Pressure reducing orifice plates

AI Thread Summary
To solve the problem of two pressure reducing orifice plates in series with seawater, it is essential to determine the flowrate and pressure after the orifice plates, despite not knowing these values initially. The input pressure is 9 bar, and the system includes an oil cooler with specific flow requirements. The orifice plates are designed to drop pressure, and each should ideally reduce the remaining pressure equally. Calculating the resultant flowrate and pressure drop when deviating from the design supply pressure can be complex, as it involves iterative equations dependent on velocity and Reynolds number. Resources for orifice plate calculations can provide guidance, but understanding the relationship between pressure and flow in this context is crucial.
clint84
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Hi,

I would like to know how would i be able to solve a problem involving two (2) pressure reducing orifice plates in series with seawater as medium.

I know the orifice diameters, the supply pressure, but i don't know the overall flowrate, and pressure after the orifice plates.

The Ship's firemain which is the source of pressure = 9 bar, has a branch which is connected to an
Oil cooler downstream. Downstream from the oil cooler the pipe discharge into the sea (3m below waterline). The total length of branch pipe is 10m and the supply point is 5 m above the discharge point, with the discharge point being 3 m below waterline.

If I know the pressure but don't know the pressure drops or flowrate, is it possible to solve for the flowrate and pressure after the multiple orifice plates by hand?

I'm guessing this would be an iterative equation because the pressure drop over the orifice plates will be dependent on velocity - which i don't know, and K, which is dependent on Reynold's number and also related to velocity. Is there a method to solving this problem?

The only standards i find are on flowrate measuring orifice plates which are not the same as pressure reducing orifices.

Any help would be much appreciated

Cheers

Clint
 
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The oil cooler will require a minimum flow and so you must design for that, with a safety margin.
You know your input pressure, outlet head, pipe sizes and the pressure drop across the oil cooler at that design flow.
The two orifice plates will have to each drop half the remaining pressure.
 
I already know the minimum flow into the oil cooler, but what if i wanted to calculate/estimate the resultant flowrate from reducing supply pressure from 9 bar down to 6, 4, and 2, keeping orifice plate dimensions constant?

The orifice plates in series at the moment are designed for a specific supply pressure and design flowrate into oil cooler. I want to know how the flowrate and pressure drop over the orifices will change if i deviate from the design supply pressure, i.e. supply pressure is reduced significantly
 

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