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Research on Bubble Detatchment Characteristics of Subcooled Flow Boiling in Narrow Channel under Rolling Motion

Author: GaoFeng
Tutor: GaoZuoZhen
School: Harbin Engineering University
Course: Nuclear Energy Science and Engineering
Keywords: bubble detachment narrow rectangular channel rolling motion High-speedphotography
CLC: TK124
Type: Master's thesis
Year: 2013
Downloads: 19
Quote: 0
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Abstract


Narrow rectangular construction gets more and more applications as its compactstructure and higher heat transfer efficiency, especially in the aerospace and nuclear powerequipment. Research on two-phase flow characteristics in the narrow channel plays asignificant role in the application of the narrow rectangular channel structure. The bubbledetachment characteristic in subcooled flow boiling in the narrow rectangular channel wasinvestigated in this paper. The experimental pressure mainly focused on atmospheric pressure.Deionized water was used as working fluid. The subcooling ranged from10to30K, with themass flow rate ranged from80to250kg/h, and the heat flux ranged from0.03to0.5MW/m2.The experimental loop was a closed loop fixed on a rolling platform, which could carry outrolling motion with different angle and period to simulate the ocean conditions. And a largeangle of inclination experiments also could be carried out. The effect of rolling motion andincline on bubble detachment could be researched with the experimental facility.In present experiment, the test section was a single-side heated rectangular channel. Ahigh-speed camera was used to record the bubble behaviors from inception to collapse at therate of5000fps. In order to obtain the bubble parameters, e.g. position, size, quantity, theimage procedures were developed.The bubble had a larger growth diameter and larger condensation rate at atmosphericpressure in subcooled flow boiling. Zuber bubble growth model was suitable for theexperiment. Bubble growth force had greater effect on the bubble behavior, especially on thebubble vertical detachment. Bubbles parallel detachment was prior over the bubble lift-off.The lift off of the bubbles was mainly due to condensation.The mass flow, subcooling and heat flux had greater effect on bubble behaviors. Themaximum diameter and lift-off diameter of the bubble reduces with the increasing mass flow;when the mass flow reduced, the maximum diameter and lift-off diameter of the bubbleincreased. The bubble sliding velocity increased with the increase of mass flow. When thesubcooling reduced and the heat flux increased, the nucleate sites increased, the bubbledetachment frequency; the maximum diameter and lift-off diameter also increased. When thesubcooling increased and the heat flux decreased, the maximum diameter and lift-off diameterdecreased, the bubble departure frequency also decreased. In present experiment, Zuber model over-predicted the lifetime of the bubble. New formula was proposed for the presentbubble growth and condensation rates with a good prediction of the present date. The rollingangle and period had little impact on bubble departure frequency, but the rolling motionaffected much on the maximum diameter of the bubble. The maximum diameter of the bubbleat positive angle was larger than that in the negative angle. The bubble departure frequencyand maximum diameter were larger at positive angles than those at the negative angles ininclination experiments.Non-condensable gas had greater effect on bubble behavior. The non-condensable gasescould generate long-distance sliding bubbles, which took away the heat of the heating surface.And that would reduce the maximum diameter of bubbles, and the number of bubbles. Flowinstability could cause mass flow fluctuations, or even reverse the flow direction. When theflow velocity reduced or backflow occurred, the maximum diameter and number of bubblesgenerated would reduce; and when the flow velocity increased, more bubbles would generatefrom more nucleate sites with larger diameter, and the distance of bubble sliding wouldbecome longer.

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CLC: > Industrial Technology > Energy and Power Engineering > Thermal engineering, heat > Thermal Engineering Theory > Heat Transfer
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