Variation Of Specific Heat Research Articles

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.

Legendre wavelet residual approach for moving boundary problem with variable thermal physical properties

Abstract The main aim of the current article is to describe an uni-dimensional moving boundary problem with conduction and convection effect when thermal conductivity and specific heat varying linearly with temperature and time. The Mathematical model has nonlinearity due to presence of variable thermal conductivity and specific heat. A Legendre wavelet residual approach is introduced to get the solution of the problem with high accuracy. The surface heat flux is taken as an exponent function of time while latent heat is presented as an exponent function of position. Galerkin technique is used to obtain the numerical solution in case of constant physical properties while collocation technique is used for variable thermal physical properties. When it is considered that thermal physical properties are constant then obtained numerical solution was compared with exact solution and found in good acceptance. The effect of convection and variable thermal conductivity with time and temperature on the location of the moving layer thickness is analyzed. Further the effect of Peclet number and other physical parameters on the location of moving layer thickness are discussed in detail.

Multi-objective optimization and performance analyses of an endoreversible rectangular cycle

Based on the endoreversible rectangular cycle model founded in the previous literature, the rectangular cycle performance characteristics with nonlinear variable specific heats are analyzed by applying finite time thermodynamic theory when the objective functions are efficient power and power density, respectively. The different four-objective, three-objective and two-objective combinations are optimized based on the four objectives of the power density, efficient power, power output and efficiency by using the NSGA-II, then the results of the multi-objective optimizations are compared with those of the single-objective optimizations. The results show that, compared with the maximum power output point, although the heat engine efficiency at the maximum power density working point reduces by 10.97%, the heat engine size reduces by 30.84%; compared with the maximum power output point, although the heat engine power output at the maximum efficient power working point reduces by 0.067%, the heat engine efficiency increases by 0.21%. In the MO optimization results, the smallest deviation index is 0.2371; in the single-objective optimization results, the smallest deviation index is 0.2380; so the optimization result of the MO is better than those of the single-objectives.

Coupling effect between heat flux distribution and buoyancy of supercritical CO2 heat transfer with nonuniform heat flux in parabolic-trough collector

To promote the development of concentrating solar power generation technology using supercritical CO2 (sCO2), the heat transfer under non-uniform heat flux in the parabolic-trough collector was numerically simulated with emphasis on the coupling effect of the heat flux distribution, the property variations and the buoyancy effect. The non-uniform heat flux effect was first analyzed by comparing with two typical uniform heat flux conditions, which showed that the non-uniform heat flux reduced the overall heat transfer rate below that of the average uniform heat flux. Neither the average nor the maximum heat flux predictions could accurately reflect the heat transfer uniformity characteristics with the non-uniform heat flux. The circumferential non-uniformity was underestimated even with the maximum heat flux. Then, the analysis of the interaction between property variations and buoyancy effect showed that the use of sCO2 improves the heat transfer rate. The buoyancy effect dominates in modifying the flow field, which always enlarges the difference between top and bottom. The specific heat and viscosity variation effects are canceled out by the thermal conductivity variation. The buoyancy presents a negative effect on heat transfer when acting alone, but improves the heat transfer ability and their uniformity when coupled with the other property variations. Finally, the heat flux distribution effect coupled with the buoyancy effect was analyzed through changing the solar elevation angles. The maximum heat transfer coefficient is always located near the tube bottom due to the secondary flow effect. The circumferential non-uniformity increases with increasing Δθ as the relationship between heat flux distribution and the buoyancy effects change from competing to synergistic.

Maximizing Efficient Power for an Irreversible Porous Medium Cycle with Nonlinear Variation of Working Fluid’s Specific Heat

Considering the specific heat characteristics of working fluid and existence of various losses in a porous medium (PM) cycle, this paper applies finite time thermodynamic theory to study its efficient power performance with nonlinear variable specific heat model. Range of the cycle pre-expansion ratio is obtained by solving the equation, and PM cycle is converted to Otto cycle by choosing appropriate pre-expansion ratio. Influences of pre-expansion ratio, specific heat characteristics, temperature ratio, and various losses on cycle performances are investigated. Thermal efficiencies are compared at operating points of the maximum power output and efficient power. The results show that PM cycle has better performance than Otto cycle. Under certain conditions of parameters, thermal efficiencies at the maximum efficient power and maximum power output operating points are 50.45% and 47.05%, respectively, and the former is 7.22% higher than the latter. The engine designed with the maximum efficient power as the criterion can improve thermal efficiency by losing less power output. The results of this paper can guide parameters selection of actual PM heat engine.

Influence of Multi‐Orbitals and Hund's Coupling Induced Pseudogap on Specific Heat Jump in Iron‐Pnictide High T c Superconductors

A three-orbital per site theoretical model study is attempted to analyze nature of specific heat in iron-based superconductors. Based on recent experimental data in these systems, it is found that Fe five 3d orbitals, Hund’s coupling and intra- and inter-electron orbital correlations play significant role in electronic properties of these systems. Thus, in present work, we employed model Hamiltonian, containing hopping between orbitals, Hund’s coupling and intra- and inter- orbital Coulomb interactions for iron pnictide. Employing Green’s function technique within BCS mean field approximation, expressions of superconducting energy gap parameter and quasiparticle energies are obtained. Considering these parameters, we calculated specific heat and analyzed its variation with temperature and other parameters of model Hamiltonian. Also, a pseudogap (PG) parameter, arising out of multi-orbitals’ Hund’s coupling, as supported by ARPES and STM experiments, is introduced. The expression of specific heat is numerically analyzed to pinpoint its variation below and above transition temperature (T c ). A self-consistent numerical analysis of the specific heat jump as a function of multi-orbital hopping, electron interactions and Hund’s coupling in terms of PG parameter is shown in detail. Finally, we compared outcomes with recent theoretical and experimental data available on specific heat variations in iron superconductors like LaOFeAs system. This article is protected by copyright. All rights reserved.

Three issues on nozzle thrust performance in cold-to-hot correlation considering variable specific heat effect

A high-temperature effect is crucial in cold-to-hot correlation for thrust nozzles to employ experimental data of cold flow to predict the real flight performance of hot gas. The high-temperature nozzle flow behaves beyond the classical gas dynamics and restricts the feasibility of cold-flow experiments, and it becomes more severe due to the species transformation from cold air to hot gas when safety and cost are considered. For an in-depth awareness, this work refines three fundamental issues regarding the high-temperature variable specific heat effect on nozzle flow characteristics. A comprehensive analysis is performed from theory to applications. First, the flow properties of calorically perfect gas (CPG) and thermally perfect gas (TPG) are distinguished and connected via the basic flow equations. One-dimensional flow theory is extended by the generalized stagnation–static gas functions for TPG. The unanticipated intersections within pressure are discovered, which could produce substantial perplexities in nozzle performance determinations. Second, the pros and cons of two homologous nozzle thrust coefficients are clarified on application objects, definition methods, and solution manners. It is proved that temperature has no influence on thrust coefficients for CPG, while the variable specific heat effect might induce three types of false-positive thrust coefficients, to make flow state unidentified, and further shake the baseline of nozzle performance. Third, for the aggravated variable specific heat effect in cold-to-hot correlation from air to hot gas, two methods are proposed with reliable verifications to solve this issue through introducing a novel concept of relative nozzle operating conditions.

The enthralling effect of packing on the light emission of pyridazinone based luminophore: Crystallographic, electronic absorption and computational studies

The present study unfolds the synthesis and characterization of a new butylidine linked hetero dimer of pyridazinone (PNP). The crystal structure analysis of PNP reveals that it exhibited infinite 1D linear chains connected through C-H∙∙∙O interaction and interlayer connectivity was supported by the unconventional orthogonal dipolar interaction via nitro-aromatic (ONO2···π(C)Ar). These interactions are also described using DFT calculations and are potentially studied. Here we discuss the influence of crystal structure on the photophysical properties of a new solid state emitter containing brick layer packing. Furthermore, we conducted detailed exploration of the intermolecular interactions that maintain the crystal packing of the structure by employing the Hirshfeld surface analysis and its corresponding two-dimensional fingerprint plots revealing that the C-H∙∙∙O interaction mainly stabilized the crystal structure. Time-dependent density functional theory (TDDFT) studies and observed nitro aromatic interactions (ONO2∙∙∙(C)Ar) in the crystal helped to explain the electronic behaviour of PNP. The validity of the computations is supported by a good agreement between the estimated and experimental values of the excitation energy transfer. Furthermore, we conducted detailed research on the Hirshfeld surface analysis and the intermolecular interactions that stabilize the crystal packing using their corresponding two-dimensional fingerprint plot. Some standard thermodynamical parameters such as specific heat, entropy and free energy have also been computed. In addition to this, the variation of specific heat with temperature has been explored.

Improving the indoor thermal environment in lightweight buildings in winter by passive solar heating: An experimental study

Traditional lightweight building envelopes with constant thermal properties are of small heat capacity and large thermal resistance. Lightweight building envelopes with variable thermal conductivity and variable equivalent specific heat capacity can promote passive solar heat gain for clean heating and improve the indoor thermal environment in winter. In this paper, a real-scale lightweight solar house integrated with flat gravity-assisted heat pipes and PCM (phase change material) was built up, and the indoor heating effects of four forms of the solar house were experimentally studied. The results showed that (1) the heat pipes efficiently transferred solar heat absorbed by the exterior surface of the south envelope into the indoor environment during the day and increased the average daytime indoor air temperature by 3.8°C, but this benefit was not proportional to the area of heat pipes. (2) The PCM effectively stored solar energy during the day and released heat to the indoor environment at night, and the daily range of indoor air temperature was reduced by 8.7°C, with only 81% mass and 33% volume of concrete block, respectively. (3) The solar house increased the effective proportion of solar energy for indoor heating from 8.7% to 57.5% in the form of DHP + PCM house.

Application of He's homotopy and perturbation method to solve heat transfer equations: A python approach

In this research article, an attempt has been made to solve the linear/nonlinear and steady/unsteady heat transfer equations using the Homotopy and Perturbation method (HPM). Moreover, the implementation of HPM has been done by using SymPy, a library in python, to solve problems symbolically. Total three problems were dealt viz. steady-state conduction with heat generation, lumped capacitance analysis with a variable specific heat of the material, and heat transfer in uniform rectangular fin with radiation from the surface. In all the cases, the HPM has given excellent results compared to the analytical and numerical. Finally, the execution of SymPy has been explained, and a detailed procedure to implement HPM through python has been presented for all three cases.

A New Entropy Function to Analyze Isentropic Processes of Ideal Gases with Variable Specific Heats.

A new entropy function s+ is defined in terms of the existing entropy function s° and temperature as s+ = s° − R lnT to facilitate the analysis of isentropic processes of ideal gases with variable specific heats. The function s+ also makes it possible to calculate the entropy changes of ideal gases during processes when volume information is available instead of pressure information and the variation of specific heats with temperature is to be accounted for. The introduction of the function s+ eliminates the need to use the dimensionless isentropic functions relative pressure Pr and relative specific volume vr of ideal gases and to tabulate their values. The Pr and vr data are often confused with pressure and specific volume, with an adverse effect on the study of the second law of thermodynamics. The new s+ function nicely complements the existing s° function in entropy change calculations: the former is conveniently used when volume information is given while the latter is used when pressure information is available. Therefore, the introduction of the new entropy function s+ is expected to make a significant contribution to the thermodynamics education and research by streamlining entropy analysis of ideal gases.

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.

Nonequilibrium Factor in the Structure of a Curved Shock Wave Refracted Into an Intensively Heated Medium

The role of thermal nonequilibrium state in the structure of a curved shock wave during its refraction into an intensively heated medium has been studied analytically and numerically. At elevated gas temperatures common for optical discharges and for moderate-to-strong shock intensities, the width of the zone of variable specific heat is on sub- to mm scale, and thus is comparable to the geometrical scale of the problem. The asymptotic temperature gap, the specific temperature distribution in the zone, and the relaxation zone width are discussed in connection with the changes in the contrast level of the shock images obtained with shadow techniques. Numerical examples are presented in spherical and elliptical geometries for the conditions of a laser-induced breakdown in pure nondissociating nitrogen gas.

DFT study of structural, electronic, magnetic, elastic, vibrational, thermodynamic and thermoelectric properties of XCrP (X= Ni, Pd and Pt)

This study of physical properties of the half-Heuslers compounds of XCrP (X = Ni, Pd, Pt) is performed in the framework of density functional theory (DFT). The results show that all compounds are stable in the ferromagnetic state. The DOSs reveal that NiCrP is half-metallic, whereas, PdCrP and PtCrP are nearly half-metallic. The elastic properties indicate that these compounds are ductile and anisotropic. The phonons dispersions show that NiCrP is dynamically stable, while the two others are unstable. The variation of specific heat at constant volume Cv with temperature obeys the Debye's law at low-temperature, and it obeys the classical Dulong–Petit's law at high temperature for NiCrP, while Cv of PdCrP and PtCrP don't follow the Debye law due to the negative phonons frequencies. The thermoelectric properties (TE) indicate that these compounds are n-type materials and suitable for TE applications.

Numerical Study on the Effect of Natural Gas on Aircraft Turbofan Engine Propulsion

The world has been concerned and worried about the depletion of the liquid oil fuel, besides new environmental rules are to be followed to reduce pollution hazards and global warming. The utilization of natural gas (as a near term fuel) and hydrogen (as long-term fuel) are receiving great attention, because they have less pollution effects. Since the aviation has a great deal in environmental pollution effects due to the cruise flight in the upper troposphere (supersonic aircraft) or in the lower stratosphere (subsonic aircraft) where most of the ozone concentrate, which helps in protecting the earth form ultra violet radiation. Therefore, the use of alternate fuel has a great attention in aviation. In the present study, the thrust specific fuel consumption and specific thrust for the aircraft during aircraft flight profile are predicted, when using aviation fuel and natural gas. The P&W JT9D –7R-turbofan jet engine is taken as a base line engine propelling the Boeing 747-200 aircraft as a base line aircraft with four engine nacelles mounted on wings. The model engine fuel-air cycle representation is carried out for design point calculations based on sea level static conditions and variable specific heats along engine components. The predicted engine performance results compared very well with the reported values by the manufacture. Predictions carried out using aviation fuel and natural gas show an increase in the specific thrust by 3% and decrease in the thrust specific fuel consumption by 14% and fuel to air ratio by 11%, when using natural gas.

Application of Euler Neural Networks with Soft Computing Paradigm to Solve Nonlinear Problems Arising in Heat Transfer.

In this study, a novel application of neurocomputing technique is presented for solving nonlinear heat transfer and natural convection porous fin problems arising in almost all areas of engineering and technology, especially in mechanical engineering. The mathematical models of the problems are exploited by the intelligent strength of Euler polynomials based Euler neural networks (ENN’s), optimized with a generalized normal distribution optimization (GNDO) algorithm and Interior point algorithm (IPA). In this scheme, ENN’s based differential equation models are constructed in an unsupervised manner, in which the neurons are trained by GNDO as an effective global search technique and IPA, which enhances the local search convergence. Moreover, a temperature distribution of heat transfer and natural convection porous fin are investigated by using an ENN-GNDO-IPA algorithm under the influence of variations in specific heat, thermal conductivity, internal heat generation, and heat transfer rate, respectively. A large number of executions are performed on the proposed technique for different cases to determine the reliability and effectiveness through various performance indicators including Nash–Sutcliffe efficiency (NSE), error in Nash–Sutcliffe efficiency (ENSE), mean absolute error (MAE), and Thiel’s inequality coefficient (TIC). Extensive graphical and statistical analysis shows the dominance of the proposed algorithm with state-of-the-art algorithms and numerical solver RK-4.

LATTICE DYNAMICAL STUDY OF TITANIUM (TI) BY USING CGW-VTBFS MODEL

In measurements of the phonon dynamics of bcc Titanium (Ti), In the present paper we have reported the lattice dynamical calculations which are performed by using the Clark-Gazis-Wallis (CGW) and Van der Waalsthree body force shell model (VTBFS).The theory is used to compute the phonon dispersion curves(PDC), the Specific heat variation &frequency distribution with the used temperature. The frequencies along the symmetry directions have plotted against the wavevector to obtain the phonon dispersion curves(PDC)from the present models, with the help of available experimental values. The obtained results are agreed well with experimental data.

A Comparative Study on Opto-Thermal Properties of Natural Clay Bricks Incorporating Dredged Sediments

The brick industry is currently facing a shortage of natural resources. Despite this, the demand for construction bricks is progressively increasing. Alternative materials, such as dredged sediments and solid organic waste, have been recently proposed as options to replace natural clay in brick manufacturing. Potential exploitation of dredged sediments in clay bricks is evaluated in this study. The chemical composition of the mixtures and the opto-thermal properties of brick samples, which differed for the dredged sediment content (from 10% to 50% of the clay weight), were investigated. Chemical analyses detected lower concentrations of heavy metals in bricks incorporating dredged sediments (DS). Negligible variations in thermal conductivity, thermal diffusivity, and specific heat were observed by increasing the amount of DS in the mixture. In particular, the thermal conductivity values ranged between 0.45 ± 0.03 W m−1 K−1 (DS-50) and 0.50 ± 0.03 W m−1 K−1 (DS-30). Conversely, the color shift value and spectral reflectance in the infrared field were found directly proportional to the concentration of DS. Using dredged sediments as building material demonstrated to be a solution to the problem of their disposal and the scarcity of raw materials, reducing the global warming score by up to 2.8%.

APPLICATION OF HOMOTOPY PERTURBATION METHOD TO THE MATHEMATICAL MODELLING OF TEMPERATURE RISE DURING MICROWAVE HYPERTHERMIA

We study a one dimensional non-linear model of multi-layered human skin exposed to microwave heating during cancer therapy. The model is analyzed using homotopy perturbation method and the fact that there are variations in specific heat, thermal conductivity and blood perfusion from one individual to another were considered. The purpose of this study was to investigate the effect of variable blood perfusion, microwave heating and thermal conductivity on the temperature field during microwave hyperthermia. By varying the parameters, we were able to determine maximum rise of temperature as an individual undergoes cancer therapy. The results were presented in graphs and it was discovered that the temperature of the tumor increases with increase in the microwave heating index while the blood perfusion remain constant.

Thermal Modelling and Multi Decision Making Optimization of EDM of Non Conductive SiC-CNT Ceramic Composite Used for Li-ion Battery and Sensor

In this research work the thermal modeling of a nonconductive Silicon carbide Ceramic matrix composite (CMC) machined by Die Sinking Electric Discharge Machining (EDM) has been done. Though SiC is a non-conductive material but the presence of CNT makes it a conductive material which can be machined with EDM. The modeling procedure carried out by considering some realistic approach like Gaussian heat Flux, Specific Discharge Energy, Variable Latent heat etc. For this analysis a 2D continuum has been designed as work domain. By simulating the work domain model by a Finite Element Analysis (FEA) Software (COMSOL), material removal rate (MRR) has been estimated with variable thermal properties. Parametric analysis of effect of Variable Specific heat on MRR by considering different current, Voltage and Pulse-On time has been performed. The effect of different input parameters (peak current and Pulse-on time) on Crater geometry has been done. A new concept of Specific discharge energy has been introduced during modelling to make it a more realistic model which can also be used as electrode support for electrochemical energy devices as Polymer Electrolyte Membrane Fuel Cells on Li-ion battery. Desirability analysis has been done to get an optimize set of input parameters for I= 3A, V=30V, Ton= 75 µs for machining ceramic matrix composite by EDM. The optimized MRR at this setting is 7.25 mm3/min whereas PFE is 87%. The experimental analysis has been also performed to strengthen the thermal and mathematical modelling.