22
votes
What is the purpose of these "steps" in rivers?
The 'steps' are called weirs, and they are used for a number of flow control reasons in rivers. In the case of the images you posted, they are probably being used to stabilize the grade (slope) of ...
- 6,306
20
votes
Accepted
What is the purpose of these "steps" in rivers?
The two photos in the post show the same structure: Pulteney Weir, downstream of Pulteney Bridge on the River Avon in Bath. The shot of the "Seine" in Les Miserables was filmed on location in Bath.
...
- 446
5
votes
Can ultrasonic sound pass through solid medium?
Ultrasound partially reflects when it encounters a medium with different acoustic impedance. It behaves like light and obeys Fresnel equations. If the angle of incidence is smaller than the total ...
- 1,045
4
votes
How to determine whether a particular velocity vector will result in a laminar flow?
I am afraid the question you are asking might not even be a valid question.
This is because of the correlation between the Reynolds-Number ($Re$) and the occurrence of turbulence. $Re$ is not a fluid ...
- 1,202
4
votes
Accepted
Ideal funnel design for powders
The problem you have is more complicated than you think. Any industry that deals with the storage and movement of granulated/powdered materials has to deal with this and most have unique solutions.
...
- 9,527
3
votes
Established Patterns and Designs for Measuring Powder by Volume
I suppose you need some kind of powder doser or volumetric feeder
It might work on measuring time. Very easy principle, you need valve (maybe solenoid valve or for some sort of flap door) and timer ...
- 314
3
votes
How to determine whether a particular velocity vector will result in a laminar flow?
You are correct, the Reynolds number is what determines whether a flow is laminar or turbulent. The formula for the Reynolds number is
$$Re = \frac{\rho vL}{\mu}$$
$\rho$ is the density, $v$ is the ...
- 2,799
3
votes
3
votes
Given flow rate of an orifice at one pressure, how do I calculate flow rate for a different pressure?
Here is a reference from RoyMech, see section under "Orifice Flow Meter". The setup has the orifice placed in a pipe.
Below is a similar, perhaps simpler, expression, from Jobson 1955, part ...
- 1,367
2
votes
Accepted
Best way to get rid of turbulent flows?
Assuming you are wanting to minimize turbulence in the region of the pump, you would probably need to use flow straighteners somewhere upstream of the pump. You would have to study the optimal ...
- 493
2
votes
Best way to get rid of turbulent flows?
In wind tunnels usually meshes and/or honeycombs are used to reduce turbulence.
However, to really achieve low turbulence it's probably not enough to add a single component to your facility. I rather ...
- 679
2
votes
Gear pump has backflow and does not stop forced flow
You will probably need to install a check valve (or manual valve) to prevent the backflow, and rebuild the pump heads periodically. Over time, the gears wear down and small gaps form. This both leads ...
- 51
2
votes
Why doesn't steam/water flow backwards from expansion in power plant feedwater pump/boiler?
Google "Rankine cycle". The boiler operates at an elevated pressure (sometimes several atmospheres). But because steam at a given pressure is many times bigger than liquid water at the same pressure,...
- 2,228
2
votes
Pneumatic Can Crusher (Number of holes allowed for crushing plate)
The number isn't as important as total surface area of the holes - it doesn't need to be greater than the can opening for the remaining pressure resistance to be entirely negligible. Decision on the ...
- 6,133
2
votes
Could a water stream be used as a fiber optic sensor and detect when the stream is broken?
As long as you are not sending data, any light input in one end should be detectable with a color filter covered light sensor at the other end. Example: green film for a green led/laser. Light at the ...
- 7,489
2
votes
Accepted
Liquid Level Control System Resistance
I'm an electrical engineer so this problem looks to me like an RC (resistor-capacitor) discharge. In the case of a resistor discharging a capacitor the time constant is given by τ = RC. In your case C ...
- 8,469
2
votes
When designing a carburetor, is the air to fuel ratio calculated or just experimentally adjusted?
Yes.
The range of airflow required is established by the swept volume of the engine and the max rpm. That will then define the pressure drop and venturi needed - which is often controlled by a moving ...
- 14.1k
2
votes
How can I ensure steady flow to all the valves?
One basic way is to adjust the valves, the dry ones fully open and the ones bleeding all the pressure just slightly open, or even restricted permanently by a smaller size bushing just before the valve....
- 21.1k
2
votes
How can I ensure steady flow to all the valves?
The most precise way to control flow is with valves/flow regulator. The main problem is the cost. Although, its a very basic component and its not too costly if you have too many outlets the cost ...
- 22.7k
2
votes
Given flow rate of an orifice at one pressure, how do I calculate flow rate for a different pressure?
If you know the external diameter and orifice diameter, From Wikipedia the orifice plate equation :
$$q_m =\frac{ C_d}{\sqrt{1-\beta^4}}\epsilon\frac{\pi}{4} d^2 \sqrt{2\Delta p \cdot \rho_1} $$
...
- 22.7k
2
votes
Accepted
Given flow rate of an orifice at one pressure, how do I calculate flow rate for a different pressure?
Flow rate is directly proportional to the square root of pressure. So for any given orifice, all else being equal, $\frac{GPM}{\sqrt{PSI}}$ is constant. Technically PSI here is the pressure ...
- 161
1
vote
Accepted
Relative improvement in flow from diameter change with sub-milliimeter tubing
You made a small mistake if we are going to use Poiseuille's law.
$ Q_{final}= Q_{initial}\Delta r^4 \rightarrow \Delta Q =(\frac{r_{final}}{r_{itial}})^4$
Plugging your numbers,
$ Q_{final}=Q_{...
- 21.1k
1
vote
Accepted
Proper Flow Meter Installation
The flow meter needs to be installed such that it is always under pressure (in normal operation). That is it should be after the regulator but before the on/off valve. That way you will get no surge ...
- 308
1
vote
Accepted
How can I confirm nL Volume Measurement for Pump and Sensor Calibration
This is a challenging measurement. In my opinion best done with a very good balance. Fully shielded from thermals and vibration, obviously. Use a small container with small opening diameter to limit ...
- 1,367
1
vote
Cheapest way to measure gas flow (mass)?
By knowing the volume flow rate of a gas , you can also find the mass passing through a cross section area for certain thermodynamic conditions.
- 11
1
vote
Do pressure regulators restrict the mass flow rate?
Your assessment of the situation is correct - the solution is of course to specify a pressure regulator with a large enough orifice that it does not cause you a problem.
Pressure regulators are ...
- 7,684
1
vote
Accepted
Flow control experiment
The Objective of this experiment is by the way to investigate the
linearity and hysteresis of the flow sensor.
The key word here is hysteresis: the output of the sensor at the same flow rate might ...
- 1,806
1
vote
Water loop with a drop output?
Drip irrigation parts cost about five cents a piece. They come in fractional gallons per hour at 25 psi. So pump the water into the tank from the bucket via a drip head, and use a simple float valve ...
- 3,590
1
vote
Water loop with a drop output?
Yes, you definitely can do that.
There are small filler pumps that will automatically kick into power when the water falls below the present level and the floater activates the pump.
So you can have ...
- 21.1k
1
vote
Modeling Water Flow Through Saturated Medium
Saturated flow through sediments is governed by Darcy's Law, which relates the pressure drop across the porous medium to the permeability of the medium to calculate the fluid flow rate. The fluid ...
- 111
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