The air is exhausted from the dryer with a temperature of 50°C and a relative hu

Question

The air is exhausted from the dryer with a temperature of 50°C and a relative humidity of 50%.

Questions:

It is not uncommon in tropical countries to see local residents set up small-scale food processing operations to dry fruits or vegetables. In one such facility, air is brought into the building where a dryer for dehydrating cassava is housed. The incoming air has a temperature of 28°C and a relative humidity of 80%. After filtering, the air is heated to 60°C and used to dry the cassava slices in the dryer. While in the dryer, the air loses some of its heat and picks up moisture.

What is the relative humidity of the heated air entering the dryer? (2 marks)

How much moisture was picked up per kilogram of dry air while it was in the dryer? (2 marks)

If the exhaust air from the dryer was cooled, at what temperature would it become saturated? (2 marks)

Being concerned about the environment, the processor feels that she should filter and cool the exhaust air back to its original temperature of 28°C before venting it to the outside atmosphere. If the dryer exhaust air was cooled to 27°C, what would be its relative humidity? To cool the outgoing air, the processor uses an air-to-air countercurrent heat exchanger that takes heat from the outgoing air and uses it to warm the fresh incoming air. In this way, the process becomes more energy efficient. (2 marks)

Why does the processor filter the incoming air that is going to the drying process? (2 marks)

Explanation / Answer

1) Relative Humidity will be

Temp 273+28=301

80%=.8

301*.8=24.8

2) Zero Degree Celsius

5) So that the heat will be in such a way it can only dry up the water rather than to heat the proes of the hair.

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