CAVITATION
The maximum flow rate, Q max
, is required in the calculation of the liquid pressure recovery factor, F L
. For a given upstream pressure, the quantity Q max is defined as that flow rate at which a decrease in downstream pressure will not result in an increase in the flow rate( horizontal line in image). The test procedure to calculate FL is described in ANSI / ISA-75.02.01. Designers can use these parameters to optimize flow paths and make informed design decisions.
Staged pressure drop
Typical cavitation index levels and acceleration readings
Computational Fluid Dynamics( CFD)
Computational Fluid Dynamics( CFD) simulation uses numerical methods to solve fluid flow, heat transfer, and related phenomena. The fluid domain is divided into discrete mesh cells and the governing Navier-Stokes equations are solved in each cell. The Reynolds-Averaged Navier-Stokes( RANS) approach is typically used to model the turbulent behaviour of flow.
Validation study: sharp-edge orifice
This validation study compares CFD results with experimental data from“ Calibration and Verification of Cavitation Testing Facilities Using an Orifice” by William Rahmeyer and Fred Cain. The orifice, with a 1.534-inch throat diameter, was tested across seven laboratories. For this CFD validation, data from Lab B was selected. The orifice was modelled as 2D axisymmetric geometry, with the fluid domain meshed using quadrilateral cells and prism layers near the orifice edges for accurate flow resolution.
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Step 1: Single-phase flow simulation for incipient cavitation index
The first step is the single-phase flow simulation to determine the flow capacity
C V and the incipient cavitation index. The inlet pressure was set to 50 psig( 64.7 psi absolute), and the outlet to 50 psi absolute, resulting in a 14.7 psi( 1 atm) pressure drop. The simulation showed a minimum pressure of 28.8 psi, which was used to calculate the σ I
. The CFD results closely matched the experimental data, confirming the simulation’ s accuracy.
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Choked Flow
Liquid pressure recovery factor, F L
F L is the liquid pressure recovery factor of the valve. This factor accounts for the influence
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of the valve internal geometry on the valve capacity at choked flow. The formula for the Liquid Pressure Recovery Factor is: |
Step 2: Multi-phase flow simulations for liquid pressure recovery factor
The next step is multi-phase flow simulations to determine the maximum
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π |
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