Daniel Hatton
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Why not use sodium hydroxide to reduce carbon dioxide emissions?
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Total worldwide demand for sodium carbonate is about $0.6\,\mathsf{Tmol}/\,\mathsf{y}$. Total worldwide carbon dioxide emissions from fossil-fuel burning and cement production are about $800\,\mathsf{...

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Interpretation of dx/dt and u in CFD
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Tentatively, this looks like it's analysing a sound wave, $\mathsf{d}x/\mathsf{d}t$ is the phase velocity of the wave in the lab frame, $\pm c$ is the phase velocity of the wave in the rest frame of ...

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How to calculate the viscous damping coefficient given drag force
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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 ...

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Drag coefficient of a complex object made using simple objects (with known drag coefficient) in small Re?
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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 ...

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I am struggling to get the right answere regarding the quantification of entropy
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You can work out how much the internal energy of the air has changed ($mc_V\mathrm{\Delta}\!\!T$). You know how much work has been done on the air ($10\,\mathsf{kJ}$). The difference between the two ...

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Are there any instances on Earth where it must be necessary to distinguish between center of mass and center of gravity?
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Yes: any structure intended to be partly submerged in water, such as a ship. The submerged part is subject to a "reduced" (often reduced so much that its sign changes) value of $g$ that is ...

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Calculating entropy change with Tds relations
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To answer the second half of the question first, $c_{\textsf{Cu}}$ is the quantity commonly known as the specific heat capacity of copper, where "specific" means "per mass". Hence,...

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How to determine the "complete turbulence" boundary line in a Moody diagram?
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3 votes

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 ...

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Isn't the Bernoulli equation just a special case of the Steady-flow equation?
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No, the logic flows the other way around. Bernoulli's equation is derived from conservation of momentum plus some special conditions, not from conservation of energy plus some special conditions. As ...

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Euler's Turbomachinery Formula
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"The position vector is purely radial" means that the position vector is aligned along the direction from the origin (or rather, the $z$ axis) to the location of interest. The cross product ...

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Mechanics: example of less mass/volume gives more strength
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If the load is applied in flexure (i.e. bending), then a small amount of material a long way from the neutral plane can contribute more to the load-bearing capacity than a large amount of material ...

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Why do we always need to calculate the 'Moment of Inertia' about neutral axis for bending?
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Because we're not interested in the moment of inertia or the "c" ordinate of a particular area element of the beam for their own sake - we're interested in them as intermediate steps on the ...

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Is heat transfer = potential energy in formula of 1st law of thermodynamics?
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When energy is being transferred, it can be classified as "work" or "heat" (it looks like this textbook/online lecture is using the name "macroscopic work" for what's ...

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Pumps' geometric similarity
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The key principle is that, when expressed in terms of the non-dimensional head coefficient $K_H := gH/\left(D\omega\right)^2$ and the non-dimensional flow coefficient $K_Q := Q/\left(D^3\omega\right)$,...

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Why is the head loss in submerged pipe is 0
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The symbol $H_{\mathsf{C}}$ here doesn't represent a head loss, it represents an "absolute" head at point $\mathsf{C}$. Assuming that the fluid velocity in the region vertically above $\...

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Specific heat at constant volume used in non constant volume processes
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Your problem is that much of the terminology of thermodynamics was defined before the underlying physical concepts were properly understood, which leaves us stuck with a lot of confusing names for ...

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Why does exit pressure match back pressure in Converging Diverging Nozzles?
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It's kind of a matter of semantics: if the fluid is still in a "jet" that's undergoing significant broadening or narrowing, and therefore significant acceleration that can match a pressure ...

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Calculating the change in flow rate with a change in pipe diameter
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Yes, you do have enough information. The equations you've seen that require a pressure measurement are the Colebrook-White equation (or its embodiment in the Moody chart) and the Darcy-Weisbach ...

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When can the thermal and mechanical energies of a fluid control volume be considered separately?
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You can't do it with conservation of energy alone: you need another physical principle, namely conservation of momentum in the form of the Navier-Stokes momentum equation (or, if the shear stresses ...

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Why does local derivative and convective derivative only apply to spatial descriptions?
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2 votes

Yes, your second paragraph is a pretty good natural-language explanation. The way I'd have put it is as follows: A partial derivative is a derivative with respect to (something), calculated on the ...

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When doing Mohr's circle, why do we rotate by twice the angle?
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A stress component is the quotient of a force resolved along a particular axis by the area of a surface perpendicular to a particular axis (in the same set of mutually perpendicular axes), on which ...

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Eulerian description of fluid flow
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The key is what's called "scale separation". For continuum hydrodynamics to work, there has to exist a length scale that is much smaller than the smallest length scale on which any ...

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Error propagation in reciprocal of a measurement
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The standard method, as set out in the BIPM Guide to the Expression of Uncertainty in Measurement, is to work out the derivative of $y$ with respect to $x$ (in this case, $\mathsf{d}y/\mathsf{d}x = -1/...

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I cannot properly understand the "pressure" referred to in Bernoulli's Principle despite my efforts
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The static pressure is the compressive longitudinal stress exerted by the pipe walls on the fluid and vice versa, but perhaps more importantly in this context, it is also the compressive longitudinal ...

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Some questions about the specific speed (Ns) of hydro turbines
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'Is there something wrong with my understanding of $N_{\textrm{s}}$?' Two things. Firstly, the formula you've quoted does not give the true dimensionless specific speed: to correct it, you'd need the ...

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How is fire risk reduced in dense contemporary timber neighbourhoods?
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For England, the relevant techniques can be found in section 11 of requirement B4 of Approved Document B of the Building Regulations. The measures essentially consist of: spacing buildings ...

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Glue a sample at -40 Degrees
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If you can find a liquid whose melting point is slightly above $-40\,\mathsf{^{\circ}C}$, pre-chill it to just above its melting point, then squirt some on to your bridge (in a controlled environment ...

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Extracting other mineral from salt in evaporated seawater
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There are two common techniques. The first is "crystallization separation", which takes advantage of the fact that not all species of salt precipitate out of aqueous solution in the same ...

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How is the ideal Euler line on a pump curve derived?
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You'll notice that at one point on the web page you linked, it says 'we assume that the flow enters exactly normal to the impeller, so tangential component of [lab frame] velocity [at the inlet] is ...

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Thermodynamic energy balance
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I'm guessing you got your maximum velocity of $12.64\,\mathsf{m}/\,\mathsf{s}$ from the idea that the fan power has to be enough to add kinetic energy to the air to speed it up from stationary to the ...

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