Subcooled Pool Boiling Research Articles

Steady and Transient CHF in Subcooled Pool Boiling of Water under Sub-atmospheric Pressures

Steady and Transient CHF in Subcooled Pool Boiling of Water under Sub-atmospheric Pressures

1003 Subcooled Pool Boiling CHF on Horizontal Cylinders with Different Surfaces in a Pool of Water at Pressures due to Pre-pressurization and Exponentially Increasing Heat Inputs

1003 Subcooled Pool Boiling CHF on Horizontal Cylinders with Different Surfaces in a Pool of Water at Pressures due to Pre-pressurization and Exponentially Increasing Heat Inputs

102 非経験的な沸騰・凝縮モデルを用いたサブクール・プール沸騰の数値シミュレーション(OS1-1.数値シミュレーションの原子力への応用(1),OS・一般セッション講演)

102 非経験的な沸騰・凝縮モデルを用いたサブクール・プール沸騰の数値シミュレーション(OS1-1.数値シミュレーションの原子力への応用(1),OS・一般セッション講演)

Photographic Study on Bubble Motion in Subcooled Pool Boiling

Using a static contact angle of a vertical heated wall as a main experimental parameter, a photographic study was carried out to elucidate the mechanisms to determine the vapor bubble dynamics during subcooled pool boiling. The test fluid was distilled water and the experiments were performed under the atmospheric pressure; liquid subcooling was set to around 5 K. To enable clear observation of bubble behavior with a high speed camera, the experiments were conducted in an isolated bubble regime near the onset of nucleate boiling. Distinctly different bubble behaviors were observed on hydrophobic and hydrophilic surfaces: the bubbles were adhered to the surface for a long period of time when the contact angle was large while lifted-off the surface within a short period of time after the nucleation when the contact angle was small. Since buoyancy does not remove the bubble from the vertical surface, the mechanisms of bubble lift-off were investigated. It was indicated that the change in bubble shape induced by the surface tension force, unsteady growth force, and local liquid flow induced by heterogeneous condensation around the bubble are considered to promote the bubble lift-off while the surface tension force acting on the three-phase common line prevented the lift-off. Effects of the surface wettability on the lift-off bubble diameter, the elapsed time from the nucleation at the lift-off, and the condensation rate after the lift-off were also investigated.

サブクール沸騰高熱流束域における伝熱面近傍の温度場の測定(熱工学,内燃機関,動力など)

サブクール沸騰高熱流束域における伝熱面近傍の温度場の測定(熱工学,内燃機関,動力など)

Transient Critical Heat Fluxes in Subcooled Pool Boiling of FC-72

Critical heat fluxes (CHFs) in a pool of Fluorinert FC-72 were measured for period from transient heat inputs up to steady-state ones. Measurements were made using 1.0 mm diameter of platinum and gold horizontal cylinders in wide ranges of liquid subcoolings and pressures. The steady-state CHFs for saturated condition almost agree with the hydrodynamic instability (HI) model. However, in higher subcoolings, the increasing rate of steady-state CHFs is lower than HI model and it was suggested due to the heterogeneous spontaneous nucleation (HSN). The CHFs for period are clearly categorized into the first, second, and third groups for long, short, and intermediate periods, respectively. Transient CHFs on semi-direct and direct transitions from non-boiling heat conduction to film boiling, exist predominantly during short periods. Those transition processes were assumed due to the explosive-like HSN in originally flooded cavities on cylinder surface. Each of the steady-state and transient CHFs that were obtained from both heaters in various liquid subcoolings and pressures, generally well agree each other.

A Study of Subcooled Pool Boiling of Water: Contact Area of Boiling Bubbles with a Heating Surface During a Heating Process

The contact area of bubbles with a transparent heating surface was optically measured during subcooled pool boiling of water on the ground. In the experiments, boiling bubbles were attached to the heating surface with a bubble holder and nearly reproduced the bubble behavior observed in low gravity. DC power was applied to the ITO heater and increased until the heater surface burned out. In quick heating, that is about 20 second until burnout and equal to the heating time during the low gravity period, the contact area was smaller than that for long time heating at the same heat flux. The experimental results suggest the reason why the critical heat flux in pool boiling is higher than the widely accepted predictions in microgravity. In a drop shaft experiment with constant heating, the contact area increased dramatically at the start of microgravity and became constant. Boiling bubbles coalesced and remained just over the heating surface.

Subcooled Pool Boiling of Water in Microgravity (Observation of bubble behaviors and burnout)

Subcooled Pool Boiling of Water in Microgravity (Observation of bubble behaviors and burnout)

Study of Boiling Characteristic Curves in Subcooled Pool Boiling of Water (4th Report, The Mechanism of Heat Transfer in Transition Boiling)

Pool boiling experiments were conducted on a 10 mm dia. heated surface facing upwards in the range of subcooling from 15 to 50K at atmospheric pressure. The heat transfer mechanism in the transitional boiling region can be estimated by a mathematical model based on the mass transfer mechanism of evaporation and condensation through a coalescent vapor bubble. The changes with time of the mass flux of condensation and the dried area on the heated surface, which are important factors governing the characteristics of transition boiling heat transfer, are estimated by a model based on this mass transfer mechanism. An explanation was obtained on the mechanism of liquid invasion onto the heated surface from the correspondence between the change with time of the dried area and local temperature fluctuations of the heated surface.

Study of Boiling Characteristic Curves in Subcooled Pool Boiling of Water : 1st Report, Effect of Subcooling on Local Characteristics of Boiling Heat Transfer

強い凝縮作用のもとでは, バーンアウト点をすぎ, さらにそれを越える第2バーンアウト点まで安定した沸騰曲線をえることが可能である. このことを伝熱面表面局所について実証し, 高熱流束城の伝熱機構解明の手がかりとした. またバーンアウト点をすぎ, 遷移沸騰的傾向のみられる領域から再び熱流束が急上昇する特異現象の存在を明らかにし, この現象はサブクール度と伝熱面汚損度とのかね合いに支配されることを見いだした.

Study of Boiling Characteristic Curves in Subcooled Pool Boiling of Water : 2nd Report, Effect of Contamination of Surface on Boiling Heat Transfer and Collapse Vapor Slug

伝熱面に付着するスケールの生成過程, 形状, あらさおよびその面での液滴の蒸発の挙動を調べた結果, 伝熱面のスケール層は蒸気膜を介して液体を加熱面に導き固液接触に寄与することが判明した. また固液接触によって生ずる気化は急速であり気ほう塊は瞬時にサブクール液中に崩壊して微妙な蒸気ほうとなることがわかった.

Study of Boiling Characteristic Curves in Subcooled Pool Boiling of Water : 3rd Report, Behavior of a Vaper Mass and Surface Temperature Variations in Transitional Pool Boiling

遷移沸騰域から第2バーンアウト点にいたるまでの合体二次気ほうの挙動とそれによっておこる伝熱面温度の変動を同時記録した結果, あるサブクール度とそれに相当した過熱度の範囲の遷移沸騰域では, サブクール液体が伝熱面全面をおおうミクロンオーダの薄い蒸気膜を突き破っておこす固液接触が主要な伝熱機構となりうることが判明した.

Study of Boiling Characteristic Curves in Subcooled Pool Boiling of Water : 4th Report, The Mechanism of Heat Transfer on Transition Boiling

本報は伝熱面直径10mm, サブクール度15～50Kの範囲で水のプール沸騰実験をおこない, 遷移沸騰的領域の伝熱機構を蒸発と凝縮が同時におこる質量輸送機構にもとづいて考察したものである. この領域の沸騰特性に対して影響をおよぼす重要な因子である凝縮質量流束と伝熱面の乾燥部面積の時間変化を見積り, さらに伝熱面局所の温度変動との対応からサブクール遷移沸騰の液侵入機構に対する一つの解釈を与えることを試みた.