Download Aptitude Crack
img not found img not found

Mass Transfer - Engineering

Q1:

In case of unsaturated air

A dew point < wet bulb temperature

B wet bulb temperature < dry bulb temperature

C both (a) and (b)

D neither (a) not (b)

ANS:C - both (a) and (b)

  1. Dew Point < Wet Bulb Temperature:
    • The dew point temperature is the temperature at which air becomes saturated with water vapor and starts to condense into liquid water (dew), given its current humidity and pressure. It's essentially the temperature at which the air is holding as much moisture as it can at a particular pressure. If the air temperature decreases below this point, moisture will begin to condense out of the air.
    • The wet bulb temperature is the temperature recorded by a thermometer that has its bulb wrapped in a wet wick or cloth, with air flowing over it. As water evaporates from the wet surface, it cools the thermometer to a lower temperature than the dry bulb temperature. This temperature represents the cooling effect of evaporation and is a measure of the air's humidity and thermal comfort.
    • In unsaturated air, where the air is not holding as much moisture as it can at the given temperature and pressure, the dew point temperature is lower than the wet bulb temperature. This is because the dew point represents the temperature at which saturation occurs, while the wet bulb temperature reflects the cooling effect of evaporation, which occurs even in unsaturated conditions.
  2. Wet Bulb Temperature < Dry Bulb Temperature:
    • The wet bulb temperature represents the temperature recorded by a thermometer with its bulb wrapped in a wet wick or cloth, with air flowing over it, as described above.
    • The dry bulb temperature is the traditional air temperature measured with a standard thermometer.
    • The wet bulb temperature is typically lower than the dry bulb temperature because the evaporation of water from the wet surface cools the thermometer. This cooling effect is greater when the air is dry and less saturated with moisture, resulting in a larger difference between the wet bulb and dry bulb temperatures.
In summary, in unsaturated air:
  • The dew point temperature is lower than the wet bulb temperature because the dew point represents the temperature at which saturation occurs, while the wet bulb temperature reflects the cooling effect of evaporation.
  • The wet bulb temperature is lower than the dry bulb temperature due to the cooling effect of evaporation, which is more pronounced in dry air.