It's that time of year again. I've been on the verge of a mental breakdown for two weeks. I'm mentally and physically exhausted but I just need to make it through tomorrow so just trying to smile through the struggle :)
Hi all, I have a strange problem I am working on and require some guidance. Say you have a ball and you want to pump it to a certain diameter. From my understanding, you would do this by using the ideal gas law, but since it is just a ratio between the initial and final values, the constants will cancel out, leaving us with Boyle's law: P1V1 = P2V2. We can therefore assume the ball at P1 = 1 atm has a radius of R1 and we know the radius of the ball at P2 is R2, allowing us to solve for P2.
However, say you were to now pump the ball up with an incompressible fluid. The ideal gas law no longer applies and I don't think you can use pascal's law P = F/A or hydrostatic pressure P = rou*g*h. What equations are you able to use to relate the pressure and volume of the ball?
I'm asked to calculate the shear stress on a free surface of flowing water, the shear stress according to the equation equals zero on the free surface, the HW is asking if this makes sense? i dont know if zero makes sense and if so then why?
the question is simple water flowing horizontally on a wall from one side only
First off, I apologize if my assumption of pressure occurring due to particles pushing on surfaces as they bounce off them is just a highschool approximation. But I don't think I've seen any other model of pressure.
It seems that if particles create pressure by bouncing off the wall, then to get double the pressure you'd need them to bounce with double the force. So you'd need either twice as many bouncing particles, or make them bounce twice as fast- which would mean increasing the temperature since that dictates the average speed of the particles. And in an ideal gas, the math checks out with PV=nRT.
But it doesn't seem to make any sense for a liquid. Liquids are (close to) incompressible, so if I use a pump to raise the pressure of a tank of water from 2 bar to 4 bar, the volume increases by only a tiny fraction-nowhere near half. But the temperature also is not going to increase. Yet, the tank's walls are experiencing twice as much force from the bouncing molecules as before. So where is the new force coming from?
(I originally put this on /r/askscience but they removed it for being too open-ended. Is it that complex a matter?)
Hi all,
I am looking to simulate an interesting scenario where solid melts into a liquid and the density of the liquid is much smaller than the solid so the fluid now takes up a greater space. Furthermore, a compressible gas is above this liquid in a closed container and is being compressed by this fluid.
Maybe I don't know where to start, but here are the multi-phase solvers in OpenFOAM: https://www.openfoam.com/documentation/guides/latest/api/group__grpMultiphaseSolvers.html
I could do without the compressible gas and simulate the liquid expansion maybe with a dynamic mesh if that is more possible. I'd appreciate any thoughts or guidance you guys have.
What are the best yt channel(s) that you have found for incompressible fluids? Plz help!!
Hey all.
Does anybody know of a good source of learning material for compressible and incompressible fluid flow systems? Figured I'd take the opportunity while quarantined and teleworking to do some Independent learning.
Edit: just to clarify, I'm looking for sources that teach you the specifics of system components. Like all MEs, I got the theory down from school. But school doesn't teach you about the different types of valves, compressors, motors, pumps, and what to keep in mind when you are designing a system. Basically I'm looking for practical knowledge for liquid and gas flow system design.
I know that a fluid is a substance that constantly deforms, but I was wondering if incompressibility somehow changes this. If they do in fact deform, what is the reason behind it? Is there shear stress in incompressible flow?
Hey guys,
i was wondering if axial/radial pump would be able to build up pressure when the fluid is inviscid. Forces can be transfered to the fluid by either pressure or shear. How is that in pumps? When I cant transfer a shear force to the fluid, can the rotor still build up pressure?
I need help to get to the first equality given an incompressible fluid.
At the end of my try (written in black) I can identify the Laplacian from the div(grad(v)) but I can't get rid of the other term.
Am I doing something wrong?
By the way, I'm terrible with this kind of notation so it will be very apreciated if you could show me how to do it with indices.
Thanks! :)
https://preview.redd.it/r6zuykfx3vj41.jpg?width=1169&format=pjpg&auto=webp&s=4158baa1c6b1629d2d17afae137f180ae458292f
Problem Solution given in book (Sorry I'm unable to upload images from my phone for some reason).
I don't quite understand how they've written the pressure of point A as P(A) + P0 while applying Bernoulli's equation. The rest of the solution is clear to me but this part isn't. Thanks!
Hi, I'm a student, but not an engineering student, so I know this is a full rookie question, but if it's it's a homework question, it's not my homework question. I want to understand something that I think is probably pretty simple.
I'm interested in understanding the amount of work the heart is doing in various states, if I can measure the pressure drop through the circulatory system, and volume and mass of the flow. I could take a stab at viscosity, but would stick with the values that can be measured.
I'd like to know, what formula and theories should I learn about, that don't need any information about any of the physical qualities of the circuit, except that there is net zero change in height and momentum.
is it as simple as saying :
i have x volume per second m^3 / s
i have y pressure change kg / m s ^ 2
x * y = kg m^2 / s ^ 3 = watts?
thanks
EDIT:
The other detail is that as I am really looking at the heart, for the level of precision I'm after, velocity might not matter too much.
At the moment the aortic valve opens most of the pressurising has already happened while the blood was static in the left ventricle.
hi everyone. im not an engineer or a physicist but i have been working on a fun project and decided it would be even more fun to understand the physics of it rather than just putting all the pieces together.
I basically will have a syringe that will be used to displace fluid from in the syringe to the barrel . so say it is a pipe that starts out as a cylinder of constant diameter than attaches to a barrel of smaller diameter. i wish to push the fluid through and find out the velocity of the fluid coming out. this is pretty straightforward with bernoulli and mass flow stuff.
but what i really wish to do is have a piston located at the beginning of the barrel and push the plunger of the piston at a non steady velocity (by a compressed spring) and find out the momentum and energy imparted to the piston in the barrel. I d like to eventually find out the length of the barrel in which the piston is experiencing work by the fluid being shoved against it.
can you guys help me figure this out? i've been rattling around with bernoulli, transient flow, reynolds displacement, pouiseuille and just having a hard time finding out how to get my answer. it sounds so straightforward but im having a really hard time.
incase you were wondering, it's for the mechanics of a nerf toy i want to make. i understand room temp air is compressible but i wish to get an idea of this all by assuming incompressible fluid.
edit: here is a quick drawing of what i mean.
https://imgur.com/gallery/jvOA5
so piston 1 is driven by a spring of spring constant k and pushes the fluid in the fluid chamber against piston 2 in the barrel. assuming incompressible fluid and no friction, how can i find out the momentum and energy imparted to piston 2 and what length of the barrel. i understand this will have to do with the time the spring takes to de compress as well and im ready to go through the math and physics of it.
I'm more curious about what physically happens to a fluid, not the mathematical part of it (pressure increases etc. etc.)
Considering the massive amount of space in between atoms, and the ability of fluid to move around, how it is possible that it cannot be compressed? What happens when water falls into a black hole?
Hey everyone! I'm working on the conservation of momentum in fluids. This exercise requires me to extrapolate the value of the flowrate in an horizontal bend, taking into account a variation of entrance/exit sections, the variation in pressure at those sections which results in a friction for the fluid and the effect of an external force that keeps the curved tube in place.
I only have a partial solution for this problem: the flowrate must be 0.2 cubic meters per second.
Now, i'm applying the equation for the conservation of linear momentum, but i end up with a dependency of the flowrate by the value of the friction, whereas i should be able to calculate the flowrate exact value from the data i am given since i need to calculate the vertical external force (and i need to know the value of the friction).
Here is the calculations i've done so far.
Regarding friction: i don't know what is the orientation of R, so in this first step i'm only taking into account its horizontal component R*x*
Can you see what am i doing wrong? Living perhaps? :D
Thank you!
What will happened if incompressible fluid is used in a compressor? And what will happened if compressible fluid is used in a pump?
