Question

3. In an air conditioning system, the air from the refrigeration cooing coils at 10°C and 100% relative humidity is to be mixed adiabatically with 20% outside fresh air at 36°C and 30% relative humidity. Determine the final temperature and relative humidity of the mixed stream by use of (20 pts) (a) appropriate formulas/equations and stean property tables and (b) the Psychrometric Chart, showing all appropriate points on the chart.

Answer 1

Given:

air 1 : temperature
10"
, relative humidity
100
%

air 2 (20 %) : temperature $36\degree$ , relative humidity %

First of all let us locate these two points on psychrometric chart,

Now,

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from the chart $w1=$ 0.0075 and $w2=$ 0.0115

for adiabatic mixing of air 1 and 20% air 2,

$\\\frac{w_2-w_3}{w_3-w_1}=\frac{m_{a1}}{m_{a2}}\\ \\\therefore \frac{0.0115-w_3}{w_3-0.0075}=\frac{m_{a1}}{0.2m_{a1}}\\ \therefore w_3=0.008166$

Now, locate the point where $w3=0.008166$ on the line joining point 1 and point 2

from the chart,

temperature of the mixed stream is $17\degree$ C and relative humidity is 70%