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Record 1 of 25763
Investigation of Body Force Effects on Flow Boiling Critical Heat Flux
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Author and Affiliation:
Zhang, Hui(Purdue Univ., Boiling and Two-Phase Flow Lab., West Lafayette, IN United States)
Mudawar, Issam(Purdue Univ., Boiling and Two-Phase Flow Lab., West Lafayette, IN United States)
Hasan, Mohammad M.(NASA Glenn Research Center, Cleveland, OH United States)
Abstract: The bubble coalescence and interfacial instabilities that are important to modeling critical heat flux (CHF) in reduced-gravity systems can be sensitive to even minute body forces. Understanding these complex phenomena is vital to the design and safe implementation of two-phase thermal management loops proposed for space and planetary-based thermal systems. While reduced gravity conditions cannot be accurately simulated in 1g ground-based experiments, such experiments can help isolate the effects of the various forces (body force, surface tension force and inertia) which influence flow boiling CHF. In this project, the effects of the component of body force perpendicular to a heated wall were examined by conducting 1g flow boiling experiments at different orientations. FC-72 liquid was boiled along one wall of a transparent rectangular flow channel that permitted photographic study of the vapor-liquid interface at conditions approaching CHF. High-speed video imaging was employed to capture dominant CHF mechanisms. Six different CHF regimes were identified: Wavy Vapor Layer, Pool Boiling, Stratification, Vapor Counterflow, Vapor Stagnation, and Separated Concurrent Vapor Flow. CHF showed great sensitivity to orientation for flow velocities below 0.2 m/s, where very small CHF values where measured, especially with downflow and downward-facing heated wall orientations. High flow velocities dampened the effects of orientation considerably. Figure I shows representative images for the different CHF regimes. The Wavy Vapor Layer regime was dominant for all high velocities and most orientations, while all other regimes were encountered at low velocities, in the downflow and/or downward-facing heated wall orientations. The Interfacial Lift-off model was modified to predict the effects of orientation on CHF for the dominant Wavy Vapor Layer regime. The photographic study captured a fairly continuous wavy vapor layer travelling along the heated wall while permitting liquid contact only in wetting fronts, located in the troughs of the interfacial waves. CHF commenced when wetting fronts near the outlet were lifted off the wall. The Interfacial Lift-off model is shown to be an effective tool for predicting the effects of body force on CHF at high velocities.
Publication Date: Nov 01, 2002
Document ID:
20030003651
(Acquired Jan 17, 2003)
Subject Category: FLUID MECHANICS AND THERMODYNAMICS
Document Type: Conference Paper
Publication Information: Sixth Microgravity Fluid Physics and Transport Phenomena Conference; Volume 1; 553-578; (NASA/CP-2002-211212/VOL1); (SEE 20030003624)
Financial Sponsor: NASA Glenn Research Center; Cleveland, OH United States
Organization Source: NASA Glenn Research Center; Cleveland, OH United States
Description: 26p; In English
Distribution Limits: Unclassified; Publicly available; Unlimited
Rights: No Copyright
NASA Terms: BOILING; FLOW VELOCITY; HEAT FLUX; VAPORS; BUBBLES; GRAVITATIONAL EFFECTS; TWO PHASE FLOW; TEMPERATURE CONTROL; WALLS; MICROGRAVITY; FLOW CHARACTERISTICS
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