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1. What is traffic? What are the two categories? Flow rate refers to the amount of fluid that passes through a cross-section of a pipe per unit of time. It is divided into volumetric flow rate and mass flow rate. 2. Flow rate is measured using an orifice plate; why is it reasonable to install the orifice plate in front of the control valve? In the theoretical derivation for measuring flow rate using throttling devices, there are two assumptions: that the fluid flow is continuous, and that the law of conservation of energy applies during the flow process. This tells us that orifice plates cannot be installed in areas where gas and liquid coexist, in order to avoid increased measurement errors. Some fluids (such as liquefied hydrogen), after having their pressure reduced by a control valve, sometimes partially vaporize, resulting in the coexistence of two phases. Therefore, it is reasonable to install the flow orifice plate as close as possible in front of the control valve. 3. What are the requirements for the straight pipe sections upstream and downstream of the orifice plate? For standard orifice plates to operate in a turbulent flow state, it is generally required that there be 10D of straight pipe section upstream of the orifice plate, and 5D of straight pipe section downstream of it. To ensure accurate measurements, it is preferable to have 30–50D of straight pipe section upstream of the orifice plate, especially when there is a pump or control valve ahead of it. 4. What are the requirements for installing orifice plates? (1) The front surface of the throttling element should be perpendicular to the pipeline axis, with a deviation of no more than 1° ； (2) The opening of the throttle element should be concentric with the pipeline ； (3) The gasket used to clamp the throttle element must not protrude into the inner wall of the pipe ； (4) New pipes must have their throttling components installed after “purging” ； (5) There shall be no sudden changes in pipe diameter at the connections of various pipe sections and fittings of the throttling device. 5. What is the function of a throttling device? It is to cause a local reduction in flow velocity, thereby creating a pressure difference. Moreover, the greater the flow rate, the larger the pressure difference generated before and after the throttling device; therefore, the flow rate of the fluid can be determined by measuring this pressure difference. 6. What are the five pressure tapping methods for orifice plates? 1) Corner pressure extraction method 2) Flange pressure extraction method 3) Theoretical pressure extraction method 4) Radial distance pressure extraction method 5) Pipe connection pressure extraction method