Min Depth

ON SALE FOR FREE FOR 1 DAY--Determine the minimum liquid depth required for preventing vortexes or preventing vapor entrainment in a liquid pool, in vessels, or any draining application.

This app presents two different calculations for determining minimum depth of liquid above a nozzle to avoid entraining vapors in the liquid leaving through the nozzle:
1) Vortex avoidance, and
2) Minimum depth calculation due to change in momentum, using Bernoulli’s equation.

The first mentioned, vortex avoidance, is based on several different equations found at the following references. In addition, in case the depth you have in the vessel you are evaluating is in fact too low and vortexing is predicted, I’ve included output of the Froude number. See my app called “Froude” for a full description.

The refernce materials I used are included in the app on the 'notes' tab.

If you have determined that vortexing depth is not an issue, you still should check your system to ensure that you don’t have vapor entrainment due to the change in velocity from a vessel down to the nozzle. This change in velocity, or the “suction velocity” through the nozzle, requires a certain minimum liquid depth above the upper most section of the nozzle to be absolutely certain that vapor entrainment won’t occur.

The app also assumes that the initial velocity inside the vessel (in the direction of flow) is zero. In reality, there is usually some small amount of velocity (very often less than 0.1 or even 0.01 ft/s) in the direction of flow, but when squared, becomes even more of an insignificant term.

In the iPad app (only, not available on iPhone due to limited screen space) the user can also specify whether a vortex breaker is installed inside the nozzle projection. This is especially important as the presence of a vortex breaker consumes cross-sectional area and increases, often significantly, the velocity through the nozzle, consequently, impacting the “S” result significantly.

Two styles of vortex breakers are assumed, the triangular patterned 3-cross hair design (imaging a peace symbol if you will) and a 4 way cross hairs like a gun sight or target (or a true cross). The thickness of these cross hairs is usually on the order of 1/8”. Some designs are more or less, and should be checked if your inside depth is close to the calculated depth. Most construction drawings will call out this detail adequately.

What is NOT included in this calculation is the frictional losses as it enters the nozzle. Usually it’s negligible, and is constrained to an entrance loss value for frictional drop through a nozzle (sudden contraction, see my other app “TEL” for total equivalent length calculations). If there’s enough requests from users, I’ll eventually add this feature to the app, but fully expect it not to be a significant variable. Just keep this possibility in mind if troubleshooting a real world application. This would be especially important if a vortex breaker is present in a small diameter nozzle, as the equivalent diameter through a vortex breaker is significantly smaller than the actual diameter of the nozzle.