Thermal Conductivity Of Liquids Research Articles

Numerical/experimental strategies to infer enhanced liquid thermal conductivity and roughness in laser powder-bed fusion processes

Modelling the thermal behaviour of the melt pool produced in Laser Powder-Bed Fusion (L-PBF) processes is not an easy task, as many complex non-linear thermal phenomena are involved. An effective way to make the computational cost of these analyses affordable is to model powder and molten metal as continuous media, wherein all the heat transfer modes occurring in the liquid are simulated as lumped fictitious heat conduction. The augmentation factor used to enhance the thermal conductivity of the liquid is in general calibrated through experimental estimations of the melt pool size. The present work is aimed at devising a robust method for the calibration of such thermal parameters. A specific point of novelty of the present paper is the definition of a method to correlate surface roughness and numerically predicted melting pool size. This strategy is able to predict with good accuracy the roughness of L-PBF fabricated parts and could pave the way for calibration strategies based on roughness measurements. For this purpose, a 3-factor, 3-level Design of Experiment (DoE) has been carried out to investigate melting pool size and roughness by changing the machine process parameters: laser power, hatch distance, time exposure. In this way, the calibration of the thermal properties is made less sensitive to the large uncertainty usually affecting the melt pool size measurements and the range of applicability of the thermal model is explored over a broad spectrum of L-PBF process parameters. Anisotropic and isotropic enhanced thermal conductivity approaches are applied in combination with a laser source modelled either as a 2D or 3D heat source, respectively. The latter approach proved to be more accurate and robust against experimental uncertainties.

The role of particle dopant to the thermal conductivities of PCM coconut oil by means of the T-history method

We described in this paper the role of chemical dopant to the thermal conductivity of organic phase change material (PCM) of coconut oil (co_oil) based on T-history method. We used the nanoparticle dopant, namely graphite, CuO, and ZnO. Each kind of dopant was added to co_oil in a certain amount of 1 wt% and 2 wt%. For comparison, the data of pure co_oil was also taken and compared to the data from direct measurement. Because of the smaller diameter to height ratio, the lumped capacitance method is applicable here. Hence, the heat transfer between PCM and water during solidification or melting process is one dimensional, so that the one-dimensional transient heat diffusion equation for cylindrical geometry is applicable. Analysis of the data for solidification and melting processes led to the values of solid and liquid thermal conductivities. We note that in general 1 wt% dopants have effectively increased the thermal conductivities of co_oil, which is important for the effective heat transport of the material in response to the heat from the environment. More increase of dopant concentration has resulted in the reduction of thermal conductivities, which might be due to the agglomeration of particle dopant due to van der Waals interaction between particles.

MODELING OF IN-MOLD PLACED MG-CONTAINING MODIFIER BRIQUETTES MELTING DURING PIG-IRON CASTING

Computer simulation methods were used to analyze the effect of the shape of magnesium-containing modifier briquettes placed in the gating system on the time of their melting. Modeling of hydrodynamics of the flow of liquid metal and thermal conductivity was carried out by the finite element method. As the material of castings, pre-eutectic cast iron is adopted, which is poured into rectangular plates into a sand mold.

Efficient Characterization of Macroscopic Composite Cement Mortars with Various Contents of Phase Change Material

The determination of both the thermal and thermodynamical properties of a composite material containing phase change material is done thanks to an inverse method, which combines experimental measurements and numerical computations. Given first an in-house experiment, which allows us to test samples at a macroscopic scale (i.e., close to the real conditions) and to set various types of thermal stresses, and secondly the simulation of the corresponding thermal behavior, relying on an accurate thermodynamical modeling and taking into account the real operating parameters (e.g., thermal contact resistances and non-symmetric heat fluxes on each side), it is possible to characterize the solid and liquid thermal conductivities and heat capacities, as well as the temperature range associated with a non-isothermal phase transition and the associated latent heat. The specificity of the present approach is to allow, in a single step, a characterization of all the involved thermo-physical parameters that are usually required in simulation tools (e.g., EnergyPlus…). Moreover, the hitherto studies dealing with repeatability and uncertainties of the enthalpy characterization are generally very scant and not encountered very often or only with qualitative assessments. This is a clear caveat, especially when considering any system design. Therefore, for the first time ever, the present paper pays a special attention to the repeatability of the identification method and studies the scedasticity of the results, that is to say the deviations of the determined enthalpy curves, not only from a qualitative point of view but also by proposing quantitative arguments. Finally, the results are very promising since the agreement between all trials is excellent, the maximum error for all parameters being lower than 4%. This is far below the current quality thresholds admitted when characterizing the enthalpy of a phase change material.

ИССЛЕДОВАНИЕ ТЕПЛОПРОВОДНОСТИ НАНОМОДИФИЦИРОВАННЫХ ЖИДКОСТЕЙ

ИССЛЕДОВАНИЕ ТЕПЛОПРОВОДНОСТИ НАНОМОДИФИЦИРОВАННЫХ ЖИДКОСТЕЙ

Theoretical Elucidation of an Effect of Liquid Viscosity and Thermal Conductivity on Nonlinear Pressure Waves in Liquids Containing Many Air Bubbles

Theoretical Elucidation of an Effect of Liquid Viscosity and Thermal Conductivity on Nonlinear Pressure Waves in Liquids Containing Many Air Bubbles

Theoretical Study on an Effect of Liquid Viscosity and Thermal Conductivity on Weakly Nonlinear Propagation of Long Pressure Waves in Bubbly Liquids

Theoretical Study on an Effect of Liquid Viscosity and Thermal Conductivity on Weakly Nonlinear Propagation of Long Pressure Waves in Bubbly Liquids

Thermal conductivity and thermal diffusivity of Pyrrolidinium-BasedIonic liquids at atmospheric pressure

The thermal conductivity of two pyrrolidinium-based ionic liquids (ILs) 1-propyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (short name is [C3C1pyr][NTf2]) and 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl) imide (short name is [C4C1pyr][NTf2]) have been measured over the temperature range from (279–438) K at atmospheric pressure. Measurements were made using the steady-state hot-wire technique. The combined expanded uncertainty of the temperature and thermal conductivity measurements at the 95% confidence level with a coverage factor of k = 2 is estimated to be 0.02 K and 3.2%, respectively.The measured thermal conductivities (λ) together with our previously reported heat capacity (CP) and density (ρ) data were used to calculate thermal diffusivity (a) of the ILs using well-known thermodynamic relation a=λ/ρCP.The new measured values of the thermal conductivity have been also used to check the reliability and accuracy of the various predictive methods (generalized model, group contribution method).

Thermal management of water-based carbon nanotubes enclosed in a partially heated triangular cavity with heated cylindrical obstacle

The aim of present article is to investigate the thermal management of water-based single wall carbon nanotubes (SWCNTs) inside the partially heated triangular cavity with heated cylindrical obstacle. In this model, thermal conductivity of liquid is comprehensively improved by introducing the SWCNT and specific conditions are introduced at the inner circular cylinder. Three various conditions (cold, heated and adiabatic) are defined at the surface of heat cylinder to maintain the thermal management. Convection in the cavity takes place due to difference between cold inclined walls and partially heated bottom wall. This phenomenon is governed by set of nonlinear partial differential equations, including continuity, momentum and energy equation. Apart from other thermophysical properties of nanofluid, effective thermal conductivity model has also been incorporated. The numerical solution is sought using Finite Element Method (FEM). The simulation is performed for the effects of cylindrical obstacles (cold, adiabatic and hot), heated lengths A⩽LH⩽B, Rayleigh number 104⩽Ra⩽108, nanoparticle volume fraction (0⩽ϕ⩽0.2), and magnetic parameter (0⩽M⩽500) on the heat transfer rate, flow velocity fields, and temperature distribution. The study concludes that at the heated length the heat transfer rate for hot cylinder is less than that of cold cylinder. Whereas, it is increased due to increase in Rayleigh number and nanoparticle volume fraction. Moreover, temperature distribution inside the cavity is increased by increasing the nanoparticles volume fraction. On the other hand, increase in magnetic field effects does not have significant impact on the temperature distribution.

Impact of non-uniform heat sink/source and convective condition in radiative heat transfer to Oldroyd-B nanofluid: A revised proposed relation

Nanofluids are embryonic as auspicious thermo liquids for application of heat transfer which have been scrutinized precisely, in current eons. Thermo-physical properties of these liquids have noteworthy stimulus on their heat transfer features. The manifestation of dense nanoparticles in the base liquid ominously intensifies the effective liquid thermal conductivity and therefore heightens the features of heat transfer. The highest attention of this exertion is to investigate the features of nanoparticles mass flux conditions and non-uniform heat sink/source on magnetite Oldroyd-B nanofluid. Additionally, heat convective and thermal radiation mechanisms are considered. Homotopic approach has been established for the solution of non-linear structures. The upshots elucidate that the Brownian and thermophrosis nanoparticles exaggerate the temperature field, however analogous tendency is being noted for thermal radiation and non-uniform heat sink/source parameters. This exertion also investigated that the concentration of Oldroyd-B nanofluid decline for curvature parameter and augment for thermophrosis parameter. In addition, for the endorsement of up-to-date derived clarifications a comparison table of skin friction coefficient is organized in limiting circumstances.

Condensation heat transfer and pressure drop of refrigerants HFO-1234yf and HFC-134a in small circular tube

HFO-1234yf has similar thermodynamic properties to HFC-134a but much lower GWP value. It is expected as a good candidate to replace the refrigerant HFC-134a in the near future. However, only very few papers have been published in the past years regarding to the flow condensation heat transfer performance of this new refrigerant. This study provides an experimental analysis of flow condensation heat transfer and pressure drops of refrigerants HFO-1234yf and HFC-134a in a small circular tube. The test results show that both pressure drop and condensation heat transfer performance depend on the fluid properties, flow conditions and flow patterns. The major controlling properties on pressure drops and heat transfer coefficients is strongly depending on their two-phase flow pattern at various flow conditions. At the lowest mass velocity, gravity is the major force that dominates the heat transfer mechanism and the flow pattern is slug. Higher liquid viscosity retarded the condensate flow but higher liquid conductivity provided better heat transfer through the liquid film. Both liquid viscosity and conductivity are the important controlling properties. While mass velocity and vapor quality increased, the effect of shear force increased and the flow pattern transferred to annular. Liquid thermal conductivity became the major controlling property at high vapor qualities. But at low vapor qualities, gravity is still important and therefore liquid viscosity is one the major controlling parameter. At the highest mass velocity conditions, gravity effect is negligible even though at very low vapor quality condition. Shear force dominated the condensation heat transfer mechanism and liquid conductivity is the most important controlling property. It can be concluded that the flow condensation heat transfer performance is strongly depending on the two-phase flow patterns at various flow conditions.

Measurement on the thermal conductivity of five saturated fatty acid ethyl esters components of biodiesel

The utilization of biodiesel, which is considered as a renewable, biodegradable and clean-burning transportation fuel consisting of fatty acid alkyl esters, is a promising way to replace fossil fuels. Thermal conductivity is a very important thermophysical property of the biodiesel. In this work, the liquid thermal conductivity of five saturated fatty acid ethyl esters (ethyl myristate, ethyl laurate, ethyl caprate, ethyl caprylate and ethyl heptanoate) were measured with the temperature ranging within (290.64–393.88) K, (274.73–400.08) K, (270.00–400.44) K, (254.76–400.37) K, (250.38–393.46) K, respectively. The total relative standard uncertainty of the experimental results was estimated to be less than 2% and repeatability was better than ±0.5%. The experimental results of each substance were fitted as a function of temperature. The average absolute relative deviation and maximum absolute relative deviation between the experimental data and calculated results were 0.19% and 0.36% for ethyl myristate, 0.15% and 0.54% for ethyl laurate, 0.17% and 0.38% for ethyl caprate, 0.23% and 0.66% for ethyl caprylate, 0.19% and 0.52% for ethyl heptanoate, respectively.

Experimental studies on the liquid thermal conductivity of three saturated fatty acid methyl esters components of biodiesel

Abstract One of the attempts to reduce the consumption of fossil fuels is to replace them with renewable and clean fuels. Among these fuels, biodiesel has been considered as a promising alternative to petroleum diesel fuel. Thermal conductivity of biodiesel is a very important thermophysical property for its applications. In this work, the liquid thermal conductivity of three saturated fatty acid methyl esters (methyl myristate, methyl laurate and methyl caprate), usually the significant biodiesel components, was measured with the temperature ranging within (304–402) K, (283–402) K, (267–400) K, respectively. The total standard uncertainty of the experimental results was estimated to be less than 2% and the repeatability was better than ± 0.5%. The thermal conductivity data of each substance were fitted as a function of temperature, and the average absolute relative deviation and maximum absolute relative deviation between the experimental data and calculated results were 0.13% and 0.44% for methyl myristate, 0.21% and 0.53% for methyl laurate, 0.28% and 0.80% for methyl caprate, respectively.

Experimental investigations on the liquid thermal conductivity of five saturated fatty acid methyl esters components of biodiesel

Abstract The utilization of biodiesel is a promising way to replace fossil fuels, and thermal conductivity of biodiesel is a very important thermophysical property for its applications. In this work, the transient hot-wire instrument with one bare platinum wire was used to measure the thermal conductivity of five pure components of biodiesel in liquid phase at atmospheric pressure. The measured substances include methyl butyrate, methyl pentanoate, methyl caproate, methyl caprylate, and methyl pelargonate, and the temperature range was from (283 to 358) K, (285 to 362) K, (263 to 368) K, (273 to 393) K, (278 to 383) K, respectively. The total standard uncertainty of the experimental results was estimated to be less than 2% and the repeatability was better than ±0.5%. The thermal conductivity data of each substance were fitted as a function of temperature. The average absolute relative deviation and maximum absolute relative deviation between the experimental data and calculated results were 0.17% and 0.44% for methyl butyrate, 0.25% and 0.58% for methyl pentanoate, 0.16% and 0.44% for methyl caproate, 0.15% and 0.47% for methyl caprylate, 0.15% and 0.33% for methyl pelargonate, respectively.

An experimental study of R410A condensation heat transfer and pressure drops characteristics in microfin and smooth tubes with 5 mm OD

Heat transfer and pressure drop characteristics of R410A condensing flow in horizontal small microfin and smooth tubes with outer diameter of 5.0 mm were studied experimentally at relatively high mass fluxes ranging from 390 to 1583 kg/m2 s with different saturation temperatures of 309.15 K, 316.15 K, and 323.15 K. The results indicate that heat transfer coefficients and pressure gradients increase with increasing mass flux and with decreasing saturation temperature for both microfin and smooth tubes. The lower vapor density, higher liquid thermal conductivity, and higher surface tension effect all contribute to the higher heat transfer coefficients at a lower saturation temperature. The experimental heat transfer coefficients and frictional pressure gradients fit well with the empirical correlations. The heat transfer coefficient ratios between microfin and smooth tube range from 1.65 to 1.28 which means that microfin tubes can enhance heat transfer coefficients efficiently. Both heat transfer enhancement ratio and pressure drop penalty ration decrease with increasing mass flux and saturation temperature. Compared with other refrigerant properties, the liquid-vapor density contributes more to the heat transfer enhancement ratio at high mass flux.

Thermal Conductivity of Ionic Liquids and IoNanofluids and Their Feasibility as Heat Transfer Fluids

Ionic liquids and ionanofluids were studied in recent years as possible alternatives to current engineering fluids, namely in the area of heat transfer. Excellent thermal properties, like high heat capacity per unit volume and thermal conductivity, allied to the dispersion of nanoparticles in them, have created great expectations, as the enhancement of their thermophysical properties liquids can contribute to better efficiency in heat transfer. The thermal conductivity of [P66614][N(CN)2], [P66614][Br], [C2mim][SCN], [C4mim][SCN], [C2mim][C(CN)3], and [C4mim][C(CN)3] in the temperature range of 293–343 K at 0.1 MPa and their ionanofluids with multiwalled carbon nanotubes are reported in the present work. While we could not obtain stable suspensions with phosphonium based ionic liquids, thermal conductivity enhancement of cyano-based ionic liquids was compared with our previous work using dicyanamide ionic liquids. The thermal conductivity of C2mim+ ionic liquids and ionanofluids is generally higher than t...

A modified Kardos equation for the thermal conductivity of refrigerants

This work presents a modification of the Kardos equation specifically oriented to refrigerants. The proposed equation was tested for both liquid and vapor thermal conductivities along saturation of the main refrigerants. In the Kardos equation, the thermal conductivity of liquids is a function of the density of the liquid, heat capacity at constant pressure, speed of sound in the liquid and average distance between the centers of the molecules. In the present version, the liquid molar volume and the distance between the surfaces of adjacent molecules were replaced by two constant parameters widely available for all the fluids: the critical density and radius of gyration. In this way, the resulting equation is much simpler, still being a scaled equation. In the proposed equations, an adimensional factor was regressed to minimize the deviations. The final equations were able to predict the thermal conductivity with AAD[Formula: see text] for liquids and AAD[Formula: see text] for vapors.

On the instability of a liquid sheet moving in vacuum

A linear stability analysis of a non-isothermal liquid sheet moving in vacuum is studied taking into account the temperature dependencies of the liquid viscosity, thermal conductivity, and surface tension coefficients. It is found that there are two mechanisms of instability. The short-wave instability is caused by viscosity stratification across the sheet due to nonuniform temperature profiles developed downstream in the cooling sheet. The long-wave thermocapillary instability is caused by the temperature gradient along the sheet surfaces. Computed examples of steady flows and their instabilities demonstrated that the unstable short waves have much larger amplification factors.

HEAT AND MASS TRANSFER IN SOLID – LIQUID SYSTEM WITH SUPERFICIAL HEAT SOURCE

The interaction between a solid (zinc) and a liquid reagent (a solution of hydrochloric acid) was studied theoretically and experi-mentally. These processes are used in the dimensional processing of metals in order to give those appropriate shapes. A cylindrical zinc billet was used as the object of the study. The billet lateral surface is protected by an acid-resistant coating and the dissolution process occurred only along the plane of the work piece section. The experimental installation scheme with the description of ex-perimental researches technique is resulted too. The zinc billet dissolution proceeds with the release of the gaseous phase during the nucleation of the bubbles, growth and separation from the solid surface where they nucleate. It promotes intensive mixing of the liq-uid and turbulizes the boundary diffuse layer. As a result, the process of maso-visualization is intensified. This process is controlled by diffusion and its intensity is determined by the mass-transfer coefficient. The value of the mass-transfer coefficient is presented in this work. The interaction is accompanied by significant thermal effects. This enhances the process of dissolving zinc with hydro-chloric acid. The heat source is located on the interaction surface and spreads by convection in a liquid reagent and thermal conduc-tivity in a solid, respectively. The temperature at the interaction surface is important to know, since it determines the values of the physical quantities that are used to mass-exchange processes calculation. The process of thermal conductivity in a semibounded body with a continuously operating surface heat source is considered in the condition of constant convective heat flow into liquid medium. A differential heat equation with a constantly acting heat source on the solid surface with the corresponding initial and boundary conditions is used to describe the dissolution process. The results of experiments are shown in the graphs form. The temperature of the interaction surface is determined as a function of time. It is also found that the largest surface temperature gradients are observed at the initial periods. The temperature field in a bar-shaped metal blank was determined theoretically and experimentally and it ade-quacy has been confirmed.

Modelling the thermodynamics of air-component mixtures (N2, O2 and Ar): Comparison and performance analysis of available models

With a view to finding which of the available equations of state is the most suitable for the representation of the thermodynamics of mixtures containing nitrogen, oxygen and argon, this paper mainly intends to address the comparison of the performance of the - already optimized - GERG-2008, Bender and Peng-Robinson (PR) Equations of State (EoS) in the calculation of Vapour-Liquid Equilibrium (VLE) and volumetric properties of N2-O2-Ar mixtures. The comparison between experimental measurements collected in the literature and model calculations has led to conclude about the overall superiority of GERG-2008. It is also shown that the Peng-Robinson EoS leads to comparable results in VLE calculations and that the use of Bender EoS should be avoided as it leads, despite its complex multiparameter formulation, to very inaccurate results in the calculation of VLE properties of the binary Ar-O2 and of volumetric properties. For completeness, the paper also shows the poor accuracy of the PR EoS in calculating VLE properties when zero-kij are selected. Moreover, the paper evaluates the impact of deviations on densities, calculated with the different equations of state, on the computation of transport properties (thermal conductivity, viscosity), in turns determined by means of correlations which are typically applied. Liquid thermal conductivity is highly affected by errors on liquid density calculations while the liquid viscosity is independent of density. Differently, errors on vapour thermal conductivity and dynamic viscosity are lower than those observed on vapour density.