The air supply for a dryer has a dry-bulb temperature of 32^DegC and a wet-bulb

Question

The air supply for a dryer has a dry-bulb temperature of 32^DegC and a wet-bulb temperature of 25 5^DegC. It is heated to 90^DegC by coils and blown into the dryer. In the dryer, it cools along an adiabatic cooling line as it picks up moisture from the dehydrating material and leaves the dryer fully saturated. What is the dew point of the initial air? What is its humidity? What is its percent relative humidity? How much heat is needed to heat 100 m3 of initial air to 90^DegC? How much water will be evaporated per 100 m3 of air entering the dryer? At what temperature does the air leave the dryer?

Explanation / Answer

Data supplied:

Dry bulb temperature =32°C

Wet bulb temperature =25.5°C

Heated to 90°C

From the psychrometric chart

a) dew point=23.196°C

b) humidity ratio=0.018032 kg/kg

c) 59.758%

d) Amount of heat needed: (Volume of air/Humidity volume) *t * Humid heat

Humid heat = 0.24 + 0.45*humidityratio = 0.24 + 0.45*0.018032 = 0.2481 Kcal/°C*kg

Therefore, Amount of heat needed=(100m^3/0.888m^3/kg)*(90°C-32°C)*0.2481 Kcal/°C*kg =16.205 kCal/min

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