Fluid Thermal Conductivity Research Articles

Review on Thermal Conductivity of Nanofluids

Among the thermo physical properties of the nano fluids thermal conductivity is the key property which depends on the pertinent parameters of nanoparticles material, volume fraction, size, aspect ratio, base fluid thermo physical properties, temperature, and surfactant. Over last decades, numerous works have reported the higher thermal conductivity of nano fluids than that of the conventional heat transfer fluids with the reason of random motion of nanoparticles and a number of numerical and theoretical models have been proposed. In this article, the current state of knowledge on the several thermal conductivity measurement techniques employed by the researchers along with the factors affecting the thermal conductivity of nano fluids have been presented. This review leads to some directions for future research in nano fluids.

ESTUDIO DE UN NUEVO PROCEDIMIENTO PARA MEDIR LA CONDUCTIVIDAD Y DIFUSIVIDAD TÉRMICAS DE MATERIALES

<p>En este trabajo se estudia las posibilidades y limitaciones de un método no-estacionario, que utiliza como fuente de calor la radiación luminosa. En el mismo, que es una nueva variante propuesta por este grupo, la luz se hace incidir homogéneamente sobre una de las superficies extremas de un cilindro de superficie lateral termoaislada, manteniéndose constante la temperatura en el otro extremo.</p><p>Asimismo, se analiza la posibilidad de utilizar dicho método para medir la difusividad y conductividad térmicas (α,χ) de fluidos; igualmente, la forma en que este pudiera ser empleado para comprobar la validez del modelo de Hamilton y Crosser (HC) para el caso de los nanofluidos. Se le llama nanofluido a todo aquel fluido que, convencionalmente, es utilizado para intercambiar calor, al cual se le agregan nanopartículas con el propósito de aumentar su conductividad térmica, mejorando así su capacidad para intercambiar calor.</p>

Magnetic field simulation of a thermal conductivity measurement instrument for magnetorheological fluid

Technological advancements in thermal systems demand an innovative heat dissipation technology. Magnetorheological (MR) fluid has a huge potential to solve the problem. However, characterising thermal conductivity of the materials in magnetic fields required tailored instruments. This paper presents a concept design of the MR fluids thermal conductivity measurement instrument. The developed instrument was designed to be able to measure thermal conductivity in both parallel and perpendicular orientations with magnetic field. Magnetic fields distribution of the proposed concept design was analysed using finite element method for magnetics. Design modification then conducted to improve the magnetic fields strength. Findings of this study showed that gap thickness played a significant factor in determining the optimal design. Simulated magnetic fields strength at both parallel and perpendicular orientations were found identical, yet varied in distributions.

A DNS study of flow and heat transfer through slender fixed-bed reactors randomly packed with spherical particles

A fully resolved direct numerical simulation of flow and heat transfer is presented for slender randomly packed bed reactors. The flow and temperature field are solved over a non-body fitted, non-conformal Cartesian computational domain. The coupling between fluid and solid (both spherical particles and cylindrical wall) is enforced by a second order accurate, sharp interface immersed boundary method (IBM). The present numerical technique neither requires any challenging volumetric mesh generation process nor demands manipulation of the geometry near the particle-particle and particle-wall contact points. Conjugate heat transfer has been considered where the temperature field is calculated both inside the solid particles and in the fluid. A discrete element method (DEM) is used to generate the random packings of spherical particles in the cylindrical column, and a methodology is proposed to calculate the radial porosity profile of the bed.The column-to-particle diameter ratio (N) is varied from 4 to 8, and two separate cases have been considered where N→∞. The particle Reynolds number (Red) is varied from 1 to 500. The numerically obtained pressure drop and overall wall-to-bed heat transfer coefficient for different simulation cases are critically compared with empirical correlations and a good agreement is reported. Moreover, based on the current numerical results, correlations are proposed for the pressure drop and the wall-to-bed heat transfer coefficient. The effect of the column-to-particle diameter ratio (N) on both the flow and heat transfer, as-well-as the effect of the solid to fluid thermal conductivity ratio on the conjugate heat transfer are discussed. Furthermore, the fully resolved accurate numerical simulations have helped to elucidate the detailed pore-scale flow and heat transfer feature in the packed beds.

Graphite Dispersions as a Basis for Development of High Thermal Conductivity Fluids

Both conductivity and thermal resistivity measurements of commercial graphite dispersions in non-aqueous polar fluids and non-polar fluids were carried out. Fluids exhibiting different densities as: mineral oil, ethylene glycol, glycerin bidistilled and liquid vaseline were used. Dispersions of commercial graphite containing 5, 10, 20, 40, 60 and 80 weight percent were prepared by sonication technique. The thermal conductivity of each fluid increases as a function of the increasing of the volumetric density of fluid and of the fraction of graphite. Values of thermal conductivity of graphite dispersion were at around ten times higher than that value of the base-fluid. Effects of processing parameters of graphite dispersions on the magnitude of its thermal conductivity are discussed.

Effect of Nano Fluids in Solar Flat Plate Collector Systems

Nano fluids are one of the combination of fluid and nano-sized solid particles which they are relatively used for some application. In general, nano fluids were used for various applications like heat transfer and solar energy applications. Nowadays the high usage of fossil fuel, which it is coming down in quantity in the earth. So we will go for alternate energy sources of solar, wind, tidal, etc. In a heat transfer system contain many losses, In order to overcome the losses, we will use some effectual heat transfer substance. So far reviews were done about nano fluids preparation, thermal conductivity, and performance. The main objective of this paper is to study about enhanced heat transfer in solar collector systems with the effect of various nano fluids.

Stagnation point flow towards nonlinear stretching surface with Cattaneo-Christov heat flux

Here the influence of the non-Fourier heat flux in a two-dimensional (2D) stagnation point flow of Eyring-Powell liquid towards a nonlinear stretched surface is reported. The stretching surface is of variable thickness. Thermal conductivity of fluid is taken temperature-dependent. Ordinary differential systems are obtained through the implementation of meaningful transformations. The reduced non-dimensional expressions are solved for the convergent series solutions. Convergence interval is obtained for the computed solutions. Graphical results are displayed and analyzed in detail for the velocity, temperature and skin friction coefficient. The obtained results reveal that the temperature gradient enhances when the thermal relaxation parameter is increased.

Lattice Boltzmann Pore Scale Simulation of Natural Convection in a Differentially Heated Enclosure Filled with a Detached or Attached Bidisperse Porous Medium

In this research, pore scale simulation of natural convection in a differentially heated enclosure filled with a conducting bidisperse porous medium is investigated using the thermal lattice Boltzmann method. For the first time, the effect of connection of the bidisperse porous medium to the enclosure walls is studied by considering the attached geometry in addition to the detached one. Effect of most relevant parameters on the streamlines and isotherms as well as hot wall average Nusselt number is studied for two of the bidisperse porous medium configurations. It is observed that effect of geometrical and thermo-physical parameters of the bidisperse porous medium on the heat transfer characteristics is more complicated for the attached configuration. To assess the validity of the local thermal equilibrium condition in the micro-porous media, the pore scale results are used to compute the percentage of the local thermal non-equilibrium for two of the bidisperse porous medium configurations. It is concluded that for the detached configuration, the local thermal equilibrium condition is confirmed in the entire micro-porous media for the ranges of the parameters studied here. However, for the attached geometry, it is shown that departure from the local thermal equilibrium condition is observed for the higher values of the Rayleigh number, micro-porous porosity, solid–fluid thermal conductivity ratio, and the smaller values of the macro-pores volume fraction.

3ω slope comparative method for fluid and powder thermal conductivity measurements

By analyzing the relationship among the heat penetration depth, measurement frequency and detector characteristic parameters, a simple and practical [Formula: see text] slope comparative method has been proposed. The corresponding measurement system for measuring the thermal properties of fluids and powder materials was established and verified using several specimens with known thermophysical parameters, such as alcohol, distilled water, and air. Compared to the two-dimensional model, the data processing of the method is relatively simple and quick. Due to the elimination of errors introduced by the detector parameter measurement, the measurement accuracy of the method is higher than the conventional one-dimensional model. By using an appropriate frequency range, the new method is time saving and convenient for measuring the thermal conductivity of fluids and powders with low thermal conductivity. Based on the analysis, the effective thermal conductivity of nano-SiO2 powder is accurately determined.

Analysis of the volumetric phenomenon in porous beds subject to irradiation

ABSTRACTThis work examines the volumetric effect of convection within a packed bed in the presence of collimated irradiation. Using a modified P-1 approximation incorporating a local thermal nonequilibrium (LTNE) model, the energy transportation through convection and thermal conduction, and collimated and diffuse radiative transfer are investigated. The impact of pertinent parameters such as porosity φ, pore diameter dp, and optical thickness τ on the volumetric effect are analyzed. In addition, the mechanisms of how the volumetric effect impacts LTNE and radiative heat loss are revealed. The effect of the volumetric heat transfer coefficient hv, the fluid flow velocity u, and the ratio of solid to fluid thermal conductivities ζ versus the volumetric effect are systematically analyzed and displayed through a number of contour maps to assess the efficiency η. Our analysis shows that enhancing the volumetric effect and extending the thickness of the porous medium improves the efficiency η.

Melting heat and mass transfer in stagnation point micropolar fluid flow of temperature dependent fluid viscosity and thermal conductivity at constant vortex viscosity

Abstract Steady mixed convection micropolar fluid flow towards stagnation point formed on horizontal linearly stretchable melting surface is studied. The vortex viscosity of micropolar fluid along a melting surface is proposed as a constant function of temperature while dynamic viscosity and thermal conductivity are temperature dependent due to the influence of internal heat source on the fluid. Similarity transformations were used to convert the governing equation into non-linear ODE and solved numerically. A parametric study is conducted. An analysis of the results obtained shows that the flow-field is influenced appreciably by heat source, melting, velocity ratio, variable viscosity and thermal conductivity.

Theoretical Study of Heat Transfer through a Sun Space Filled with a Porous Medium

A theoretical study had been conducted to detect the effect of using a porous medium in sunspace to reduce heating load and overcoming coldness of winter in the cold regions. In this work, the heat transferred and stored in the storage wall was investigated. The mathematical model was unsteady, heat conduction equation with nonlinear boundary conditions was solved by using finite difference method and the solution technique of heat conduction had based on the Crank Nicholson method. The results had adopted on the aspect ratio (H/L=30), Darcy number (Da=10-3), porosity (φ=0.35) and particle to fluid thermal conductivity ratio (kp/kf=38.5). The results showed that using the porous medium had enhanced the heat transferred and stored in the storage wall. For the outside storage wall temperature, an increase of 19.7% was achieved by using the porous medium instead of the air, while it was 20.3% for the inside storage wall temperature.

Free convection effects on a vertical cone with variable viscosity and thermal conductivity

The present paper deals with a flow of a viscous incompressible fluid along a heated vertical cone, with due allowance for variations of viscosity and thermal diffusivity with temperature. The fluid viscosity is assumed to be an exponential function of temperature, and the thermal diffusivity is assumed to be a linear function of temperature. The governing equations for laminar free convection of the fluid are transformed into dimensionless partial differential equations, which are solved by a finite difference method with the Crank–Nicolson implicit scheme. Dependences of the flow parameters on the fluid viscosity and thermal conductivity are obtained.

Modern Heat Extraction Systems for Power Traction Machines—A Review

This paper presents a review of modern cooling system employed for the thermal management of power traction machines. Various solutions for heat extractions are described: high thermal conductivity insulation materials, spray cooling, high thermal conductivity fluids, combined liquid and air forced convection, and loss mitigation techniques.

Impact of Cattaneo–Christov heat flux model in flow of variable thermal conductivity fluid over a variable thicked surface

Here temperature dependent thermal conductivity in stagnation point flow toward a nonlinear stretched surface with variable thickness is considered. Heat flux in formulation is based upon Cattaneo–Christov theory. Double stratification and chemical reaction effects are further retained. Convergent series solution for flow of Jeffrey fluid and heat and mass transfer are developed. Residual errors are calculated for the velocity, temperature and concentration equations and results are discussed through graphs. Influences of skin friction coefficient is also studied. It is observed that temperature profile decreases for higher thermal relaxation parameter.

Radiative heat transfer of variable viscosity and thermal conductivity effects on inclined magnetic field with dissipation in a non-Darcy medium

The study of thermal radiative heat transfer of an electrically conducting fluid over a continuously stretching sheet in the presence of a uniform inclined magnetic field with dissipation in a porous medium is investigated for power-law variation in the sheet temperature. The fluid viscosity and thermal conductivity are assumed to vary as a function of temperature. The governing partial differential equations of the model are reduced to a system of coupled non-linear ordinary differential equations by applying similarity variables and then solved numerically using shooting technique with fourth-order Runge–Kutta method. The results for Skin friction and Nusselt numbers are presented and discussed.

Characterisation of thermal properties and charging performance of semi-clathrate hydrates for cold storage applications

Thermal storage for air conditioning applications has potential to flatten peak load on electricity grids and improve energy savings of cooling systems. Phase change materials (PCMs) for thermal storage have much greater energy storage density than sensible thermal storage materials. It is proven that semi-clathrate hydrates of tetra-n-butylammonium fluoride (TBAF) can offer appropriate phase change temperatures and rapid formation rates, thus they are considered favourable for cold storage. To demonstrate the feasibility of TBAF hydrate as a cold storage medium, its thermal properties are determined. TBAF aqueous solutions are tested at a mass fraction range of 15–40wt% in the presence or absence of another two quaternary ammonium/phosphonium salts – tetra-n-butylammonium bromide (TBAB) and tetra-n-butylphosphonium bromide (TBPB). The T-history method is employed to determine the enthalpy and heat capacity of the material while the heat diffusion equation is used to obtain the material’s thermal conductivity. The material with the highest formation enthalpy was selected for further analysis. For this material, a model of hydrate formation in a cold storage tube is established using the enthalpy method. By this means, the accumulated cooling capacity and charging rate of the tube is predicted, and the influencing factors on the charging performance are studied. The results indicate that careful selection of the heat transfer fluid (HTF) temperature, tube diameter, thermal conductivity and thickness of the tube wall can all potentially shorten the required charging time of the cold storage tube.

Temperature profile for nanoscale Poiseuille flow: a multiscale study

In this study, we calculated the temperature profile for a nanoscopic Poiseuille flow system via two methods. The first method involved employing the tools of Molecular dynamics (MD) simulation, and the second method involved solving Navier’s equation analytically while the rates of fluid dynamic viscosity and thermal conductivity were calculated through MD. We used a temperature jump model as the boundary condition required for the latter method, which was also calculated through MD. We repeated the calculations for various amounts of wall temperature and fluid-wall interaction strength, and we observed a satisfactory agreement between the results of the two methods.

Hot soup! Correlating the severity of liquid scald burns to fluid and biomedical properties

Burns caused by hot drinks and soups can be both debilitating and costly, especially to pediatric and geriatric patients. This research is aimed at better understanding the fluid properties that can influence the severity of skin burns. We use a standard model which combines heat transfer and biomedical equations to predict burn severity. In particular, experimental data from a physical model serves as the input to our numerical model to determine the severity of scald burns as a consequence of actual fluid flows. This technique enables us to numerically predict the heat transfer from the hot soup into the skin, without the need to numerically estimate the complex fluid mechanics and thermodynamics of the potentially highly viscous and heterogeneous soup. While the temperature of the soup is obviously is the most important fact in determining the degree of burn, we also find that more viscous fluids result in more severe burns, as the slower flowing thicker fluids remain in contact with the skin for longer. Furthermore, other factors can also increase the severity of burn such as a higher initial fluid temperature, a greater fluid thermal conductivity, or a higher thermal capacity of the fluid. Our combined experimental and numerical investigation finds that for average skin properties a very viscous fluid at 100°C, the fluid must be in contact with the skin for around 15–20s to cause second degree burns, and more than 80s to cause a third degree burn.

Radiation Effects in Flow through Porous Medium over a Rotating Disk with Variable Fluid Properties

The present study investigates the radiation effects in flow through porous medium over a permeable rotating disk with velocity slip and temperature jump. Fluid properties density(ρ), viscosity(μ), and thermal conductivity(κ)are taken to be dependent on temperature. Particular case considering these fluid properties’ constant is also discussed. The governing partial differential equations are converted into nonlinear normal differential equation using similarity alterations. Transformed system of equations is solved numerically by using Runge-Kutta method with shooting technique. Effects of various parameters such as porosity parameterK, suction parameterWs, rotational Reynolds number Re, Knudsen number Kn, Prandtl number Pr, radiation parameterN, and relative temperature difference parameterεon velocity profiles along radial, tangential, and axial direction and temperature distribution are investigated for both variable fluid properties and constant fluid properties. Results obtained are analyzed and depicted through graphs and table.