Experimental investigation of frequency and amplitude of density wave oscillations in vertical upflow boiling

Abstract

Historically, study of two-phase flow instabilities has been arguably one of the most challenging endeavors in heat transfer literature due to the wide range of instabilities systems can manifest depending on differences in operating conditions and flow geometry. This study utilizes experimental results for vertical upflow boiling of FC-72 in a rectangular channel with finite inlet quality to investigate Density Wave Oscillations (DWOs) and assess their potential impact on design of two-phase systems for future space missions. High-speed flow visualization image sequences are presented and used to directly relate the cyclical passage of High and Low Density Fronts (HDFs and LDFs) to dominant low-frequency oscillations present in transient pressure signals commonly attributed to DWOs. A methodology is presented to determine frequency and amplitude of DWO induced pressure oscillations, which are then plotted for a wide range of relevant operating conditions. Mass velocity (flow inertia) is seen to be the dominant parameter influencing frequency and amplitude of DWOs. Amplitude of pressure oscillations is at most 7% of the time-averaged pressure level for current operating conditions, meaning there is little risk to space missions. Reconstruction of experimental pressure signals using a waveform defined by frequency and amplitude of DWO induced pressure fluctuations is seen to have only moderate agreement with the original signal due to the oversimplifications of treating DWO induced fluctuations as perfectly sinusoidal in nature, assuming they occur at a constant frequency value, and neglecting other transient flow features. This approach is nonetheless determined to have potential value for use as a boundary condition to introduce DWOs in two-phase flow simulations should a model be capable of accurately predicting frequency and amplitude of oscillation.

Flow condensation pressure oscillations at different orientations

“…Vertical upflow once again exhibits the most dynamic (meaning large frequencies and amplitudes of oscillation) behavior, but the lack of trends for each plot indicates factors governing frequency of oscillation are independent from those determining amplitude. This is an important conclusion, as it indicates fundamentally different instability mode from that recently analyzed for flow boiling [81][82][83][84].…”

“…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].…”

Mechanistic model to predict frequency and amplitude of Density Wave Oscillations in vertical upflow boiling

“…Present day researchers continue characterizing instabilities and transient behavior observed in experimental two-phase flow systems, focusing on DWOs [51][52][53][54][55], Parallel Channel Instability (PCI) [56][57][58], Pressure Drop Oscillations (PDOs) [59][60][61], and interaction of multiple instability modes [62,63]. Recent reviews, such as those by Tadrist [64], Kakac and Bon [65], and Ruspini et al [66] provide updated surveys of literature relating to phenomena first reported by Boure et al [50].…”

“…This work builds directly on prior studies by the current authors [53,54], which detected and investigated the DWO phenomenon using transient pressure measurements throughout the system. It should also be noted that the present work is the companion study to another [55] presenting extensive analysis of the DWO phenomenon as it manifests in vertical upflow boiling with finite inlet quality using flow visualization images and experimentally determined values of frequency and amplitude of oscillation. Experimental outcomes from these studies help inform the modeling work undertaken here.…”

Boiling Flow Pattern Identification Using a Self-Organizing Map

“…During boiling instabilities, the various two-phase flow patterns were observed in variously enhanced microchannels, e.g., in channels with porous walls [8], in channels with triangular corrugations [9]. Many studies report that different types of instabilities are superimposed on each other [10][11][12]. There are articles concerning flow pattern transition models [13] The Phantom v1610 high-speed camera (6- Figure 1) was used to record the flow patterns inside the minichannel at a frame rate equal to 1000 fps.…”