Experimental investigation on the thermophysical properties of moist porous materials

A method has been developed for the combined measurement of thermal conductivity and diffusivity. The proposed method is based on an extension of the transient probe theory. The developed technique, the differential sensor method, is then used here for the measurement of thermal conductivity and diffusivity of glycerin, dry and moist porous materials in the temperature range of –20 to 80°C. Calculations have been doneby IBM PC/XT using a data fitting program. The effect of water content and temperature on the thermophysical properties has been elucidated in frozen as well as unfrozen states. The experimental results of thermal conductivity and diffusivity obtained by the differential sensor method have been compared with the results of other methods.     

Thermal conductivity and thermal diffusivity of the R134a refrigerant in the liquid state

Thermal conductivity and thermal diffusivity of “ozone-safe” refrigerant R134a in liquid state within the range of temperatures 295.9–354.9 K and pressures from the liquid — vapor equilibrium line up to 4.08 MPa have been studied by high-frequency thermal-wave method. The experimental uncertainties of the temperature, pressure, thermal conductivity and thermal diffusivity measurement errors were estimated to be 0.1 K, 3 kPa, 1.5 and 2.5 %, respectively. Values of thermal conductivity and thermal diffusivity of liquid R134a on saturated line have been calculated. Approximation dependences for thermal conductivity and thermal diffusivity within the whole studied range of temperatures and pressures as well as on the saturated line have been obtained. The work was financially supported by the Russian Foundation for Basic Research (grant No. 07-08-00295-a).     

Classical and photopyroelectric studies of optical and thermophysical properties of starch sheets: dependence on water content and temperature

The optical and thermophysical parameters of starch films (obtained by extrusion) were determined in order to obtain input data for photothermal studies of water migration in such films. The optical spectra, sorption isotherm, and volume change were measured for samples equilibrated at different levels of relative humidities. The photopyroelectric method was used to measure thermal parameters as a function of water content and temperature. The thermal conductivity, thermal effusivity, and volume specific heat all increase with water content while the thermal diffusivity remains almost constant. The temperature behaviour of the thermal parameters in the -15+70 °C temperature range was measured for samples with different water contents. No phase transition was observed at 0 °C, which proves either that water in the starch matrix is not in a free form, or the fact that water dissolved other particles shifting the melting point to a lower temperature. Received: 1 June 1999 / Final version: 13 March 2000 / Published online: 7 June 2000     

Determination of thermal conductivity and diffusivity of soaked steels using the “Mirage effect” method

In this work, we intend to study the thermal properties of the soaked steels like XC48 and their evolution according to the heating temperature and for different soaking media, using the “Mirage effect” method which permits the simultaneous determination of thermal conductivity and diffusivity. We have observed a discontinuity of thermal conductivity and diffusivity at the temperature of the ferro-paramagnetic transition.     

Capillary cohesion and mechanical strength of polydisperse granular materials

We investigate the macroscopic mechanical behaviour of wet polydisperse granular media. Capillary bonding between two grains of unequal diameters is described by a realistic force law implemented in a molecular-dynamics algorithm together with a protocol for the distribution of water in the bulk. Axial-compression tests are simulated for granular samples at different levels of water content, and compared to experiments performed in similar conditions. We find good agreement between numerical and experimental data in terms of the rupture strength as a function of water content. Our results show the importance of the distribution of water for the mechanical behaviour.     

Simultaneous heat capacity and thermal-diffusivity photoacoustic measurement at liquid-crystal phase transitions

Summary The photoacoustic-technique application to the simultaneous characterization of the thermal diffusivity, specific-heat capacity and thermal conductivity of a liquid crystal at a phase transition is presented for the first time. The first two parameters show a critical decrease and increase, respectively, while the third one does not exhibit any critical behaviour. To speed up publication, the authors of this paper have agreed to not receive the proofs for correction.     

The water molecule and its interactions: the interaction between theory, modelling, and experiment

Understanding the behaviour of water at the molecular level requires a quantitative understanding of the water molecule and its interactions. Although many current empirical potential functions are able to reproduce some of the known behaviour, our understanding of the water molecule and its interactions is not yet sufficient for our modelling to reproduce much of the subtleness of the water molecule's behaviour in both the pure liquid and in solution. Some recent experimental and theoretical developments are discussed that may lead to an improvement in our understanding of the water molecule and its interactions in a range of environments and over a range of experimental conditions.     

Analytical solutions of accreting black holes immersed in a ΛCDM model

The evolution of the mass of a black hole embedded in a universe filled with dark energy and cold dark matter is calculated in a closed form within a test fluid model in a Schwarzschild metric, taking into account the cosmological evolution of both fluids. The result describes exactly how accretion asymptotically switches from the matter-dominated to the Λ-dominated regime. For early epochs, the black hole mass increases due to dark matter accretion, and on later epochs the increase in mass stops as dark energy accretion takes over. Thus, the unphysical behaviour of previous analyses is improved in this simple exact model.     

Evaluation ofk ± p forward dispersion relations

Kaon-nucleon forward scattering amplitudes have been calculated from dispersion relations using recent experimental data on the total cross sections. In the unphysical region the analytical continuation of theK ^? p effective range theory has been done and for the asymptotic behaviour of the total cross sections a parametrization, suggested by the Regge-pole models, has been used. The calculated real parts of the scattering amplitude are compared with the existing experimental values, as found by the optical theorem and the extrapolation of the angular distribution to the forward direction.     

Thermal conductivity and thermal diffusivity of SiO<Subscript>2</Subscript> nanopowder

A 3ω approach for the simultaneous determination of the effective thermal conductivity and thermal diffusivity of nanopowder materials was developed. A 3ω experimental system was established, and the thermal properties of water and alcohol were measured to validate and estimate the accuracy of the current experimental system. The effective thermal conductivity and thermal diffusivity of the SiO₂ nanopowder with 375, 475, and 575 nm diameters were measured at 290–490 K and at different densities. At room temperature, the effective thermal conductivity and thermal diffusivity of the SiO₂ nanopowder increased with temperature; however, both values decreased as the particle diameter was reduced. An optimum SiO₂ powder density that decreased with decreasing diameter was also observed within the measurement range. The minimum effective thermal conductivity and maximum effective thermal diffusivity were obtained at 85 × 10⁻³ kg/L, when the particle diameter was 575 nm. The optimum densities of the particles with 375 and 475 nm diameters were less than 50.23 × 10⁻³ and 64.82 × 10⁻³ kg/L, respectively.