A technique is presented to determine when anisotropic fracture systems can be modeled as equivalent porous media (continua) for transport. In order to use the continuum approach, one must demonstrate that the fracture system has the same transport behavior as an equivalent porous medium. Hydraulic effective porosity is calculated as the product of specific discharge and mean travel time, divided by linear length of travel. Specific discharge and hydraulic effective porosity are measured in different directions of flow in regions of varying size with constant hydraulic gradients. If the fracture system behaves like an equivalent porous medium, directional flow has the following properties: (1) specific discharge can be predicted from a permeability tensor and (2) hydraulic effective porosity is independent of direction of flow. A numerical model has been developed to simulate mechanical transport under steady flow in a discrete fracture network. The model is used to determine the distribution of travel times from inlet to outlet for fluid traveling in stream tubes. We have examined only systems with parallel fracture sets in which all fractures are long compared to the region under study. These systems satisfy criterion 1 in that flux can be calculated using a porous medium equivalent. However, these systems do not satisfy criterion 2 because hydraulic effective porosity is shown to be directionally dependent. Thus, even though flux can be accurately predicted using porous medium assumptions for some fracture systems, it may not be possible to accurately predict mechanical transport using these same assumptions.

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The objectives of this research are to evaluate directional mechanical transport parameters for anisotropic fracture systems, and to determine if fracture systems behave like equivalent porous media. The tracer experiments used to measure directional tortuosity, longitudinal geometric dispersivity, and hydraulic effective porosity are conducted with a uniform flow field and measurements are made from the fluid flowing within a test section where linear length of travel is constant. Since fluid flow and mechanical transport are coupled processes, the direc tional variations of specific discharge and hydraulic effective porosity are measured in regions with constant hydraulic gradients to evaluate porous medium equivalence for the two processes, respectively. If the fracture region behaves like an equivalent porous medium, the system has the following stable properties: 1) specific discharge is uniform in any direction and can be predicted from a permeability tensor and, 2) hydraulic effective porosity is directionally stable. Fracture systems with two parallel sets of continuous fractures satisfy criterion 1. However, in these systems hydraulic effective porosity is directionally dependent, and thus, criterion 2 is violated. Thus, for some fracture systems, fluid flow can be predicted using porous media assumptions, but it may not be possible to predict transport using porous media assumptions. Two discontinuous fracture systems were studied which satisfied both criteria. Hydraulic xv CHAPTER 1 INTRODUCTION I CHAPTER 2 LITERATURE REVIEW 2.1 INTRODUCTION 3 2.2 DISPERSION IN POROUS MEDIA 3 2.

A hybrid anti-/de-icing system combining a superhydrophobic coating and an electrothermal heater is an area of active research for aircraft icing prevention. The heater increases the temperature of the interaction surface between impinging droplets and an aircraft surface. One scientific question that has not been studied in great detail is whether the temperatures of the droplet and the surface or the temperature difference between the two dominate the anti-/de-icing performance. Herein, this scientific question is experimentally studied based on the mobility of a water droplet over a superhydrophobic coating. The mobility is characterized by the sliding angle between the droplet and the coating surface. It was found that the temperature difference between the droplet and the coating surface has a higher impact on the sliding angle than their individual temperatures.

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