Chapter 5 – Surge Protection
Surge Analysis and the Wave Plan Method
Supplementary Material: Example Problems and Solutions
Chapter 5 – Problem 5.6
5.6 Compute the Cavitation Index of the PRV described in the previous example.
Solution:
Cavitation Index (CI) is defined two different ways, and one definition is the exact inverse of the other!
The definition used by the scientific literature is:
CI for a device is the ratio of the actual difference in pressure across the device and the difference between the upstream pressure and the liquid vapor pressure, where all pressure terms are expressed in the same units.
Therefore, CI = (Pv – Pd) / (Pu – Pv) where Pu is pressure on the upstream side of the device, Pd is pressure on the downstream side of the device, and Pv is the liquid vapor pressure.
With this definition, the lowest value for CI would be close to 0 (when the downstream pressure is almost same as the upstream pressure) and the highest value is 1 (when the downstream pressure is same as the liquid vapor pressure).
Calculate the CI value for the PRV described in the previous example using the above scientific definition. Device manufacturers specify limits on these indices (e.g., the maximum permissible CI is 0.6) to prevent cavitation and the associated damages to these devices.
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