11 - Measurement of flow velocity and flow rate

Abstract

To clarify fluid phenomena, it is necessary to measure quantities as pressure, flow velocity, and flow rate. This chapter discusses the measurement of flow velocity and flow rate. Fluid includes both gas and liquid. According to the type and condition of the fluid, or if it flows in a pipeline or open channel, various methods of measurement are developed and are of practical use. The chapter further discusses pitot tubes that are used to measure the flow in a large-diameter pipe. In this case, the cross-section of the pipe is divided into ring-like equal areas, and the flow velocity at the center of the area of every ring is measured. The mean flow velocity is obtained from their mean value, and the total flow rate is obtained from the product of the mean velocity and the section area. The chapter also discusses the hot-wire anemometer. If a heated fine wire is placed in a flow, the temperature of the hot wire changes according to the velocity of the fluid, thereby changing its electrical resistance. A meter which measures the flow by utilizing this change in resistance is called a hot-wire anemometer.