Liquid Phase Thermal Conductivity Research Articles

Inverse method for simultaneously estimating temperature-dependent solid- and liquid-phase thermal conductivities during phase transition

As phase change material (PCM) undergoes the phase transformation under the working conditions such as thermal energy storage (TES), it is essential to simultaneously and accurately measure the temperature-dependent thermal conductivities (TCs) of solid and liquid phases. In this study, a novel inverse method is proposed to simultaneously estimate the temperature-dependent solid and liquid phase TCs of a PCM. Several theoretical issues such as the parameter sensitivity, discretization schemes, estimation algorithms are clarified. The Monte Carlo method is used to verify the three discretization schemes, and the results show that both the solid and liquid TCs have high sensitivity coefficients. Additionally, the estimation algorithm results are strongly related to the temperature measurement position, measurement time, boundary conditions, and discrete scheme of the mathematical model. The uncertainty analysis shows that the error caused by the position of the temperature sampling point accounts for approximately 50% of the total estimation error, which suggests that the time-discrete scheme is preferred for the application of the proposed method in real experiments. This study demonstrate that the proposed algorithms provide accurate and reliable estimates of temperature-dependent TC for solid and liquid phases.

Evaluation of material property estimating methods for n-alkanes, 1-alcohols, and methyl esters for droplet evaporation calculations

Modeling of heat and mass transfer in liquid fuel combustion requires several material properties in a wide temperature and pressure range. The unavailable data are commonly patched with various estimation methods. In this paper, group contribution methods (GCM) and law of corresponding states (LCS) were analyzed for estimating material properties of n-alkanes (up to C10H22 and C12H26), 1-alcohols (up to C10H22O), and methyl esters (up to C19H38O2 and C19H36O2). These were compared to reference data to evaluate their applicability. LCS suggested by Poling et al. provides proper estimation for the acentric factor. GCM of Joback accurately estimates normal boiling point, critical properties, and specific heat capacity of the vapor-phase, the latter was corrected for methanol, however, GCM of Constantinou is more accurate for critical pressure of methyl esters. GCM of Ruzicka is suitable for estimating liquid-phase specific heat capacity. This method was updated for methanol. GCM of Elbro gives a proper estimation for liquid-phase density, while LCS of Lucas estimates vapor-phase viscosity properly. LCS of Chung and the modified Eucken method for vapor-phase and GCM of Sastri for liquid-phase thermal conductivity are appropriate. Considering the gas-phase mutual diffusion coefficient, the method of Fuller provides the best estimation, while LCS methods of Riedel and Chen are suitable for the enthalpy of vaporization at the normal boiling point.

Simultaneously estimate solid- and liquid-phase thermal conductivities

This paper proposes a method for simultaneously estimating solid- and liquid-phase thermal conductivities of phase-change materials (PCMs). This parameter-estimation method is built on a phase-change line-source solution. Several theoretical issues of parameter estimation were discussed, including sensitivity, identifiability, and uncertainty. The analysis reveals that the liquid- and solid-phase thermal diffusivities (αl and αs) are insensitive to temperature responses and are difficult to estimate. Although the solid-phase conductivity ks have large sensitivity coefficients, they are linearly dependent on the sensitivity coefficients of αl and αs. This paper proposes estimating solid- and liquid-phase thermal conductivities simultaneously by a fitting and a non-fitting algorithms because they have large, uncorrelated sensitivity coefficients. The non-fitting algorithm differs the fitting one in that it produces a set of estimates, which can be considered as a set of samples involving experimental errors and can be used to estimate the uncertainty of the estimated parameters by variances, confidence limits, etc.

Thermophysical Properties of Liquid Al–Cu Alloys

With the rapid development of concentrating solar power stations, Al–Cu eutectic alloy can be potentially used as a latent heat storage material to provide heating during periods without sunlight. During heat storage system designs, knowledge of the liquid phase thermal conductivity is indispensable, and yet there has been no detailed report published on the thermal conductivity of liquid Al–Cu alloys. To determine thermal conductivity, one can calculate using either electrical conductivity with the Lorenz number or from thermal diffusivity. To not make any assumptions on the Lorenz number, we calculated the thermal conductivity from thermal diffusivity data obtained by laser flash. We also provided data for the liquid Al-rich region by adapting the van der Pauw method for liquids. The obtained thermal conductivity shows the excellent heat transfer ability of liquid Al–Cu alloys.

Passive thermal management of a simulated battery pack at different climate conditions

This study contains a systematic investigation of RT-44 and GNP/RT-44 composite performance in passive thermal management of a battery pack operating at different climate temperatures. The thermal characterization of RT-44 and GNP/RT-44 composites was also carried out. For 7% GNP/RT-44 composite, solid phase and liquid phase thermal conductivities were enhanced by 230% and 130%, respectively. On the other hand, loss of energy storage capacity is about 7.5% compared to RT-44. During the passive thermal management, the temperature increase of battery was significantly reduced by RT-44 due to their sensible and latent energy storage capability. This superior performance is further enhanced by the increased thermal conductivity of 7% GNP/RT-44 composites. At the highest discharge rate (3.90 W) and at the highest ambient temperature (30 °C), the effective thermal protection duration was extended as 1.96 and 7.90 times compared to RT-44 and natural convection cases. Moreover, it is further extended by the reduction both the discharge rate and ambient temperatures. 7% GNP/RT-44 also reduced the maximum temperature difference within the battery pack at low ambient temperatures. On the other hand, RT-44 performed better maximum temperature difference at higher ambient temperatures due to phase change and constant temperature plateau effect.

Evaluation of thermophysical properties of refrigerant clathrates with additives

A modeling study is conducted to evaluate the heat transfer properties of novel refrigerant clathrate-based phase change materials (PCMs). Novel PCMs with large specific energy densities are formed by using different additives in the refrigerant clathrates. Refrigerant clathrates of R134a, R1234yf and R32 are investigated at different refrigerant mass percentages with water. Glycols, sodium chloride, magnesium nitrate hexahydrate, nanoparticles of pure aluminum, copper and graphene are used as additives. Empirical correlations are used to predict the liquid-phase thermal conductivities of refrigerant clathrates and the improvement obtained with the addition of different additives. The results show that an increase in refrigerant mass percentage lowers the thermal conductivity of the refrigerant clathrate but not extensively. The addition of salt results in a minor improvement in thermal conductivity while addition of glycols as liquid additives greatly improves the liquid-phase thermal conductivity. The inclusion of nanoparticles significantly improved the thermal conductivity of the phase change material. The liquid-phase specific heat capacity, however, is not generally improved by the nano-particles as it depended on the additive used.

Experimental evaluation of thermal properties of R134a clathrates based PCMs for cooling applications

The thermal properties of R134a clathrates with additives, which are treated as phase change materials (PCMs), are experimentally determined. The formation of refrigerant clathrates is investigated due to their potential use in active as well as in passive cooling applications. The PCMs are formed using R134a clathrate and distilled water with different refrigerant proportions and five different additives. The main objective of using additives is to study their potential for enhancing the clathrate thermal properties under direct contact heat transfer. PCMs are formed in glass tubes and their temperatures are recorded, at two different locations inside the tube, after regular intervals. The R134a percentages of 35% are used to form clathrate. For the additives, ethanol, sodium chloride, magnesium nitrate hexahydrate, copper and aluminum are used. PCMs are formed using a controllable constant energy water bath. The thermal properties determined are the liquid phase thermal conductivity, mushy phase thermal conductivity, and specific latent heat of the PCMs. A comparative study is conducted to compare the thermal properties of different PCMs using the suggested additives. The copper additive improves the thermal conductivity the most while sodium chloride reduces the thermal conductivity. Ethanol additive improves the specific latent heat the most while magnesium nitrate hexahydrate reduced the specific latent heat.

Ion exchange synthesis and thermal characteristics of some $\left[ \rm{\mathbf{N}}_{{2222}}^{{+}} \right]$ based ionic liquids

Eight salts were obtained by reacting tetraethylammonium cation $\big[ {{\rm {\bf N}}_{{\rm {\bf 2222}}}^{{+}} } \big]$ with inorganic anions like BF $_{{4}}^{{-}}$ , NO $_{{3}}^{{-}}$ , NO $_{{2}}^{{{-}}}$ , SCN − , BrO $_{{3}}^{{-}}$ , IO $_{{3}}^{{-}}$ , PF $_{{6}}^{{-}}$ and HCO $_{{3}}^{{-}}$ using ion exchange method. These ionic liquids (ILs) were characterized using thermal methods, infrared spectroscopy and densitometry. Thermophysical properties such as density, coefficient of volume expansion, heat of fusion, heat capacity and thermal energy storage capacity were determined. Thermal conductivity of the samples was determined both in solid and liquid phases. Owing to high values of thermal energy storage capacity coupled with handsome liquid phase thermal conductivity, ILs under investigation were recommended as materials for thermal energy storage (TES) as well as heat transfer applications.

Ion exchange synthesis and thermal characteristics of some [N+4444] based ionic liquids

Eight salts, derived from tetrabutylammonium cation [N+4444] and inorganic anions like BF4−, NO3−, NO2−, SCN−, BrO3−, IO3−, PF6− and HCO3− were synthesized using the ion exchange method. These ionic liquids (ILs) were characterized using thermogravimetry, differential scanning calorimetry and infrared spectroscopy. Thermophysical properties such as density, volume expansion, heat of fusion, heat of solid–solid transitions, specific heat capacity and thermal energy storage capacity were determined. The total of heat of solid–solid transitions observed below the melting points exceeded the heat of fusion in some cases. The thermal conductivity of the samples was determined both in solid and liquid phases. High values of thermal energy storage capacity and handsome liquid phase thermal conductivities made many of the ionic liquids under investigation were recommended as Thermal Energy Storage Devices (TESDs) as well as heat transfer fluids.

Energetic Fuel Droplet Gasification with Liquid-Phase Reaction

Abstract An exploratory analytical and computational study of gasifying energetic liquid fuel droplets is presented. The liquid-fuel reaction, heating, and breakup are modelled and characterized. A spherically-symmetric geometry is considered, and the problem is described by considering a general formulation capable of resolving the solution domain consisting of a liquid-phase region, a bubbly two-phase region, and a gas-phase region. The transient, two-phase, governing equations are solved numerically for various values of the nondimensional rate constant, heat of decomposition, activation energy, number of bubbles per unit mass, and ratio of gas-phase to liquid-phase thermal conductivities.

Coefficients for Solution of the Analytical Freezing Equation in the Range of States for Rapid Solidification of Biological Systems

Solution of the classical solidification heat transfer problem for many biological applications involves states for which roots of the transcendental equation associated with the governing differential equation are not available. These roots are calculated and presented for conditions that characterize a large ratio of solid to liquid phase thermal conductivities and diffusivities and large differences between the initial and final temperatures for the cooling process.

Benzene: A Further Liquid Thermal Conductivity Standard

The available experimental liquid-phase thermal conductivity data for benzene have been examined with the intention of establishing a further liquid thermal conductivity standard along the saturation line. The quality of the available data is such that new standard reference values can be proposed with confidence limits better than ±1% for most of the normal liquid range.

Standard Reference Data for the Thermal Conductivity of Liquids

The available experimental liquid-phase thermal conductivity data for water, toluene, and n-heptane have been examined with the intention of establishing standard reference values along the saturation line. The quality of available data is such that for toluene and water new standard reference values can be proposed with confidence limits better than ±1.0% for most of the normal liquid range. For n-heptane there are insufficient reliable experimental data for the system to be treated as a primary reference standard, so a lower quality correlation has been developed which yields a set of secondary reference data with confidence limits of ±1.5% for most of the normal liquid range.

The determination of thermal conductivity coefficients of liquids by a thermal lens technique

The thermal lens technique, already established for gases, is extended to the measurements of liquid-phase thermal conductivity coefficients, the best values obtained at 300±2 K being 0.59, 0.171, 0.116, 0.149 and 0.110 W m−1 K−1 for water, acetone, chloroform, butan-2-one and chlorobenzene respectively. It is also shown that the accuracy of measurement of the curvature of the axial-pulsed-laser beam intensity, with an array of resolution equal to the pinhole diameter, is not sufficient to give the precision of measurement associated with a calibration approach.

Liquid-phase thermal conductivities of isotopically substituted molecules

The first page of this article is displayed as the abstract.