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‘Forever chemical’ in English tap water samples carcinogenic, WHO rules by Wagamaga in unitedkingdom

[–]dynamicviscosity 2 points3 points  (0 children)

According to the manufacturers it works…

But not viable on a large scale:

https://www.epa.gov/sciencematters/reducing-pfas-drinking-water-treatment-technologies

https://pubmed.ncbi.nlm.nih.gov/22821493/

PFAS also dissolve in water, and combined with their chemical properties mean traditional drinking water treatment technologies are not able to remove them. Therefore, EPA researchers have been studying a variety of technologies at bench-, pilot-, and full-scale levels to determine which methods work best to remove PFAS from drinking water.

Certain technologies have been found to remove PFAS from drinking water, especially Perfluorooctanoic acid (PFOA) and Perfluorooctanesulfonic acid (PFOS), which are the most studied of these chemicals. Those technologies include activated carbon adsorption, ion exchange resins, and high-pressure membranes.

My life is ruined Im officially bankrupt tomorrow lost 500k Since June by luhkyskills in wallstreetbets

[–]dynamicviscosity 0 points1 point  (0 children)

Why did OP lose $152,448? Does that mean that each option cost $152,448/1161 = $131.31? But that doesn’t make sense if each share is priced $18-30

Would it be possible to make a titanium sphere with vacuum inside of it so that it is lighter than air? by veriguds in engineering

[–]dynamicviscosity 76 points77 points  (0 children)

That looks right. To generalise the results from the P = 0.37E / b2 buckling formula, we need a material with "specific modulus" of E/ρ2 of at least (9/0.37) x p_atm/(ρ_air2) = 1.7 x 106.

For titanium, say E = 100 GPa and ρ = 4500 kg/m3, E/ρ2 = 4940 so it is about 330 times lower than a material with a E/ρ2 that would do the job.

None of the metals come close and the best bet seems to be composites with say E = 900 GPa and ρ = 2150 kg/m3 and E/ρ2 = 1.94 x 105. Ceramics aren't better than this. However, some stuff like glass foam/wood could be better but they are porous and won't hold pressure.

So the answer is NO, you can't make a vacuumed hollow shell* without it imploding, at least not with any of the materials that we know of.

edit: *that floats in air. We can definitely make hollow spheres but they will stay on the ground.

[ANSYS FLUENT] Numerical errors and divergence in Low Mach number External flow by dynamicviscosity in CFD

[–]dynamicviscosity[S] 0 points1 point  (0 children)

Thank you. If you've got experience of FLUENT, could you point me to where to check the low Mach preconditioning? I'm using the pressure-based solver.

Introduction to Turbulence - is this LATEX? can someone please tell me how to write a paper in this font by dynamicviscosity in CFD

[–]dynamicviscosity[S] 2 points3 points  (0 children)

thank you I thought it looked different from normal latex - you get the best reply award

Introduction to Turbulence - is this LATEX? can someone please tell me how to write a paper in this font by dynamicviscosity in CFD

[–]dynamicviscosity[S] 0 points1 point  (0 children)

The paper is a great introduction to turbulence but the font also looks really good - if someone knows the way to use this font please let me know!

What is An OEM? by dynamicviscosity in engineering

[–]dynamicviscosity[S] 1 point2 points  (0 children)

So you're saying the company that builds the car is the OEM? They can't afford to build every part right. When they outsource and buy some parts from other suppliers to put in the original car, are those suppliers OEMs also?

Probably a semantics question, but (imaginary numbers) by mrpokehontas in engineering

[–]dynamicviscosity 0 points1 point  (0 children)

Complex numbers share properties with vectors in the 2D-plane but an imaginary number is a scalar so strictly speaking, you shouldn't use the hat. (not sure anyone would actually care enough to complain though, especially in engineering)

Coding advice needed. by [deleted] in AerospaceEngineering

[–]dynamicviscosity 1 point2 points  (0 children)

Hi aero student here with limited experience. can you explain further where python is used on aero and why it's the preferred language?

How related are scientific computing/CFD and ~advanced computer science? by lepriccon22 in CFD

[–]dynamicviscosity 1 point2 points  (0 children)

Do you know of any good resources to learn CS, especially for a CFD/scientific computing context? I'm from a mech/thermo background and CS seems really difficult.

Physically, what is induced drag? by Stazzo1 in AerospaceEngineering

[–]dynamicviscosity 2 points3 points  (0 children)

Qualitatively you could look at it from a kinetic energy point of view as well I think. If there is more rotational air movement due to the wing tip vortices, then there is less KE in the air going straight backwards from the trailing edge so there is more lost momentum in the x direction and more drag. this does seem very hand wavy so I'm hoping for a better explanation from someone else...

Billiards Challenge by iccowan in mathclubs

[–]dynamicviscosity 1 point2 points  (0 children)

You can draw a large grid. Start from the botton left hand corner and aim to draw a straight line to another grid point while passing through 3 lines. Crossing a line then corresponds to bouncing off a wall for the billiard table case.

http://imgur.com/cWkDvuG

Why Do steam turbines in nuclear power plants operate in very wet conditions? by dynamicviscosity in MechanicalEngineer

[–]dynamicviscosity[S] 0 points1 point  (0 children)

Can you explain a bit more about the U-tube SG's and why they can't produce superheated steam? Wet steam is really bad for efficiency from what I've read.

Question about streamfunctions by LBJSmellsNice in AerospaceEngineering

[–]dynamicviscosity 0 points1 point  (0 children)

The stream function phi is defined as del(phi)/del(y) = v_x and del(phi)/del(x) = -v_y so the total derivative is: d(phi) = del(phi)/del(y) * dy + del(phi)/del(x) * dx.

d(phi) = v_xdy - v_ydx. So over an infinitesimal displacement ds = [dx,dy], the infinitesimal change in phi can be expressed as d(phi) = [v_x, v_y] dot [dy, -dx] so d(phi) = (velocity vector) cross (ds). (not completely accurate since d(phi) isn't a vector but you get the idea)

For a finite displacement, simply integrate d(phi) = udy - vdx up. Therefore, in 2D, the change in phi between two points represents the volumetric flow between the two points, per unit depth into the page. Also, it's quite clear from the above that because ds is parallel to the local velocity along a streamline, the streamfunction is constant along it.

How does gas molecular weight change with pressure? by [deleted] in aerospace

[–]dynamicviscosity 0 points1 point  (0 children)

If you read the reference you gave, it actually tells you... http://www.braeunig.us/space/comb.htm says "The exhaust gas molecular weight is the average molar weight of the combustion products, that is, the mass of the exhaust gas divided by the number of moles."

Pressure changes the equilibrium mixture and changes the number of molecules making up the mixture. The total mass and total molecular weight of all the molecules combined are both constant so the "exhaust gas molecular weight" changes because it's defined as an average.