GAS-NON-NEWTONIAN LIQUID FLOW THROUGH GLOBE AND GATE VALVES

Experimental investigations have been carried out to evaluate the two-phase pressure drop across half-inch globe and gate valves for gas-non-Newtonian liquid flow. The non-Newtonian liquids used were different concentrations of dilute solutions of the sodium salt of carboxymethyl cellulose (SCMC), which behaved as pseudoplastic liquids. Generalized correlations in terms of the various physical and dynamic variables of the system have been developed for prediction of the two-phase frictional pressure drop for each valve. Statistical analysis of the correlations suggest that they are of acceptable accuracy.     

GAS-NON-NEWTONIAN LIQUID FLOW THROUGH ELBOWS

Experimental investigations have been carried out to evaluate the two-phase pressure drop across different types of elbows in the horizontal plane for gas-non-Newtonian pseudoplastic liquid flow. A generalised correlation have been developed to predict The two-phase pressure drop as a function of various physical and dynamic variables of the system. Statistical analysis of the correlation suggests that the correlation is of acceptable accuracy.     

DISPERSE PHASE STRESS IN TWO-PHASE FLOW

The usual two-fluid models for disperse two-phase flows feature an average disperse-phase stress in the disperse-phase momentum equation. It is shown that it is possible to derive an expression for this quantity without considering the detailed nature of the constitutive relation of the disperse phase. The result, which is more general than other relations of the same nature, is illustrated with a number of examples. It is also shown that a new formulation of the averaged equations recently proposed by the authors is equivalent to the more usual one.     

PRESSURE LOSSES IN TWO-PHASE GAS-NON-NEWTONIAN LIQUID FLOW IN A VERTICAL TUBE

Experimental data on pressure drop for two-phase gas-non-Newtonian ps:udoplastic liquid vertical slug flow have been analysed. Correlation have been proposed for predicting the two-phase friction factor as a function of the physical and dynamic variables of the system.     

A MODEL FOR PULSING FLOW IN COCURRENT DOWN-FLOW TRICKLE-BED REACTORS

Based on macroscopic mass and momentum balances, a model is developed to characterize the hydrodynamic behavior of pulsing flow in cocurrent down-flow trickle-bed reactors. Predictions of the model regarding liquid saturation, length and velocity of both the liquid rich slug and gas rich pulse are reported. Also presented are experimental data of an air-water system for the effects of varying gas and liquid flow rates on pulse frequency, total pulse length and apparent slug velocity. To confirm the theory, predictions are compared with measured overall pressure gradient. Agreement is reasonably good.     

UNSTEADY CONVECTIVE DIFFUSION IN BLOOD FLOW THROUGH A TUBE

The paper presents an exact analysis of unsteady convective dispersion of a solute in a Casson fluid (assumed as the non-Newtonian behaviour of blood) flowing in a tube. Using a generalized dispersion model, which is valid for all time after the injection of the solute in the flow, we evaluate the axial dispersion coefficients as functions of time. The variation of the asymptotic dispersion coefficient K₂* with y₀ (the dimensionless radius of the plug flow region) shows that K₂* first increases with y₀, reaches a maximum and then decreases. The behaviour of the dimensionless dispersion coefficient K₂(T) - Pe^-2 with time T is also shown graphically.     

CHARACTERISTICS OF PULSING FLOW IN TRICKLE BEDS. IMPROVEMENTS OF A MACROSCOPIC MODEL

A rather simple macroscopic model, originally proposed by Dimenstein and Ng (1986), is examined by comparison with results of experimental work carried out in this laboratory recently. Several improvements are proposed relying either on new correlations or in better physical understanding obtained from the recent experiments. The model, despite its simplicity, is considered quite comprehensive and reliable (for the range of physical properties examined) providing good estimates of essentially all the significant time averaged characteristics of pulsing flow.     

COMPTON PROFILE MEASUREMENT OF TWO-PHASE FLOW DISTRIBUTION

To improve the proposed technique of Compton profile measurements and develop an accurate density distribution measurement technique, the detected scattered spectrum in a system of collimated source and uncollimated detector is expressed in terms of the density distribution and a multiple-scattering factor.

A particular experimental approach to this technique is outlined. Multiple-scattering is carefully considered in the analytical-numerical interpretation of the problem. The proposed technique is shown to be clearly valuable for stochastically steady flows in which relatively low frame rates for local time average two-phase flow parameters are acceptable.     

TWO-PHASE FLOW PRESSURE CHANGE ACROSS SUDDEN EXPANSIONS IN DUCT AREAS

A new model to calculate the two-phase flow pressure change across a sudden expansion in a duct area was developed and checked against data measured with mixtures of air and water, aqueous glycerol, watery calcium nitrate and with refrigerant R 12. In the model all relevant physical parameters are included and, in contrast to equations in the literature, the entrainment of liquid in the gas stream is considered. The predictions are validated for a wide range of conditions, pipe diameters and physical properties typically encountered in industrial pipe line systems: Calculations based on the new approach are sufficiently accurate for engineering purposes.     

BASIC EQUATION OF TURBULENCE AND MODELING OF INTERFACIAL TRANSFER TERMS IN GAS-LIQUID TWO-PHASE FLOW

Turbulence is one of the most important phenomena in analyzing thermohydrodynamic characteristics of gas-liquid two-phase flow. For the purpose of accurate prediction of the turbulence phenomena, a basic conservation equation of Reynolds stress was derived based on the local instant formulation of mass and momentum conservations of two-phase flow. In this equation, interfacial transfer terms of turbulence appear as source terms. Detailed considerations on these transport terms were carried out. It was shown that they consist of a viscous damping term due to small scale interfacial structures, a drag induced turbulence generation term due to large scale interfacial structures and a term representing the exchange between surface energy and turbulence. Based on the mechanistic modeling and turbulence modulations, carried out were physical interpretations of interfacial area concentrations of small and large scale interfacial structures, a viscous damping term due to small scale interface and turbulence generation term due to large scale interface.     

APPLICATION OF HOT-FILM ANEMOMETRY TO AIR-WATER FLOW IN AERATED STIRRED TANKS

The subject of this paper is the evaluation of the applicability of constant temperature anemometry (CTA) with a modified version of Delhaye's method to aerated stirred tanks. A calibration technique that takes into account the variation in medium temperature was developed and verified experimentally. The directional sensitivity of the conical film probe was investigated in a streamline flow field as well as in the impeller discharge stream in an stirred tank.

The reliability of the setup and the technique was verified through the comparison of the vertical and radial velocity profiles of water in a stirred tank with those obtained from the literature. The directional response of the conical probe follows the cosine law for intersection angles smaller than 45° in a streamline flow field, but the directional sensitivity in the impeller discharge stream is rather poor, owing to the rolling characteristics of flow in this region. Due to the inability to detect bubbles smaller than the sensing element of the conical probe, the CTA usually gives lower values of local gas holdup. However, this discrepancy is considered to have no influence on the velocity measurement.     

LAMINAR FLOW HEAT TRANSFER WITH INLINE MIXERS INSERTS

Heat transfer coefficients were measured for heat transfer to a Newtonian fluid flowing in laminar flow through a tube with inline mixer inserts. Kenics “Static” mixer and Ross LPD mixer inserts were studied as heat transfer augmentation devices. The mixer inserts were in the inner tube of a concentric tube heat exchanger. Steam was condensed in the annulus of the exchanger. Significant heat transfer enhancement was obtained with both inserts at the expense of even greater pressure drop increases. The use of the Ross mixer insert gave greater augmentation than did the use of the kenics insert. An analysis using the analogy between momentum and heat transfer allowed the prediction of heat transfer coefficients from pressure drop measurements. The predicted coefficients were in good agreement with experimentally measured heat transfer coefficients for laminar flow.     

EFFECT OF A MAGNETIC FIELD ON TWO-PHASE LIQUID METAL FLOW AND CAVITATION OCCURRENCE

To clarify the effect of a magetic field on two-phase bubble flow characteristics and cavitation occurrence, an analytical study of two-phase MHD flow with low quality is developed, taking into account slip and bubble expansion. Numerical calculation shows that the application of a magnetic field causes a decrease in pressure in the diverging passage and an increase in the incipient cavitation number.     

EFFECT OF A MAGNETIC FIELD ON TWO-PHASE LIQUID METAL FLOW AND CAVITATION OCCURRENCE

To clarify the effect of a magetic field on two-phase bubble flow characteristics and cavitation occurrence, an analytical study of two-phase MHD flow with low quality is developed, taking into account slip and bubble expansion. Numerical calculation shows that the application of a magnetic field causes a decrease in pressure in the diverging passage and an increase in the incipient cavitation number.     

ONE- AND TWO-PHASE FLOW IN NETWORK MODELS OF POROUS MEDIA

We discuss the low Reynolds number flow of one or two immiscible Newtonian fluids in network models of microscopically random porous media. For the case of a single fluid, we reduce the flow problem to an analog random electrical resistor problem and use an 'effective medium theory' to express the permeability of such networks in terms of the pore space geometry. For the flow of two fluids we use the Washburn approximation to incorporate capillary pressure differences, and show that this problem may also be formulated as a random electrical network. In this case, the capillary menisci correspond to moving batteries, and we follow the motion of the fluid-fluid interface (the ensemble of analog batteries) by a time-step procedure. We study the time evolution of the interface and the dynamics of blobs of one fluid contained in the other, as a function of the network geometry.'     

ONE- AND TWO-PHASE FLOW IN NETWORK MODELS OF POROUS MEDIA

We discuss the low Reynolds number flow of one or two immiscible Newtonian fluids in network models of microscopically random porous media. For the case of a single fluid, we reduce the flow problem to an analog random electrical resistor problem and use an 'effective medium theory' to express the permeability of such networks in terms of the pore space geometry. For the flow of two fluids we use the Washburn approximation to incorporate capillary pressure differences, and show that this problem may also be formulated as a random electrical network. In this case, the capillary menisci correspond to moving batteries, and we follow the motion of the fluid-fluid interface (the ensemble of analog batteries) by a time-step procedure. We study the time evolution of the interface and the dynamics of blobs of one fluid contained in the other, as a function of the network geometry.’     

ANALYTICAL SOLUTION FOR LAMINAR-LAMINAR TWO-PHASE STRATIFIED FLOW IN CIRCULAR CONDUITS

Many attempts made in modelling stratified two-phase flow for predicting the operational flow characteristics (pressure drop, holdup, etc.) assume mostly plane interface between the phases. Obviously, the interaction between the stratified layers and the resulting flow characteristics may be significantly affected by the configuration of the interface. Moreover, complete analytical solutions for stratified flows in circular conduits a re not yet available even for laminar flows with plane interface and most of previous studies resort to average two-fluid modelling.

The present study presents analytical solutions for laminar stratified two-phase flows in pipes with plane and curved interfaces.     

SIMULATION OF OSCILLATIONS IN BOILING FLOW IN A NATURAL CIRCULATION EVAPORATOR

This article presents both experimental and theoretical investigations on the nature of oscillations of void fraction and temperature in a boiling natural circulation loop of a short-tube natural circulation evaporator at low pressure and low heat flux conditions. The experimental study includes online measurement of void fraction and temperature in the loop. The proposed moving boundary model equations for boiling channel in the loop have been solved by a finite volume scheme and subsequently nonlinear ODEs have been solved by Gear's method. The proposed model equations have been validated with experimental data and the data taken from literature. The periodic nature of the pulse-variation of both void fraction and temperature has been identified. A comparison has been made on the applicability of homogeneous flow model and nonhomogeneous flow model to predict the void-fraction pulses and the temperature pulses. Measurement uncertainties and model uncertainties have also been discussed.