Heat Transfer in Unfrozen and Frozen Porous Media: Experimental Measurement and Pore‐Scale Modeling

Abstract

In this work, we conducted a mechanistic study on pore-scale mechanisms controlling heat transfer in partially saturated porous media at unfrozen and frozen conditions. Experimental measurement of effective thermal conductivity (ETC) of simulated partially saturated sediments was carried out to explore the effect of different parameters including pore and overburden pressures, temperature, and water/ice saturation on the pore-scale mechanisms governing heat transfer in multiphase porous media. The experimental measurements show that the heat transfer is a complex phenomenon affected by several important pore-scale mechanisms such as particle-particle conduction and particle-fluid-particle conduction, which are governed by water content and distribution, packing structure, wettability characteristics of grains, coordination number, and physical contact among sediment particle. A numerical model was also developed for prediction of ETC using free-energy lattice Boltzmann model and a space renormalization method. The model predictions were in good agreement with the experimental data, showing that the model is able to reliably estimate ETC with average relative deviations of less than 10%, as it appropriately incorporates the pore-scale mechanisms influencing ETC. The numerical model predictions were also compared with those of six predictive models available in the literature, and root-mean-square errors were calculated to assess its accuracy against the existing models.

Effect of thermal formation/dissociation cycles on the kinetics of formation and pore-scale distribution of methane hydrates in porous media: a magnetic resonance imaging study

“…It should also be noted that the porosity values of the sediment samples were assumed to be around 40-43%, according to our previous studies. 66,67 The procedure includes three steps. The rst step is to analyse the high-resolution image at the fully water-saturated state to obtain the spatial distribution of the grains as well as the pore space throughout the image in compliance with the porosity of the sample.…”

Insights into the climate-driven evolution of gas hydrate-bearing permafrost sediments: implications for prediction of environmental impacts and security of energy in cold regions

“…29 A detailed discussion regarding the test method can be found elsewhere. 29,37 The ETC measurements were carried out using a calibrated purpose-built needle probe (TP08, Hukseux, The Netherlands) which can accurately measure the thermal conductivity at elevated pressures in compliance with the ASTM D5334-14 standard. 37 The thermal conductivity data were recorded in a measurement and control unit connected to a PC.…”

“…47 It is observed that ETC decreases as the hydrate saturation increases at both unfrozen and frozen conditions. At unfrozen conditions, such behavior could be attributed to three main factors: (i) the intrinsic thermal conductivity of methane hydrates is slightly lower than that of water, 48,49 (ii) the heat transfer in the hydrate-gas interface is less efficient than in water-gas interface due to the fact that the mass transfer in a uid-uid interface may facilitate the energy transfer, 29 (iii) the sand particles could be rearranged by hydrates at higher saturations where the dominant pore-scale habit is load-bearing and the hydrate crystals could push apart the sediment grains, a phenomenon known as hydrateforced heave, which could result in enlarging the sediment pores and increasing TCR. 5 At frozen conditions, it is observed that ETC decreases when the hydrate saturation increases because less water is available to turn into ice at higher hydrate saturations.…”

“…In particular, we discussed how the effective thermal conductivity (ETC) is inuenced by the co-existence of ice, unfrozen water, and gas at frozen conditions. 29 It should be noted that the presence of different minerals (silt, clay, .) and their interaction with pore water inuence not only the physical properties of the host sediment, but also the pore-scale distribution of the co-existing phases in pore space, 40 particularly at frozen conditions, where the unfrozen water content occupying small pores critically contributes to the heat tranfer.…”

“…In particular, we discussed how the effective thermal conductivity (ETC) is influenced by the co-existence of ice, unfrozen water, and gas at frozen conditions. 29 It should be noted that the presence of different minerals (silt, clay, …) and their interaction with pore water influence not only the physical properties of the host sediment, but also the pore-scale distribution of the co-existing phases in pore space, 40 particularly at frozen conditions, where the unfrozen water content occupying small pores critically contributes to the heat tranfer. 29 The presence of hydrates adds further complexities, which is required to be well understood and accounted for in both lab- and field-scale studies; otherwise, the prediction of the thermal response of gas hydrate-bearing permafrost sediments would be erroneous.…”