Abstract:
Most work in literature on condensation in tubes has been done for smooth tubes in the horizontal
and vertical configurations. Recent experimental works with condensation at different inclination
angles showed that the heat transfer characteristics were a function of inclination angle. These
works were limited to heat transfer and pressure drop measurements with visual observations.
However, no work has been done on measuring the void fractions during condensation at different
inclination angles. The purpose of this study was to measure void fractions and heat transfer
coefficients during condensation for tube inclinations ranging from vertical downwards (-90ᵒ) to
vertical upwards (90ᵒ) at a saturation temperature of 40 ᵒC. Measurements were taken in an
experimental set-up in which condensation occurred on the inside of a test section. The test section
was a circular tube with an inner diameter of 8.38 mm and a heat transfer length of 1.488. The
refrigerant used was R134a, and the void fractions were measured using two capacitive void fraction
sensors. Mass fluxes ranging from 100 – 400 kg/m2.s and vapour qualities ranging from 10 – 90%
were considered. Heat transfer coefficients were also compared with void fractions. It was found
that at combinations of low mass fluxes and vapour qualities, void fraction and heat transfer were
significantly affected by changes in inclination angle. Generally, void fractions and heat transfer
coefficients increased with downward inclination angles with an optimum angle between -10ᵒ and -
30ᵒ (downward flow). At some intermediate mass flux and vapour quality conditions, the void
fraction and heat transfer coefficients were observed to be independent of the inclination angle
despite changes in the prevailing flow patterns.
