The relationship between gas pressure and flow rate
Thread Content
In practice, it sometimes seems that the higher the pressure, the higher the flow rate, but other times the flow rate increases even when the pressure decreases. I would appreciate some advice from those who are more experienced
In a closed system, with no external work input, the energy remains constant; if potential energy stays unchanged, an increase in kinetic energy leads to a decrease in static pressure energy
A high flow rate doesn’t necessarily mean high pressure; that’s just your perception! Why does high traffic necessarily mean high pressure? Sometimes when the pressure decreases, it might be because the resistance behind is reduced; with less resistance, the flow rate increases! It might not be appropriate to use an example: when pumping a fluid with a pump, if the outlet valve of the centrifugal pump is closed, what is the pressure at the pump’s outlet, and what is the flow rate? The traffic is the lowest. Once the outlet valve is opened, does the pressure decrease? And as a result, does the flow rate increase? The example might not be appropriate!
Generally, under certain piping conditions, flow rate is directly proportional to the pressure difference
For a pipe of a certain diameter, within its capacity range, increasing the pressure difference will result in an increase in flow rate; however, once the flow rate reaches a certain value, increasing the pressure difference further will not cause any additional increase in flow rate. So it’s not necessarily the case that higher pressure always results in a higher flow rate; rather, it is related to the pressure difference within a certain range of flow rates.
In the first case, an increase in pressure leads to an increase in flow rate. For example: if the liquefied gas control valve remains stationary, increasing the pressure before the valve will result in an increase in flow rate. In the second case, as pressure increases, flow decreases. For example: with all other operating conditions unchanged, reducing the control valve will increase the pressure before the valve, but the flow rate will decrease.
I also want to learn about the relationship between gas pressure and flow rate
Gas pressure has basically no relation to its flow rate; the idea that higher pressure means a higher flow rate is completely wrong. To give a simple example: once a high-pressure gas cylinder is filled with high-pressure gas, the pressure can reach 15 MPa, but the flow rate will be zero. Another example: when there is wind, the air flow between two buildings can sometimes be very high, but does atmospheric pressure change significantly? Everyone should understand a basic principle: the flow rate of a gas is proportional to the cross-sectional area through which the gas flows and to its flow velocity. The flow velocity, in turn, is proportional to the square root of the pressure difference across the channel through which the gas flows, and it is independent of the static pressure of the gas.
If we apply the equation of effort, it becomes clear: resistance is proportional to the square of velocity. An increase in pressure means an increase in resistance; once the velocity reaches a certain level, an increase in pressure does not increase the velocity any further, as all the energy is consumed by the resistance. As for the poster’s claim about reduced pressure and increased speed, it might be an illusion. With all other conditions of the piping system remaining unchanged, depressurization will not increase the speed. For reference
When the pipe diameter is the same, the gas flow rate is related to the pressure difference in the channel, and not directly to the pressure itself; the original poster is mistaken@@
This is my personal opinion for reference only.