New answers tagged

0

If it really is the case that $F_{\textrm{d}} = -c_1V$, with constant $c_1$, then there's an acceleration $\mathsf{d}V/\mathsf{d}t =-\left(c_1/m\right)V$. That differential equation is solved by an exponential decay with decay constant $c_1/m$. So it looks like, by the definition of $c_2$ you provide, $c_1 = c_2/2$.


1

At such very low Reynolds numbers, skin friction drag will (Landau and Lifshitz, 1987, Fluid mechanics, Butterworth-Heinemann, section 45) dominate over pressure drag (this is despite the sharp edges at the ends of the rods making this shape pretty thoroughly optimized to maximize the pressure drag coefficient at any given Reynolds number). The low ...


0

The top bucket will fill up first because the water needs less time to fall from the reservoir to the bucket.


0

A similar question is asked about conservation of mass in water from a faucet here and is partially answered in the comments. The buckets should fill up at the same time, since the mass flowrate at any point in the falling stream is equal. As velocity increases further down the stream, the cross-sectional area of the stream will decrease so that $\rho ua$ ...


1

I'm going to assume the piston is moving subsonically here (since you indicated velocity decreases with increasing area). The key here is that the end of the pipe is not a closed boundary, so the piston is not compressing the gas or doing work in the sense of $P \Delta V$. As long as the flow is subsonic and not choked via a constriction, pressure will not ...


0

This might explain. Turbulent boundary layer consists of three main layers formed in the direction normal to the wall: Viscous Sub-layer, Buffer Layer, Turbulent Region. Friction velocity is calculated using the wall shear stress and fluid density U* = friction velocity = sqrt (wall shear stress/density) , m/s Non-dimensional distance and velocity are ...


1

Hydrogen will not liquify no matter how high it is compressed. Unless it is cooled down to its critical temperature which is $ - 252.8^{\circ}C$ Hydrogen can be physically stored as either a gas or a liquid. Storage as a gas typically requires high-pressure tanks (5000–10,000 psi tank pressure). Storage of hydrogen as a liquid requires cryogenic ...


1

You need to find the compressibility factor, which is defined as $Z = \dfrac{pV}{nRT}$ of the hydrogen, then correlate to the "ideal gas", which has a compressibility factor of 1. https://en.wikipedia.org/wiki/Compressibility_factor


0

Ansys has versatile CFD applications, and many free sites with free examples and some free books, some discounted books. It offers student prices and some start-up versions with lower prices. one of the sites that have some free tutorials is this Ansys .


1

I assume you refer to a schematic like the following If the actual pressure is needed you would need to do it experimentally: to create a replica of the body surface and locate around it (as many as you can afford and its possible) pitot-tubes. Then you would need to find a calibrated wind tunnel that fits the object Perform a wind tunnel test for the ...


1

First of all, having the same flow in both pipes without flow control valves on both is set by the characteristics of the dwnstream piping in each. Unless they are mirrors of each other, all valves open will likely not have the same flow in both. You could throttle one if desired to make them the same if that is a goal. Second, you could control flow ...


0

If the lower grade pipe is not rated for that pressure, it'll bust. The solution is to transfer the water to a water reservoir/tank in a lower elevation, which acts to relieve the excessive pressure by reducing the head. But you might have to adjust the pipe size to maintain the flow rate.


1

Theories are developed to represent something happening in reality, in a form of mathematical model. Theory is not the benchmark, reality is. You cannot use a theory to prove something which is happening in reality, but can only develop a theory so that this reality can be represented correctly. Sometimes, using a specific theory to gain reasoning for a ...


3

Moody (1944, Trans. ASME 66(8):671-684) gives the following equation for the onset of complete turbulence: $$\frac{1}{\sqrt{f}} = \frac{\textit{Re}}{200}\frac{\epsilon}{D}$$ and attributes it to a 1943 conference paper by Rouse. I've been unable to obtain a copy of the Rouse paper, but from hints given by Moody, I think the equation represents the surface ...


2

I would be surprised if the determination of this line is theoretical. I would expect that the exact shape and position has been derived after a lot of experiments and fitting data. Excerpt from Wikipedia In 1944, Lewis Ferry Moody plotted the Darcy–Weisbach friction factor against Reynolds number Re for various values of relative roughness ε / D. This ...


1

I have the same pump and I use it to hold (no flow) vacuum without any problems (my use case is to hold vacuum while in epoxy mixture so that all bubbles can be extracted before pouring it into the mold, which usually takes 30min). But don't expect to get 5 Pa from this pump, I'd say 50 Pa is more realistic.


1

Wind will not stop collecting dust on the panels, due to the effect of the boundary layer. The speed of the layer of a stream of air next to a stationary surface is zero. Otherwise, people would take their cars instead of car wash to a race track! To have the dust blasted away. seasonal rain will clean them.


1

Given you are contemplating manufacturing solar panels, as an alternative, may I suggest you consider using something like self-cleaning glass and market your product as either "Smart Solar Panels" or "Clean Solar Panels". Self-cleaning glass has a coating that helps to break down organic material so that water can remove it as it sheets ...


0

Since you seem to be designing a product a word of caution: Of course it would be possible to design vents that use the air currents to keep the dust off. However, you will probably end up needing to be looking into many parameters (e.g. wind direction and speed at the installation area, wind "shading", solar shading of the vents, size of dust and ...


2

Our panels stay relatively dust free as they are at an angle of 70 degrees. This means the rain flows off nicely taking dust with it and the snow slides off as well also taking dust with it. Having checked the panels regularly over the years (installed 13 years ago) we have not cleaned them ourselves at all - nature has done it for us.


0

Trying to "see" your experience without pictures. First, when you inserted your spoon, you could have lowered it at an angle causing it to displace the liquid like a row causing two trailing vortices at the edges. Later when you dipped it into circulating tea, the current interacted with the two vortices. The current would accentuate and pull in a ...


0

To my understanding the circulation of the tea when you stirred it was not zero. So the vortex that formed from the two smaller one must have had the same direction of the initial stir. I would consider that they if there is any difference in vorticity "strength" is probably due to viscous phenomena when the spoon gets inside a fluid which is ...


0

One implementation is given in Large eddy simulations of incompressible turbulent flows using parallel computing techniques, Int. J. Numer. Meth. Fluids 2008; 56:1819–1843, on pg. 1833. In order to maintain the mass flow rate in the system equal to its initial value, a mean streamwise pressure gradient term $F^{n+1}\overrightarrow{e}_1$ is added to the ...


Top 50 recent answers are included