Abstract:
Due to tube enhancements being used to achieve higher process efficiencies, heat exchangers are starting
to operate in the transition region of flow. The paucity of data, however, has the implication that no correlation
exists for enhanced tube transition flow. This article, being the first of a two-part paper, presents
adiabatic friction factor data for four enhanced tubes for fully developed and developing flow in the transition
region. Three inlets were used for developing flows, namely square-edged, re-entrant and bellmouth
inlets. It was found that, as in the case of smooth tubes, transition was affected by the type of
inlet used, with transition being delayed the most for the smoothest inlet. Correlations were developed
to predict the fully developed critical Reynolds numbers and friction factors in the transition region. The
correlations predicted the critical Reynolds numbers on average to within 1% with a root mean square
deviation of less than 8%, while transition friction factors were predicted with a mean absolute error
of 6.6%, predicting 89% of the data to within a 15% error.
