Question

= Q.5: A granular wet solid is taken on a tray (1mx0.6m) and dried in a stream of hot air (120°C; humidity = 0.02 kg/kg dry air, u = 4.5 m/s). The initial moisture content of 28% is to be dried to 0.5% (All on dry basis). From lab tests it is known that the critical moisture content is 12% and the equilibrium moisture is negligible. If the solid loading is 35 kg dry solid /m², calculate the drying time. Use he = 0.0204G08 , G in kg/m².h and he is in W/m².K. 2

Answer 1

To calculate the drying time, we need to determine the rate of moisture removal and the amount of moisture that needs to be removed. The rate of moisture removal can be calculated using the given equation. The drying time can then be calculated by dividing the moisture to be removed by the drying rate.

Step-by-step explanation:

To calculate the drying time, we need to determine the rate of moisture removal and the amount of moisture that needs to be removed. The rate of moisture removal can be calculated using the equation:

he = 0.0204G08

where he is the drying rate in kg/m².h and G is the moisture content in kg/m².

The amount of moisture that needs to be removed can be calculated using:

Moisture to be removed = Initial moisture content - Final moisture content

Using these values, we can calculate the drying time by dividing the moisture to be removed by the drying rate:

Drying time = Moisture to be removed / Drying rate

Substituting the given values into the equations will give us the drying time.

Answer 2

The drying time for the granular wet solid can be calculated using the given equation and information provided. First, the amount of water that needs to be removed is calculated, then the mass of water vapor in the air is determined. Next, the mass of dry air is calculated, and finally, the drying time can be solved for.

Step-by-step explanation:

The drying time for the granular wet solid can be calculated using the equation he = 0.0204G08, where he is in W/m².K and G is in kg/m².h. From the given information, we can calculate G as follows:

1. Calculate the amount of water that needs to be removed: 28% of 35 kg/m² = 9.8 kg/m²
2. Calculate the mass of water vapor in the air: 0.02 kg/kg × mass of dry air = 0.02 × (35 kg/m² / (1 - 0.28)) = 1.17 kg/m²
3. Calculate the mass of dry air: mass of dry air = mass of wet solid - mass of water removed = 35 kg/m² - 1.17 kg/m² = 33.83 kg/m²
4. Calculate G: G = mass of water vapor / drying time = 1.17 kg/m² / drying time

Solving for drying time: drying time = 1.17 kg/m² / G