Heat Capacity Of Fluid Research Articles

The effect of magnetic-field-dependent viscosity on ferroconvection in a porous medium in the presence of dust particles

This paper deals with the theoretical investigation of the effect of magnetic-field-dependent (MFD) viscosity on the thermal convection in ferromagnetic fluid saturating a porous medium in the presence of dust particles. For a flat ferromagnetic fluid layer contained between two free boundaries, the exact solution is obtained using a linear stability analysis. For the case of stationary convection, medium permeability and dust particles always have a destabilizing effect whereas the MFD viscosity has a stabilizing effect on the onset of convection. In the absence of MFD viscosity, the destabilizing effect of magnetization is depicted but in the presence of MFD viscosity, magnetization may have a destabilizing or stabilizing effect on the onset of convection. The critical wave number and critical magnetic thermal Rayleigh number for the onset of stationary convection are also determined numerically for sufficiently large values of buoyancy magnetization parameter M1. Graphs have been plotted by giving numerical values to the parameters to depict the stability characteristics. It is observed that the critical magnetic thermal Rayleigh number is reduced solely because the heat capacity of clean fluid is supplemented by that of the dust particles. The principle of exchange of stabilities is found to hold true for the ferromagnetic fluid saturating a porous medium heated from below in the absence of dust particles. The oscillatory modes are introduced due to the presence of the dust particles, which were nonexistent in their absence. A sufficient condition for the nonexistence of overstability is also obtained.

Effect of dust particles on thermal convection in ferromagnetic fluid saturating a porous medium

This paper deals with the theoretical investigation of the effect of dust particles on the thermal convection in ferromagnetic fluid saturating a porous medium subjected to a transverse uniform magnetic field. For a flat ferromagnetic fluid layer contained between two free boundaries, the exact solution is obtained using a linear stability analysis. For the case of stationary convection, medium permeability, dust particles and magnetization have always a destabilizing effect on the onset of instability. The critical wave number and critical magnetic thermal Rayleigh number for the onset of instability are also determined numerically for sufficiently large values of buoyancy magnetization parameter M 1. Graphs have been plotted by giving numerical values to the parameters to depict the stability characteristics. It is observed that the critical magnetic thermal Rayleigh number is reduced solely because the heat capacity of clean fluid is supplemented by that of the dust particles. The principle of exchange of stabilities is found to hold true for the ferromagnetic fluid saturating a porous medium heated from below in the absence of dust particles. The oscillatory modes are introduced due to the presence of the dust particles, which were non-existent in their absence. A sufficient condition for the non-existence of overstability is also obtained.

Influences of fluid property variation on the boundary layers of a stretching surface

In this work, the influences of temperature-dependent fluid properties on the boundary layers over a continuously stretching surface with constant temperature are investigated. Based on the boundary layer assumptions, the coupled similarity equations are obtained for special situations, in which the fluid density and heat capacity are assumed without dependence on the temperature. Those similarity equations are solved numerically. The influences of property variation on wall stresses and heat fluxes are discussed. It is found that the property variation can influence the distributions of both fluid velocity and temperature across the boundary layers. For the thermal boundary layer, using mean properties evaluated at the average temperature of wall and ambient fluid can give good results for the temperature distribution. However, for the momentum boundary layer, the difference of velocity distributions can be large.

Thermal Transport in High Porosity Cellular Metal Foams

The heat dissipation capability of highly porous cellular metal foams with open cells subject to forced air convection is studied using a combined experimental and analytical approach. The cellular morphologies of six FeCrAlY (an iron-based alloy) foams and six copper alloy foams with a range of pore sizes and porosities are quantified with the scanning electronic microscope and image analysis. Experimental measurements on pressure drop and heat transfer for copper foams are carried out. A numerical model for forced convection across opencelled metal foams is subsequently developed, and the predictions are compared with those measured. Reasonably good agreement with test data is obtained, given the complexity of the cellular foam morphology and the associated momentum/energy transport. The results show that cell size has a more significant effect on the overall heat transfer than porosity. An optimal porosity is obtained based on the balance between pressure drop and overall heat transfer, which decreases as the Reynolds number is increased. Nomenclature ˜ a = specific surface area per unit volume C f = heat capacity of fluid C I = inertial coefficient d f = diameter of cell edge ligament d p = pore size FI = inertial variable f = friction factor H = channel height h sf = interfacial heat transfer coefficient

A Review and Evaluation of Specific Heat Capacities of Rocks, Minerals, and Subsurface Fluids. Part 2: Fluids and Porous Rocks

Heat capacities of solid sediments and pore fluids within a basin can influence geothermal gradients when sedimentation or erosion is rapid. This paper provides data on specific heat capacities of pore fluids and porous rocks. It includes data on specific heat capacities of water, ice, and gas hydrates at reference temperatures, as well as equations for calculating the specific heat capacity of those substances as a function of temperature. It also provides values for specific heat capacities of oil and natural gases at low temperatures, as well as equations describing the temperature and pressure dependence of the specific heat capacities of those substances. Finally, it shows how to calculate the specific heat capacity of mixtures of solid materials, or of mixtures of solids and pore fluids. The data and equations provided herein can be incorporated directly into existing modeling software by users and software developers.

A Review and Evaluation of Specific Heat Capacities of Rocks, Minerals, and Subsurface Fluids. Part 1: Minerals and Nonporous Rocks

A Review and Evaluation of Specific Heat Capacities of Rocks, Minerals, and Subsurface Fluids. Part 1: Minerals and Nonporous Rocks

Heat capacity of square-well fluids of variable width

We have obtained by Monte Carlo NVT simulations the constant-volume excess heat capacity of square-well fluids for several temperatures, densities and potential widths. Heat capacity is a thermodynamic property much more sensitive to the accuracy of a theory than other thermodynamic quantities, such as the compressibility factor. This is illustrated by comparing the reported simulation data for the heat capacity with the theoretical predictions given by the Barker-Henderson perturbation theory as well as with those given by a non-perturbative theoretical model based on Baxter's solution of the Percus-Yevick integral equation for sticky hard spheres. Both theories give accurate predictions for the equation of state. By contrast, it is found that the Barker-Henderson theory strongly underestimates the excess heat capacity for low to moderate temperatures, whereas a much better agreement between theory and simulation is achieved with the non-perturbative theoretical model, particularly for small well widths, although the accuracy of the latter worsens for high densities and low temperatures, as the well width increases.

The constant-volume heat capacity of near-critical fluids with long-range interactions: A discussion of different Monte Carlo estimates

The constant-volume heat capacities, CV, of various near-critical fluids with long-range potentials have been obtained using both canonical and grand-canonical Monte Carlo (GCMC) calculations. In the case of the restricted primitive model it is shown that the large discrepancies between previously reported results arise from the use of different simulation ensembles. In order to investigate how well the different ensemble estimates of CV obtained with small systems can indicate the universality class of the bulk fluid, calculations have been performed for fluids with attractive pair interactions which vary like −1/ra, with a=6, 4, and 3.1. For a=6, Ising-type criticality is expected, while for a=4 and 3.1 the criticality is mean-field. For each of these models the canonical-ensemble estimates of CV do not provide unambiguous confirmation of the expected critical behavior, and hence this is not a reliable method for determining the universality class. This is also true of the GCMC estimates of CV, which appear consistent with Ising-type behavior for all of the systems studied, even for those which are known to exhibit mean-field criticality in the thermodynamic limit. We suggest that these are artifacts associated with finite system size, and we speculate as to why they appear in canonical and GCMC calculations.

Phonon velocity of [formula omitted] Bose fluid formed in one-dimensional [formula omitted] pores

We discuss the one-dimensional (1D) phonon velocities of 4 He adsorbed on straight 18 A ̊ pores deduced from our recent two experiments, the vapor pressure and the heat capacity measurements. The heat capacity of the second layer fluid is proportional to temperature below 0.2 K , which is attributed to 1D phonon excitations along the tube. The phonon heat capacity gives us the phonon velocity, v C. While, the phonon velocity, v P, also can be deduced from the vapor pressure. The magnitude and coverage dependence of v P and v C agree well. This fact strongly supports that the temperature-linear heat capacity is the 1D phonon heat capacity.

Specific heat of magnetic fluids under a modulated magnetic field

Due to the increasing importance of thermal devices in engineering applications, the investigation of the thermal properties of magnetic fluids has become necessary. In this work, we report both the temperature and field dependence of the specific heat of a water-based magnetic fluid. The results show that the specific heat of the magnetic fluid is almost independent of temperature under lower-field strengths (<50 Oe), but decreases significantly upon increasing temperature under higher fields. To clarify this effect of the magnetic field on the specific heat capacity of the magnetic fluid, the evolution of the structure of the magnetic fluid film is examined and compared with its field-modulated heat capacity of the fluid.

Optimal Endoreversible Heat Engines with Polytropic Branches

Endoreversible engine cycles with two adiabatic and two heat transfer branches are in-vestigated and optimized for maximum work output. The heat transfer branches are described as general polytropic processes which include common standard branches, like isotherms, isobars and isometrics, as special cases. The study considers the finite heat capacity of the working fluid and the finite-time character of the heat transfer processes, determines the optimal allocation of branch times, and derives analytic expressions for the maximized work output. The efficiency at maximum work is found to coincide with the Curzon-Ahlborn efficiency for endoreversible Carnot engines and does not depend on design parameters of the engine if the degree of the polytropic processes is equal in both heat transfer branches.

AN INVERSE METHOD FOR ESTIMATING THERMOPHYSICAL PROPERTIES OF FLUID FLOWING IN A CIRCULATING DUCT

The objective of this work is to propose an on-line system for estimating the temperature dependent thermophysical properties of fluid without duct impairments. Amongst the many advantages of inverse methods, the in-situ application is attractive. The proposed inverse method considers the thermal conductivity and the volumetric heat capacity of fluid flowing in a circular duct. An on-line temperature measurement system with the direct heating method is postulated. The corresponding computer software for inversely estimating the thermophysical properties using the data transmitted from the measurement system is developed. The parameterized form is used for rapid and stable estimation. The method is verified for virtual fluids with simulated measurement data.

Determination of constant volume heat capacity of mixed supercritical fluids and study on the intermolecular interaction

The constant volume heat capacities ( C V) of CO 2, propane-CO 2, n-pentane-CO 2, n-heptane-CO 2, acetone-CO 2, and ethanol-CO 2 were measured at 308.15 K in the pressure range from 6 to 11 MPa, and the concentration of the solutes was 0.5 mol%. The results show that there is a maximum in each C V versus pressure curve which occurs at the pressure where the isothermal compressibility k T is largest. The peak in the C V curve of propane-CO 2 is higher than those of n-pentane-CO 2 and n-heptane-CO 2 mixtures. For the mixtures with polar solutes, the magnitude of the peaks in C V curves is nearly the same although the structure and polarity of the solutes are different. The intermolecular interaction in the mixtures is discussed on the basis of the C V.

Impurity effects on the two-phase isochoric heat capacity of fluids near the critical point

It has been generally assumed that the asymptotic critical behavior of real fluids can be characterized in terms of the same physical variables as that of the lattice gas. This assumption implies that, below Tc, the second derivative of the pressure with respect to temperature should asymptotically diverge like the isochoric heat capacity CV, while the second derivative of the chemical potential with respect to the temperature should remain finite at the critical point. The validity of this assumption has recently been questioned on the basis of an analysis of experimental two-phase CV data in terms of the so-called Yang–Yang relation. In this paper we show how such an analysis may be affected by the presence of a small amount of impurity as well as by other nonasymptotic deviations from lattice-gas symmetry. When corrections for a small amount of impurity are applied and allowance is made for the leading asymmetric Wegner correction, the experimental CV data are not inconsistent with previous treatments in which the second derivative of the chemical potential exhibits a cusplike singularity with a finite limiting value at the critical temperature.

Helium-4 Bose fluids formed in one-dimensional 18 A diameter pores.

Bose fluids restricted in one dimension (1D) are realized by adsorbing 4He atoms on the 1D pore walls with a diameter of about 18 A. The Bose fluid appears above an adsorbed amount after the pore walls are coated with the inert 4He atoms. Heat capacity of the fluid was observed to have a temperature-linear term at low temperatures. This corresponds to the phonon heat capacity of the Bose fluid in the 1D pores. We estimate the phonon velocity and the interaction of the 1D Bose fluid.

Use of the Refractive Index in the Estimation of Thermophysical Properties of Hydrocarbons and Petroleum Mixtures

In this paper we show application of the refractive index in the estimation of various thermodynamic and physical properties of pure hydrocarbons and undefined petroleum mixtures. In particular, we demonstrate how one can use the refractive index to estimate equation of state parameters, critical constants, the composition of petroleum mixtures, and temperature-dependent properties such as heat capacity, PVT, and transport properties of hydrocarbon fluids. The refractive index is an easily measurable property; however, when it is not available, methods of estimation of this property through other available parameters are also presented.

Specific Heat of the Surface Layers on the Amorphous Substrate in Solid and Liquid 3He

We have observed an excess heat capacity in liquid and bcc solid 3He at low temperatures. The heat capacity in the normal fluid is found to be the sum of the heat capacity of bulk normal fluid and a temperature-independent heat capacity ΔC due to amorphous solid layers on the silver sinter surface, where ΔC=7.3±6.8 μJK−1m−2 corresponds to 1.6±0.6 amorphous solid layers. The heat capacity for bcc solid 3He is the sum of the heat capacity originating from the multiple-exchange interaction and a temperature independent heat capacity. The excess heat capacity ΔC=12.1±3.1 μJK−1m−2 for bcc solid corresponds to 1.9±0.3 amorphous solid layers. Our result indicates that the amorphous solid layers on an amorphous substrate yield a universal ΔC in unit area throughout liquid, solid and adsorbed 3He.

Adjoint Sensitivity Analysis of the RELAP5/MOD3.2 Two-Fluid Thermal-Hydraulic Code System—II: Applications

This work presents results that illustrate the validation of the Adjoint Sensitivity Model (ASM-REL/TF) corresponding to the two-fluid model with noncondensable(s) used in RELAP5/MOD3.2. This validation has been carried out by using sample problems involving (a) a liquid phase only, (b) a gas phase only, and (c) a two-phase mixture (of water and steam). Thus, the “Two-Loops with Pumps” sample problem supplied with RELAP5/MOD3.2 has been used to verify the accuracy and stability of the numerical solution of the ASM-REL/TF when only the liquid phase is present. Furthermore, the “Edwards Pipe” sample problem, also supplied with RELAP5/MOD3.2, has been used to verify the accuracy and stability of the numerical solution of the ASM-REL/TF when both (i.e., liquid and gas) phases are present. In addition, the accuracy and stability have been verified of the numerical solution of the ASM-REL/TF when only the gas phase is present by using modified “Two-Loops with Pumps” and the “Edwards Pipe” sample problems in which the liquid- and two-phase fluids, respectively, were replaced with pure steam. The results obtained for these sample problems depict typical sensitivities of junction velocities and volume-averaged pressures to perturbations in initial conditions and indicate that the numerical solution of the ASM-REL/TF is as robust, stable, and accurate as the original RELAP5/MOD3.2 calculations.This work also illustrates the role that sensitivities of the thermodynamic properties of water play for sensitivity analysis of thermal-hydraulic codes for light water reactors. The well-known 1993 ASME Steam Tables are used to present typical analytical and numerical results for sensitivities of the thermodynamic properties of water to the numerical parameters that appear in the mathematical formulation of these properties. Particularly highlighted are the very large sensitivities displayed by the specific isobaric fluid and gas heat capacities Cpf and Cpg, respectively; the specific fluid enthalpy hf; the specific gas volume Vg; the volumetric expansion coefficient for gas βg; and the isothermal coefficient for gas kg. The dependence of βg and kg on the most sensitive parameters turns out to be nonlinear, while the dependence of Cpf, Cpg, hf, and Vg on the most sensitive parameters turns out to be linear, so the respective sensitivities predict exactly the effects of variations in the respective parameters. On the other hand, the sensitivities of the specific fluid volume Vf, the volumetric expansion coefficient for fluid βf, the specific gas enthalpy hg, and the isothermal coefficient of compressibility for fluid kf to the parameters that appear in their respective mathematical formulas are quite small. Finally, it is noted that such deterministically calculated sensitivities can be used to rank the respective parameters according to their importance, to assess the effects of nonlinearities and, more generally, to perform comprehensive sensitivity/uncertainty analyses of thermal-hydraulic codes that use a water substance as the working fluid.

Temperature-Squared Terms in the Heat Capacities of 3He Fluid Films

Recently the heat-capacity of a two-dimensional Fermi fluid is theoretically shown by Misawa to vary as C(T) = γ0 T - γ2 T 2 as a function of temperature T at low temperature, where γ 0 and γ 2 are constants. To check this prediction our measured heat-capacities of three different systems are reexamined, i.e., the first-layer and second-layer 3 He fluid films adsorbed on a bare graphite surface and monolayer 3 He films floated on a 4 He thin film adsorbed on graphite. The measured heat-capacities are reproduced well by the predicted formula. The areal-density dependence of γ 2 on each system also coincides with Misawa's prediction if the second order perturbation treatment by Fujimoto is adopted as the self-energy calculation.

Measuring the Specific Heat Capacity of Magnetic Fluids Using a Differential Scanning Calorimeter

The specific heat capacity of magnetic fluids was measured using a heat-flux-type differential scanning calorimeter (DSC). Magnetic fluids which contain 10 to 43 wt% ultrafine magnetite (Fe3O4) particles dispersed with surfactants in water or kerosene were used. The DSC was operated with the optimum heating rate (10 K·min−1) and with equal heat capacities of sample and standard materials in the temperature range, 295 to 345 K. Synthetic sapphire (α-Al2O3) was used as the standard reference material, and the sample pan was made from aluminum. The differences between the measured specific heat capacity values of pure water and pure copper and the recommended values were within ±3 and ±1%, respectively. The specific heat capacity data of magnetic fluids showed weak temperature dependence, but strong concentration dependence. The measured values of specific heat capacity of magnetic fluids were compared with calculated values using a mixing rule.