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3.14. Cooling Tower - TOWER
The air could ideally come out at a temperature equal to the water inlet
temperature, but due to resistances, heat transports, mixing etc. the real
outlet temperature of the air is expected to be somewhat lower. This is
modeled by means of the approach temperature difference ∆T minair,o :
∆T minair,o = T w,i − T air,o (3.108)
3. Since some of the water in the water circuit has been lost to the air
during the evaporation process, some new water is added (ṁ add ).
A mass balance is made for each of the steps for both the water flow
and air flow. The overall mass balances becomes:
ṁ w,o = ṁ w,i (3.109)
ṁ air,o = ṁ air,i + ṁ w,add (3.110)
An energy balance is also added for each step:
Ḣ air,i +Ẇ f an = Ḣ air,mp pressurizing (3.111)
Ḣ air,mp + Ḣ w,i = Ḣ air,o + Ḣ w,mp evaporation (3.112)
Ḣ w,mp + Ḣ w,add = Ḣ w,o water side refill (3.113)
The variable (W Q r atio ) expresses how much power the fan consumes
relative to how big a cooling service the tower delivers to the water
circuit.
W Q r atio =
Ẇ f an
˙Q cool
(3.114)
˙Q cool = Ḣ w,i − Ḣ w,o (3.115)
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