Modifications and Extensions to the Annular Flow Model

2006 ◽  
Author(s):  
Priyadarshan U. Patankar ◽  
Bhalchandra P. Puranik
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Annular Flow ◽  
Flow Model ◽  
Heat Sinks ◽  
Phase Flow ◽  
Uniform Heating ◽  
Two Phase

Boiling heat transfer to fluid flow in microchannel heat sinks is being looked upon as a promising solution to the problem of cooling microprocessors with large power densities. In the present work, an annular flow model [1] is implemented to investigate the boiling heat transfer and two-phase flow characteristics in microchannel heat sinks. A modification in the model for the deposition mass transfer coefficient is proposed to better compare the existing experimental data [2]. The deposition mass transfer coefficient affects the distribution of liquid in the form of entrained droplets and the liquid film. The liquid film thickness is the most significant parameter in the determination of the heat transfer coefficient. The suggested change ensures consistent results for the behavior of the entrained fraction. We further report pressure drop results obtained using the modified annular flow model and a comparison with existing experimental data. Finally, we present results predicted by the annular flow model for non-uniform heating of a microchannel, in an effort to simulate hot spots on a microprocessor chip. A few preliminary results obtained from the modified model to simulate boiling and two-phase flow in a parallel microchannel device with non-uniform heating are presented.

CFD Simulation of Boiling Heat Transfer Using OpenFOAM

2014 ◽  
Author(s):  
Mehrdad Shademan ◽  
Ram Balachandar ◽  
Ron Barron
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Boiling Heat Transfer ◽  
Flow Model ◽  
Cfd Simulation ◽  
Two Phase Flow ◽  
Phase Flow ◽  
Two Phase ◽  
Adiabatic Flow ◽  
Heat Transfer Phenomenon

An Eulerian-Eulerian two-phase flow model has been developed to simulate the boiling heat transfer phenomenon in a pipe flow. The model was implemented in the OpenFOAM source code. The code development process was divided into two sections. In the first step, an adiabatic two-phase flow model which takes into account the effect of interfacial forces was developed. In the second step, the energy equation was activated to account for non-adiabatic conditions. In order to include the boiling effect, several different subroutines which model evaporation and condensation phenomena were attached to the solver. Results of the two-phase adiabatic flow and from the boiling model are compared with available numerical and experimental data. The simulation predictions are in reasonable agreement with the experimental data and show significant improvement relative to previous numerical results, which suggests the validity of the developed model for boiling heat transfer problems.

Experimental Investigation and Empirical Analysis of Non-Boiling Gas-Liquid Two Phase Heat Transfer in Vertical Downward Pipe Orientation

2012 ◽  
Author(s):  
Swanand M. Bhagwat ◽  
Mehmet Mollamahmutoglu ◽  
Afshin J. Ghajar
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Annular Flow ◽  
Single Phase ◽  
Phase Flow ◽  
Upward Flow ◽  
Two Phase ◽  
Reynolds Analogy ◽  
Two Phase Heat Transfer

The non-boiling gas-liquid two phase flow is pertinent to industrial applications like the reduction of paraffin wax depositions in petroleum transport lines, air lift systems and the chemical processes such as ethanol-water fractionation seeking enhanced heat and mass transfer. The non-boiling two phase heat transfer mechanism in horizontal and vertical orientations has been investigated by many researchers. However, till date very little experimental work and investigation has been performed for vertical downward flow. In order to contribute more to this research and have a better understanding of the non-boiling two phase heat transfer phenomenon for this pipe orientation, experimental investigation is undertaken for a vertical downward oriented 0.01252 m I.D. schedule 10 S stainless steel pipe using air-water as fluid combination. The influence of different flow patterns on the two phase convective heat transfer coefficient is studied using experimental measurements of 165 data points for bubbly, slug, froth, falling film and annular flow patterns spanned over the entire range of the void fraction. In general the two phase heat transfer coefficients are found to be consistently higher than that of the single phase flow. This tendency is observed to increase with increase in the gas flow rate as the flow regime migrates from bubbly to the annular flow. The concept of Reynolds analogy as implemented by Tang and Ghajar [1] for horizontal and vertical upward flow is analyzed against the vertical downward flow data collected in the present study. Due to lack of correlations available for predicting the two phase heat transfer coefficient in vertical downward orientation it was decided to perform the quantitative analysis of the seventeen two phase heat transfer correlations available for vertical upward flow. This analysis is concluded by the recommendation of the top performing correlations in the literature for each flow pattern. Based on the pressure drop data and using Reynolds analogy, a simple equation is proposed to correlate the two phase heat transfer coefficient with the single phase heat transfer coefficient.

scholarly journals Evaluation of Heat Transfer Coefficient of Two-Phase Flow Boiling with R290 in Horizontal Mini Channel

2021 ◽  
Vol 88 (3) ◽  
pp. 88-95
Author(s):  
Ronald Akbar ◽  
Jong Taek Oh ◽  
Agus Sunjarianto Pamitran
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Two Phase Flow ◽  
Flow Boiling ◽  
Phase Flow ◽  
Two Phase ◽  
The Heat Transfer Coefficient

Various experiments have been conducted on the heat transfer coefficient of two-phase flow boiling in mini channel tubes. In addition to obtaining data on the heat transfer coefficients through experiments, many researchers have also compared their experimental data using existing correlations. This research aims to determine the characteristics of the heat transfer coefficient of refrigerant R290 from the data used by processing and knowing the best heat transfer coefficient correlation in predicting the experimental data so that the results are expected to be a reference for designing a heat exchanger or for further research. The experimental data predicted is the two-phase flow boiling in a horizontal tube 3 mm diameter, with the mass flux of 50-180 kg/m2s, heat flux of 5-20 kW/m2, saturation temperature of 0-11 °C, and vapor quality of 0-1. The correlation used in this research is based on the asymptotic flow model, where the model is a combination of the nucleate and convective flow boiling mechanisms. The results show an effect of mass flux and heat flux on the experimental heat transfer coefficient and the predicted R290 heat transfer coefficient with asymptotic correlations had a good and similar result to the experimental data.

The effect of surfactant concentrations and surface material on heat transfer coefficient in nucleate boiling regime

Kerntechnik ◽  
2021 ◽  
Vol 86 (5) ◽  
pp. 365-374
Author(s):  
A. M. Refaey ◽  
S. Elnaggar ◽  
S. H. Abdel-Latif ◽  
A. Hamza
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Boiling Heat Transfer ◽  
Two Phase Flow ◽  
Surfactant Solution ◽  
Nucleate Boiling ◽  
Phase Flow ◽  
Two Phase

Abstract The nucleate boiling regime and two-phase flow are greater importance to the safety analysis of nuclear reactors. In this study, the boiling heat transfer in nuclear reactor is numerical investigated. The computational fluid dynamics (CFD) code, ANSYS Fluent 17.2 is used and the boiling model is employed. The numerical predictions obtained are compared with the experimental data reported by A. Hamza et al. [9]. An experimental test rig is designed and constructed to investigate the effect of cooling water chemistry control and the material of heater surface. CFD software, allows the detailed analysis of the two-phase flow and heat transfer. In this paper, we evaluate the accuracy of the boiling model implemented in the ANSYS Fluent code. This model is based on the heat flux partitioning approach and accommodates the heat flux due to single-phase convection, quenching and evaporation. The validation carried out of surfactant fluid/vapor two-phase flow inside the 2-D cylindrical boiling vessel. A heated horizontal pipe with stainless steel, Aluminum, and Zircalloy surface materials are used to numerically predict the field temperature and void fraction. Different surfactant concentrations ranging from 0, (pure water) to 1500 ppm, and heat fluxes ranging from 31 to 110 kW/m2 are used. The results of the predicted model depict that the addition of SDS Surfactant and increasing the heat flux improves the coefficient of boiling heat transfer for a given concentration. Also, it was found that the increasing of the concentration of aqueous surfactant solution increases the pool boiling heat transfer coefficient. The aqueous surfactant solution SDS improved the heat transfer coefficient of Aluminum, Zircalloy and stainless steel surface materials by 135%.138% and 120% respectively. The results of the numerical model are nearly in agreement with that measured in experimental.

Heat Transfer in Vapour-Liquid Flow at High Reduced Pressures

2010 ◽  
Author(s):  
Victor Yagov ◽  
Maria Minko
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Boiling Heat Transfer ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
Phase Flow ◽  
Two Phase ◽  
Co2 Flow ◽  
Reduced Pressures ◽  
Good Agreement

During the last decade a number of studies of boiling heat transfer in carbon dioxide notably increase. As a field of CO2 practical using corresponds to high reduced pressures, and a majority of available experimental data on CO2 flow boiling even in submillimetric channels relate to turbulent liquid flow regimes, a possibility arises to develop sufficiently general method for HTC predicting. Under the above conditions nucleate boiling occurs up to rather high flow quality, even in annular flow regime due to extremely small size of an equilibrium vapour bubble. This conclusion is in agreement with the available experimental data. The predicting equation for nucleate boiling heat transfer developed by one of the present authors in 1988 is valid for any nonmetallic liquid. A contribution of forced convection in heat transfer is calculated according to the Petukhov et al. equation with correction factor, which accounted for an effect of velocity increase due to evaporation. This effect can be essential at relatively small heat fluxes and rather high mass flow rates. The Reynolds analogy and homogeneous model are used in order to account for the convective heat transfer augmentation in two-phase flow. Due to low ratio of liquid and vapour densities at high reduced pressures the homogeneous approximation of two-phase flow seems to be warranted. A total heat transfer coefficient is calculated as an interpolated value of boiling and convective HTCs. The experimental data on CO2 flow boiling related to regimes before heated wall dryout incipience are in rather good agreement with the calculations. Besides the data on carbon dioxide flow boiling, the results on water, helium, nitrogen and some refrigerants were used for comparison; at rather high reduced pressures the computed and the measured values of HTCs are in a good agreement. The data include results obtained in the channels of a diameter from 0.6mm up to 18mm. It is clear that at high reduced pressures there is no strong variation in boiling heat transfer with channel size decrease, it means that a classification on channel size has no sense if it does not consider liquid/vapour densities ratio.

Forced Convective Boiling Heat Transfer and Pressure Drop Characteristics of Two-Phase Flow Inside a Small Horizontal Helically Coiled Tubing Once-Through Steam Generator

2003 ◽  
Author(s):  
Liang Zhao ◽  
Liejin Guo ◽  
Bofeng Bai ◽  
Yucheng Hou ◽  
Ximin Zhang
Keyword(s):  
Heat Transfer ◽  
Experimental Data ◽  
Heat Flux ◽  
Pressure Drop ◽  
Boiling Heat Transfer ◽  
Phase Flow ◽  
Two Phase ◽  
Convective Boiling ◽  
Coiled Tube ◽  
Helically Coiled Tube

The pressure drop and boiling heat transfer of steam water two-phase flow were studied in a small horizontal helically coiled tube once-through steam generator of 9-mm inside diameter with 292-mm coil diameter and 30-mm pitch. Experiments were performed at a range of qualities up to 0.95, a system pressure range of 0.5∼3.5MPa, a mass flux range of 236∼943kg/m2s and a heat flux range of 0∼900kW/m2. Based on the experimental results, a new two-phase frictional pressure drop correlation was developed on the basis of Chisholm’s B-coefficient method. In the present experimental range, boiling heat transfer was found to be dependent not only on mass flux but also on heat flux. This result implies that both the nucleation mechanism and the convection mechanism have the same importance to forced convective boiling heat transfer in small horizontal helically coiled tube over the full range of qualities (pre-critical heat flux qualities of 0.1∼0.9) which is contrary to situations in larger helically coiled tube where the convection mechanism dominates at qualities typically > 0.1. Traditional single parameter Lockhart-Martinelli type correlations failed to satisfactorily predict present experimental data and in this paper a new flow boiling heat transfer correlation was put forward to better predict the experimental data of the present study.

Analytical Modeling of Annular Flow Boiling Heat Transfer in Mini- and Microchannel Heat Sinks

2010 ◽  
Vol 132 (4) ◽  
Author(s):  
A. Megahed ◽  
I. Hassan
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Analytical Model ◽  
Boiling Heat Transfer ◽  
Annular Flow ◽  
Flow Boiling ◽  
Heat Sinks ◽  
Flow Boiling Heat Transfer ◽  
The Heat Transfer Coefficient

An analytical model is proposed to predict the flow boiling heat transfer coefficient in the annular flow regime in mini- and microchannel heat sinks based on the separated model. The modeling procedure includes a formulation for determining the heat transfer coefficient based on the wall shear stress and the local thermophysical characteristics of the fluid based on the Reynolds’ analogy. The frictional and acceleration pressure gradients within the channel are incorporated into the present model to provide a better representation of the flow conditions. The model is validated against collected data sets from the literature produced by different authors under different experimental conditions, different fluids, and with mini- and microchannels of hydraulic diameters falling within the range of 92–1440 μm. The accuracy between the experimental and predicted results is achieved with a mean absolute error of 10%. The present analytical model can correctly predict the different trends of the heat transfer coefficient reported in the literature as a function of the exit quality. The predicted two-phase heat transfer coefficient is found to be very sensitive to changes in mass flux and saturation temperature. However, it is found to be mildly sensitive to the change in heat flux.

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