Show me a question about stress
Thread Content
When studying the principles of chemical engineering, there was a question like this: as shown in the diagram, the point where the fluid pressure is highest… I thought it should be at position 3-3, since that is the deepest point. However, the correct answer was 2-2. If anyone knows why, please explain it. Thank you
The prerequisite is system flow, with 3-3 and 1-1 representing standard atmospheric pressure; here, 3-3 denotes an open system, not the closed system shown in the diagram. In a closed system, the pressure at 3-3 is the highest. 2-2 seems a bit forced as a maximum value, since the system is dynamic; therefore 2-2 is the maximum, but it’s also possible that 2-2 equals 4-4.
Pay attention to the question: the pressure in a flowing system
As I understand it, there is fluid flow at points 3 and 4; according to Bernoulli’s equation, these two locations have kinetic energy while their potential energy is slightly lower
Agree with the view from the 2nd floor. To compare the pressures at points 2 and 4, it is necessary to determine whether the sum of the pressure head difference and the dynamic pressure head difference between these two points is positive or negative. The conditions given in the problem are not very precise, so it is possible that the values are equal.
I looked up some information online and learned that this question is likely testing Bernoulli’s principle, which is essentially the conservation of mechanical energy in ideal fluids. Under ideal conditions, at any cross-section of the same flow tube, the sum of the kinetic energy, potential energy, and pressure potential energy per unit volume of fluid is a constant. During isochoric flow, the greater the flow velocity, the lower the pressure; therefore, the difference in pressure at points 2 and 4 mentioned in the question can be ignored