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A chemical engineer interested in physics.


Dec
1
awarded  Popular Question
Sep
22
comment What makes water boil?
One interesting thing is that due to heat transfer effects, the temperature of the (usually metallic) heat transferring surface has to be somewhat (usually 5 degC depending on surface metallurgy and finish) above the boiling point for boiling to actually start.
Sep
14
accepted In the classic viscosity definition, why does doubling the plate gap cause the force to halve (intuitive)?
Sep
14
accepted What is the molecular model of heat of mixing?
Sep
10
comment In the classic viscosity definition, why does doubling the plate gap cause the force to halve (intuitive)?
The implication of this analogy is that it takes less effort (force) to move a thicker stack of paper than a thinner stack at the same top sheet velocity?!? The bulk system momentum would seem to be the same in both cases since I have twice the mass each "new" piece with half the velocity of the old piece. But my force has decreased per the equation so it would seem I got something (same momentum) for nothing (half the force). Sorry, I can't tell whether this means your analogy fails this thought experiment or my thinking is just wrong (the probable case).
Sep
10
accepted What is an intuitive picture of the motion of nucleons?
Sep
10
asked In the classic viscosity definition, why does doubling the plate gap cause the force to halve (intuitive)?
Sep
5
asked What is an intuitive picture of the motion of nucleons?
Aug
29
comment Pressure change due to fan removing air from a non-airtight room
Wow, I'm just a chemical engineer but statistical mechanics certainly isn't how I would have solved this problem. Where exactly is the fan located? If it is freestanding in the large room then the fan will just recycle the air in circles and the pressure in the room will equilibrate with the outside pressure. If the fan is located in the hole then the equilibrium pressure in the room will depend on the head curve of the fan and will be outside pressure minus the maximum head developed by the fan at zero flow.
Jul
6
awarded  Yearling
May
7
awarded  Commentator
May
7
comment Why is compressible flow near the choke point so efficient?
To clarify slightly: I am interested in why the conversion of enthalpy into kinetic energy becomes more efficient (my definition of efficiency as: less relative entropy production per unit production of kinetic energy) as you approach the choke point (Mach 1 for Fanno flow). Maybe another way of saying it that reinforces @kleingordon post is "What is occurring at the microscopic level in terms of reducing production of disorder when the flow is near the choke point?"
Apr
27
awarded  Critic
Apr
4
revised Why is compressible flow near the choke point so efficient?
added 1 characters in body
Mar
29
comment Why is compressible flow near the choke point so efficient?
@RonMaimon Interesting that you believe the "slowness" of the flow is important. This would make sense as the reversibility of a process is related to its "slowness" (really meaning differential driving forces). Also, while Fanno and Rayleigh flow show the referenced behavior near Mach 1 which would support your pressure wave propagation speed theory, note that isothermal flow shocks at subsonic speeds at Mach 1/sqrt(gamma) (~ Mach 0.88 for steam), and that the flow approaches frictionless (i.e. the process entropy generation is zero) at this lower Mach number as well.
Mar
29
comment Why is compressible flow near the choke point so efficient?
@kleingordon I agree that the flow always experiences friction since you can only asymptotically approach isentropic flow. I am interested in why the relative effect of friction decreases as velocities approach Mach 1 from either side. Also, the Fanno flow model doesn't have to assume any particular friction factor nor that it's constant across the flow. These curves can be developed strictly from the mass and energy balance w/o reference to the momentum balance (4 equations in 4 unknowns). You only need the momentum balance when you are interested in the length traversed by the flow.
Mar
28
awarded  Editor
Mar
28
revised Why is compressible flow near the choke point so efficient?
clarification
Mar
27
asked Why is compressible flow near the choke point so efficient?
Mar
24
awarded  Enthusiast