Preheating air by steam for use in a dryer. an air stream at 32.2°c is to be used in a dryer and is first preheated in a steam heater, where it is heated to 65.5°c. the air flow is 1000 kg mol/h. the steam enters the heater saturated at 148.9°c, is condensed and cooled, and leaves as a liquid at 137.8°c. calculate the amount of steam used in kg/h.

Explanation:

Given data:

air stream temp 32.2 degree celcius

steam heater is at 65.5 degree celcius

flow of air 1000 kg mol/h

we know that = 29.2 Kj/KG-MOL

Saturated stream is at 148.9 and from steam table hg is 2745.12 kJ/kg

saturated water us 148.9 degree  and from steam table hf = 627.46 kJ/kg

then cooled to saturated water with temperature 137.8 degree celcius and hf = 579.71 kJ/kg

from energy balanced

solving for m_w