Specific Heat Coefficient Research Articles

Raspberry pulp pasteurization: Computational fluid dynamics modeling and experimental validation of color and bioactive compound retention

AbstractThis work evaluated the heat transfer, fluid flow, and different reactions that occur during the pasteurization of raspberry pulp. The pulp was packed in glass jars and thermal processing was conducted by immersion in a water bath. The process was evaluated by multiphysics modeling, with the aim of determining the temperature distribution, flow pattern, the slowest heating zone (SHZ) location, the microbial inactivation, and the quality changes taking place during processing. In order to simulate the process accurately, a model was developed using experimentally measured product and heat transfer properties (density, thermal expansion, specific heat, thermal conductivity, apparent viscosity, and convective heat transfer coefficient) and kinetics of thermal degradation of quality parameters (color, anthocyanin, and ascorbic acid). The model was successfully validated against experimental measurements of both temperature and quality losses. After validation, the model was used to design and evaluate equivalent thermal processing conditions. Improved processes were identified that minimized the changes of color and the bioactive compounds, while maintaining product safety and stability.Practical ApplicationsThermal processing of raspberries may induce several physicochemical changes that impair their sensorial properties, and may reduce the content of nutrients and bioactive compounds. Hence, the design and optimization of heat treatments is a key tool to guarantee safety while, at the same time, minimizing detrimental side effects which involve a loss of quality. In this investigation, we assessed the actual thermo‐physical properties of raspberry pulp and the system heat transfer coefficients. Then, we developed a CFD model to predict the temperature and velocity transient profiles, the location of the SHZ, and the quality changes occurring in raspberry pulp during pasteurization. The findings of this study could be useful to food processors for optimizing pasteurization conditions in order to obtain safe and high‐quality raspberry pulp preserves, as well as for reducing processing energy requirements.

Modified stability analysis of double‐diffusive convection in viscoelastic fluid layer saturating porous media

AbstractThe present analysis mathematically investigates the thermohaline convection problem in viscoelastic fluid layer saturating porous media by utilizing the modified Boussinesq approximation. By performing linear stability analysis, the Darcy–Rayleigh numbers for stationary and oscillatory modes of convection are derived. The effects of different parameters describing the problem are studied numerically. In nonlinear stability analysis, the heat and mass transfer rates in the form of Nusselt and Sherwood numbers, respectively, are obtained for oscillatory convection using the derived Ginzburg–Landau equation. From the results, it is observed that overstability is the preferred mode of instability in linear stability. It is found that in linear double‐diffusive convection problems, the stress relaxation imparts a destabilizing effect whereas the strain retardation time, the coefficient of specific heat variation due to temperature, and the concentration gradient have a stabilizing effect on the system's stability. The numerical values of heat and mass transfer rates varied with the coefficient of specific heat showing that the heat transport decreases while the mass transport increases. Also, the stress relaxation time, the concentration gradient, and the gravity modulation's amplitude increase while the strain retardation time decreases the heat and mass transfer rates. The wavelength of oscillations remains unaltered with the variation of specific heat variation due to temperature. The modulation frequency does not affect the heat/mass transfer rate; though, the wavelength of oscillations decreases with increasing frequency.

Comparative studies on superconductivity in Cr3Ru compounds with bcc and A15 structures

Chromium (Cr) is a transition metal element with 3d orbital electrons. In most compounds containing Cr, due to the correlation effect, twofold features, namely localization and itinerancy are expected. The localization gives rise to a magnetic moment, while the latter exhibits as the effective coherent weight for conductivity. Here we report the physical properties of Cr3Ru compounds with body-centered cubic (bcc) and A15 structures by using multiple experimental tools. The resistivity measurements show sharp superconducting transitions at = 2.77 K and = 3.37 K for the bcc and A15 structures, respectively. A high residual resistivity exists in both phases. Magnetization measurements also show rather narrow superconducting transitions, with a clear hump feature in the intermediate temperature region (about 150 K), which may be ascribed to the remaining antiferromagnetic spin fluctuations. A pronounced second peak effect has been observed in magnetization hysteresis loops in the superconducting state only for samples with bcc structure. The specific heat coefficient reveals a clear jump at critical temperatures (). We find that s-wave gaps can be adopted to fit the low temperature specific heat data of both samples yielding ratios of about 3.6, indicating a moderate pairing strength. Interestingly, the Wilson ratios are 3.81 and 3.62 for the bcc and A15 phases, suggesting a moderate correlation effect of conducting electrons in the normal state. Besides, for samples with A15 structure, another specific heat anomaly occurs at about 0.85 K and is sensitive to magnetic fields. In addition, by applying high pressures, both systems will exhibit an enhancement of with a rate of about 0.019 K GPa−1 and 0.013 K GPa−1 for the bcc and A15 phases, respectively. Our combinatory results point to unusual behavior of both superconducting and normal states in these two Cr based alloys.

Explorations on properties of ε′ phase and new crystalline phase of Fe3Ge alloy under high pressures

We calculated the lattice dynamics, elasticity, electron spin polarizability P(EF), and electron specific heat coefficient γ of the L12-Fe3Ge crystalline alloy under high pressure using first-principles method based on density functional theory. By comparing the lattice dynamics and elasticity of the ferromagnetic and non-magnetic systems, it can be found that the spontaneous magnetization of the system induces the dynamic stability of the system at low pressure (less than 6 GPa). Furthermore, the magnetostriction induced by the spontaneous magnetization enhances the elastic modulus of the system. With the increase of pressure, in the pressure range of 130-290 GPa where the spin magnetic moment of the system decreases sharply, the elastic modulus exhibits an abnormal behavior, which leads to double peaks in Poisson's ratio v and Pugh's ratio B/G, correspondingly, double valleys appear in shear modulus G, Young's modulus E and Debye temperature ΘD, which are associated with dynamic instability in the 130-290 GPa. Finally, for the phonon spectrum at 260 GPa with a significant imaginary frequency, the metastable orthogonal Fmmm structure is obtained using the soft mode phase transition theory. After comparing the enthalpy differences with different structures, it is found that the ferromagnetic Fmmm structure is a metastable phase, which is dynamic stable at 0 GPa and 260 GPa.

Investigating the limits of superconductivity in UTe2

Spin-triplet bulk superconductors are a promising route to topological superconductivity, and UTe2 is a recently discovered contender. The superconducting properties of UTe2, however, vary substantially as a function of the synthetic route, and even nonsuperconducting single crystals have been reported. To understand the driving mechanism suppressing superconductivity, we investigate UTe2 single crystals grown close to the nonsuperconducting boundary (growth temperature ∼710 ∘C) through a combination of thermodynamic and x-ray diffraction measurements. Specific heat measurements reveal a sharp decrease in the superconducting volume and a concomitant increase in the residual specific heat coefficient close to the nonsuperconducting boundary. Notably, these crystals are inhomogeneous and show an apparent double transition in specific heat measurements, similar to samples grown at much higher temperatures (∼1000 ∘C). Our single crystal x-ray diffraction measurements reveal that there are two important tuning parameters: uranium vacancies and the atomic displacement along the c axis, which shows a twofold increase in samples with a reduced superconducting volume. Our results highlight the key role of local disorder along the uranium-uranium dimers and suggest that the apparent double superconducting transition is more likely to emerge close to the superconducting limits of UTe2.

Nanofluid applications in pressurized water reactors: A review

The main purpose of this paper was to review nanofluid applications as the main coolant of pressurized water reactors (PWRs) with both solid and dual-cooled annular fuel. In this regard, first, theoretical and experimental models for calculating thermo-physical properties of nanofluids including density, specific heat, thermal conductivity, viscosity, and heat transfer coefficient were reviewed and the effects of different variables such as particle volume concentration, particle size, shape, and temperature on these parameters were determined. In the following, research related to neutronic, thermal-hydraulic, and safety investigations of nanofluids as the main coolant of PWRs with solid and dual-cooled annular fuel were reviewed. Corresponding methods, codes, and results were discussed and compared. Based on studies, it was concluded that nanofluids' effects on key neutronic parameters (keff, neutron flux and radial and axial power peaking factor) depend on the used nanoparticle, volume concentration, and nanoparticle deposition on the cladding, while nanofluids can increase heat transfer, critical heat flux, and minimum departure from nuclear boiling ratio (MDNBR). Also, it was found that nanofluids with low volume concentration in reactor core with dual-cooled annular fuel can replicate the same advantages. Furthermore, using dual-cooled annular fuel instead of solid fuel increases MDNBR margin and reduces coolant flow which leads to a more compact design of the reactor core and a reduction of capital cost. Finally, incoming challenges and future works were presented.

Inheritance factor on the physical properties in metallic glasses

Material genetic engineering can significantly accelerate the development of new materials. As an important topic in material science and condensed matter physics, the development of metallic glasses (MGs) with specific properties has largely been the result of trial and error since their discovery in 1960. Yet, property design based on the physical parameters of constituent elements of MGs remains a huge challenge owing to the lack of an understanding of the property inheritance from constitute elements to the resultant alloys. In this work, we report the inherent relationships of the yield strength σ y, Young’s modulus E, and shear Modulus G with the valence electron density. More importantly, we reveal that the electronic density of states (EDOSs) at the Fermi surface (E F) is an inheritance factor for the physical properties of MGs. The physical properties of MGs are inherited from the specific element with the largest coefficient of electronic specific heat (γi ), which dominates the value of the EDOS at E F. This work not only contributes to the understanding of property inheritances but also guides the design of novel MGs with specific properties based on material genetic engineering.

Insulator–metal phase transition in novel Sr2OsTiO6 double perovskite via doping - Computational FP study

The structural, electronic, bonding, magnetic, optical and thermal properties of parent perovskite namely SrTiO3 (STO) and novel double perovskite namely Sr2OsTiO6 (SOTO) compounds are analyzed by using Full Potential (FP) - Linearized Augmented Plane Wave (LAPW) method through WIEN2K code. The optimized lattice parameter, bond length, bond angles, Fermi energy (EF), Density of States (DOS) at Fermi Level (FL), electronic specific heat coefficient are computed for the optimized STO and SOTO compounds. At ambient condition SrTiO3 is behaving as a semiconductor with a band gap 1.966 eV and via doping of SrOsO3 and SrTiO3, the resultant product of double perovskite phase namely Sr2OsTiO6 is shifted from the semiconductor state to a normal conductor state. Electron density plots, band structure plots and DOS are illustrated and compared for both STO and SOTO compounds. Diverse bonding and electronic band characteristics are noted and compared. Our band structure calculation results are reveal that the possibility of Electronic Topological Transition (ETT) in these compounds under the effect of doping. Since there is a predominant variation over the structural, electronic and magnetic properties of double perovskite even though not much variation over their mechanical properties. To illustrate the illumination properties of the compounds under study, the optical properties are also analyzed. Hence this study helps to lead the complete examination of suitable photovoltaic properties of STO and SOTO compounds.

Antiferromagnetic order in Yb4Ru7As6 with the cubic U4Re7Si6-type structure

We investigated the electronic properties of Yb4Ru7As6 using single crystalline samples grown by the Bi-flux method. Yb4Ru7As6 crystallizes in the cubic U4Re7Si6-type structure. From the electrical resistivity, magnetic susceptibility, and specific heat measurements, we have found that Yb4Ru7As6 orders antiferromagnetically below the Néel temperature of 2.5 K with the moderately enhanced electronic specific heat coefficient of 120 mJ/(Yb-mol⋅K2). A rapid increment in magnetization of about 0.25 μB/Yb has been detected at low magnetic field below 4 K, implying a weak ferromagnetic component.

Estimation of heat transfer model parameters by using recursive least square (RLS) method for a shape memory alloy wire

The thermal model of shape memory alloy (SMA) wires is improved by identifying the convectional heat transfer model (htm) parameters. Recursive Least Square (RLS) Method is used to estimate heat transfer coefficient, specific heat and latent heat coefficient. The parameters are estimated altogether with the surface area, volume and density of the wire. Also, after measuring the resistance by using multimeter, the value of each parameter was separately determined. Heat transfer coefficient is ambient dependent and dominant in the heat transfer model. The estimation of heat transfer coefficient is important and this is shown in this study. The proposed method builds an improved heat transfer model for SMA wire by using a single set of experimental data. Performance of the estimation with RLS is validated by using the measured data. It is shown that heat convection coefficient can be estimated with high accuracy. Thus, it is revealed that addition of the latent heat term during phase transformation into the model resulted in a more accurate model. The accuracy of the model can be enhanced by 28% by the addition of latent heat term.

Derivation of a governing rule in triboelectric charging and series from thermoelectricity

Friction-driven static electrification is familiar and fundamental in daily life, industry, and technology, but its basics have long been unknown and have continually perplexed scientists from ancient Greece to the modern high-tech era. Despite its simple manifestation, triboelectric charging is believed to be very complex because of the unresolvable interfacial interaction between two rubbing materials. Here, we for the first time reveal a simple physics of triboelectric charging and triboelectric series based on friction-originated thermoelectric charging effects at the interface, characterized by the material density (${\rho}$), specific heat (c), thermal conductivity (k), and Seebeck coefficient (S) of each material. We demonstrate that energy dissipational heat at the interface induces temperature variations in the materials and thus develops electrostatic potentials that will initiate thermoelectric charging across the interface. We find that the trends and quantities of triboelectric charging for various polymers, metals, semiconductors, and even lightning clouds are simply governed by the triboelectric factor ${\xi}=S/\sqrt{{\rho}ck}$. The triboelectric figure-of-merit is expressed with the triboelectric power K=${\xi}\sqrt{t/{\pi}}$, of which the difference can be maximized up to 1.2 V/W cm$^{-2}$ at the friction time t = 1 s. Our findings will bring significant opportunities for microscopic understanding and management of triboelectricity or static electrification.

Bridgman growth and characterization of Dy:YCa4O(BO3)3 crystal

A 1-inch Dy3+:YCa4O(BO3)3 single crystal has been grown by the Bridgman method. The segregation coefficient of Dy3+ is 0.784. The structures, thermal and optical properties of Dy3+:YCOB crystal was studied. The results show that the Dy3+:YCOB crystal has high transmittance, specific heat and thermal diffusion coefficient. The Y-axis-oriented Dy3+:YCOB crystal has the largest absorption cross-section σabs(0.85×10−21cm2@444nm) and emission cross-section σem(2.54×10–21cm2@585nm). In addition, the J-O intensity parameters Ωt(t=2,4,6) of the Dy3+:YCOB crystal were calculated, where Ω2, Ω4, Ω6 are 5.01×10−20cm2, 0.33×10−20cm2, 0.52×10−20cm2 respectively. The fluorescence branching ratio β is 78.7%, and the radiative lifetime τrad is 1.588 ms. The fluorescence lifetime τf is 384.47 μs at 585 nm. The above data confirms that the Y-axis-oriented Dy3+:YCOB crystal is a good yellow laser gain material, which has potential application value in the field of yellow laser operation.

Experimental Determination of Polycrystalline Salt Rock Thermal Conductivity, Diffusivity and Specific Heat From 20 to 240°C

Salt rock is recognized as one of the most suitable parent rocks for geological disposal of high level radioactive waste due to its low permeability, good ductility, good thermal conductivity and damage self-healing properties. The thermal conductivity of salt rock directly affects the temperature of disposal storage and surrounding rock, high temperature will lead to a series of problems such as nuclear waste storage tank rupture, mechanical and permeability reduction of surrounding rock. In this paper, the thermal conductivity, specific heat and thermal diffusion coefficient of NaCl single crystal made by crystallization method in the laboratory and polycrystalline salt rock from Khewra salt mine were measured in the range of 22–240°C by the transient plane source method. The results showed that the thermal conductivity and thermal diffusivity of salt rock decrease gradually with the increase of temperature, while the specific heat capacity increases with the increase of temperature. The thermal conductivity of salt rock is slightly lower than that of single-crystal NaCl. The reason for this phenomenon may be that there are a few pores in salt rock. Based on the experimental data, the models of thermal conductivity, thermal diffusivity and specific heat of salt rock with temperature were established. The results can provide a reference for the construction of underground salt rock high-level radioactive waste disposal repository. Based on the thermal conductivity model of polycrystalline salt rock established in this paper, the temperature field evolution during the operation of the underground salt rock high-level nuclear waste repository in 1,000 years was studied. It was found that the temperature of the glass solidified of high-level radioactive waste reached the highest (177.6°C) and then dropped rapidly. The decay heat radiation influence radius of the nuclear waste reaches its maximum in about 50 years of operation of the repository and then gradually decreases.

Performance parameters evaluation and comparison of passive and active indirect type solar dryers supported by phase change material during drying ivy gourd

Experimental investigations were carried out by drying ivy gourd slices to evaluate the performance of passive and active indirect type solar dryers (PITSD and AITSD) supported with a thermal energy storage unit. The PITSD was restructured with central processing unit fans powered by photovoltaic solar panels to form the AITSD. Performance parameters and drying kinetics were evaluated from the data recorded during experiments. The average values of heat supplied, activation energy and specific energy consumption of PITSD and AITSD were 735.9 and 761.2 W, 38.95 and 36.35 kJ/mol, and 00.228 and 0.265 kWh/kg, respectively. Average collector and drying efficiencies were 66.7 and 69.87%, and 13.15 and 15.2% for PITSD and AITSD, respectively. The mean values of effective diffusivity, specific moisture extraction rate, heat and mass transfer coefficients of PITSD and AITSD were 8.06 × 10−9 and 10.00 × 10−9 m2/s, 78 and 4.380 kg/kWh, 0.0041 and 0.0055 m/s, and 4.7 and 6.28 W/m2 K, respectively. Moisture diffusivity, heat and mass transfer coefficients were negatively related in a logarithmic trend with moisture content. The AITSD performed well as compared to the PITSD. Uncertainty analysis was made to ascertain the reliability of the outcomes.

Evidence of fully gapped superconductivity in NbReSi: A combined μSR and NMR study

We report a comprehensive study of the noncentrosymmetric NbReSi superconductor by means of muon-spin rotation and relaxation ($\mu$SR) and nuclear magnetic resonance (NMR) techniques. NbReSi is a bulk superconductor with $T_c = 6.5$ K, characterized by a large upper critical field, which exceeds the Pauli limit. Both the superfluid density $\rho_\mathrm{sc}(T)$ (determined via transverse-field $\mu$SR) and the spin-lattice relaxation rate $T_1^{-1}(T)$ (determined via NMR) suggest a nodeless superconductivity (SC) in NbReSi. We also find signatures of multigap SC, here evidenced by the field-dependent muon-spin relaxation rate and the electronic specific-heat coefficient. The absence of spontaneous magnetic fields below $T_c$, as evinced from zero-field $\mu$SR measurements, indicates a preserved time-reversal symmetry in the superconducting state of NbReSi. Finally, we discuss possible reasons for the unusually large upper critical field of NbReSi, most likely arising from its anisotropic crystal structure.

Band Structure Studies of the R5Rh6Sn18 (R = Sc, Y, Lu) Quasiskutteridite Superconductors.

We report on X-ray photoelectron spectroscopy and ab initio electronic structure investigations of the skutterudite-related RhSn superconductors, where R = Sc, Y, and Lu. These compounds crystallise with a tetragonal structure (space group I) and are characterised by a deficiency of R atoms in their formula unit (RhSn, ). Recently, we documented that the vacancies and atomic local defects (often induced by doping) are a reason for the enhancement in the superconducting transition temperature of these materials, as well as metallic () or semimetallic () behaviours in their normal state. Our band structure calculations show the pseudogap at a binding energy of −0.3 eV for the stoichiometric compounds, which can be easily moved towards the Fermi level by vacancies . As a result, dychotomic nature in electric transport of RhSn (metallic or semimetallic resistivity) depends on , which has not been interpreted before. We have shown that the densities of states are very similar for various RhSn compounds, and they practically do not depend on the metal R, while they are determined by the Rh d-and Sn s- and p-electron states. The band structure calculations for ScRhSn have not been reported yet. We also found that the electronic specific heat coefficients for the stoichiometric samples were always larger with respect to the of the respective samples with vacancies at the R sites, which correlates with the results of ab initio calculations.

Hybrid Manufacturing of Aluminium Parts Combining Additive and Conventional Technologies—Mechanical and Thermal Properties

Metal additive-manufacturing technologies enable the production of complex geometries. However, high manufacturing costs hinder these technologies being employed in some industries. In this sense, a hybrid strategy is presented in this paper, to achieve the best of additive and subtractive technologies, offering economic advantages. AlSi10Mg aluminium powder was deposited on AW-6082 pre-machined substrates and mechanical and thermal properties of these specimens were evaluated considering the application of a stress relief heat treatment. The results were especially good in the compressive mechanical properties and in the thermal properties: compressive properties were improved by up to 27%, and the specific heat capacity and coefficient of thermal expansion were reduced by up to 38%, compared to additively manufactured AlSi10Mg. Therefore, hybrid manufacturing can be a profitable solution (i) in thermal management applications, (ii) when compressive loads are presented, or (iii) to repair damaged parts, providing a circular economy, as presented in a case study of this paper.

Frustrated antiferromagnetism and heavy-fermion-like behavior in PrPdAl

We report on the long-range antiferromagnetic ordering with two successive phase transitions at ${T}_{\mathrm{N}1}=4.0\phantom{\rule{0.16em}{0ex}}\mathrm{K}$, ${T}_{\mathrm{N}2}\phantom{\rule{4pt}{0ex}}\ensuremath{\approx}1.3\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and the heavy-fermion-like behaviors in PrPdAl, a Kondo lattice with kagome-like structure of non-Kramers Pr ions in the hexagonal basal plane. The ground-state antiferromagnetism forms by two-thirds Pr ions with nearly full magnetic moment and one-third with strongly frustrated and reduced moment. The easy magnetization axis points along $c$ whereas the ordered Pr $4f$ moments reside in the basal plane, mirroring the important effect of spin frustrations. The electronic specific-heat coefficient is strongly enhanced to $\ensuremath{\sim}940\phantom{\rule{0.16em}{0ex}}\mathrm{mJ}/\mathrm{mol}\phantom{\rule{4pt}{0ex}}{\mathrm{K}}^{2}$, and the Kadowaki-Woods ratio is factor-of-25 smaller than that of conventional heavy-fermion compounds with Kramers doublet ground state. The effective Gr\"uneisen ratio estimated from thermal expansion reveals large values in the vicinity of the broadened phase transition at ${T}_{\mathrm{N}2}$, manifesting its instability against pressure. Accordingly, PrNiAl, a chemically pressurized analog of the titled compound, was found to reveal only one antiferromagnetic transition at a considerably higher temperature of 6.9 K. These results demonstrate that PrPdAl and related homologues can offer excellent cases for investigating competing ground states in frustrated Kondo lattices formed by non-Kramers magnetic ions.

Rubber Material-Model Characterization for Coupled Thermo-Mechanical Vulcanization Foaming Processes.

A novel experimental methodology is developed for the characterization of the vulcanization and foaming processes of an ethylene propylene diene (EPDM) cellular rubber and for establishing the relationship of its physical and mechanical property evolution with vulcanization and foaming process temperature. To establish this relationship, the vulcanization and foaming reaction kinetics and their coupling have been determined, as well as important parameters in the behaviour of the material, such as conductivity, specific heat capacity and coefficients of expansion and foaming. This aforementioned strategy allows the setting of a material model that can be implemented into finite-element (FE) codes to reproduce the material changes during the vulcanization and foaming processes. The material model developed reproduces with enough accuracy the coupling of chemical kinetics of vulcanization and foaming reactions. The results provided by the numerical material model fit a similar trend, and values with an accuracy of 90–99% to those observed in the experiments conducted for the determination of the cellular rubber expansion in function of the temperature. Moreover, the cellular rubber expansion values agree with the structural analysis of vulcanized and foamed samples at different isothermal temperatures and with the proportional loss of mechanical properties in the function of the vulcanization and foaming degree.

A Combined Experimental-Numerical Investigation of the Thermal Efficiency of the Vessel in Domestic Induction Systems

New studies are emerging to reduce energy costs and become a more sustainable society. One of the processes where the greatest savings can be made is in cooking, due to its large-scale global use. In this vein, this study aims to analyse the influence of the vessel in the thermal efficiency at the cooking process. For that purpose, a numerical model of a cooking vessel was designed and validated with three different experimental heating tests. One of the key factors of the process is the contact between the vessel and the glass, therefore, two new approaches to model the thermal contact between the vessel and the cooktop were explored. Once the numerical models were calibrated, a full factorial analysis was performed to quantify the influence of the key parameters of the vessel in the heating process during cooking (thermal conductivity, specific heat, convection and radiation coefficients, and vessel concavity). Two of the most influential parameters in the heating process are the conductivity and the thermal contact between the vessel and the glass. Higher cooking efficiency can be achieved both with a low thermal conductivity vessel and with a high concavity, i.e., increasing the isolation between the vessel and the glass.