"In a sling psychrometer(with dry and wet bulbs), if the moist air is not saturated(with water vapour) then it evaporates some water on the wet bulb and in turn cools the wet bulb.So the wet bulb temperature falls below the dry bulb temperature" .This is the explanation given in the book Iam using(Fundamentals of thermodynamics by Moran and Shapiro). 1)Does this mean, the wet bulb and dry bulb temperatures are initialy same(before exposing to air)? 2)If evaporation occurs continuously as air is blown over the bulbs, why isnt the temperature reducing continuously(it stops at a point)?
2) evaporation continues which reduces the wet bulb temperature until the temperature stays constant because the rate of evaporative heat loss is balanced by the heat absorbed due to the temperature difference between the wet bulb temperature and ambient temperature is in equilibrium. The humdity can then be obtained from a Mollier or psychrometric chart.