scholarly journals The Variation Mechanism of Thermal Properties of Loess with Different Water Contents during Freezing

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Xihao Dong ◽  
Shuai Liu ◽  
Yuanxiang Yu
Keyword(s):  
Heat Transfer ◽  
Phase Transition ◽  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Properties ◽  
Water Content ◽  
Volumetric Heat Capacity ◽  
Soil Particles ◽  
Water Ice ◽  
Variation Mechanism

The thermal properties of soils are affected by many factors, such as temperature, water content, and structure. Based on the transient plane source method of thermal physics, the thermal properties of loess with different water content during the freezing process were tested. We analyzed the variation mechanism of thermal properties from the perspective of phase change. Based on the Pore/Particle and Crack Analysis System (PCAS) and theory of heat transfer, we then analyzed the microstructure and heat conduction process of loess. And a calculation model of volumetric heat capacity of frozen soil was presented. The results show that, in the major phase transition zone, the variation of the thermal properties of loess with temperature is the most significant. And the thermal diffusivity increases sharply with the significant increase of thermal conductivity and the rapid decrease of volumetric heat capacity. Moisture content not only increases the thermal conductivity and volume heat capacity of loess but also makes the influence of temperature on the thermophysical parameters more significant. The effect of temperature on thermal properties is mainly due to the change of heat transfer media caused by phase transition of water-ice, followed by the change of thermal properties of heat transfer media such as soil particles, water, ice, and air with temperature. Increasing the water content reduces the contact thermal resistance between soil particles because of the increase in the thickness of the water film on the surface of soil particles and the thermal conductivity of the heat transfer medium between particles, thus changing the thermal properties of soils.

scholarly journals Testing a Gypsum Composite Based on Raw Gypsum with a Direct Admixture of Paraffin and Polymer to Improve Thermal Properties

Materials ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3241
Author(s):  
Krzysztof Powała ◽  
Andrzej Obraniak ◽  
Dariusz Heim
Keyword(s):  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Properties ◽  
Phase Change ◽  
Large Scale ◽  
Building Materials ◽  
Residential Buildings ◽  
Energy Performance ◽  
Polymer Content ◽  
Volumetric Heat Capacity

The implemented new legal regulations regarding thermal comfort, the energy performance of residential buildings, and proecological requirements require the design of new building materials, the use of which will improve the thermal efficiency of newly built and renovated buildings. Therefore, many companies producing building materials strive to improve the properties of their products by reducing the weight of the materials, increasing their mechanical properties, and improving their insulating properties. Currently, there are solutions in phase-change materials (PCM) production technology, such as microencapsulation, but its application on a large scale is extremely costly. This paper presents a solution to the abovementioned problem through the creation and testing of a composite, i.e., a new mixture of gypsum, paraffin, and polymer, which can be used in the production of plasterboard. The presented solution uses a material (PCM) which improves the thermal properties of the composite by taking advantage of the phase-change phenomenon. The study analyzes the influence of polymer content in the total mass of a composite in relation to its thermal conductivity, volumetric heat capacity, and diffusivity. Based on the results contained in this article, the best solution appears to be a mixture with 0.1% polymer content. It is definitely visible in the tests which use drying, hardening time, and paraffin absorption. It differs slightly from the best result in the thermal conductivity test, while it is comparable in terms of volumetric heat capacity and differs slightly from the best result in the thermal diffusivity test.

scholarly journals Novel Dual Walling Cob Building: Dynamic Thermal Performance

Energies ◽  
2021 ◽  
Vol 14 (22) ◽  
pp. 7663
Author(s):  
Kaoutar Zeghari ◽  
Ayoub Gounni ◽  
Hasna Louahlia ◽  
Michael Marion ◽  
Mohamed Boutouil ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Properties ◽  
Water Content ◽  
Wheat Straw ◽  
Numerical Study ◽  
Energy Performance ◽  
Climatic Conditions ◽  
Structural Walls ◽  
Hemp Shiv

This paper emphasizes the experimental and numerical study of new cob mixes used for insulation and load bearing wall elements. The experimental study provides complete datasets of thermal properties of the new walling materials, using cob with density ranging from 1107 kg/m3 to 1583 kg/m3 for structural walls and less than 700 kg m−3 for insulation walls. Various mixes of French soils and fibres (reed, wheat straw, hemp shiv, hemp straw, and flax straw) with different water contents are studied. The lowest average thermal conductivity is obtained for the structural cob mix prepared of 5% wheat straw and 31% of water content. The insulation mix, prepared with 25% reed and 31% water content, has the lowest thermal conductivity. Investigation of diffusivity, density, and heat capacity shows that, when thermal conductivity is lower than 0.4 W m−1 K−1, the decrease in cob density leads to better insulation values and higher heat capacity. Little variation is noticed regarding the density and heat capacity for cob mixes with thermal conductivity higher than 0.4 W m−1 K−1. Furthermore, the non-uniformity of local thermal conductivity and heat losses through the samples is due mainly to the non-uniform distribution of fibres inside the mixes inducing an increase in heat loss up to 50% for structural walls and 25% for insulation walls. Cob thermal properties are used in a comparative simulation case study of a typical house under French and UK climatic conditions. The energy performance of the conventional building is compared to a dual walled cob building, showing remarkable reduction in energy consumption as the cob walls, whilst maintaining comfortable indoor conditions without additional heating.

scholarly journals Identification of thermophysical characteristics of materials using heating probe

2016 ◽  
Vol 5 (1) ◽  
pp. 25 ◽  
Author(s):  
Abdelaziz Nasr ◽  
Abdulmajeed S. Al-Ghamdi ◽  
Mohammad S. Alsoufi
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Inverse Problem ◽  
Heat Capacity ◽  
Heat Transfer Coefficient ◽  
Cylindrical Sample ◽  
Heat Power ◽  
Volumetric Heat Capacity ◽  
Thermophysical Characteristics ◽  
The Heat Transfer Coefficient

This paper investigates the numerical analysis to determine the thermo-physical characteristics of materials. This method is based on a heating probe kept at a constant temperature and maintained in contact with a cylindrical sample. The heat power dissipated in the sample is measured by the probe. The results address to identify simultaneously the thermal conductivity, the volumetric heat capacity and the heat transfer coefficient using the inverse problem.

Exact Solution of Heat Conduction in a Two-Domain Parallelepiped With an Orthotropic Layer and Its Application to the Estimation of the Three-Dimensional Thermal Conductivity Tensor and Volumetric Heat Capacity of the Orthotropic Layer

2002 ◽  
Author(s):  
Cuauhtemoc Aviles-Ramos
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Exact Solution ◽  
Heat Capacity ◽  
Thermal Properties ◽  
Hybrid Algorithm ◽  
Three Dimensional ◽  
Volumetric Heat Capacity ◽  
Parameter Estimation Problem ◽  
Orthotropic Layer

The three-dimensional exact solution of heat conduction in a two-layer composite is found applying the method of separation of variables. One layer is orthotropic and the other layer is isotropic. This solution is used to calculate sensitivity coefficients with respect to the thermophysical properties of the orthotropic layer at fourteen thermocouple locations. Numerical experiments are carried out to solve a parameter estimation problem that involves the estimation of the thermal conductivities in the x-, y-, and z-directions, the volumetric heat capacity of the orthotropic layer, the effective thermal conductivity of the isotropic layer, and the heat flux input. The exact solution is used to generate temperature readings at fourteen thermocouple locations. First, the parameter estimation problem is solved using the exact temperatures and a hybrid algorithm to estimate the thermal properties and the heat flux. Second, random noise is added to the exact temperatures and the thermal properties and heat flux are estimated using the same hybrid algorithm. It is found that when using the exact temperatures, the minimized quadratic functional has a value of 2.4×10−16 (°C)2 and the estimated properties agree to the ninth decimal place with the “exact” properties.

scholarly journals Теплофизические свойства мультиферроиков Bi-=SUB=-1-x-=/SUB=-Tm-=SUB=-x-=/SUB=-FeO-=SUB=-3-=/SUB=-

2022 ◽  
Vol 64 (2) ◽  
pp. 305
Author(s):  
С.Н. Каллаев ◽  
А.Г. Бакмаев ◽  
З.М. Омаров ◽  
Л.А. Резниченко
Keyword(s):  
Heat Transfer ◽  
Phase Transition ◽  
Thermal Conductivity ◽  
Heat Capacity ◽  
Phase Transitions ◽  
Thermal Diffusivity ◽  
Mean Free Path ◽  
Antiferromagnetic Phase ◽  
Temperature Dependences ◽  
Additional Anomaly

Investigations of the heat capacity, thermal diffusivity, and thermal conductivity of multiferroics Bi1-xTmxFeO3 (x = 0, 0.05, 0.10, 0.20) have been carried out in the high temperature range of 300-1200 K. and thermal conductivity in the region of phase transitions. The temperature dependences of the specific heat for compositions with x = 0.10 and 0.20 exhibit an additional anomaly characteristic of the phase transition at T = 580 K. The dominant mechanisms of phonon heat transfer in the region of ferroelectric and antiferromagnetic phase transitions are considered. The temperature dependence of the average phonon mean free path is determined.

New borehole heat exchanger thermal enhanced grout formulations

2021 ◽  
Author(s):  
Eloisa Di Sipio ◽  
Enrico Garbin ◽  
Laura Fedele ◽  
Davide Menegazzo ◽  
Ludovico Mascarin ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Properties ◽  
Heat Exchange ◽  
Specific Heat ◽  
Specific Heat Capacity ◽  
Operation Mode ◽  
Silica Sand ◽  
Geothermal Systems

<p>In shallow geothermal systems, especially ground source heat pumps (GSHP), cementitious grouts play a decisive role in guaranteeing an efficient heat transfer between the probe and the surrounding ground. Several studies have been devoted to understand the effect of different additives (silica sand, graphite, fluorspar, glass and fly ash …) in improving especially the thermal conductivity of such mixtures, maintaining at the same time physical properties as viscosity and workability suitable for in situ application. In fact, when continuous operation mode is running, thermal conductivity shows a positive effect on the mean heat exchange rate of vertical borehole heat exchangers (BHE). However, when an intermittent operation mode is selected, the BHE performance improves when a high thermal conductivity is coupled with a high specific heat capacity.</p><p>This research focus on assessing the contribution of two specific thermal additives (silica sand and molybdenum disulphide powder) to the thermal properties’ improvements of a specific commercial cementitious grout. These components are added in different proportion to the grout, up to the creation of 6 different mixtures. For each mixture 3 specimens are prepared, in order to perform the thermo-physical analyses. In addition, other 3 commercial grouts are considered. A total of 10 mixtures, leading to the creation of 30 specimens, have been analyzed. Then, thermal conductivity, thermal diffusivity and specific heat capacity of each specimen measured in anhydrous and saturated conditions are considered.</p><p>The commercial grouts prepared as stated by the producers show, as expected, a minimum variation of their thermal properties in wet and anhydrous conditions. Instead, when the additives are used, a noticeable improvement of the thermal properties is observed in saturated conditions, where the effect of silica sand seems dominant. The best thermal properties improvement obtained by combining the two additives is also considered.</p><p>However, the grouts suitability to be easily managed on site must be considered because, even if the new mixtures show a general gain of the thermal properties, these can be difficult to apply going from laboratory to full scale.</p><p>Anyway, the characterization of the grouts thermal properties based on composition and saturation variations is important not only in numerical simulations, but also in analytical approaches, typical of the heat exchange probe fields sizing processes. In fact, the cementitious grouts play a key role in determining the shallow geothermal systems efficiency in transient mode operation, often neglected by sizing programs. In fact, those characterized by better thermal performances will contribute to the reduction of the borehole thermal resistances, interposed in the heat exchange processes between the heat transfer fluid and the ground. Finally, this research contributes to fill the gap between numerical simulation and experimental data, providing real data to be used as database for further numerical modelling analysis improvement.</p><p> </p><p>GEO4CIVHIC project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No. 792355.</p>

Comparison of single and dual probes for measuring soil thermal properties with transient heating

Soil Research ◽  
1994 ◽  
Vol 32 (3) ◽  
pp. 447 ◽  
Author(s):  
KL Bristow ◽  
RD White ◽  
GJ Kluitenberg
Keyword(s):  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Properties ◽  
Thermal Diffusivity ◽  
Heat Pulse ◽  
Volumetric Heat Capacity ◽  
Transient Heating ◽  
Single Probe ◽  
Soil Thermal Properties ◽  
Dual Probe

Storage and transfer of heat in soils is governed by the soil thermal properties and these properties are therefore needed in many agricultural and engineering applications. In this paper we discuss solutions of the heat flow equation applicable to single and dual probe transient heating methods, and describe measurements made on air-dry sand to show how these methods can be used to obtain soil thermal properties. Measurements show that the two methods yield similar values of thermal conductivity. When determining thermal conductivity from the single probe data, it is best to use nonlinear curve fitting and to include a correction term in the model to account for the presence of the probe. Measurements of volumetric heat capacity made by using the dual probe heat-pulse method agreed well with independent estimates obtained using the de Vries method of summing the heat capacities of the soil constituents. The advantage of using the dual probe method together with the appropriate heat-pulse theory rather than the single probe is that all three soil thermal properties, the thermal diffusivity, volumetric heat capacity, and thermal conductivity, can be determined from a single heat-pulse measurement. Instantaneous heat-pulse theory can be used with the dual probe method to determine heat capacity from short duration heat-pulse data, but it should not be used to determine the thermal diffusivity and thermal conductivity.

scholarly journals Transient method measured thermal properties of concrete with microspheres and latex based addition

2018 ◽  
Vol 196 ◽  
pp. 04037
Author(s):  
Roman Jaskulski ◽  
Wojciech Kubissa
Keyword(s):  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Properties ◽  
Fly Ash ◽  
Thermal Diffusivity ◽  
Thermal Conductivity Coefficient ◽  
Transient Method ◽  
Volumetric Heat Capacity

The goal of the performed research was to determine the influence of microspheres from fly ash and the latex based addition on the thermal properties of concrete. The tested additions were used in two different proportions each and they were combined with each other. As a reference two series of concrete were used: one without any addition and another with 0.2% of air entraining agent. The thermal properties were measured using transient method with ISOMET 2114 apparatus. No clear trends were observed in case of the results of the measurements of the thermal diffusivity and the volumetric heat capacity. While the results of the thermal conductivity coefficient show that both additions has a potential of lowering the thermal conductivity but they are not so efficient as air entraining agent.

Thermal conductivity, thermal diffusivity, and volumetric heat capacity of silicone elastomer nanocomposites

2017 ◽  
Vol 30 (3) ◽  
pp. 365-374 ◽  
Author(s):  
Govind Sahu ◽  
VK Gaba ◽  
S Panda ◽  
B Acharya ◽  
SP Mahapatra
Keyword(s):  
Electron Microscopy ◽  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Properties ◽  
Thermal Diffusivity ◽  
Temperature Response ◽  
Silicone Elastomer ◽  
Positive Temperature ◽  
Volumetric Heat Capacity ◽  
Multiwalled Carbon

Silicone elastomer (SiR) nanocomposites were prepared using multiwalled carbon nanotubes (MWCNT) and nano-graphite (NG). The morphology of the SiR nanocomposites has been studied using scanning electron microscopy and high-resolution transmission electron microscopy techniques. Detailed analysis of the morphology reveals a uniform distribution of the MWCNT and NG filler particles in the silicone matrix. On increasing the filler loading, a continuous network structure is formed and aggregation takes place. The effect of the MWCNT and NG loadings on the thermal properties of the silicone elastomer has been investigated. The thermal properties of the SiR nanocomposites were measured by a thermal properties analyzer based on the transient hot-wire method. Studies also suggest that incorporation of nanoparticles improves the thermal conductivity of SiR nanocomposites. The thermal conductivity of SiR nanocomposites increased from 0.200 W/(m K) to 0.440 W/(m K) and to 0.310 W/(m K) for 6 wt% MWCNT and NG loadings, respectively. Because of the positive temperature coefficient and the conductive nature of the nanoparticles, the thermal conductivity of the material increased on increasing the temperature. The thermal diffusivity and the volumetric heat capacity of the SiR nanocomposites were measured. The thermal diffusivity of the SiR nanocomposites increased from 0.1194 mm2/s to 0.3209 mm2/s and to 0.2050 mm2/s for 6 wt% MWCNT and NG loadings, respectively. This indicates that the temperature response becomes faster with MWCNT and NG loadings. The volumetric heat capacity of the silicone elastomer nanocomposites decreased from 1.80 MJ/(m3K) to 1.34 MJ/(m3K) and to 1.40 MJ/(m3K) for 6 wt% MWCNT and NG loadings, respectively. Thus, MWCNT particles are more effective in increasing the thermal conductivity and diffusivity of the SiR nanocomposites, when compared to NG fillers at any loading.

scholarly journals Thermal properties of representative soils of the Czech Republic

2013 ◽  
Vol 8 (No. 4) ◽  
pp. 141-150 ◽  
Author(s):  
R. Kodešová ◽  
M. Vlasáková ◽  
M. Fér ◽  
D. Teplá ◽  
O. Jakšík ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Properties ◽  
Czech Republic ◽  
Water Content ◽  
Soil Water Content ◽  
Linear Equations ◽  
Volumetric Soil Water Content ◽  
The Czech Republic ◽  
Volumetric Soil Water

Knowledge of soil thermal properties is essential when assessing heat transport in soils. Thermal regime of soils is associated with many other soil processes (water evaporation and diffusion, plant transpiration, contaminants behaviour etc.). Knowledge of thermal properties is needed when assessing effectivity of energy gathering from soil profiles using horizontal ground heat exchangers, which is a topic of our research project. The study is focused on measuring of thermal properties (thermal conductivity and heat capacity) of representative soils of the Czech Republic. Measurements were performed on soil samples taken from the surface horizons of 13 representative soil types and from 4 soil substrates, and on mulch (bark chips) sample using KD2 PRO device with TR-1 and SH-1 sensors. The measured relationships between the thermal conductivity and volumetric soil-water content were described by the non-linear equations and those between the volumetric heat capacity and volumetric soil-water content were expressed using the linear equations. The highest thermal conductivities were measured in soils on quartz sand substrates. The lowest thermal conductivities were measured in the Stagnic Chernozem Siltic on marlite and the Dystric Cambisol on orthogneiss. The opposite trend was observed for maximal heat capacities, i.e. the highest values were measured in the Stagnic Chernozem Siltic and the lowest in sand and soils on sand and sandy gravel substrate.

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