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1

Perturbation solutions for magnetohydrodynamics (MHD) flow of in a non-Newtonian fluid between concentric cylinders

Yurusoy M., Guler O. F.

International Journal of Applied Mechanics and Engineering

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2019

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Vol. 24, no. 1

199--211

EN

The steady-state magnetohydrodynamics (MHD) flow of a third-grade fluid with a variable viscosity parameter between concentric cylinders (annular pipe) with heat transfer is examined. The temperature of annular pipes is assumed to be higher than the temperature of the fluid. Three types of viscosity models were used, i.e., the constant viscosity model, space dependent viscosity model and the Reynolds viscosity model which is dependent on temperature in an exponential manner. Approximate analytical solutions are presented by using the perturbation technique. The variation of velocity and temperature profile in the fluid is analytically calculated. In addition, equations of motion are solved numerically. The numerical solutions obtained are compared with analytical solutions. Thus, the validity intervals of the analytical solutions are determined.

2

Investigations of mass transfer in annular gas-liquid flow in a microreactor

Sobieszuk P., Napieralska K.

Chemical and Process Engineering

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2016

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Vol. 37, nr 1

55--64

EN

The paper presents an investigation of mass transfer in gas-liquid annular flow in a microreactor. The microreactor had a meandered shape with a square cross-section of the channel (292×292 μm, hydraulic diameter 292 μm) and 250 mm in length. The rate of CO2 absorption from the CO2/N2 mixture in NaOH (0.1 M, 0.2 M, 0.7 M, 1.0 M and 1.5 M) water solutions was measured. Two velocities of gas flow and two velocities of liquid flow were used. In two cases a fully developed annular flow at the beginning of the channel was observed, whilst in two cases annular flow was formed only in about 2/3 of the microchannel length. Based on the measurements of CO2 absorption rate, the values of volumetric liquid – side mass transfer coefficients with the chemical reaction were determined. Then physical values of coefficients were found. Obtained results were discussed and their values were compared with the values predicted by literature correlations.

3

Modeling of liquid film flow in annuli

Anglart H.

Journal of Power Technologies

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2014

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Vol. 94, nr 5

8--15

EN

One of the challenges in thermal-hydraulic analyses of BWRs is correct prediction of dryout occurrence in fuel assemblies. In practical applications the critical powers in fuel assemblies are found from correlations that are based on experimental data. The drawback of this approach is that correlations are valid only for these fuel assemblies on which the experiments have been conducted. Other restrictive factors are the limited ranges of experimental working conditions including pressure, mass flux and axial power distributions. To overcome the above-mentioned limitations, several different approaches have been proposed to predict the dryout occurrence. One of them is to employ a phenomenological model of annular flow, in which the mass transfer between the liquid film and the gas core is based on entrainment and deposition correlations. Most of these correlations are derived from water-air flows in vertical tubes and their applicability to other geometries in general, and rod-bundles in particular, should be analysed. This paper presents an analysis of the entrainment rate in vertical annuli. Using the standard approach to calculate the entrainment rate, one can demonstrate that the results deviate from measurements. It has been shown that modifying the entrainment correlation based on data obtained in the annulus geometry leads to an essential improvement in the predictive capability of the phenomenological model of annular two-phase flow.

4

Dry patch formation in diabatic annular two-phase flows

Anglart H.

Journal of Power Technologies

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2014

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Vol. 94, nr 5

85--95

EN

Conditions for the formation of a stable dry patch in vertical annular two-phase flows in heated channels are investigated. An analytical model of the force balance for the leading edge of the liquid film is developed. In addition to surface tension, evaporation thrust and capillary forces, the model includes the effect of turbulence, the pressure gradient and the interfacial shear stress. Numerical evaluations are performed to validate the model and to indicate the importance of various factors on the dry patch stability and on the resulting minimum wetting rate of the liquid film. The analyses indicate that good agreement with measurements is obtained in the case of a stagnant patch formed on liquid film flowing down a vertical surface. It is shown that for low and moderate mass flow rate of the gas phase in vertical co-current annular flow, the force balance is dominated by the stagnation and the shear stress forces. With growing mass flow rate of the gas phase, the pressure gradient and the interfacial shear stress become increasingly important. As a result, in accordance with measurements, the predicted minimum flow rate of the liquid film at which the patch is re-wetted decreases.

5

Experimental and theoretical study of dryout in annular flow in small diameter channels

Mikielewicz D., Gliński M., Wajs J.

Archives of Thermodynamics

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2011

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Vol. 32, no. 1

89-109

EN

In the paper the experimental analysis of dryout in small diameter channels is presented. The investigations were carried out in vertical pipes of internal diameter equal to 1.15 mm and 2.3 mm. Low-boiling point fluids such as SES36 and R123 were examined. The modern experimental techniques were applied to record liquid film dryout on the wall, among the others the infrared camera. On the basis of experimental data an empirical correlation for predictions of critical heat flux was proposed. It shows a good agreement with experimental data within the error band of 30%. Additionally, a unique approach to liquid film dryout modeling in annular flow was presented. It led to the development of the three-equation model based on consideration of liquid mass balance in the film, a two-phase mixture in the core and gas. The results of experimental validation of the model exhibit improvement in comparison to other models from literature.

6

Dryout in annular flow - theoretical analysis

Mikielewicz D., Wajs J., Gliński M., Zrooga A.

Archives of Thermodynamics

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2009

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Vol. 30, no. 2

77-90

EN

In the paper a two-equation model of mass balance of liquid in the film and in the core for calculation of dryout at high vapour quality is modified from the earlier version presented by Sedler and Mikielewicz [1]. Additionally, the mass balance equation for the liquid film contains a modified evaporation term. Modified is the heat flux density applied in evaporation of liquid film which now is variable within film thickness. The solution of such equations requires prior knowledge of rates of deposition and entrainment. The theoretical determination of there quantities involves serious difficulties. The relations for determination of deposition and entrainment rate are taken therefore from Okawa et al. [3], The results of calculations are validated against experimental data of Sedler and Mikielewicz [1], showing a satisfactory consistency.

7

Flow controlled critical heat flux: developments in annular flow modelling

Azzopardi B.

Archives of Thermodynamics

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2006

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Vol. 27, no. 2

3-22

EN

Critical heat flux at higher steam qualities is accepted to correspond to the dry out of the wall film in the annular flow pattern where the film is depleted by evaporation and entrainment of liquid into drops and augmented by redeposition of drops. Since the first complete model for annular flow there have been many developments in the understanding and modelling of these flows, which are reviewed here. Latest developments on the rates of entrainment and deposition are described as well as the application of the model to multicomponent mixtures. Another area that has received attention is the start of annular flow and the boundary with churn flow. Applications for more complex geometies, namely annuli, rod bundles, horizontal pipes, Venturis and to the serpentine tubing of fired heaters have been developed and are presented.

8

Additive method for determination of flowrate of viscoplastic fluids in annuli

David J., Filip P.

Applied Mechanics and Engineering

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1999

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Vol. 4, no spec.

103-108

EN

The aim of this contribution is to present an additive method enabling a direct determination of axial flowrate for viscous (of power-law model) and viscoplastic (of Robertson-Stiff model) fluids in concentric annuli. This is based on addition of axial flowrates through individual partial concentric annuli forming the actual concentric annulus. The resulting relations for axial flowrate is possible to express in analytical forms without necessity of otherwise complicated derivations. The only numerical calculation consists in a determination of location of a zero shear stress for the original whole concentric annulus.