 are used to provide comparative context to the results from Fast Differential Scanning Calorimetry.

Catalytic performances of fluorine-doped graphene/Pb composite for thermal decomposition of ammonium perchlorate

Fluorine-doped graphene supported PbO (F-rGO/PbO) composite was prepared through a facile water bath method to study an improvement strategy for its catalytic performance in thermal decomposition of ammonium perchlorate (AP). The characterization results showed that the PbO with the size of 20 ∼ 30 nm are highly dispersed on the surface of F-doped graphene (F-rGO). Compared with other samples, the F-rGO/PbO exhibited superior catalytic performance, as 3 wt% of catalyst added in AP, the peak temperature for HTD reduced by 124°C, and the peak temperature for LTD increased by 8°C. The released apparent specific heat of the thermal decomposition of AP catalyzed by F-rGO/PbO (3603.7 J/g) is five times of that of pure AP (603.5 J/g). The doping of F atoms in graphene increased BET surface areas of the F-rGO carrier and enhanced the content of hydroxyl groups on the surface of graphene, which improved the thermal decomposition rate of AP. While the highly dispersed PbO NPs further increased BET surface areas of F-rGO/PbO to provide more active sites during the thermal decomposition of AP.

Evaluation of building integrated with phase change material considering of ASHRAE classification using seasonal and annual analysis

Considering the energy demand (ED) of 2.9×1010 and of 2.9×1010 MWh in the period between 2010 and 2020, China is one of the largest energy consumers when the world total ED in this period was equal to 14×1010 and 15.46×1010 MWh. By concentrating on the building sector, paraffin-based phase change materials (PCMs) are used to reduce ED associated with air conditioning. For building walls with a thermal resistance of 1.056 m2.KW and a thickness of 21.7 cm, paraffin C18 with a melting temperature of 22–27°C was selected and added as a layer to all external walls of the building at thicknesses of 5, 10 and 15 cm. The Fourier equation for walls, the energy equation modified with the apparent specific heat method was developed to PCM enclosures to specify the temperature of the building transiently to determine its energy exchange across boundaries. According to the classification provided by ASHRAE, four areas in the first (very hot), second (hot), third (warm) and fourth (mixed) groups were selected and the effect of paraffin C18 on ED related to temperature regulation was discussed. In all four areas, paraffin C18 had an amazing effect. At a thickness of 5 cm for area-based ASHRAE types of 1, 2, 3 and 4, ED throughout the year fell sharply by 82.6%, 77.4%, 61.8% and 58.3%, respectively.

Simulation Study on Burning Test of Solid Propellant Based on Apparent Specific Heat Capacity

This document In the process of propellant heat transfer, the specific heat capacity is an important thermodynamic parameter, and temperature is an important factor affecting the specific heat capacity. In this paper, the initial specific heat capacity of HTPB propellant and its components was measured by DSC, and the specific heat capacity value was modified based on the synchronous weight loss curve, and the variation law of specific heat capacity of propellant and its components with temperature increase was obtained. The modified variable specific heat capacity is used to simulate the burning experiment of solid propellant, and the macroscopic curve is compared with the experimental curve. The results show that the absolute error between the simulated ignition delay time and ignition temperature and the experimental results is less than 10%, which indicates that this method provides the key technical parameters for evaluating the weight loss material of propellant, and provides an important parameter basis for designing the heat dissipation mechanism of new propellant.

Method for estimating change over time of the amount of heat stored in a semi-infinite phase-change material with a broad phase-change-temperature range

In this paper, equations are proposed that can predict the change over time of the amount of heat stored in a semi-infinite phase-change material (PCM) that has a broad phase-change-temperature range and apparent specific heat that can be approximated by a Gaussian distribution. The proposed equations can be applied under the condition that the initial temperature distribution is uniform below Tc-3σ and the surface temperature is maintained warmer than Tc+3σ. Here, Tc is the central temperature of the apparent specific heat when the apparent specific heat is approximated by a Gaussian distribution and σ is the standard deviation. The change over time of the amount of sensible heat in the semi-infinite PCM is approximately expressed using equations obtained by integrating the temperature distributions. In addition, the distribution of the latent heat is approximated from the temperature distribution, and the change over time of the amount of latent heat in the semi-infinite PCM is derived by integrating the distribution of the latent heat. Therefore, the change over time of the total amount of heat in a semi-infinite PCM is expressed as the sum of the change over time of the amounts of sensible heat and latent heat in the semi-infinite PCM.

PCM, nano/microencapsulation and slurries: A review of fundamentals, categories, fabrication, numerical models and applications

Sustainable energy is among the ever-increasing concerns in modern society. In this regard, thermal energy storage (TES) working based on latent heat has shown great potential by using phase change materials (PCM) with high heat capacity. However, PCM-TES has several challenges, such as material dispersion, possible chemical reactions with the environment and low thermal conductivity. Embedding PCM in a shell or porous network known as encapsulated PCM (EPCM) in both micro and nano sizes is proposed as a promising solution for these issues. In this study, a state-of-art review of PCM fundamentals, nano/micro EPCM, PCM slurries, coating materials, selection criteria, available fabrication methods, numerical models for latent heat simulation and prominent recent advances is presented. The review has addressed both experimental and numerical studies in detail by providing comparison tables and first of their kind figures. Based on the reviewed articles, chemical encapsulation methods, especially in-situ polymerization, provide a better particle size range and distribution with smooth surfaces, while they cause considerable environmental issues. Moreover, Paraffin wax is the most widely used core material mainly because of its affordability, while inorganic PCM and eutectics are suitable for high-temperature applications and refrigeration, respectively. Among available latent heat simulation models enthalpy-porous and apparent specific heat, that provide capturing solid–liquid interface and ease of use, respectively, are the highly used techniques in different industrial applications. Also, the important subjects and research gaps are detected, and suggestions for future investigations are provided.

Phase Change Dispersion Made by Condensation-Emulsification.

Cooling processes require heat transfer fluids with high specific heat capacity. For cooling processes below 0 °C, water has to be diluted with organic liquids to prevent freezing, with the undesired effect of reduced specific heat capacity. Phase change dispersions, PCDs, consist of a phase change material, PCM, being dispersed in a continuous phase. This allows for using the PCD as heat transfer fluid with a very high apparent specific heat capacity within a specified, limited temperature range. So far, the PCMs being reported in the literature are paraffins, fatty acids, or esters and are used for isothermal cooling applications between +4 and +50 °C. They are manufactured by high shear equipment like rotor-stator systems. A recently published method to produce emulsions by the direct condensation of the dispersed phase into the emulsifier-containing continuous phase is applied on this PCD. n-Decane is used as PCM, and the melting temperature is −30 °C. The achieved apparent specific heat capacity lies above 15 kJ/kg·K, more than 3 times the value of water. This paper presents experimental methods and data, formulation details, and thermophysical and rheological properties of such new PCD. Food conservation or isothermal cooling of lithium-ion batteries is a potential application for the presented method. The properties of the developed PCD were determined, and the successful application of such a PCD at −30 °C has been demonstrated.

Zeolite Imidazolate Frameworks-67 Precursor to Fabricate a Highly Active Cobalt-Embedded N-Doped Porous Graphitized Carbon Catalyst for the Thermal Decomposition of Ammonium Perchlorate.

The more apparent specific heat release at a lower high-temperature decomposition (HTD) temperature of ammonium perchlorate (AP) poses a challenge for the development of highly active catalysts. In this work, a well-designed cobalt-embedded N-doped porous graphitized carbon (Co@NC) catalyst is obtained by high-temperature calcination of a zeolite imidazolate frameworks-67 precursor, in which the cobalt catalytic active center realizes effective nanoscale dispersion; meanwhile, the cobalt and N-doped porous graphitized carbon can release considerable heat after oxidation, and the cobalt oxides have an excellent catalytic effect on reducing the HTD temperature of AP. The catalytic activity of Co@NC was tested by a differential thermal analytical method. The results indicated that the HTD peak of AP was significantly decreased by 100.5 °C, the apparent activation energy of the HTD reaction of AP was reduced by 82.0 kJ mol–1, and the heat release compared with pure AP increased 2.9 times. On teh basis of these findings, Co@NC is expected to be one of the best candidate materials for AP thermal decomposition.

Study on the apparent specific heat of sugar alcohol slurries

Sugar alcohols are used as heat storage materials, having a high latent heat. Their melting points are suitable for the recovery and reuse of unused heat at medium/low temperatures. A sugar alcohol slurry is a heat transfer medium in which solid sugar alcohol particles are dispersed in an aqueous solution that can efficiently transport heat through pipes to where there is heat demand. In this study, the apparent specific heat of sugar alcohol slurries was investigated to estimate the heat storage amount. Erythritol and mannitol were used as the sugar alcohols. The apparent specific heat was measured experimentally, and a model of the apparent specific heat of the slurry is proposed. The enthalpy difference between the solid and liquid sugar alcohol owing to freezing-point depression was considered in the model. The results showed that apparent specific heat increased with temperature and peaked 3–5°C below the saturation temperature. The maximum value of apparent specific heat of the slurry increased with initial concentration. The experimental and calculated values were compared to validate the model. The apparent specific heat values calculated with the model showed good agreement with the experimental values and freezing-point depression had a large effect on the apparent specific heat of the sugar alcohol slurries. The proposed model is valuable to design heat transport and storage systems using sugar alcohol slurries.

Sensitivity analysis of the frozen soil nonlinear latent heat and its precise transformation method

SUMMARY Latent heat of soil water phase transition is an important parameter affecting the prediction of the temperature field in a frozen soil. With the nonlinear change of unfrozen water content in freezing soil, the latent heat appears nonlinearly in a frozen soil. To evaluate the influence of the estimation of phase quantity and phase change interval on the formation of the temperature field in a frozen soil, the thermal parameters at different temperatures are measured, and a soil freezing model test is carried out. Meanwhile, based on the evolutionary trend of the unfrozen water content, a precise method of transforming the latent heat of phase change into specific heat and a segment processing method of latent heat in a frozen soil are proposed. Also, these methods are used in the ABAQUS to simulate the temperature of the soil freezing model. The sensitivity of the estimation of phase quantity and phase change interval on the formation of the temperature field in a frozen soil is analysed based on the numerical calculation values and model test values. The results show that the estimation accuracy of phase change interval greatly affects the prediction accuracy of the temperature field in the warm temperature stage, and the method of transforming latent heat into apparent specific heat can improve the prediction accuracy of the temperature field.

Comprehensive Mathematical Model for Freezing Time Prediction of Finite Object

Frozen food sees a continuous increase in consumption thanks to the capability to preserve the organoleptic properties and, at the same time, to increase the shelf-life of the food itself. Therefore, a proper design of the freezing process is crucial and is strictly related to an accurate evaluation of freezing time because this establishes the minimum residence time of the product in a continuous freezer. For this reason, several mathematical models have been proposed and investigated for predicting the freezing time, starting from empirical models (lower accuracy and computational time) up to computational fluid dynamics simulation (higher accuracy and computational time). An excellent compromise between accuracy and computational effort seems to be a model that combines empirical laws for property evaluation and heat diffusion equation solved in one dimension. This model can numerically be solved using the method of lines in which spatial derivatives are discretized by the finite difference method and the resulting system of ordinary differential equations is integrated using an appropriate solver. This work aimed to fill some gaps to develop a comprehensive and more accurate model for freezing time prediction. Indeed, the key idea is to validate a model that could be used to optimize the refrigeration process for energy-saving and be the base for a design of experiment in case of lack of experimental data. The newly developed model includes the evaluation of freezing time for finite food shapes because, in some cases, it is not possible to assume a characteristic direction for heat flux. The property of unfrozen and frozen food (e.g. density, thermal conductivity, apparent specific heat, etc.) are evaluated basing on the principal constituent of food (e.g. water, fiber, protein, etc.), while heat transfer coefficient is evaluated using empirical equations, depending on adimensional numbers. In this way, it is possible to be flexible and not strictly related to the evaluation of the properties of food for each different case. The proposed model was validated with different sets of experimental data related to beef and strawberry pulp freezing. For these cases, the R2 index is equal to 0.982 and 0.996 respectively, showing a good agreement between experimental and predicted data. Finally, a case study of spinach cubes freezing was provided to show the potentiality of the novel model.

Microencapsulated Phase Change Material Suspension for Cold Start of PEMFC.

We added microencapsulated phase change materials (MPCMs) into the homemade antifreeze fluid to take advantage of the latent heat of phase change materials, and explored the possibility of solving the cold start problem of proton exchange membrane fuel cells (PEMFC) with variable specific heat capacity antifreeze. The physical and chemical properties of the MPCMs and their suspensions were tested, and a PEMFC platform for cold start with a thermal management system was established to compare the exothermic performance of MPCS and commercial antifreeze fluid. According to the output voltage, temperature and polarization curves before and after cold start, the MPCMs has a stronger heat transfer capacity than the commercial antifreeze fluid, and the addition of MPCMs can transform the latent heat generated during the phase transition into apparent specific heat capacity, leading to a better solution to the problem of PEMFC cold start.

Performance enhancement of a photovoltaic module using phase change material nanoemulsion as a novel cooling fluid

Maintaining a suitable temperature for the photovoltaic (PV) module is of great significance but a challenge. Herein, a low-supercooling phase change material (PCM) nanoemulsion was developed as a promising coolant for use in the PV module thermal management system. OP35E was used as the paraffinic PCM and the phase change characteristics and thermophysical properties of the as-prepared PCM nanoemulsions were investigated. It is shown that OP35E-nanoemulsions possess a melting point of roughly 34 °C and ignorable supercooling. The apparent specific heats of low-supercooling OP35E-nanoemulsions are 2.29–3.29 times that of water at the phase transition range, and its viscosities is slightly higher than that of water. Furthermore, the thermal management performance of water and OP35E-nanoemulsions on PV modules was evaluated. Compared with water, the PV module temperature further reduced by 5.3% when employing 20 wt% OP35E-nanoemulsion. More importantly, using 10 wt% and 20 wt% OP35E-nanoemulsions only required less than 50% of the pumping power consumption of the water-cooling system to reduce the PV module temperature to the same. On the contrary, owing to the lower apparent specific heat caused by the futile latent heat, the OP35E-nanoemulsion with large supercooling exhibited the worst thermal management performance with the highest PV module temperature and pumping power consumption, and lowest output power. Therefore, the outstanding characteristics and better cooling performance than water of the low-supercooling nanoemulsions make them show great potential in the PV module thermal management system as a novel kind of heat transfer fluids with improved specific heat.

Influence of Hemp Shives Size on Hygro-Thermal and Mechanical Properties of a Hemp-Lime Composite.

Different fractions of hemp shives are used in the mixtures of the hemp–lime composite. The market offers shives of different granulation. It depends on the type of industrial hemp and on the capabilities of decortication machines. The aim of the research presented in the article is to check differences in the mechanical and hygro-thermal properties of composites with different shives fractions. The research part of the paper presents the preparation method and investigation on hemp–lime composites. Apparent density, total porosity, thermal conductivity, capillary uptake, vapor permeability, specific heat, mass absorptivity, flexural and compressive strength were examined. The results confirm that the shives fraction influences the individual properties of the composites. Hemp–lime composites with fine shives are characterized by higher water absorption, thermal conductivity, mechanical strength, vapor permeability as well as lower capillary-lifting capacity and specific heat than composites with thick shives.

Highly active catalysts based on 3D hierarchically ordered porous carbon with entrapped Fe2O3 nanoparticles for the thermal decomposition of ammonium perchlorate

Highly active catalyst with excellent ability to reduce the high-temperature decomposition (HTD) temperature and increase the apparent specific heat releases of ammonium perchlorate (AP) is an urgent requirement for the development of composite solid propellants. To this end, three-dimensional hierarchically ordered porous carbon (3D HOPC)/Fe2O3 composite scaffolds with high BET surface area (964–1697 m2/g) and large pore volume (1.40–2.36 cm3/g) are synthesized for higher catalytic activity. The entrapment of Fe2O3 nanoparticles (3.8–10.6 nm) inside 3D HOPC ensures their high dispersion and stability during the catalysis, and their size and content are readily tunable by adjusting the iron source concentration. The catalytic activity of HOPC/Fe2O3 composite scaffolds is investigated through synthesizing AP/HOPC/Fe2O3 nanocomposites, in which AP nanocrystals are homogeneously confined. Owing to the synergistic effect between 3D HOPC and Fe2O3 nanoparticles, HOPC/Fe2O3 composite scaffolds exhibit outstanding catalytic activity for AP thermal decomposition in decreasing the HTD peak temperature from 440.9 to 280.5 °C, lowering the activation energy from 176.4 to 132.2 kJ/mol, and increasing the heat release from 371 to 2114 J/g. This work constructs a highly active catalyst configuration by entrapping nano transition metal oxides inside carbon scaffolds, which has broad application prospects in AP-based composite solid propellants.

Processing spent coffee ground powders for renewable energy generation: Mechanical dewatering and thermal drying

Mechanical dewatering and thermal techniques were evaluated as pre-treatment steps to reduce the water content of spent coffee ground (SCG) powders to thermal conversion. An exploratory evaluation of the fluid dynamic patterns in fluidization of wet SCG powders showed that stable fluidized regimes were achieved with powders of moisture levels under 50 %. Mechanical dewatering was effective to reduce the powder moisture content to 45 %. Adding vibration enhanced the powder feed rate in the drying bed, even for powders with moisture levels that lead to negligible cohesiveness. Using a dimensionless vibration number Γ = 4 with different vibration amplitudes (A = 0.015 and 0.003 m) resulted in different dynamic behaviors and influenced the solids feeding rate but did not affect the mean Sauter diameter of the elutriated powder. Thermal drying at Γ = 4 and A = 0.015 m allowed a steady and continuous operating regime for powder production. Under these vibration parameters, the optimum condition concerning moisture content (22 % w.b.) and mean particle size (0.37 mm) was predicted to occur at 70 °C, and U/Umf = 6. The dry powder was thermally characterized and confirmed the feasibility of using this residue in pyrolysis and combustion processes. The parameters of the reaction kinetic model and the apparent specific heat were obtained.