# Thermodynamics-psychrometry question, mixing two streams of warm moist air

1. Jul 17, 2011

### DSoup

1. The problem statement, all variables and given/known data

I'm trying to determine how to go about attacking this problem that I'm doing to

I have 2 streams of air mixing, and I'm trying to find the temperature and relative humidity of the third stream.

Stream 1: 2bar, 20C, 40%rh, and 1kg/s
Stream 2: 1bar, 20C, 4kg/s

So I know I can find all my values for the first stream, but the second stream doesn't give me enough to find it on the psychometric charts.

2. Relevant equations

m=mass of mixture
ma=mass air
mv=mass vapour
h=enthalpy of mixture
ha= enthalpy dry air
hv=enthalpy of water

Mass Balance
m1+m2=m3
ma1+ma2=ma3
mv1+mv2=mv3
m=ma+mv

Energy balance
m1h1+m2h2=m3h3 and all variations of this with the contents of the air

phi1=rh=Pv1/Pg1

where phi is the relative humity
Pv1 is the partial pressure of water
Pg1 is the saturation pressure of water at the given temperature

w=mv/ma for all values.

energy=mc(delta)T

where c is the constant used to determine this (name escaping me right now) (units of kj/kg.C)

3. The attempt at a solution

I got my values for state one, I've tried energy balance and mass balance, but I end up with more variables than equations and I've been confusing myself all day trying to do this. I can't find ANY question in over 3 books that excludes all data about state three other than the mass flow rate, and excludes the data required from the second stream of air.