Flow is the general movement of fluids. Although this seems like nonsense, many basic concepts sound like nonsense.
There are two major factors to consider in the law of fluid flow: flow rate and flowvelocity. Let’s look at each separately.
1. Flow rate
Flow rate refers to the amount of fluid flowing through a certain cross-sectional area per unit time. This quantity can be measured by volume (volume flow) or by mass (mass flow).
We usually say that the flow rate is generally a volume flow rate, and the unit is GPM (gallon per minute) or LPM (liter per minute). The conversion relationship between them is as follows, just remember:
1 gallon (US) = 3.785 411 784 liters
1 gallon (UK) = 4.546 091 88 liters
The flowmeter in Fig. 1 is measured by the above two unit systems.
Figure 1
2. Flow velocity
Velocity refers to the distance a fluid flows in a unit of time.
Flow velocity is not a directly measurable quantity, we usually calculate it indirectly using the following formula:
Flow velocity V = (flow Q) ÷ (Cross-sectional area A)
In other words, the flow velocity depends on the flow rate Q and the size of the cross-sectional area A.
As shown in Figure 2, if we increase or decrease the outlet flow of the pump, but the diameter of the outlet pipe does not change, then the flow rate will change.
which is:
Reduce the flow rate and slow the flow velocity;
Increase the flow rate and accelerate the flow velocity.
Figure 2
Similarly, as shown in Figure 3, if we keep the outlet flow of the pump unchanged and only increase or decrease the diameter of the outlet pipe, the flow rate will also change.
which is:
Reduce the pipe diameter and speed up the flow rate;
Increasing the pipe diameter slows down the flow rate.
Figure 3
Of course, the increase in flow rate will cause the tube to heat up, we all know that this is caused by friction, as shown in Figure 4.
Figure 4
However, how friction is generated, perhaps Figure 5 will give us some inspiration.
Figure 5
Figure 5 mainly expresses that the collision between the fluid molecules and the inner wall of the tube causes the pressure energy and kinetic energy of the fluid to be converted into heat energy and emitted to the atmosphere.
Of course, this is just a schematic diagram, not very accurate.
That’s all for today.
