Stagnation Pressure
 The stagnation pressure at a point in a fluid flow is the pressure which could result if the fluid were brought to rest isentropically.
 The word isentropically implies the sense that the entire kinetic energy of a fluid particle is utilized to increase its pressure only. This is possible only in a reversible adiabatic process known as isentropic process.
Fig 16.2 Measurement of Stagnation Pressure
 Let us consider the flow of fluid through a closed passage (Fig. 16.2). At Sec. ll let the velocity and static pressure of the fluid be uniform. Consider a point A on that section just in front of which a right angled tube with one end facing the ﬂow and the other end closed is placed.
 When equilibrium is attained, the fluid in the tube will be at rest, and the pressure at any point in the tube including the point B will be more than that at A where the flow velocity exists.
 By the application of Bernoulli’s equation between the points B and A, in consideration of the flow to be inviscid and incompressible, we have,
 (16.6) 
where p and V are the pressure and velocity respectively at the point A at Sec. II, and p_{0} is the pressure at B which, according to the definition, refers to the stagnation pressure at point A.
 It is found from Eq. (16.6) that the stagnation pressure p_{0} consists of two terms, the static pressure, p and the term ρV^{2}/2 which is known as dynamic pressure. Therefore Eq. (16.6) can be written for a better understanding as
 (16.7) 
 Therefore, it appears from Eq.(16.7), that from a measurement of both static and stagnation pressure in a flowing fluid, the velocity of flow can be determined.
 But it is difficult to measure the stagnation pressure in practice for a real fluid due to friction. The pressure in the stagnation tube indicated by any pressure measuring device (Fig. 16.2) will always be less than p_{0}, since a part of the kinetic energy will be converted into intermolecular energy due to fluid friction). This is taken care of by an empirical factor C in determining the velocity from Eq. (16.7) as
 (16.8)

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