James A. Throop

Transport and Retention Mechanisms of Colloids in Partially Saturated Porous Media

The transport, retention, and release of hydrophobic and hydrophilic polystyrene latex microsphere colloids were examined in 0.5-cm-thick, 26-cm-long slab chambers filled with either regular (hydrophilic) or weakly water-repellent sand. The water-repellent sand consisted of a mixture of 0.4% strongly water-repellent grains with unmodified regular sand for the remainder. The concentration of colloids in the outflow water was measured at the same time as the pore-scale distribution of colloids was recorded in still and video images. Although the type of sand affected the flow pattern in the top of the chamber, it did not affect the breakthrough for the same type of colloids. More hydrophilic colloids were eluted in the drainage water than hydrophobic colloids. Images showed that there was a greater retention of the hydrophobic colloids due to strongly attractive hydrophobic interaction forces between colloids and subsequent filtering of colloidal aggregates in the narrow passages between grains. Once filtered, these aggregates then served as preferred sites for attachment of other hydrophobic colloids. The hydrophilic colloids were retained primarily in a thin film of water at the edge of the menisci, the air–water–solid (AWS) interface. Centrifugal motion within the pendular rings observed in the videos contributed to movement of the colloids toward the AWS interface, where colloids were retained due to both low laminar flow velocities near the grain surface and straining in the thin water film at the edge of the meniscus. Except near the solid interface, sorption at the air–water (AW) interface was not observed and appeared unimportant to the retention of colloids. The findings form an essential link between colloid retention and transport processes at the interfacial, pore, and Darcy scales.

Pore-Scale Visualization of Colloid Transport and Retention in Partly Saturated Porous Media

In unsaturated porous media, sorption of colloids at the air–water (AW) interface is accepted as a mechanism for controlling colloid retention and mobilization. However, limited actual pore-scale observations of colloid attachment to the AW interface have been made. To further investigate these processes, a real-time pore-scale visualization method was developed. The method builds on the light transmission technique for fingered flow studies in packed-sand infiltration chambers and combines it with high-resolution, electro-optical hardware and public domain imaging software. Infiltration and drainage of suspensions of hydrophilic negatively charged carboxylated latex microspheres provides compelling visual evidence that colloid retention in sandy porous media occurs via trapping in the thin film of water where the AW interface and the solid interface meet, the air–water–solid (AWS) interface. With this modified theory of trapped colloids at the AWS interface, we are able to explain the apparent discrepancy between previous experimental evidence of hydrophilic colloids seemingly partitioning to the AW interface and more recent findings that suggest this type of colloid does not adsorb at the AW interface.

Visualization by light transmission of oil and water contents in transient two-phase flow fields

Abstract The difficulty of determining transient fluid contents in a soil–oil–water system is hampering an understanding of the systems flow characteristics. In this paper, we describe a light transmission method (LTM) which can rapidly obtain oil and water contents throughout a large two-dimensional flow field of silica sand. By appropriately coloring the water with 0.005% FD&C blue #1, the hue of the transmitted light is found to be directly related to the water content within the porous media. The hue provides a high resolution measurement of the water and oil contents in transient flow fields (such as unstable flow). Evaluation of the reliability of LTM was assessed by checking the mass balance for a known water injection and its utility in visualizing a whole flow field was exemplified for unstable fingered flow by comparing fluid contents to those obtained with synchrotron X-ray radiation.

Measurement of fluid contents by light transmission in transient three-phase oil-water-air systems in sand

Most three-phase flow models lack rigorous validation because very few methods exist that can measure transient fluid contents of the order of seconds of whole flow fields. The objective of this study was to develop a method by which fluid content can be measured rapidly in three-phase systems. The method uses the hue and intensity of light transmitted through a slab chamber to measure fluid contents. The water is colored blue with CuSO4. The light transmitted by high-frequency light bulbs is recorded with a color video camera in red, green, and blue and then converted to hue, saturation, and intensity. Calibration of hue and intensity with water, oil, and air is made using cells filled with different combinations of the three fluids. The results show that hue and water content are uniquely related over a large range of fluid contents. Total liquid content is a function of both hue and light intensity. The air content is obtained by subtracting the liquid content from the porosity. The method was tested with static and transient experiments. Measurements made with the light transmission method (LTM) and synchrotron X rays of the static experiment agreed well. In the transient experiments, fingers were formed by dripping water on the surface in a two-dimensional slab chamber with partially oil-saturated sand. The LTM is able to capture the spatial resolution of the fluid contents and can provide new insights in rapidly changing, three-phase flow systems.

Influence of Time, Bruise-type, and Severity on Near-infrared Reflectance From Apple Surfaces for Automatic Bruise Detection

Near-infrared imaging was used to characterize the influence of time, bruise-type, and severity on the near-infrared (NIR) reflectance from bruised and unbruised regions on ‘Delicious’ and ‘Golden Delicious’ apples. Images of apples were captured on five dates for both impact- and compression-type bruises. Changes in the NIR reflectance were characterized by comparing the contrast which was measured by a difference calculation between two concentric circular profiles from bruised and unbruised areas. Within 24 h after inducing damage, a maximum contrast in NIR reflectance occurred for both bruise types. Afterwards, the contrast decreased until it equaled the contrast for an unbruised region. This change usually occurred between 1 and 42 days. The time at which the contrast at a bruised region exceeded that at an unbruised one depended upon the severity and type of bruise. Changes in contrast after one day were more gradual for impact-type bruises than bruises created by compression.

Detecting internal breakdown in apples using interactance measurements

Abstract A technique using body transmittance in the 450- to 1050-nm region was evaluated as a non-destructive technique for identifying apples with internal breakdown. Apples with internal breakdown absorbed shorter wavelengths of light ( 750 nm) was absorbed more by good apples than detective ones. A classifier based on the ratio between the light intensity at 720 and 810 nm was used to segregate apples with internal breakdown from good apples. Only 6.3% of the good apples were incorrectly classified; however. bruises on the apples contributed to the incorrect classification of good apples. None of the apples with severe internal breakdown were incorrectly classified. Apples with very slight internal breakdown contributed to most of the 12.0% error of misclassifying defective fruit as good. The number of misclassified apples was reduced by adjusting the cut-off; however, the number of good fruit that would be discarded increased.

Pattern recognition models for spectral reflectance evaluation of apple blemishes

Abstract Surface blemishes of various apple varieties were analyzed by their reflectance characteristics between 460 and 1130 nm. Normalized reflectance data were collected at 10 nm increments with liquid crystal tunable filters. Data were utilized as input values for various pattern recognition models specifically multi-layer back propagation, unimodal Gaussian, K-nearest neighbor and nearest cluster algorithms. Partitioning data into 50:50 training and test sets, correct classification in separating unflawed versus blemished areas ranged from 62 to 96% (Year I) and from 73 to 85% (Year II). The algorithm which yielded the highest correct classification was the multi-layer back propagation but minor variation was found for number of hidden nodes or neural net architecture.

Apple orientation on two conveyors: Performance and predictability based on fruit shape characteristics

Two sizes of H apple cultivars were placed on a bicone conveyor used in commercial sorting machines and on an experimental conveyor. In less than 18 seconds, apples were oriented into one of two modes, either parallel (desired) or nonparallel (undesired) to the stem/calyx axis. The commercial conveyor gave desired orientation to 94% of 88 Washington State Red Delicious apples but to only 4% of 772 apples from eastern cultivars. The experimental conveyor gave desired orientation to 83.4% of the apples from cultivars normally produced in the eastern United States but to only <1% of Washington State Red Delicious apples. Cortland, Empire, small Fuji, Jonagold, McIntosh. and Rome apples, when placed so that they rotated perpendicular to the stem/calyx axis, moved to the desired orientation 95% to 100% of the time. Only 82% of large Fuji apples moved to the desired orientation. In addition, 47% to 80% of the Golden Delicious, Granny Smith, Crispin, Eastern Red Delicious, and Gala apples, when placed to rotate on the undesired axis, moved to the desired orientation. Washington State Red Delicious apples, when placed on the experimental conveyor to rotate on the desired axis, changed to the undesired orientation for 87 of 88 apples. Linear discriminate analysis was performed using up to 19 of the shape factors measured from silhouette images of the side and top views of each apple. The height-width ratio of the side view of the apples predicted both desired and undesired orientation on both conveyors almost as well as any combination of shape factors. Cortland, Empire, small Fuji, Jonagold, Mclntosh, and Rome apples have height-width ratios of approximately 0.8, and all oriented to the desired axis on the experimental conveyor and to the undesired axis on the commercial conveyor. Washington State Red Delicious apples had height-width ratios of 1.03 and oriented to the undesired axis on the experimental conveyor and to the desired axis on the commercial conveyor. Apples with average height-width ratios between 0.8 and 1.0 were inconsistent, but more than half of these apples oriented correctly on the experimental conveyor, The commercial conveyor oriented elliptically shaped objects to rotation about an axis passing through the center of gravity and where the center of gravity is lowest. This axis typically corresponded to the stem/calyx axis of the Washington State Red Delicious apples. The experimental conveyor oriented elliptically shaped objects to rotation about the shortest axis where the contact point on the powered roller was the highest, For both devices, the height-width ratio from the side views of each apple was a measure of this ellipticity.

Camera System Effects on Detecting Watercore in ‘Red Delicious’ Apples

Watercore damage was quantified in ‘Red Delicious’ apples by measuring light transmitted through the apple along the stem/calyx axis. Two black and white video cameras with different intensity sensitivities were used to capture images of the stem-end of each fruit. Two patterns, rings and squares, were analyzed in each image. For one camera, rings and squares of different sizes were analyzed. Apples were scored into five classes of watercore damage.

Detection of internal browning in apples by light transmittance

Light transmittance in the 450 to 1050 nanometer (nm) region was evaluated as a nondestructive technique for identifying apples with internal browning. Shorter wavelengths of light (< 800 nm) were attenuated more than longer wavelengths (> 800 nm). A transmission difference between 720 and 810 nm was used to segregate apples with internal browning from good apples. Only 7.4% of the apples were misclassified in a training set. When applied to a larger validation set, 8.0% of the apples with internal browning were misclassified. For both sets, the only apples misclassified were those with very slight browning that was very difficult to detect visually were misclassified, but none of the apples with slight to severe browning was misclassified. For nondefective apples, 6.1% were identified as having internal browning, because bruises and internal browning had the same effect on the spectral composition.