Thermal Properties Of Liquids Research Articles

Analytical Model for Pulsed-Laser Induced Mode-Mismatched Dual-Beam Thermal Lens Spectroscopy in Liquids.

Analytical models are very important to understand physical, chemical, and biological phenomena. In many cases, obtaining an analytical model is a complex, even an impossible task. In this work, an analytical model for thermal lens spectroscopy has been developed. The model considers light absorbing liquids, a laser pulsed beam as the heat source, timescale thermal regime, and small phase change produced by heating. A simplification for low-absorption samples is obtained. A complete theoretical study of their utilization is shown. Measurements of the thermal diffusivity of water-ethanol sample mixtures in the liquid phase are analyzed. These values for pure substances are in good agreement with those reported in the literature. Our methodology could be very useful in the analysis of the optical and thermal properties of liquids.

Dielectric and thermal performance of a C60-based nanofluid and a C60-loaded ferrofluid

Liquids in electrical devices often act as electrical insulators and cooling media. To enhance both dielectric and thermal properties of liquids, various nanoparticles can be dispersed in the liquids resulting in effective nanofluids. In this research, a new generation transformer oil prepared by a gas-to-liquid technology has been used to prepare a mono-nanofluid with fullerene C60 nanoparticles (0.01%w/V) and a hybrid nanofluid with C60 (0.01%w/V) and iron oxide nanoparticles (0.01%w/V), so-called C60-loaded ferrofluid. Both nanofluids and the oil were subjected to experimental investigation of frequency-dependent dielectric response, dielectric breakdown, and thermal conductivity at various temperatures. Finally, the three liquids were applied in a single-phase transformer, and temperature rise tests of the loaded transformer were conducted. The dielectric spectroscopy revealed three orders of magnitude higher dielectric losses in C60-loaded ferrofluid than in the oil and C60 nanofluid, where the losses are of conducting nature. In C60-loaded ferrofluid, an interfacial relaxation process is considered in addition. C60 particles in the oil increased its breakdown voltage by 17%, while the mixture of C60 and magnetic nanoparticles resulted in a 12.5% reduction of the breakdown voltage. The enhancement has been ascribed to the strong capacity of C60 to absorb electrons and their ability to weaken the photoionization in the head of the streamer. The thermal conductivity of both nanofluids decreases with temperature, and the effective medium theory can well predict it. A significant decrease in the transformer temperature rise up to 8 K has been found for C60 nanofluid, as compared with the temperature rise achieved with the transformer oil. The temperature rise was also reduced with C60-loaded ferrofluid (up to 5.6 K). The lower cooling efficiency of the hybrid nanofluid was attributed to the high dielectric losses generating undesirable heat with a counter-productive effect on the cooling process.

Exploring the fusion hindrance phenomenon: the case of 32,34S + 89Y

The sub-barrier fusion data of 32,34S + 89Y colliding systems are analyzed using the coupled-channels (CC) calculations, including couplings to the low-lying 2+ and 3− states in reacting nuclei as well as mutual and multi-phonon excitations of these states, based on the proximity potential model. In this scheme, we focus upon the the effect of surface energy coefficient γ and also thermal properties of liquids and hot nuclei on the inner part of the nuclear potential and thus on the fusion cross sections at bombarding energies far below the Coulomb barrier. As expected, our primary calculations using the original proximity potential 1977 show that this model underestimates the measured fusion cross sections at the whole energy region. It is shown that the mentioned physical effects bring significant cross sections enhancements for both reactions. The indications of the fusion hindrance phenomenon in the fusion cross sections at energies far below the Coulomb barrier show up. The observed S factors for the above-mentioned systems develop a maximum at low energies which can also be predicted by the phenomenological extrapolations. Our results within the framework of the modified form of the proximity potential reveal that the calculated fusion cross sections, S factors, and logarithmic slopes for the two systems are in good agreement with the corresponding experimental data even at the lowest energies.

Thermocapillary deformation induced by laser heating of thin liquid layers: Physical and numerical experiments

Characterizing the profile of the laser-induced thermocapillary deformation of a thin liquid layer on a laser absorbing solid is of great fundamental and applied importance. The thermocapillary effect is the basis of several non-contact methods for measuring the physicochemical and thermal properties of liquids and solids, and methods of non-destructive testing in material science and thermal physics. The study of the layer rupturing caused by laser beam heating could contribute to solving the problem of the dry spots formation in thin–film heat exchangers. In this regard, the development of physical and numerical tools to determine the thermocapillary profiles of thin liquid layers is of great interest to researchers. In the present work, we developed a home-made setup to scan a deformed surface of a liquid layer with a laser sheet. Its accuracy was verified by scanning the surface of a solid standard specimen with a given Gaussian profile. By scanning the thermocapillary deformed layers of silicone oil, we found that for the Gaussian distribution of the radiation intensity in the heating laser beam, the thermocapillary deformations are significantly not the Gaussian. A modified Agnesi function, which is characterized by high accuracy and allows defining the surface profile using a minimum of experimental data, is shown to be an optimal function for approximating the thermocapillary deformation. Using Agnesi approximation can significantly reduce the time of the experiment and the processing of results. To validate new experimental data, an axisymmetric numerical model of the thermocapillary convection in a thin liquid layer was developed using commercial software Comsol Multiphysics. It helped calculating the surface profile and the temperature field on the substrate for two boundary conditions of radiative heat exchange in the system corresponding to maximum and minimum radiation heat loss. For the case of the ebonite-silicone oil system, when the laser beam is absorbed by the ebonite surface, it was numerically shown that the difference between the types of boundary conditions becomes noticeable only on very thin layers close to the pseudo-rupture. In general, a comparison of the stationary profiles of the thermocapillary surface deformation and temperature distributions obtained experimentally and numerically for the entire range of the studied layer thicknesses shows satisfactory agreement between the physical and numerical results.

Application areas and calculation method for capillary-porous heat exchangers of the new heat-removing class

The paper is centered on research focused on the fundamental studies of capillary-porous systems working in the mass forces field. Examined are the effects of pressure, excess fluid, the methods for heating and for supplying coolant, as well as the type of material used, in addition to the intensifier type amongst others, on the integral and thermo-hydraulic characteristics of the heat transfer process. The information obtained from the research can be used in the design, engineering calculations and operation of different energy installations of power plants. Experimentally obtained approximation for the law of the growth of a bubble in a cell of a porous structure, taking into account the influence of underheating, velocity and thermal properties of liquid and a heating surface, was used for determination of the radius of a “dry” spot. The heat transfer control permits to form a new class in the system for heat removing. Devices for heat exchange were built to raise their efficiency, reliability and to be loyal to environment. Capillary-porous heat exchanger shaped as a box provides safety from an explosion. The engineering method for calculation is done for limiting and operational characteristics of capillary-porous heat exchanger. The heat transfer control permits the development of a new class in the system for heat removal. Devices for heat exchange were built with the purpose of increasing both efficiency and dependability in an environmentally conscious manner. A capillary-porous heat exchanger shaped as a box provides protection against an explosion. Obtaining Its limiting and operational characteristics is done by means of an engineering method for calculation.

Proximity potential and temperature effects on α-decay half-lives

In order to calculate the \ensuremath{\alpha}-decay half-lives of a wide range of heavy and superheavy nuclei, we introduced a modified temperature-dependent surface energy coefficient in the proximity potential based on thermal properties of liquids and hot nuclei. An increase in the \ensuremath{\alpha}-decay half-life was observed by decreasing the surface energy coefficient as a result of temperature incorporation of the parent nuclei. The introduced temperature-dependent surface energy coefficient evaluated the half-lives which were in good agreement with the experimental data. Moreover, the results of the present paper confirm the closed-shell effects.

Analysis of the characteristic perturbations spectrum of the exact invariant solution of the microconvection equations

The properties of an exact invariant solution of the equations of microconvection of isothermally incompressible liquids have been investigated. The solution describes a stationary fluid flow in a vertical channel. The temperature or heat flux can be given at the solid boundaries of the channel. A classification of the solutions and their physical interpretation are suggested. In accordance with the classification the solutions describe different types of flows. The solution of the stability problem of all classes of flows in the vertical channel with the given temperature on the walls is presented. The structure of the spectrum of small non-stationary spatial perturbations for the model medium (silicon dioxide melt) has been studied, depending on the configuration of the perturbation wave, thickness channel, thermal and gravitational effects. The formation regularities of different types of the thermal and hydrodynamic disturbances have been determined. The interaction of the thermal and hydrodynamic perturbations leads to the formation of various convective structures. Typical patterns of the velocity and temperature perturbations and relations of critical characteristics of the instability are presented, depending on the problem parameters. The most dangerous mechanisms change from hydrodynamic to thermal ones with the variation of the viscous and thermal liquid properties.

Synthesis and characterization of physical, thermal and thermodynamic properties of ionic liquids based on [C12mim] and [N444H] cations for thermal energy storage

This work characterizes the ionic liquids (ILs) [N444H][Cl], [N444H][Tf2N], [N444H][PF6], [C12mim][Cl], [C12mim][Tf2N] and [C12mim][PF6] for use in thermal energy storage. The thermal properties of these liquids have not been reported previously. The liquids were synthesized and characterized by nuclear magnetic resonance (NMR), elemental analysis (EA), and Fourier transform infrared spectroscopy (FTIR). Physical properties including density, speed of sound, and dynamic viscosity were measured at different temperatures. Thermal properties were determined by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The results showed that the ILs combined with the [Tf2N] anion had good thermal properties for use as heat transfer fluids (HTF), such as wide temperature ranges as liquids and high decomposition temperatures. The thermal storage densities of [C12mim][Tf2N] and [N444H][Tf2N] are 177 and 200MJm−3, respectively.

Graphene-enhanced nanorefrigerants

Recent reports that a host liquid's thermal properties can be augmented by dispersal of small quantities of nanoparticles have stimulated intense interest as an intriguing avenue to produce advanced heat transfer fluids. But effects are challenging to exploit in practical settings because it is difficult to prepare refrigerant-based dispersions displaying sufficient long-term stability. Moreover, the most dramatic enhancements in thermal conductivity obtained using anisotropic nanomaterials (e.g., carbon nanotubes) are achieved at the expense of a severe viscosity increase. Here we overcome these limitations by introducing a robust surfactant-mediated dispersal method that enables stable suspensions containing a range of nanomaterials to be straightforwardly prepared as additives to ordinary commercial refrigerants. We apply this approach to formulate a new class of nanorefrigerants containing graphene nanosheets that uniquely match the superior thermal conductivity enhancements attained in carbon nanotube suspensions without their accompanying viscosity penalty. These suspensions can be directly substituted for conventional refrigerants to inexpensively achieve increased efficiency in many thermal management applications.

Thermal Characterization, Using the Photopyroelectric Technique, of Liquids Used in the Automobile Industry

Thermal properties of liquids used in the automobile industry such as engine oil, antifreeze, and a liquid for windshield wipers were obtained using the photopyroelectric (PPE) technique. The inverse PPE configuration was used in order to obtain the thermal effusivity of the liquid samples. The theoretical equation for the PPE signal in this configuration, as a function of the incident light modulation frequency, was fitted to the experimental data in order to obtain the thermal effusivity of these samples. Also, the back PPE configuration was used to obtain the thermal diffusivity of these liquids; this thermal parameter was obtained by fitting the theoretical equation for this configuration, as a function of the sample thickness (called the thermal wave resonator cavity), to the experimental data. All measurements were done at room temperature. A complete thermal characterization of these liquids used in the automobile industry was achieved by the relationship between the obtained thermal diffusivities and thermal effusivities with their thermal conductivities and volumetric heat capacities. The obtained results are compared with the thermal properties of similar liquids.

A Phase-Sensitive Technique for Measurements of Liquid Thermal Conductivity

An experimental technique based on the thermal wave approach for measuring the thermal conductivity of liquids is developed in this paper. A stainless steel strip functions as both a heating element and a sealing cover for a chamber containing a test liquid. A periodic current passing through this metal strip generates a periodic Joule heating source. An infrared detector measures the temperature response at the front surface of the stainless steel strip. The phase and magnitude of the temperature response with respect to the heating signal were measured by a lock-in amplifier at various frequencies from 22 Hz to 502 Hz. A one-dimensional, two-layered transient heat conduction model was developed to predict the temperature response on the front surface of the stainless steel strip. The phase information from this temperature response shows high sensitivity to the change in thermal properties of the liquid layer and is employed to match experimental data to find the thermal properties of the test liquid. The measured thermal conductivities of water and ethylene glycol agree quite well with the data from literature and support the validity of this measurement technique. An aqueous fluid consisting of gold nanoparticles is tested and anomalous thermal conductivity enhancement is observed. A discrepancy in the thermal transport behavior between pure liquids and nanofluids is suggested from our experimental results.

Thermal Wave Resonator Cavity Applied to the Study of the Thermal Diffusivity of Coffee Infusions

Among the photothermal methods, the photopyroelectric technique, in its several experimental configurations, has been extensively used to measure the thermal properties of liquids, mainly the thermal effusivity and diffusivity. In this paper, the use of the so-called thermal wave resonator cavity method, in the cavity-length-scan mode, to measure the thermal diffusivity of commercial coffee infusions with samples at different concentrations and degrees of degradation induced by heating cycles is reported. A linear relationship between the logarithm of the pyroelectric signal amplitude and the sample thickness was observed, in agreement with the basic theory for the experimental configuration used here, from which the thermal diffusivity values of the samples were obtained. The thermal diffusivity was found to be almost independent of the coffee concentration in water but that this parameter is sensitive to sample modifications induced by degradation. This work represents another step to demonstrate the capability of the used method for characterization of the thermal properties of liquids.

Photoacoustics of Two‐Layer Systems: Thermal Properties of Liquids and Thermal Wave Interference

A general description of the photoacoustic (PA) technique applied to characterize thermal properties of liquids is presented. The effects of different supporting substrates on measurements of thermal properties and data analysis are discussed in detail. Likewise, the use of the proposed experimental configuration for the monitoring of dynamic processes occurring in liquid solutions, such as, solvent evaporation and polymer casting from solutions is also considered.

Measurement of the thermal properties of liquid mixtures using a thermal wave interferometer

In this paper we discuss the use of an alternative photothermal technique for measurements of thermal properties of liquid mixtures. The proposed technique is based upon the concept of a thermal wave interferometer. The liquid sample is confined between two thin pyroelectric detectors. One of these detectors acts as a modulated light absorber while the other is used for sensing the temperature fluctuations transmitted through the liquid layer. It is demonstrated that the proposed experimental configuration allows us to fully characterize the thermal properties of the constituent liquids.

Method of measurement and a computerized workbench for a researcher on the thermal properties of liquids

Physical and mathematical models of a measuring instrument are considered. A method of determining the thermal properties of materials is proposed. The structure of a measuring instrument and a computerized workplace for a researcher on the thermal properties of materials are developed. Estimates of the measurement error are given.

Limit of absolute stability for crystal growth into undercooled alloy melts

The limit of absolute stability for crystal growth of binary alloys into an undercooled melt is discussed in respect of a positive temperature gradient in the solid and different thermal properties of liquid and solid. It is shown that the positive temperature gradient and the better heat conductivity and diffusivity of the solid phase reduce the velocity corresponding to the limit of absolute stability. Thus although the solid grows into an undercooled melt a planar interface may be stable with a quite lower growth rate than the absolute thermal velocity.

Photoacoustic monitoring of adhesive curing

AbstractThe crosslinking reaction of an epoxy‐based resin has been monitored by observing the time evolution of the thermal diffusivity of the mixture, using photoacoustic spectroscopy. The results are interpreted in terms of the expected thermal properties of liquids, polymers and solids, and a comparison with the reported viscosity behavior in similar systems is also made. The potential of the technique for following the curing process is discussed.

Properties of melting 3He: Specific heat, entropy, latent heat, and temperature

A sequence of experiments has been performed to measure thermal properties of liquid and solid 3 He between the temperatures 1 and 25 mK at melting curve densities. A two-phase mixture of 3 He sample was self-cooled by the Pomeranchuk method. A heat pulse technique was used, combined with measurements of pressure and volume, to yield separate determinations of liquid and solid properties: the specific heat of liquid 3 He in the normal Fermi liquid and superfluid phases; the entropy of solid 3 He above and through a nuclear magnetic transition at 1.10 mK; and an absolute thermodynamic temperature scale based on measurement of latent heat of conversion of liquid to solid.

Theory of the Melting Anomaly of Helium Four

The melting anomaly of ${\mathrm{He}}^{4}$ predicted earlier will be accounted for in detail by two different methods. In the first or thermodynamic approach, the thermal properties of the liquid and solid at melting are used to evaluate the temperature derivative of the melting pressure and the ensuing difference between the melting pressure at temperature $T$ and absolute zero. In the second method, these same melting-pressure functions are derived theoretically from the elementary excitation spectra of the liquid. In the elaboration of the latter approach, the thermal properties of liquid ${\mathrm{He}}^{4}$ II, arising from the approximate high-energy branch of its elementary excitations, will be given exactly. Both methods yield similar results in quantitative agreement with recent melting-pressure data over most of the region explored.

The cooling of irregularly shaped igneous bodies

On the assumptions that thermal properties of liquid and solid magma and country rock are the same,and that cooling of the magma takes place by conduction and not by development of systematic convection cells, temperature values are calculated for several types of cooling lava sheets. Isotherms for these conditions are presented. In light of the data derived by formulation of the pattern of isotherms, the assumption that joint columns form perpendicular to isotherms in a cooled igneous body is not necessarily valid. Metamorphism of country rock at specific sites related to the cooling magma is discussed.