The influence of inclination angle on void fraction and heat transfer during condensation inside a smooth tube

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/m 2 .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.2

Numerical investigation into the inclination effect on conjugate pool boiling and the condensation of steam in a passive heat removal system

“…Such trend can also be seen in the previous experimental of Meyer and his co-workers [9,10,37], in which the heat transfer coefficients were larger for upward and downward flow direction compared to the horizontal case. It should be noted that such cases are observed for high mass flow rates and vapour qualities, which happen in the present study as well.…”

“…Furthermore, in all the previous studies, only the horizontal or nearly horizontal direction of the tubes was considered for condensation [1,19,30,35]. Previous studies [9,10,36,37], of the authors showed the potential improvement capacity of the condensation heat transfer coefficient when an inclination angle was imposed on the tube orientation In this paper, conjugate heat transfer, pool boiling outside and condensation inside a smooth tube were investigated numerically. The effects of various parameters, such as steam mass flow rate, steam quality and tube inclination angle on the boiling and condensation heat transfer coefficients, are considered.…”

Numerical study of steam condensation inside a long, inclined, smooth tube at different saturation temperatures

“…The tube orientations varied between -60° to 60°. The selection of this range of tube inclination angles was based on the conclusions of prior experimental works by Lips and Meyer [10,11] and Olivier et al [6], that reported that the optimum inclination angle would range between -30° to 0° for the condensation of R134a inside a tube. They also observed that the minimum heat transfer coefficient would be at an inclination angle of +90° or -90°.…”

“…For designs applicable to these industries, an accurate and in-depth understanding of the flow patterns and the heat transfer phenomenon is of major importance [1][2][3][4][5]. Many applications involve condensation inside inclined tubes such as, in A-frame steam condensers used in air-cooled, power generation plants, some rooftop air-cooled refrigeration systems, and also in the low temperature multi-effect evaporation in desalination industry [6]. However, a literature review by Lips and Meyer [7], showed that very limited work was conducted on condensation inside inclined tubes.…”

“…They studied the effect of tube inclination angles on the pressure drop, void fraction, and heat transfer coefficient, and also captured the flow regime at the tube outlet. Their most important result was that the optimum heat transfer coefficients occurred at a downward inclination angle in the range of 15°-30°, and specifically at mass fluxes lower than approximately 200 kg/m 2 s. 6 Xu et al [14] studied gas-liquid, two-phase flows inside an inclined tube. They focussed on the influence of the liquid phase properties on flow patterns, void fractions, and pressure drops.…”