Question

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.

Answer 1

Answer:

$m_w  = 449.04 kg/hr$

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 $C _{AIR}$ = 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

$mC\Delta T \for\ air  = mC\Delta H$

$1000\times 29.2\times (65.5 -32.2) = m_w\times (2745.12 - 579.71)$

solving for m_w

$m_w  = 449.04 kg/hr$