- #1
threy
- 21
- 0
Fluid flows faster in a narrow tube which results in low pressure and high pressure in a large tube?
Why does fluid flow faster in a narrow tube?
- Thread starter threy
- Start date
-
- Tags
- Flow Fluid Fluid flow Tube
In summary, when fluid flows from a large pipe to a narrow pipe, the fluid must flow faster in the narrow pipe to maintain the same flow rate. This is due to the conservation of energy and Bernoulli's equation, which states that as the fluid's speed increases, its pressure decreases. This principle applies to a single tube with variations in width, but not necessarily to multiple separate tubes. The flow rate must remain constant for incompressible fluids, resulting in a change in velocity when the cross-sectional area changes.
- #2
mfb
Mentor
- 37,141
- 13,983
Some context would be helpful.
If you have a fluid going from a large pipe to a narrow pipe (or vice versa), the fluid has to flow quicker in the narrow pipe to get the same flow rate ([strike]volume[/strike] mass per time).
If you have a fluid going from a large pipe to a narrow pipe (or vice versa), the fluid has to flow quicker in the narrow pipe to get the same flow rate ([strike]volume[/strike] mass per time).
Last edited:
- #3
gauss44
- 49
- 0
mfb said:
This is correct. And I'll add that there is a distinction to be made between this (a single tube with variations in width), and multiple (different) tubes.
In the later scenario: If you have 2 separate tubes which are not connected, there is no guarantee that water will flow faster through a narrower tube.
- #4
- 3,447
- 1,236
mfb said:
More correctly, the mass flow rate must be maintained (continuity). Volumetric flow rate only works here for an incompressible fluid.
- #5
tiny-tim
Science Advisor
Homework Helper
- 25,839
- 258
hi threy! 
pressure is not only force per area, it is also energy per volume
(1 Pa = 1 J/m3)
therefore conservation of energy requires that if the kinetic energy increases (ie if the speed increases), then the pressure must decrease
(mathematically, this is Bernoulli's equation … P + 1/2ρv2 + ρgh = constant along any streamline)
threy said:
pressure is not only force per area, it is also energy per volume
(1 Pa = 1 J/m3)
therefore conservation of energy requires that if the kinetic energy increases (ie if the speed increases), then the pressure must decrease
(mathematically, this is Bernoulli's equation … P + 1/2ρv2 + ρgh = constant along any streamline)
- #6
- 12,175
- 182
Or put another way: the fluid speeds up when it enters a narrower portion of the tube. Since it speeds up, it has an acceleration, therefore a net force, in the direction it is moving. This net force must result from a higher pressure behind the fluid (in the larger tube portion) and a smaller pressure ahead of the fluid (in the smaller portion).
- #7
john bastian
- 1
- 2
but why the fluid go faster in narrow tube than a thicker tube?gauss44 said:
- #8
CWatters
Science Advisor
Homework Helper
Gold Member
- 10,544
- 2,323
Perhaps it's this simple...
If the fluid is incompressible the flow rate (in cubic meters per second) must be the same at all points along the pipe. What goes in must come out.
If the cross sectional area (in square meters) changes the velocity (in meters per second) must change to maintain the same flow rate.
If the fluid is incompressible the flow rate (in cubic meters per second) must be the same at all points along the pipe. What goes in must come out.
If the cross sectional area (in square meters) changes the velocity (in meters per second) must change to maintain the same flow rate.
- #9
enorbet
- 481
- 85
There are some really great graphical and mathematical descriptions at http://en.wikipedia.org/wiki/Bernoulli's_principle
- #10
mfb
Mentor
- 37,141
- 13,983
Right.CWatters said:
This thread is from 2013. If there is a new question, please open a new thread.
Related to Why does fluid flow faster in a narrow tube?
1. Why does fluid flow faster in a narrow tube?
Fluid flows faster in a narrow tube due to the principle of continuity, which states that the volume of fluid that enters a section of a tube must be equal to the volume of fluid that exits that section. In a narrow tube, the cross-sectional area is smaller, meaning that the same volume of fluid must pass through a smaller space, resulting in faster flow velocity.
2. How does the diameter of a tube affect fluid flow?
The diameter of a tube has a direct effect on fluid flow. A smaller diameter results in faster flow velocity due to the principle of continuity, as mentioned above. On the other hand, a larger diameter will result in slower flow velocity since the same volume of fluid can pass through a larger space.
3. What is the relationship between pressure and fluid flow in a narrow tube?
In a narrow tube, the pressure decreases as the fluid flows faster. This is due to the Bernoulli's principle, which states that as the velocity of a fluid increases, its pressure decreases. Therefore, the faster flow velocity in a narrow tube results in lower pressure compared to a wider tube.
4. Can fluid flow be increased in a narrow tube by increasing the pressure?
Yes, increasing the pressure can result in faster fluid flow in a narrow tube. This is because a higher pressure will push the fluid with more force, resulting in a higher flow velocity. However, this increase in flow velocity will also result in a decrease in pressure, as explained by the Bernoulli's principle.
5. Are there any other factors that can affect fluid flow in a narrow tube?
Aside from the diameter and pressure, other factors that can affect fluid flow in a narrow tube include the viscosity of the fluid, the length of the tube, and the surface roughness of the tube. Viscous fluids, such as honey, flow slower in narrow tubes compared to less viscous fluids, such as water. Longer tubes also result in slower flow velocity, and a rougher surface can cause turbulence and decrease flow velocity.
Similar threads
-
Other Physics Topics
-
Other Physics Topics
-
Materials and Chemical Engineering
-
Other Physics Topics
-
Other Physics Topics
-
Other Physics Topics
-
Other Physics Topics
-
Mechanical Engineering