Convective condensation at low mass flux: Effect of turbulence and tube orientation on the heat transfer. (December 2019)

• Record Type: Journal Article
• Authors: Azzolin, Marco; Bortolin, Stefano; Del Col, Davide
• Is Part Of: International journal of heat and mass transfer. Volume 144(2019)
• Publication Date: 2019-12
• Subjects: Heat -- Transmission -- Periodicals; Mass transfer -- Periodicals; Chaleur -- Transmission -- Périodiques; Transfert de masse -- Périodiques; Electronic journals; 621.4022
• DOI: 10.1016/j.ijheatmasstransfer.2019.118646
• Languages: English
• ISSNs: 0017-9310

Abstract

Highlights: Condensation of R134a in vertical and horizontal configuration between 50 and 200 kg m −2 s −1 is studied. The heat transfer coefficient in vertical can be as low as half the value in horizontal. A transition criterion to set the effect of turbulence in vertical channel is proposed. Abstract: It is well proved in the literature that gravity affects in-tube condensation heat transfer at low mass flux. Nevertheless very limited data are taken at low mass flux when changing tube orientation, despite the many practical applications. In this paper, convective condensation inside a 3.4 mm inner diameter tube is investigated in horizontal and vertical downflow using R134a as the working fluid. The experiments are performed at low mass flux, between 50 kg m −2 s −1 and 200 kg m −2 s −1, which are usually the less investigated despite the relevance of gravity force at such low velocities. The condensation heat transfer coefficient in vertical downflow can be as low as half the value in horizontal flow at the same operating conditions, since gravity acts for the thinning of the liquid film in the horizontal tube. In vertical downflow, the heat transfer coefficients show an early effect of turbulence, thus a new transition criterion is here proposed. Criteria for predicting the relevance of channel orientation on the heat transfer coefficient are also assessed.