HVAC SYSTEMS - HFT Stuttgart

Page - 33 -
CHAPTER 02
heated up and a part of the water is evaporated which increases the vapour
pressure. The water vapour flows to the condenser where it is condensed at
high vapour pressure and high condensation temperature. The condensed
water is then led back to the evaporator for a closed cycle. Due to the pressure
difference between condenser and evaporator a throttle is integrated in the back
flow tubing. The heat of the condenser and of the absorber is rejected to the
environment in a dry heat rejection system or an open wet cooling tower.
Evaporator
Fig. 2-7 shows the evaporator of the ACM model with the inlet and outlet
conditions of the internal circuit.
Fig. 2-7: Evaporator of the ACM model
The cooling capacity of the evaporator can be described by the mean
temperature difference between the external and the internal temperature
multiplied by the overall heat transfer coefficient of the heat exchanger which is
equal to the internal evaporator enthalpy difference qe multiplied by the vapour
mass flow rate.
e
( t e −T
e ) UAe
m&
V qe
Q&
=
= (2.2.2-1)
The factor qe is defined as the enthalpy difference between the produced water
vapour h10 and the water entering the evaporator h9.
q e
= h − h
(2.2.2-2)
10
9
9
E
Qe &
10