Page 3 of 3 FirstFirst 123
Results 27 to 32 of 32
  1. #27
    Join Date
    Jul 2001
    Location
    Buffalo N.Y.
    Posts
    1,571
    A cloud forms when air heated by the sun rises like a balloon. As it rises, it slowly cools until it reaches the saturation point and water condenses, forming a cloud. As long as the cloud (and air its made of) is warmer than the outside air around it, it "floats", or stays suspended.
    Once it cools enough or gets heavy enough water drops out.

    Clouds are ususally a mixture of water droplets and ice crystals.

  2. #28
    Join Date
    Sep 2002
    Location
    South Dakota
    Posts
    6,579


    In order to have true condensation occur you must have a surface at or below dewpoint. According to the meteorology books dust or microscopic particles at or below dewpoint must be present before it can rain. I question the assertion that clouds are actually liquid as opposed to high concentrations of uncondensed vapor. Another interesting fact is that there is more to the process of rain than condensation. When clouds are seeded the seeding material not only provides a surface for condensation but according to the meteorology books there is some sort of chemical process that takes place. Seeding clouds does not always work because of this process. I have yet to understand the chemical process involved.

    In addition, microscopic particles are easily dept adrift in air. Dust is an example and extremely small microscopic water particles would also be easy to keep suspended with even small wind currents.

    In fact, it would never rain if it were not for the suspended dust particles in the air giving the moisture in clouds a surface to condense on. You cannot have condensation without a surface. All clouds are already at 100% RH which means they are already at their dewpoint, yet it does not guarantee condensation and rain.

    Am I missing something?


  3. #29
    Join Date
    Apr 2002
    Posts
    11,808
    Originally posted by lmtd
    Dry air.

    70 F air
    100% RH = Density .0742
    50% RH = Density .0746
    10% RH = Density .0749

    Cubes to make a pound of air:

    100% RH = 13.7
    50% RH = 13.5
    10% RH = 13.4

    Water vapor molecules are VERY far apart compared to many other substances. Tis also a portion of WHY so much energy is required to seperate them, or draw them back together, aka latent heat.
    Specific volumes on the p-chart are always given as cubic feet per "pound of dry air".

    Fill a very elasitc balloon with a cubic foot of bone dry air to atmospheric pressure.

    Make an assumption that no tension builds up in the balloon skin.

    Heat the air inside this balloon and the balloon will expand and the internal pressure will still be atmospheric. This is how adding sensible heat increases the specific volume.

    Add a small amount of steam to this balloon and it will expand more, and it will still be at atmospheric pressure.

    The volume of the balloon is now greater however it still holds the same amount of "dry air" with respect to mass. The denisty of the air inside of the balloon is the mass of the original air, plus the mass of the steam all divided by the volume of the expanded balloon. With steam being lighter than both oxygen and nitrogen, the density of the air/water vapour mixture is decreasing because we have added a lighter substance and we have increased the volume. This is how latent heat increases specific volume.

    Concerning the atmospheric pressure inside the balloon, it is created by the gas components inside the ballon. The oxygen contributes a partial pressure, the nitrogen contributes its partial pressure and the steam contributes its partial pressure. These three partial pressures add up to create the atmospheric pressure inside the balloon.

    When the partial pressure of the water vapour in the balloon is equal to the vapour pressure of steam at the balloon temperature, that is when the air/vapour mixture inside the balloon is saturated or has 100% RH.






    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  4. #30
    Join Date
    Apr 2002
    Posts
    11,808
    Originally posted by NormChris


    In order to have true condensation occur you must have a surface at or below dewpoint. According to the meteorology books dust or microscopic particles at or below dewpoint must be present before it can rain. I question the assertion that clouds are actually liquid as opposed to high concentrations of uncondensed vapor. Another interesting fact is that there is more to the process of rain than condensation. When clouds are seeded the seeding material not only provides a surface for condensation but according to the meteorology books there is some sort of chemical process that takes place. Seeding clouds does not always work because of this process. I have yet to understand the chemical process involved.

    In addition, microscopic particles are easily dept adrift in air. Dust is an example and extremely small microscopic water particles would also be easy to keep suspended with even small wind currents.

    In fact, it would never rain if it were not for the suspended dust particles in the air giving the moisture in clouds a surface to condense on. You cannot have condensation without a surface. All clouds are already at 100% RH which means they are already at their dewpoint, yet it does not guarantee condensation and rain.

    Am I missing something?

    The clouds have to be liquid, else they would be invisible.

    Do we exhale dust, and that explains how we see our breath in the winter. Ever see a fog stream entrained by a Bard Wall Unit cooling a packed bar?

    I believe with the Dri_Steem Humidifiers they inject steam 'against the air flow'. The steam condenses to droplets and re-evaporates.

    Interesting concept of needing a surface to condense upon, I always use that concept in sales pitches in reference to humid outdoor air infiltrating in and looking for a surface at our below its dewpoint to condensate and cause mold problems.
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  5. #31
    Join Date
    Apr 2003
    Location
    Iowa
    Posts
    2,652
    Question......In the case of clouds, could an upwards current of air in the atmosphere be what is suspending them?

    The warm surface air rising into the cool upper atmosphere is causing a current....The vapor in that warmer air is infact invisible but it is carried upward with the warmer air into the cooler stratosphere where is condenses into small droplets and ice crystals. It is said to be suspended by the upward lift until the droplets become large enough(grouping together) to weigh enough to overcome the lift and fall from the sky, rain.

    After all, lightning is more concentrated at an area of lift in a thunderstorm(I used to chase storms), therefore, we know there are vertical currents in our atmosphere.

    Just thought maybe I'd add another twist
    There are 3 ways to do anything in life; Good, Fast, Slow: You can pick any 2.

  6. #32
    Join Date
    Jul 2001
    Location
    Buffalo N.Y.
    Posts
    1,571
    "Thermal UpDrafts"

Page 3 of 3 FirstFirst 123

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Comfortech Show Promo Image

Related Forums

Plumbing Talks | Contractor Magazine
Forums | Electrical Construction & Maintenance (EC&M) Magazine
Comfortech365 Virtual Event