Determination of the effective thermal conductivity of solid fuels by the laser flash method

Kosowska-Golachowska, Monika; Gajewski, W.; Musiał, Tomasz

doi:10.2478/aoter-2014-0018

Cited by 24 publications

(10 citation statements)

References 17 publications

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“…Our result is close to that range. The reported thermal conductivity data (see also Singer et al, Stanger et al, and Kosowska-Golachowska et al) for various types of coals are basically increasing with temperature. However, the rate of the temperature variation of the thermal conductivity is very small at temperatures up to 773 K, and rapid changes were observed above 873 K due to devolatilization, the combustion of char, and other structural changes.…”

Section: Resultsmentioning

confidence: 91%

“…Coal decomposition involves many coupled physical and chemical phenomena, and it is difficult to isolate one phenomenon in order to study it separately. The design of solid fuel combustion to enhance the efficiency of coal combustion and conversion processes to protect the environment, using new technology of coal gasification and liquefaction and coal-related processes, required knowledge of the thermophysical characteristics of solid fuels as a function of temperature. − On the basis of thermophysical property data, the study of the expansion of the burned-out areas, thermal conduction, and temperature field distribution of the surrounding rocks in the process of underground coal gasification is possible …”

Section: Introductionmentioning

confidence: 99%

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Temperature Effect on the Thermal Conductivity of Black Coal

2018

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The guarded parallel-plate technique was employed on a black coal sample for an accurate measurement of the thermal conductivity over the temperature range from 298 to 496 K. The combined expanded uncertainties of the temperature (T) and thermal-conductivity (λ) measurements at the 95% confidence level with a coverage factor of k = 2 are estimated to be 20 mK and 5%, respectively. It was experimentally observed that the measured thermal conductivity (λ) of the wet and dry coal samples increases with temperature passes through a maximum around 390 K, and then it decreases gradually at higher temperatures. We attribute this maximum to the evolution of the volatile matter (VM) (devolatilazation) and aromatization of the carbon (pyrolysis), which is known to occur under heat treatment, and therefore, tends to increase the thermal conductivity. Over the experimental temperature range, the measured thermal-conductivity varied from 0.341 to 0.497 W·m–1·K–1 for wet coal samples before thermal treatment and from 0.272 to 0.316 W·m–1·K–1 for dry samples after thermal treatment. A considerable difference in thermal conductivity behavior was observed for the primary (originally nonthermally treated) and the second (thermally treated) repeated run. No temperature maximum or minimum (regular behavior) was observed in the thermal conductivity behavior for the thermally treated coal sample. The observed temperature behavior of the black coal’s thermal conductivity (λ) is a result of the complexity of the temperature behaviors of a, C P, and ρ, i.e., is the superposition of various temperature behaviors of a, C P, and ρ, and it reflects the temperature behavior of the heat capacity. This means that the temperature behavior of C P dominates the thermal diffusivity in λ = ρaC P. This means that the temperature behavior of λ and C P is strongly correlated.

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Section: Resultsmentioning

confidence: 91%

Section: Introductionmentioning

confidence: 99%

Temperature Effect on the Thermal Conductivity of Black Coal

2018

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“…We compare numerically the three models for the effective thermal conductivity due to radiation within the gas voids. We choose parameter values corresponding to those used in [39], in order to calibrate our model to obtain physically meaningful results. We apply the models obtained in earlier sections to a solid matrix made of anthracite with gas pores inside.…”

Section: Resultsmentioning

confidence: 99%

“…In general, due to the high-temperature regime required in many industries, it is very difficult to conduct experiments, which supports the need for good models for predicting the effective thermal conductivity of composite materials. Some experimental methods for determining this can be seen in [39], while a review of experimental methods for characterising thermal contact resistance is given in [40]. Loeb [41] obtained a variety of formulae for thermal conductivity of porous media, which involve the conductivity of the solid material, the emissivity of the surface of the pores, and the size, shape, and distribution of the pores.…”

Section: Introductionmentioning

confidence: 99%

Maxwell-type models for the effective thermal conductivity of a porous material with radiative transfer in the voids

Kiradjiev

Halvorsen

Gorder

et al. 2019

International Journal of Thermal Sciences

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There are several models for the effective thermal conductivity of two-phase composite materials in terms of the conductivity of the solid and the disperse material. In this paper, we generalise three models of Maxwell type (namely, the classical Maxwell model and two generalisations of it obtained from effective medium theory and differential effective medium theory) so that the resulting effective thermal conductivity accounts for radiative heat transfer within gas voids. In the high-temperature regime, radiative transfer within voids strongly influences the thermal conductivity of the bulk material. Indeed, the utility of these models over classical Maxwell-type models is seen in the high-temperature regime, where they predict that the effective thermal conductivity of the composite material levels off to a constant value (as a function of temperature) at very high temperatures, provided that the material is not too porous, in agreement with experiments. This behaviour is in contrast to models which neglect radiative transfer within the pores, or lumped parameter models, as such models do not resolve the radiative transfer independently from other physical phenomena. Our results may be of particular use for industrial and scientific applications involving heat transfer within porous composite materials taking place in the high-temperature regime.Common models for calculating the effective thermal conductivity of a solid composite material include the Maxwell model (based on the pioneering work of Maxwell [3], where an expression for the effective thermal conductivity was derived via far-field perturbations to solutions of the steady heat equation), as well as variants thereof, including the effective medium theory (EMT) model and the differential effective medium theory (DEMT) model. EMT uses a similar approach to that used in deriving the Maxwell model, and can be applied to many other physical properties (see [4], for instance, for the electrical resistance problem). In [5,6], there is a comparison between the Maxwell model and EMT, and those works outline how certain bounds on the thermal conductivities can be obtained. The multipole expansion method [7] gives similar results. In applying the DEMT, one incrementally adds one of the materials to the composite, and considers the effect of an infinitesimal change in the composite material composition on the effective thermal conductivity, obtaining a differential equation for the effective thermal conductivity in terms of the volume fraction of inclusions; see [8,9]. Reviews of many current models and methodologies, including those outlined above, can be found in [10,11,12].Recent work has involved the application of Maxwell-like models to the study of composite materials [13], including polymer composites [14,15]. Such models have recently proven useful in understanding nanoflake thermal annealing [16], and in the understanding of effective thermal conductivity in a variety of materials, such as for a wood cell modelled as a constituent element of briquette c...

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“…It involves the inclusion of the constitutive relationship that describes the temperature or pressure dependent material parameter and key processes. Specifically, the heat capacity and thermal conductivity of various rocks are introduced as temperature-dependent constitutive relationships (Kosowska-Golachowska et al, 2014;Otto and Kempka, 2015;Tang et al, 2015;Zagorščak et al, 2019). Furthermore, geochemical reactions are considered via the equilibrium/kinetic adsorption/desorption module in COMPASS (Hosking et al, 2018).…”

Section: The Developed Numerical Methods and Code Introductionmentioning

confidence: 99%