Thermophysical Properties Of Gases Research Articles

Three-dimensional analysis of gas flow and heat transfer in a regenerator with alumina balls

A three-dimensional (3D) unsteady mathematical model for regenerator with alumina balls has been developed based on the assumption of porous media and solved by a commercial computational fluid dynamics (CFD) software, FLUENT. The standard k–ɛ turbulence model combined with standard wall functions is used for modeling gas flow. Momentum equation is revised to consider the impact of porous media on fluid flow. Radiation from combustion gas to the storage materials is considered in the model. User-defined functions (UDFs) program has been developed in C language and linked to FLUENT to define user-defined scalar (UDS) transport equation of energy conservation for solid phase, and to calculate interphase heat transfer as well as thermophysical properties of gas and solid phases, which are dependent on temperature. The calculated results were compared with test data, and the maximum relative error is 3.73%. Results of the model calculation showed that after 25 times of alternate changes in heating and cooling cycles, the heat absorption of regenerative balls is equal to heat released to air, implying the operation of regenerator reaches steady state. As the ball diameter decreases, the pressure gradients become steep and fluid velocity decreases. To reduce temperature difference in the horizontal plane, the geometry of the regenerator has been optimized by the model.

Properties of Humid Air for Calculating Power Cycles

Accurate calculation algorithms for the thermodynamic and transport properties of humid air are required for modeling compressed air energy-storage power cycles and designing their individual components. The development of such algorithms was part of the Advanced Adiabatic Compressed Air Energy Storage (AA-CAES) project, which had been supported by the European Commission. To obtain the statements of this paper, all available experimental data and new experimental data generated within the AA-CAES project were used as basis for comparisons between the different models for thermodynamic and transport properties. As a result, one model for calculating thermodynamic and one model for transport properties of humid air in AA-CAES cycle design and operation is recommended. Their application is possible for wide ranges of temperature from 243 K up to 2000 K, total pressure from 0.611 kPa up to 100 MPa, and water content up to 10% mass fraction with some restrictions concerning the calculation of viscosity η and thermal conductivity λ (up to 1000 K for both and up to 40 MPa for λ). These models have been implemented into a property library, which meets the requirements of programs for calculating compressed air energy-storage cycles. The developed property library can be used for the daily work of an engineer who calculates such cycles. The results summarized in this paper have been used for preparing Section 6, “Real Gas” of the ASME Report No. STP-TS-012, “Thermophysical Properties of Gases used in Working Gas Turbine Applications.”

Automated System for Calculating Thermophysical Properties of Fluids and Thermal Processes of Cryogenic Plants

An automated system for calculating thermophysical properties of gases and liquids over a wide range of parameters has been developed. On the basis of values of the properties, the processes of isothermal compression, adiabatic throttling, polytropic expansion, heat exchange in two- and multi-stream heat exchangers, separation of vapor-liquid mixtures in the liquid vessel, and rectification in an air separation plant can be analyzed. For a specified structure scheme of a cryogenic plant, optimization of a corresponding thermodynamic cycle can be fulfilled.

Thermophysical properties of gases, liquids, and solids composed of particles interacting with a short-range attractive potential.

A short-range polynomial interaction potential is introduced which has both a repulsive core and an attractive part. It is cut off smoothly such that its first and second derivatives vanish at the cutoff distance. The potential therefore enables efficient simulation studies of a model material that exhibits similarities to a full (but computationally expensive) classical Lennard-Jones system. Thermophysical properties of the model are calculated by (nonequilibrium) molecular dynamics computer simulations and compared with analytical results. Among the quantities studied is the pressure as a function of the density for various temperatures. Equations of state for the fluid and the solid are tested. The coexistence of gaseous, (metastable) liquid, and fcc solid phases is found for a range of temperatures. Bulk and shear moduli are computed. The response of the system to a shear deformation with a constant shear rate is analyzed. The liquid shows viscoelastic behavior that can be described with a Maxwell model. The solid behaves as an elastic medium up to a finite deformation and then undergoes a transition to plastic flow, which is stick-slip-like at small shear rates and continuous at higher ones.

Transient Phenomena in d.c. Plasma‐Spray Torches

ABSTRACT: D.c. plasma torches have been involved for many years in industrial applications such as welding, cutting or deposit elaboration by plasma spraying or plasma assisted vapor deposition. These techniques use specific properties of plasmas produced by d.c. arcs where high temperatures (up to 25000 K) and high flow velocities (up to few km/s) are available. A considerable amount of experimental work was devoted, in the past, to characterize the properties of arc jets as a function of arc current, torch design and configuration, plasma forming gas thermophysical properties and flowrate. In the same time models approached more and more accurately the behavior of arc jets, testifying of a real advance in both knowledge and understanding of the different implicated processes and mechanisms.Nevertheless, and mainly because of experimental difficulties, transient phenomena due to arc instabilities have been less intensively studied and their interest has only been underlined the last decade, although they were mentioned more than thirty years ago.Due to the extraordinary progress accomplished in the field of instrumentation, new diagnostic techniques have become available, accompanied by powerful signal processing methods which are now easy to apply thanks to the development of computers and associated software. It has been experimentally demonstrated in plasma torches that the arc is submitted to gas dynamic forces which give rise to two different modes of instability among which two major cases can be distinguished. The first one is the so‐called “take‐over” mode, characterized by rather low fluctuations of arc voltage compared to the mean value, the second one being the “restrike” mode, for which the fluctuations of arc voltage are about the same in amplitude than the mean value. The restrike mode is clearly identified as the result of the stretching of the arc by the cold gas flow, followed by electrical breakdown of the cold gas layer which gives rise to a new arc‐anode attachment. The stretching‐rearcing sequences are repeated at a frequency which is governed by experimental conditions and give a sawtooth shaped voltage signal, the analysis of which provides clear information about the arc dynamics. The fluctuations of arc length generate strong voltage variations which are correlated to the electrical power supplied to the gas and, as a consequence, to the variations of the arc jet temperature and velocity. The amplitude and frequency of voltage fluctuations can be related to the torch working and geometrical parameters and dimensional analysis allow to establish reliable semi‐empirical correlations. Temperature and velocity distributions are strongly correlated to the torch working conditions and the resulting fluctuations. It will be illustrated for different operating conditions of a d.c. spray torch.

Pyroelectric anemometry: Theory of operation

A thermal model is developed to describe the electrical response of a new thermal flow sensor, the pyroelectric anemometer (PA), as a function of the laminar flow rate. For low Reynolds numbers ( Re ), i.e., Re ≤ Re c , the PA response is proportional to Re . For Re > Re c , the PA response is proportional to . The critical Reynolds number, Re c , is a function of the gas's thermophysical properties, the thermal excitation frequency, and the spacing of the measuring electrodes relative to the central heater strip. The theoretical predictions are compared with experimental observations. The Reynolds numbers examined in this study range from 0.01 to 10 4 . To provide a more critical test of the model, no 'adjustable' parameters are introduced into the theory. The deviations between the theory and experiment can be accounted for by the limitations of the idealized theoretical treatment of the problem.

Pyroelectric anemometry: Theory of operation

A thermal model is developed to describe the electrical response of a new thermal flow sensor, the pyroelectric anemometer (PA), as a function of the laminar flow rate. For low Reynolds numbers (Re), i.e., Re ≤ Rec, the PA response is proportional to Re. For Re > Rec, the PA response is proportional to . The critical Reynolds number, Rec, is a function of the gas's thermophysical properties, the thermal excitation frequency, and the spacing of the measuring electrodes relative to the central heater strip. The theoretical predictions are compared with experimental observations. The Reynolds numbers examined in this study range from 0.01 to 104. To provide a more critical test of the model, no 'adjustable' parameters are introduced into the theory. The deviations between the theory and experiment can be accounted for by the limitations of the idealized theoretical treatment of the problem.

ACCURATE CALCULATION OF THE HIGH TEMPERATURE THERMOPHYSICAL PROPERTIES OF GASES

The kinetic theory of gases can be used to accurately calculate the transport properties of gases based on knowledge of the intermolecular potential between the interacting atoms, molecules or ions. This approach has been especially useful at high temperatures where experimental transport data are either sparse or unavailable. In recent years, increasingly accurate potentials for atom-atom and atom-ion interactions have become available for such calculations, and approaches for applying these potentials to calculate the high temperature thermophysical properties of gases are described.

Review on Heat Transfer in Gas Solid Fluidized Beds

This review covers those aspects of heat transfer in fluidized beds related to bed/immersed tubes and bed/vessel walls heat transfer coefficients correlations. These correlations generally incorporated the effects of operating conditions, bed and gas thermophysical properties and bed size and geometry. Experimental as well as empirical dimensionless models are presented. The general tendency in the literature is towards building up more realistic hydrodynamic models which incorporate particle and gas convective heat transfer components, solids residence time and local bubble behaviour at immersed surfaces. It is also generally recognized in the literature that heat transfer cannot be satisfactorily explained on the basis of stationery models but rather on the basis of unsteady state heat conduction models of solids movement induced by rising bubbles. The aspects of research mostly overlooked in the surveyed investigations were those related to interphase heat transfer and the effect of operation under elevated temperatures and pressures.

Thermophoretically augmented mass-, momentum- and energy-transfer rates in high particle mass loaded laminar forced convection systems

In previous treatments of thermophoretically modified aerosol particle transport, even those which allowed for variable host gas thermophysical properties, it has been assumed that the particle mass fraction is small enough to neglect the influence of the suspended particles on the hot gas momentum density and energy density fields. However, in high-intensity materials processing applications [e.g. optical waveguide (OWG) “preform” deposition from silica-mist-laden combustion products] particle mass loadings often exceed 1 3 , and the thermophoretically enhanced particle mass deposition flux itself modifies the local mixture velocity and temperature fields in the vicinity of the deposition surface. A self-consistent pseudo-single-phase mixture (“diffusion”) approximation, which exploits the fact that the volume fraction of suspended particles is negligible even when the particle mass fraction is quiet near the unity, is introduced here to calculate the fully coupled problem of mass, energy and momentum diffusion-convection for laminar boundary layer (LBL) flows of a combustion gas mixture containing submicron particles of appreciable thermophoretic diffusivity but negligible Brownian diffusivity. It is shown that high particle mass loading systematically increases the wall fluxes of momentum (shear stress), heat and particle mass, much like the effects associated with “massive suction” in the single-phase LBL theory. Indeed, a simple rational correlation approach is introduced to capture the essential interactions leading to higher transport coefficients in such high mass loaded aerosol systems. The transfer coefficients we obtain from our “exact” numerical integrations of the self-similar LBL equations can be used to estimate LBL development and associated particle mass fluxes to surfaces of “arbitrary” shape. Moreover, we illustrate how they can also be used to predict the mass transfer behaviour of systems governed by more complex (radiation-convection) boundary conditions. Under conditions relevant to OWG perform deposition, we demonstrate, a posteriori, that our tractable mathematical model, which neglects the mass transfer effects of particle inertia (momentum, thermal), infrared-radiation absorption, DuFour energy transfer, and particle-particle coagulation, is fully self-consistent. This approach to high particle mass loaded materials processing applications has also opened the door to rational predictions of the partitioning of dopants (e.g. Ge, B, P, …) between the vapor and particle phases and, hence, the rather complex connection between deposit (OWG perform) and process feed compositions.

Evaluation of Peng-Robinson Equation of State in Calculating Thermophysical Properties of the Gas Turbine Combustion Gases

Abstract Abstracl-A number of thermophysical properties of combustion gases of gas turbin e engine using the Peng-Robinson equ ation of state have been compared to experimental values obtained in this study and shown to be more accurate than those obtained from virial equation of state. The studied properties were: density, specific heat, enthalpy, entropy, viscosity and thermal conductivity in a temperature range of 200-2600 K and a pre ssure range of 3-12 atmospheres.

Thermodynamic and transport properties of gases from sophisticated potential models

The statistical mechanical equations for the thermophysical properties of dilute gases are evaluated using sophisticated, but still practical potential models with no more than three adjustable parameters. Universal combination rules for these parameters are formulated. It is shown that some data of dilute gas thermophysical properties of monatomic and simple linear molecules yield potential parameters that can be used to predict all other thermophysical properties of the pure gases and their mixtures with excellent accuracy. For monatomic fluids, these potentials are shown to give excellent results of the thermodynamic functions also in the liquid and dense gaseous state.

Japanese research on thermophysical properties of fluids

Japanese research activities on thermophysical properties of gases and liquids, as well as some historical background, are outlined. The current situation is explained for industrially important substances, such as water and steam, high pressure gases and liquids, refrigerants, molten salts, and other fluids. Related activities are also briefly introduced. Although some of the Japanese studies can be traced back to more than 50 years ago, a systematic effort has been visible only in the last 20 years. However, quite recently, thermophysical properties research has begun to attract attention of more people in science and industry in Japan, probably as the natural sequence to the progress of technology.

Calculation of thermophysical properties of gases for certifying gas mixtures with respect to composition

Calculation of thermophysical properties of gases for certifying gas mixtures with respect to composition

Effect of the thermophysical properties of gases and molten metals on the properties of atomized powders

1. A study was made of the disintegration of molten metals in argon, helium, nitrogen, and air streams. It was found that gaseous energy carriers having low values of thermophysical parameter (II = λg ·γ0.5/η0.5) ensure that the drops remain longer in the liquid state, thereby promoting more intense comminution. 2. It was established that the intensity of disintegration of molten metals grows with increase in their heat capacity. Using iron and silver as examples, it is demonstrated that the effect of η and σ of molten metals on the resultant particle size manifests itself clearly only when similar drop cooling rates are employed. 5. It is shown that the size of the particles being formed depends on the length of the zone in which the particles remain in the liquid state; this is evidence that the process of molten metal comminution is a continuous one, taking place both in the atomization focus and outside this zone. 4. The differences in microstructure found among equal-sized 80NM alloy particles are linked with variations in the velocity of the gas stream, resulting in different particle solidification rates.