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Thread: Vapor Pressure
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08-03-2002, 04:23 PM #1
Vapor Pressure
If I plot design room temperatures on the (ASHRAE) psychrometric chart, say room (1) @36degF @60%R.H. and Room (2) @ 28degF @ 80% R.H., whereas the "line" is horizontal straight across the chart, would my vapor pressure be the same?
And as such, would that make the latent load of infiltration between the spaces null?
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08-03-2002, 07:42 PM #2If I plot design room temperatures on the (ASHRAE) psychrometric chart, say room (1) @36degF @60%R.H. and Room (2) @ 28degF @ 80% R.H., whereas the "line" is horizontal straight across the chart, would my vapor pressure be the same?
And as such, would that make the latent load of infiltration between the spaces null?Prof Sporlan
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09-03-2002, 01:35 PM #3
Ok, let's say there is a large vapor pressure difference. Would an air curtain do anything to impede the flow of moisture? If so, how?
Dan
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09-03-2002, 03:42 PM #4
One would need a vapor barrier to prevent the flow of moisture to an area of lower humidity ratio. It would seem an air curtain would not make an effective vapor barrier.
Prof Sporlan
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09-03-2002, 04:26 PM #5
Prof.,
Have you followed the thread that Dan and I have been exchanging in regarding air curtains - "infiltration".
Would any forced air movement (at an entry) decrease infiltration in such the same manner as pressure drop occurs due to "friction of such movement" of gasses or liquids? Would not the same effect of movement/friction, such as say refrigerant in transport tubing, cause a decrease in the "pressure", or difference thereof in a gaseous (air) medium?
Could creating the intrained movement and velocity of (air) cause an opposing force to the force of pressure difference resulting from air densities and pressures?.
Can such effects of pressure drops (or forces) resulting from air movements be determined in relation to the force of infiltration vs. the opposing force of the pressure drop (or opposing force) created by some recirculatory air movement (at an entry)?
Can it be said, that if such air movement can oppose the measureable force of infiltration as demonstrated by Newton's second law, that only the sensible infiltration could be negated, however latent (water) infiltration/exchange would occur through the opposing force of the airstream(s), nonetheless?
To what extent is the water intrained into the air mass which contains it? would it be less than the "heat" which suspends it? Or would OSMOSIS persist and overcome any mechanical forces or venturi type effects?
Would that be REVERSE osmosis?Last edited by herefishy; 09-03-2002 at 08:47 PM.
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13-03-2002, 01:23 AM #6
Yeah, that's what I have been wondering. Does vapor pressure permit moisture to sneak through an air curtain even when the dry air is impeded. Or is the air to be considered a homogeneous enthalpic mass?
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13-03-2002, 04:58 AM #7Yeah, that's what I have been wondering. Does vapor pressure permit moisture to sneak through an air curtain even when the dry air is impeded.Prof Sporlan
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14-03-2002, 12:16 PM #8
Partial pressures is a term that I have never understood. I was wondering if the answer lie in whether air is an enthalpic indivisible sum of how we see air, or.... let me try a different tact:
Can it be that the force of air from warmer toward cooler be simply a reflection of vapor pressure differences? Does a dry bulb temperature exert any force besides conduction on a cooler dry bulb temperature?
Beyond air density, what resistance does a downward flowing air curtain have toward impeding flow between one vapor pressure and another? Surely, just because air is flowing downward there shouldn't be a greater resistance to vapor flow?
We know that a cold surface collects moisture from air in varying degrees relative to dry bulb cooling. I suspect if we had perfectly still air between a warm surface and a cold surface, we would not be able to have still air.
Is it perhaps vapor pressure that moves all the air as an enthalpic mass that creates the breeze?
That we could have no breeze between these surfaces beyond that which would result from the smaller change in dry air density differences?
Clumsy kindergarten wonderings. Perhaps if I understood the concept of partial pressures, I would understand.
But is it wrong to think that differences in vapor temperature/pressures can be independent of differences in dry air temperature/pressures within the same air mass?
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14-03-2002, 04:00 PM #9
..... keep in mind..... THE WATER IS MOVING TOO! And it has momentum.
What (vapor) pressure difference would be necessary to overcome the path (momentum), at a given velocity, of the (hypothetically) recirculating vapor?