Gas Crossflow Research Articles

Calculation of flow of a viscous compressed Gas in the casing of low-flow centrifugal Compressor stages

UDC 621.515.5:533.21.001.24 Calculations of the flow of three-dimensional viscous compressed gas in the casing of low-flow stages of centrifugal compressors (CC) are very laborious. Many problems, for example, determination of the turbulent viscosity of such flow, have not been solved sufficiently accurately and clearly. The complexity of the problem is also due to the nonstationary character of the flow itself. However, even approximate solutions make it possible to refine the physical and mathematical models of the flow and find ways of further improving the design of the casing. A method of calculating the flow with the method of finite differences in radial vaneless slots (vaneless diffusers (VLD), side pockets around the impeller (Im) disks, etc.) used for analyzing the flow in VLD was developed at SPSTU [I]. A comparison of the calculated and experimental data demonstrated the sufficiently high efficiency of the method for use as an algebraic model of turbulence, like the k---e model, and the possibility of taking into consideration the anisotropy of the roughness of the diffuser walls. The distribution of the values of the local loss factor by radius in VLD behind half-open Im for different angles ot 2 at the inlet with constant (5, 10, 15 ~ and also at variable (5-15 ~ and 15-5 ~ values along axis z is shown in Fig. 1. The first maximum is due to restructuring of the flow at the inlet to VLD behind Ira, and the second corresponds to local burbling zones. With a decrease in angle tx2, the values of the local loss factor increase as a result of an increase in the path length for a given Ar. The presence of flanges decreases the losses for small angles ct 2 around it and increases them for constant angle cr 2 or for higher values around it due to warping of the flow. Figure 2 shows the important effect of angle ct 2 and the ratio b 2 = b2/D 2 on the losses in VLD [ 1, 2]. We now propose investigating the flow in the side pockets around Im with the method developed. In the second stage, the analysis of the flow in the casing of a CC stage was conducted together with the Institute of Turbomachines at Hannover University (Germany) with Start CD software by the finite volumes method [3, 4]. The calculation was performed for a series of low-flow closed Ira, including Im of the "channel type," and immobile stage elements [VLD + reverse control apparatuses (RCA)]. The general shape of the region of the flow in the immobile elements is shown in Fig. 3. Note the reciprocal effect of the elements of the rotating elbow (RE) on flow in VLD. The existence of secondary flows is characteristic of RCA. For qb = 0.0188 (significantly lower than the calculated value) on the side of the vacuum, burbled flow arises again at the beginning of RCA and develops along its length due to secondary flows (Fig. 4). In tests of the SVD-6 low-flow "channel" impeller having qbop t -- 0.014, relatively high indexes and a wide zone of stable operation were obtained [4]. For modes close to the calculated mode, flow had a relatively stable character (Fig. 5a), while for low flow rates, developed burbled zones were observed in the channel (Fig. 5b). The third stage of the studies consisted of developing target software for calculating three-dimensional compressed viscous flow in the casing of a CC stage by the method of finite volumes based on the data on turbulent viscosity in [5]. A three-dimensional network sufficiently completely describes the geometry of the casing. The network is constructed with consideration of the effect of internal gas leaks and cross flows. The casing of the stage is divided into two parts: ultralow-flow Im with VLD and immobile elements (part of the VLD, RE, RCA, and ring confusor (RC). The stage casing is divided into two

A nonisothermal model of a spouted bed gasifier

A two-region model of a spouted bed gasifier devised by the present authors has been further developed to include an enthalpy balance. As before, the present model assumes first-order reaction kinetics for the gasification reactions and the spout is treated as a plug flow reactor of fixed diameter with cross flow of gas into the annulus. The annulus region is considered to be a single plug flow reactor. Solids move in plug flow in both annulus and spout, independent of temperature and reaction. The model allows predictions of axial profiles of temperature and gas in the spout and annulus as well as exit gas compositions and overall carbon conversion. The exit gas compositions were compared with those of the previous two-region and streamtube isothermal models. The effect of hydrodynamic parameters on model predictions are illustrated and a comparison made with experimental temperature profiles obtained in a 0.30 m diameter gasifier.

Experimental and numerical simulation of discrete liquid flow in a packed bed

This paper presents a combined experimental and numerical method to simulate the liquid flow in a packed bed. Two types of the experiments, i.e. liquid percolation without gas flow and liquid flow with gas cross flow, were conducted using a three- or two-dimensional cold model, respectively. A mathematical model has been proposed for the numerical simulation of the liquid flow. This model was developed using a force balance approach combined with stochastic considerations, in which the liquid flow was treated as a discrete phase with stochastic dispersion based on the experimental observations. Accordingly, the interactions between liquid and the packed bed, and liquid and gas have been experimentally investigated and then were used to determined the model parameters involved in the model. The behavior of the liquid flow in packed beds can numerically be simulated using the proposed model. A reasonable agreement has been achieved between the model predictions and the experimental measurements.

Intermixing of fluidizing gas streams in a compartmented circulating fluidized bed

AbstractThe intermixing of fluidizing gas between the compartments of a compartmented circulating gas fluidized bed fitted with a V‐valve and riser combination has been experimentally studied. The intermixing of fluidizing gas that flows co‐current (cross flow) as well as counter‐current (back flow) to the circulating solids has been investigated. At low aerations, gas cross flow increased proportionally with the increase in solid circulation rate. But at high aerations, gas cross flow increased with aeration even when solid circulation decreased. Studies on back flow of gas revealed some interesting observations. At high fluidizing bed height on upstream side back flow of V‐valve, gas has been negligible. But at low upstream bed heights and low aeration in V‐valve and riser back flow of V‐valve, gas has been substantial.

Nonwetting flow of a liquid through a packed bed with gas cross-flow

In this study, the effect of a cross-flow gas field on the percolating flow of a non-wetting liquid through a packed bed was investigated. Experiments were conducted to measure the liquid shift, due to the cross-flow of air, for the flow of aqueous barium chloride solutions and mercury percolating through beds of polyethylene and expanded polystyrene particles. An X-ray technique was used to visualize the liquid flow pattern through the packed bed. The liquid percolates through a packed bed as a series of rivulets and droplets which are continuously breaking up and coalescing. A mathematical model to predict the direction of the liquid rivulet/droplet flow under the influence of a gas flow field was developed. The model treats the liquid as a discrete phase and includes the effects of gravity, gas drag, and inertial and viscous bed resistance. The effective droplet/rivulet size is an important model parameter, and the model postulates that the droplet/rivulet size is a function of both the effective capillary size of the bed and the liquid flow rate. A simplified population balance analysis for droplet coalescence is used to predict the effect of liquid flow rate on droplet/rivulet size. The model predictions are consistent with the experiments.

A MODEL FOR A DENSE PHASE CIRCULATING FLUIDIZED BED

A model for a dense phase circulating fluidized bed (DPCFB) is proposed. The model incorporates a new approach to the modelling of the riser and gas cross-flow between interconnected sections around the circulation loop. It is found that gas leakage is inevitable and must be incorporated in the modelling of solids circulation. Model predictions compare well with experimental results from a compartmented DPCFB.

Monitoring and Controlling of Oil and Gas Cross Flow During Production of Daqing Lamadian Laminated Oil Field with Gas-Cap

Abstract Daqing Lamadian oil field is the largest oil field with a gascap in China. Monitoring, controlling and adjusting techniques have been used extensively to minimize cross flow. An inverted nine-spot pattern was used in the oil-bearing area. Gas-bearing layers were not perforated and there was a 400 to 600m buffer zone of oil and gas migration left between oil-and gas-bearing areas. A monitoring system for gas-cap performance was established. Flow between the oilbearing and gas-bearing layers has been successfully controlled and a relatively stable oil-gas interface has been maintained for 20 years.

The Effect of Boundary Conditions on the Downstream Penetration of Pulsed Sprays After Impaction on a Flat Surface

An experimental study has been conducted of the wall sprays produced after impaction on a flat surface by the pulsed spray from a single hole nozzle. The experiments are of relevance to direct injection diesel engines and they extend the range of boundary conditions covered in previous work, with variation of gas density, spray wall angle, gas cross-flow velocity and cross-flow turbulence level. The initial and boundary conditions are documented to provide a database which is suitable for computational fluid dynamics (CFD) model validation of an important aspect of diesel engine in-chamber flow. Previous work in the area is described and published empirical correlations are reviewed. The measurements of wall spray penetration as a function of time are presented and described and a correlation equation is proposed which fits the data with good accuracy.

Modeling wall impaction of diesel sprays

A model for diesel spray wall impaction is presented, which is assessed against experiments for a number of test cases, including normal or angled injection to a wall into a quiescent space or a cross-flowing gas at various gas pressures. New relationships are given for the velocities of the droplets rebounding from the wall. These relationships take into account the wall roughness and the possible break-up of the droplets during their impingement. The impingement model was incorporated in a spray model based on the stochastic particle technique (Dukowicz 1980) and accounts for the phenomena of droplet injection, break-up, collision and coalescence, turbulent dispersion, and evaporation. The spray model was incorporated in a recently developed three-dimensional (3-D) computational fluid dynamics (CFD) code that simulates the unsteady compressible flow of the gas in internal combustion engines by solving the full Navier-Stokes equations. It was found that the motion of the surrounding gas caused by the spray injection plays a minor role on the predicted results. The latter concern the wall spray radius and the wall spray height. The validity of the spray model is demonstrated through extensive comparisons with experiments over a wide range of gas conditions.

Possible mechanism of nonsteady-state erosion combustion of composite solid propellants

It has been demonstrated that in the combustion of composite solid propellants the instantaneous mass burning rate can depend on variations in the velocity of cross-flow of gases even if in the steady-state regime the combustion is insentitive to cross-flow velocity. A method has been proposed for studying the nonsteady-state erosion combustion in experiments with composite systems.

Numerical modeling of diesel spray wall impaction phenomena

A model for diesel spray impaction on walls is presented that is based on experimental observations. The model, which is incorporated into a two-phase CFD code employing a discrete droplet model for the liquid spray and the implicit noniterative PISO algorithm for gas equations, is assessed against experiments for a number of test cases including normal or angled injection into a quiescent space or a cross-flowing gas. In most of the cases studied, the wall spray radius is reasonably well predicted, but the wall spray height is always underpredicted. In order to capture the dispersive nature of the wall spray that contributes to the wall spray height, the original drop-drop collision model of O'Rourke and Bracco is extended to allow for the effects of multicollisions between two drop parcels in a the thick spray. The extended collision model works well in two-dimensional cases but is not fully assessed in three-dimensional cases. The wall impaction model is also implemented in the three-dimensional EPISO engine code. Preliminary results on the simulation of diesel spray impingement in an actual engine suggests that the model is there also capable of producing reasonable wall sprays.

FOUR-PHASE MODEL FOR FLUIDIZED-BED CATALYTIC REACTORS

A four-phase model for fluidized-bed catalytic reactors is developed. The bed is divided into four phases, i.e., bubble, cloud-wake, emulsion upflow, and emulsion downflow phases. In the model, gas back mixing in the emulsion phase and gas interchange as well as gas cross flow between phases are all considered. Model predictions are shown to compare well with various published experimental data on both axial concentration profiles and overall conversions. Parameters effects on the reaction performance were also illustrated. It was found that neglecting cross flow will result in 13% lower on the predicted conversion.

Challenging the Presence of Natural Gas Hydrate in the Messoyakha Pool

The Messoyakha gas field with a pool in Cenomanian sediments lies in north Siberia. Some authors consider it a gas hydrate field mainly because initial pressure and temperature in a part of the pool fit hydrate stability. Other hydrate indications are also reported: characteristic features of logging records, intricate distribution of gas and water in the pool, low productivity of some wells, amount and composition of produced water, gas reservoir drive, and thermodynamic behavior of some beds. However, al the above could be due to specific geology of the pool and inadequate development rather than to the presence of hydrate in the reservoir. Long-term observations have been conducted on the alteration of gas composition using a special technique based on the measurement of helium concentration. The latter highly varied, showing and amplitude of more than three orders of magnitude. The data obtained prove that there are no natural hydrates in the upper part of the pool, which is reported as hydrate bearing. Technogenic hydrates are forming in this part in bottom-hole zones of idle wells as a result of gas cross flow, while natural hydrates are likely to exist in the lower part of the pool. This research is tomore » be continued. Actual gas reserves of the pool cannot be determined without evaluated hydrate content. A solution to this problem is important for the evaluation of gas reserves elsewhere in the cold regions.« less

Pinning in a rectangular moving bed reactor with gas cross-flow

In the petroleum and process industries, renewed interest is being directed towards more efficient ways for contacting granular solid and gas. Within the last decade one novel way, now finding acceptance, is the formation of granular solid into a descending bed through which gas is then passed transversely, a cross-flow moving bed. This arrangement is advantageous in that a process such as catalyst regeneration (say) can be effected without removal of the solid from the process and thereby permits continuous operation. In practice, however, the physical interaction of gas and solid is known to cause adverse phenomena and these are addressed here. Experimental studies have been carried out in some four narrow sized granular materials of mean diameters from 1.6 to 7.0 mm. In beds where the distance separating the two parallel gas screens was 0.1 m, FOUR distinct modes by which the bed ceased to descend, termed pinning, were identified by altering the gas flow. Each was characterized by a particular behaviour of the particles adjacent to the gas screens. At each screen, the particles either moved as a block or displaced relative to each other. Displacement, termed particle drag, when adjacent to the gas inlet screen, was found to promote cavity formation. When adjacent to the gas outlet screen, particle drag was found to cause lower gas throughputs at which the bed ceased to descend. Whereas some granular solids were found to exhibit all four modes, others did not. In large sized beds, where screen separation was 0.3 m, only two of the four modes were identified since particle drag was either present at both gas screens or not. When the separation was 0.5 m, only the former mode was observed. The key to the occurrence of the phenomenon of particle drag is considered to be in the packing developed in the feeding system and its dilation against the surface of the gas screens.

Solids flow in a vertical moving bed with cross flow of gas. Flow pattern and stress distribution.

Solids flow in a vertical moving bed with cross flow of gas. Flow pattern and stress distribution.

Conditions and nature of gas flow in spiral-elliptical binary galactic systems

The process of gas flow from a spiral to an elliptical galaxy has been modeled numerically in the framework of the circular restricted three-body problem. It has been found that the possibility of gas loss by the spiral galaxy depends strongly on the relationship between the direction of its axial rotation and the orbital motion of the galaxies of the binary system. When these motions are in opposite directions, gas crossflow does not occur. In addition, an important parameter of the problem is the size of the disk of the spiral galaxy. According to the calculations, the rate at which gas can pass to the elliptical galaxy for a statistically average S-E pair with signs of interaction in the catalog of I.D. Karachentsev is /approx/0.2M/circled dot/ per year. This value is quite sufficient to explain the enhanced abundance of neutral hydrogen (/approx/10/sup 8/ M/circled dot/) in a number of galaxies of early types. The calculations have also shown that during the time of one or two revolutions of the disk of the spiral galaxy there is a strong distortion of its shape by the tidal interaction. This fact must be taken into account when the individual masses of spiral galaxiesmore » belonging to binary systems are determined from the rotation curves.« less

Mass transfer efficiency of screen packings with gas crossflow

The efficiency of screen packings in the distillation of a model benzene-toluene mixture at total reflux was assessed in a 1200-mm diameter column with gas crossflow. The packings were tested at 100-110 C and 110-133 kPa and liquid feed rates of 2.5-14 cubic meters per hour. Compositions of samples withdrawn from the packings were determined chromatographically and these data were used to calculate the number of theoretical plates under total reflux with the Fensek-Underwood equation. Mass transfer efficiency of the crossflow packings was found to increase with increasing vapor and liquid load and to depend also on the dimensions of the packings. When the reflux load was increased from 12.9 to 44.5 cubic meters per hour, the efficiency changed very little, indicating a broad range of stable operation for the crossflow system.

The phenomenon of pinning in an annular moving bed reactor with crossflow of gas

Certain catalytic reactors with reversibly decaying catalysts use continuous replacement and regeneration of the catalyst. A bed of the catalyst pellets moves through the reactor between two co-axial cylinders and the reactant mixture passes radially, either inward or outward, through this bed. There is then an upper bound on the flow of reactants imposed by the mechanical phenomenon of “pinning”, in which the drag force exerted on the particles by the reaction mixture induces frictional forces between the particles and the downstream wall which are sufficient to prevent motion of the bed. A model has been developed to account for pinning behaviour in an annular moving bed reactor of finite length. It is assumed that the catalyst bed behaves as a Coulomb material, with forces of dry friction where it slides over solid surfaces. The results give an excellent qualitative account of the phenomenon, as observed in a small laboratory test system. The predicted gas pressure drops required for pinning are larger than those observed, but never by as much as a factor of two.

Design calculation for crossflow gas absorption towers with heat generation.

Methode de calcul exacte appliquant une methode d'optimisation non lineaire. Calcul de la concentration et de la temperature a l'interface gaz-liquide par la methode de Newton-Raphson (estimation des valeurs avec une erreur de l'ordre de 10 −6 , avec un temps de calcul tres court). Le calcul de conception de la colonne est effectue par la methode Complex

Pinning of a bed of particles in a vertical channel by a cross flow of gas

Dans certains types de reacteurs dont le catalyseur se desactive de facon reversible et assez rapidement, un fonctionnement continu est possible en utilisant un lit mobile de catalyseur qui glisse vers le bas du reacteur sous l'effet du poids, le melange reactionnel etant envoye horizontalement dans le lit. Il y a une limite superieure au debit des reactifs, due au phenomene de «pinning» par lequel la force de trainee exercee sur les particules par le melange reactionnel presse le lit contre la paroi du reacteur de facon telle que le frottement contre la paroi empeche le lit de glisser. Analyse simple de ce phenomene