scholarly journals WALL HEAT FLUX PARTITIONING ANALYSIS FOR SUBCOOLED FLOW BOILING OF WATER-ETHANOL MIXTURE IN CONVENTIONAL CHANNEL

2019 ◽  
Vol 13 ◽  
Author(s):  
B.G. Suhas ◽  
A. Sathyabhama ◽  
Kavadiki Veerabhadrappa ◽  
U. Suresh Kumar ◽  
U. Kiran Kumar
Keyword(s):  
Heat Flux ◽  
Flow Boiling ◽  
Wall Heat Flux ◽  
Subcooled Flow Boiling ◽  
Ethanol Mixture ◽  
Subcooled Flow ◽  
Flux Partitioning

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: Part II—Model Validation

2005 ◽  
Vol 127 (2) ◽  
pp. 141-148 ◽  
Author(s):  
Nilanjana Basu ◽  
Gopinath R. Warrier ◽  
Vijay K. Dhir
Keyword(s):  
Experimental Data ◽  
Heat Flux ◽  
Flow Boiling ◽  
Mechanistic Model ◽  
Wall Heat Flux ◽  
Experimental Conditions ◽  
Subcooled Flow Boiling ◽  
Subcooled Flow ◽  
Flux Partitioning ◽  
Model Predictions

A mechanistic model for wall heat flux partitioning during subcooled flow boiling proposed in Part I of this two-part paper, is validated in this part. As the first step of the validation process, the developed model was applied to experimental data obtained as part of this study. Comparison of the model predictions with the present data shows good agreement. In order to further validate/exercise the model, it was then applied to several data sets available in the literature. Though the data in the literature were for experimental conditions vastly different from those from which the model was originally developed, reasonable agreement between the model predictions and the experimental data were observed. This indicates that the proposed model can be extended to other flow conditions provided the submodels cover the conditions of the experiments. Future work should be directed towards improvement of the various submodels involved to extend their range of applicability, especially the ones related to bubble dynamics. Additionally, it must be kept in mind that the model as proposed is strictly only applicable to vertical up-flow and may not be applicable to other orientations.

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.

Investigations on Effect of Lift and Wall Lubrication Forces on the Subcooled Flow Boiling

2020 ◽  
Vol 6 (4) ◽  
Author(s):  
Sai Raja Gopal Vadlamudi ◽  
Arun K. Nayak
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Eulerian Model ◽  
Subcooled Flow Boiling ◽  
Void Fractions ◽  
Subcooled Flow ◽  
Flux Partitioning ◽  
The Impact

Abstract Subcooled flow boiling is widely used as a mode of heat transfer in many industries, especially in nuclear reactors. Despite its advantages, the heat transfer is hampered beyond a certain flux due to a phenomenon known as departure from nucleate boiling (DNB). It is important to determine the void fraction profiles, especially the near-wall void fractions, to evaluate the limiting heat flux conditions. The two-fluid Eulerian model, coupled with the heat flux partitioning model, is widely used to predict subcooled flow boiling characteristics. Over the years, many researchers have not considered lift and wall lubrication forces in their modeling of subcooled flow boiling. Few researchers have considered the Tomiyama model for lift force; however, their results were not encouraging. Moreover, there is no systematic study in evaluating the impact of lift and wall lubrication forces on subcooled flow boiling. In this paper, various lift and wall lubrication models are compared to understand the implications of these forces on void distribution. The advantages and limitations of the models are discussed in detail.

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