Why is choked flow bad

How a piping system model can recognize potentially hazardous scenarios and control valves. Engineered Software, Inc. When designing and installing a piping system for liquid service in industrial or commercial applications, the location and type of valve selected for process control plays a major role in whether the valve will operate smoothly or if it may experience cavitation or choked flow.

This is the point of highest velocity and lowest pressure Bernoulli principle in action. Image 1. Severe pitting damage from cavitation resulted in a pinhole leak on the valve body of a V-notch ball valve used to regulate the cooling water flow to aluminum casting molds.

Image courtesy of the author. Image 2. Graph of flow rate versus the square root of the pressure drop across the valve Image courtesy of Crane Technical Paper TP Image 3. Pressure profile for various types of valves for a given pressure drop. Image 4. Control valve at 30 feet elevation. Image 5. This heat exchanger and control valve is located at an elevation of 45 feet. Choked flow is indicated.

Image 6. Colder water does not result in choked flow, even with the valve at the higher elevation. Image 7. A different control valve with a lower FL selected for the original system valve at lower elevation with F results in choked flow.

To read more Pump System Improvement columns, click here. Issue March Related Articles Pumps. Amine scrubbing is one way to remove flue gas from these applications. Factors to consider to avoid risk and increase reliability in your power generation facility. The type of water will influence the material selection and service life. Columnist Lev Nelik discusses pump selection in part one of this two-part column.

An in-depth look into rotating equipment—and industrial pumps in particular—with the aim to empower users to maximize efficiency. Sponsored by Voith. Click Here to join Eng-Tips and talk with other members! Already a Member? Join your peers on the Internet's largest technical engineering professional community.

It's easy to join and it's free. Register now while it's still free! Already a member? Close this window and log in. Join Us Close. Are you an Engineering professional? Join Eng-Tips Forums! Join Us! By joining you are opting in to receive e-mail. Promoting, selling, recruiting, coursework and thesis posting is forbidden. Students Click Here. Related Projects. When dealing with liquid sizing for a control valve, what is really meant by choked flow? Sorry if this sounds like a dumb question The vapour pressure is 0.

So that tells me that if I drop roughly psi from my inlet pressure, I will flash and the system will recover to 80 psig and I will cavitate. So why is the max pressure drop for choked flow only about Doesn't choked mean the formation of vapour bubbles? This is substantially less than psi. Is this strictly based on turbulence velocities that are higher than bulk flow velocities such that local low pressure areas can form? TIA jrjones. For a valve in liquid service choked flow refers to the situation where the pressure at vena contrator drops below the vapour pressure of the liquid.

Best regards Morten. So, if you decrease the downstream pressure, the mass flow will not increase. This is why you have a critical pressure higher than the vapour pressure. Did it make any sense? BigInch Petroleum 17 Apr 07 tiny correction. The mass flow will increase if the differential pressure is increased by increasing the upstream pressure with all other conditions remaining fixed.

This is a quote from Fishers web page: "Aside from the possibility of physical equipment damage due to flashing or cavitation, formation of vapor bubbles in the liquid flowstream causes a crowding condition at the vena contracta which tends to limit flow through the valve. How do I stop choked flow? Why is choked flow bad? What is the condition at throat in CD nozzle?

What is critical flow condition? What is choking in Fanno flow? What is pressure drop ratio? What is the critical pressure ratio? Is mass flow rate constant in a nozzle? How does a flow control valve work? How do you prevent valve cavitation? What happens if the downstream pressure continues to decrease? What is critical flow in control valve? What is critical pressure for control valve? What is the relationship between pressure and mass flow rate?

Why do we need mass flow rate? How do you find volumetric flow rate? Flow rate formulas. This website uses cookies to ensure you get the best experience on our website. More info.