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  1. Compressible flow through arrays of circular micro-orifices was experimentally and numerically studied to better understand how the characteristic dimensions of micro-orifices used in macroscale fluidic systems using a plurality of micro-orifices impacts discharge coefficient. The studies were carried out with micro-orifice diameters ranging from 125 μm to 1000 μm, with the number of micro-orifices in an array ranging from 2 to 64, and at gauge inlet pressures ranging from 25 to 600 kPa venting to atmospheric pressure. Results showed `that micro-orifice diameter to thickness aspect ratio and wall profile were significant factors in determining discharge coefficient. The number of micro-orifices in a system was found to have negligible impact on discharge coefficient so long as the micro-orifices were separated by two diameters or more. When this spacing was maintained, two dimensional axisymmetric micro-orifice numerical studies produced discharge coefficients that agreed well with experimental data gathered on three dimensional micro-orifice arrays. The micro-orifice arrays produced discharge coefficients as high as 0.997 using photochemically etched micro-orifices, 0.981 using silicon etched micro-orifices, and 0.831 with drilled micro-orifices. 
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    Free, publicly-accessible full text available October 1, 2024
  2. This work describes an efficient means to adjust the power level of an axial piston hydraulic pump/motor. Conventionally, the displacement of a piston pump is varied by changing the stroke length of each piston. Since the losses do not decrease proportionally to the displacement, the efficiency is low at low displacements. Here, with partial-stroke piston pressurization (PSPP), displacement is varied by changing the portion of the piston stroke over which the piston is subjected to high pressure. Since leakage and friction losses drop as the displacement is decreased, higher efficiency is achieved at low displacements with PSPP. While other systems have implemented PSPP with electric or cam-actuated valves, the pump described in this paper is unique in implementing PSPP by way of a simple, robust hydro-mechanical valve system. Experimental testing of a prototype PSPP pump/motor shows that the full load efficiency is maintained even at low displacements. 
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