Temperature-dependent Specific Heats Research Articles

Thermal Behavior of a Flow in a Pulsed Detonation Thermal Spraying Device

In the present work, a numerical investigation has been performed to study the thermal behavior of a flow through a pulsed detonation thermal spray device that employs a hydrogen-air mixture. In this device, a detonation wave travels inside a detonation tube and eventually exits the tube and impinges against a substrate. Two types of substrates have been investigated, namely, a sphere and a flat-plate. The present model is based on solving the two dimensional, axisymetric Euler reactive flow equations with temperature-dependent specific heats. A global single step finite rate reaction has been considered. The present results demonstrate the effects of two main parameters on the thermal performance of the device under consideration. These parameters are: the size and shape of the substrate, and the stand off distance.

Effects of radiative heat transfer on the structure of turbulent supersonic channel flow

The interaction between turbulence in a minimal supersonic channel and radiative heat transfer is studied using large-eddy simulation. The working fluid is pure water vapour with temperature-dependent specific heats and molecular transport coefficients. Its line spectra properties are represented with a statistical narrow-band correlated-k model. A grey gas model is also tested. The parallel no-slip channel walls are treated as black surfaces concerning thermal radiation and are kept at a constant temperature of 1000 K. Simulations have been performed for different optical thicknesses (based on the Planck mean absorption coefficient) and different Mach numbers. Results for the mean flow variables, Reynolds stresses and certain terms of their transport equations indicate that thermal radiation effects counteract compressibility (Mach number) effects. An analysis of the total energy balance reveals the importance of radiative heat transfer, compared to the turbulent and mean molecular heat transport.

Effects of radiative heat transfer on the structure of turbulent supersonic channel flow

The interaction between turbulence in a minimal supersonic channel and radiative heat transfer is studied using large-eddy simulation. The working fluid is pure water vapour with temperature-dependent specific heats and molecular transport coefficients. Its line spectra properties are represented with a statistical narrow-band correlated-k model. A grey gas model is also tested. The parallel no-slip channel walls are treated as black surfaces concerning thermal radiation and are kept at a constant temperature of 1000 K. Simulations have been performed for different optical thicknesses (based on the Planck mean absorption coefficient) and different Mach numbers. Results for the mean flow variables, Reynolds stresses and certain terms of their transport equations indicate that thermal radiation effects counteract compressibility (Mach number) effects. An analysis of the total energy balance reveals the importance of radiative heat transfer, compared to the turbulent and mean molecular heat transport.

Performance of Diesel cycle with heat transfer, friction and variable specific heats of working fluid

AbstractThe performance of an air standard Diesel cycle with heat transfer loss, friction-like term loss and variable specific heats of working fluid is analysed by using finite time thermodynamics. The relationships between the power output and the compression ratio, between the thermal efficiency and the compression ratio, as well as the optimal relationship between the power output and the efficiency of the cycle are derived by detailed numerical examples. Moreover, the effects of temperature dependent specific heats of working fluid on the irreversible cycle performance are analysed. The results show that the effects of temperature dependent specific heats of working fluid on the irreversible cycle performance are obvious, and they should be considered in practice cycle analysis. The results obtained in the present paper may provide guidance for the design of practice Diesel engines.

Effects of heat loss as percentage of fuel’s energy, friction and variable specific heats of working fluid on performance of air standard Otto cycle

The objective of this study is to analyze the effects of heat loss characterized by a percentage of the fuel’s energy, friction and variable specific heats of working fluid on the performance of an air standard Otto cycle with a restriction of maximum cycle temperature. A more realistic and precise relationship between the fuel’s chemical energy and the heat leakage that is based on a pair of inequalities is derived through the resulting temperature. The variations in power output and thermal efficiency with compression ratio, and the relations between the power output and the thermal efficiency of the cycle are presented. The results show that the power output as well as the efficiency where maximum power output occurs will increase with increase of the maximum cycle temperature. The temperature dependent specific heats of the working fluid have a significant influence on the performance. The power output and the working range of the cycle increase with the increase of specific heats of the working fluid, while the efficiency decreases with the increase of specific heats of the working fluid. The friction loss has a negative effect on the performance. Therefore, the power output and efficiency of the cycle decrease with increasing friction loss. It is noteworthy that the effects of heat loss characterized by a percentage of the fuel’s energy, friction and variable specific heats of the working fluid on the performance of an Otto cycle engine are significant and should be considered in practical cycle analysis. The results obtained in the present study are of importance to provide good guidance for performance evaluation and improvement of practical Otto engines.

Venus atmosphere profile from a maximum entropy principle

Abstract. The variational method with constraints recently developed by Verkley and Gerkema to describe maximum-entropy atmospheric profiles is generalized to ideal gases but with temperature-dependent specific heats. In so doing, an extended and non standard potential temperature is introduced that is well suited for tackling the problem under consideration. This new formalism is successfully applied to the atmosphere of Venus. Three well defined regions emerge in this atmosphere up to a height of 100 km from the surface: the lowest one up to about 35 km is adiabatic, a transition layer located at the height of the cloud deck and finally a third region which is practically isothermal.

Influence of heat loss on the performance of an air-standard Atkinson cycle

This study is aimed at investigating the effects of heat loss, as characterized by a percentage of fuel’s energy, friction and variable specific heats of the working fluid, on the performance of an air-standard Atkinson cycle under the restriction of the maximum cycle-temperature. A more realistic and precise relationship between the fuel’s chemical-energy and the heat leakage is derived through the resulting temperature. The variations in power output and thermal efficiency with compression ratio, and the relations between the power output and the thermal efficiency of the cycle are presented. The results show that the power output as well as the efficiency, for which the maximum power-output occurs, will rise with the increase of maximum cycle-temperature. The temperature-dependent specific heats of the working fluid have a significant influence on the performance. The power output and the working range of the cycle increase while the efficiency decreases with the rise of specific heats of working fluid. The friction loss has a negative effect on the performance. Therefore, the power output and efficiency of the Atkinson cycle decrease with increasing friction loss. It is noteworthy that the results obtained in the present study are of significance for providing guidance with respect to the performance evaluation and improvement of practical Atkinson-cycle engines.

Numerical simulation of a dual-source supersonic plasma jet expansion process: continuum approach

Expanding thermal plasma (ETP) is a versatile technology for thin film deposition process with directional plasma flux and high deposition rates. This process involves expansion of supersonic plasma jets through a steep pressure ratio into a chamber maintained at near vacuum. Usually the plasma jets deviate from chemical and thermal equilibrium and the continuum approach is insufficient to describe the phenomena. In the current work, the continuum approach based Navier–Stokes equations have been implemented to study and understand the jet expansion process in a typical dual-arc plasma deposition reactor. The numerical predictions have been compared against in-house experimental data obtained by thermocouple measurements. For the range of back pressures (6–200 Pa) considered, it was observed that the jet core is supersonic and transitions to a subsonic zone downstream without the formation of any Mach disc for the prevalent operating parameters. Indications of thick and smeared barrel shocks were however observed in the computed flow-thermal fields. The modelled fluid was assumed to be a perfect gas with temperature dependent specific heats, thermal conductivity and viscosity coefficients, with constant Prandtl number of order unity. The radial spreads of the jets increase with increasing pressure ratio thus leading to enhanced interactions within reduced distances downstream of the nozzle exit. The jet core Mach number also increases, but moderately, with decreasing backpressure. It is concluded that within reasonable accuracy, continuum approach based calculations are able to capture most of the important phenomena involved in compressible, high-temperature, supersonic jet expansion processes which are essential in designing chambers relevant to the mentioned processes.

Performance analysis of an air-standard Miller cycle with considerations of heat loss as a percentage of fuel's energy, friction and variable specific heats of working fluid

This study is aimed at examining the effects of heat loss characterized by a percentage of fuel's energy, friction and variable specific heats of working fluid on the performance of an air-standard Miller cycle under the restriction of maximum cycle temperature. A more realistic and precise relationship between the fuel's chemical energy and the heat leakage that is constituted on a pair of inequalities is derived through the resulting temperature. The variations in power output and thermal efficiency with compression ratio, and the relations between the power output and the thermal efficiency of the cycle are presented. The results show that the power output as well as the efficiency where maximum power output occurs will increase with the increase of maximum cycle temperature. The temperature-dependent specific heats of working fluid have a significant influence on the performance. The power output and the working range of the cycle increase while the efficiency decreases with the increase of specific heats of working fluid. The friction loss has a negative effect on the performance. Therefore, the power output and efficiency of the cycle decrease with increasing friction loss. Comparison of the performance of air-standard Miller and Otto cycles are also discussed. Miller cycle has larger power output and efficiency than Otto cycle does, i.e., Miller cycle is more efficient than Otto cycle. It is noteworthy that the effects of heat loss characterized by a percentage of fuel's energy, friction and variable specific heats of working fluid on the performance of a Miller-cycle engine are significant and should be considered in practice cycle analysis. The results obtained in the present study are of importance to provide a good guidance for the performance evaluation and improvement of practical Miller engines.

Lattice dynamics for fcc rare gas solids Ne, Ar, and Kr fromab initiopotentials

Specific heat at constant volume calculations are presented from lattice dynamic calculations of harmonic phonon branches for the face-centered cubic crystals of Ne, Ar, and Kr using ab initio two-body potentials. The calculated temperature-dependent specific heats and derived Debye temperatures are in good agreement with experimental results. The unusually low Debye temperature of Ne in comparison to the heavier rare gas solids is analyzed in detail.

Thermodynamic modeling of spark-ignition engine: Effect of temperature dependent specific heats

This paper presents thermodynamics analysis of spark-ignition (SI) engine. A theoretical model of air-standard Otto cycle having temperature dependent specific heats has been implemented. It was compared to that which uses constant temperature specific heats. Wide range of engine parameters was studied. In most cases there were significant variations between the results obtained by using temperature dependent specific heats with those obtained at constant specific heats especially at high engine speeds. Therefore, it is more realistic to use temperature dependent specific heat. This should be considered in cycle analysis; especially that temperature variation in the actual cycles is quite large.

Flammes planes avec transport multi-espèce et chimie complexe

We consider plane laminar flames with multicomponent transport and complex chemistry. The governing equations are derived from the kinetic theory of gases. An arbitrary number of reversible chemical reactions and temperature dependent species specific heats are considered in the model. The most general form for multicomponent transport fluxes given by the kinetic theory is also taken into account. Upon first considering a bounded domain and then letting the size of the domain to go to infinity, we obtain an existence theorem. A priori estimates fundamentally rely on the entropy which correlates the transport fluxes and the gradients.

A phase change problem with temperature-dependent thermal conductivity and specific heat

A semi-analytic solution is obtained to model conduction heat transfer with phase change into a semi-infinite slab, where the thermal conductivities and specific heats of both phases are a linear function of the temperature. This model extends the model of a previous work to include temperature-dependent specific heats.

Temperature-dependent Specific Heats of Dry Soil Materials

Specific heat measurements have been made on several soil materials at different temperatures in order to obtain a generalized functional relation between specific heat and temperature. Specific heats were found to vary linearly with temperature from 200 to 300 °K (−73 °C to + 27 °C) and extrapolated close to zero at 0 °K. Consequently, the functional relation between specific heat and temperature for soil materials may be approximated as Cp = mT where Cp is the specific heat, T is the absolute temperature (°K), and m is a proportionality constant. Such a relation permits the prediction of the specific heats at any temperature normally encountered in the field once reliable specific heats have been determined at a single temperature.

Models of the Lunar Surface with Temperature-Dependent Thermal Properties.

view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Models of the Lunar Surface with Temperature-Dependent Thermal Properties. Linsky, Jeffrey Abstract For the interpretation of recent data on lunar thermal emission, I have written a Fortran encoded computer program to solve the heat conduction equation and to compute radio brightness temperatures for a medium having conductive and radiative energy transport and characterized by arbitrary temperature- and depth-dependent thermal properties. This program will also solve periodic heat conduction problems of a more general nature. A number of models were constructed with a range of temperature-dependent conductivities and specific heats, but each was consistent with the minimum surface temperature of 900 K observed l~y Low (Astrophys. J. 142, 806, 1965) at the morning terminator. All of these models predict infrared and radio brightness temperatures for eclipses and lunations which agree favorably with high-resolution data for the center of the lunar disk. If there are no internal heat sources, a significant increase in the mean radio brightness temperature with wavelength occurs when the conductivity, but not the specific heat, increases with temperature. This increase in the mean radio brightness temperature results from the nonlinear nature of heat conduction under these circumstances, and is sufficient to explain the observed increase with wavelength described by Krotikov and Troitskii (Soviet Phys. Usp. 6, 841, 1964), without requiring as a postulate an unusually high level of radioactivity in the moon. The general behavior of silicates at lunar temperatures and laboratory measurements of probable lunar materials suggest that radiative energy transport is the most probable mechanism to account for an increase in the conductivity with temperature. Several models in which radiative transfer and thermal conduction are of comparable importance at 3500K agree favorably with the data of Krotikov and Troitskii. The present findings support the hypothesis that porous or frothy material characterize the lunar surface at least to a depth of 20 cm, and are in agreement with radar depolarization studies. This research was sponsored by NASA. Publication: The Astronomical Journal Pub Date: 1966 DOI: 10.1086/110133 Bibcode: 1966AJ.....71S.168L full text sources ADS |