toabhijeet
Post above is very general and has more unsaid than said. I am going to make some assumptions and give some general information.
Assumption: Tank with bottom or lower side drain; feeds pump or some other vessel. Vortex forms in liquid during drain if there is insufficient liquid level above the discharge nozzle. Minimum submergence can be calculated from the following:
[blue] S = d + 2.3 * {(4/(pi*9.81^.5))*(Q/(s^1.5))}[/blue]
d = discharge nozzle diameter, m
Q = discharge flowrate, m3/s
Minimum submergence is the level of fluid at which vortices do not form under the vessel conditions. Levels above this do not produce surface vortices. Minimum submergence is a function of nozzle diameter and flowrate. For liquid levels less than the minimum submergence where surface vortices can form, the following have been observed:
1. The greater the exit velocity, the larger the vortices.
2. The less the discharge submergence, the larger the vortices.
Vortex formation at the free surface in a tank is important because gas can be entrained in the vortex. If a pump is removing liquid from the tank, the pump can become vapor locked. Similarly, gas entrainment by vortices may put gas where gas is unwanted or dangerous.
Submergence is not a very good tool to control vortex formation. In a working tank the level may move considerably with time and enter zones where vortices can form. Vortex breakers are used to prevent gas entrained by vortices from exiting the discharge nozzle. These devices are constructed to break the vortex stream lines above the discharge nozzle. Vortex breakers may be grids, radial vane, or flat plate devices installed at the nozzle. Both both and side nozzles can and should be equipped with vortex nozzles.
You asked about designing such a nozzle. I have not come across anything that describes an empirical method to design vortex breakers. But we can do a thought exercise to check their impact on the application. Vortex breakers can impact the operation of a pump connected to the discharge nozzle. The NPSHA available for the pump may be diminished but the decrease is likely to be small.
In the NPSHA calculation the head losses through the suction line are calculated. There is a contraction from the tank diameter to the nozzle diameter. Compared to the tank without a vortex breaker, the area of the discharge nozzle is decreased by the cross sectional area of the vortex breaker elements. This is likely a very small change. Proper design and selection of the pump will likely make this difference unimportant.
I have offered some very general comments about a very open question.
Contained within is a description of pump troubleshhoting.....one of the things to look for is :
"Vortex breakers not accounted for in nozzle losses. Pressure drop caused by vortex breakers rarely is included in calculations; these losses are a significant source of NPSH problems"
??????
Personally, I would simply double the entrance/exit losses at the tank nozzle...
I typically neglect vortex breakers as well, though as a process designer I leave a substantial safety factor between NPSH available and NPSH required.
I'm hypothesizing that you could get an estimate by calculating entrance losses for the hydraulic diameter rather than the nozzle diameter.
bchoate - in your equation, what is the lower case s (raised to the 1.5 power)? Can you share with us where this equation comes from, what it's derivation is or what the constants represent? Do you have an equivalent one for Imperial units? Not bustin you - just trying to understand... Thanks!
There is no way to calculate the head loss through a vortex breaker. The head loss is basically velocity head. It will depend on the pipe size and the dimensions of the vortex breaker. There are no standard dimensions of vortex breakers.
A reasonable assumption for the head loss would probably be the height of water over the outlet that is required to prevent the formation of a vortex. This can be obtained from the curve on the link:
