Fluid Thermal Conductivity Research Articles

Effect of fibrous porous material on natural convection heat transfer from a horizontal circular cylinder located in a square enclosure

A numerical simulation study was carried out to investigate a steady two-dimensional laminar natural convective heat transfer from a uniformly heated inner circular cylinder placed inside an air-filled square enclosure with a porous material. The enclosure’s side and upper walls were isothermal, while the bottom wall was adiabatic. All the numerical calculations were performed in the range of Rayleigh numbers between 103 and 107. The material porosity (ε), the solid to fluid thermal conductivity ratio (kr), and Darcy number in the present study were 1.0, 0.5, and 0.01, respectively. The results showed that for Rayleigh numbers that are less than 106, the isotherms are almost parallel inside the three cold walls except for the corners of the adiabatic bottom wall. The rates of vertical velocity are higher than the horizontal velocity, especially at higher Grashof numbers. Also, the use of fibrous porous material with low thermal conductivity relative to the fluid thermal conductivity reduces the values of average Nusselt number, in addition to reducing the horizontal and vertical velocities along the horizontal axis.

Thermodynamic Analysis of Magnetohydrodynamic Third Grade Fluid Flow with Variable Properties

This article aims to computationally study entropy generation in a magnetohydrodynamic (MHD) third grade fluid flow in a horizontal channel with impermeable walls. The fluids viscosity and thermal conductivity are assumed to be dependent on temperature. The flow is driven by an applied uniform axial pressure gradient between infinite parallel plates and is considered to be incompressible, steady and fully developed. Adomian decomposition method (ADM) is used to obtain series solutions of the nonlinear governing equations. Thermodynamic analysis is done by computing the entropy generation rate and the irreversibility ratio (Bejan number). The effects of the various pertinent embedded parameters on the velocity field, temperature field, entropy generation rate and Bejan number are analysed through vivid graphical manipulations. The analysis shows that an appropriate combination of thermophysical parameters efficiently achieves entropy generation minimization in the thermomechanical system. The analysis shows that entropy generation minimization is achieved by increasing the magnetic field and the third grade material parameters, and therefore designs and processes incorporating MHD third grade fluid flow systems are far more likely to give optimum and efficient performance.

Thermosolutal natural convection in a partly porous cavity with sinusoidal wall heating and cooling

PurposeThis paper aims to consider numerical analysis of laminar double-diffusive natural convection inside a non-homogeneous closed medium composed of a saturated porous matrix and a clear binary fluid under spatial sinusoidal heating/cooling on one side wall and uniform salting.Design/methodology/approachThe domain of interest is a partially square porous enclosure with sinusoidal wall heating and cooling. The fluid flow, heat and mass transfer dimensionless governing equations associated with the corresponding boundary conditions are discretized using the finite volume method. The resulting algebraic equations are solved by an in-house FORTRAN code and the SIMPLE algorithm to handle the non-linear character of conservation equations. The validity of the in-house FORTRAN code is checked by comparing the current results with previously published experimental and numerical works. The effect of the porous layer thickness, the spatial frequency of heating and cooling, the Darcy number, the Rayleigh number and the porous to fluid thermal conductivity ratio is analyzed.FindingsThe results demonstrate that for high values of the spatial frequency of heating and cooling (f = 7), temperature contours show periodic variations with positive and negative values providing higher temperature gradient near the thermally active wall. In this case, the temperature variation is mainly in the porous layer, while the temperature of the clear fluid region is practically the same as that imposed on the left vertical wall. This aspect can have a beneficial impact on thermal insulation. Besides, the porous to fluid thermal conductivity ratio, , has practically no effect on , contrary to where a strong increase is observed as is increased from 0.1 to 100, and much heat transfer from the hot wall to the clear fluid via the porous media is obtained.Practical implicationsThe findings are useful for devices working on double-diffusive natural convection inside non-homogenous cavities.Originality/valueThe authors believe that the presented results are original and have not been published elsewhere.

Numerical simulation on performance evaluation among metal and oxide based nanofluids for power savings application of a circular tube

The advancement of heat transfer techniques is a challenge to the researcher in this era. Implementation of nanotechnology is one of the potential techniques which enhance the heat transfer rate in a significant amount. Subsequently, nanotechnology can reduce the requirement of pumping power. However, suspension of nanoparticle with liquid to produce a new working fluid called nanofluid which has better thermal and fluid dynamic properties in comparison to pure liquid is introduced as a typical nanotechnology technique in the heat transfer area. In this study, the thermal performance of two categories of nanofluids metal-based (Cu-water and Ag-water) and oxide-based (Al2O3-water, CuO-water, BeO-water) with 1–5% volume fractions have been analysed for the laminar flow region of a circular tube which is fully developed under 2D control volume finite element method. The heat transfer was analysed for a range of Reynolds numbers from 100 to 1000 with a constant heat flux of 500 W/m2 applied on the tube wall. For evaluating the performance among nanofluids, the Figure of Merits (FOM), pumping power, Nusselt number enhancement ratio, and heat transfer coefficient ratio of the base fluid and nanofluids have been calculated and compared. The computational results show that in terms of Nusselt number and heat transfer coefficient, all nanofluids provide higher enhancement compared to pure water. Meanwhile, for this higher enhancement, nanofluids required significantly power pumping power in comparison to pure water. However, the power has been saved 86.26% for Ag-water nanofluid, 72.84% for Cu-water, 42.36% for CuO-water, 40.99% for Al2O3-water, and 26.58% for BeO-water. Between the mentioned two categories of nanofluids, metal-based nanofluids provide the highest heat transfer enhancement and lowest pumping power requirement compared to oxide-based because of their higher thermal conductivity and other fluid and thermal properties. For clearing the enhancement of heat transfer rate over-pumping power, a dimensionless number FOM has been calculated whereas metal-based nanofluids provide the highest value of FOM (1.863 for Ag-water nanofluid) in comparison to oxide-based (1.266 for BeO-water). In the meantime, the comparison between nanofluids also reveals that among all the nanofluids, metal-based Ag-water nanofluids provide the highest heat transfer enhancement and oxide-based BeO-water provide the lowest heat transfer enhancement in terms of pumping power requirements. Lastly, the study concluded that suspension of metal-based nanoparticles with base fluid has better capability to save pumping power (86.26% for Ag-water nanofluid) by providing the highest enhancement of heat transfer rate whereas oxide-based nanoparticles show the lowest capability to save pumping power (26.58% for BeO-water) compared to the base fluid.

A Review on the Use of Hybrid Nanofluid in a Solar Flat Plate and Parabolic Trough Collectors and Its Enhanced Collector Thermal Efficiency

Energy demand is high in all parts of the world, mostly in all industrial sectors. To meet the energy demand the fossil fuel is the only way. Due to rapid industrial growth and use of fossil fuel result in global warming and environmental pollution. Moreover, the limited availability of the fossil fuels, it is necessary to depend on the renewable energy sources. Promising renewable energy in the world is solar energy, which is available largely on the earth surface. The solar energy can be converted into thermal energy in the solar flat plate collector. The collector thermal efficiency is purely depends on the working fluid used in it. Most of the studies revealed that replacing the working fluid with high thermal conductivity fluids called as nanofluids and hybrid nanofluids can improve the collector thermal efficiency. Few decades back studies have been conducted with nanofluids in solar collectors. Currently the researchers are working on solar collectors for further improvement of its efficiency using hybrid nanofluids. In this review paper, we will discuss about the synthesis of hybrid nanoparticles, hybrid nanofluids, characterization, thermophysical properties, and application of hybrid nanofluids in solar flat plate collector under natural and forced circulation of fluid. The research gap in the solar collector is also discussed in this article. This paper also explains about the heat transfer capabilities of hybrid nanofluids especially used solar collectors.

Soret and Radiation Effects on Mixture of Ethylene Glycol-Water (50%-50%) Based Maxwell Nanofluid Flow in an Upright Channel

In this article, ethylene glycol (EG) + waterbased Maxwell nanofluid with radiation and Soret effects within two parallel plates has been investigated. The problem is formulated in the form of partial differential equations. The dimensionless governing equations for concentration, energy, and momentum are generalized by the fractional molecular diffusion, thermal flux, and shear stress defined by the Caputo–Fabrizio time fractional derivatives. The solutions of the problems are obtained via Laplace inversion numerical algorithm, namely, Stehfest’s. Nanoparticles of silver (Ag) are suspended in a mixture of EG + water to have a nanofluid. It is observed that the thermal conductivity of fluid is enhanced by increasing the values of time and volume fraction. The temperature and velocity of water-silver nanofluid are higher than those of ethylene glycol (EG) + water (H2O)-silver (Ag) nanofluid. The results are discussed at 2% of volume fraction. The results justified the thermo-physical characteristics of base fluids and nanoparticles shown in the tables. The effects of major physical parameters are illustrated graphically and discussed in detail.

Implementation of DTM as a numerical study for the Casson fluid flow past an exponentially variable stretching sheet with thermal radiation

This paper introduces a theoretical and numerical study for the problem of Casson fluid flow and heat transfer over an exponentially variable stretching sheet. Our contribution in this work can be observed in the presence of thermal radiation and the assumption of dependence of the fluid thermal conductivity on the heat. This physical problem is governed by a system of ordinary differential equations (ODEs), which is solved numerically by using the differential transformation method (DTM). This numerical method enables us to plot figures of the velocity and temperature distribution through the boundary layer region for different physical parameters. Apart from numerical solutions with the DTM, solutions to our proposed problem are also connected with studying the skin-friction coefficient. Estimates for the local Nusselt number are studied as well. The comparison of our numerical method with previously published results on similar special cases shows excellent agreement.

Production of Uniformly Sized Gallium-Based Liquid Alloy Nanodroplets via Ultrasonic Method and Their Li-Ion Storage.

Gallium-based liquid alloys are attractive due to their unique properties, and they can potentially be applied in the field of flexible electronics as coolant materials for nuclear and liquid batteries, due to the high thermal conductivity and excellent fluid properties of liquid metals. However, it is still challenging to fabricate gallium-based liquid alloy nanodroplets with uniform and small size. Here, we performed a systematical study on the influence of various factors affecting the size of nanodroplets. Liquid metal nanodroplets with an average size of 74 nm and narrow size distribution were successfully fabricated. Li-ion half-cells were assembled with eutectic GaIn (eGaIn) nanodroplets as anode active materials, which showed higher specific capacity than the bulk eGaIn alloy under the same testing conditions.

Heat Transfer in Laminar Flow of a Herschel-Bulkley Fluid between Parallel Plates

In this work, the heat transfer, subject to the effect of viscous dissipation, in a laminar fully-developed flow of a Herschel-Bulkley fluid between parallel plates was analyzed analytically. Both constant and asymmetric wall heat fluxes are considered. For a power-law index, n, higher than 0.5 the average calorific power generated by viscous effects only depends on the ratio between the fluid yield and wall stresses, c. In dimensional form, the temperature difference between the two walls and the temperature gradient at the duct symmetry plane, are independent of the rheological characteristics of the fluid, only depending on the fluid thermal conductivity, the distance between the walls and the difference between the wall heat fluxes. When the Brinkman number, Br*, is equal to 0.25 a singular point arises where the Nusselt numbers, Nu, remains constant and equal to 4 regardless of the values of n, c and wall heat fluxes. This behavior can be explained by the competing effects of n or c on the heat transfer. While decreasing n or increasing c increases the value of Nu for Br*<0.25 and decreases it for Br*>0.25, an increase in the Brinkman number always decreases the Nusselt number.

Heat Transfer Analysis of Graphene Reinforced PCM for Thermal Energy Storage

In this experiment, the charging rate of PCM is compared in the summer and winter seasons, while PCM does not charge effectively in winter season due to lower atmospheric temperature but such effects are not seen in summer season. The key objective of this analysis is to increase the thermal efficiency and charging rate by using different nano material concentrations (COOH) varying from 0.25 volume % to 0.75 volume %. This work also includes testing of thermal conductivity, density, specific heat and Nano fluid properties at varying functionalized graphene (COOH) concentrations and temperatures at the heat tranfer fluid (HTF) inlet. Paraffin wax is implemented as a PCM in this process and carboxylic group (COOH) based graphene is the nano material used. The present research’s outcome is that the PCM charging time decreases with increasing carboxylic (COOH) graphene concentration in terms of volume percentage. The charging time decreases with the mixing of carboxylic group (COOH) graphene concentration in this experiment in the winter season. The charging rate increases with graphene concentration, as opposed to without the nanomaterial PCM. In this experiment, In the short period of the process time, the significant volume of energy can be retained as charging period is decreased by 25% to 60% by the implementation the carboxylic group(COOH) based nano powder in PCM.

Heat transfer from a particle in laminar flows of a variable thermal conductivity fluid

We revisit the classical problem of steady-state heat transfer from a single particle in a uniform laminar flow with the assumption that the thermal conductivity of the fluid changes linearly with the temperature. We use a combination of asymptotic and scaling analyses to derive approximate expressions for the dimensionless heat transfer coefficient, i.e., the Nusselt number Nu, of arbitrarily shaped particles. The results cover the entire range of the Peclet number Pe. We find that, for a constant temperature boundary condition and fixed geometry, the Nusselt number is essentially equal to the product of two terms, one of which is only a function of Pe while the other one is nearly independent of Pe and mainly depends on the proportionality constant of the conductivity-temperature relation. We also show that, in contrast, when a uniform heat flux is imposed on the surface of the particle, Nu can be estimated as a summation of a Pe-dependent piece and one that solely varies with the proportionality constant.

Natural convection heat transfer using water-based nanofluid in a shell and helical coil heat exchanger

Industry is looking for more efficient ways to use nanomaterials to decrease water consumption. The addition of greater thermal conductivity nanoparticles to the water enhances the fluid's thermal conductivity and, thus, increases the coefficient of heat transfer. In this work, water-based nanofluids were used to perform heat transfer enhancement studies in a shell and helical coil heat exchanger. Natural convection heat transfer using three water-based nanofluids (Al2O3, CuO and TiO2/water) was investigated in shell and helical coil heat exchanger. Experiments were performed at different hot water flow rates through coil (Dean number) and hot water feed temperatures (40, 50 and 60 °C). The use of water-based nanofluid led in a greater coefficient of shell-side heat transfer compared to the use of pure water on the shell side. The Nusselt number improved due to an increase in nanoparticle concentration. It was observed that with a rise in nanofluid concentration, Dean number and greater coil-side fluid feed temperature, the Rayleigh number increased.

Direct effect of nanoparticles on the thermal conductivity of CuO-water nanofluid in a phase transition phenomenon using molecular dynamics simulation

The thermal behavior of CuO-water nanofluid is examined on an aluminum surface. The dimensions of simulation boxes are 70 × 70 × 30 A3, 60 × 60 × 30 A3, and 50 × 50 × 30 A3, with the corresponding number of atoms of 104,351, 123,958, and 145,980. Thermal conductivities of fluid and nanofluid are calculated using the Green–Kubo formula. Molecular dynamics simulation results confirm the direct effect of nanoparticles on the values of thermal conductivities of fluid and nanofluid. The value of 0.59 Wm−1 K−1 is obtained for the thermal conductivity of water. But adding three CuO nanoparticles into the water increases this value to 0.85 Wm−1 K−1. The same effect is observed on the thermal behavior of nanofluid upon increasing the size of CuO nanoparticles that raises the value of the thermal conductivity of nanofluid to 0.99 Wm−1 K−1. The heat flux is increased by adding the nanoparticles into the base fluid; thereby, the phase transition (evaporation) occurs in fewer time steps.

FBG-Based Measurement Systems for Density, Specific Heat Capacity and Thermal Conductivity Assessment for Liquids

This paper presents the development of a thermal measurement system for density, specific heat capacity and thermal conductivity in fluids. Due to toxic and flammable environment often found in oil industry, Fiber Bragg Gratings (FBGs) were used in the sensor development, which consists in a diaphragm-embedded FBG, to estimate density, and a FBG temperature sensor, to estimate specific heat and thermal conductivity. The diaphragm system, with sensitivity of 0.025 nm/kPa, was employed for density measurements in water, diesel and crude oil, becoming a feasible option for density estimation in fluids. The temperature sensor, with sensitivity of 11.5 pm/°C, was used to propose a method to estimate specific heat and thermal conductivity. The method uses the quantity of heat equation to estimate specific heat, then, density and specific heat to estimate thermal conductivity. To validate the method, it was presented three setups based in an acrylic tank, a Becker and a test tube. The tests were performed with water, mineral oil and kryo 51 oil. In addition the proposed system can be integrated in order to realize simultaneous measurements of density, specific heat and thermal conductivity with the same structure.

Thermal conductivity analysis of Al2O3/water-ethylene glycol nanofluid by using factorial design of experiments in a natural convection heat transfer apparatus

Thermal conductivity of a heat transfer fluid plays a significant role in improving the heat transfer performance of a heat exchanger. In this work, experiments were performed in a natural convection heat transfer apparatus by mixing homogenized Al2O3 nanoparticles in a base fluid of water-ethylene glycol mixtures. The effects of heat input, nanoparticle volume content in the base fluid, and ethylene-glycol volume content in the base fluid on thermal conductivity of the nanofluid were analyzed. Based on results obtained by MINITAB? design software (factorial design matrix), 16 experimental runs were performed with the lower and higher levels of input factors. The levels for heat input were 10 and 100 W; for nanoparticle volume content in the base fluid 0.1 and 1 vol.% and for the base fluid composition 30 and 50 vol.% of ethylene glycol in water. From the obtained experimental results, a Pareto chart, normal probability plot, contour plot and surface plot were drawn. Based on the results, a new correlation was proposed, and predictions were compared with the experimental results. From the study, the maximum thermal conductivity value 0.49 W m-1 K-1 was observed at a nanoparticle volume content in the base fluid of 1.0 vol.%, ethylene glycol volume content in the base fluid of 30 vol.% and heat input of 100 W.

Processing and Generalization of Experimental Data on Thermal Diffusivity and Thermal Conductivity of Magnetic Fluids Depending on the Impact of the Magnetic Field

The paper presents the results of experimental studies of the thermal diffusivity and thermal conductivity of magnetic fluids based on transformer oil, depending on the effect of a magnetic field in the range of B = 1.59...3.866 mT, and the addition of iron powder 0.1...0.3 g with an interval of 0.05 g. Equations were obtained for calculation with a certain fraction of error in thermal diffusivity and thermal conductivity of unexplored magnetic fluids.

Fluid flow structures in an evaporating sessile droplet depending on the droplet size and properties of liquid and substrate

We investigate numerically quasi-steady internal flows in an axially symmetrical evaporating sessile droplet depending on the ratio of substrate to fluid thermal conductivities, fluid volatility, contact angle and droplet size. Temperature distributions and vortex structures are obtained for droplets of 1-hexanol, 1-butanol and ethanol. To this purpose, the hydrodynamics of an evaporating sessile drop, effects of the thermal conduction in the droplet and substrate and diffusion of vapor in air have been jointly taken into account. The equations have been solved by finite element method using ANSYS Fluent. The phase diagrams demonstrating the number and orientation of the vortices as functions of the contact angle and the ratio of substrate to fluid thermal conductivities, are obtained and analyzed for various values of parameters. In particular, influence of gravity on the droplet shape and the effect of droplet size have been considered. We have found that the phase diagrams of highly volatile droplets do not contain a subregion corresponding to a reversed single vortex, and their single-vortex subregion becomes more complex. The phase diagrams for droplets of larger size do not contian subregions corresponding to a regular single vortex and to three vortices. We demonstrate how the single-vortex subregion disappears with a gradual increase of the droplet size.

The Impact of Nanofluids on Droplet/Spray Cooling of a Heated Surface: A Critical Review

Cooling by impinging droplets has been the subject of several studies for decades and still is, and, in the last few years, the potential heat transfer enhancement obtained thanks to nanofluids’ use has received increased interest. Indeed, the use of high thermal conductivity fluids, such as nanofluids’, is considered today as a possible way to strongly enhance this heat transfer process. This enhancement is related to several physical mechanisms. It is linked to the nanofluids’ rheology, their degree of stabilization, and how the presence of the nanoparticles impact the droplet/substrate dynamics. Although there are several articles on droplet impact dynamics and nanofluid heat transfer enhancement, there is a lack of review studies that couple these two topics. As such, this review aims to provide an analysis of the available literature dedicated to the dynamics between a single nanofluid droplet and a hot substrate, and the consequent enhancement or reduction of heat transfer. Finally, we also conduct a review of the available publications on nanofluids spray cooling. Although using nanofluids in spray cooling may seem a promising option, the few works present in the literature are not yet conclusive, and the mechanism of enhancement needs to be clarified.

Significance evaluation of performance factors on horizontal spiral-coil ground heat exchangers

Ground-coupled heat pump systems using horizontal spiral-coil ground heat exchangers (HSGHE) are being utilized for an increasing number of applications due to the efficiency in terms of thermal performance. To optimize design accuracy and thermal performance, significant design factors of HSGHEs should be identified. Thus, this study investigates the effects of influential factors on the thermal performance of HSGHEs through sensitivity analysis. Numerical models were established with respect to the operation of HSGHEs using the finite element method. Variance-based sensitivity analysis was conducted using the numerical results to quantitatively evaluate the overall effects, which include the main effects as well as interaction effects between the design factors. Furthermore, case studies of two different regions were applied to the sensitivity analysis to compare the effects of regional climate factors on the order of significance of the input factors. As a result, ground thermal conductivity, installation depth, and inlet fluid temperature were determined as major design factors. On the other hand, the order of significance of the major factors was found to be dependent on regional climate factors. This result implies that it is necessary to consider different critical factors of HSGHE design according to the ambient conditions of the installation region.

Instability and energy budget analysis of viscous coaxial jets under a radial thermal field

Temporal linear instability of viscous coaxial jets under a radial thermal field is carried out by considering axisymmetric and non-axisymmetric disturbances. The interfacial tensions of different fluids are taken to be temperature dependent. The para-sinuous, para-varicose, and helical unstable modes are identified in the Rayleigh regime. The energy budget is also employed to explore the relative importance of thermal-induced stresses on the jet instability at the most unstable wavenumber by changing the dimensionless parameters. It is shown that decreasing the temperature ratio of inner fluid to surrounding fluid (T13) promotes the jet instability. For coaxial jets at T13 &amp;gt; 1, the Marangoni flow makes coaxial jets more stable, and increasing the fluid thermal conductivity suppresses the jet instability. For coaxial jets at T13 &amp;lt; 1, however, their influences on the jet instability are opposite. Compared with the thermal-induced stresses at the inner and outer interfaces, the inner interfacial tension is the main factor dominating the flow. Increasing either inner interfacial tension or outer surface tension and decreasing viscosity of any fluid can promote the instability of coaxial jets. The variations of thermal conductivity and specific heat capacity of either inner or surrounding fluids apparently influence the jet instability of the para-varicose mode, but hardly influence that of the para-sinuous mode. This work would provide great insight into the physical mechanism of thermal jet instability in various applications.