Convective and conductive thermal homogenization for non-saturated porous building materials: Application on the thermal conductivity tensor

Porous materials possess a complex structure on a microscopic scale and present strong heterogeneities, which makes their precise study extremely complex. In fact, the macroscopic behavior of these materials is strongly dependent on mechanisms that act to the scale of their components. The present work focus on the development of a macroscopic conductive and convective fluid heat transfer model, with a heat source in the unsaturated porous materials. This model is established by periodic homogenization of energy conservation equations written on a microscopic scale in each phase (solid, liquid and gas). The resulting input parameters formulations of the submodel were explicitly identified. Numerical calculations of the homogenized thermal conductivity tensor are performed on a representative 3-D elementary cell of the porous medium. Finally, a sensitivity study of this tensor depending of the variation of the water content and porosity of the concerned elementary cell has been performed. This sensitivity is required to be considered in simulations to better understand the behavior of building materials and improve the prediction of energy performance.

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

Materials ◽

10.3390/ma14123241 ◽

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.

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Comparison of the thermal performance between conventional and cob building

E3S Web of Conferences ◽

10.1051/e3sconf/201911103003 ◽

2019 ◽

Vol 111 ◽

pp. 03003

Author(s):

Kaoutar Zeghari ◽

Hasna Louahlia ◽

Malo Leguern ◽

Mohamed Boutouil ◽

Hamid Gualous ◽

...

Keyword(s):

Thermal Conductivity ◽

Thermal Behaviour ◽

Calculation Method ◽

Building Materials ◽

Residential Building ◽

Local Heat ◽

Energy Performance ◽

Stationary Regime ◽

Thermal Regulation ◽

Climate Data

The appliance of sustainable development approach in building has urged construction industry to adopt proper measurements to protect environment and reduce residential building energy consumption and CO2 emissions. Thus, an increasing interest in alternative building materials has developed including the use of bio-based materials such as cob which is studied in this paper. In the previous work, many experimental and numerical studies have been carried out to characterize thermal behaviour of earth buildings, reduce its thermal conductivity and water content. In this paper, an experimental study is carried out to determine the thermal properties and energy performance of cob building. Cob samples within different soil and fiber contents are studied using an experimental set up instrumented with flux meters and micro-thermocouples in order to evaluate the local heat flux and thermal conductivity during stationary regime. The results are analysed and compared to deduce the performant mixes in terms of thermal behaviour while respecting the French thermal regulation. A static thermal simulation based on RT 2012 calculation method (the official French calculation method for the energy performance of new residential and commercial buildings according to France thermal regulation) is used to compare energy performance between conventional and cob building using the French climate data base .

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Thermal conductivity tensor of NbO2

International Journal of Heat and Mass Transfer ◽

10.1016/j.ijheatmasstransfer.2019.03.135 ◽

2019 ◽

Vol 137 ◽

pp. 263-267 ◽

Cited By ~ 2

Author(s):

Hai Jun Cho ◽

Gowoon Kim ◽

Takaki Onozato ◽

Hyoungjeen Jeen ◽

Hiromichi Ohta

Keyword(s):

Thermal Conductivity ◽

Conductivity Tensor ◽

Thermal Conductivity Tensor

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Determination of the thermal conductivity tensor of the n = 7 Aurivillius phase Sr4Bi4Ti7O24

Applied Physics Letters ◽

10.1063/1.4733616 ◽

2012 ◽

Vol 101 (2) ◽

pp. 021904 ◽

Cited By ~ 5

Author(s):

M. A. Zurbuchen ◽

D. G. Cahill ◽

J. Schubert ◽

Y. Jia ◽

D. G. Schlom

Keyword(s):

Thermal Conductivity ◽

Conductivity Tensor ◽

Aurivillius Phase ◽

Thermal Conductivity Tensor

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The Impact of Variable Thermal Conductivity of Insulation Materials on the Building Energy Performance in Hot Climate

E3S Web of Conferences ◽

10.1051/e3sconf/201910302001 ◽

2019 ◽

Vol 103 ◽

pp. 02001 ◽

Cited By ~ 3

Author(s):

Maatouk Khoukhi ◽

Ahmed Hassan ◽

Shaimaa Abdelbaqi

Keyword(s):

Thermal Conductivity ◽

Energy Performance ◽

Variable Thermal Conductivity ◽

Transfer Model ◽

Ambient Conditions ◽

K Value ◽

Hot Climate ◽

Building Wall ◽

Wall Assembly ◽

The Impact

This paper illustrates the impact of embedding an insulation layer of variable thermal conductivity in a typical building wall on the cooling effect and energy performance. The evaluation was performed by applying a conjugate heat transfer model, which was tested in extremely hot conditions of Al Ain (UAE). The thermal performance of a building incorporating insulation layers of variable thermal conductivity (k-value) was compared to a non-variable thermal conductivity system by quantifying the additional heat transferred due to the k-relationship with time. The results show that, when the k-value is a function of operating temperature, its effects on the temperature profile through the wall assembly during daytime is significant compared with that obtained when a constant k-value for the polystyrene (EPS) insulation is adopted. A similar trend in the evolution of temperatures during the day and across the wall section was observed when EPS material with different moisture content was evaluated. For the polyurethane insulation, the inner surface temperature reached 44 °C when constant k-value was adopted, increasing to 48.5 °C when the k-value was allowed to vary under the same ambient conditions.

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Numerical identification of the thermal conductivity tensor and the heat capacity per unit volume of an anisotropic material

Mechanics & Industry ◽

10.1051/meca/2019026 ◽

2019 ◽

Vol 20 (6) ◽

pp. 603

Author(s):

Kossi Atchonouglo ◽

Jean-Christophe Dupré ◽

Arnaud Germaneau ◽

Claude Vallée

Keyword(s):

Thermal Conductivity ◽

Finite Element Method ◽

Heat Capacity ◽

Unit Volume ◽

Time Integration ◽

Volume Measurement ◽

Conductivity Tensor ◽

Inverse Approach ◽

Thermal Conductivity Tensor ◽

Principal Axes

In this paper, an inverse approach based on gradient conjugate method for thermal conductivity tensor and heat capacity per unit volume measurement is summarized. A suitable analysis is done for the mesh in finite element method and for the time steps for the time integration. For a composite material, it is shown the importance to identify the thermal conductivity tensor components in the principal axes.

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