Determining permafrost active layer thermal properties of the Qinghai–Tibet Plateau using field observations and numerical modelling

2021 ◽  
Author(s):  
Jelte de Bruin ◽  
Victor Bense ◽  
Martine van der Ploeg
Keyword(s):  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Properties ◽  
Numerical Modelling ◽  
Active Layer ◽  
Optimal Parameter ◽  
Tibet Plateau ◽  
Active Layer Thickness ◽  
Geophysical Research ◽  
Field Samples

<p>Permafrost has become thermally instable as a result of surface warming, which has an uncertain impact on future hydrogeological conditions and the associated mobilisation of carbon and release into the atmosphere. Numerical modelling can provide insights into future permafrost spatial and temporal dynamics. However, crucial observational data of permafrost active-layer thermal properties; thermal conductivity and heat capacity are sparse, resulting in a large uncertainty in forecasts of the future development of the active layer. Therefore, our study aims to develop a methodology to numerically determine the permafrost thermal and soil properties from observations of temperature time-series in the subsurface, in order to reduce the current model uncertainty.</p><p>We used an ensemble of 786 numerical 1D permafrost models fitted against observed active layer temperature data from the Qinghai-Tibetan Plateau (QTP)<sup>1</sup> to find the optimal values for the soil thermal conductivity, heat capacity and porosity. Optimal parameter values are determined by finding the minimum RMSE, KGE and using the Russell error measure. We find optimized values for bulk volumetric heat capacity 1.3-1.85 10<sup>6</sup><em>J/m<sup>3</sup></em><em>°C</em> , bulk thermal conductivity 0.9-1.1 <em>W/m</em><em>°C</em> and porosity between 0.25-0.35 (-), which are in agreement with typical ranges reported in literature for similar settings on the QTP. In a further sensitivity study, the 3 optimal parameter combinations were used to model the active layer thickness over a 100-year period with a gradual hypothetical air temperature increase of 5<em>°C</em>. The results indicate a substantial difference in rate of thawing and increase in depth of the active layer for these models, with a maximum time-lag of roughly 15 years in before the models reach the same active layer thawing depth. The study shows how numerical models can be applied to determine active layer thermal properties without the need for field samples, opening up new possibility for in-situ permafrost temperature observation.</p><p>1. Luo, D. L., Jin, H. J., He, R. X., Wang, X. F., Muskett, R. R., Marchenko, S. S., & Romanovsky, V. E. (2018). Characteristics of water-heat exchanges and inconsistent surface temperature changes at an elevational permafrost site on the Qinghai-Tibet Plateau. <em>Journal of Geophysical Research: Atmospheres</em>, 123, 10,057–10,075. https://doi.org/10.1029/2018JD028298</p>

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.

Determination of the Thermal Properties of a PCB by Coupled Numerical and Experimental Approach

2020 ◽  
Author(s):  
Yener Usul ◽  
Mustafa Özçatalbaş
Keyword(s):  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Properties ◽  
Numerical Analysis ◽  
Specific Heat ◽  
Specific Heat Capacity ◽  
Thermal Analyses ◽  
Analysis Model ◽  
Linear Temperature ◽  
Coefficient Of Thermal Conductivity

Abstract Increasing demand for usage of electronics intensely in narrow enclosures necessitates accurate thermal analyses to be performed. Conduction based FEM (Finite Element Method) is a common and practical way to examine the thermal behavior of an electronic system. First step to perform a numerical analysis for any system is to set up the correct analysis model. In this paper, a method for obtaining the coefficient of thermal conductivity and specific heat capacity of a PCB which has generally a complex composite layup structure composed of conductive layers, and dielectric layers. In the study, above mentioned properties are obtained performing a simple nondestructive experiment and a numerical analysis. In the method, a small portion of PCB is sandwiched from one side at certain pressure by jaws. A couple of linear temperature profiles are applied to the jaws successively. Unknown values are tuned in the analysis model until the results of FEM analysis and experiment match. The values for the coefficient of thermal conductivity and specific heat capacity which the experiment and numerical analysis results match can be said to be the actual values. From this point on, the PCB whose thermal properties are determined can be analyzed numerically for any desired geometry and boundary condition.

scholarly journals Mechanisms behind the enhancement of thermal properties of graphene nanofluids

Nanoscale ◽  
2018 ◽  
Vol 10 (32) ◽  
pp. 15402-15409 ◽  
Author(s):  
M. R. Rodríguez-Laguna ◽  
A. Castro-Alvarez ◽  
M. Sledzinska ◽  
J. Maire ◽  
F. Costanzo ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Properties ◽  
Specific Heat ◽  
Specific Heat Capacity

While the dispersion of nanomaterials is known to be effective in enhancing the thermal conductivity and specific heat capacity of fluids, the mechanisms behind this enhancement remain to be elucidated.

Influence of Mesocarp Fibre Inclusion on Thermal Properties of Foamed Concrete

2021 ◽  
Vol 87 (1) ◽  
pp. 1-11
Author(s):  
Siti Shahirah Suhaili ◽  
Md Azree Othuman Mydin ◽  
Hanizam Awang
Keyword(s):  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Properties ◽  
Thermal Diffusivity ◽  
Specific Heat ◽  
Specific Heat Capacity ◽  
Volume Fraction ◽  
Thermal Constant ◽  
Volume Fractions ◽  
Foamed Concrete

The addition of mesocarp fibre as a bio-composite material in foamed concrete can be well used in building components to provide energy efficiency in the buildings if the fibre could also offer excellent thermal properties to the foamed concrete. It has practical significance as making it a suitable material for building that can reduce heat gain through the envelope into the building thus improved the internal thermal comfort. Hence, the aim of the present study is to investigate the influence of different volume fractions of mesocarp fibre on thermal properties of foamed concrete. The mesocarp fibre was prepared with 10, 20, 30, 40, 50 and 60% by volume fraction and then incorporated into the 600, 1200 and 1800 kg/m3 density of foamed concrete with constant cement-sand ratio of 1:1.5 and water-cement ratio of 0.45. Hot disk thermal constant analyser was used to attain the thermal conductivity, thermal diffusivity and specific heat capacity of foamed concrete of various volume fractions and densities. From the experimental results, it had shown that addition of mesocarp fibre of 10-40% by volume fraction resulting in low thermal conductivity and specific heat capacity and high the thermal diffusivity of foamed concrete with 600 and 1800 kg/m3 density compared to the control mix while the optimum amount of mesocarp fibre only limit up to 30% by volume fraction for 1200 kg/m3 density compared to control mix. The results demonstrated a very high correlation between thermal conductivity, thermal diffusivity and specific heat capacity which R2 value more than 90%.

A COMPREHENSIVE TISSUE PROPERTIES DATABASE PROVIDED FOR THE THERMAL ASSESSMENT OF A HUMAN AT REST

2010 ◽  
Vol 05 (03) ◽  
pp. 129-151 ◽  
Author(s):  
ROBERT L. MCINTOSH ◽  
VITAS ANDERSON
Keyword(s):  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Properties ◽  
Thermal Modeling ◽  
Blood Perfusion ◽  
Human Tissues ◽  
Tissue Properties ◽  
Future Studies ◽  
Average Value ◽  
Metabolic Heat

Accurate numerical calculation of the thermal profile in humans requires reliable estimates of the following five tissue properties: specific heat capacity (c), thermal conductivity (k), blood perfusion rates (m), metabolic heat production (A0), and density (ρ). A sixth property, water content (w, as a %), can also be used to estimate c and k. To date, researchers have used various and inconsistent estimates of these parameters, which hinders comparison of the corresponding results. In an effort to standardize and improve the accuracy of these parameters for future studies, we have documented over 150 key papers and books and developed a database of the six thermal properties listed above for 43 human tissues. For each tissue and each property the following were obtained: the average value, the number of source values, the minimum and maximum of source values, and the reference for each source value. A key premise for the development of the database was to only use references that provided the original measurements. This database is offered for use by the biological thermal modeling community to help improve the accuracy and consistency of thermal modeling results.

Permafrost and active layer research on James Ross Island: An overview

2019 ◽  
Vol 9 (1) ◽  
pp. 20-36 ◽  
Author(s):  
Filip Hrbáček ◽  
Daniel Nývlt ◽  
Kamil Láska ◽  
Michaela Kňažková ◽  
Barbora Kampová ◽  
...  
Keyword(s):  
Thermal Conductivity ◽  
Layer Thickness ◽  
Active Layer ◽  
Air Temperature ◽  
Thermal Regime ◽  
Ground Temperature ◽  
Active Layer Thickness ◽  
Near Surface ◽  
James Ross Island ◽  
The Mean

This study summarizes the current state of the active layer and permafrost research on James Ross Island. The analysis of climate parameters covers the reference period 2011–2017. The mean annual air temperature at the AWS-JGM site was -6.9°C (ranged from -3.9°C to -8.2°C). The mean annual ground temperature at the depth of 5 cm was -5.5°C (ranged from -3.3°C to -6.7°C) and it also reached -5.6°C (ranged from -4.0 to -6.8°C) at the depth of 50 cm. The mean daily ground temperature at the depth of 5 cm correlated moderately up to strongly with the air temperature depending on the season of the year. Analysis of the snow effect on the ground thermal regime confirmed a low insulating effect of snow cover when snow thickness reached up to 50 cm. A thicker snow accumulation, reaching at least 70 cm, can develop around the hyaloclastite breccia boulders where a well pronounced insulation effect on the near-surface ground thermal regime was observed. The effect of lithology on the ground physical properties and the active layer thickness was also investigated. Laboratory analysis of ground thermal properties showed variation in thermal conductivity (0.3 to 0.9 W m-1 K-1). The thickest active layer (89 cm) was observed on the Berry Hill slopes site, where the lowest thawing degree days index (321 to 382°C·day) and the highest value of thermal conductivity (0.9 W m-1 K-1) was observed. The clearest influence of lithological conditions on active layer thickness was observed on the CALM-S grid. The site comprises a sandy Holocene marine terrace and muddy sand of the Whisky Bay Formation. Surveying using a manual probe, ground penetrating radar, and an electromagnetic conductivity meter clearly showed the effect of the lithological boundary on local variability of the active layer thickness.

Thermal Properties of Selected Timbers

2014 ◽  
Vol 982 ◽  
pp. 100-103 ◽  
Author(s):  
Dana Koňáková ◽  
Monika Čáchová ◽  
Eva Vejmelková ◽  
Martin Keppert ◽  
Robert Černý
Keyword(s):  
Thermal Conductivity ◽  
Heat Capacity ◽  
Thermal Properties ◽  
Moisture Content ◽  
Specific Heat ◽  
Heat Transport ◽  
Specific Heat Capacity ◽  
Open Porosity ◽  
Building Structures ◽  
The Difference

This article deals with thermal properties of selected kinds of timber. Wood, generally, is one of often used natural materials in building structures. For our research, woods were selected according to frequency of utilization in civil engineering branch. Four different timbers were chosen, and experimental determinations of their properties were performed. Basic physical properties as well as thermal properties belong among studied characteristics. From achieved results, it is obvious, that the bulk density of studied wood ranges between 373 kg m-3 and 649 kg m-3, the open porosity differ by 13%. Regarding thermal properties, values of the thermal conductivity as well as the specific heat capacity are influenced mainly by the open porosity and moisture content. The thermal conductivity in dry state varies by about 31% while in the case of the specific heat capacity the difference is about 19%. Obtained date will be used in the mathematical analysis of heat transport in building structures.

scholarly journals Thermal and thermodynamic characterization of a dye powder from liquid turmeric extracts by spray drying

2016 ◽  
Vol 69 (1) ◽  
pp. 7845-7854 ◽  
Author(s):  
Aura Yazmin Coronel Delgado ◽  
Héctor José Ciro Velásquez ◽  
Diego Alonso Restrepo Molina
Keyword(s):  
Thermal Conductivity ◽  
Heat Capacity ◽  
Glass Transition ◽  
Thermal Properties ◽  
Transition Temperature ◽  
Glass Transition Temperature ◽  
Mass Loss ◽  
Spray Drying ◽  
Transient Flow ◽  
Sorption Isotherms

This study aimed to evaluate the thermodynamic properties of sorption isotherms and glass transition temperature (Tg) and the thermal properties of a dye powder obtained from turmeric extracts using spray drying. The sorption isotherms were evaluated at 15, 25 and 35 °C using the dynamic gravimetric method, wherein the isotherm data of the experiment were fit to GAB and BET models. Likewise, the Tg was measured using differential scanning calorimetry (DSC). Thermogravimetric analysis (TGA) was used to determine the mass loss, and the thermal properties (heat capacity, diffusivity and thermal conductivity) were determined using transient flow method. The results demonstrated that the GAB model best fit the adsorption data. The DSC analysis presented a glass transition temperature of 65.35 °C and a loss of volatiles at 178.07 °C. The TGA analysis indicated a considerable mass loss starting at 193 °C, resulting in degradation of the product. The thermal properties demonstrated a heat capacity of 2.45 J/g °C, a thermal conductivity of 0.164 ± 0.001 W/mK and a thermal diffusivity of 8.7x10-8 ± 0.000 m2/s.

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