Variation Of Specific Heat Research Articles

Effect of Temperature and Nanoparticle Concentration on Free Convective Heat Transfer of Nanofluids

A theoretical analysis of the influence of temperature and nanoparticle concentration on free convection heat transfer from a horizontal tube immersed in an unbounded nanofluid was presented. The Nusselt (Nu) number and heat transfer coefficient were parameters of the intensity of the convective heat transfer. For free convection, the Nu number was a function of the Rayleigh (Ra) number and Prandtl (Pr) number. The Rayleigh (Ra) number and Prandtl (Pr) number were functions of the thermophysical properties of nanofluids. The thermophysical properties of nanofluids varied with temperature and nanoparticle concentration. Therefore, an analysis was conducted to evaluate the effects on the performance of nanofluids due to variations of thermal conductivity, viscosity, thermal expansion, density, and specific heat, which are functions of nanoparticle concentration and temperature. Water- and ethylene glycol (EG)-based nanofluids with dispersed alumina (Al2O3) nanoparticles at mass concentrations of 0.01%, 0.1%, and 1% were considered. Calculated Nu numbers and heat transfer coefficients were compared with experimental values taken from the published literature.

Reliable methods to look for analytical and numerical solutions of a nonlinear differential equation arising in heat transfer with the conformable derivative

The main purpose of this paper is to conduct a complete study on analytical and numerical solutions of a nonlinear differential equation arising in heat transfer with the conformable derivative. To this end, the governing model, which is about the cooling of a lumped system with a variable specific heat, is considered, and its analytical and numerical solutions are obtained through adopting a group of well‐designed techniques such as the homotopy analysis method, the operational collocation method based on Jacobi polynomials, and the finite difference method. To show the effectiveness of the schemes, comparisons are given in two‐dimensional postures demonstrating an agreement between analytical and numerical solutions. In the end, the effect of the parameter α on the dynamical features of the obtained solutions is investigated graphically.

A molecular field approach to pressure-induced phase transitions in liquid crystals: Smectic–nematic transition

Since a rigorous microscopic treatment of a nematic fluid system based on a pairwise interaction potential is immensely complex, we had introduced a simple mean field potential, which was a modification of the Maier–Saupe potential in a previous paper [S. DasGupta et al., “Pressure-induced phase transitions in liquid crystals: A molecular field approach,” Phys. Rev. E 98, 022701 (2018)]. Building upon that, here we have modified that potential to take into account the various aspects of a smectic A–nematic phase transition. In particular, we have studied the dependence of the phase transition on the coupling coefficient between the nematic and smectic order parameters, which in turn depends on the length of alkyl chain, variation of density, entropy, and specific heat. Detailed investigation on the coupling parameter shows the existence of a smectic A–nematic–isotropic triple point as well as a tricritical point where the smectic–nematic phase transition changes its nature from the second to the first order. It is also seen that the application of pressure can result in the appearance of a nematic phase.

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.

LATTICE DYNAMICALSTUDY OF EUROPIUM SULFIDE (EUS) USING TRI & TRSMODEL

In the present communication authors are reportinglattice dynamical study of Europiumsulfide (EuS).Which is based on the two phenomenological models, by including the effect of three-body interactions(TBI) in the frame work of rigid ion model(TRIM) & rigid shell model (TRSM) with the satisfactory description of all phonon properties.The model parameters of both have used to the phonon spectra for the allowed 48-nonequivalent wave vectors in the first Brillouin zone.The frequencies along the symmetry directions have plotted against the wavevector to obtain the phonon dispersion curves(PDC)from both the models. With the help of available experimentaldata.We have also reportedthe Specific heat variation& Combined density of states (CDS) for complete description of the frequencies for the Brillouin zone included theoretical Debye temperature and elastic property of (second-third order) of EuS. So by using the present model the complete lattice property of EuS is reported successfully.

Combustion, performance and emissions of Acacia concinna biodiesel blends in a diesel engine with variable specific heat ratio

An experimental assessment based on combustion, heat transfer, performance and emission behavior of a 3.5 kW light duty commercial diesel engine have been executed to explore the viability of Acacia Concinna biodiesel (ACBD) (unexplored and produced from new non-edible forest feedstock) as surrogate to mineral diesel in the prevailing CI engines. The result enumerates that effect of variation in specific heat ratio as a function of in-cylinder gas temperature, on combustion heat release rate, cumulative heat release and power output is significant. Higher fraction of diffusion combustion phase with extended overall combustion duration and slightly higher heat loss per cycle was recorded for AC biodiesel fuel blends than that of diesel. The engine operation was smooth with no negative effect (except NOx emission) when fueled up to B30 (AC30D70) fuel blend compared to those of diesel.

Vibrational spectra of MO (M = Sn/Pb) in their bulk and single-layer forms: role of avoided crossing in their thermodynamic properties

We report ab-initio calculations of phonon dispersion relationship on bulk and single layers of SnO and PbO. In agreement with experimental observations of Raman spectroscopy measurement, we find that A1g mode is higher in frequency than Eg mode. Moreover, the reason behind the shift of A2u mode to higher frequency for monolayers of both SnO and PbO is clearly understood from our calculations. In addition to vibrational spectroscopy, we also find avoided crossing or Landau quasi-degeneracy between the longitudinal acoustics (LA) and low-energetic transverse optical (TO) modes in bulk form of both SnO and PbO and in monolayer SnO. The signature of such avoided crossing can be found in the variation of both specific heat and entropy with temperature. Although both specific heat and entropy decrease at the temperature corresponding to the crossing region, the specific heat value shows a kink in that region. In contrast, such lowering/kink in thermodynamic variables does not appear in monolayer PbO. The reason behind the crossing can be analysed using the concept of Born effective charge and dielectric tensor. To further verify the crossing, we calculate phonon group velocity for every band as a function of phonon wave vector for each of these oxides, where the role of avoided crossing has been clearly shown and explained.

Heat generation quantification of high-specific-energy 21700 battery cell using average and variable specific heat capacities

The electrical performance, safety and life of a battery are closely related to its operating temperature; therefore, a thermal management system is necessary to ensure that the battery operates within its most suitable temperature range. Accurately testing the heat generation of a battery is necessary for the design of a thermal management system. Specific heat capacity is one of the most important parameters of thermophysical properties, and its accurate measurement is a prerequisite for the quantitative analysis of battery heat generation. In the literature on battery heat generation tests, the average specific heat capacity is usually used to calculate the battery heat generation. Thus, the change in the specific heat capacity of the battery is not considered. Considering the high-specific-energy 21700 battery made with a nickel-cobalt-manganese (NCM)/graphite material system, this paper compares for the first time the difference between using the average specific heat capacity and variable specific heat capacity to calculate the instantaneous heat generation of a battery. The experimental results showed that the specific heat capacity in the target temperature range during the actual use of power batteries (i.e., a low temperature range of 25–35 °C) had a more significant impact on the heat generation power calculation error, and the relative error could reach 30%. In addition, based on the obtained variable specific heat capacity, the heat generation characteristics of the 21700 battery under different operating conditions were analysed. The results showed that this battery has a higher specific volume heat generation power compared with the pouch-type batteries reported in the literature. This article provides guidance for battery cell thermal simulation, more accurate quantitative measurement of battery heat generation and thermal management system design.

Heat Transfer Enhancement of Supercritical Nitrogen Flowing Downward in a Small Vertical Tube: Evaluation of System Parameter Effects

In this paper, the heat transfer enhancement (HTE) of supercritical nitrogen flowing downward in a vertical small tube (diameter 2 mm) is studied using the commercial software CFX of Ansys16.1, to provide theoretical guidance on the design of high-performance heat transfer systems. An effective numerical simulation method, which employs the SSG Reynolds stress model with enhanced wall treatment, is applied to study the heat transfer of supercritical nitrogen under typical working conditions. The objective is to evaluate the effect of the main parameters taking into account the buoyancy and flow acceleration effects. Simulation results are compared with results calculated from three well-known empirical correlations and the applicability of empirical correlation is discussed in detail. It is discovered that the Watts and Chou correlation accurately fits the simulation results of supercritical nitrogen and the Dittus-Boelter and Jackson correlations can only be used for high-pressure conditions. The HTE of supercritical nitrogen is closely related to the laminar sub-layer and buffer layer of a boundary layer. The buoyancy effect on the HTE should be considered at low mass flux conditions, and thermal acceleration can be completely ignored for the cases studied. The special HTE featured by the increment in heat transfer coefficient with increasing heat flux is discovered at low pressure, and simulation results proved that this HTE is caused by the combined actions of buoyancy as well as significant variations in specific heat and viscosity.

A freezing problem with varying thermal coefficients and convective boundary condition

This study investigates a one-dimensional Stefan problem by taking variable specific heat and thermal conductivity which depends on temperature. Time dependent heat flux is also assumed at the boundary x = 0 in the problem. The similarity solution for the problem is constructed when $$ \alpha = \beta $$ and $$ p = q = 1 $$ . The uniqueness and existence of the similarity solution to the problem have been also established. The problem is solved approximately for all $$ \alpha $$ and $$ \beta $$ with the aid of the shifted Chebyshev tau method. To check the precision of the proposed approximate solution, we have made its comparisons with the obtained exact solution. The comparisons done are shown by tables which sufficiently agree with the exact solution. The effects of the parameters on the movement of interface and temperature profiles are also carried out.

Thermodynamic-dynamic analysis of gamma type free-piston stirling engine charged with hydrogen gas as working fluid

ABSTRACT In this study, the combined thermodynamic and dynamic model of a new concept of gamma type free-piston Stirling engine is conducted. The engine consists of two identical displacer cylinders, a power cylinder, a linear alternator, and three-cushion pistons. Two displacer cylinders are symmetrically positioned on each side of the power cylinder for minimizing the rotational vibrations. Hydrogen is used as the working gas and the effect of gas temperature on the specific heat capacity is considered. The analysis carried out in this study involves the prediction of the thermodynamic-dynamic performance characteristics of the engine. In the thermodynamic section of the analysis, the working space of the engine is divided into 31 nodal volumes and the gas pressures in nodal volumes are assumed to be equal to each other. The conservation of mass and energy equations is obtained for each nodal volume. Instantaneous gas temperatures of nodal volumes are calculated by the first law of thermodynamics given for the unsteady open systems. The dynamic section of the analysis involves the motion equations of displacer, power and cushion pistons. The motion equations are derived using the Newton method. In the calculations done for variable specific heat capacity, it has been determined that there is 1% cyclic work reduction compared to the constant heat capacity. It is estimated that the maximum effective power that can be produced by the linear alternator will be around 1.6 kW. The working frequency range of the proposed engine is found to be suitable to generate electrical power.

Effect of Impurities on Binary Manganese–Bismuth System: a Monte Carlo Study

In this work, we have used the Monte Carlo simulation to study the effect of impurities on the magnetic properties of Mn1-pBi system. Free boundary conditions for our system were applied to simulate Hamiltonian system of Mn1-pBi. The exchange interactions are calculated using the ab initio calculations. The variation of magnetization, magnetic susceptibility, and magnetic specific heat vs. temperature was given for a pure (p = 0) and a several impurities (p) for Mn1-pBi. The critical temperature of Mn1-pBi was determined. The effects of impurities (p), crystal field, and impurities on the magnetic hysteresis cycle were investigated.

Investigation of specific heat in the monolayer graphene

In this paper, we have investigated the specific heat of the monolayer graphene under the polaron effect. For this purpose, we have first considered an electron coupled to the longitudinal acoustic (LA) phonon on the surface of the graphene with Coulomb impurity. Then, we have obtained the ground state energy of the polaron by employing the variational method and unitary transformation. We have used non-extensive thermodynamics to calculate specific heat different substrates like SiC, HfO2, h-BN, and SiO2. The specific heat variation with Coulomb bound parameter, magnetic field, temperature, and charge is then studied for these different substances.

Exergy-based performance analysis and evaluation of a dual-diesel cycle engine

Performance examinations of a dual-Diesel cycle engine in point of engine performance characteristics such as exergy efficiency, power and power density have been conducted. The effect of design parameters of the engine cycle such as intake temperature, intake pressure, piston friction coefficient, average piston velocity, engine revolution, stroke length, residual gas fraction, engine pressure ratio, engine temperature ratio, compression ratio, ratio of bore diameter to stroke length, and equivalence ratio, on the performance characteristics are evaluated by considering variable specific heats and irreversibilities resulting from exhaust output, heat transfer, incomplete combustion and friction. The results can provide substantial information researchers who study on dual-Diesel cycle engine design and manufacture.

An analytical expression for temperature in a thermodynamically consistent model with a Mie-Gruneisen equation for pressure

The objective of this paper is to develop an analytical expression for temperature in a thermodynamically consistent model with a Mie-Gruneisen equation for pressure. This expression for the temperature is obtained for both constant and variable specific heat models and can be used in common models for the material yield strength that include thermal softening due to increase in temperature. Also, the material parameters in the model can easily be calibrated to match known experimental data and the model has been used to determine the value of the shock pressure at the onset of melting during shock loading.

Structural, thermal, dielectric and multiferroic investigations on LaFeO3 composite systems

The present study focuses on developing multiferroic properties in the perovskite orthoferrite LaFeO3 (LFO) at room temperature. The effect of perovskite ferroelectric and spinel magnetic interface has been investigated on the ferroelectric and magnetic properties of LFO. The composite systems are prepared by solid-state reaction route, using BaTiO3 (BTO) as the perovskite ferroelectric phase and CoFe2O4 (CFO) as the magnetic phase. The phase purity of the samples is confirmed through X-ray diffraction and the Fourier transform infrared spectroscopy. The physical interaction of BTO and CFO with LFO is perceived from the peak broadening and shifting. Rietveld refinement confirms the single-phase orthorhombic formation of LaFeO3–CoFe2O4–BaTiO3 composites. The energy dispersive X-ray analysis reveals that the samples are without any impurity and the relative concentrations of constituent phases are close to the expected values. High-resolution transmission electron microscopy is utilized to determine the interplanar spacing and hence Bragg planes. Selected area electron diffraction (SAED) patterns reveal the polycrystalline nature of samples with a small local ordering. Specific heat variation against temperature depicts an anomaly at lower temperature around 130 °C that represents the transition of BaTiO3 from tetragonal ferroelectric to cubic paraelectric phase. The variation of dielectric constant with frequency is consistent with Maxwell–Wagner interfacial polarization model. The dielectric behavior of the composite systems reveals the frequency independent anomaly at the Curie temperature of BaTiO3, consistent with specific heat measurements. The simultaneous presence of ferroelectric and magnetic hysteresis loops confirms the multiferroism in the samples. The exchange bias effect is observed in all the samples and coercivity decreases with the increase in BaTiO3 concentration.

Performance of Universal Reciprocating Heat-Engine Cycle with Variable Specific Heats Ratio of Working Fluid.

Considering the finite time characteristic, heat transfer loss, friction loss and internal irreversibility loss, an air standard reciprocating heat-engine cycle model is founded by using finite time thermodynamics. The cycle model, which consists of two endothermic processes, two exothermic processes and two adiabatic processes, is well generalized. The performance parameters, including the power output and efficiency (PAE), are obtained. The PAE versus compression ratio relations are obtained by numerical computation. The impacts of variable specific heats ratio (SHR) of working fluid (WF) on universal cycle performances are analyzed and various special cycles are also discussed. The results include the PAE performance characteristics of various special cycles (including Miller, Dual, Atkinson, Brayton, Diesel and Otto cycles) when the SHR of WF is constant and variable (including the SHR varied with linear function (LF) and nonlinear function (NLF) of WF temperature). The maximum power outputs and the corresponding optimal compression ratios, as well as the maximum efficiencies and the corresponding optimal compression ratios for various special cycles with three SHR models are compared.

Automatic differentiation approach for property computations in nanoscale thermal transport

We present the automatic code differentiation technique to perform derivative computations in nanoscale phonon transport simulations. This method exploits the concepts of templating and operator overloading in C++ and other similar programming languages to unintrusively convert existing codes into those yielding derivatives of arbitrary order. The idea is demonstrated through the computation of phonon properties such as second and third order force constants, the Gruneisen parameter, group velocities, and the temperature variation of specific heat for materials like graphene and graphene nanoribbons. Derivative values so computed are compared with those obtained using finite difference approaches or with analytical values. The method is found to yield derivative values to machine accuracy, with none of the round-off issues associated with finite difference approaches.

Theoretical study of Specific heat and thermal conductivity variation in nanomaterials

In the present paper, the authors study the specific heat dependence on shape, size and dimension of the nanomaterials. Using an analytic quantitative model for melting temperature, the expression of specific heat for nanomaterials is deduced. Further, the model is extended to study the shape, size and dimension effect on thermal conductivity of nanoparticles. Phonon scattering term is taken into consideration for calculation of thermal conductivity of nanomaterial to explain the roughness and scattering effect on thermal property. The specific heat is observed to increase from model calculations as size of the nanomaterial decreases. However, the thermal conductivity in nanoparticles is observed to decrease with size decrement of nanoparticle. It is observed that inclusion of phonon scattering term help to better understand the variation in thermal conductivity. The variation in specific heat and thermal conductivity with size is determined for spherical, regular tetrahedral, octahedral nanoparticles, cylindrical and hexagonal nanowires and nanofilms. The results calculated from model are in good consistency with the available experimental and simulated results and help to judge the suitability of the present model.

Heat transfer model of a particle energy storage‐based moving packed bed heat exchanger

AbstractMoving packed bed particle/supercritical carbon dioxide (SCO2) heat exchanger (MPBE) is a critical equipment to integrate particle thermal energy storage technology with SCO2 power cycle block in the next‐generation concentrated solar power plants. A predictive heat transfer model for designing and evaluation of shell and plate particle/SCO2 moving packed bed heat exchanger is presented, with radiation, pressure drop and SCO2 property variation taking into account. It is found that increasing particle diameter and solids bulk voidage will lower the overall heat transfer coefficient. Change of channel width imposes little effects on the overall heat transfer coefficient, while influences the total heat exchange greatly. MPBE with longer channel length allows smaller overall heat transfer coefficient. Due to approximate linear variation of specific heat and low pressure drop in the nominal boundary operating condition range, ignoring SCO2 Cp variation is valid, and the relative error due to adopting a Cp invariable evaluated at the bulk temperature and constant pressure is less than 1%. Convection resistance generally ranks first in the contribution to thermal resistance, followed by solids‐wall resistance and conduction resistance. Nevertheless, solids‐wall resistance dominates at larger particle diameter (≥550 μm). Radiation is an important contributor to heat transfer behavior, especially at high particle diameter and solids bulk voidage. The relative error caused by neglecting radiation can be up to 23.76%.