sethoflagos

There was another definition of energy which has fallen out of favour over the last 50 years or so. 'Everything that is not matter is energy' Since it is now apparent that matter is at least overwhelmingly, if not entirely, a highly structured manifestation of energy itself, then that old definition simplifies to: 'Energy is Everything' As axioms go, it's a fairly comprehensive one. Whether or not one agrees with it depends upon whether you can answer a slightly different question. 'What is NOT energy?'

.....actually, the concept may not be that inefficient. See Van de Ven JD, Li PY, Liquid piston gas compression, Appl Energy (2009), doi:10.1016/ j.apenergy.2008.12.001

Good luck with finding a backer.

The most economic methods of achieving this are based on gas scrubbing. (see https://en.wikipedia.org/wiki/Scrubber) But that does not make them necessarily profitable, There are generally cheaper methods of generating these gases. Separation by density difference is a very expensive method, and very limited in its application.

What a depressing thread. And one that a board dedicated to science should be ashamed of. Because there is no science here. Just the recycling of political dogma that has poisoned the intelligence of one particular race of humanity for centuries.

How do you replenish the compressed air that you use? I guess you could reroute the liquid back to the pump suction to drain it, open another valve to admit new intake air, and you end up with a batching process that approximates to a reciprocating compressor with a liquid piston. Sounds fairly inefficient. Even for an air compressor.

Which gases are you wanting to separate? Are you researching uranium enrichment?

See https://en.wikipedia.org/wiki/Mass%E2%80%93energy_equivalence If you drop down to the section headed 'Low Speed Expansion' you'll discover where Einstein thought 'the half' came from.

Maybe this is just a characteristic of my own particular field, and I'd be interested in others viewpoints. Authors of technical papers who use SI, or similar consistent system of units (typically Europeans) seem to have a tendency to define coefficients as a fractional energy (sometimes force) conversion ratio - so a dimensionless coefficient of say, 0.70, would correspond to some kind of efficiency of 70%. Authors more familiar with historic systems of units (typically US) seem more comfortable with dimensioned coefficients with no significance other than they balance the proportionality. I appreciate that, at best, this is a gross generalisation, but the thought has struck me often enough to ask the question...

If I'd thought for a little longer, I might have come up with this derivation: Calculate the change in kinetic energy of a body of mass m accelerating from u to v in time t Force = rate of change of momentum = m*(v-u)/t Distance = time x average velocity = t*(v+u)/2 Delta KE = force*distance = 0,5*m*(v+u)*(v-u)

It's easy enough to do a few calculations of typical kinetic to internal (thermal) energy equivalences. Typically the temperature changes are small. Turbulent flow in long pipelines is usually treated as an isothermal (constant temperature) process with acceptable accuracy. Moreover, since a fluid often sources its kinetic energy by conversion of some of its internal energy, with an associated cooling effect, reversing that conversion will only restore the original temperature. The First Law tells us this. A problem that is more frequently encountered is when the pressure transients discussed previously start dipping below the liquid bubble point. This leads to localised bubble formation followed by extremely rapid collapse - cavitation. A major part of the hydraulic design of pumped circuits focuses on ensuring that this doesn't occur in the eye of the pumps (the pressure low point in the circuit) as heavy cavitation can chew through a pump impeller in no time.

Thanks! I think I would always describe an eddy as flowing, even if it were basically static and self-contained. like swirling tea in a cup after it had been stirred. That would be an example of a circulating flow. Not necessarily going anywhere, but its still converting momentum to heat via rotational flow which is basically an eddy's job description. Many of course are typically carried along at moreorless the fluid bulk velocity, so these have both rotational and linear flow components

Yes, the aerofoil lift equation is that form because of the relationship q=0.5 r u^2 where u is air speed, r, air density, and q the dynamic pressure (the additional theoretical pressure you could get if you brought the air to a standstill). The right hand expression is the kinetic energy of the airstream. So the same 'half'. Don't worry about too much about the coefficient/proportionality thing. A mathematician might possibly be offended by the way I used the term, but I'm certainly not going to lose sleep over it. Except the capital 'C' that comes with your lift coefficient does stand for 'coefficient', so perhaps best to stick with that one, PS No need to be shy about your level of understanding. It's pretty impressive. I wish a few of my clients were as quick on the uptake!

It is the same 'half'. And it comes from being the arithmetic mean of zero and one(!). Imagine a pneumatic 'gun' that applies a precise 1 Newton force to a 1 kg mass projectile through its barrel for precisely 1 second. From Newton's second law, and the definition of the Newton, we know that the acceleration will be 1 m/s2 and therefore the projectile will leave the barrel at 1 m/s. But the total distance travelled during linear acceleration is the time multiplied by the arithmetic mean of initial and final velocities. As the projectile starts at rest with respect to the equipment(!), and leaves at 1 m/s, the average velocity (again with respect to the equipment) is 0.5 m/s and therefore the scientist, being an excellent Newtonian, has designed his barrel to be 0.5 metres in length. The same 'half'. As for the kinetic energy, the scientist tells me with confidence that from the definition of the Joule, a constant force of 1 Newton acting over a distance of half a metre imparts an energy of 0.5 Joules (the same 'half'). But I disagree with him. I've been carefully watching his experiment with the aid of my trusty laser ruler and stopwatch, while walking towards the gun at the speed of 1 m/s. We agree on the mass of the projectile; we agree on the force applied; we agree on the time period the force was applied; we even agree on the rate of acceleration; but we disagree on initial and final projectile velocities (which I have measured to be 1 and 2 metres per second respectively); and also the distance over which the force acts, which I carefully measured as 1.5 metres. So I believe that the projectile has gained not 0.5 but 1.5 Joules of kinetic energy (NB the arithmetic mean of 1 & 2!) He of course quickly points out to me that if we can both agree that a projectile travelling at one metre per second has a kinetic energy of 0.5 Joules (his final value, my initial one), Then my final kinetic energy would be 0.5 + 1.5 = 2 Joules. So a doubling of velocity quadruples the kinetic energy per kilogramme (providing the mv2), and the constant of proportionality is the same 'half' it has always been.

Eddies are a result rather than a cause. The root cause tends to be two fluid parcels attempting to occupy the same space. The parcels tend to break up into rotating parcels of ever decreasing size ('shrapnel'), and the transient pressure wave from the 'collision' changes the upstream conditions that initiated that particular conflict, spawning different conflicts with different geometries. In my world (there are always different ways of viewing these complex phenomena) I view turbulence as being characterised by these unpredictable (I use neither 'random' nor 'chaotic' in this context) pressure transients from downstream events impacting upstream flow patterns thus creating sustained flow instability with a great variety of structures on many scales. In contrast, in laminar flow, such peturbations are damped out almost immediately by viscous diffusion due to their low energy content.

The Navier-Stokes equations ARE the general equations of turbulent systems. (Noting that turbulence is the general state of a dynamic universe - orderly, low entropy laminar flow something of a peculiarity existing on the boundary of dynamic and static structures). Anything else is an approximation. In chemical engineering we tend towards semi-empirical equations, usually based on overall energy balance considerations ranging from the (near) isentropic - such as gas expansion through a turbine, to (near) isothermal - such as flow through a long pipeline. Deep, deep down, there is some rooting in Navier-Stokes, but this is not obvious at first glance. You might gain some insight into the subject by studying Richardson and Kolmogorov's theories of energy cascades from large inertia dominated fluid parcels down through the Kolmogorov scales to the microscales where viscous shear is once again dominant and where the system waste heat (in the thermodynamic sense) is finally dissipated. It's more of a statistical, fractal geometry approach than a purely analytic one. But since the purely analytic solution will be a while getting into print, it's as good as anything for providing a perspective.

Couette flow as a concept is a 100% shear-driven flow regime. Many turbulent flow cases are more than adequately described by assuming an inviscid fluid - one where there is no viscous shear. So how can turbulence ever be described by Couette (which is just a simple case of laminar flow), or vice versa, when the dominant physical mechanism of each case is so insignificant in the other that it can be (and is) ignored in most practical applications? Vorticity is also, I feel, an inappropriate guide. Any pure laminar flow regime passing through a right angle tube bend will develop a pair of symmetrical 'D'-shaped vortices if only by the consideration that the streamlines must negotiate the change in direction somehow. It is difficult to see how any attempt at understanding the different fluid flow regimes can progress unless we start with their common ground, which is the transformation of internal energy to kinetic energy and back. This inevitably calls into play the governing thermodynamics which can begin to shed some light on the development of high entropy flow regimes. One reason laminar flow is a poor choice of starting point is that the equations that are normally used to describe it do not explicity indicate the energy sources and destinations. That the driving force derives (as typically presented) from the expansion of an 'incompressible' fluid is just one of a number of confusing paradoxes here.

Which one? Depending on context, there's 70 odd distinct terms in the Navier-Stokes equations alone (to which must be added the continuity equation and applicable equations of state plus an infinity of variations in boundary conditions......) In short, an infinity of mathematical challenges, a few of which have (near) exact analytic solutions, and many more of which are amenable to numerical methods. It so happens, that for low Reynolds numbers and steady boundary conditions in simple geometries, all but two terms tend to zero after some settling time. So the mathematics of laminar flow tends to be steady state and simply analytic. As Reynolds numbers increase, new terms gain significance; the mathematical complexity increases exponentially (for want of a better term); and almost invariably, the partial time derivatives remain significantly and indefinitely non-zero. This, we call turbulence. But it covers a myriad of flow regimes from the stirring of a coffee cup to the expansion of the universe. And yes, even the flap of a Brazilian butterfly's wing. There is no sense in which the richness of turbulence somehow emerges from the Couette scenario. Better to wonder that somewhere within the infinite ocean of possible fluid flow regimes, there is one tiny island where 80 or so parameters are practically zero, and the regime is sufficiently simple that we can actually start to get our heads around it.

For the record, the Hagen-Poiseuille equation is only applicable to low velocities in small pipes (laminar flow regime). It only crops up (typically) in small chemical dosing systems and the like. Friction loss in the vast majority of process liquid systems is calculated via the Darcy-Weisbach equation (https://en.wikipedia.org/wiki/Darcy%E2%80%93Weisbach_equation) with friction factor f read off a Moody diagram. It simplifies to Hagen-Poiseuille at low Reynolds number. But all this is irrelevant in the context of the OP. The wrong question has been asked, The '....engineering development group we are dealing with seem all at sea' comment tells me a lot about the quality and style of management.

Not at all. Much of what you quote centres on studies (I use the term lightly) of small samples of the Igbo tribe - one of about 250 tribes in Nigeria. Most of these, particularly the older ones but some more recent too, have obvious non-scientific agendas. On this basis alone, attempting to extrapolate conclusions (such as they are) to the human population in general is just simply crass. Attitudes towards colour within sub-saharan tribes are (in my limited experience) varied and complex. Within Igbo culture in particular, there is at least some tie up with https://en.wikipedia.org/wiki/Osu_caste_system. As none of the references you quote even mention this factor, their conclusions are generally (for me) not worth the paper they're written on.

I find this argument for an underlying non-local, stochastic, time symmetric quantum foundation very persuasive: http://philsci-archive.pitt.edu/8959/ I realise that that probably doesn't mean too much to you, but the OP was specifically referring to our subjective intuitive reaction to various levels of determinism. A fully deterministic universe and random. non-causal one disturb me in about equal measure (as do anthropocentric and religious models). I feel the need for a golden mean. Ruth Kastner seems to be offering one. If she's got the maths wrong, I'm sure one of you good souls will enlighten me

The eternalist model certainly has a certain mathematical neatness to it. However, your excision of my reference to evolutionary arms races is telling, as I've since discovered that that was raised by Popper in his discussion with Einstein as an example of the model's apparent absurdity. Maybe I've read something about this in the dim and distant past. It seems to remain an open and valid objection, Once, in an attempt to get my head around QM, an image arose in my head of a transistor radio (yes, this was a long time ago!) floating in a far future infinite space of low temperature radiation. And how QM might attempt to make sense to this isolated instant by an act of creation in reverse, inventing one, perhaps the only(?) past that could explain that particular scenario. Such a long range time reversed causality is admittedly, far-fetched in the extreme, But it does away with a few philosophical problems such as the anthropic principle. And what you end up with is a block universe with human consciousness sailing through the advancing entropy time line in its pre-ordained destiny to create a transistor radio, Contrast this with a strict growing block universe with a zero width time slice of 'now' which denies any quantum advanced waves impacting the past, and by logical extension, an indeterminate future. Coincidently, I raised a topic on John G. Cramer's Transactional Interpretation about a week ago. Kastner ("The Quantum Liar Experiment Kastner". Studies in History and Philosophy of Modern Physics. 41) seems to believe that some form of this is necessary for the eternalist model. So it may come down to how far back in time an advanced quantum wave can project. Somewhere between the absolute end members of zero and the lifetime of the universe. Maybe a little smeared out muddiness around an absolute present would help solve some issues.

If absolute determinism were possible, I'm not sure we can avoid the agent. It would give us the potential power to predict the future; and the power to predict all possible alternative futures that could be realised by tinkering with the initial boundary conditions (our present); and hence, the power to change the future, perhaps to our benefit through some minimum calculated action in the present. It becomes the time reversal of the https://en.wikipedia.org/wiki/Grandfather_paradox. In, short, we become the agent. But here's the counter paradox. If we could exploit absolute determinism to change the future in this way, then there can be no absolute determinism, Different parties would engage in a frantic evolutionary technological arms race to gain some measure of control over their destiny. In short, each successive absolute deterministic path is annihilated by destructive interference in proportion to the evolutionary development of predictive power. This is what life does. It evolves, and in doing so, it alters the future. My own philosophical view? Existence is not absolutely predetermined, but neither is it entirely unpredictable. It's somewhere in between that approximately corresponds to 'absurd'. Not exactly a scientific concept, but one pretty well established in philosophical thought.

Perhaps you need to experience both to mature well. The small pond to learn how to take full responsibility for your actions; the big pond to learn humility and an appreciation of diversity. The skills you learn in one environment help you to function successfully in the other. If forced to choose at my stage of life (which makes a difference), the big pond probably offers more opportunities for the experienced.

And where exactly in this thread did I claim any meaningful prior knowledge of cosmology? Though in the last 48 hours Mordred has been kind enough to open quite a few doors that were previously closed to me, I don't really know why I'm bothering to respond to this. If you've nothing better than petulant ad hominems to offer, then you've nothing to offer. I suggest you learn to live with your mixed feelings.