Development of bubble departure and lift-off diameter models in low heat flux and low flow velocity conditions

Cho, Yun-Je; Yum, S.; Lee, Jeonghun; Park, Goon-Cherl

doi:10.1016/j.ijheatmasstransfer.2011.04.007

Cited by 50 publications

(32 citation statements)

References 25 publications

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“…Two main issues can be pointed out regarding equation (13): the value of the constant b and the exponent of t. While originally b was supposed to take values between 1 and 1.73, depending on the flow conditions and the characteristic of the nucleation site, Steiner et al (2005) obtained the best fit to their measurements in water with b = 0.21, whereas Cho et al (2011) reported values ranging from 0.48 to 24.24 depending on the working fluid, the pressure, the wall superheat, etc. With respect to the time exponent, Thorncroft et al (1998) found that r ∝ t n with n between 1/3 and 1/2, whereas Chen et al (2010) reported a value of about 1/4.…”

Section: Mechanistic Modelmentioning

confidence: 99%

“…Now, as suggested by Cho et al (2011), the bubble growth model defined by equation (13) is modified so that the point of bubble departure is explicitly expressed, as…”

Section: Mechanistic Modelmentioning

confidence: 99%

“…where t d is the departure time, and G bd = 2b d Ja(α f /π) 1/2 , being b d the growth constant after departure, which in general should be smaller than the growth constant b before departure, since the contact diameter decreases after the bubble departure (Cho et al 2011). Now, the lift-off radius can be expressed in terms of the sliding time t sld = t lo −t d , i.e.…”

Section: Mechanistic Modelmentioning

confidence: 99%

“…The formation, growth and detachment of bubbles are governed by a number of forces, and from their balance it is possible to determine approximately the diameter of the vapor bubble, as first developed in the case of flow boiling by Zeng et al (1993), considering the balance on the entire bubble, and by Kandlikar and Stumm (1995) considering two separate control volumes for the front and rear regions of the bubble. This force-based approach has been applied to different fluids and flow configurations (Steiner et al 2005;Situ et al 2008;Cho et al 2011;Chen et al 2012). However, a serious difficulty comes from the uncertainties in the expressions for some of the forces governing the size of the vapor bubble as it grows in its nucleation site.…”

Section: Introductionmentioning

confidence: 99%

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A Note on Bubble Sizes in Subcooled Flow Boiling at Low Velocities in Internal Combustion Engine-Like Conditions

Torregrosa

Broatch

Olmeda

et al. 2016

JAFM

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Current trends in engine design indicate the necessity to take advantage of the highest rates of heat transfer associated with nucleate boiling, mostly at high engine loads. When used in conjunction with advanced thermal management strategies, subcooled boiling may take place at very low velocities, for which little information is available, and in ducts with small cross-sectional area, so that undesired effects of the relative sizes of ducts and bubbles may appear. In this paper, experiments on subcooled boiling flow at low velocities and engine-like temperature conditions were conducted with a usual engine coolant. A high-speed photographic camera was used to collect images of the detached vapor bubbles, and the microscopic characteristics of the heating surface were determined. Experimental results for the mean values show acceptable agreement with the results of a mechanistic radius model, when assuming that departure and lift-of radius are related through the flow boiling suppression factor. Additionally, the results obtained are compatible with the sizes of the nucleation sites estimated from the surface characterization. The results obtained for the size distribution are consistent with those found in the literature.

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Section: Mechanistic Modelmentioning

confidence: 99%

“…Now, as suggested by Cho et al (2011), the bubble growth model defined by equation (13) is modified so that the point of bubble departure is explicitly expressed, as…”

Section: Mechanistic Modelmentioning

confidence: 99%

Section: Mechanistic Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

A Note on Bubble Sizes in Subcooled Flow Boiling at Low Velocities in Internal Combustion Engine-Like Conditions

Torregrosa

Broatch

Olmeda

et al. 2016

JAFM

View full text Add to dashboard Cite

show abstract

“…For the critical situation of bubble departure, many correlations [12][13][14][15] have been presented by deriving the force equilibrium equation including the surface tension force, the drag force, the buoyancy force, the lift force, etc. Some modifications [16][17][18] have also been done considering the heat transfer effect through the Jacob number and the contact angle.…”

Section: Bubble Departure Diametermentioning

confidence: 99%

An Overall Bubble Diameter Model for the Flow Boiling and Numerical Analysis through Global Information Searching

Zhang

Lin

et al. 2018

Energies

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Bubble diameter is important for the three-dimensional nucleate boiling two-phase flow simulation. However, the bubble diameter is rarely considered as a variable because it is difficult to estimate. In this paper, a novel bubble diameter model is proposed for the boiling flow. The heat transfer growth, the breakup or coalescence of collision and the liquid impacting separation are considered as the factors affecting the bubble diameter, and three bubble diameter sub-models are developed to calculate the overall bubble diameter based on a departure diameter. In the model, the heat transfer growth is calculated after estimating the bubble location. The collision variation is deduced from the interfacial area concentration equation. The liquid impacting variation is calculated through phase interaction force and gas viscous force. The proposed model is conducted through global information searching in the flow boiling simulation and validated using the void fraction and temperature data from the literature. The effects of the heat transfer growth, the collision, and the separating volume on the bubble diameter are discussed.

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Bubble departure size in flow boiling

et al. 2014

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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)

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Development of bubble departure and lift-off diameter models in low heat flux and low flow velocity conditions

Cited by 50 publications

References 25 publications

A Note on Bubble Sizes in Subcooled Flow Boiling at Low Velocities in Internal Combustion Engine-Like Conditions

A Note on Bubble Sizes in Subcooled Flow Boiling at Low Velocities in Internal Combustion Engine-Like Conditions

An Overall Bubble Diameter Model for the Flow Boiling and Numerical Analysis through Global Information Searching

Bubble departure size in flow boiling

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