Jump to content

sethoflagos

Senior Members
  • Posts

    303
  • Joined

  • Last visited

  • Days Won

    1

Posts posted by sethoflagos

  1. On 6/16/2021 at 9:57 PM, Nick German said:

    Hi! I am new there. Right now i'm writing a paper on granular motion and dymanics of two-phase solid-gas systems (smoke, aerosoles, etc). Planned to use Chorin A.J. Vorticity And Turbulence for citations and calculus, but found out, this book does not cover up two-phase flow. If there any gas dynamics pros/scientists, what book or articles can you suggest to look for?
    I am not aiming for strong math backup, but it would be great addition to theory, if book has one. Looking forward for your suggestions! 

    Starting point without a doubt is Coulson and Richardson's Chemical Engineering: Volume 2A: Particulate Systems and Particle Technology, Sixth Edition.

     

    Quote

    ...Particulate Systems and Particle Technology has been developed from the series’ volume 2, 5th edition. This volume covers the properties of particulate systems, including the character of individual particles and their behavior in fluids. Sedimentation of particles, both singly and at high concentrations, flow in packed and fluidized beds and filtration are then examined.

    Readership

    Academic and Professional Chemical and Process Engineers

    Table of Contents

    1. Introduction
    Abhijit Deshpande and Kanjarla Anand Krishna
    2. Particulate Solids
    Anurag Tripathi
    3. Particulate solids in bulk: Storage and Flow
    Anurag Tripathi
    4. Mixing and segregation of bulk solids
    Anurag Tripathi
    5. Classification of solid particles from liquids and gases
    Madivala G. Basavaraj
    6. Particle size reduction and enlargement
    Jayanta Chakraborty
    7. Motion of particles in a fluid
    Rajendra P. Chhabra
    8. Flow of fluids through granular beds, packed columns and porous media
    Rajendra P. Chhabra
    9. Sedimentation
    Rajendra P. Chhabra
    10. Fluidisation
    Anand Prakash
    11. Liquid Filtration
    Rajendra P. Chhabra
    12. Centrifugal separations
    Rajendra P. Chhabra
    13. Product design and process intensification
    Rajendra P. Chhabra
    14. Particles in Solution – Colloids and Nanoparticles
    Madivala G. Basavaraj
    15. Particle handling, safety and health hazard
    Rajendra P. Chhabra
    16. Advanced Topics in Particle Technology
    Madivala G. Basavaraj and V Shankar

    Details

    No. of pages: 871

    Language: English

    Copyright: © Butterworth-Heinemann 2019

    Published: 12th April 2019

    Imprint: Butterworth-Heinemann

    Paperback ISBN: 9780081010983

    That's your broad brush introduction to the subject. But the range of application is extremely diverse - many, many specialist study areas with not so much common ground to unite them (or so it seems to me).

    If you have particular interest in some particular field, I may be able to give some relevant further references.

     

     

  2. 22 minutes ago, geordief said:

    Yes,that is what I meant.Suppose that there were eddies  in the medium(caused by local areas of pressure differences,I think) then that would alter the characteristics of the medium and the speed of sound in it.

    Nearly. But it isn't the properties of the medium that are changing: it is whether or not the medium is flowing away from you toward the trains, which would delay your detection of the whistles; or flowing toward you from the trains, which would advance the detection. 

    If you had no information on airspeed, say for instance you were observing via a remote video camera and microphone, your measurements of the (apparent) speed of sound would vary according to wind speed and direction wouldn't they? 

    This is an example of Galilean non-invariance.

    Now substitute 'speed of light' & 'luminiferous aether' for 'speed of sound' & 'air'. What happened when Mickleson & Morley tried looking for these telltale Galilean non-invariances in their measurements of the speed of light through the medium of the luminiferous aether? They found none!

    This is why there is a fundamental difference between the non-invariant measured speed of sound in air and the invariant measured speed of light in vacuum. 

    1 hour ago, geordief said:

    Thanks for your help.I hope I wasn't too confusing.

    No worries. We've all had to work our way through this some time or other.

     

  3. 10 hours ago, geordief said:

    ... as well as specifying that the medium is at rest with respect to itself can I say that the speed of sound is "invariant" in the same sense

    In what circumstance would a medium be not at rest with respect to itself?

    Perhaps you intended "... at rest with respect to the observer", ie. a restatement of our 'still air' constraint.

    Could another restatement of this constraint be that observer and medium must be in the same Galilean reference frame?

    If so, then if the constraint was a necessary precondition, wouldn't this imply that the apparent speed of sound was not invariant under a Galilean transformation? 

    I stress the word 'apparent' to distinguish between transmission over a measured distance in a measured time interval, as distinct from a physical property of the medium itself. These are two different quantities. Whether the latter is invariant to Galilean transformation is a moot point. 

     

  4. 22 hours ago, geordief said:

    At the moment that the two meteorites are in very close proximity to each other, they explode  in a symmetrical way and create sound waves (that do not interfere with each other)

    Meteorites survive passage through the atmosphere, so perhaps you intend 'audible fireballs'.

    Even so, these propagate, initially at least, as supersonic bow shocks (sudden pressure discontinuities) rather than sound waves - at velocities dependent on their initial trajectories, and independent (for a while at least) of atmospheric properties.

    23 hours ago, geordief said:

    My question is "Does the observer hear  the two explosions at the same time,albeit at different pitches?"

    If one bolide were travelling towards the observer, and one away, they would be experienced as two blast wave fronts, the first perhaps considerably more powerful than the second. 'Pitch' is meaningless here. There may be some reflected aftershocks, but not necessarily in any ordered sequence.

     

    Perhaps your enquiries would be better served with a simpler less energetic case, such as two locomotives in still air, sounding their steam whistles as they passed each other in opposing directions.

    In the absence of relatavistic effects, and if the locomotives were perfectly streamlined (ie they weren't dragging a large envelope of air with them) an observer on the station platform would hear two perfectly simultaneous sounds pitched according to their respective Doppler shifts.     

     

  5. On 5/14/2021 at 6:54 PM, apeg said:

    My goal is to see if I can economically create a large floor covering that would have the ability to detect when an object has been placed or removed from the surface. 

    The idea originated from a BMI scale that uses electrical impedance to make rough calculations of the person's body composition. The problem there is the contact points are not connected on their own, it's the person who completes the circuit. 

    I'm curious if there is a way to adapt the idea; if the contact points are connected via the surface material (a sheet of metal) and the impedance is constantly measured will placing or removing an object (of any material) create a change in the measurement, enabling me to trigger a change event, or better yet determine if something was removed or added to the surface. 

    The only ace up my sleeve is that I don't need to know the weight/mass, only the change even and direction of. Weight/mass would be a great tertiary bonus, but not required. 

    'Robotic skin' is a highly active area of current research, and your OP seems to require a relatively low resolution, planar version of the same thing.

    I'm puzzled why you pick impedance as the sensed property for this. Most work in this field has been focused on traditional resistance strain gauges, piezoresistance, and capacitance methods though Fibre Bragg Gratings (FBGs) seem to have received a lot of attention recently.

    The EU Roboskin Project is funded to the tune of about 5 million Euros: details at https://cordis.europa.eu/project/id/231500

     

  6. 20 minutes ago, exchemist said:

    There are plenty of houses left with solid fuel fires that rely on the chimney draught principle. I remember my mother used to hold a sheet of newspaper across the fireplace when starting the fire, to help it draw at the bottom. Once the suction was so great the newspaper slipped from her palms and went up the chimney, alight, where it started a chimney fire. That was in Edinburgh in the 1950s, before the Clean Air Act put a stop to such things. 

    I clearly remember my grandmother starting the fire like that as the family gathered for christmas dinner. The sudden updraught caught her pet budgie by surprise and... it didn't end well. 

  7. On 5/13/2021 at 1:22 PM, exchemist said:

    Thanks for posting this. I was scratching my head thinking I had read something about chimneys. But they seem to need to be very tall, and are even more of a blot on the landscape than wind turbines. I wonder what sort of payback time they achieve and how they compare in Watts/m² with solar panels these days.  

    Natural draught is used extensively as a power source, but not in an obvious way.

    It doesn't provide enough power to pull combustion air through a commercial power station, but it contributes significantly in reducing the power requirement of the forced- & induced-draught fans. Similarly, natural draught cooling towers (and domestic coal fires for those old enough to remember them) don't need forced ventilation in order to maintain air flow.

     

  8. On 5/17/2021 at 1:29 AM, swansont said:

    It’s a huge leap from a quantum object behaving a certain way to having a liquid behave that way

    Would I be reasonably correct in thinking that the product of mean particle momentum and mean particle separation would need to be oto Planck's constant?

  9. On 5/10/2021 at 8:07 PM, DeepSeaBase said:

    All I want to know is why creating 100GPa in a diamond anvil cell is consider godlike when we have presses capable of exceeding that by a huge amount?

    Very few materials we commonly encounter have a structure that is stable under a pressure of 1 GPa. Most, much less.

    We do not have presses capable of exceeding 100GPa by a huge amount, because we do not have the commercially available materials to construct such presses. Give or take the odd colliding celestial body. And they are a one shot deal.

  10. 58 minutes ago, Tom Booth said:

    Yes, I thought so, as I mentioned, something didn't look right. The result of a hasty cut n paste on the Stirling engine forum, which I then repeated here.

    Sorry, but I don't buy this explanation. 

    Take this example from a previous post:

    7 hours ago, Tom Booth said:

    If my heat engine utilizes ALL the heat fed into it, and converts every bit of it into useful work so no heat whatsoever "flows out" into the sink, carnot efficiency might be calculated at almost any arbitrary number represented by the temperature difference.

     If there was "no heat whatsoever" flowing into your cold sink, that would imply that the thermal efficiency of your machine was 100% (it can't be, but we'll let that pass for now). In other words, you were extracting every last milliJoule of work allowed by the 2nd Law of Thermodynamics.

    However, if your heat engine did indeed "utilize ALL the heat fed into it" from say 1 kg of hot cocoa, then you would not only have your 100% thermal efficiency, but you would also have attained 100% Carnot efficiency

    Congratulations!

    Now explain to me what you did with that 1 kg lump of cocoa at absolute zero. 

    Because that is what "ALL the heat" means.

    If on the other hand, you actually ended up with luke warm cocoa, the Carnot efficiency simply tells you what percentage of "ALL the heat" was actually available to you. It says nothing whatsoever about the virtues or quirks of your machine - it is an absolute limit for any machine that was fueled by 1 kg of hot cocoa and exhausted 1 kg of luke warm cocoa. And it's a simple function of those two temperatures.

    Please pause and reread the last few paragraphs. You've wasted a fair chunk of the last few years through not understanding the difference between the highlighted terms. How much more time can you afford to waste?

    1 hour ago, Tom Booth said:

    Please site an example.

    I've heart this affirmation repeated over and over and over, but that seems to be all it is. I've scoured through the available literature for ten years and find no accounts whatsoever of any detailed experiment demonstrating, for example, the actual heat flow in and out of a Stirling engine, running a Stirling heat engine on ice, insulating the sink, nothing whatsoever that would either add weight to or call into question Carnot's conclusions.

    Carnot's equation is a simple algebraic manipulation of the 2nd Law limit - delta S = 0

    Experimental verification of the 2nd Law automatically verifies the Carnot limit.

    The first item to pop up on Google was: 

    "Experiment to verify the second law of thermodynamics using a thermoelectric device", Gupta, V. K.; Shanker, Gauri; Saraf, B.; Sharma, N. K.  American Journal of Physics, Volume 52, Issue 7, pp. 625-628 (1984).

    I've not read it, but I'm sure it's fine, and typical of many thousands of similar published papers. It's actually based on a Seeback-effect heat engine, but the underlying principles are just the same.

    If you want to see more, just Google "experimental verification of 2nd law of thermodynamics" as I did. There's over 6 million results for you to sift through.

    Good hunting.

     

  11. You're confusing Carnot efficiency, 1 - TC/TH

    ... with thermal efficiency, 1 - QC/QH

    It is entirely consistent with both classical thermodynamic theory, and centuries of detailed empirical observation by the most gifted of experimentalists, for a machine to have a low Carnot efficiency (the fraction of energy in an input stream that is available for conversion to work) and a high thermal efficiency (the fraction of that available work you manage to convert to actual work)

    The following demonstrates most clearly that you are totally unaware of this distinction:

    1 hour ago, Tom Booth said:

    If my heat engine is 500 degrees on one side and 250 degrees on the other than the "caloric" can only fall 250 degrees from 500 down to 250 which is 50% of the "fall" on the way down to absolute zero. (Arbitrary numbers on the Kelvin scale but it works out the same way on any other) That makes my engine 50% efficient, at best, because that is as far as the "caloric" can possibly fall.

    With an inescapable effect on the authority of your output:

    1 hour ago, Tom Booth said:

    It's complete hogwash.

     

  12. 7 hours ago, studiot said:

    If this does not happen then you will not have the required water for the hydroturbine to operate. It cannot do so in a slush.

    Please give me a credible mechanism for the creation of a slush (suspension of ice particles in water) in the system I have described. I currently regard the idea as a deus ex machina, but would be delighted to be shown otherwise.

  13. 35 minutes ago, MigL said:

    I'm not convinced of that either.
    A Martian day is similar to an Earth day, which might not be enough time to freeze or liquify completely, leading to a perpetually liquid or ice ring around the planet.
    Or possibly a state of 'slush' as a large buffer between the ice and water sections.

    I find it interesting as an idealized mental exercise, but the 'realities' which Studiot mentions, make it impractical, if not impossible.

    Average low night temperatures on mars are below 200 K throughout the year. There is next to no atmospheric blanketing and the (blackened) pipes are shielded from the ground by mirror finish parabolic troughs. They are in thermal communication with nothing but the empty vacuum of space. 

    You may have noticed that I switched from an initial single 48" ND pipe to multiple 8" ND pipes. This was specifically directed at providing the necessary 'A' in sigma.A.T^4 to meet the night side heat shedding load.

    You may also have noticed that I've switched to extracting the 18 m^3/s via multiple tapping points (oto 10,000 spread over 1,000 km) so that it is drawn off at practically zero velocity. If there is any ice nucleation in the body of liquid (rather than at the annular interface), then it will float upwards as far as it can. There is insufficient fluid shear to overcome buoyancy forces. And certainly insufficient fluid shear to start ripping consolidated phase Ih ice away from the pipe wall.

    And yes, the project is impractical if not impossible. That was never in doubt.

    Of course, I'd like to carry everyone along with me on this. But it's as clear as day that there are a few individuals who will never concede as a matter of principle. And bottom line is, I don't see I'm under any real obligation to convince anybody. Except possibly myself.  

    32 minutes ago, swansont said:

    I don’t recall these being described in the OP. You had a tube and a turbine. I think my disbelief was well-founded, based on the available information.

    I'm sure your disbelief was exemplary.

    But now that you have updated information, do you agree that the interface pressures can be subject to operator control?

  14. 2 minutes ago, swansont said:

    That wasn’t one, so...

    ... So... Well you expressed disbelief that the interface pressures could be controlled by the operator. My second to last post sort of covered that, but maybe I could flesh out some details for you.

    It is relatively easy to set the pressure of a ringmain. A very simple example would be to fit it with an open header tank set at the appropriate elevation and sized to accommodate any expansion/contraction or temporary fluctuations in inventory.

    Something a little more sophisticated would be called for here. Maybe an underground reservoir with a substantial gas blanket to absorb the fluctuations within a tight pressure band. From a functional point of view, it's identical to the elevated tank, but without the open connection to the martian atmosphere.

    So we can create two ringmains with tightly controlled operating pressures.

    We now install tapping lines equipped with one-way flow valves (check valves) into the freeze/thaw system. Those connected to the high pressure ringmain would have their check valves so oriented to only allow flow into the ringmain. These will draw flow from the freeze/thaw system only when its pressure at that point exceeds that of the high pressure ringmain - ie in the vicinity of the freezing interface. Conversely, those tapping lines connected to the low pressure ringmain would be oriented in the opposite sense, feeding the freeze/thaw system only at those locations at a pressure below that of the low pressure ringmain - ie in the vicinity of the thawing interface.

    Obviously, the ringmains and tapping lines would be fully insulated and traced to prevent them from freezing up.

    Once the high pressure ringmain is pressurised, the turbine sluices can be opened, controlling the high pressure ringmain to a setpoint somewhere in the middle of its design operating band, this will automatically feed the low pressure ringmain with precisely the volume required to feed the low pressure injection tappings.

    Since it's a closed, very nearly constant volume system, fluctuations should be very small, and self-regulating.

    I trust this rather long and detailed post is sufficient to quell your disbelief.   

  15. 26 minutes ago, studiot said:

    I'm glad you are beginning to do some thinking about it.

     

    16 minutes ago, swansont said:

    You made an assertion without backing it up, so thou doth protest too much, methinks.

    Not that interested in ad hominems.

    Guess we're done.

  16. 20 hours ago, swansont said:

    How big of a gradient are you expecting?

    I'm comfortable with a waterside delta P of ~100 bar (10^7 Pa).

    Over 10,000 km, this equates to a pressure gradient of 1 kPa/km.

    This gradient is compatible with a line velocity of 0.15 m/s in 8" double extra strong (XXS) linepipe.

    This is less than 1% of the flow generated by the freeze thaw cycles making ~ 18 m^3/s available to be tapped off into a high pressure ringmain operating at say 10 bar less than the high pressure (freezing) interface.

    Similarly, a low pressure ringmain operating at 10 bar above the pressure of the low pressure (thawing) interface will return the 'borrowed' 18 m^3/s back into the thawing zone.

    The residual 0.15 m/s water velocity in the freeze/thaw system will be naturally maintained as a consequence of the imposed delta P.

    Hydroelectric generators linking high and low pressure ringmains will utilise the 18 m^3/s flowing between them with a delta P of 80 bar (8 x 10^6 Pa) to yield:

    Est. Power Output = 0.9 x 18 x 8 x 10^6 = 129.6 MW (continuous)

     

     

  17. 42 minutes ago, studiot said:

    and simply asking how you would transfer that amount of energy into a block of ice in one second, since you would need to do the same again with the next block of ice in the next second and so on.

    Why would any particular m^3 of ice need to be thawed in 1 second?

    So long as it's fully thawed by mid afternoon, say, before the heat input has reduced to the point where it starts to refreeze, then it's done its job. 6 hrs to thaw = ~5,000 km of the collection array doing the thawing. Actually, if your figure of 590 W/m^2 is good, a high efficiency collection strip 100 m wide will do the job over ~1,200 km or about an hour and a half. So there's a fair safety margin to play with.   

    PS. Thinking about it, since I'm going to be reinjecting the somewhat warmish low pressure discharge from the water turbines back into the thawing zone to meet the contraction demand, that fact in itself should significantly accelerate the thawing process.

  18. 29 minutes ago, MigL said:

    So, using water which expands on freezing, you expect a higher pressure on th day-to-night freezing interface, and a lower pressure on the night-to-day thawing interface, leading to a pressure gradient, and a net flow of water, from which you hope to generate power.

    Obviously if a liquid other than water was used, that doesn't change density on freezing, you would have no pressure gradient, and no flow. The frozen section would just move around following the night-side.

    But what if you had any other liquid that contracts on freezing. Your analysis would then indicate a reverse pressure gradient, and a flow in the opposing direction ?

    Exactly put. +1

  19. 8 hours ago, studiot said:

    So let me get this straight.

    You are envisaging using the entire output from a 100m wide strip, one quarter of the way round the martian globe to melt the ice in one metre of the pipeline ?

    Why the tone of ridicule?

    You state that 6 x 10^5 m^2 of collected solar radiation will melt 1 m^3 of ice in one second

    So 240 x 6 x 10^5 = 1.44 x 10^8 m^2 will melt 240 m^3 of ice per second, the thermal duty we are looking for.

    My order of magnitude guess of a 100 m strip around the planet seems to meet the requirement several times over. 

    5 hours ago, swansont said:

    IOW, you are in a steady-state condition.

    Yes

    5 hours ago, swansont said:

    The gradient causes flow, it is not preserved by it. 

    They come as an indivisible pair. The one leads to the other and vice versa.

    5 hours ago, swansont said:

    I seriously doubt that.

     

     Argument from incredulity? 

    5 hours ago, swansont said:

    Which is what I expect will happen if you tried this.

    The safety systems could well be a challenge

    5 hours ago, swansont said:

    So the pressure will equilibrate much faster than any flow you are expecting.

    Following a dynamic peturbation (passing dust cloud, for example), steady state will reestablish itself (if this is what you mean by 'equilibrate') not by transmission of pressure waves as such, but rather by their attenuation due to viscous dissipation, which can take a significant length of time. With such a long pipeline, water hammer effects would be a significant concern (because spontaneous disassembly again).

  20. 2 minutes ago, Tom Booth said:

    I don't know where you're coming from but Turbo-expanders are WIDELY used for gas liquefaction. It has practically replaced every other method there is in every industry involved in gas liquefaction all around the world.

    First you try to deny it exists, apparently because it wasn't on Wikipedia from which you were apparently cp'ing, now you are trying to demonize a standard industrial process, used all around the world.

    What's your game dude?

    Seriously?

    Non-cowboy operations condition their gas in a proper gas plant with the full demethaniser, deethaniser, depropaniser and debutaniser set to maximise LPG extraction and ensure their sales gas output is fit for purpose.

    Cowboy operations cherry pick a rough LPG cut with a single stage J-T or turboexpansion stage and more often than not screw up the national sales gas supply grid with intermittent slugs of condensate. 

    Don't confuse typical US practice for global practice. Most of the world falls into the first of these two categories.

  21. 1 minute ago, Tom Booth said:

    What?

    It's friggin' common knowledge except maybe for people in the industry who try to guard it like some kind of trade secret or other.

    It isn't right though is it, Tom.

    Right would be investing in the appropriate refrigeration system to take out the condensate cut you want in a conventional condenser. Just like the textbooks say.

    Just sayin'

  22. 37 minutes ago, Tom Booth said:

    How about you stop devolving the conversation into petty attempts at character assassination.

    If that's how you read my posts then, I'm sorry, it was not my intent.

    37 minutes ago, Tom Booth said:

    If you are unfamiliar with such a use for turbo-expanders, I can provide references...

    Having spent the last 22 years in the West African oilfields, I am unfortunately more familiar with such malpractices than you can possibly imagine. Unless that is you've done time with Shell Petroleum Development Company of Nigeria which would put us on a par. Using a turboexpander as a souped up J-T valve is simply something you should not be broadcasting to the world in my view. At best, people won't have a clue what you're on about, and those who do understand will assume you've worked for Shell Petroleum Development Company of Nigeria. Lose-lose.

  23. 12 minutes ago, Tom Booth said:

    Your referring to a different use case.

    That's like saying the evaporator in a refrigerator is undesirable because it doesn't produce heat or pressure.

    A turbo-expander when used to liquefy gases is not meant to produce work, it's meant to liquefy gases.

    That it succeeds in liquefying gas does not "reduce it's performance" because it does less work. Doing work is not it's purpose.

     

    This is about as a valid a use case as calling your car a tractor to explain why its upside down in a potato field.

    Turboexpanders, if they were in the slightest way relevant to your OP which they are not, are NEVER designed for the purpose you describe and to infer that they are serves no purpose other than to mislead the membership of this site. 

      

     

     

     

     

×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.