×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Are you an
Engineering professional?
Join Eng-Tips Forums!
• Talk With Other Members
• Be Notified Of Responses
• Keyword Search
Favorite Forums
• Automated Signatures
• Best Of All, It's Free!

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

#### Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

# Does a Restriction Orifice (RO) Actually Limit Flow???

## Does a Restriction Orifice (RO) Actually Limit Flow???

(OP)
I'm not clear on this issue...share your thoughts to enable me clear up this issue..

My thought is this...from the laws of conservation of mass and energy...when a restriction is created on the flow path of a fluid, pressure reduces, velocity increases and density reduces as well so that both mass and energy are conserved. (i.e for compressible flow a simple relation is m1 = m2 ==> rho1.A1.V1 = rho2.A2.V2. Obviously, for a gas at flowing conditions, the Volume or volumetric flow increases, but mass flow rate is conserved.
How then is it popularly said that restriction orifices (ROs) limit flow.?
Does this use of the term "flow" actually mean volumetric flow rate?
In a relief header how does an RO downstream of a BDV for instance limit the peak blowdown rate in order not the exceed the capacity of the vent handling system?

### RE: Does a Restriction Orifice (RO) Actually Limit Flow???

For something like an RO on a blowdown line you often hit critical velocity, i.e. the gas is at sonic velocity.

Even if not critical, ROs result in pressure drops for certain flowrates and inlet / outlet pressures.

Increasing pressure upstream or lowering pressure downstream doesn't / can't change the volumetric flow rate through the orifice, but increasing upstream pressure does increase the mass flow as the density increases.

Yes mass is conserved.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

### RE: Does a Restriction Orifice (RO) Actually Limit Flow???

Showboy, this RO example is a very good illustration of the law of conservation of energy, but it doesn't illustrate anything interesting about the law of conservation of mass. The RO causes the fluid velocity to increase (downstream side). That is, the fluid's kinetic energy is increasing, which means the potential energy (static pressure) must decrease such that the total amount of energy is conserved. This is easily observed, and it's a great illustration of conservation of energy.

The presence of an RO will absolutely result in a reduction in mass flow, as compared to a line that doesn't have an RO. The fact that the mass flowrate on the upstream side of the RO is the same as the mass flow on the downstream side is a obvious and sensible observation, which doesn't illustrate anything of interest relative to the law of conservation of mass. Conservation of mass is illustrated by things like chemical reaction, or combustion.

### RE: Does a Restriction Orifice (RO) Actually Limit Flow???

A RO represents a pressure loss; the sum of the total pressure losses seen in the system will determine the mass flow rate of the system based on the pump curve or whatever is driving flow.

As don explained quite while, a RO will definitely effect the overall mass flow rate of a system.

### RE: Does a Restriction Orifice (RO) Actually Limit Flow???

Showboy,

Read this thread798-51260: Orifice Plate Critical Pressure Ratio and this, for a somewhat thorough understanding of compressible flow through a thin plate orifice.

Good luck,
Latexman

Engineers helping Engineers

### RE: Does a Restriction Orifice (RO) Actually Limit Flow???

@op you forgot the temperature of the fluid. For both a gas and a liquid the fluid is heated when pasning an orifice. For the gas the expansion Will also cool the gas. The constant enthalpy process such as a orifice will cool less than an expander where the enthrophy is (almost) constant. For a liquid it’s always warmer.

#### Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

#### Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

#### Resources

eBook - 10 Reasons to Choose CATIA on the Cloud
To compete in todayâ€™s fast-paced and competitive market, smaller and newer firms need a powerful platform that will enable them to compete with bigger players, without the heavy investments needed in computer hardware, software and personnel. Download Now
White Paper - Smart Manufacturing for Electronics
This white paper describes a transformative approach to electronics manufacturing made possible by the addition of Mentor Graphics to the Siemens family. It describes a completely digitalized strategy that supports both printed circuit board (PCB) and mechanical design and manufacturing, uniting the entire product lifecycle â€“ from idea and production to customers and back. Download Now

Close Box

# Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

• Talk To Other Members
• Notification Of Responses To Questions
• Favorite Forums One Click Access
• Keyword Search Of All Posts, And More...

Register now while it's still free!