Gas transport in partially-saturated sand packs

Understanding gas transport in porous media and its mechanism has broad applications in various research areas, such as carbon sequestration in deep saline aquifers and gas explorations in reservoir rocks. Gas transport is mainly controlled by pore space geometrical and morphological characteristics. In this study, we apply a physically-based model developed using concepts from percolation theory (PT) and the effective-medium approximation (EMA) to better understand diffusion and permeability of gas in packings of angular and rounded sand grains as well as glass beads. Two average sizes of grain i.e., 0.3 and 0.5 mm were used to pack sands in a column of 6 cm height and 4.9 cm diameter so that the total porosity of all packs was near 0.4. Water content, gas-filled porosity (also known as gas content), gas diffusion, and gas permeability were measured at different capillary pressures. The X-ray computed tomography method and the 3DMA-Rock software package were applied to determine the average pore coordination number z. Results showed that both saturation-dependent diffusion and permeability of gas showed almost linear behavior at higher gas-filled porosities, while deviated substantially from linear scaling at lower gas saturations. Comparing the theory with the diffusion and permeability experiments showed that the determined value of z ranged between 2.8 and 5.3, not greatly different from X-ray computed tomography results. The obtained results clearly indicate that the effect of the pore-throat size distribution on gas diffusion and permeability was minimal in these sand and glass bead packs

Effect of Prefilmer Edge Thickness on Breakup Phenomena of Liquid Film in Prefilming Airblast Atomizer

[EN] This paper describes the investigation of the effect of a prefilmer edge thickness on the breakup phenomena of a liquid film in a prefilmer airblast atomizer. The breakup phenomena of the liquid film at five prefilmer edge thicknesses (160, 500, 1250, 2000, and 3000 μm) under various conditions was observed using a high-speed camera. The breakup length of the liquid film was calculated by an image processing technique developed in this study. In order to quantitatively evaluate the effect of the prefilmer edge thickness on the breakup frequency, the Fast Fourier Transformation (FFT) analysis was conducted based on the time evolution of the breakup length. The results indicated that the breakup length increase and the breakup frequency decreases by increasing prefilmer edge thickness due to a larger volume of a liquid accumulation attaching to the prefilmer edge. The FFT analysis showed that the increase in prefilmer edge thickness causes the transition of the maximal power spectrum to a lower frequency (i.e. less than 100 Hz) due to the increase in the liquid accumulation at the edge as well. Finally, a dimensionless correlation has been proposed for the breakup length of a liquid film.Okabe, T.; Katagata, N.; Sakaki, T.; Inamura, T.; Fumoto, K. (2017). Effect of Prefilmer Edge Thickness on Breakup Phenomena of Liquid Film in Prefilming Airblast Atomizer. En Ilass Europe. 28th european conference on Liquid Atomization and Spray Systems. Editorial Universitat Politècnica de València. 154-161. https://doi.org/10.4995/ILASS2017.2017.4931OCS15416

Measurements and Modeling of Thermal Conductivity of Recycled Aggregates from Concrete, Clay Brick, and Their Mixtures with Autoclaved Aerated Concrete Grains

Cool road pavements contribute to mitigating urban heat islands. To evaluate the heat balance in paved surfaces and to select appropriate road construction materials that help suppress heat islands, an accurate understanding of heat transport parameters such as thermal conductivity (λ) and heat capacity (HC) is important. Recycled aggregates from construction and demolition waste, including scrap construction materials and industrial by-products, are often used for road construction; however, λ and HC of recycled aggregates especially for roadbeds are not fully understood. This study involved a series of laboratory tests to measure λ and HC of recycled concrete and clay brick aggregates (λ and HC increased with increasing volumetric water content (θ). Closed-form models for estimating λ(θ) were proposed using normalized thermal conductivity (λe) and effective saturation (Se). The new λe(Se) models performed well for the measured data compared to previously proposed models and would be useful to evaluate λ of recycled aggregates for roadbed materials

AGU hydrology days 2009

2009 annual AGU hydrology days was held at Colorado State University on March 25 - March 27, 2009.Includes bibliographical references.Recently developed, relatively low cost, ECH₂O soil moisture sensors have received considerable attention by both laboratory and field scientists. For these sensors to be installed properly, the sampling volume that defines the volume of soil zone where the soil moisture affects the sensor readings has to be known. These dielectric sensors comprise plus and ground prongs, where the sensitivity of the plus prong is higher than that of the ground prong. Moreover, the sensor head in which the circuitry is embedded has some sensitivity. It is not straightforward to incorporate these characteristics into numerical quantification of the sampling volume that is often used for conventional TDR probes. Therefore, we revisited a "classic" experimental approach for quantifying the bulk sampling volume of these sensors. We obtained sensor readings under varying distances between the sensor and a water-air interface, and determined the bulk sampling volume when the sensor readings start to show an "abrupt" change. Firstly, we tested two TDR probes (CS-640 and CS-630, Campbell Scientific, Inc.) and showed that the experimental procedure yielded results that were consistent with the previous findings. Secondly, we examined four ECH₂O soil moisture sensors that differ in design (EC-5, TM, 5TE, and 10HS, Decagon Devices, Inc.). The results showed that: 1) the sensitivity of the plus prong was generally higher and the contribution of the ground prong varied depending on whether or not the ground prong was in air or under water, 2) abrupt changes were generally limited within small distances (order of ~1 to 2 cm) from the prongs, and 3) the sensor head affected the output readings by 35 % for EC-5, TM, and 10HS, and 34% for 5TE. Since the experiments were performed in air and under water, where soil moisture conditions are expected to be in between these extreme conditions, the estimated bulk sampling volumes should be valid in soils

AGU hydrology days 2009

2009 annual AGU hydrology days was held at Colorado State University on March 25 - March 27, 2009.Includes bibliographical references.A class of problems in hydrology and remote sensing requires improved understanding of how water and heat flux boundary conditions affect the soil moisture processes in the shallow subsurface near the land/atmospheric interface. In these systems, a clear understanding of how variations in water content, soil drainage/wetting and porosity conditions affect the soil's thermal behavior is needed for the accurate detection of buried objects such as landmines, however, very few experimental data showing the effects of these variations are available. In this study, the effect of soil moisture, soil hysteretic behavior and porosity on the thermal conductivity of some sandy soils was investigated. For this experimental investigation, a Tempe cell was modified to have a network of sampling ports, continuously monitoring water saturation, capillary pressure, temperature, and soil thermal properties. The water table was established at mid elevation of the cell and then lowered slowly. The initially saturated soil sample was subjected to slow drainage, wetting, and secondary drainage cycles. After liquid water drainage ceased, evaporation was induced at the surface to remove soil moisture from the sample to obtain thermal conductivity data below the residual saturation. For the test soils studied, thermal conductivity increased with increasing soil density and moisture content while thermal conductivity values were similar for soil drying/wetting behavior. Thermal properties measured in this study were then compared with independent estimates made using empirical models from literature. These soils will be used in a proposed set of experiments in intermediate scale test tanks to obtain data to validate methods and modeling tools used for landmine detection