Print this page Compressible Flow Modeling in a Constant Area Duct
Neil Hicks, P.E.
Course Outline
This two hour online course reviews the fundamentals of adiabatic flow with friction, and then derives an algorithm for predicting pressure, temperature, density, velocity, and Mach number in a constant area duct at any point along the duct's length. It is important to understand gas flow behavior were pressure and temperature changes due to friction will affect gas density, velocity, and ultimately mass flow rate control. Designing a gas flowing system to supply a constant mass flow rate using sonically flow controlling devices and providing end item interface pressure depends on accurately predicting static condition either at the inlet or outlet of a pipe or duct. This is specifically true for systems that require high mass flow rates. This course will enable the designer to design gas flow systems with the proper inside diameters, normal operating pressures, and constant mass flow rate for specified system requirements.
This course includes
a multiple-choice quiz at the end, which is designed to enhance the understanding
of the course materials.
At the conclusion of this course, the student will:
- Understand how pressure and temperature changes due to frictional losses of gases flowing through a constant area duct affect gas density, gas velocity, and mass flow rate;
- Derive an algorithm of equations to predict pressure, temperature, density, velocity, and the Mach number of a gas flow at any point of a constant area duct; and
- Use that algorithm
in a spread sheet or program to design or analyize a gas flowing system with
the proper duct sizing so as to prevent FANNO flow choking at the end of the
duct
This course is intended for mechanical engineers, aeronautical engineers, and technically interested individuals.
Benefit to the Audience
This course will enable the reader to design a gas flow system with the proper inside diameters, normal operating pressures, and constant mass flow rate for specified system requirements.
Course Introduction
Designing or modeling
controlled gas mass flow rate systems requires proper pipe geometry to achieve
a specific end item interface pressure. Using adiabatic flow with friction in
a constant-area duct is one method for predicting pressure and temperature changes
of a gas flow stream in a long insulated duct or a short uninsulated high gas
velocity application where heat transfer from the surroundings to the flow stream
is negligible. In addition, this technique enables the engineer to predict the
sonic point (choke point) of the gas, and design the specific duct lengths with
the proper diameter to ensure that choke point know as L* is located downstream
of the duct outlet.
Course Content
The course content is in Compressible Flow Modeling in a Constant Area Duct (PDF File). You need to open or download any of these documents to study this course.
Course Summary
Compressible flow
gases are subject to density changes based on pressure and temperature changes.
In a constant area duct were the mass flow rate of the gas is constant, pressure,
temperature, and density changes will increase or decrease gas velocity. If
the gas velocity entering a duct is traveling at a velocity less than mach 1,
the pressure, temperature, and density will decrease to a point were the gas
velocity becomes equal to mach 1. If this occurs at a point inside the duct,
the flow will become sonic at the outlet and take control of the total mass
flow rate. Once this occurs, the upstream flow controlling device (valve, orifice,
venturi, …… etc) that was intended to control mass flow rate may not have control
of the total flow rate. This is known as Fanno choking. This course is designed
to aid engineers in avoiding Fanno choking by building an algorithm to designed
constant area duct geometry so as to prevent Fanno choking by ensuring gas velocities
remain below the speed of sound.
Quiz
Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.
DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.
