The upstream and downstream flow is assumed to be isentropic. For supersonic flow a shock wave forms in front of the Pitot tube, and the pressure and temperature measurements must be compensated. However, at point 2 the fluid is brought to rest and the energy has been converted to pressure energy. The flow velocity can be calculated from the staganation pressure, static pressure and temperature. Consider two points 1 and 2 at the same level in such a way that point 1 is at the inlet of the pitot tube and point 2 is at the outlet.Īt point 1 the pressure is \(P_1\) and the velocity of the stream is \(v_1\). The pitot tube can measure the stagnation pressure head (or total head) using a differential manometer connected between the open end of the pitot tube and the pressure taping which is present at the pipe surface. Assume the coefficient of the pitot tube as 0.98. If the density of air and water are 1.13 kg/m kg/m3, respectively, determine the velocity of air. The manometer shows a difference in head of 5 cm of water. The pressure head may be determined directly by connecting a differential manometer between the Pitot tube and pressure taping at the pipe surface. A pitot static tube is used to measure the velocity of air flowing through a duct.
Since a Pitot tube measures the stagnation pressure head (or the total head) at its dipped end. However, mean velocity will be same across the cross-section. With the help of Pitot static tube, we can find the actual velocity at different points of a cross-section. Pitot static tube is one of the applications of Bernoulli’s Theorem which is valid in regions of steady, incompressible flow where net frictional forces are negligible. By measuring the height of the fluid which has risen in the tube, one can calculate flow velocity. The lower end of the tube is placed in flow such that it faces the upstream direction and the fluid rises in the tube because of change in kinetic energy into pressure energy. The pitot tube is a capillary tube bent at right angle. It works on the principle that if the flow velocity at any point is brought to rest, there will be an increase in pressure at the point because of the conversion of kinetic energy into pressure energy. Pitot tube is a flow-measuring device which is used to measure the flow velocity at any chosen point in the flow-field.