Effects of two-phase inlet quality, mass velocity, flow orientation, and heating perimeter on flow boiling in a rectangular channel: Part 1 – Two-phase flow and heat transfer results

Abstract

Lack of understanding of flow boiling behavior in reduced gravity poses a major challenge to the development of future space vehicles utilizing two-phase thermal control systems (TCSs). A cost effective method to investigating the influence of reduced gravity on flow boiling is to perform ground experiments at different orientations relative to Earth gravity. This paper is the first part of a two-part study aimed at exploring flow boiling mechanisms of FC-72 in a rectangular channel heated along one wall or two opposite walls. Experiments are performed in vertical upflow, vertical downflow and horizontal flow, subject to large variations in mass velocity, inlet quality and wall heat flux. Detailed measurements are used to investigate the influences of orientation, and therefore gravity, on boiling curve, local and average heat transfer coefficients, and pressure drop, and their relationship with interfacial behavior is captured with high-speed video. For horizontal flow, the effects of gravity are reflected in appreciable stratification across the channel at low mass velocities, with gravity aiding vapor removal from, and liquid return to the bottom heated wall, while accumulating vapor along the top heated wall. For vertical upflow and vertical downflow, with both single-sided and double-sided heating, there is far better symmetry in vapor formation along the channel. The heat transfer coefficient shows significant variations among the different orientations and heating configurations at low mass velocities, but becomes insensitive to orientation above 800 kg/m 2 s, proving inertia around this mass velocity is effective at negating any gravity effects. For low mass velocities, pressure drops are fairly equal for vertical upflow and vertical downflow, but greater than for horizontal flows. However, fairly equal pressure drops are achieved at high mass velocities for all orientations. Overall, this study proves that gravity effects on two-phase pressure drop and two-phase heat transfer are dictated mostly by mass velocity and, to a lesser extent, by inlet quality.

Experimental investigation into the impact of density wave oscillations on flow boiling system dynamic behavior and stability

“…In an effort to complement previous studies conducted as part of the ongoing project between PU-BTPFL and NASA GRC dealing primarily with characterization and prediction of important time-averaged design parameters such as heat transfer coefficient [44][45][46][47], pressure drop [31,[48][49], and CHF [50][51][52][53], the present study will also present and evaluate several flow boiling stability maps commonly found in literature.…”

Effects of two-phase inlet quality, mass velocity, flow orientation, and heating perimeter on flow boiling in a rectangular channel: Part 2 – CHF experimental results and model

“…Increasing the mass velocity to G = 406.1-409.0 kg/ m 2 s with an inlet quality of x e,in = 0.03 is shown producing interfacial behavior similar to that for the lower mass velocity. are lowest for top-wall heating (h = 180°) due to vapor stratification along the heated wall, while vertical uplow (h = 90°) and vertical downflow (h = 270°) show better performances, a trend shared with heat transfer coefficients and pressure drops in the first part of this study [40]. CHF values for vertical upflow are slightly higher than those for vertical downflow.…”

“…This study is part of a NASA project whose ultimate goal is to develop the Flow Boiling and Condensation Experiment (FBCE) for the International Space Station (ISS). The first part of the study [40] examined flow boiling interfacial behavior, boiling curves, local and average heat transfer coefficients, and pressure drop. This part of the study will be focused entirely on the combined influences of mass velocity, inlet quality, flow orientation, and both single-sided and double-sided heating on flow boiling CHF, and on CHF modeling.…”

“…Additional details concerning the experimental methods are provided in the first part of the study [40]. Fig.…”

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

“…The current study deals with flow boiling and augments prior work dealing with experimental investigation and prediction of key design parameters including heat transfer coefficient [86][87][88][89], pressure drop [53,[90][91], and critical heat flux [92][93][94][95][96][97][98], with development of a mechanistic model for prediction of frequency and amplitude of DWO induced pressure oscillations evident in vertical upflow boiling with finite inlet quality.…”