Thermal Conductivity Of Suspensions Research Articles

Experimental investigation of nanofluids for heat pipes used in solar photovoltaic panels

The current study is aimed to measure and analyze the impact of temperature (10°C < T < 90°C) and particle concentration (0.05% < ϕ < 1.5%) on thermo-physical properties of TiO2, ZnO and CuO nanoparticles suspended in Therminol-55. The nanoparticles were characterized by using various techniques, including TEM, XRD, FTIR, TGA/DSC. TEM images reveal that the morphology of TiO2 and ZnO as spherical nanoparticles whereas that of CuO is in the form of flakes. XRD pattern for TiO2, ZnO and CuO nanoparticles possess anatase, heaxagonal and monoclinic phase respectively. TGA results show that that TiO2 losses less mass than the ZnO and CuO nanoparticles at each stage of decomposition. Thereby making it more stable thermally as compared to the other samples. Two-step method has been employed to formulate stable Therminol-55 based nanofluids containing TiO2, ZnO and CuO nanoparticles for varying particle concentrations. Results show that the thermal conductivity of suspensions containing solid conducting particles increase with increasing nanoparticle content and temperature of dispersions in the fluid. The thermal conductivity of TiO2/Therminol-55, ZnO/Therminol-55 and CuO/Therminol-55 nanofluids increases up to 17.62%, 21.55% and 24.32% at particle concentration of 1.5 wt%. Further, the experimental results demonstrate that the density of nanofluids increased significantly with increase in concentration and decreased with temperature. Surface tension of nanofluids shows decrease with increase in particle concentration. This indicates that adding nanoparticles improve thermo-physical properties of nanofluid, making it suitable for use in heat pipe. The measured data for thermal conductivity and density are compared with existing theoretical models of nanofluids to check the effectivity of conventional models. A multi-variable new generalized correlations for thermal conductivity and density of Therminol-55 based nanofluids containing TiO 2, ZnO and CuO nanoparticles are proposed.

Nanoparticles impacts on natural convection nanofluid flow and heat transfer inside a square cavity with fixed a circular obstacle

Many significant applications may be acquired in specific nanoparticle shapes as well as size range or size. The shape of nano-sized particles is significant in every field of trace metal detection, for biomolecular assays, molecular labeling and the application of nanotechnology. The nanoparticle's shape effects are very noteworthy on the thermal conductivity of suspension. The main focus of the current study is to elaborate the nanoparticles shape impacts on nanofluid flow in a lid-driven square cavity with a fixed circular obstacle at the center. The top wall of the square cavity is adiabatic and moving. The circular cavity and bottom wall of the cavity is heated, while the remaining walls of the cavity are cold. The diamond-water nanofluid contained three kinds of nanoparticles shape namely Sphere, Column (nonspherical) and Lamina (nonspherical). The flow-modeled phenomena is governed in form of coupled partial differential equations and is tackled with finite element method (FEM). The flow distribution analysis is deliberated in form of streamlines, isothermal contour patterns, velocity distribution, temperature distribution, kinetic energy and Nusselt number. The graphical results indicate that the Lamina (nonspherical) shape nanoparticles have higher performance in (diamond-water) temperature distribution and heat transfer.

Study of the Viscosity Coefficient and Thermal Conductivity of Suspensions with Single-Walled Carbon Nanotubes

The viscosity coefficient and thermal conductivity of suspensions with single-wall carbon nanotubes have been experimentally studied. The nanotube mass concentrations are varied from 0.05 to 0.25 wt %. The suspensions exhibit non-Newtonian behavior. The dependences of the rheological suspension parameters on the nanotube concentration are obtained. It is established that the properties of the carrier liquid affect the viscosity coefficient and thermal conductivity of the suspensions.

Исследование коэффициентов вязкости и теплопроводности суспензий с одностенными углеродными нанотрубками

The results of an experimental study of the viscosity and thermal conductivity coefficients of suspensions with single-walled carbon nanotubes are presented. The range of nanotube mass concentrations ranged from 0.05 to 0.25 wt.%. The studied suspensions showed non-Newtonian behavior. Dependences of rheological parameters of suspensions on nanotube concentration were obtained. The influence of the base liquid on the viscosity and thermal conductivity of suspensions was established.

Thermal Conductivity of Suspensions Based on Core–Shell Particles

An analytical solution of the problem of the thermal conductivity of a suspension containing core–shell particles was found. Solutions were found under the thickness of the shell tending to zero while the thermal conductivity of the shell was tending to zero and infinity. In the first case, the solution is shown to be equivalent to the solution that takes into account Kapitza interfacial thermal resistance. The role of contact Kapitza resistance in the processes of the thermal conduction of nanofluids is discussed.

An Experimental Study on the Thermal Conductivity of Carbon Nanotubes/Oil (TECHNICAL NOTE)

[if gte mso 9]> In the present work, the thermal conductivity coefficients of nanoparticle-oil suspensions for two types of carbon nanotubes, single-walled (SWNTs) and multi-walled (MWNTs) carbon nanotubes at 0.1, 0.2 and 0.3 wt.% were measured by a modified transient hot wire method (KD2-pro thermal property meter). Results showed that the thermal conductivity of suspension containing single-walled carbon nanotubes is higher than that of suspension containing multi-walled carbon nanotubes. It was also observed that the thermal conductivity coefficients of both nanofluids increase with increasing temperature.

Multiaxial fields drive the thermal conductivity switching of a magneto-responsive platelet suspension

We demonstrate the ability to change the thermal conductivity of a magnetic platelet suspension from insulating to conducting by using either uniaxial or multiaxial ac magnetic fields to control the suspension structure and dynamics. The equivalent thermal conductivity of the suspension can be modified either by creating static particle structures that facilitate or block heat transfer, or by using multiaxial ac fields to drive emergent particle dynamics that create vigorous, organized, non-contact flow. The equivalent thermal conductivity of a single suspension can be varied over a 100-fold range, and an equivalent thermal conductivity as high as 18.3 W m−1 K−1 has been achieved in an aqueous suspension containing only 2.0 vol% platelets. This value is more than twice the conductivity of liquid mercury.

Experimental Investigation of Convective Heat Transfer in Circulating Water System

The laminar convective heat transfer behavior of CuO nanoparticle dispersions in water with three different particle sizes (23 nm, 51 nm, and 76 nm) is investigated experimentally in a flow loop with constant heat flux. The main purpose of this study is to evaluate the effect of particle size on convective heat transfer in laminar region. The experimental results show that the suspended nanoparticles remarkably increase the convective heat transfer coefficient of the base fluid, and the nanofluid with 23nm particles shows higher heat transfer coefficient than nanofluids containing the other two particle sizes about 10% under the same Re. Based on the effective medium approximation and the fractal theory, the effective thermal conductivity of suspension is obtained. It is shown that if the new effective thermal conductivity correlation of the nanofluids is used in calculating the Prandtl and Nusselt numbers, the new correlation accurately reproduces the convective heat transfer behavior in tubes.

Modified self-consisted scheme to predict the thermal conductivity of nanofluids

Abstarct In this study, the self-consisted scheme is generalized to predict the thermal conductivity of nanofluids containing spherical nanoparticles with a conductive interface. We assume a flux jump in the particle–fluid interface in the opposite to the assumption for temperature jump in the case of thermal barrier resistance. We have obtained an upper and lower bounds to the homogenized suspension thermal conductivity according to the particle packing, which is particle surface state dependent. A comparison with the Hashin–Shtrikman bounds and the Maxwell equation is made. The proposed model is evaluated using published experimental data of the thermal conductivity enhancement for different nanofluids.

Thermal conductivity of nanoparticle suspensions in insulating media measured with a transient optical grating and a hotwire

The thermal conductivities of nanoparticle suspensions of Al2O3 in C10H22 (decane) and isoparaffinic polyalphaolefin (PAO) have been measured using two dissimilar techniques: a transient hotwire measurement based on the heat loss and resistivity of a heated wire in solution, and the thermal decay of a transient grating generated by the interference of two picosecond light pulses. Agreement between the two techniques is good, indicating that either is a reliable way for measuring the thermal conductivity of colloidal suspensions. Suspensions with volume concentrations from 0.125% to 1% were measured. The Al2O3 particles were suspended by means of surfactants added to the base fluids and sonication. The thermal conductivity of the suspensions was greater than expected from classical continuum models, with a greater enhancement observed in decane than in PAO.

Effect of Morphology of Carbon Nanotubes on Thermal Conductivity Enhancement of Nanofluids

An experimental study was conducted to investigate the effect of the morphology of carbon nanotubes on the thermal conductivity of suspensions. Three different types of carbon nanotubes, classified by aspect ratio well their aqueous suspensions, were prepared and characterized through the analyses of Raman spectroscopy: thermogravimetric analyzer, scanning electron microscopy, and transmission electron microscopy. The effective thermal conductivities of the samples were measured using a steady-state cut bar apparatus method. Enhancements based on the thermal conductivity of the base fluid are presented functions of both the volume fraction and the temperature. Although functionalized single-walled nanotubes a more stable and homogeneous suspension, the addition of small amounts of surfactant to suspensions of as produced single-walled nanotubes demonstrated a greater increase in effective thermal conductivity than functionalized single-walled nanotubes alone. The effective thermal conductivity enhancement corresponding to 1.0% by volume approached ≈10%, which was observed to be lower than expected but more than twice the value, 3.5%, obtained for similar tests conducted using aluminum oxide suspensions. However, for suspensions of multiwalled nanotubes, the degree of enhancement was measured to be approximately 37%. Comparison of the measured data and that predicted by a previously developed theoretical model indicated good agreement for a corresponding shape factor, n, of 12 for the single-walled nanotubes, whereas multiwalled nanotube suspensions were well matched when the shape factor was 36, indicating that extension of the theoretical model may allow it to be applied to carbon nanotube suspensions if the effect of clustering can be accurately predicted.

Thermal Conductivity of Suspensions Containing Nanosized SiC Particles

Nanosized SiC suspensions were prepared, and their thermal conductivities were measured using a transient hot-wire method. The experimental results showed that the thermal conductivities of the studied suspensions were increased as expected, and the enhancement was proportional to the volume fraction of the solid phase, but the increasing ratio of the thermal conductivity was not significantly related to the base fluid. The effects of the morphologies (size and shape) of the added solid phase on the enhancement of the thermal conductivity of the nanoparticle suspension are reported for the first time.

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)

K-1728 氷蓄熱を対象とした氷-水サスペンションの非定常線熱源法による熱伝導率測定(S20-1 複合領域の熱物性)(S20 複合領域の熱物性)

K-1728 氷蓄熱を対象とした氷-水サスペンションの非定常線熱源法による熱伝導率測定(S20-1 複合領域の熱物性)(S20 複合領域の熱物性)

Thermal conductivity of suspensions in shear flow fields

In the present article, the rheological behavior and the thermal conductivity of suspensions were investigated experimentally by examining the effects of shear rate, particle size, and volume concentration. The thermal conductivity measurements were conducted under rotating Couette flow conditions with a varying rotational speed of the outer cylinder. Homogeneous test suspensions were prepared with uniformly dispersed and neutrally buoyant micro-particles. Four different sizes of plastic particles (25–300 μm) were used as suspended particles. The volume concentrations of the particles and shear rates varied within the ranges of 0–10% and 0–900 1/s, respectively. For the test suspensions, the limiting viscosities at high shear rates were correlated with the Batchelor equation. The highly concentrated suspension in the present study showed the shear thinning viscosity. The thermal conductivities measured at stationary condition showed excellent agreements with values in saturated water table and were correlated satisfactorily with the Brailsford–Major equation. The thermal conductivity of the test suspensions in shear flow increased with shear rate and displayed asymptotic plateau values at high shear rates. The shear-rate-dependent conductivity was strongly affected by both particle size and volume concentration in shear flow field.

Thermal conductivity of suspension and emulsion materials

AbstractA technique for the prediction of effective thermal conductivity of porous materials previously developed by the authors has been extended to suspension and emulsion systems and its capability is supported by the available experimental data. A nomogram which estimates the effective thermal conductivity for these systems from the knowledge of constituent conductivities and proportions is also provided.

Thermal Conductivity of Suspensions : Measurements and Shape Effects of Suspended Particles on Conductivity

Experiments have been carried out to measure the thermal or electrical conductivity or suspensions composed of variously shaped particles dispersed in gelatin gel at volume fractions from 0 up to 0.6. On the basis of these measurements as well as the values previously published by other authors, the dependence of conductivity on the shape of suspended particles is discussed and some of explicit and theoretical expressions proposed up to data are evaluated. For the purpose or predicting the conductivity of suspensions the Bruggemann equation is most promising for spherical dispersion and the Fricke equation is more reliable than others for dispersion of which the shape is significantly different from a sphere, if the shape of suspended particles is well approximated to an ellipsoid.

Thermal Conductivity of Suspensions : Measurements and Discussions of the Shaped Effects of Dispersions

Thermal Conductivity of Suspensions : Measurements and Discussions of the Shaped Effects of Dispersions