Abstract:
The performance of a transcritical CO2 based refrigeration
system is highly sensitive to the gas cooler pressure and exit
temperature. This is due to the peculiar s-shape of the isotherm
in the supercritical region. Hence proper design of the gas
cooler is crucial to extract optimum performance from the CO2
based systems. The gas cooler considered for the current
application is an air cooled, counter cross-flow spiral fin-andtube
heat exchanger. A discretized node-by-node approach is
adopted here to model the gas cooler. The governing equations
for each node are formulated based on the NTU-ε method.
Using the developed model, a study has been conducted to
optimize the geometrical dimensions of the heat exchanger
based on the minimization of the total entropy generation due
to fluid friction and heat transfer. The total entropy generation
is indicated in terms of a non-dimensional entropy generation
number. The variations of this non-dimensional number with
changes in face velocity, fin pitch, and total number of tubes in
each row are investigated in the present study. It is observed
that entropy generation number decreases with the increase in
fin pitch for higher flow rate. However, at a lower flow rate,
entropy generation number lines for different fin pitches
overlap. On the other hand, entropy generation number
decreases with increase in the total number of tubes. Finally,
from the results, the mentioned parameters are optimized to
achieve lower entropy generation number with lower fan power
consumption.
Description:
Papers presented at the 13th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Portoroz, Slovenia on 17-19 July 2017 .
