What is Dew point: Definition and 27 Discussions

The dew point is the temperature to which air must be cooled to become saturated with water vapor. When cooled further, the airborne water vapor will condense to form liquid water (dew). When air cools to its dew point through contact with a surface that is colder than the air, water will condense on the surface.When the temperature is below the freezing point of water, the dew point is called the frost point, as frost is formed via deposition rather than condensation to form dew. The measurement of the dew point is related to humidity. A higher dew point means there is more moisture in the air.In liquids, the cloud point is the equivalent term.

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  1. P

    A Too much cooling air? (Power supply failures due to condensation)

    I have a situation that I cannot explain so I need the assistance of someone with a good understanding of thermodynamics. I have 36 AC to DC power supplies located in an equipment rack. These power supplies are failing after some time. The failures appear to be moisture related. We put...
  2. abolfazlghasemi

    Hydrogen dew point in power generators

    Large power generators (for example 200 MW) are cooled by H2 in gas form. H2 temperature is +45 to +75 "C. So why hydrogen dew point is important in generator while the lowest hydrogen temperature is 45 "C? And in some Power Stations is monitored online... Thanks, a lot
  3. I

    Dew Point -- will we be able to see our breath?

    Homework Statement The dew point is the temperature at which moist air becomes saturated with water vapor. We can therefore represent how moist a particular parcel of air is by comparing its actual temperature with its dew point temperature. We see the practical effect of reaching the dew...
  4. R

    Thermodynamics Gas Mixture - Dew Point Temperature

    Homework Statement Only Number 1, not number 2 Homework Equations Dew Point Temperature T = Saturated Temperated at Vapor Pressure Partial Pressure = (mole fraction) x (Mixture Pressure) The Attempt at a Solution The dew point temperature is only dependent on the pressure of the water...
  5. R

    Gas Mixture - Dew Point Temperature

    Homework Statement Only Number 1, not number 2 Homework Equations Dew Point Temperature T = Saturated Temperated at Vapor Pressure Partial Pressure = (mole fraction) x (Mixture Pressure) The Attempt at a Solution The dew point temperature is only dependent on the pressure of the water...
  6. Robert James Liguori

    I Humid Air Density Forumulas

    I'm trying to compile a complete list of available humid air density formulas that work with air pressure, temperature and dew point (or RH). If you know any, please advise. Thanks, Robert
  7. I

    Calculating saturation and dew point given pressure and temperature

    Hi guys and gals. Hobbyist, not a student. I've had great input here in the past. Thank you in advance for any direction and help figuring this out. -Seth- 1. Homework Statement I'd like to learn how to calculate relative humidity, saturation, and dew point under differing pressures and...
  8. Ravi Singh choudhary

    I Why evaporative cooling is a constant wet bulb temp process?

    Wet bulb temperature is the lowest thermodynamic temperature of air that can be achieved at ambient condition, by creating 100% relative humidity in the immediate surrounding of the thermometer using cotton wick. As Wikipedia says "By contrast, the dew point is the temperature to which the...
  9. C

    Vapour Pressure at Dew Point

    THERE IS NO TEMPLATE BECAUSE GHIS HOMEWORK WAS PLACED IN AN INCORRECT FORUM Equimolar benzene and and toluene form essentially ideal solutions. At 20degC the vapour of benzene and toluene are 9.866kPa and 2.933kPa respectively. The solution is boiled by reducing the external pressure below the...
  10. Raptor112

    Condensation of your Breath

    Homework Statement On a winter day, suppose your breath has a temperature of 30°C and a dew point of 28°C,and it mixes with the ambient air of temperature –10°C and a dew point of –11°C. Will you see your breath? Assume you are at sea level, and that your breath and the environment mix in...
  11. MtnXfreeride

    Preventing Condensation in Outdoor Enclosure

    Hi, I have comes across bits and pieces of what I want to do online but haven't gotten the answers I need so I'm reaching out for help. This is my first post here. I'm planning to create a box to house an AV receiver outdoors (late spring/summer/early fall only in Maine) inside a screen...
  12. P

    How to reduce RH of air from evaporative cooler?

    Hi guys! I'm new here and this is my first post! I'm a fresh engineering graduate and I'm facing a dilemma. I'm currently in charge of a project. We intend to use an evaporative air cooler for a carbonated soft drink filling line. The flow of air intake is as follows: evaporative cooler -->...
  13. K

    Dew point more important than boiling point

    I was thinking, the critical point between the liquid and gas phases is the dew point, not the boiling point, right? Melting/freezing on the solid/liquid boundary is analogous to evaporation/condensation on the liquid/gas boundary. Boiling is something totally different, and is not possible in...
  14. K

    Dew point and absolute humidity

    Homework Statement Room temperature is 200C and relative humidity is 60%. what is the absolute moisture Homework Equations Vapor pressure at 200C=17.5[atm] PV=nRT Molecular weight of water=18[gr/mol] The Attempt at a Solution The vapor pressure at 200C: $$\frac{x}{17.5}=0.6\rightarrow...
  15. M

    Moving up to dew point and saturation line

    Hi, If we start humidifying an unsaturated air for some dry-bulb temperature, can we move up to dew point for that processes also moving up to saturation line? In other words, Can we make a process in which process line goes up with 90 degrees up to saturation line? Thank you.
  16. P

    What Happens When Water Vapor Cools at Constant Pressure?

    Homework Statement This is a diagram T-v diagram for a closed system consisting of a sample of moist air that is cooled at constant pressure can someone explain what happens for the state of the water vapor to move from d to 2? if its cooling at constant pressure, why does it not stay on the...
  17. P

    Dew point and exhaust temperature

    Homework Statement I'm trying to find some information on "How does the dew point control the exhaust temperature of a thermodynamic cycle?" Homework Equations "The dew point is the temperature at which the water vapor in a sample of air at constant barometric pressure condenses into liquid...
  18. K

    The physics behind the Dew Point phase shift

    Many websites gives the results of Dew Point but not the reason. What is going on at the dew point? Not the result (at a certain VSP vapour becomes liquid if it can find nuclei to coat) but the reason for the result. I have been reading up on this – just out of curiosity – and would like...
  19. M

    Relationship of vapour pressure and Dew Point

    Homework Statement Moist air at 32 degrees C has a dew point of 26 degrees C. The total or atmospheric pressure is 100.7kPa. find the: Molal Humidity Relative Humidity Homework Equations Molal Humidity = \frac{P_{i}}{P_{tot} - P_{i}} Relative Humidity = \frac{P_{i}}{P_{vap}}...
  20. H

    Relative Humidity and Dew Point after compression

    Hello all, Would appreciate some guidance here. I have an air compressor compressing ambient air to 3000 psi into a 425cu-in tank. I have the volumetric flow rate at the exit. If I was looking for relative humidity, dew point, and moisture content/accumulation at the exit, how would I go...
  21. R

    Dew Point Calculation: Find the Temperature

    Hi I am currently writing my master's thesis on preparation of a ceramic powder by spray pyrolysis, and have a question I hope you could help me with. I have a sample of water vapor mixed with air, and I know the specific amount of water vapor (grams of vapor per unit volume of the gas). How...
  22. R

    Thermodynamics is air ducts, dew point

    Can anyone confirm if the flow of air inside an air conditioning duct, when cooled, behaves as constant volume as compared to constant pressure? I am trying to determine the dew point of the flow and, depending of how it behaves inside the duct, this value will depend on if it is at constant...
  23. K

    H20 Molecular shift - what is the initial state just below the Dew Point

    Hi all Another question (sorry) Water vapour in the air will phase shift back to liquid when it reaches its Dew Point temp (Partial Pressure = the Saturated Vapour Pressure), OK I have this. For this phase shift I assume that there are Condensation Nuclei and these nuclei are at a lower...
  24. S

    Dew Point Calculation and Cloud Formation in Mountain Wind Flow

    Dew point Calculation-Please help me! Homework Statement Consider a strong wind aloft that forces air to flow over the mountains from A to E, as in the diagram below. Assume the surface temperature at A is 21 degrees C and the dew point temperature is 5 degrees C; and that any moisture that...
  25. T

    Dew Point Temp: Does it Change with Altitude, Pressure & Density?

    Does dew point temperature remain constant over altitude, pressure, and density? I have to admit that I am having difficulties fully understanding dew point temperature. I understand that dew point temperature is simply the temperature to which a given parcel of air must be cooled under constant...
  26. P

    Dew point of a gas mixture

    Dear All... For my first post in this forum I have choosen an easy question for you all! If I have a gas at room temperature and I start to compress it, when the gas reach its dew point, condensation starts What about for a gas mixture?? I try to be clear! I have two real gasses: A &...
  27. D

    Understanding the Isobaric Cooling of Air and its Effects on Dew Point

    Hi! My Physics introductory book states the following: "A dew point is a state defined by the temperature to which the air has to be cooled isobarically (with constant absolute humidity) for the vapour to become saturated." Humidity is defined as m/V, where m is weight of the vapour, V is...
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