David C. Wiggert

Cavitation Inception in Spool Valves

Cavitation has been investigated in directional control valves in order to identify damage mechanisms characteristic of components of aircraft hydraulic systems. Tests have been conducted in a representative metal spool valve and in a model three times larger. Data taken under non-cavitating conditions with both valves showed that the position of the high-velocity annular jet shifts orientation depending upon valve opening and Reynolds number. By means of high-frequency response pressure transducers strategically placed in the valve chamber cavitation could be sensed by the correlation of noise with a cavitation index. The onset of cavitation can be detected by comparing energy spectra for a fixed valve opening and a constant discharge. Another sensitive indicator of cavitation inception is the ratio of cavitating to non-cavitating spectral densities. The incipient cavitation number as defined in this investigation is correlated with the Reynolds number for both valves.

Frozen soil subsurface barriers: formation and ice erosion

Abstract Before and during soil remediation, frozen soil barriers are used to provide containment of liquid contaminants so as to prevent their migration to adjacent areas. Questions concerning formation of frozen gravelly sand barriers in the vadose zone and barrier resistance to ice erosion by liquid contaminants provided the impetus for this study. Bench-scale barriers with full and partial ice saturation were studied. For comparison, one barrier was formed in gravelly sand using water injection via a bentonite-water slurry. The bentonite increased the slurry viscosity, thereby providing a water retention period suitable for freezing. Liquid contaminants included a sodium nitrate solution (freezing point of −5°C) and an antifreeze solution (freezing point of −33°C). Results showed that ice erosion in the bench-scale barriers occurred when the contaminant freezing point depression was lower than the temperature of the frozen soil. When liquid contaminants entered the voids of partially ice saturated frozen soil, the rate of ice erosion was significantly increased. Full ice saturation and barrier temperatures below the freezing point depression of the contaminant are needed to minimize ice erosion.

Movement of liquid contaminants in partially saturated frozen granular soils

Abstract Understanding the migration of nonaqueous phase liquids in frozen subsurface soils is becoming increasingly important in permafrost regions and in temperate zones where frozen subsurface barriers have been proposed to confine contaminants. Tests were performed on 32 specimens of gravelly sands from the Hanford, Washington reservation to determine the relationship between degree of ice saturation and intrinsic permeability. Decane, a representative nonaqueous phase liquid, was employed as the permeant, and was infiltrated through the frozen specimens at −10°C. In addition to pure water, a NaCl brine and a mixture of water and decane were utilized as the pore liquids. For all specimens the intrinsic permeability correlated linearly with the ice saturation, varying from approximately 2.7× 10−7 cm2 at 0% saturation to negligible values at nearly 100% saturation. The different pore liquids did not affect the correlation significantly. Bentonite was added to some of the specimens prior to freezing, reducing the intrinsic permeability to negligible levels.

Impact of Surfactant on Configuration of Petroleum Hydrocarbon Lens

A laboratory-scale physical model was constructed for visual observation of the basic 2-D flow characteristics of a gasoline spill through an unconfined aquifer and the subsequent treatment with a surfactant. The model consists of a parallel-plate glass tank (1 m×1 m×5 cm) packed with Ottawa sand. Gasoline was released from a point source in the vadose zone. As the specific gravity of gasoline is less than one (LNAPL), it pooled above the water saturated pores of the tension saturated region of water. Beyond the lens of gasoline, the height of the capillary fringe was reduced due to capillary pollution. The gasoline lens was then treated with an aqueous phase surfactant solution of 2% dodecyl benzene sulfonate (anionic) and 2% polyethoxylate nonyl phenol (nonionic). This surfactant solution reduced the interfacial tension between the gasoline and the aqueous phase by an order of magnitude. The surfactant solution was released from the same point source in the vadose zone as the gasoline. As a result, the ...

Dynamic Response of Ductwork Laboratory Exhaust Systems

A numerical model based on the method of characteristics is developed to analyze unsteady flows in laboratory ductwork systems. Damper opening and/or closing initiate time-variable boundary conditions at hood inlets. Minor losses and ductwork friction are included, as well as interaction with fans. Extensive data are obtained from two university laboratory systems for purposes of code verification. Comparisons between experiments and simulations demonstrate the accuracy and versatility of the numerical model.