30 May 2005

FLOW DISTRIBUTION IN A HERRINGBONE MICROFIN EVAPORATION TUBE


An experimental investigation of in-tube evaporation of R134a, R410A and R407C has been carried
out for a 4 m long herringbone microfin tube with an outer diameter of 9.53 mm. Local circumferential
wall temperatures are measured in ten sub-sections. The objective of the work was to determine the
specific flow distribution caused by the herringbone structure and to compare measured results to reported
results for helical microfin tubes. Also distribution differences between the pure fluid R134a and mixtures
R407C and R410A at similar evaporation temperatures should be studied. Generally the herringbone tube
shows wall dry-out at vapour qualities between 50-60%, which is lower than reported for helical microfin
tubes, where local dry-out usually occurs at vapour qualities around 80%. The effect of swirl flow,
characteristic for helical microfins, is non-existent in herringbone tubes. The V-shaped grooves in
herringbone tubes combined with vapour density effects result in a rather complex flow pattern situation,
which is discussed. It is also shown that the herringbone structure orientation plays an important role for
the liquid film distribution and heat transfer in the investigated herringbone tube.