Bubble departure size in flow boiling

Abstract

HHeight from the beginning of heated portion of rod (m) JaJacob number k w Dimensionless bubble contact diameter L Perimeter of heated rod (m) n Constant p Pressure (Pa) q w Heat flux (kW/m 2 ) r Bubble radius (m or mm) Re b Bubble Reynolds number t Time (s) T Temperature (°C) U b Bubble velocity (m/s) U(x) Liquid velocity profile near wall (m/s) V b Bubble volume (m 3 ) u l Mean velocity of two phase (m/s) u* Friction velocity (m/s) X Vapor quality Greek symbols α Advancing contact angle β Receding contact angle δ Liquid film thickness (m or mm) η Thermal diffusivity (m 2 /s) θ Inclination angle ν Kinematic viscosity (m 2 /s) ρ Density (kg/m 3 ) σ Surface tension coefficient (N/m) τ Deviatoric stress tensor (N/m) Subscripts in Inlet l Liquid sat Saturation v Vapor w Wall (heated surface) Abstract Flow boiling experiments were conducted in a vertical annular channel to study bubble departure characteristics. Deionized water was used as the working fluid, and the tests were performed at atmospheric pressure. Bubble departure diameters were obtained from the images which were captured by a high-speed digital camera. The relationship between bubble contact diameter and departure diameter was discussed. A new model base on force balance analysis, taking bubble contact diameter into account for predicting bubble departure diameter is proposed in this study. A good agreement between predicted and measured results is achieved. List of symbols A Area (m 2 ) b Constant c Constant c pl Specific heat at constant pressure [J/(kg °C)] d w Bubble contact diameter (m or mm) D Equivalent diameter or bubble diameter (m or mm) D d Bubble departure diameter (m or mm) F Force (N) g Gravitational acceleration (9.81 m/s 2 ) G Mass flux [kg/(m 2 s)] h fg Latent heat (J/kg)

An experimental investigation on bubbles departure characteristics during sub-cooled flow boiling in a vertical U-shaped channel utilizing high-speed photography

“… Proposed correlation by Prodanovic et al [24] was modified and adapted for predicting bubbles departure diameter and nucleation frequencies in U-shaped channels through adding Dean number as a new factor, which considers the influence of the curved geometry and subsequently, radial pressure gradient on bubbles characteristics. Ghunther [19] 0.32-1.02 0.8-3 Tolubinsky and Kostanchuk [20] 0.47-1.24 1.2 Ünal [5] 0.11-0.18 Klausner et al [22] 0.1-0.65 Thorncroft et al [23] 0.09-0.25 0.12-45 1-1.8 17-30 Prodanovic et al [24] 0.3-2.68 0.37-2.86 0.41-9.5 0.81-18.6 Situ et al [42] 0.145-0.6 Cho et al [1] 0.46-0.56 0.55-0.9 Chu et al [9] 0.51-1.71 77-300 Euh et al [41] 20-900 Zou and Jones [27] 0.15-0.45 Sugrue et al [3] 0.22-0.66 Guan et al [28] 0.62-1.85 Brooks et al [29] 0.05-0.3 120-1450 Goel et al [30] 0.31-0.58 0.31-0.96 3-7 22-90 10-41 Ooi et al [31] 0.2-0.5 10-600 Vlachou and Karapantsios [16] 0.02-0.66 Zhou et al [33] 0.21-0.31 Ren et al [34] 0.01-0.78 Abdous et al [17] 0.53-1.67 0.82-2.4 Holagh et al [18]…”

“…They found that the biggest bubbles depart in the downward-facing horizontal heater configuration and the smallest bubbles from a vertically positioned heater. Guan et al [28] investigated bubbles departure diameter in water sub-cooled flow boiling at atmospheric pressure and proposed a model for departure diameter prediction. An experimental study of wall nucleation characteristics, embracing departure diameter and frequency, during subcooled flow boiling of water in a vertical straight channel was carried out by Brooks et al [29] at various working pressures.…”

Editors' Choice—Critical Review—Mathematical Formulations of Electrochemically Gas-Evolving Systems

“…89,90 Bubble detachment at a heat transfer surface has been extensively studied in which the bubble departure relative to a general wall is investigated. [89][90][91][92] For gas-evolving electrochemical systems, bubbles at an electrode surface are further influenced by two additional forces: the electrostatic force, F e , and the Marangoni force, F M . 86 The electrostatic interactions between the electrode surface charge and the bubble surface can cause a premature departure of the bubble from the electrode surface, or F e may oppose the direction of bubble growth retaining the bubble at the electrode surface.…”

Flow Boiling Heat Transfer Enhancement Using Tuned Geometrical Contact-Line Pinning

“…A common theme in biphilic flow boiling studies is the hastening of bubble departure through exploitation of contact line pinning and drag forces; considering a force balance on a growing bubble, there is an impetus to decrease the stiction forces and/or increase departure forces in order to enhance the sweeping of the bubbles from their nucleation sites. − Recent work has connected contact-line pinning to the bubble force balance as proposed by Klausner and colleagues, , indicating that control over the bubble’s perimeter can shift the force balance in favor of departure.…”