What is the principle of throttling?
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Fluid mechanics often discusses the \"throttling principle\": when a fluid passes through a flow-restricting element, throttling occurs. However, according to the continuity equation, the flow rate of the fluid is the same at any cross-section within the pipe. So how should we understand the term “throttling”? :lol
It’s not the flow rate that’s being reduced, it’s the velocity of the flow: lol
Throttling means changing the flow velocity of the fluid.....
This question from the original poster has also troubled me for a long time; it’s indeed quite complicated. My understanding is that throttling definitely means reducing the flow rate; otherwise, why would the flow rate behind the valve decrease when the valve is closed? The flow rate decreases after throttling; according to the continuity equation, the flow rate before the throttling element also decreases (due to the reduced flow velocity), and it equals the flow rate after throttling.
Based on the theory that the flow rate remains constant while the flow volume changes, it becomes easier to understand. So, if the flow rate changes, will the pressure and temperature also change accordingly?
Rate refers to both flow volume and flow velocity. Otherwise, how can FV control the flow?
A brief discussion on the differences between throttle orifice plates and flow-limiting orifice plates. I. Throttle orifice plate: The orifice plate throttling device is a primary component in differential pressure flow measurement systems; it consists of an orifice plate, pressure sensing elements, straight sections before and after the orifice plate, as well as connection flanges. Used in conjunction with differential pressure transmitters, it enables the measurement of the flow rate of various single-phase, homogeneous liquids, gases, and vapors in pipes. Manufacturing standards: GB2624-93, ISO5167-91. Measurement principle: When the fluid filling the pipeline flows through the orifice plate, a local contraction occurs, causing the flow to concentrate and the flow velocity to increase, while the static pressure decreases. As a result, a static pressure difference is created before and after the orifice plate; this pressure difference has a certain functional relationship with the flow rate – the greater the flow rate, the greater the pressure difference. The differential pressure signal is transmitted to the differential pressure transmitter via a pressure guiding tube, where it is converted into a 4–20 mA.DC standard signal; through the flow display instrument, the instantaneous and cumulative flow rate in the pipeline is shown. There are three common pressure tapping methods for throttle orifice plate devices: corner tapping (annular chamber, drilled hole) and flange tapping. II. Flow control orifice plate: The flow control orifice plate is installed in pipes to limit the flow rate of the fluid or reduce its pressure. Throttle orifice plates are used in the following areas: 1. When the process material requires pressure reduction and low precision is sufficient. 2. When a large pressure drop is required upstream and downstream of a valve in a pipeline, in order to reduce fluid erosion on the valve, an orifice plate can be connected in series upstream of the valve, provided that throttling through the orifice plate does not result in the formation of a gas phase. 3. Places where the fluid needs to flow in small quantities and continuously, such as the flushing pipes of pumps, the bypass pipes of hot standby pumps (low-flow protection pipes), analysis sampling pipes, etc. 4. Areas where pressure reduction is needed to reduce noise or wear, such as vent systems.