An assessment of the subsurface thermal diffusion regime at some sites in the Sierra de Guadarrama 

2021 ◽  
Author(s):  
Félix García Pereira ◽  
Jesús Fidel González Rouco ◽  
Camilo Melo Aguilar ◽  
Thomas Schmid ◽  
Cristina Vegas Cañas ◽  
...  
Keyword(s):  
Heat Conduction ◽  
Thermal Diffusivity ◽  
Thermal Structure ◽  
Ground Surface ◽  
Monitoring Network ◽  
Conduction Model ◽  
Negative Exponential Function ◽  
Mean Values ◽  
One Dimensional ◽  
Negative Exponential

<div> <div> <div> <p>An analysis of the subsurface thermal structure of Sierra de Guadarrama, in central Spain, is provided. The question addressed herein is how the temperature perturbations at the land-atmosphere interface propagate into the subsoil and change with depth. To respond, we analyse subsoil temperature data coming from four monitoring stations belonging to Guadarrama Monitoring Network (GuMNet; https://www.ucm.es/gumnet/), which cover a vertical slope ranging from 900 to 2200 m.a.s.l and a depth profile from ground surface down to 20 m. Time series span from 2015 to 2020, with some missing periods. Thermal diffusivity values are estimated from them under the assumption of heat downward propagation according to the one-dimensional heat conduction model solution, by considering the annual cycle attenuation and phase shift with depth. In addition, the aforementioned estimation is also accomplished from adjusting amplitude attenuation curves between temperature spectra at different depths to the theoretical spectral attenuation solution for one-dimensional heat conduction, which is a negative exponential function of frequency.</p> <p>Preliminary results show that thermal diffusivity increases with depth at every site. Major changes take place in the soil-bedrock transition, which is found between 5-8 m deep, depending on the site. Some material samples extracted show that bedrock consists mainly of gneiss at three sites, and granite at the other one. Mean values calculated through the whole profiles lie within 1-1.4 10<sup>-6</sup> m<sup>2</sup>/s, which are in the range of diffusivity coefficients of gneiss and granite.</p> </div> </div> </div>

scholarly journals Fractional Heat Conduction Models and Thermal Diffusivity Determination

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
Monika Žecová ◽  
Ján Terpák
Keyword(s):  
Heat Conduction ◽  
Thermal Diffusivity ◽  
Numerical Methods ◽  
Fractional Order ◽  
Experimental Verification ◽  
Heat Conduction Equation ◽  
Historical Overview ◽  
One Dimensional ◽  
The One ◽  
Fractional Heat Conduction

The contribution deals with the fractional heat conduction models and their use for determining thermal diffusivity. A brief historical overview of the authors who have dealt with the heat conduction equation is described in the introduction of the paper. The one-dimensional heat conduction models with using integer- and fractional-order derivatives are listed. Analytical and numerical methods of solution of the heat conduction models with using integer- and fractional-order derivatives are described. Individual methods have been implemented in MATLAB and the examples of simulations are listed. The proposal and experimental verification of the methods for determining thermal diffusivity using half-order derivative of temperature by time are listed at the conclusion of the paper.

Numerical Investigation of Heat Transfer Characteristics of Debris Bed After Severe Accident of SFR Based on 1-D Heat Conduction Model

2018 ◽  
Author(s):  
Mengwei Zhang ◽  
Bin Zhang ◽  
Jianqiang Shan
Keyword(s):  
Heat Transfer ◽  
Heat Conduction ◽  
Transfer Process ◽  
Severe Accident ◽  
Heat Transfer Characteristics ◽  
Conduction Model ◽  
One Dimensional ◽  
The Core ◽  
Transfer Characteristics ◽  
Core Catcher

Nuclear reactor severe accidents can lead to the release of a large amount of radioactive material and cause immense disaster to the environment. Since the Fukushima nuclear accident in Japan, the severe accident research has drawn worldwide attention. Based on the one-dimensional heat conduction model, a DEBRIS-HT program for analyzing the heat transfer characteristics of a debris bed after a severe accident of a sodium-cooled fast reactor was developed. The basic idea of the DEBRIS-HT program is to simplify the complex energy transfer process in the debris bed to a simple one-dimensional heat transfer problem by solving the equivalent thermal conductivity in different situations. In this paper, the DEBRIS-HT program code is prepared by using the existing model and compared with the experimental results. The results show that the DEBRIS-HT program can correctly predict the heat transfer process in the fragment bed. In addition, the heat transfer characteristics analysis program is also used to model the core catcher of the China fast reactor. Firstly, the dryout heat flux when all of molten core dropped on the core catcher was calculated, which was compared with the result of Lipinski’s zero dimensional model, and the error between two values is only 11.2%. Then, the temperature distribution was calculated with the heat power of 15MW.

Modified Laser Flash Method for Thermal Property Measurements and the Influence of Heat Convection

2003 ◽  
Author(s):  
Bochuan Lin ◽  
Shen Zhu ◽  
Heng Ban ◽  
Chao Li ◽  
Rosalia N. Scripa ◽  
...  
Keyword(s):  
Heat Conduction ◽  
Natural Convection ◽  
Thermal Diffusivity ◽  
Laser Pulse ◽  
Rear Surface ◽  
Front Surface ◽  
Laser Flash ◽  
Laser Flash Method ◽  
Flash Method ◽  
Conduction Model

This study examined the effect of natural convection in the modified laser flash method for the measurement of thermo physical properties of semiconductor melts. Common laser flash method uses a laser pulse to heat the front surface of a thin circular sample and measures the temperature transient of the rear surface. Thermal diffusivity is calculated based on the analysis of the transient heat conduction process. For semiconductor melts, the sample is contained in a specially designed quartz cell with optical windows. When the laser pulse heats the melt front surface, the resulting natural convection can introduce errors in the calculation of thermal diffusivity based on the heat conduction model. The effect of natural convection was evaluated by Computational Fluid Dynamics (CFD) simulations in this study. The results indicated that natural convection can decrease the time needed for the rear surface to reach its peak temperature, and can also decrease the peak temperature slightly. Based on our experimental data for Tellurium, the calculation using only heat conduction model resulted in a thermal diffusivity about 3% greater than that using the heat transfer model with natural convection.

Heat Conduction in a Thin Film which Reflects Size and Memory Effects Induced by an Ultra-Fast Laser

2015 ◽  
Vol 723 ◽  
pp. 873-877
Author(s):  
Yu Dong Mao ◽  
Ming Tian Xu
Keyword(s):  
Thin Film ◽  
Heat Conduction ◽  
Thermal Wave ◽  
Memory Effects ◽  
Wave Effect ◽  
Conduction Model ◽  
Wave Speeds ◽  
One Dimensional ◽  
Higher Temperature ◽  
Cv Model

An improved heat conduction model which reflects size and memory effects based on the CV model is proposed to simulate a one-dimensional thermal transport problem in a thin film induced by the ultra-fast laser. The results show that a thermal wave effect is appeared in heat conduction. We find that for the improved CV model in this work a larger Knudsen number will lead to a higher temperature. Although the improved CV model and the CV model lead to the similar thermal wave behavior, the thermal wave speeds for the two models are different.

Particle temperature distribution in a dust flame

2010 ◽  
Vol 224 (2) ◽  
pp. 363-367
Author(s):  
A S Shahrbabaki ◽  
M Dodangeh
Keyword(s):  
Particle Size ◽  
Heat Conduction ◽  
Temperature Profile ◽  
Particle Temperature ◽  
Transient Heat Conduction ◽  
Order Model ◽  
Conduction Model ◽  
One Dimensional ◽  
Dust Flame ◽  
Good Agreement

An unsteady one-dimensional heat conduction model is used to determine the particle temperature profile in suspension fuels by using a perturbation method. A second-order model is presented for transient heat conduction in a spherical particle. The radiation term is considered in the boundary conditions, which plays an important role in the dust flame. The effects of particle size and Biot number on the temperature profile are investigated. The results are in good agreement with the numerical solution.

scholarly journals Comparison of six algorithms to determine the soil thermal diffusivity at a site in the Loess Plateau of China

2009 ◽  
Vol 6 (2) ◽  
pp. 2247-2274 ◽  
Author(s):  
Z. Gao ◽  
L. Wang ◽  
R. Horton
Keyword(s):  
Heat Transfer ◽  
Heat Conduction ◽  
Thermal Diffusivity ◽  
Soil Temperature ◽  
Loess Plateau ◽  
One Dimensional ◽  
Boundary Temperature ◽  
Soil Thermal Diffusivity ◽  
Thermal Diffusivities ◽  
Upper Boundary

Abstract. Soil thermal diffusivity is a crucial physical parameter that affects soil temperature. Six prevalent algorithms to calculate soil thermal diffusivity are inter-compared by using soil temperature data collected at the depths of 0.05 m and 0.10 m at a bare site in the China Loess Plateau from DOY 201 through DOY 207 in 2005. Five of the six algorithms (i.e., Amplitude, Phase, Arctangent, Logarithm, and Harmonic or HM algorithms) are developed from the traditional one-dimensional heat conduction equation. The other algorithm is based on the one-dimensional heat conduction-convection equation which considers the vertical heterogeneity of thermal diffusivity in soil and couples thermal conduction and convection processes (hereinafter referred to as the Conduction-convection algorithm). To assess these six algorithms, we (1) calculate the soil thermal diffusivities by using each of the algorithms, (2) use the soil thermal diffusivities to predict soil temperature at the 0.10 m depth, and (3) compare the estimated soil temperature against direct measurements. Results show that (1) HM algorithm gives the most reliable estimates among the traditional five algorithms; and (2) generally, the Conduction-convection algorithm provides the second best estimates. Among all of the algorithms, the HM algorithm has the best description of the upper boundary temperature with time, but it only includes conduction heat transfer in the soil. Compared to the HM algorithm, the Conduction-convection algorithm has a less accurate description of the upper boundary temperature, but by accounting for the vertical gradient of soil diffusivity and the water flux density it includes more physics in the soil heat transfer process. The Conduction-convection algorithm has potential application within land surface models, but future effort should be made to combine the HM and Conduction-convection algorithms in order to make use of the advantages of each.

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