Simplified Model for Prediction of Bubble Growth at Nucleation Site in Microchannels

2014 ◽  
Vol 136 (6) ◽  
Author(s):  
Sambhaji T. Kadam ◽  
Kuldeep Baghel ◽  
Ritunesh Kumar
Keyword(s):  
Vapor Phase ◽  
Waiting Time ◽  
Bubble Growth ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Nucleation Site ◽  
Simplified Model ◽  
Phase Flow ◽  
Two Phase ◽  
Proposed Model

Formation of the first bubble at nucleation site is an inception of the two phase flow in pool boiling and flow boiling. Bubble dynamics (bubble nucleation, growth, and departure) plays an important role in heat transfer and pressure drop characteristics during two phase flow in microchannels. In this paper, a simplified model has been developed for predicting bubble growth rate at nucleation cavity in microchannel. It is assumed that heat supplied at nucleation site is divided between the liquid phase and the vapor phase as per instantaneous void fraction value. The energy consumed by the vapor phase is utilized in bubble growth and overcoming resistive effects; surface tension, inertia, shear, gravity, and change in momentum due to evaporation. Proposed model shows a good agreement with available experimental works. In addition, the bubble waiting time phenomenon for flow boiling is also addressed using proposed model. Waiting time predicted by the model is also close to that obtained from experimental data.

Bubble Growth at Nucleation Cavity in Microchannels

2013 ◽  
Author(s):  
Sambhaji T. Kadam ◽  
Ritunesh Kumar ◽  
Kuldeep Baghel
Keyword(s):  
Vapor Phase ◽  
Waiting Time ◽  
Bubble Growth ◽  
Bubble Dynamics ◽  
Flow Boiling ◽  
Nucleation Site ◽  
Bubble Nucleation ◽  
Two Phase ◽  
Proposed Model ◽  
Gravity Effects

Bubble dynamics i.e. bubble nucleation, growth and departure plays an important role in heat transfer and pressure drop characteristics during two phase flow of microchannels. A simplified mathematical model has been developed to predict the bubble growth rate in microchannels at nucleation cavity after its inception. It is assumed that heat supplied at nucleation site is divided between liquid phase and vapor phase as per instantaneous void fraction value. The energy consumed by vapor phase is utilized in overcoming evaporation, surface tension, inertia, shear and gravity effects. Proposed model shows good agreement (∼14 % error) with available experimental work. In addition, the physical phenomena of the bubble waiting time for flow boiling is also addressed utilizing proposed model. The waiting time predicted by the model is close to that obtained from experimental data.

Pressure Drop in a Capillary Tube in Boiling Two-Phase Flow

2003 ◽  
Author(s):  
Fumito Kaminaga ◽  
Baduge Sumith ◽  
Kunihito Matsumura
Keyword(s):  
Pressure Drop ◽  
Vapor Phase ◽  
Mass Flux ◽  
Two Phase Flow ◽  
Capillary Tube ◽  
Flow Boiling ◽  
Phase Flow ◽  
Two Phase ◽  
System Pressure ◽  
Phase Pressure

Two-phase pressure drop is experimentally examined in a flow boiling condition in a tube of diameter 1.45 mm using water in ranges of pressure from 10 to 100 kPa, mass flux from 18 to 152 kg/m2s, heat flux from 13 to 646 kW/m2, and exit quality from 0.02 to 0.77. Also, pressure drop in an adiabatic air-water two-phase flow is measured at atmospheric pressure using the same test section and mass flux ranges of liquid and gas as those in the flow boiling. Decreasing system pressure the pressure drop significantly increases at a given mass flux. Influence of vapor phase on the pressure drop is found to be large both in the adiabatic and the diabatic conditions. The frictional pressure drop correlation for the adiabatic two-phase flow is developed and applied to predict pressure drop in the flow boiling. But it cannot give satisfactory predictions. The Chisholm correlation calculating a two-phase pressure drop multiplier is modified to account the influence of vapor phase in a capillary tube and the modified correlation can predict the pressure drop in the flow boiling within an error of 20%.

Suppression of Flow Boiling Nucleation

1997 ◽  
Vol 119 (3) ◽  
pp. 517-524 ◽  
Author(s):  
G. E. Thorncroft ◽  
J. F. Klausner ◽  
R. Mei
Keyword(s):  
Heat Transfer ◽  
Dimensionless Parameter ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Nucleation Site ◽  
Complete Suppression ◽  
Phase Flow ◽  
Two Phase ◽  
Nucleation Sites

A simple model is presented for estimating the ratio of the maximum to minimum cavity radius required for ebullition in two-phase flow with heat transfer. The resulting dimensionless parameter, rmax/rmin, is demonstrated to correlate flow boiling nucleation site density. As the convective heat transfer associated with bulk turbulence in two-phase flow is enhanced, rmax→rmin, and the probability of finding surface cavities whose radii lie between rmaxandrmin is reduced. Thus, active nucleation sites become deactivated. A vertical flow boiling facility was fabricated in which the nucleation suppression point can be measured. Experiments conducted for mass flux ranging from 183–315 kg/m2-s and inlet quality ranging from 0–0.151, along with data available from the literature, suggest that rmax/rmin is the leading order dimensionless parameter on which the complete suppression of nucleation sites depends. Although the suppression of nucleation sites also depends, to a certain extent, on the surface/fluid combination and heat flux, it is found that complete suppression occurs for rmax/rmin ranging from 40 to 120. This is proposed as a criterion to discriminate the purely convective regime from the nucleate boiling regime.

scholarly journals Experimental Investigation and Prediction on Pressure Drop during Flow Boiling in Horizontal Microchannels

Micromachines ◽  
2021 ◽  
Vol 12 (5) ◽  
pp. 510
Author(s):  
Yan Huang ◽  
Bifen Shu ◽  
Shengnan Zhou ◽  
Qi Shi
Keyword(s):  
Pressure Drop ◽  
Flow Model ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Separated Flow ◽  
Heat Fluxes ◽  
Phase Flow ◽  
Vapor Quality ◽  
Two Phase ◽  
Gas Flux

In this paper, two-phase pressure drop data were obtained for boiling in horizontal rectangular microchannels with a hydraulic diameter of 0.55 mm for R-134a over mass velocities from 790 to 1122, heat fluxes from 0 to 31.08 kW/m2 and vapor qualities from 0 to 0.25. The experimental results show that the Chisholm parameter in the separated flow model relies heavily on the vapor quality, especially in the low vapor quality region (from 0 to 0.1), where the two-phase flow pattern is mainly bubbly and slug flow. Then, the measured pressure drop data are compared with those from six separated flow models. Based on the comparison result, the superficial gas flux is introduced in this paper to consider the comprehensive influence of mass velocity and vapor quality on two-phase flow pressure drop, and a new equation for the Chisholm parameter in the separated flow model is proposed as a function of the superficial gas flux . The mean absolute error (MAE ) of the new flow correlation is 16.82%, which is significantly lower than the other correlations. Moreover, the applicability of the new expression has been verified by the experimental data in other literatures.

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