The paper presents the results of measurements of the effective thermal conductivity of three sandstone samples exhibiting different structural ordering in the temperature range 273-523 K and pressures from atmospheric to 400 MPa, as well as (2) a low-parameter model, described as a temperature dependence at a fixed pressure and the pressure dependence at a fixed temperature. It also describes the influence of pressure on the nature of the temperature dependence. The samples from the following deposits were studied: (1) Kochubei, the Republic of Dagestan, (2) Buinaksk, the Republic of Dagestan, and (3) the Tyumen superdeep well. It was shown that the cumulative increase in temperature and pressure for sandstones with different structural ordering (even when the absolute values of the effective thermal conductivity at atmospheric pressure and room temperature are close) can have a qualitative difference and with a predominantly amorphous ordering, it must be taken into account when compiling temperature models in the terrestrial bark.

The paper presents the results of experimental studies of the temperature-baric effective thermal con-ductivity of a number of sandstones and granites. For the presentation we have chosen four sandstone samples from Dagestan and Tyumen deposits, two of which have a prevailing crystalline ordering, and two - a structure close to amorphous, and two samples of granite from Dagestan and Kola deposits. The experiment was provided by the absolute stationary compensation method of flat plates in the tem-perature range of 273-523 K in the range of hydrostatic pressures from atmospheric to 400 MPa. The results confirmed the proposed low-parameter model. The measured values of the thermal conductivity of the samples at 300 K were in the range from 0.7 to 3.5 W/m K. The temperature dependence in the considered range in all cases is well described by the power-law dependence. In addition, we have found a fairly significant correlation between the baric dependence of the effective thermal conductivity itself in the normalized dimensionless representation and the baric dependence of the exponent in the temper-ature dependence. This correlation can be traced for all studied samples of granites and sandstones and it makes possible to reduce the number of independent parameters. We have also shown that for sand-stones with an amorphous structure, a simultaneous increase in temperature and pressure can lead to a rather significant total contribution. If taking into account the temperature-baric dependence of the effective thermal conductivity for rocks with a more common predominantly crystalline order, as noted by a number of authors, is not necessary due to the compensation of the pressure and temperature con-tributions, then for significantly amorphous rocks these contributions are summed up, and the total con-tribution may turn out to be significant.Copyright (c) 2022 Elsevier Ltd. All rights reserved. Selection and peer-review under responsibility of the scientific committee of the International Confer-ence on Thermal Analysis and Energy Systems 2021.

Республика Дагестан, 367008, г. Махачкала, ул

We have studied the behavior of the effective thermal conductivity of rocks (as natural heterogeneous materials) for the pressure range 0.1-400 MPa (initial region) and the temperature range 273-523 K. We propose a low-parametric empirical equation with great accuracy describing the effective thermal conductivity dependence, and discuss the physical meaning of its parameters.

We have proposed a low-parameter description of the thermal conductivity temperature-pressure dependence of natural and artificial composite materials describing the initial pressure region for the majority composites with great accuracy. It was found that the increase in pressure as usual leads to a decrease in the temperature dependence of the thermal conductivity. Moreover, if for some compounds the decrease for the power factor with pressure is linear (or quasi-linear) in the whole range of 0-400 MPa, then for others, a rapid change to 100 MPa takes place, after which the value of the power factor varies little.

The results from experimental studies on the effect hydrostatic pressure of up to 400 MPa has on the thermal conductivity of fluid-saturated sandstone samples are analyzed. It is shown that moisture saturation strongly affects the processes of heat transfer in the initial range of pressures. Hydrostatic pressure affects the volume and elastic parameters, resulting in a phase transition of the second kind.

A model for the structure of a rock as a heterogeneous system of two components, amorphous and crystalline, is considered. A formula is proposed for calculating the thermal conductivity of rocks with different temperature dependences of the thermal conductivity of their components. When the temperature dependence of the thermal conductivity of the components and their volume fractions is known, the thermal conductivity of the actual rock can be predicted for different combinations of amorphous and crystalline phases.

Experimental results are presented on the effective thermal conductivity of rocks (sandstone and granite) and polycrystalline arsenic chalcogenides. Measurements are made using an absolute steady-state approach in the temperature range of 273–523 K and at hydrostatic pressures of up to 400 MPa. A power-law temperature dependence of thermal conductivity with a negative exponent is specific to the investigated samples at a fixed pressure. A description of this dependence is proposed. The values used in the equation are calculated from the experimental data.

The results from experimental studies of the impact of hydrostatic pressures of up to 400 MPa on the thermal conductivity of fluid-saturated sandstone specimens are analyzed. The substantial impact water saturation has on heat transfer processes in the initial zone of pressure is demonstrated.

Experimental measurements of the effect high pressure and temperature have on the thermal conductivity of silicon carbide SiC–BeO ceramics are presented. The pressure is varied in an interval of up to 400MPa; temperature, in the range of 273–523 K. The results reveal there is a reversible second-order phase transition at pressures of 100–150 MPa.