Term In Specific Heat Research Articles

Non-magnetic regenerator material of silver oxide for 4 K cryocoolers

In regenerative cryocoolers, magnetic specific heat is often utilized for heat regeneration at cryogenic temperature, such as below 20 K. Magnetic regenerator materials of rare earth compound which have sufficient specific heat enabled cryocooler to reach below 4 K. However, the magnetic noise emitted from the magnetic materials during the refrigeration cycle affects the performance of noise-sensitive devices. In this study, we propose a non-magnetic regenerator material having “optical phonon degree of freedom” even at cryogenic temperatures, in which silver oxide (Ag2O) is selected. Ag2O decomposes at temperature above 410 K in ambient atmosphere, whereas we succeeded in fabricating a sintered Ag2O bulk and small particles of the size of 0.5 mm with high-density more than 90%. Specific heat measurement down to 100 mK was performed for the sintered bulk sample of Ag2O. Below 10 K, a non-Debye behavior was observed, suggesting the contribution from optical phonon modes. Calculation of the phonon density of state (phDOS) performed by the Evolution Strategy algorithm in addition to the first-principles calculation reveals that phDOS has several distinct peaks at low energies, and the low-energy optical phonons contribute to the non-Debye behavior. The low temperature specific heat of Ag2O enhanced by the optical phonons is larger than conventional non-magnetic regenerator materials when compared in terms of specific heat per volume. Moreover, the calculation of cooling performance of cryocooler using Ag2O particles is found to be reached below 4.2 K. This study shows that non-magnetic material with low temperature specific heat enhanced by optical phonon mode can be used as a regenerator material for regenerative cryocoolers.

An analysis of the effectiveness of new generation self-levelling lightweight composite screed for underfloor heating systems

Energy saving has become a significant concern in recent years due to increasing carbon emis- sions and environmental pollution. When examined from a global perspective, it is known that the energy consumed for heating and cooling of buildings is relatively high. In this regard, researchers attach great importance to energy efficiency issues. In recent years, an issue that has been given priority in heating buildings more efficiently is underfloor heating systems. Underfloor heating systems are composite structures of slab concrete, insulation material, hot water pipes, and screed. Here, the thermal performance of the screed is vital as the hot water pipes remain embedded in the screed. This study has produced a new composite and self-leveling screed type that can transfer heat easily. For this purpose, nine screed mixtures were prepared, including a reference (nearly conventional) screed mortar. The screed mortars’ flowability, density, and compressive strength were determined regarding physical properties. Thermal properties, thermal conductivity, specific heat, thermal diffusivity, and heat storage analyses were carried out. In the second stage of the study, a basic underfloor heating system was installed, and the temperatures of the water circulating in the system, the outer surface of the pipe carrying the water, and the outer surface of the screed were measured at specific peri- ods. According to the study results, it has been observed that depending on the thermal prop- erties of the screeds produced within the scope of this study, when used in underfloor heating systems, it can transfer heat from the hot water pipes to the surface with minimum losses.

Bipartite entanglement via distance between the states in a one dimensional spin 1/2 dimer copper acetate monohydrate

In this paper, we used a theoretical measure known as distance between the states, , to determine the bipartite entanglement of a one dimensional magnetic dimer system. The calculation was compared with the well-known entanglement measure, concurrence, and found to be the same. was, then, expressed in terms of two thermodynamic quantities, namely, magnetic susceptibility and specific heat. Experimental verification of temperature variation of the bipartite entanglement measure in terms of magnetic susceptibility and specific heat was done on single crystals of copper acetate-an excellent one dimensional dimer system. The results showed the existence of bipartite entanglement till temperatures as high as room temperature! Large sized single crystals of copper acetate were grown by a new evaporation technique and characterised by thermogravimetric analysis, IR and Raman spectroscopy measurements. Density functional theory calculations were done to calculate the delocalisation index which showed much lower values of than other bonds, implying that the probability of direct Cu–Cu exchange in copper acetate is very small. Band structure calculations revealed the presence of flat bands at the Fermi level implying very weak intermolecular interactions in copper acetate.

DFT and experimental investigations on CdTe1-xSex for thermoelectric and optoelectronic applications

The optical and electronic characteristics of CdTe-based semiconductors play an important role in modern optoelectronic devices. In the current study, pure and Se doped CdTe compositions were theoretically investigated through density functional theory within the framework of Wien2k code using a modified Becke–Johnson technique. Experimentally CdTe1−xSex (x = 0, 3.125 %, 6.25 %, and 12.5 %) uniform and evenly distributed thin films were successfully deposited through a chemically derived sol-gel-based spin coating technique. The morphological, electronic, thermoelectric, and optical properties were studied through comparative simulations and experimental investigations. Ab-initio and experimental results reveal the similarities and correlation among the findings. The experimental energy band gap was found to reduce from 1.84 eV for pure CdTe to 1.55 eV by incorporation of Se in the pristine CdTe structure. The thermoelectric response in terms of electrical conductivity, Seebeck coefficient, thermal conductivity, and specific heat was recorded and a significant variation was observed. The optical parameters show an enhanced trend in the visible regime with the incorporation of Se content in structure. Absorption coefficient and real epsilon were shown to a sharp increase with increment of Se content. The outcomes of this work are considered that Se containing CdTe composition are promising candidates for enhanced thermoelectric and optoelectronic applications.

THE THERMAL FORM OF THE PHOTOEFFECT WITH THE DEBYE AND THE WIGNER CRYSTAL

We define the photoelectric effect with the specific heat term replacing the work function. The photon propagator involving the radiative correction is also considered. We consider the Debye specific head for the 3D crystal medium, the specific heat for the 2D medium and specific heat for the Wigner crystal.

Formulation of empirical correlation for internal forced convection

Empirical equations correlating experimental results with the aid of dimensional analysis or analogies are not able to explain heat transfer mechanism convincingly. Therefore, the experimental results for low viscous liquids like acetone, benzene, n-butyl alcohol, kerosene and water are correlated in terms of tube diameter, mass velocity, thermal conductivity, viscosity and specific heat by considering their effect individually. It is found that the heat transfer coefficient increases with the ascending value of tube diameter, attain maxima at about 20 mm and then reduces when the tube diameter is further increased to 50 mm. The mechanism of heat transfer is presented by considering overall turbulence which depends upon the mobility of sub-layer and core turbulence.

Thermal energy storage characteristics of binary molten salt nanofluids: Specific heat and latent heat

This study aims to examine the thermal energy storage characteristics, in terms of specific heat and latent heat, of nanoparticle-doped binary molten salt nanofluids. Two different binary molten salt mixtures, namely carbonate salts (Li2CO3 and K2CO3) and nitrate salts (NaNO3 and KNO3), were used as base solvents. Graphite nanoparticles were dispersed into the salt mixtures. The chemical compositions (molar fractions) of the two salt components were varied from hypoeutectic to hypereutectic, including eutectic compositions, to investigate their effects on the specific heat and latent heat of both the pure salts and their nanofluids. The specific heat of the carbonate salt nanofluid was enhanced, irrespective of the chemical composition, and the enhancement was proportional to the nanoparticle concentration. However, the specific heat of the nitrate salt nanofluid was decreased by the addition of 0.1 wt% of graphite nanoparticles and increased by the addition of a larger amount of 1 wt%. The latent heat of the nanofluids was enhanced by doping nanoparticles into the salt mixtures and was affected by the chemical composition of the solvent salt mixtures. The distinct behaviors of specific heat and latent heat obtained in this study were discussed based on a compressed liquid (solid-like) layer formed near the nanoparticles. The thermal energy storage capacities of the nanofluids were estimated and compared by using their specific heat and latent heat.

Development of Solar Accumulating Drying Equipment Based on the Theoretical Studies of Solar Energy Accumulation

The process of heating a dewatered object in an infrared solar drying plant (with paraffin on the bottom) with solar energy storage is considered. To solve this problem, it is assumed that the heat capacity of paraffin exceeds the heat capacity of the dehydrated object. Infrared rays fall on the upper layer, and heat exchange takes place due to heat and mass transfer with the surface air located between the metal plate and the object to be dehydrated. The equations of thermal conductivity for a dewatered object are given, its relationship at the phase interface is determined using the equality of temperature and heat flow. For an exposure of overheating with a period of 6.5 h, the time of passage of the phase boundary in accordance with the law of motion of the spreading (hardening), was determined according to the formula of ξ = α √6,5 h ≅ 12 h.The optimal thickness of the accumulating paraffin layer was ascertained. On the basis of the theoretical studies, experiments were conducted to study the temperature field of various heataccumulating materials in the laboratory of Tashkent State Technical University. It was found that of all heat-accumulating materials, paraffin has the best heat retention ability when its thickness is of 2–4 cm. The optimal variant of a solar accumulator drying plant with a heat accumulator, viz. paraffin has been designed. In particular, 2–4 cm of paraffin layer with a mass of 50 kg with a corresponding flat surface in terms of specific heat of evaporation is 2400 kJ/kg. The specific melting value of paraffin (150 kJ/kg) allows additional evaporation of 5.8 l of moisture when drying objects. The proposed solar accumulator drying plant can be used for dehydration of medicinal herbs.

Effect of Ag and γ-ray irradiation on the specific heat of glass transition of Se78Te20Sn2 glassy alloy

The specific heat of glassy materials is a significant parameter that reveals useful information about the local circumstances for the vitrification of a glass-forming melt through its solidification. However, the melt after the formation of glass is known as a highly viscous liquid. In the present work, we are reporting the effect of silver (Ag) on specific heat capacity of glass transition of Se78Te20Sn2 glass alloy in terms of glass and equilibrium specific heats (i.e., Cpg, and Cpe) and then in addition to it, we are reporting the effect of gamma-ray (γ-ray) irradiation (60Co source, 12 kGy dose) on the same glassy alloy. A comparative analysis of Ag addition and γ-ray irradiation on these thermodynamic parameters for the parent glass is discussed in detail.

Specific heat capacity enhancement studied in silica doped potassium nitrate via molecular dynamics simulation

Molten salts serve an important purpose for short term heat energy storage and as heat transfer fluids in solar power plants. Different experimental groups have shown that certain mixtures containing salts doped with small amounts of nanoparticles exhibit much greater specific heat capacities compared to the same base salts without nanoparticles. This effect is technically interesting and economically important. Thus far, however, it is not understood. Our aim is the theoretical investigation of the specific heat capacity in the aforementioned nanofluids on the molecular level using simulations. Here we present results for liquid potassium nitrate doped with silica nanoparticles. We discuss the observed increase of the specific heat in terms of the particle induced hydrodynamic reinforcement and liquid structure. The theoretical background of this discussion is a ω-space resolved phonon theory of liquids in conjunction with differential spectral densities, computed for the different systems with and without nanoparticles.

Comparative Analysis of Thermohydraulic Properties of Nano-Refrigerants

The nano-particles achieved the focus of the researchers in the field of refrigeration, due to its capability to change the properties of refrigerants upto a large extent. Nanofluids based on refrigerant is known as nano refrigerants and provided an improvement in thermophysical properties of various refrigerants in different terms. Different theoretical and experimental models are provided by the researchers have been used for the evaluation of different properties of refrigerant in terms of thermal conductivity, density, specific heat and viscosity of the refrigerants. In this effort, a number of models, and correlations have been used to result in the improvement in these properties of nano refrigerants. This is achieved by the addition of nanoparticles with varying volume concentration of 1% to 5 %. The analyses have been made within a temperature range of 190K- 269K at a constant pressure of 0.3 MPa. The study is elaborated to compare the various refrigerants which are R11, R12, R22, R134a and R141b with the addition of different nano-particles which are TiO2, Al2O3, ZnO and CuO at evaporator conditions. The addition of ZnO has given a good impact on the thermal conductivity of refrigerants. Effective viscosity of nano refrigerants depends upon the viscosity of refrigerants and volumetric concentration of nano-sized particles. Specific Heat shows the negative variation with the addition of nanoparticles but increased with the rise in temperature. The density of nano refrigerants depends upon the density of base refrigerant, Density of nanoparticles, volumetric concentration of nanoparticles. In future, the study can be elaborated in terms of compressor work, power consumption and overall performance of refrigeration system.

Field-induced phase transition in [formula omitted] with M = Co, Rh, and Ru

Large electronic specific heat coefficient, C(T)/T, suggests that the family of Ce3M4Sn13 heavy-fermions (HF) is near a magnetic quantum critical point (QCP). We analyze the 4f contribution to the specific heat in terms of the single-ion Kondo resonance model. An unexpected change in the Kondo temperature TK versus magnetic field B signals a field-induced phase transition between the magnetically correlated HF phase and a single-ion Kondo impurity state.

On the effect of calcium lignosulfonate on the rheology and setting time of cement paste

The effect of softwood calcium lignosulfonate, LSs, on the rheology and setting time of cement paste has been investigated. Two Portland cements with different surface area and C3A content were used. The lignosulfonate was added either immediately with the mixing water or delayed after 10min of hydration. The cement pastes were characterized in terms of specific surface, rheology and heat of hydration. Extracted pore solutions were analysed for free lignosulfonate concentration and for changes in elemental composition. Immediate addition of LSs increased the specific surface, but not delayed addition. Correlations were found between rheology and surface coverage by LSs, as determined by adsorption isotherms, and between the setting time and the amount of free LSs in the pore solution. An increased setting retardation upon delayed addition related to an increased concentration of Al in the pore solution.

Models for Predicting Free Water and Specific Heat of Pastes Containing Ground Granulated Blast Furnace Slag

This paper aims to investigate early age behavior in terms of free water content and specific heat for hardening cement paste incorporating Ground Granulated Blast Furnace Slag. Experiments were conducted to obtain free water and specific heat of slag-cement pastes by varying water to binder ratios and slag replacement levels. Free water to total binder ratios for pastes with w/b of 0.40 and slag replacements of 45% and 75% are 0.23 and 0.25 at 3 days and 0.17 and 0.19 at 28 days, respectively. Specific heat values for similar mixtures are 0.26 and 0.30 at 3 days and 0.23 and 0.25 at 28 days. Results showed that specific heat decreases as the amount of free water decreases. The slag substitution resulted in high specific heat and free water at early age but tends to decrease in long term due to enhanced reaction kinetics. Models were proposed to compute free water and specific heat by modifying existing models. The model simulations can be used to predict the measured values accurately.

Electronic specific heats for amorphous and crystallized alloys.

The low temperature specific heats of (Fe0.5Co0.5)72B20Si4Nb4 amorphous and crystallized alloys are measured and analyzed from 1.4 to 110 K. Specific heats can be well fitted by electronic and phonon contribution terms. It is found that the electronic contribution term in specific heat for amorphous alloy is larger than that for crystallized one, and this phenomenon has been interpreted in detail. The research shows that the electronic density of states at the Fermi level and the localized loose “rattler” atoms in oversized cage structure may make contributions to the enhancement of electronic specific heat coefficient γ, and result in a larger electronic contribution term. This study is significant for further understanding the structure–property relationship for amorphous alloys at low temperature.

A review of unconventional sustainable building insulation materials

Building insulation is commonly realized using materials obtained from petrochemicals (mainly polystyrene) or from natural sources processed with high energy consumptions (glass and rock wools). These materials cause significant detrimental effects on the environment mainly due to the production stage, i.e. use of non-renewable materials and fossil energy consumption, and to the disposal stage, i.e. problems in reusing or recycling the products at the end of their lives. The introduction of the concept of “sustainability” in building design process encouraged researches aimed at developing thermal and acoustic insulating materials using natural or recycled materials. Some of them, such as kenaf or wood fiber, are already commercialized but their diffusion could be further improved since their performance is similar to the synthetic ones. Others are currently under study and their development is only at an early stage. The goal of the paper is to report a state of the art of building insulation products made of natural or recycled materials that are not or scarcely commercialized. Comparative analyses were carried out considering in particular thermal characteristics in terms of thermal conductivity, specific heat and density. Data on the acoustic performance of the materials were also reported. Life Cycle Assessment data were finally collected, in order to put in evidence the environmental advantages of these materials. Particular attention was paid to researches focused to exploit local materials and even industrial byproducts, since these approaches respectively limit transportation and disposal impacts.

Performance Optimization of the Carnot and Joule Cycles and Relationship with the Formulation of Physical Exergy Property

The present theoretical study proposes an analysis, underpinned by the basic foundations reported in the literature, aimed at establishing a generalization of the relationship between cyclic thermo-mechanical conversion processes and the physical exergy property defined for a system interacting with two different and independent reservoirs. The outcome of the study is the demonstration that physical exergy expresses both useful work or useful heat, if these interactions undergo conversion when withdrawn from a system. The approach to conversion consists in comparing the efficiency of (ideal) Carnot and Joule cycles leading to the argument that the Joule cycle is the one performing at maximum efficiency between two constant pressures, similarly to the Carnot cycle performing at maximum efficiency between two constant temperatures. In terms of specific (per cycle) work or heat of Carnot and Joule cycles, the study proves that the roles of temperature and pressure are opposed as evidenced by a performance optimization analysis for the two cycles. Interactions between a system and two independent reservoirs undergoing isothermal and isobaric processes respectively are examined in relation to useful work and useful heat. The aim and the novelty of this analysis is to explore the role of the Joule cycle and the pressure of system and isobaric reservoir, which are similar to the role of the Carnot cycle and the temperature of system and isothermal reservoir. This implies a generalized formulation of physical exergy which, for this reason, may be regarded as a temperature-and-pressure-dependent property in Original Research Article British Journal of Applied Science & Technology, 4(2): 261-278, 2014 262 the general case of a system interacting with two reservoirs. Finally, the expression of the thermal and mechanical components of physical exergy, depending on temperature and pressure, and their relationship with the Carnot and Joule cycles, are envisaged as possible consequences of this analysis representing the basis for future research.

Cosmographic study of the universe’s specific heat: a landscape for cosmology?

We propose a method for constructing the specific heat for the universe by following standard definitions of classical thermodynamics, in a spatially flat homogeneous and isotropic spacetime. We use cosmography to represent the specific heat in terms of measurable quantities, and show that a negative specific heat at constant volume and a zero specific heat at constant pressure are compatible with observational data. We derive the most general cosmological model which is compatible with the values obtained for the specific heat of the universe, and show that it alleviates the fine-tuning and the coincidence problems of the \(\Lambda \)CDM model.

Specific heat versus field for LiFe1−xCuxAs

LiFeAs is one of the new class of iron superconductors with a bulk in the 15–17 K range. We report on the specific heat characterization of single crystal material prepared by self-flux growth techniques with significantly improved properties, including a much decreased residual gamma, γr (≡C/T as T → 0), in the superconducting state. Thus, in contrast to previous explanations of a finite γr in LiFeAs being due to intrinsic states in the superconducting gap, the present work shows that such a finite residual γ in LiFeAs is instead a function of sample quality. Further, since LiFeAs has been characterized as nodeless with multiple superconducting gaps, we report here on its specific heat properties in zero and applied magnetic fields, to compare to similar results on nodal iron superconductors. For comparison, we also investigate LiFe0.98Cu0.02As, which has the reduced Tc of ≈9 K and an Hc2 of 15 T. Interestingly, although presumably both LiFeAs and LiFe0.98Cu0.02As are nodeless, they clearly show a non-linear dependence of the electronic density of states (∝ specific heat γ) at the Fermi energy in the mixed state with the applied field, similar to the Volovik effect for nodal superconductors. However, rather than indicating nodal behavior, the satisfactory comparison with a recent theory for γ(H) for a superconductor with two isotropic gaps in the presence of impurities argues for nodeless behavior. Thus, in terms of specific heat in a magnetic field, LiFeAs can serve as the prototypical multiband, nodeless iron superconductor.

Biphasic Investigation of Tissue Mechanical Response During Freezing Front Propagation

Cryopreservation of engineered tissue (ET) has achieved limited success due to limited understanding of freezing-induced biophysical phenomena in ETs, especially fluid-matrix interaction within ETs. To further our understanding of the freezing-induced fluid-matrix interaction, we have developed a biphasic model formulation that simulates the transient heat transfer and volumetric expansion during freezing, its resulting fluid movement in the ET, elastic deformation of the solid matrix, and the corresponding pressure redistribution within. Treated as a biphasic material, the ET consists of a porous solid matrix fully saturated with interstitial fluid. Temperature-dependent material properties were employed, and phase change was included by incorporating the latent heat of phase change into an effective specific heat term. Model-predicted temperature distribution, the location of the moving freezing front, and the ET deformation rates through the time course compare reasonably well with experiments reported previously. Results from our theoretical model show that behind the marching freezing front, the ET undergoes expansion due to phase change of its fluid contents. It compresses the region preceding the freezing front leading to its fluid expulsion and reduced regional fluid volume fractions. The expelled fluid is forced forward and upward into the region further ahead of the compression zone causing a secondary expansion zone, which then compresses the region further downstream with much reduced intensity. Overall, it forms an alternating expansion-compression pattern, which moves with the marching freezing front. The present biphasic model helps us to gain insights into some facets of the freezing process and cryopreservation treatment that could not be gleaned experimentally. Its resulting understanding will ultimately be useful to design and improve cryopreservation protocols for ETs.