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Environmentally Friendly Hydraulic Fluids
Published in Leslie R. Rudnick, Synthetics, Mineral Oils, and Bio-Based Lubricants, 2020
Since pressure transmission is involved, compressibility of the hydraulic fluid can be a critical factor. Compressibility is measured by bulk modulus (which is the fluid’s resistance to compression). Under normal operating conditions the commonly used base oils, including bio-based (vegetable) oils, have similar compressibility, hence they do the job of transmitting pressure equally as well as mineral oil fluids. A comparison of the bulk modulus of various commonly used lubricating oils is shown in Table 42.14.
Fluid Mechanics
Published in Michael A. Crabtree, The Concise Industrial Flow Measurement Handbook, 2019
However, in what is normally regarded as a non-compressible fluid such as oil, we would expect that the speed of response would be virtually instantaneous. In reality, all fluids have some degree of compressibility that can lead to a delayed response resulting for example in an actuator failing to move until the upstream fluid has been compressed.
Classical Biodynamics and Biomechanics
Published in Thomas M. Nordlund, Peter M. Hoffmann, Quantitative Understanding of Biosystems, 2019
Thomas M. Nordlund, Peter M. Hoffmann
Physicists know how to change the volume of an object: change the pressure. The compressibility β of a bulk substance is defined as (–) the fractional change in volume per unit incremental pressure increase. Water is generally described as an incompressible fluid. While the majority of liquids are, in fact, incompressible to good accuracy, the incompressibility of water is directly related to the strong interactions and close packing between water molecules. At 0°C and low pressure the compressibility is 5.1 × 10–10 Pa–1, so for most practical purposes water does not compress. The bulk modulus of water is 2.2 GPa, the inverse of the compressibility. The low compressibility of water means that even at an ocean depth of 4 km, where pressures are 40 MPa (~400 atm), there is only a 1.8% decrease in volume.
An implicit implementation of the characteristic boundary condition in a fully coupled pressure-based flow solver
Published in Numerical Heat Transfer, Part B: Fundamentals, 2020
M. M. Alloush, F. Moukalled, L. Mangani, M. Darwish
A large number of engineering problems involves compressibility, among which are external flows. These problems often involve the so-called pressure far field boundary condition at which free stream conditions could be assumed. This boundary condition is also known as the characteristic boundary condition because it applies the Riemann invariants, which correspond to incoming and outgoing characteristic waves, to determine the flow variables at the boundaries. Within the density-based framework [19–24], this boundary condition is well developed and accurately described. In pressure-based methods however, its implementation is not well documented. Till recently, the article by Mathur and Murthy [25] was the only article reporting vaguely on its use in a pressure-based solver. In a more recent article, Moukalled et al. [26] clearly described an efficient implementation of the characteristic boundary condition in a pressure-based method, where they apply an implicit formulation for the pressure at the boundary, leading to a linear, yet strong coupling between the pressure and density. Both articles [25, 26] dealt with the implementation of the pressure far field condition in a segregated pressure-based solver. Its implementation in a pressure-based coupled solver has never been reported.
Effect of liquid addition on the bulk and flow properties of cohesive powders
Published in Particulate Science and Technology, 2022
Tianyi Li, Wei Meng, Yifan Wang, Anand Valia, Rhea Jamsandekar, Ravish Kumar, Fernando J. Muzzio, Benjamin J. Glasser
Compressibility is a measure of how density changes as a function of applied normal stress. This bulk property is influenced by factors, such as particle size distribution, cohesion, and particle shape. The powder was first conditioned by a helical blade in order to create a uniform and reproducible packing. A normal force was then slowly applied by a vented piston. The change of volume due to compression was measured, and the compressibility (CPS %) was calculated as the percent change in volume after compression: where Vc is the bulk volume after the conditioning step and Vp is the volume after compression.