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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

Hydrodynamic regimes of gas-liquid flow in a microreactor channel

Pohorecki R., Sobieszuk P., Kula K., Moniuk W., Zieliński M.

Prace Naukowe Instytutu Inżynierii Chemicznej Polskiej Akademii Nauk

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2006

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nr 7

53-58

EN

The hydrodynamic regimes of gas-liquid flow in a microreactor channel have been investigated, using water and 1-propanol (liquids with different contact angle and surface tension values) and nitrogen as an inert gas. The microreactor was Y shaped. Experiments were carried out to determine the character ofgas and liquid flow ("regime map"). Four main flow types were observed: bubbie, sług, slug/annular and annular.

PL

Zbadano reżimy hydrodynamiczne w mikroreaktorze gaz - ciecz. Użyto wody oraz 1-propanolu (cieczy o zróżnicowanych kątach zwilżania i napięcia powierzchniowego) i azotu jako gazu inertnego. Kanał mikroreaktora miał kształt litery Y. Eksperymenty były prowadzone w celu zdefiniowania charakteru przepływu gazu i cieczy ("mapa reżimów"). Zaobserwowano główne 4 typy przepływów: pęcherzykowy "bubble", rzutowy "slug", rzutowo - pierścieniowy "slug/annular" oraz pierścieniowy "annular".