Simulation of Single Bubble Growth in a Planar Microchannel With Temperature Recovery Model

2017 ◽  
Author(s):  
Yang Luo ◽  
Jingzhi Zhang ◽  
Wei Li ◽  
Zhengjiang Zhang ◽  
Jincai Du ◽  
...  
Keyword(s):  
Surface Tension ◽  
Heat Flux ◽  
Bubble Growth ◽  
Flow Boiling ◽  
Wall Heat Flux ◽  
Recovery Model ◽  
Vapor Interface ◽  
Wall Superheat ◽  
Temperature Recovery ◽  
Liquid Vapor

In the study numerical simulations are performed to investigate the saturated fluid flow through a two dimensional microchannel (1000μm×200μm, with a superheated bottom wall) by building a comprehensive physical method and updating the standard solver in the OpenFOAM software package. On basis of previous numerical study, most of the numerical methods for the micro-scale flow boiling emphasizes the mass transfer and interfacial heat exchange. Simultaneously, geometric reconstruction technology for liquid-vapor interface is widely used, which evidently captures the interfacial boundary characteristic accurately but costs lots of computational resources. In the present study, the temperature recovery model is adopted to maintain the liquid-vapor interface temperature, and an interface-cell searching algorithm is added into the model, while the geometric interface reconstruction technology is abandoned. For the validation of the new codes developed in OpenFOAM, 1-d Stefan Problem and the experimental results of Mukherjee are both utilized to compare with our simulation results. The growth process of a single bubble in the laminar flow regime is studied in order to explore the underlying mechanism of flow boiling in microchannels. The qualitative investigation for effects of wall superheat, Reynolds number, contact angle and surface tension on heat transfer are comprehensively discussed. In general, heat flux of the bottom wall increases because of the motion of liquid-vapor interface. Wall superheat determines the rate of bubble growth on the heated wall, which is roughly proportional to wall heat flux due to the Fourier’s Law. The distribution of velocity and temperature fields in the channel refresh progressively with increasing inflow Reynolds number, which speeds up the evolution of interface position and augments the wall heat flux significantly. Furthermore, the area of thin liquid film between the wall and the bubble is enlarged by reducing the contact angle, thus augmenting the wall heat flux by several times compared with the single phase microchannel flow. However, surface tension and gravitational acceleration are found to be negligible in the present study.

Force Analysis of Bubble Dynamics in Flow Boiling Silicon Nanowire Microchannels

2016 ◽  
Author(s):  
Tamanna Alam ◽  
Wenming Li ◽  
Fanghao Yang ◽  
Ahmed Shehab Khan ◽  
Yan Tong ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Surface Tension ◽  
Bubble Growth ◽  
Bubble Dynamics ◽  
Flow Boiling ◽  
Silicon Nanowire ◽  
Bubble Nucleation ◽  
Force Analysis ◽  
Vapor Interface ◽  
Liquid Vapor

In microchannel flow boiling, bubble nucleation, growth and flow regime development are highly influenced by channel cross-section and physical phenomena underlying this mechanism are far from being well-established. Relative effects of different forces acting on wall-liquid and liquid-vapor interface of a confined bubble play an important role in heat transfer performances. Therefore, fundamental investigations are necessary to develop enhanced microchannel heat transfer surfaces. Force analysis of vapor bubble dynamics in flow boiling Silicon Nanowire (SiNW) microchannels has been performed based on theoretical, experimental and visualization studies. The relative effects of different forces on flow regime, instability and heat transfer performances of flow boiling in Silicon Nanowire microchannels have been identified. Inertia, surface tension, shear, buoyancy, and evaporation momentum forces have significant importance at liquid-vapor interface as discussed earlier by several authors. However, no comparative study has been done for different surface properties till date. Detailed analyses of these forces including contact angle and bubble flow boiling characteristics have been conducted in this study. A comparative study between Silicon Nanowire and Plainwall microchannels has been performed based on force analysis in the flow boiling microchannels. In addition, force analysis during instantaneous bubble growth stage has been performed. Compared to Plainwall microchannels, enhanced surface rewetting and critical heat flux (CHF) are owing to higher surface tension force at liquid-vapor interface and Capillary dominance resulting from Silicon Nanowires. Whereas, low Weber number in Silicon Nanowire helps maintaining uniform and stable thin film and improves heat transfer performances. Moreover, force analysis during instantaneous bubble growth shows the dominance of surface tension at bubble nucleation and slug/transitional flow which resulted higher heat transfer contact area, lower thermal resistance and higher thin film evaporation. Whereas, inertia force is dominant at annular flow and it helps in bubble removal process and rewetting.

Wall Heat Flux Partitioning During Subcooled Flow Boiling: Part 1—Model Development

2005 ◽  
Vol 127 (2) ◽  
pp. 131-140 ◽  
Author(s):  
Nilanjana Basu ◽  
Gopinath R. Warrier ◽  
Vijay K. Dhir
Keyword(s):  
Heat Flux ◽  
Flow Boiling ◽  
Model Development ◽  
Wall Heat Flux ◽  
Vapor Generation ◽  
Subcooled Flow Boiling ◽  
Wall Superheat ◽  
Subcooled Flow ◽  
Flux Partitioning ◽  
Transient Conduction

In this work a mechanistic model has been developed for the wall heat flux partitioning during subcooled flow boiling. The premise of the proposed model is that the entire energy from the wall is first transferred to the superheated liquid layer adjacent to the wall. A fraction of this energy is then utilized for vapor generation, while the rest of the energy is utilized for sensible heating of the bulk liquid. The contribution of each of the mechanisms for transfer of heat to the liquid—forced convection and transient conduction, as well as the energy transport associated with vapor generation has been quantified in terms of nucleation site densities, bubble departure and lift-off diameters, bubble release frequency, flow parameters like velocity, inlet subcooling, wall superheat, and fluid and surface properties including system pressure. To support the model development, subcooled flow boiling experiments were conducted at pressures of 1.03–3.2 bar for a wide range of mass fluxes 124-926kg/m2 s, heat fluxes 2.5-90W/cm2 and for contact angles varying from 30° to 90°. The model developed shows that the transient conduction component can become the dominant mode of heat transfer at very high superheats and, hence, velocity does not have much effect at high superheats. This is particularly true when boiling approaches fully developed nucleate boiling. Also, the model developed allows prediction of the wall superheat as a function of the applied heat flux or axial distance along the flow direction.

Wall Heat Flux Partitioning During Subcooled Flow Boiling at Low Pressures

2003 ◽  
Author(s):  
Nilanjana Basu ◽  
Gopinath R. Warrier ◽  
Vijay K. Dhir
Keyword(s):  
Heat Flux ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Wall Heat Flux ◽  
Superheated Liquid ◽  
Pressure Data ◽  
Vapor Generation ◽  
Subcooled Flow Boiling ◽  
Wall Superheat ◽  
Subcooled Flow

In this work a mechanistic model for nucleate boiling heat flux as a function of wall superheat has been developed. The premise of the proposed model is that the entire energy from the wall is first transferred to the superheated liquid layer adjacent to the wall. A fraction of this energy is then utilized for vapor generation. Contribution of each of the heat transfer mechanisms — forced convection, transient conduction, and vapor generation, has been quantified in terms of nucleation site densities, bubble departure and lift off diameters, bubble release frequency, flow parameters like velocity, inlet subcooling, wall superheat, and fluid and surface properties including system pressures. To support the model development, subcooled flow boiling experiments were conducted at pressures of 1.03 to 3.2 bar for a wide range of mass fluxes (124 to 926 kg/m2s), heat fluxes (2.5 to 90 W/cm2) and for contact angles varying from 30° to 90°. Model validation has been carried out with low-pressure data obtained from present work and the wall heat flux predictions are within ± 30% of experimental values. Application of the model to high-pressure data available in literature also showed good agreement, signifying that the model can be extended to all pressures.

Numerical Analysis of Vapor Bubble Growth and Wall Heat Transfer During Flow Boiling of Water in a Microchannel

2005 ◽  
Author(s):  
Abhijit Mukherjee ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Cross Section ◽  
Vapor Bubble ◽  
Bubble Growth ◽  
Stokes Equations ◽  
Flow Boiling ◽  
Navier Stokes ◽  
Channel Cross Section ◽  
Wall Heat Transfer ◽  
Wall Superheat

The present study is performed to analyze the wall heat transfer mechanisms during growth of a vapor bubble inside a microchannel. The microchannel is of 200 μm square cross section and a vapor bubble begins to grow at one of the walls, with liquid coming in through the channel inlet. The complete Navier-Stokes equations along with continuity and energy equations are solved using the SIMPLER method. The liquid vapor interface is captured using the level set technique. The bubble grows rapidly due to heat transfer from the walls and soon turns into a plug filling the entire channel cross section. The average wall heat transfer at the channel walls is studied for different values of wall superheat and incoming liquid mass flux. The results show that the wall heat transfer increases with wall superheat but is almost unaffected by the liquid flow rate. The bubble growth is found to be the primary mechanism of increasing wall heat transfer as it pushes the liquid against the walls thereby influencing the thermal boundary layer development.

Shape of a Vapor Stem During Nucleate Boiling of Saturated Liquids

1995 ◽  
Vol 117 (2) ◽  
pp. 394-401 ◽  
Author(s):  
J. H. Lay ◽  
V. K. Dhir
Keyword(s):  
Heated Surface ◽  
Nucleate Boiling ◽  
Nonlinear Ordinary Differential Equation ◽  
Transport Processes ◽  
Maximum Diameter ◽  
Limited Data ◽  
Flat Bottom ◽  
Vapor Interface ◽  
Wall Superheat ◽  
Liquid Vapor

The transport processes occurring in an evaporating two-dimensional vapor stem formed during saturated nucleate boiling on a heated surface are modeled and analyzed numerically. From the heater surface heat is conducted into the liquid macro/microthermal layer surrounding the vapor stems and is utilized in evaporation at the stationary liquid–vapor interface. A balance between forces due to curvature of the interface, disjoining pressure, hydrostatic head, and liquid drag determines the shape of the interface. The kinetic theory and the extended Clausius–Clapeyron equation are used to calculate the evaporative heat flux across the liquid–vapor interface. The vapor stem shape calculated by solving a fourth-order nonlinear ordinary differential equation resembles a cup with a flat bottom. For a given wall superheat, several metastable states of the vapor stem between a minimum and maximum diameter are found to be possible. The effect of wall superheat on the shape of the vapor stem is parametrically analyzed and compared with limited data reported in the literature.

On the Dependence of Surface Tension of Liquids on the Curvature of the Liquid−Vapor Interface

2001 ◽  
Vol 105 (5) ◽  
pp. 1050-1055 ◽  
Author(s):  
Vladimir B. Fenelonov ◽  
Gennady G. Kodenyov ◽  
Vitaly G. Kostrovsky
Keyword(s):  
Surface Tension ◽  
Vapor Interface ◽  
Liquid Vapor
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