A Numerical Analysis of the Influence of Nozzle Geometric Structure on Spontaneous Steam Condensation and Irreversibility in the Steam Ejector Nozzle

The spontaneous condensation of wet steam often occurs in the steam ejector nozzle, this deteriorates the performance of the steam ejector. In this paper, we take changing the geometric parameters of the nozzle as the focus of our research and construct an internal connection between steam’s condensation behavior and the nozzle’s throat radius, the nozzle’s divergent section expansion angle, and the nozzle’s divergent section length. Our numerical simulation results indicate that an increase in the throat diameter and reduction of the divergent section’s expansion angle can inhibit steam condensation behavior, to a certain extent. In particular, the steam condensation behavior will disappear at a 0° expansion angle, but it is not affected by the change in the divergent section’s length. In addition, the irreversibility that is seen under different changes to the nozzle’s structure parameters was investigated and the results show that the entropy generation that is caused by a phase change accounts for a much higher proportion of the total entropy generation than heat transport and viscous dissipation do. This indicates that steam’s condensation behavior makes a large amount of irreversible energy, resulting in energy waste and reducing the performance of the nozzle. Therefore, this study can provide a theoretical reference for suppressing the spontaneous condensation behavior of steam by changing the nozzle’s geometry.

Numerical investigation on the effect of second throat diameter on two-throat nozzle ejector

The employment of two-phase ejectors in the CO2 refrigeration systems is widely developed recently. Due to the lack reports on the two-throat nozzle ejectors, the performance of CO2 two-throat nozzle ejector varied with different second throat diameter (D t ) was numerically investigated under different primary pressures (P p ). The accuracy of established numerical simulation model was confirmed with the assistance of experimental data summarized in the literature. The simulated results show that the two-throat nozzle ejector performance corresponding to entrainment ratio (Er) is of better stability with relatively bigger D t under different working conditions. Next, the axial static pressure corresponding to bigger D t is lower than that of smaller one at pre-mixing chamber. And the secondary flow velocity of bigger D t is accelerated better as compared to that of smaller one.

Design and Development of Biogas Venturi Mixture for Stationary Diesel Engine Using Analytical and CFD Approach

The major problem to use biogas as an alternative fuel in diesel engines is the modification needed for converting the current diesel engine into an enriched biogas engine. The fuel intake system is one of the major modifications required for the diesel engine. To overcome this problem, a new biogas venturi mixture has been designed by using an analytical and Computational Fluid Dynamics (CFD) approach. With the new fuel intake system, the engine runs effectively and properly using enriched biogas as an alternative fuel. It has been observed that simple modifications are required in the fuel intake system such that convergent divergent angle, throat diameter, etc. for uniform mixing of enriched biogas and air for complete combustion of fuel for improving engine performance and efficiency. This paper focuses on the design and development of a biogas venturi mixture with different convergent angles (20°, 24° & 28°, etc.) and different throat diameters (22 mm, 21mm, 20mm, 18mm & 16 mm etc.) used in a 3.5 kW, 661CC, 4-stroke stationary diesel engines using an analytical and CFD approach. This paper concludes that 16 mm throat diameter and 24° convergent angle, the maximum pressure drop and maximum velocity observed in a uniform and homogenous mixture. Better mixing can affect combustion, which leads to improved volumetric efficiency, brake thermal efficiency with reduced emission.

Development of converging-diverging multi-jet nozzles for molten smelt shattering in kraft recovery boilers

The effective shattering of molten smelt is highly desired in recovery boiler systems. Ideally, shatter jet nozzle designs should: i) generate high shattering energy; ii) create a wide coverage; and iii) minimize steam consumption. This study proposes a novel converging-diverging multi-jet nozzle design to achieve these goals. A laboratory setup was established, and the nozzle performance was evaluated by generating jet pressure profiles from the measurement of a pitot tube array. The results show that the shatter jet strength is greater with a large throat diameter, high inlet pressure, and a short distance between the nozzle exit and impingement position. Increasing the number of orifices generates a wider jet coverage, and the distance between the orifices should be limited to avoid the formation of a low-pressure region between the orifices. The study also demonstrates that an optimized converging-diverging multi-jet nozzle significantly outperformed a conventional shatter jet nozzle by achieving higher energy and wider coverage while consuming less steam.

Effect of Jetpump Throat Diameter and Secondary Discharge on Suction Pressure and Pump Efficiency

The throat diameter is one of the main parts of the jetpump, the throat diameter is a mixing chamber which has the function of mixing low-speed secondary fluids with high-speed primary fluids. The purpose of this study was to determine the effect of the throat jetpump diameter with a variation of 7,9,11 mm and secondary discharge with a variation of 10,15,20 L / minute on the suction pressure and pump efficiency. The highest test results were variations in the throat diameter of 11 mm and secondary discharge of 20 L / minute with a net discharge of 3.8 L / minute, an average discharge of 23.8 L / minute, a suction pressure of -0.25 and an efficiency value pump by 50%, the larger the throat diameter the greater the flow rate obtained.

Geometrical Optimization of a Venturi-Type Microbubble Generator Using CFD Simulation and Experimental Measurements

Microbubble generators are of considerable importance to a range of scientific fields from use in aquaculture and engineering to medical applications. This is due to the fact the amount of sea life in the water is proportional to the amount of oxygen in it. In this paper, experimental measurements and computational Fluid Dynamics (CFD) simulation are performed for three water flow rates and three with three different air flow rates. The experimental data presented in the paper are used to validate the CFD model. Then, the CFD model is used to study the effect of diverging angle and throat length/throat diameter ratio on the size of the microbubble produced by the Venturi-type microbubble generator. The experimental results showed that increasing water flow rate and reducing the air flow rate produces smaller microbubbles. The prediction from the CFD results indicated that throat length/throat diameter ratio and diffuser divergent angle have a small effect on bubble diameter distribution and average bubble diameter for the range of the throat water velocities used in this study.

Deformable Microgel for Enhanced Oil Recovery in High-Temperature and Ultrahigh-Salinity Reservoirs: How to Design the Particle Size of Microgel to Achieve Its Optimal Match with Pore Throat of Porous Media

Summary Conformance control treatment in high-temperature and ultrahigh-salinity reservoirs for easing water/gas channeling through high-permeability zones has been a great challenge. In this work, we propose a deformable microgel that can be used at more than 373.15 K and ultrahigh-salinity conditions (total dissolved solids > 200 kg/m3, Ca2+ + Mg2+ > 10 kg/m3) and present a method for choosing the suitable particle size of the microgel to achieve an optimal match with the pore throat of the core. First, the particle size distribution of the microgel was analyzed to decide d50, d10, and d90 (diameter when cumulative frequency is 50, 10, and 90%, respectively). Coreflooding experiments were conducted under different permeability conditions from 20 to 900 md to investigate the migration and plugging patterns of the microgel by analyzing and fitting injection pressure curves together with the change in the morphology of the produced microgel analyzed by a microscope. The migration and plugging patterns were divided into three patterns: complete plugging; plugging—passing through in a deformation or broken state—deep migration; and inefficient plugging—smoothly passing through—stable flow. The second pattern can be further divided into three subpatterns as strong plugging, general plugging, and weak plugging. Finally, on the basis of five patterns, we build a quantitative matching relation between the particle size distribution of microgel and the pore-throat size of cores by defining three matching coefficients a = d10/d, ß = d50/d, γ = d90/d (d is the average pore-throat diameter). The effectiveness of this quantitative matching relation was verified by evaluating the plugging ability (residual resistance factor) in a post-waterflooding process after the injection of 1.5 pore volume (PV) of microgel. For a strong permeability heterogeneity, the strong plugging is believed to be the expected pattern. The particles size and the pore-throat size should meet the following relationship: 1 < a < 2, 2 < ß < 4, 4 < γ < 6. In this scenario, the deformable microgel particles could achieve both an effective plugging and a deep migration. The quantitative matching relation with multiple matching coefficients determined based on the particle size distribution might help to choose suitable particles more precisely in comparison to the method based on one matching coefficient (mostly, the ratio of the average diameter of particles to the average pore-throat diameter). In addition, the method itself to build a quantitative matching relation according to particle size distribution can be used for designing different particle-type conformance control agents for profile control and water shutoff treatment in field applications.

Computational fluid dynamics analysis of the effect of throat diameter on the fluid flow and performance of ejector

Purpose Using the computational fluid dynamics (CFD) technique, this paper aims to investigate the influence of key parameters such as throat diameter; the suction ratio on the flow field behaviors such as Mach number; pressure; and temperature. Design/methodology/approach To investigate the effect of throat diameter, it is simulated for 4, 6, 8 and 10 mm as throat diameters. The governing equations have been solved by standard code of Fluent Software together with a compressible 2 D symmetric and turbulence model with the standard k–ε model. First, the influence of the throat diameter is investigated by keeping the inlet mass flow constant. Findings The results show that a place of shock wave creation is changed by changing the throat diameter. The obtained results illustrate that the maximum amount of Mach number is dependent on the throat diameter. It is obtained from the results that for smaller throats higher Mach numbers can be obtained. Therefore, for mixing purposes smaller throats and for exhausting bigger throats seems to be appropriate. Originality/value The obtained numerical results are compared to the existing experimental ones which show good agreement.