Question

A dryer must remove 200 kg of H2​O per hour from a certain material. Air at 22∘C and 50% relative humidity enters the dryer and leaves at 72∘C and 80% relative humidity What is the weight (in kilograms) of bone-dry air used per hour? The barometer reads 103.0kPa.

Answer 1

The weight of bone-dry air used per hour in a dryer can be determined through psychrometric calculations, which require the use of a psychrometric chart or relevant equations to find the humidity ratios of the air entering and leaving the dryer. The mass flow rate of dry air is then calculated with the given water removal rate and the difference in the humidity ratios. Specific numeric values cannot be provided without the necessary psychrometric data.

Step-by-step explanation:

To determine the weight of bone-dry air used per hour in the drying process, we need to use psychrometric principles to find the moisture content of the air before and after the drying operation. Assuming ideal gas behavior and using a psychrometric chart or relevant equations, we find the moisture content (also known as the 'humidity ratio') of the air entering and leaving the dryer. We would subtract the humidity ratio of the outgoing air from that of the incoming air to find the amount of moisture picked up by the air in the dryer. With the weight of water removed known (200 kg/h), we can find the mass flow rate of dry air needed to achieve this moisture pickup. Without the psychrometric data or detailed equations, we cannot provide a specific numeric answer.

However, in practice, you would determine these humidity ratios using a psychrometric chart or equations related to air properties at specific temperatures, relative humidity levels, and atmospheric pressures. The weight of the dry air is then calculated by the formula: Mass of dry air = (Mass of water removed)/(Humidity ratio of outgoing air - Humidity ratio of incoming air).