Question

100 kg of a material with 60% humidity (wet basis), must be brought to a moisture content of 20% (wet basis) by means of an air stream with a temperature of 50 ° C and a relative humidity of 40%. Calculate the total volume of air needed to perform this process

Answer 1

Given: 100 kg of material with 60% moisture on wet basis.

Converting to dry basis:

Let X be the weight of moisture:

According to the question:

X = 60% of total weight

Total weight = Mass of material + Moisture = 100 + X

X = 0.6 x ( 100 + X)

X = 60 + 0.6X

X = 150 kg

Question: To bring the moisture down to 20% wet basis

Let X be the weight of moisture:

X = 0.2 x ( 100 + X)

X = 20 + 0.2X

X = 25 kg

So, we have to remove 125 kg of moisture

Incoming air is at 50°C and has a relative humidity of 40%

Using Psychometric chart, we see that: Humidity ratio of air at 50°C and 40% RH is 32.01 g/kg

and at 100% RH is 86.720 g/kg

Therefore, per kg of air, ( 86.72 - 32.0) = 54.71 g can be transferred.

Therefore, for 125 kg to be removed:

we need: 125/0.054 = 2,314.81 kg

Therefore, we need 2,314.81 kg of air at 50°C and 40%RH