scholarly journals Effects of temperature, test duration and heat flux in thermal conductivity measurements under transient conditions in dry and fully saturated states

2020 ◽  
Vol 195 ◽  
pp. 04007
Author(s):  
K. Aljundi ◽  
A. Vieira ◽  
J. Maranha ◽  
J. Lapa ◽  
R. Cardoso

In shallow geothermal energy systems (SGES) thermal conduction can be considered the dominant process in the heat transfer between the primary circuit (borehole heat exchanger or thermoactive geostructure) and the surrounding ground. Thus, a proper characterization of soil thermal properties, namely of its thermal conductivity, is mandatory for evaluating this energy exchange. There are difficulties associated to the assessment of soil thermal conductivity by laboratory methods related, among other factors, to the samples’ quality and to the measuring method itself. The purpose of this work is to analyse the effect of changing test control parameters in thermal conductivity measurements in transient conditions by means of a high accuracy thermal probe in both dry and fully saturated states. In order to eliminate potential measurements’ deviations and errors due to sample variability the same reconstituted samples were used several times. In each condition the sand samples were systematically tested under different ambient temperatures (10ºC, 20ºC, and 40ºC) controlled by means of a climatic chamber. The effects of changing the tests heating time and imposed thermal fluxes were also analysed.

1970 ◽  
Vol 7 (3) ◽  
pp. 982-987 ◽  
Author(s):  
E. Penner

Thermal conductivity measurements of two frozen soils, Leda clay and Sudbury silty clay, taken at temperatures between 0 and −22 °C by means of a thermal probe and a transient heat flow technique, compare favorably with estimates of thermal conductivity calculated by the DeVries method. Both measured and estimated values show a similar trend of increasing thermal conductivity as the temperature is lowered and the ice content grows. This increase is associated with the higher thermal conductivity of ice compared with that of water.


2013 ◽  
Vol 7 (1) ◽  
pp. 217-227 ◽  
Author(s):  
F. Riche ◽  
M. Schneebeli

Abstract. The thermal conductivity of snow determines the temperature gradient, and by this, it has a direct effect on the rate of snow metamorphism. It is therefore a key property of snow. However, thermal conductivities measured with the transient needle probe and the steady-state, heat flux plate differ. In addition, the anisotropy of thermal conductivity plays an important role in the accuracy of thermal conductivity measurements. In this study, we investigated three independent methods to measure snow thermal conductivity and its anisotropy: a needle probe with a long heating time, a guarded heat flux plate, and direct numerical simulation at the microstructural level of the pore and ice structure. The three methods were applied to identical snow samples. We analyzed the consistency and the difference between these methods. As already shown in former studies, we observed a distinct difference between the anisotropy of thermal conductivity in small rounded grains and in depth hoar. Indeed, the anisotropy between vertical and horizontal thermal conductivity components ranges between 0.5–2. This can cause a difference in thermal conductivity measurements carried out with needle probes of up to –25 % to +25 % if the thermal conductivity is calculated only from a horizontally inserted needle probe. Based on our measurements and the comparison of the three methods studied here, the direct numerical simulation is the most reliable method, as the tensorial components of the thermal conductivity can be calculated and the corresponding microstructure is precisely known.


2010 ◽  
Vol 38 (3) ◽  
pp. 102636
Author(s):  
M. R. Mitchell ◽  
R. E. Link ◽  
B. Pilkington ◽  
S. Goodhew ◽  
P. deWilde

Author(s):  
Nizar Ahammed ◽  
Lazarus Godson Asirvatham ◽  
Joel Titus ◽  
Jefferson Raja Bose ◽  
Somchai Wongwises

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