Is flow and speed the same thing? Ask the unit.

Flow? It refers to the amount of fluid passing through the effective cross section of closed pipeline or open channel in unit time, also known as instantaneous flow. When the amount of fluid is expressed by volume, it is called volume flow; When the amount of fluid is expressed by mass, it is called mass flow. The volume of fluid flowing through a section of pipeline in unit time is called the volume flow of the section. Referred to as flow, expressed by Q.

Flow unit: cubic meters per second (m & amp； # 179; /s)

The equation of flow is: Q=Sv= constant. (s is the cross-sectional area and v is the water flow velocity)

When the incompressible fluid flows stably, the flow through each section of the same pipeline is constant.

Speed? Refers to the distance of fluid flow per unit time.

Flow rate units: m/s and m/h.

Measurement method:

According to different situations and requirements, different methods and instruments are used for measurement. Commonly used methods and instruments are as follows.

① Pitot: it was first created by French engineer H. Pitot in 1732, and it is still a common instrument for measuring the time-average speed in the laboratory. The total pressure hole (M) at the front end and the static pressure hole (N) at the side are respectively connected with the two ends of a differential pressure gauge (see figure) through a round-headed double-layer casing, and the difference between the total pressure (p0=P∞+ρu2/2) and the static pressure (P∞) is measured, that is, the weighting. According to Bernoulli equation, the point velocity is:

Among them:

ρ is the density of liquid;

C is the correction factor and must be determined by the passing rate.

(2) Paddle (cup) current meter: There are many forms, which can be used in the field and laboratory, and all of them have a set of rotatable blades. There is a fixed relationship between the number of revolutions of blades after being impacted by water flow and the flow rate, which can be obtained by measurement. Use appropriate devices to convert the number of revolutions into electrical signals for recording and display. ③ Laser velocimeter: The biggest advantage is that it has no interference to the measured flow field. ④ Hot-wire (membrane) current meter: It can measure the random change process of instantaneous velocity, pulsating velocity and turbulent velocity. ⑤ Photography: Calculate the velocity according to the exposure time and the trace length of the bright spot.