30 May 2005

COMPARISON OF FLOW FIELDS OF A PURE FLUID AND A ZEOTROPIC MIXTURE FOR CONDENSATION IN A SHELL-AND-TUBE CONDENSER


Condensation of a pure refrigerant and a zeotropic refrigerant mixture in a shell-and-tube condenser
is investigated in an advanced calculation model based on a developed condensation routine coupled to a
commercial CFD program. The aim of the investigation is to make a three-dimensional calculation model
for mixture condensation, and to see if previous results from 2D calculations also can be seen in 3D calculations,
namely a significant difference between the flow fields of a pure fluid and a mixture. The calculation
results presented here show the same tendencies as 2D calculations in the earlier work. The flow
field of the mixture is much more complex than that of the pure refrigerant. Large vortexes arise, starting
at the top of the shell, going down along the shell and into the tube bundle from below. Vapour is therefore
mainly fed from below, causing a counterflow between vapour and condensate. A well-mixed condensate,
which here is an unfavourable situation, results in a performance 30 % lower compared to the
case where the condensate phase is unmixed. The latter is normally considered to be the inferior case.