Dry & Wet Bulb Temperature :-

Hydrometer or Psychrometer gives the dry bulb and wet bulb readings. Wet bulb is covered with a wetted gauge dipped in water. The wet bulb reading will be less than dry bulb reading, the difference in reading is called the wet bulb depression and depends on the water vapour or moisture content of air. The drier the air, the more rapid would be moisture evaporation form the wet bulb gauge giving a cooling effect. Thus greater the difference in reading, drier the air and less is the %RH. Hand sling type instrument to give air motion across the gauge gives accurate reading than still air thenno meters. As the air is cooled at constant pressure, RH gradually increases as the cold air can not hold moisture, until saturation or dew point is reached.

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