ABSTRACT
For completeness, in this chapter we present a brief introduction to the thermodynamics of flow of compressible fluids. When a gas flows at steady state in a horizontal adiabatic duct of constant cross section A, the initial velocity at the entrance of the duct determines the kind of flow that the gas will develop. The initial velocity can be subsonic, sonic, or supersonic, depending on whether it is lower than, equal to, or higher than the velocity of propagation of sound in the gas at the prevailing temperature. From basic physics, the velocity of sound is given by https://www.w3.org/1998/Math/MathML"> υ ˙ s = γ R T M https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315399065/5df30985-80c1-4e11-9533-10c20ed2604c/content/equ23_01.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/> where γ is the ratio of the constant pressure heat capacity to the constant volume heat capacity of the gas, R is the universal gas constant, T is the absolute temperature, and M is the molecular weight of the gas. The Mach number, Ma, is defined as the ratio of the linear velocity of the gas in the duct to the velocity of sound: https://www.w3.org/1998/Math/MathML"> M a = υ ˙ υ ˙ s https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9781315399065/5df30985-80c1-4e11-9533-10c20ed2604c/content/un23_e001.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/>
