Thermal Conductivity Of Base Fluid Research Articles

Experimental study of thermal conductivity and convective heat transfer enhancement using CuO and TiO2 nanoparticles

Heat transfer characteristics of CuO/water and TiO2/water nanofluids were measured in a shell and tube heat exchanger under laminar and turbulent flow condition. In shell and tube heat exchanger, water based CuO and TiO2 based nanofluids with 0.02%, 0.04% and 0.06% volume fraction have been used as working fluids for different flow rates of nanofluids. This enhancement was investigated with regard to various factors; concentration of nanoparticles, types of base fluids, sonication time and temperature of fluids. The effects of Nusselt number and Reynolds number of suspended nanoparticles, on the heat-transfer characteristics were investigated. The experimental results have been compared to those of Dittus–Boelter correlation, Xuan & Li and Gnielinski correlation for the laminar and turbulent flow region. Low thermal conductivity is a major concern in the development of the energy-efficient heat transfer fluid. In this paper, the effect of CuO and TiO2 nanoparticles on the thermal conductivity of base fluids like monoethylene glycol and water was studied. The nanofluids showed an enhancement in effective thermal conductivity, and overall heat transfer coefficient. The thermal conductivity measurement has been made for different concentrations and temperatures. As the concentration of nanoparticles increased, there was a significant enhancement in thermal conductivity and overall heat transfer due to more interaction between particles. It was also observed an improvement in thermal conductivity of base fluid as temperature increases.

Thermophysical effects of water driven copper nanoparticles on MHD axisymmetric permeable shrinking sheet: Dual-nature study.

The present study is dedicated to analyze the dual-nature solutions of the axisymmetric flow of a magneto-hydrodynamics (MHD) nanofluid over a permeable shrinking sheet. In those phenomena where the fluid flow is due to the shrinking surface, some reverse behaviors of the flow arise because of vorticity effects. Despite of heat transfer analysis, the main purpose of the present study is to attain the solutions of the complex nature problem that appear in reverse flow phenomena. Thermophysical properties of both base fluid (water) and nanoparticles (copper) are also taken into account. By means of similarity transformation, partial differential equations are converted into a system of coupled nonlinear ordinary differential equations and then solved via the Runge-Kutta method. These results are divided separately into two cases: the first one is the unidirectional shrinking along the surface (m = 1) and the other one is for axisymmetric shrinking phenomena (m = 2) . To enhance the thermal conductivity of base fluid, nanoparticle volume fractions (0≤φ ≤ 0.2)) are incorporated within the base fluid. The numerical investigation explores the condition of existence, non-existence and the duality of similarity solution depends upon the range of suction parameter (S) and Hartmann number (M). The reduced skin friction coefficient and local Nusselt number are plotted to analyze the fluid flow and heat transfer at the surface of the shrinking sheet. Streamlines and isotherms are also plotted against the engineering control parameters to analyze the flow behavior and heat transfer within the whole domain. Throughout this analysis it is found that both nanoparticle volume fraction and Hartmann number are increasing functions of both skin friction coefficient and Nusselt number.

Thermal Conductivity on the Nanofluid of Graphene and Silver Nanoparticles Composite Material.

The composite material consisted of graphene (GN) and silver nanoparticles (AgNPs) has been essential topic in science and industry due to its unique thermal, electrical and antibacterial proper- ties. However, there are scarcity studies based on their thermal properties of nanofluids. Therefore, GN-AgNPs composite material was synthesized using facile and environment friendly method and further nanofluids were prepared by ultrasonication in this study. The morphological and structural investigations were carried out using scanning electron microscope (SEM), transmission electron microscope (TEM), X-ray diffractometer (XRD) as well as ultra violet (UV)-visible spectroscopy. Furthermore, thermal conductivity measurements were performed for as-prepared nanofluids. As a result of thermal conductivity study, GN-AgNPs composite material was considerably enhanced the thermal conductivity of base fluid (water) by to 6.59% for the nanofluid (0.2 wt% GN and 0.4 wt% AgNPs).

Analysis of Using Ferrofluid as an Interface Material in a Field Reversible Thermal Connector

The electrical functionality of an avionics chassis is limited due to heat dissipation limits. The limits arise due to the fact that components in an avionic computer boxes are packed very compactly, with the components mounted onto plug-in cards, and the harsh environment experienced by the chassis limits how heat can be dissipated from the cards. Convective and radiative heat transfer to the ambient are generally not possible. Therefore, it is necessary to have heat transferred from the components conducted to the edge of the plug-in cards. The heat then needs to conduct from the card edge to a cold block that not only holds the card in place but also removes the generated heat by some heat transfer fluid that is circulated through the cold block. The interface between the plug-in card and the cold block typically has a high thermal resistance since it is necessary for the card to have the capability to be reworkable, meaning that the card can be removed and then returned to the chassis. Reducing the thermal resistance of the interface is the objective of the current study and the topic of this thesis. The current design uses a pressure interface between the card and cold block. The contact pressure is increased through the addition of a wedgelock, which is a field-reversible mechanical connector. To use a wedgelock, the cold block has channels milled on the surface with widths that are larger than the thickness of the plug-in card and the unexpanded wedgelock. The card edge is placed in the channel and placed against one of the channel walls. A wedgelock is then placed between the card and the other channel wall. The wedgelock is then expanded by using either a screw or a lever. As the wedgelock expands, it fills in the remaining channel gap and bears against the other face of the plug-in card. The majority of heat generated by the components on the plug-in card is forced to conduct from the card into the wall of the cold block, effectively a single sided, dry conduction heat transfer path. Having started as a student design competition named RevCon Challenge, work was performed to evaluate the use of new field-reversible thermal connectors. The new design proposed by the University of Missouri utilized oil based iron nanoparticles, commonly known as a ferrofluid, as a thermal interface material. By using a liquid type of interface material, the channel gap can be reduced to a few micrometers, within machining tolerances, and heat can be dissipated off both sides of the card. The addition of nanoparticles improves the effective thermal conductivity of base fluid. The use of iron nanoparticles allows magnets to be used to hold the fluid in place, so the electronic cards may be easily inserted and removed while keeping the ferrofluid in the cold block channel. The ferrofluid-based design which was investigated has shown lower thermal resistance than the current wedgelock design. These results open the door for further development of electronic cards by using higher heat emitting components without compromising the simplicity of attaching/detaching cards from cooling plates.

Application of Laplace Transform for the Exact Effect of a Magnetic Field on Heat Transfer of Carbon Nanotubes-Suspended Nanofluids

Abstract Since the discovery of the carbon nanotubes (CNTs), there is an increasing interest in their applications in industry and medical fields. Attempts of using such CNTs as drug carriers and in cancer therapy in the presence of a magnetic field are now undertaken because of their direct impacts on increasing the thermal conductivity of base fluids. Two types of CNTs are well known for the researchers, the single-walled CNT (SWCNTs) and the multi-walled CNTs (MWCNTs); however, the subject of which one is more effective in treatment of cancer deserves more investigations. The present article discusses the effect of such types of CNTs on the flow and heat transfer of nanofluids in the presence of a magnetic field. Exact analytical solution for the heat equation has been obtained by using the Laplace transform, where the solution is expressed in terms of a new special function, the generalised incomplete gamma function. The effects of various parameters on the fluid velocity, temperature distribution, and heat transfer rates have been introduced. Details of possible applications of the current results in the treatment of cancer have been also discussed.

TO STUDY THE BEHAVIOR OF NANOFLUIDS IN HEAT TRANSFER APPLICATIONS: A REVIEW

Using nanofluids as an innovative kind of liquid blend including trivial volume fraction (in percent) of millimeter or nanometer size powdered particles with base fluids is fairly a novel arena or idea. The objective of this presented review paper is to inspect the performance of the nanofluid-based solar collector (NBSC). In past few years for a number of experimental and industrial thermal engineering systems solar energy has proven to be the best input energy source. Nanofluids are the fluid that has shown various developments in the thermal properties over the past decade. In the field of nanotechnology, nano fluids have a great potential to enhance the rheological properties like thermal conductivity of base fluid like water, ethanol etc. Nanofluids are the suspension of mainly the base fluid like water in nanoparticles such as alumina (Al2O3) of size micro or milimetre and shows distinctive features than that of conservative fluids used. Because of better rheological properties nanofluids are utilized to build up the performance of conventional solar thermal engineering systems. The presented literature review presents a detailed discussion about the solar collectors, applications of nanofluids in solar collector and their augmentation in thermo physical properties.

Effect of Nanostructure on Thermal Conductivity of Nanofluids

The presence of colloidal particles is known to increase the thermal conductivity of base fluids. The shape and structure of the solid particles are important in determining the magnitude of enhancement. Spherical particles—the only shape for which analytic theories exist—produce the smallest enhancement. Nonspherical shapes, including clusters formed by colloidal aggregation, provide substantially higher enhancements. We conduct a numerical study of the thermal conductivity of nonspherical structures dispersed in a liquid at fixed volume fraction in order to identify structural features that promote the conduction of heat. We find that elongated structures provide high enhancements, especially if they are long enough to create a solid network (colloidal gel). Cross‐linking further enhances thermal transport by directing heat in multiple directions. The most efficient structure is the one formed by hollow spheres consisting of a solid shell and a core filled by the fluid. In both dispersed and aggregated forms, hollow spheres provide enhancements that approach the theoretical limit set by Maxwell’s theory.

Lignin as dispersant for water-based carbon nanotubes nanofluids: Impact on viscosity and thermal conductivity

The viscosity and thermal conductivity of water-based nanofluids containing carbon nanotubes, stabilized by lignin as surfactant, are measured. These experiments were performed at 20°C and we study the effect of nanotube volume fraction which ranges from 0.0055% to 0.55%. In comparison with SDBS, we show that lignin reduces viscosity and shear-thinning behavior of nanofluids at high volume fraction, without penalizing thermal conductivity enhancement. Viscosity enhancement at high shear rate with respect to nanoparticle content is well modeled by the Maron–Pierce equation, suggesting that lignin is better than SDBS at dispersing carbon nanotubes within water at high volume fraction. The impact of surfactant on base fluid thermal conductivity is also reported and thermal conductivity enhancement of nanofluids with nanoparticle volume fraction is finally compared with previous published models.

Axisymmetric Stagnation-Point Flow of Nanofluid Over a Stretching Surface

AbstractThis paper investigates the laminar boundary layer flow of nanofluid induced by a radially stretching sheet. Nanofluid model exhibiting Brownian motion and thermophoresis is used. Series solutions for a reduced system of nonlinear ordinary differential equations are obtained by homotopy analysis method (HAM). Comparative study between the HAM solutions and previously published numerical results shows an excellent agreement. Velocity, temperature and mass fraction are displayed for various values of parameters. The local skin friction coefficient, the local Nusselt number and the local Sherwood number are computed. It is observed that the presence of nanoparticles enhances the thermal conductivity of base fluid. It is found that the convective heat transfer coefficient (Nusselt number) is decreased with an increase in concentration of nanoparticles whereas Sherwood number increases when concentration of nanoparticles in the base fluid is increased.

The effect of silver and aluminum oxide nanoparticles on thermophysical properties of nanofluids

Abstract The present paper describes experimental and theoretical aspects of the effective thermal conductivity, electrical conductivity, and viscosity of nanofluids. The thermal conductivity, electrical conductivity, and viscosity of nanofluids increase with the nanoparticle volume fraction. The nanofluid was prepared by synthesizing Al2O3 and Ag nanoparticles using microwave-assisted chemical precipitation method and then dispersed in distilled water using a sonicator. Water nanofluid with nominal diameters of 20 and 40 nm at various volume concentrations (0.25% to 5%) at a temperature of 15°C was used for the investigation. The thermal conductivity, electrical conductivity, and viscosity of nanofluids were measured, and it was found that the viscosity and electrical conductivity increase is substantially higher than the increase in thermal conductivity. The pure base fluid thermal conductivity displayed a Newtonian behavior at 15°C; it transformed to a non-Newtonian fluid with the addition of a small amount of nanoparticles φ > 3%.

PREDICTION OF CONVECTIVE HEAT TRANSFER OF NANOFLUIDS BASED ON FRACTAL-MONTE CARLO SIMULATIONS

With the consideration of the Brownian motion of nanoparticles in fluids, the probability model for the size of nanoparticles and the model for convective heat transfer of nanofluids are derived based on the fractal character of nanoparticles. The proposed model is expressed as a function of the size of nanoparticles, the volumetric nanoparticle concentration, the thermal conductivity of base fluids, fractal dimension of nanoparticles and the temperature, as well as the random number. It is found that the convective heat flux of nanofluids decreases with increasing of the average diameter of nanoparticles. This model has the characters of both analytical and numerical solutions. The Monte Carlo simulations combined with the fractal geometry theory are performed. Every parameter of the proposed formula on convective heat transfer of nanofluids has clear physical meaning. So the proposed model can reveal the physical mechanisms of convective heat transfer of nanofluids.

Enhancing the efficiency of polymerase chain reaction using graphene nanoflakes

The effect of the recently developed graphene nanoflakes (GNFs) on the polymerase chain reaction (PCR) has been investigated in this paper. The rationale behind the use of GNFs is their unique physical and thermal properties. Experiments show that GNFs can enhance the thermal conductivity of base fluids and results also revealed that GNFs are a potential enhancer of PCR efficiency; moreover, the PCR enhancements are strongly dependent on GNF concentration. It was found that GNFs yield DNA product equivalent to positive control with up to 65% reduction in the PCR cycles. It was also observed that the PCR yield is dependent on the GNF size, wherein the surface area increases and augments thermal conductivity. Computational fluid dynamics (CFD) simulations were performed to analyze the heat transfer through the PCR tube model in the presence and absence of GNFs. The results suggest that the superior thermal conductivity effect of GNFs may be the main cause of the PCR enhancement.

Influence of CuO nanoparticles in enhancing the thermal conductivity of water and monoethylene glycol based nanofluids

In this paper the effect of CuO nanoparticles on the thermal conductivity of base fluids like mono ethylene glycol and water was studied. Both the base fluids showed enhancement in effective thermal conductivity. This enhancement was investigated with regard to various factors; concentration of nanoparticles, types of base fluids, sonication time and settlement time. For both the base fluids, an improvement in thermal conductivity was found as concentration of nanoparticles increased due to interaction between particles. It was also found that as the sonication time was increased, there was furthermore an improvement in the thermal conductivity of the base fluids. Effect of base fluids is the complex idea to understand. Lower base fluid's viscosities are supposed to contribute grater enchantment, but another factor of fluid nanoparticles surface interaction also more important. The experimentally measured thermal conductivities of base fluid's nanoparticles suspension were compared to a variety of models (Maxwell, Hamilton–Crosser and Bruggeman Model). It is observed that none of the mentioned models were found to predict accurately the thermal conductivities of nanofluids.

Thermal conductivity of polyethylene glycol nanofluids containing carbon coated metal nanoparticles

Polyethylene glycol nanofluids containing carbon coated Cu (Al, Fe) nanoparticles with core-shell structure are prepared in this paper. High efficiency on heat transfer is achieved by collaborative effect between nanocarbon and metal nanoparticles. The results show that the thermal conductivity of nanofluid is relevant to the type of filler and increases with the increasing of filler loading. An 27% enhancement in thermal conductivity is observed by adding only 0.5 wt % of carbon coated Cu nanoparticles in polyethylene glycol, and 49%, 40%, and 30% enhancement in thermal conductivity for carbon coated Cu, Al, and Fe nanoparticles loading of 1.5 wt %, respectively. The carbon coated metal nanofluid exhibit better stability after 14 days and no obvious sedimentation is observed. Compared with carbon coated Al and Fe nanoparticles, carbon coated Cu nanoparticles nanofluids have the best stability and dispersibility and can efficiently enhance the thermal conductivity of base fluid. Moreover, nanofluids stabilities are different when nanofluids were dispersed by three ways. Nanofluids dispersed by ball milling way possess the best stability, followed by nanofluids dispersed by ultrasonic dispersion way and magnetic stirring way.

Encapsulated Phase Change Material Slurry Flow in Manifold Microchannels

The heat transfer performance of water-based microencapsulated phase change material slurry (particle size 5 μm) flow inside manifold microchannels of hydraulic diameter 170 μm was experimentally and numerically investigated. Slurry performance was poorer compared with pure fluid due to the large size of particles used and lower thermal conductivity of slurry compared with water. A parametric study was performed with nanoencapsulated phase change material slurry flow (particle size of 100 nm) in microchannels of hydraulic diameters 170 and 47 μm. Two different base fluids were considered and the heat transfer enhancement of slurry with various particle mass concentrations compared with its base fluid was presented. For developing flows, the performance of phase change material slurry depends on various parameters such as base-fluid thermal conductivity, channel dimensions, amount of phase change material melted, and particle mass concentration. In the case of manifold microchannel heat sinks, where the microchannel flowpath is much shorter compared with traditional microchannels, using higher-thermal-conductivity phase change material, narrower channels, smaller particles, and optimum parameters will aid in obtaining better thermal performance of phase change material slurry compared with pure fluid.

Thermal conductivity of suspension containing SiC particles

Among various heat transfer enhancement techniques, an innovative way of improving the thermal conductivities of working media is to suspend ultrafine metallic or nonmetallic solid powders in traditional fluids since the thermal conductivities of most solid materials are higher than those of liquids. Theoretical and experimental studies have reported that suspensions containing solid particles have significantly larger thermal conductivities than the base fluids without solid particles [1, 2]. Unfortunately, suspended particles of micrometer, or even nanometer, dimensions may cause some severe problems such as abrasion and clogging in small passages. Furthermore, for all the large particle suspensions, stabilities are very poor since the coarse grained solid particles settle out eventually. Extensive research conducted on nanosized powder preparation and processing technology in recent years may offer a solution to the problem. Nanoparticle suspensions are expected to exhibit excellent properties. The large surface area and enhanced heat capacity of nanocrystalline materials [3–5] could improve the heat transfer capacities of nanoparticle suspensions. Also, Brownian movement of nanoparticles in a suspension increases stability [6]. Furthermore, nanoparticles can act as a lubricating medium because of their small sizes [7]. Adding a small amount of metal or metal oxide nanosized particles to a fluid has increased the thermal conductivity of the suspension over that of the base fluid [8–10]. The enhancement is highly dependent on the surface area of the particles and the thermal conductivity of base fluid. A nanosized metal particle suspension used as a new coolant in a microchannel heat exchanger offered significant benefits [11]. In this study, three types of α-SiC powder were dispersed in water and ethylene glycol (EG), respectively. The properties of SiC powders are summarized in Table I. SiC particles were deagglomerated by intensive ultrasonication after being mixed with base fluid and then the suspensions were homogenized by magnetic force agitation. The pH values of all the aqueous suspensions were adjusted to 10.0 such that the suspensions were stable. The thermal conductivities of the suspensions were measured by the hot-wire method [12] at a temperature of 4 ◦C. The thermal conductivities (λ) of the suspensions with SiC powers dispersed in water and EG as a function of solid particle volume fraction are shown in Fig. 1a and b, respectively. Fig. 2a and b show the ratio of the thermal conductivity enhancement (δλ = λ − λ0)