1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Fluid Flow Questions

  1. Aug 29, 2012 #1
    I have a question. All things being equal as far as flow and pressure goes...where would the gas preferentially flow in the drawing I made. To T1 or T2. Is there equation someone can point me to that will show this. Thanks.

    Attached Files:

  2. jcsd
  3. Aug 29, 2012 #2

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    Can't tell what that is a picture of.

    There seem to be three temperatures - T1 seems to be between some rectangles, T2 seems to be to one side (presumably there is a temperature gradient of some kind in there? There is an intermediate T3 which does not seem to appear anywhere.

    There is a label "gas flow" apparently along a line.

    You need a clearer diagram.
  4. Aug 29, 2012 #3
    Let me clarify. Gas enters through an orifice labled gas flow. The gas entering through this temperature is somewhere between T1 and T2. T2 is at ambient atmosphere at close to room temperature. T1 is a chamber of fluid flow also at atmospheric pressure at very high temperatures. If the gas enters through the gas flow direction through the orifice at T3 which is between T1 and T2 where will it travel.

    Thanks you.
  5. Aug 29, 2012 #4

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    What are the four blocks - cutaway of a system of pipes?
    Does the interior also have gas in it or is it evacuated?
    Is the system in equilibrium before the new gas is injected?

    Gas already in the system will want to move away from the center (T1), but there will be some flow inwards. New gas injected at the place specified would tend to move with the ambient flow.

    It "up" on the diagram is actually upwards, then the gas at T1 will prefer to exit through the top. Cool air comes in the bottom and the sides.
  6. Aug 29, 2012 #5
    Don't want to give away too much but the blocks are two plates with holes in them acting as a valve. The valve is controlling the flow of molten metal. T3 is close to ambient temperature, but will be slightly hotter than T2 because of some heating while traveling to the injection point. Picture a groove around the center hole of the two blocks that distributes gas at T3 evenly around the hole. Interior of the hole has molten metal poring through it but it is open pore so, I would think it is at atmospheric pressure.

    Not sure what you mean by equilibrium. I would say no it's more complex than that.

    Evacuation of the interior is not possible. Is it creating a possible vacuum effect because due to poring the metal? I'm not sure.
  7. Aug 29, 2012 #6

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    Well then I cannot be precise.

    If I imagine two plates with a hole in the middle, molten metal flows through the hole so no air can get in through the top or bottom, and the edges are open to the air - then some parts of the edge will have inflowing air and others outflowing with the exact places constantly changing unless the geometry is small enough for micro-cells to form.

    What do you need to know for?
  8. Aug 29, 2012 #7
    Does this picture help? The blocks are just a gate system for the flow of the molten liquid.

    I drew a top view of the blocks below on the drawing.

    Attached Files:

  9. Aug 29, 2012 #8
    I'm wondering what would happen if I play with the temperature of T3.
  10. Aug 29, 2012 #9

    by that i meant nevermind the comment not the question.
    Last edited: Aug 29, 2012
  11. Aug 29, 2012 #10
    But it gets complicated. At first pore maybe the plates are perfectly aligned. As life increases the holes become larger so they may be only partially open between subsequent pores creating air pockets as they are partially opened.
  12. Aug 29, 2012 #11

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    Nope - not at all clear.
    You've just added a hopper - in the overhead view it looks not like there is a circular chamber around the hole the metal pours through - or maybe it's just a groove between two closely fitting plates. The angle that the gas is being injected suggests a vortex is added to whatever other motion their may be.

    I have no idea. You'll just have to work it out from first principles... the hotter gas will be moving faster so it will tend to move away from the hot area ... cooler gas will try to move in to replace it.

    What are you hoping will happen? What is injecting the gas close to a column of molten metal supposed to achieve?

    Bottom line though is that I am only here to help you understand (and phrase) your problems better so that you will know how to solve them. I am prepared to do that for free you understand... up to a point. If you are unwilling to tell me about your problem then I cannot help you.
  13. Aug 29, 2012 #12
    Could you just explain how the flow of gases work first? Cool moves to hot? Or is it not that simple.

    T3 is only very slightly hotter than T1 or very very close to the temperature of T1.

    The boxes are what we call a slide gate plate system in the industry.

    The hopper could either be a ladle for molten steel or what we call a tundish used for casting.
  14. Aug 29, 2012 #13
    I'm guessing it further complicates matters that the gas coming in at T3 is argon and the gas at T2 is the atmosphere.
  15. Aug 29, 2012 #14

    Simon Bridge

    User Avatar
    Science Advisor
    Homework Helper

    Not that simple.

    In general - hot gas molecules move faster than cold ones so they tend to move away from the hot place. But that would reduce the pressure, sucking more gas in - which tends to be the cold gas. This van be chaotic (in the technical sense) but there are situations where you get circulation happening - which is called a cell.

    Hot gas is less dense (because faster) so it tends to rise.

    Think about how thunderheads form, or thermals, or how high explosive has a characteristic mushroom cloud.

    All this is for some kind of open space - you can get gas to move in a narrow pipe fairly regularly - it does so by expanding from the hot end of the pipe though you'd usually pump it.

    If the hot air escapes through a hole at the top of a chamber and you let cold air in through the bottom (it gets sucked in) you have a chimney effect.

    A bunsen burner sucks air in through holes in the bottom of a pipe which has gas flowing through it under pressure. This is why I guessed that the injected gas will go with the ambient flow.

    It is not easy.

    lets see ... argon + molten metal going through holes: casting?
  16. Aug 29, 2012 #15


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    In investment casting or a sand mold I would think that air could flow thorough the mold. Like Simon I am having trouble interpreting your drawings.

    I have done a fair amount of Aluminium investment casting.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook