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Browsing by Author "Voller, Vaughan"

Now showing 1 - 10 of 10
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    Analysis of the Elfuel Coal Drying Facility
    (St. Anthony Falls Hydraulic Laboratory, 1990-10) Rindels, Alan J.; Gulliver, John S.; Wetzel, Joseph M.; Voller, Vaughan
    The ELFUEL coal drying facility is designed to utilize the high heat transfer characteristics of a moving packed bed counter-current heat exchanger to efficiently "hot-water dry" lignite coal. Past research into hot water drying of lignite indicates the process is energy inefficient, requiring greater energy input than what can be extracted from the treated lignite. The novel approach of the ELFUEL coal drying facility utilizes the high heat transfer characteristics of a counter-current solid/liquid packed bed to efficiently add and later remove heat to and from descending coal in a pressurized cylindrical vessel. This approach uses raw coal continuously descending in a vertical cylindrical refractory. Coal, upon entering the refractory at the top, gradually heats to process temperatures near the location of hot water injection through contact with hot water flowing upward. Below the point of hot water injection, cool water is forced upward past the descending coal to trap or conserve heat or energy in the system. Sufficient energy is conserved by this design to economically hot-water dry lignite coal. Design of a counter-current energy efficient system which adds and then removes heat has not been reported in the literature. Wonchala and Wynnyckyj (1986) reports counter-current packed bed processes are common in the metallurgical industries. Some important example include the iron blast furnace and iron-ore pelletizing shaft furnace which are very useful since they exhibit a very high potential heat transfer efficiency. However, the metallurgical counter-current gas-solid heat exchangers have not been found to be energy efficient due to channeling of hot gases (Wonchala and Wynnyckyj, 1986). It was the purpose of this study to determine whether the ELFUEL coal drying facility outlined in Minnesota Power's proposal "ELFUEL Demonstration of Low-Rank Coals" to the U. S. Department of Energy, Clean Coal Technology, Round #3 will perform as described and meet the objectives of the process, the economical hot-water drying of lignite coal.
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    Bifurcation Experiments: Timeseries, Images, Topographic Scans, St. Anthony Falls Laboratory, 2016-2017
    (2019-05-17) Salter, Gerard L; Voller, Vaughan; Paola, Chris; salte040@umn.edu; Salter, Gerard L
    We ran a set of five experiments at the St. Anthony Falls Laboratory in Minneapolis, Minnesota to study how the dynamics of a bifurcation are affected by the downstream boundary (deposition vs. bypass). These data accompany our publication in Earth Surface Dynamics.
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    Cost/Benefit Study of Spring Load Restrictions
    (2005-03-01) Levinson, David M; Marasteanu, Mihai O; Voller, Vaughan; Margineau, Ioana; Smalkowski, Brian; Hashami, Maryam; Li, Ning; Corbett, Mike; Lukanen, Erland
    Across the state of Minnesota, asphalt roads under the jurisdiction of counties, cities and townships have been controlled by restrictions that limit the total weight of each truck that uses those roads during the spring thaw period. During this time, the pavement weakens and the bearing capacity of the roadway is reduced. These policies vary from county to county and from road to road, depending on the capacity of the roads--typically, 5, 7 and 9 tons. While spring load restrictions serve to extend the useful life of the road, they also add significant burdens to truckers who are forced to re-route their vehicles and/or increase the number of trips in order to adhere to the policies. This study assesses the economic impact of lifting all vehicle restrictions during the spring thaw period. Economic benefits of lifting the bans include reduced cost to carriers; potential cost includes reduced pavement life. Their research concludes that if the policy is changed, the costs of additional damage could be recovered from those who use the roads. Recovering those costs could take the form of annual fees, appropriate fuel taxes and/or user charges paid by vehicle operators.
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    Data for Response of a large, low porosity rock sample to hydromechanical loading
    (2024-10-22) Asem, Pouyan; Detournay, Emmanuel; Voller, Vaughan; Labuz, Joseph; pasem@umn.edu; Asem, Pouyan; University of Minnesota
    A unique laboratory framework is developed for measuring hydromechanical parameters in a 6025 mL confined specimen of Westerly blue granite. Tracking the water uptake in the sample shows that infiltration over a length scale of 230 mm is effectively modeled by assuming a sharp front separating saturated and dry regions. Through matching the movement of this front with the experimental data, an estimate of the sample permeability is obtained. In addition, following full saturation, Skempton coefficient B, drained bulk modulus K, unjacketed bulk modulus Ks′, and unjacketed pore modulus Ks'' are determined. Thus, we demonstrate that a single experimental framework for measuring the infiltration and saturation of a large, tight rock specimen provides a significant array of reliable parameters for use in modeling and characterizing critical hydrogeological processes.
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    Designing Pavement Drainage Systems: The MnDRAIN Software
    (2003-03-01) Voller, Vaughan
    This report outlines the development of a suite of computer codes embedded in a Microsoft Excel spreadsheet, collectively referred to as MnDrain. These codes provide a user-friendly environment in which the consequences of an edge drain design decision can be investigated. Edge drains consist of pipes that run along the length of a road to remove moisture from the granular base of the road system. The pipes are placed in a high permeability gravel trench below the shoulder/road surface. The rate at which moisture is removed will depend on the geometry and materials used in the base and the soil type in the sub-grade. A full copy of the MnDrain code, including all source programs and an on-line manual, can be downloaded on visiting http://www.ce.umn.edu/~voller/voller_research/task5/mndrainrequest.html. The main attributes of the MnDrain system are: a relevant easy to use graphical interface, meaningful drainage design scenarios, flexible assignment of materials properties, an easy to maintain database for unsaturated properties, and a state of the art saturated/unsaturated numerical solution engine. The code is freeware that can be readily reconfigured for alternative and novel applications. As it stands the MnDrain code is a solid initial framework from which further developments can be made. In this project the operation of MnDrain was purposely constrained to work with simple geometries (the scenarios) to establish a system that could be used by a field engineer with only a limited knowledge of soil physics and numerical modeling. MnDrain, however, does not need to be constrained in this way. Because MnDrain offers free access to all source codes, it can be reconfigured to deal with a large array of pavement drainage issues. To take advantage of this feature, further investigation is recommended.
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    Evaluation of a Field Permeameter to Measure Saturated Hydraulic Conductivity of Base/Subgrade Materials
    (2001-06-01) Clyne, Timothy R; Voller, Vaughan; Birgisson, Bjorn
    This report presents the results of a cooperative study on the field use of a permeameter, built by researchers at the Minnesota Department of Transportation (Mn/DOT) and the University of Minnesota, to estimate the saturated hydraulic conductivity of pavement base materials. Field measurements using the permeameter were taken on various highway construction projects, and researchers measured the saturated hydraulic conductivity of samples in the laboratory. Researchers also reviewed theories for converting a field-measured flow rate into a saturated hydraulic conductivity estimate. By numerical simulation and analysis of the field data, researchers determined an appropriate method for converting the Mn/DOT permeameter flow measurements into estimates of hydraulic conductivity. Variations between the field estimated and laboratory measured hydraulic conductivity are within one order of magnitude. Variations between the field estimate and numerical simulation, however, are much closer. The study found the Mn/DOT permeameter can be used to obtain a reliable estimate of the base hydraulic conductivity provided that the base layer is at least 15 cm (six inches) deep. When the base is to thin, permeameter readings are restricted to early infiltration times.
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    Low Temperature Cracking of Asphalt Concrete Pavement
    (2004-03-01) Marasteanu, Mihai O; Li, Xue; Clyne, Timothy R; Voller, Vaughan; Timm, David H; Newcomb, Dave
    This report investigates the low temperature behavior of asphalt pavements based on experimental results obtained for three mixtures used in the construction of cells 33, 34, and 35 at Mn/ROAD facility as well as field information acquired over the years at Mn/ROAD. As a result of this research, a new test method was developed to determine the low temperature fracture properties of asphalt mixtures based on tests performed on semi-circular specimens tested in bending. This method can be used to select materials with better fracture resistance and therefore better performance in the field. Two models were developed to predict the low temperature cracking performance of asphalt pavements. The first model predicts the crack spacing in asphalt pavements exposed to low temperatures based on continuum mechanics and the frictional restraint provided by the aggregate base. The second model predicts the accumulation of damage and the propagation of the crack through the asphalt layer as temperature drops based on cohesive zone model.
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    Measurement of Moisture in Aggregate Stockpiles
    (2001-03-01) Voller, Vaughan; McGannon, Tom; Rindal, Dave; Timm, David H; Clyne, Timothy R; Newcomb, Dave
    Asphalt mixture variations that result from moisture fluctuations in aggregate stockpiles pose a serious problem at dryer-drum plants. The moisture content of a stockpile is infrequently measured, if at all. If the proportion of aggregate is not adjusted to account for its moisture content, an improper mix will result. This project looked at identifying a practical and accurate field method or probe for measuring the moisture content of aggregates, testing the probe in a hot-mix plant, and developing a control strategy for asphalt oil addition to the mix. Researchers identified a suitable commercial probe by reviewing past research and conducting laboratory studies. Testing in the plant showed that this probe could rapidly measure aggregate moisture in plant conditions at the same level of accuracy as gravimetric measurements. Researchers also developed a control strategy for the asphalt oil addition. Testing showed the effectiveness of this control, in conjunction with commercial probe moisture measurements in the feed bin. A problem with probe operations robustness was identified.
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    Modeling of Frost Heave In Soils
    (1991-10) Michalowski, Radoslaw L.; Voller, Vaughan; Sterling, Raymond
    This report results from a research project undertaken over the period July 1, 1990 to September 30, 1991. The research project itself resulted from the combination of two proposals to the Center for Transportation Studies for research into the mechanics of frost heaving in soils. Both proposals had a general objective of creating a better understanding of the behavior of the soil-water-ice systems and frost susceptible soils at freezing temperatures and improving the capabilities of the faculty, researchers and students in an area of study which is important for road design in Minnesota.
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    Progressive Lifting of Shallow Sewers Due to Frost Heave Actions: Investigation of a Lumped Parameter Frost Heave Model
    (2003-08-01) Voller, Vaughan; Hou, Ling-Jun; Sterling, Raymond
    The objective of this report is to complete work undertaken at the University Minnesota in the mid 1990's. This work was directed at developing an understanding of frost heaves in relationship to the lifting of buried objects such as shallow sewers. The critical findings in the field investigation were detailed in a 1995 final report by Ray Sterling, Progressive Lifting of Shallow Sewers: Field Investigation. Preliminary details of the modeling work were provided in an interim project report and complete details were provided in the MS Thesis of Lingjun Hou, An Investigation of a lumped Parameter Frost Heave Model published by the University of Minnesota in January 1994. The objective of the current report is to outline the critical findings in the modeling work detailed in the previous interim report and Hou's thesis. This document should be seen as a compliment to the original final report submitted by Sterling in 1995. The central objective of the modeling study is the investigation of the lumped parameter frost heave model developed by Blanchard and Fremond. The work in this report shows that a lumped porosity model can generates an accurate comparison with experiments and is a feasible tool for the investigation of the effect of freeze thaw on buried infrastructure.