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Mass Transfer - Engineering

Q1:

Which of the following processes is followed by unsaturated air (with dry bulb temperature 12°C and relative humidity 47%) passing through water spray washer (temperature of water being constant at 40°C?

A Humidification only

B Heating only

C Both heating and humidification

D Evaporative cooling

ANS:C - Both heating and humidification

In this scenario, unsaturated air with a dry bulb temperature of 12°C and a relative humidity of 47% is passing through a water spray washer where the temperature of the water is constant at 40°C. Let's analyze the situation:

  1. Humidification: The relative humidity of the incoming air (47%) is lower than 100%, indicating that the air is unsaturated. As the air passes through the water spray washer, water vapor will evaporate into the air, increasing its moisture content. Therefore, the process of humidification occurs as water vapor is added to the air.
  2. Heating: The dry bulb temperature of the incoming air (12°C) is lower than the temperature of the water in the spray washer (40°C). As the air comes into contact with the water spray, it may absorb some heat from the water, causing its temperature to rise. Therefore, the process of heating may also occur.
Given these considerations, both heating and humidification processes are likely to occur as the unsaturated air passes through the water spray washer. The air is both warmed by the higher temperature water and humidified by the evaporation of water into the air stream.