Question

Air entering a dryer has a temperature (dry bulb) of 60°C and a dew point of 26.7°C. Using the humidity chart, determine the actual humidity H, percentage humidity HP, humid heat cS and humid volume vH.

Answer 1

Solution:

The dew point of 26.7^?0C is the temperature when the given mixture is at 100% saturation.

Starting at 26.7°C (Fig. 9.3-2), and drawing a vertical line until it intersects the line for 100% humidity, a humidity of H = 0.0225 kg H2O/kg dry air is read off the plot. This is the actual humidity of the air at 60°C.

Stated in another way. if air at 60 °C and having a humidity H = 0.0225 is cooled, its dew point will be 26.7°C. In English units, H = 0.0225 lb H2O/lb dry air.

Locating this point where H = 0.0225 and t = 60^?0C on the chart, the percentage humidity H_?p is found to be 14%, by linear interpolation vertically between the 10 and 20% lines.

The heat capacity of air and water vapor can be assumed constant over the temperature ranges usually encountered at 1.005 kJ/kg dry air•K and 1.88 kJ/kg water vapor•K,respectively.Therefore, the humid heat for H = 0.0225 is, from Eq. (9.3-6),

You can check the values from the graph given below,