Session: FSI-01-02 Thermal Hydraulic Phenomena with Vessels, Piping and Components-2

Paper Number: 123592

123592 - A Comprehensive Discussion of Sonic Choking in Pipe Systems for Steady, Compressible Flow 

Sonic choking is a phenomenon that occurs in pipe systems which involves the local bulk velocity of the gas/steam reaching the sonic velocity. When this happens the flow capacity of the system reaches a maximum for the given supply conditions. A somewhat similar mechanism occurs for multi-phase flow, but the discussion here will focus on superheated, single-phase gaseous conditions.

Common discussions of sonic choking in the literature are typically overly simplified and neglect to discuss many details important to practicing engineers. This paper will discuss all aspects of sonic choking in steady-state, compressible pipe flow including:

- all the pipe geometric situations and pipe network configurations where sonic choking can occur

- how to determine the pressure drop across a choke point

- multiple sonic choking points in series and/or in parallel

- which sonic choking point controls the flow rate

- how do determine the choked flow rate when there is significant pressure loss and/or heat transfer in the piping upstream of the choke point

- the importance of determining conditions downstream of each choke point and how these conditions can be calculated

- generalizations for real gas behavior, heat transfer, and elevation changes

- evaluation of sonic choking in orifices where the effective choke area changes with flow conditions

The principles discussed in this paper apply to all pipe system behavior including real gas behavior with heat transfer and elevation changes (more relevant for dense/high pressure gases). However, in order to better explain the principles, focus will be given to ideal gases under adiabatic conditions in horizontal pipe systems. This allows closed-form, analytic methods to be used for computational examples while still retaining the important physical principles being explained. Including real gas behavior, heat transfer and elevation changes can be achieved but this requires capable computational software designed to properly consider sonic choking in complicated pipe network systems. While this is beyond the scope of this paper, engineers will be alerted to what to look for when evaluating such software.

In summary, this paper will provide a comprehensive reference to practicing engineers for all possible sonic choking behavior in any generalized, pipe network system with superheated, steady-state, single-phase gas flow.

Presenting Author: Trey Walters Applied Flow Technology

Presenting Author Biography: Trey Walters, P.E., is the Founder and Chairman of Applied Flow Technology in Colorado Springs, Colorado. AFT develops simulation software for fluid transfer systems. At AFT Mr. Walters has developed software in the areas of incompressible and compressible pipe flow, waterhammer, slurry systems, and pump system optimization. He has performed and managed thermal/fluid system consulting projects for numerous industrial applications including power, oil and gas, chemicals and mining. He actively teaches training seminars around the world. Mr. Walters founded AFT in 1993. He has 35 years of experience in thermal/fluid system engineering. He has published 30 papers and articles.

Mr. Walters’ previous experience was with General Dynamics in cryogenic rocket design and Babcock & Wilcox in steam/water equipment design. Mr. Walters holds a BSME (1985) and MSME (1986), both from the University of California, Santa Barbara. He is an ASME Fellow.

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