Comparison of R245fa Pool Boiling Measurements to R123, and R245fa/Isopentane on a Passively Enhanced, Horizontal Surface.
Comparison of R245fa Pool Boiling Measurements to R123,
and R245fa/Isopentane on a Passively Enhanced,
Kedzierski, M. A.
International Journal of Transport Phenomena, Vol. 8,
No. 4, 331-344, 2006.
heat transfer; boiling behavior; isopentane; additives;
refrigerants; uncertainty; heat flux; experiments;
This study presents pool boiling heat transfer
measurements for R245fa, R123 and a mixture of R245fa
and isopentane on a flattened passively enhanced
low-pressure boiling surface. Possibly because the
enhanced surface was flattened from a round tube, its
performance was sensitive to vapor seeding at start up.
Consequently, the surface would operate in fully active
and partially active boiling modes. The results indicate
that the addition of 0.5% mass isopentane to R245fa
increases the heat flux by no more than 11% greater than
the heat flux of pure R245fa when the entire surface was
actively boiling. By contrast, the heat flux of the
R245fa/isopentane mixture was as much as 50% greater
than that of pure R245fa for a partially boiling-active
surface. In addition, pure R123 pool boiling data was
taken on the same passively enhanced surface that was
used with R245fa and the mixture. The ratio of the pure
R245fa heat flux to the pure R123 heat flux was
independent of the fraction of the surface that was
actively boiling. This is consistent with the hypothesis
that isopentane acts to enhance the site density. That
is, the addition of 0.5% isopentane limits the heat
transfer degradation that results from the loss of
active sites by increasing the number of active sites in
the actively boiling regions. From 8 kW/m2 to 100 kW/m2
and for fixed superheat, the R245fa heat flux was 27%
greater than that for R123. Considering only the boiling
heat transfer characteristics of R245fa, it appears to
be a good replacement for R123.