Thermal Conductivity Of Liquids Research Articles

Thermal conductivity of binary refrigerant mixtures of HFC-32/125 and HFC-32/134a in the liquid phase

The liquid thermal conductivity of mixtures of HFC-32/125 and HFC-32/134a was measured using the transient hot-wire apparatus in the temperature ranges from 213 to 293 K and from 193 to 313 K, respectively, in the pressure range from 2 to 30 MPa and with HFC-32 mass fractions of 0.249, 0.500, and 0.750 for each system. The uncertainty of the thermal conductivity was estimated to be ±0.7%. For practical applications, the thermal conductivity data for the two mixtures were represented by a polynomial in temperature, pressure, and mass fraction of HFC-32 with a standard deviation of 1.0%.

Thermal conductivity of ternary refrigerant mixtures of HFC-32/125/134a in the liquid phase

The liquid thermal conductivity of two ternary mixtures of HFC-32/125/134a (23.0/25.0/52.0 and 19.0/43.8/37.2 wt%) was measured using a transient hot-wire instrument in the temperature ranges from 193 to 293 K and from 213 to 293 K, respectively, and in the pressure range from 2 to 30 MPa. The thermal conductivity has an estimated uncertainty of ±0.7%. For engineering purposes, the thermal conductivity data were correlated using a polynomial in temperature and pressure for each mixture with a standard deviation of 0.6%.

98/04161 Saturated liquid thermal conductivity correlations for some new refrigerants

98/04161 Saturated liquid thermal conductivity correlations for some new refrigerants

Evaluated Equation Forms for Correlating Thermodynamic and Transport Properties with Temperature

Equation forms developed for use in correlating thermodynamic and transport properties with temperature have been developed and tested over almost 2 decades using a large pool of critically evaluated data over a wide temperature range. Usually only one equation form has been used for any single property in a given phase; however, alternate forms are sometimes recommended. Properties treated are solid and liquid vapor pressure, heat of vaporization, liquid and solid density, solid, liquid, and ideal gas heat capacity, second virial coefficient, liquid and vapor viscosity, liquid and vapor thermal conductivity, and surface tension. Equation forms vary from empirical polynomials to theoretically based forms, including polynomials, exponentials, inverse power, and trigonometric functions in temperature.

Absolute values of specific heat capacity and thermal conductivity of liquids from different modes of operation of a simple photopyroelectric setup

Photothermal techniques offer a nice tool for the determination of changes in thermal parameters of different types of samples. Using a very thin pyroelectric transducer, a very simple and versatile ac calorimeter can be built. The described inverse pyroelectric technique allows high-resolution ac-calorimetric measurements of the temperature dependence of the specific heat capacity. Since measuring frequencies up to a few hertz can be used, which are higher than in most alternative ac-calorimetric setups, noise can be reduced and measuring times shortened. With a small modification of the measurement cell, the determination of absolute specific heat capacity and thermal conductivity values of liquid samples was achieved. Comparison of the frequency response of the system with and without a solid thermal load in the neighborhood of the sample yields data with an accuracy of about 5% and 10% for specific heat capacity and thermal conductivity, respectively. If necessary, absolute values of specific heat capacity and thermal conductivity can also be obtained by making contact between a (solid) thermal load and the liquid. A pure ac-calorimetric operation is then no longer possible, thus restricting this mode of operation to homogeneous or to properly aligned anisotropic liquids.

Saturated liquid thermal conductivity correlations for some new refrigerants

Saturated liquid thermal conductivity correlations for some new refrigerants

Saturated liquid thermal conductivity correlations for some new refrigerants

This paper presents a set of linear equations describing the temperature dependence of the saturated liquid thermal conductivity covering the region of engineering importance for the new hydrofluorocarbons (HFC) 32, 125, 134a, 143a, 152a and hydrochlorofluorocarbons (HCFC) 123, 124, 141b and 142b. Available experimental data in the literature have been considered to arrive at a correlation of the form lambda = A - BT. It is observed that there exists an appreciable discrepancy between various sources of data in spite of the same purity of samples used and the same measurement technique being adopted. The correlations obtained here could be useful in engineering design applications. (C) 1998 John Wiley & Sons, Ltd.

A Correlation for the Prediction of Thermal Conductivity of Liquids

Correlation and prediction of transport properties are important in the design of heat- and mass-transfer equipment. Prediction of the thermal conductivity of liquids based only on theoretical grounds does not give good results because the theories describing the liquid state are far from satisfactory. In this paper, a semitheoretical method for the prediction of thermal conductivity is proposed and the results are compared with the recent methods by Arikol and Gurbuz and with the methods recommended by Reid et al.

Thermal Conductivity of HFC-32, HFC-125, and HFC-134a in the Solid Phase

Measurements of the thermal conductivity of HFC-32, HFC-125, and HFC-134a were carried out for the first time in both solid and liquid phases at the saturation pressure at room temperature and in the temperature ranges from 120 to 263, from 140 to 213, and from 130 to 295 K, respectively. A transient hot-wire instrument using one bare platinum wire was employed for measurements, with an uncertainty of less than ±2%. The experimental results demonstrated that the thermal conductivity of HFC-32, HFC-125, and HFC-134a in the solid phase showed a positive temperature dependence. For HFC-32 and HFC-125, there were big jumps between the solid and the liquid thermal conductivity at the melting point. But for HFC-134a, the solid and liquid thermal conductivity at the melting point is almost-continuous.

Spray counterflow diffusion flames of heptane: Experiments and computations with detailed kinetics and transport

Experiments and computations were conducted on counterflow spray diffusion flames of heptane under conditions of modest slip velocity between droplets and gas that ensured the validity of one-dimensional self-similar modeling. Comprisons were made at three different strain rates under conditions encompassing pseudo-gasenous flems, that is, flames without direct droplet-flame interaction, as well as a case in which some droplets penetrated the flame. Measurements of the temperature field by thermocouples and of the gaseous velocity, droplet velocity, and droplet size distribution by phase Doppler interferometric techniques were compared with the predictions of numerical simulations with detailed chemistry and transport. Droplet size distribution effects were modeled by a sectional approach. Good agreement between model predictions and measurements were found in all but one case. The discrepancy in the latter was attributed to buoyancy, a phenomenon that had not been accounted for in the model. The position of the computed flames was rather sensitive to the specification of the velocity boundary conditions, which needed to rely on experimental input rather than on common assumptions of either plug or potential flow. It was found that the rapid-mixing (infinite liquid thermal conductivity) model for individual droplet evaporation adequately described the spray evaporation in these single-compoment diluted sprays.

Dimensionless correlations for convective heat transfer to liquid and particles in cans subjected to end-over-end rotation

Dimensionless correlations, for estimating forced convection heat transfer coefficients in cans with end-over-end rotation, were investigated using multiple regression of significant dimensionless groups. Data on overall heat transfer coefficient, U, and fluid to particle heat transfer coefficient, h fp, were obtained for several processing conditions, and analyzed separately for single and multiple particles in the can. Heat transfer to a single particle was modeled based on particle settling theory, with terminal velocity resulting from the combined forces of gravity, buoyancy, centrifugal and drag acting on it, during end-over-end rotation. In the presence of multiple particles, heat transfer to the moving liquid/particles system was modeled as in a packed bed. Attempts were made to account for the particle shape and size effects on U and h fp by including particle sphericity (Ψ = surface area of an equivalent sphere/surface area of the particle) and particle equivalent diameter (as diameter of sphere of volume equal to that of particle, d e ) into the correlation equation. For U with a single particle in the can, the Nusselt number (Nu) was related to Reynolds number (Re), Prandtl number (Pr) and relative can headspace; while with multiple particles, Re, Pr, d c, the ratio of particle to liquid concentration and Ψ were found to be significant. For h fp with a single particle in the can, Nu was related to Re [or Froude number (Fr)], Pr, density simplex ( a), relative can headspace and the ratio of the sum of the diameter of rotation and diameter of the can to the can diameter, while with multiple particles, Re (or Peclet number), ratio of particle to liquid thermal conductivity, the particle to liquid concentration ratio and particle sphericity were found to be significant parameters.

Uniform Channel Micro Heat Exchangers

The performance characteristics of micro heat exchangers consisting of straight channels fabricated in a silicon wafer and operating with liquid nitrogen are evaluated theoretically. The three-dimensional conjugate temperature and flow fields are calculated numerically. The thermal resistance is computed as a function of various geometric parameters. The optimal dimensions which minimize the heat exchanger’s thermal resistance are identified. Additionally, a simple, approximate, analytical model, adequate when the ratio of the solid and liquid thermal conductivities is large, is presented and used to predict the heat exchanger’s optimal dimensions. The approximate model’s predictions are compared with the numerical results.

A General Equation for Correlating the Thermophysical Properties of n-Paraffins, n-Olefins, and Other Homologous Series. 3. Asymptotic Behavior Correlations for Thermal and Transport Properties

In this final paper of the series, asymptotic behavior correlations (ABCs) are presented for thermal properties (ideal-gas enthalpy and free energy of formation, ideal-gas heat capacity, enthalpy of vaporization, and liquid heat capacity) and for transport properties (liquid viscosity, thermal conductivity, and surface tension). The theoretical basis for asymptotic behavior of these properties is discussed. The correlations were developed using literature data for n-paraffins and n-olefins (1-alkenes) and give accurate and consistent predictions. They are preferable to existing correlations in most instances. For specific heat, viscosity, thermal conductivity, and surface tension, comparisons are made with high molecular weight, linear polyethylenes and other long-chain molecules.

Improvements to Steady-State Combustion Modeling of Cyclotrimethylenetrinitramine

Many improvements have been made to models of cyclotrimethylenetrinitramine combustion in the past few years. The one-dimensional model presented in this paper models the solid, two-phase, and gas regions using complex kinetics and concentrationand temperature-dependent thermophysical properties. Calculated values agree well with experimentally determined burning rate sp, melt layer thickness, surface temperature, and species concentration proŽ les. When including laser-assisted burning in the model, a dark zone appeared that was similar to that seen experimentally. With the laser-assisted case, the chemistry controlling the burning rate is signiŽ cantly different from cases without the laser heat  ux. Calculations show that the melt-layer thickness is determined primarily by the liquid thermal conductivity and the surface temperature is controlled by the vapor pressure correlation. All other model predictions are relatively insensitive to these parameters. The condensed-phase decomposition and evaporation/condensation submodel are the weakest areas of the model.

On the role of thermal conductivity on thermal erosion by lava

Lava channels are abundant on the surface of both the Moon and Venus. There is evidence that erosion may have played a part in their formation. Here a study of the relationship between thermal conductivity and erosion rate is presented. A numerical model is used to investigate the sensitivity of the erosion rate to the relative value of the thermal conductivity of the lava, solid substrate and liquid substrate boundary layer. Results show that the highest rates for thermal erosion are achieved by a high liquid substrate and low solid substrate thermal conductivity, and that the thermal erosion process is most sensitive to the liquid substrate's thermal conductivity.

General Equation for Correlating the Thermophysical Properties of n-Paraffins, n-Olefins, and Other Homologous Series. 1. Formalism for Developing Asymptotic Behavior Correlations

In this first in a series of three papers, a formal treatment is presented for the development of property correlations for homologous series of compounds. The theoretical basis for asymptotic behavior is discussed, and the methodology used to regress parameters is described. The equations developed are quite general and can be extended to other properties or homologous series. Parts 2 and 3 of this series present correlations developed for n-paraffins and n-olefins (1-alkenes) to predict PVT related properties, normal boiling and melting points, critical temperature, pressure, and volume, acentric factor, liquid molar volume, and vapor pressure (part 2); thermal properties, ideal-gas enthalpy and free energy of formation, ideal-gas heat capacity, enthalpy of vaporization, and liquid heat capacity (part 3); transport properties: liquid viscosity, thermal conductivity, and surface tension (part 3). It is demonstrated that these correlations are accurate, consistent, and yield reasonable extrapolations. Th...

A new correlation for thermal conductivity of liquids

On the supposition that liquid is composed of a mixture of microcrystallites and vacancies, and on the basis of significant structure theory and analysis of the radial distribution function of liquids, a new two-parameter model is presented for correlating thermal conductivities of liquids and liquid mixtures. The thermal conductivities of inorganic compounds, paraffins, olefins, cycloparaffins, aromatic hydrocarbons, alcohols, ethers, aldehydes, ketones, esters, organic acids and some refrigerants over wide ranges of temperature are calculated using the new model and compared with data reported in the literature. The method is extended to mixtures by using simple mixing rules. Calculated results show that the new model can be used for the correlation of the thermal conductivities of systems consisting of nonpolar and polar compounds and also for those of aqueous solutions. Especially, for pure compounds such as inorganic compounds, nitrogen- or sulfur-containing materials and aldehydes, and for mixtures consisting of alcohols and aqueous systems, the proposed correlation shows better agreement with experimental data than the models recommended by Reid et al. (1987, The Properties of Gases and Liquids, 4th Edition. McGraw-Hill, New York).

A formula relating the thermal conductivity of liquids to the sound velocity in them

On the basis of experimental data an analytical relationship is obtained between the thermal conductivity of liquids and sound velocity in them for wide temperature and pressure ranges.

Properties of new refrigerants and predictions for condensation heat transfer enhancement with low-finned tubes

The present article provides a review of thermophysical properties research of environmentally acceptable refrigerants. In recent years, it has become evident that common CFC type refrigerants can cause serious environmental damage when released into the atmosphere. The group of HFCs (HFC-32, HFC-125, HFC-134a, HFC-152a) with no chlorine atom in their chemical formulae and quite short atmospheric lifetime may be promising alternatives to CFCs. A compilation of properties is given which may be used to obtain arithmetic expressions for the vapour pressure, saturated liquid density, viscosity, latent heat of vaporization, saturated liquid thermal conductivity, and surface tension of these hydrofluorocarbons. For easily available comparisons, the results are presented in diagrams illustrating the dependence of thermophysical data on temperature at the saturated state. Heat-transfer predictions are specified for condensation of the HFCs on horizontal integral-fin tubes with rectangular fins. Parameters investigated include fin and tube geometry, etc. This study should be a useful input in developing new condensers with new refrigerants.

Thermal conductivity of alternative refrigerants in the liquid phase

Measurements ofthe thermal conductivity of five alternative refrigerants. namely, difluoromethane HFC-321. pentafluoroethane (HFC-125), 1,1,1-trifluoroethane (HFC-143a), and dichloropentafluoropropanes (HCFC-225ca and HCFC-225cb). are carried out in the liquid phase, The range of temperature is 253–324 K for HFC-32, 257–305 K for HFC-125, 268–314 K for HFC-134a. 267–325 K for HCFC-225ca, and 286–345 K for HCFC-225cb, The pressure rank is from saturation to 30 MPa, The reproducibility of the data is better than 0.5% and the accuracy of the data is estimated to be of the order of 1%. The experimental results for the thermal conductivity ofeach substance are correlated by an equation which is a function of temperature and pressure. A short discussion is given to the comparison of the present results with literature values for HFC-125, The saturated liquid thermal conductivity values of HFC-32. HFC-125, and HFC-143a are compared with those of chlorodifluoromethane (HCFC-22) and tetrafluoroethane (HFC-134a) and it is shown that the value of HFC-32 is highest, while that of HFC-125 is lowest, among these substances, The dependence of thermal conductivity on number of fluorine atoms among the refrigerants with the same number of carbon and hydrogen atoms is discussed.