Paper presented at the 5th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, South Africa, 1-4 July, 2007.
In-tube condensation is quite common in
refrigeration and air-conditioning applications. It
is the binding choice for air-cooled and
evaporative condensers. In-tube condensation is
often thought of as a process of film-wise
condensation of a vapor inside a tube. Since
augmentation can result in smaller and more
efficient devices, potential savings are quite
substantial. An experimental program designed
to investigate potential augmentation techniques
has been carried out worldwide as part of a large
study of in-tube condensation.
Copper circular smooth or enhanced tubes with
plate aluminum fins on the air side (fin-and-tube
heat Exchangers) are the usual geometry in aircooled
condensers. Enhanced tubes such as
micro fin tubes are typically made of copper and
have an outside diameter from 4 to 15 mm, a
single set of 50-70 fins with helix angle from 6
to 30°, fin height from 0.1 to 0.25 mm, triangular
or trapezoidal fin shapes with an apex angle from
25 to 90°.
Air-cooled condensers operate at a greater
condensing temperature than water-cooled
condensers; hence the compressor (and the
refrigeration system) delivers 15 to 20% lower
capacity. Therefore one has to use a larger
compressor. At the same time, the compressor
consumes greater power. Hence the air-cooled
system has a lower overall energy efficiency. This
paper manly emphasis on increase in overall
performance of the air-cooled condenser.
The objective of this study is to analyze the
theoretical performance of air-cooled condensers
using micro-fin tubes. The enhancement factor
(ratio of heat transfer coefficient of micro-fin tube
to heat transfer coefficient of plane tube)
considered to be 1.5. The overall performance of
condenser for different refrigerants has also been
studied. The refrigerants used for study are R-134a,
R-404a and R-22.The performance of condenser is
analyzed for 550 C condensing temperature because
most of the air cooled condensers in India are
working on this condensing temperature. The %
saving in fan power is estimated upto 90%with the
use of micro-fin tubes, 29% reduction in
compressor power; and 17% increase in cooling
capacity, on the other hand the % reduction in size
of condenser is up to 32%. It is also found that the
performance of condenser also varies with the
refrigerant used.
