In figure 4 the heat transfer results for two experimental
set-ups are plotted against the Reynolds number. The Nusselt
number result for plain double pipe heat exchanger is also
taken for comparison.
For plain double pipe heat exchanger result shows linear
tendency, since the Nusselt number is directly proportional to
Reynolds number. The results for heat exchanger with
twisted tape has parabolic tendency. In figure 8 the heat
transfer result for three set-ups is plotted against the Reynolds
number. The Nusselt number for plain double pipe is also
shown for comparison. An average increase in Nusselt
number is noted for double pipe heat exchanger with twisted
tape of twist angle 45
0
than plain double pipe heat exchanger
and twisted tape of twist angle 60
0
for counter flow.
From the results obtained it is concluded that the best
performance with twisted tape inserted into annulus of
double pipe heat exchanger is obtained at twist angle 45
due
to more swirl and turbulence induced by tape insert.