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

Abstract

This study concerns the development of a set of mechanistic criteria capable of predicting the flow conditions for which gravity independent flow condensation heat transfer can be achieved. Using FC-72 as working fluid, a control-volume based annular flow model is solved numerically to provide information regarding the magnitude of different forces acting on the liquid film and identify which forces are dominant for different flow conditions. Separating the influence of body force into two components, one parallel to flow direction and one perpendicular, conclusions drawn from the force term comparison are used to model limiting cases, which are interpreted as transition points for gravity independence. Experimental results for vertical upflow, vertical downflow, and horizontal flow condensation heat transfer coefficients are presented, and show that, for the given test section, mass velocities above 425 kg/m 2 s ensure gravity independent heat transfer. Parametric evaluation of the criteria using different assumed values of mass velocity, orientation, local acceleration, and exit quality show that the criteria obey physically verifiable trends in line with those exhibited by the experimental results. As an extension, the separated flow model is utilized to provide a more sophisticated approach to determining whether a given configuration will perform independent of gravity. Results from the model show good qualitative agreement with experimental results. Additionally, analysis of trends indicate use of the separated flow model captures physics missed by simpler approaches, demonstrating that use of the separated flow model with the gravity independence criteria constitute a powerful predictive tool for engineers concerned with ensuring gravity independent flow condensation heat transfer performance.

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

“…The second module is used to obtain detailed heat transfer measurements to explore differences in condensation heat transfer coefficient among the three flow orientations resulting from variations in the mass velocities of FC-72 and cooling water. In the second part of this study [23], the experimental findings from this part are used to develop mechanistic criteria for negating the influence of gravity in condensing flows.…”

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

“…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. They also proposed a mathematical expression for predicting the condensation heat transfer coefficient in stratified flow regimes (O'Neill et al, 2017). They validated the proposed model with their experimental data.…”

“…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.…”

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].…”