Assessment of body force effects in flow condensation, Part I: Experimental investigation of liquid film behavior for different orientations

Abstract

Body force effects in flow condensation vary depending on channel orientation and fluid mass velocity, making the design of systems intended to operate in multiple orientations more complicated than those at a fixed orientation. This study examines the effects of body force on liquid film development for flow condensation of FC-72 in horizontal, vertical upflow, and vertical downflow orientations. Two test sections are utilized, one capable of providing high-speed imaging of liquid film development, and the other designed to allow detailed measurements of flow condensation heat transfer coefficient. High speed imaging shows that for low FC-72 mass velocities, flow regimes differ significantly among the three orientations, with vertical upflow exhibiting falling film behavior, horizontal flow showing stratification, and vertical downflow displaying annular co-current flow. For the case of low mass velocity horizontal flow, interfacial disturbances in the form of a sinusoidal wave are clearly visible with wavelengths on the order of 1-10 mm. As mass velocity is increased, the liquid film is seen to exhibit similar behavior for all three orientations due to interfacial shear stress negating body force effects. Heat transfer measurements reinforce these trends, with circumferential variations in heat transfer coefficient present for horizontal flow at low mass velocities, and differences in the axial variations in heat transfer coefficient seen when comparing vertical upflow to vertical downflow. As mass velocity is increased, differences in heat transfer coefficient are reduced, with the highest mass velocities exhibiting almost no variation with orientation. This convergence of values indicates the ability of interfacial shear stress to mitigate body force effects at sufficiently high mass velocities.

Assessment of body force effects in flow condensation, part II: Criteria for negating influence of gravity

“…Additional details on the experimental methods used, including uncertainty analysis, are provided in the first part of the study [21].…”

“…For the reasons discussed above, it is the primary goal of this second part of a two-part study to develop a set of mechanistic criteria comprised of relevant dimensionless groups that are capable of predicting the onset of gravity independent flow condensation heat transfer. In the first part [21], the influence of gravity on flow condensation was isolated by conducting identical experiments in horizontal flow, vertical downflow, and vertical upflow orientations using FC-72 as working fluid. In this second part, the experimental findings from the first part are used to develop the mechanistic criteria for negating the influence of gravity in condensing flows.…”

Flow condensation pressure oscillations at different orientations

“…Although flow visualization images captured correspond to external flow condensation (as discussed in Section 2) and all results analyzed thus far have been for internal flow, it is expected that key behavior at the interface between liquid film and vapor flow will be similar for the two configurations. Differences in liquid film and interfacial behavior have been discussed in previous work as the key feature influenced by body force which may lead to differences in condensation behavior [77,78], and it will be analyzed in that context again here. Fig.…”

“…The present study deals with the condensation portion of FBCE and aims to augment prior work dealing with computational pre-diction of flow condensation [75,76], experimental and analytic assessment of the impact of body force on flow condensation heat transfer coefficient [77,78], and correlation of pressure drop and heat transfer for condensing flows using a large database from available literature [79,80]. This work also serves as a companion piece to a series of recent studies by the present authors investigating transient behavior and instabilities in flow boiling through a single rectangular mini-channel [81][82][83][84].…”

Effect of saturation temperature on the condensation of R134a inside an inclined smooth tube

“…His correlations were primarily based on the flow regimes inside the tubes, and recently, he updated his proposed correlations to consider the effect of tube inclination angles (Shah, 2016a;Shah, 2016b, c). Park et al (2017) and O'Neill et al (2017) studied the condensation of FC-72 inside an inclined smooth tube, and published their works in a two-part article. They determined that inclining the tube at low mass fluxes resulted in an increased condensation heat transfer coefficient, whereas, at higher mass fluxes, it did not have a considerable influence.…”