Secondary Inlet Research Articles

Influence of the inlet cross-sectional shape on the performance of a multi-inlet gas cyclone

The influence of inlet cross-sectional shape on the flow pattern, pressure drop, and cut-off diameter of a gas cyclone was studied using the CFD model. Accordingly, five different inlet cross-sectional shapes, namely, circle, ellipse, rectangle, square, and trapezoid, for the double-inlet gas cyclone were studied. It was observed that the maximum tangential velocity was about 1.95 times the corresponding inlet velocity for primary and secondary rectangle inlets. Furthermore, the computed tangential velocity in the cyclone with the primary and secondary rectangle inlets (R-R) was considerably greater than those obtained by the other inlet shapes. In this case, the axial gas velocity reached its highest values at the bottom of the vortex finder and the cyclone center. It was also determined that the inlet shape significantly affected the cyclone pressure drop. The Circle-Square and the Rectangle-Ellipse configurations of inlet cross-sectional shape generated, respectively, the lowest pressure drop and the highest efficiency.

Thermal-Hydraulic Performance Analysis and Tube Inlet Orifice Design of a Once-Through Steam Generator

A numerical study is conducted for a thermal-hydraulic performance analysis and secondary side screw-type tube inlet orifice design of a once-through steam generator. Various tube-plugging conditions and power levels are considered, and the secondary coolant flow rate is adjusted to maintain a constant level of thermal power. Comprehensive numerical solutions are acquired to evaluate the thermal-hydraulic performance and minimum orifice length of the once-through steam generator under various operating conditions. The results obtained show that constant thermal power can be maintained by properly adjusting the secondary coolant flow rate with variation of the steam outlet superheat degree and secondary coolant pressure drop when the once-through steam generator operates at a high power level. The secondary coolant flow rate curve for constant thermal power operation is determined, and the required minimum orifice length to suppress the flow oscillation below the allowable level is evaluated. The lowest power level results in the highest minimum orifice length, and the non-plugged condition practically limits the orifice length criterion. This orifice length and corresponding pumping power are compared with those when the secondary coolant pressure at the tube outlet is controlled for constant thermal power operation.

Investigation on particulate matter and gas motion processes in the advanced multi-channel cyclone-separator with secondary gas inlets

Research into gas flow motion as a transported phase and pollutant – particulate matter (PM) is of crucial importance, their changes in particular areas of the object require knowledge of improving the apparatus. A cyclone is considered one of the most popular devices due to the new modified multi-channel design that involves combined separation and filtration phenomena. The findings of an accurate numerical model provide an opportunity to verify long-term experimental studies. In addition, it is possible to determine the impact of the designed principal elements of the structure comprising secondary gas inlets, inner slits and the convex bottom on gas and PM motion through verification conducting experimental research. The study focuses on simulating the upgraded cyclone using the SST k-omega model. The research has been conducted under the specified gas flow conditions such as high temperature and relative humidity (aggressive) gas and presents the results of the physical model to compare with. To achieve greater computational accuracy, a digital model of the cyclone made of specific volumetric elements has been developed thus expanding the grid and stepping to form the boundary zone. As a result, numerical simulation results differ by no more than 12.8% compared to the experimental studies results.

Optimization of SOFC stack gas distribution structure based on BP Neural network and CFD

The flow field distribution of solid oxide fuel cells significantly affects the performance of the stack. The flow uniformity can be improved and the power generation efficiency can be improved by optimizing the gas distribution structure of the stack. Based on the simplified 6kW stack model, the stack gas distribution structure with two-stage buffer cavity was designed, and the stack model was numerically simulated by ANSYS Fluent software. The BP neural network model, which can predict the uniformity of the outlet of the integrated stack, is established successfully. The parameters of the gas distribution structure are analyzed and optimized by using the orthogonal test and BP neural network. The results show that at the same time considering pile distribution structure under the condition of surface area and uniformity, when the first stage inlet buffer chamber depth is 40 mm, the channel width is 40 mm, the secondary inlet buffer chamber depth is 80 mm, can effectively reduce the electric pile distribution structure, surface area, to reduce heat loss, at the same time guarantee the integrated electric reactor outlet flow uniformity of more than 96%, greatly improves the efficiency of power generation.

Performance of a miniature ejector for application in a nitrogen Joule-Thomson cycle: Experimental and numerical analysis

The performance of Joule-Thomson (JT) cryocoolers can be improved by introducing ejectors. Ejectors with various geometric features have been proposed and investigated for cryogenic cooling in earlier studies, but only limited research is done on ejectors with a nozzle throat diameter less than 1 mm. In this paper, we present a miniature ejector with a nozzle throat diameter of 162 μm that was measured using X-ray computed tomography. When the ejector was operated with nitrogen gas at 295 K with a primary inlet pressure of 80 bar, a secondary inlet pressure of 0.5 bar and an outlet pressure of 1.2 bar, the primary and the secondary mass-flow rates were 394 mg/s and 83 mg/s, respectively. The measured primary mass-flow rate was quite close to the value predicted by a dynamic model, whereas the measured secondary mass-flow rate was lower than the predicted value, which was mainly caused by a non-axisymmetric machining defect of the nozzle that was assumed to be axisymmetric in the dynamic model. Besides, the effects of operating pressures and nozzle position on the ejector performance were analyzed. The study demonstrates the applicability of a miniature ejector in a JT cooling cycle.

A high temperature turbine blade heat transfer multilevel design platform

In this work, a fast and efficiently design method has been introduced. This design process consists of the overall design and the detailed design. For the overall design, one-dimensional pipe-network computations are employed to obtain several design cases quickly at the beginning. Meanwhile the solid domain geometry and mesh with cooling structures, i.e., film holes, impingement holes, and ribs have been generated to carry out three-dimensional (3-D) heat conduction calculations. Based on the above, a detailed design has been performed by 3-D conjugate heat transfer calculations. The results show that both the average temperature and the mass flow maximum errors between the pipe-network and 3-D conjugate heat transfer calculations are about 10%. In this article, the cooling structure of a gas turbine blade is designed with this platform. The final design results show that the maximum dimensionless temperature on the blade surface is 0.813, i.e., lower than the design requirement. The dimensionless mass flow rate in the first cooling inlet is 0.0168, and the mass flow rate in the secondary inlet is 0.0231.

PM reduction and flame confinement in biomass combustion using a porous inert material

The present study aims to determine the effects caused by the inclusion of a ceramic porous material in an experimental biomass combustor. The burner is an underfed fixed-bed facility that allows air staging wood pellet burning. Air staging determines the proportion of air entering by the primary inlet below the bed and the secondary inlet above it. The value used is 30/70 (%primary/%secondary). Due to the inclusion of a porous inert material (PIM) in a specific place in the combustor, the outlet gas flow from the combustion chamber is unaffected, but the behaviour of the combustion process is remarkably altered. Tests are performed by changing the total air flow from 0.223 kg/m2s, 0.279 kg/m2s and 0.334 kg/m2s and the position of the PIM at heights of 380 and 540 mm above the bed. The results show a significant reduction in particulate matter (PM) emissions, with some quantities reaching a reduction above 50% of the original values. The best results are achieved with the material positioned closest to the bed but always above the secondary air inlet.The concentration and distribution of PM were studied. Preliminary results of analysing the temperature profile along the combustor gas phase suggest that the effect of PIM inclusion is flame confinement. A higher rate of radiation is reflected back to the bed (solid combustion) due to the PIM insertion, increasing the temperature of the whole volume beneath. This temperature increase could slightly improve the combustion process in the gaseous phase, leading to a decrease in pollutant emission formation (especially PM).

Investigation of efficient dust control strategy for construction tunnels: Ventilation System's implications for cleaner production

In order to avoid pneumoconiosis and other hazards caused by excessive concentrations of dust in construction tunnels, this paper applies CFD numerical simulation, in combination with field measurements, to study the dust control effect of a construction tunnel under the different parameters of ventilation system. Firstly, the distance between the secondary air pressure inlet and the tunnel face (Lp) in the ventilation system was studied, then the airflow transport and dust pollution and diffusion were analyzed in eight positions, before the actual results of the analysis were measured on site. The results of the CFD model were validated with field measurements in a construction tunnel, with both fully concurring, thereby demonstrating the developed simulation strategy's high-level of accuracy. The optimal range obtained regarding the distance between the secondary air pressure inlet and the tunnel face was 30 m–40 m. Moreover, the dust pollution and dispersion distance was controlled at a range of 51.10 m–54.31 m, the dust concentration ranged from 1.32 mg/m3 to 13.12 mg/m3, and therefore the dust control effect was superior. Furthermore, the research methods and findings are of great significance and provide references for the effective prevention of a construction tunnel's dust and cleaner production.

Appraisal of CFD Discrete-Phase Models to be employed for Modeling Coal Particle Feeding in a Staged, Pressurized Oxy-fuel Combustor (SPOC)

In the present computational study employing the ANSYS Fluent commercial software, two different discrete phase formulations, namely, the discrete phase model (DPM) and the dense discrete phase model (DDPM) are tested and compared. Specifically, the unsteady Reynolds averaged Navier-Stokes (RANS) simulations with the Lagrangian-Eulerian models are performed in both cases. The configuration employed is a cylindrical combustor with three inlet gas streams that feed the system with mixtures of different O2 and CO2 mole fractions under an operating condition of 15 bar, emulating the 100 kW lab-scale facility employed at Washington University in St. Louis (WUSTL). Specifically, the coal particles are fed into the system by the secondary gas stream through an annulus-axial convergent duct surrounding the primary inlet stream. Distributions of the DPM concentration (the ratio of the dispersed phase mass to the mesh cell volume; in kg/m3) of the coal particles along the axial direction within this secondary inlet agree for both the DPM and DDPM models even though these models mimic the coupling between the phases in a different manner. However, the particle grouping is observed not only axially, along the inlet duct, but also in the radial direction as there are zones experiencing non-uniform particle distribution. Overall, the impact of DPM concentration on the flame stability is shown to be minor since a continuous particle release prior to burning zone is successfully achieved for both models.

INTEGRATED MONITORING OF PHYTOPLANKTON IN A SHALLOW INLET OF PETER THE GREAT BAY (JAPAN SEA): DYNAMICS OF CHLOROPHYLL A AND NUTRIENTS

Species composition and abundance of phytoplankton, chlorophyll a concentration and chemical parameters were monitored at the coast of Russky Island in the Paris Bay, the shallow secondary inlet of Peter the Great Bay in 2014–2015. In total, 103 species and intraspecific taxa of microalgae from 4 classes are identified. Dynamics of phytoplankton abundance did not coincide with the dynamics of chlorophyll a concentration. The abundance varied from 1.3 . 103cells/L to 1.9 . 106cells/L and chlorophyll a concentration changed in the range 0.21–6.08 mg/dm3. Nutrients had the following concentrations: DSi 0.7–41.8 µM/L, DIN 0.0–7.1 µM/L, DIP 0.0–0.7 µM/L. Dynamics of microalgae density had no common seasonal pattern in 2014 and 2015, though seasonal dynamics of chlorophyll a, as well as variations of nutrients and other water properties were similar in both years.

Numerical study on operating characteristics of self-driven total heat recovery system for wet-hot flue gas

This paper proposes a self-driven wet-hot flue gas total heat recovery system according to the characteristics of the heat transfer process of flue gas condensation, which uses the sensible heat in the high-temperature section to drive the system and complete the deep waste heat recovery of flue gas. The effect of flue gas and secondary water flow rate, flue gas and secondary water inlet temperature, and flue gas moisture on system performance were investigated and analyzed. Besides, the applicability analysis of technology and economic analysis are also performed. The results show that under the rated working conditions, the flue gas outlet temperature and relative humidity are 41.39 °C and 61.25%, respectively, and the maximum heat recovery rate of the system can reach 11.6%. When the flue gas inlet temperature is increased from 350 °C to 550 °C, the heat exchange capacity of the system is increased by 46%. Besides, when the flue gas inlet parameter is 550 °C/ and 120 g/kg (a), if the expected heat recovery rate of the known project is 10%, the maximum temperature of the secondary water that can be prepared by the self-driving system is 63 °C and the payback time is 2.53 years. When the flue gas inlet temperature and the moisture content is high, the system can provide hot water with higher temperature and is more energy-efficient than the traditional scheme.

Experimental and Computational Investigations on Flow Characteristics of Supersonic Ejector

Experimental and computational investigations have been conducted to characterize the flow field in the supersonic ejector, with and without secondary inlets of two sizes, at stagnation pressures of 2, 2.5, 3, 4 and 5 bar. In the first case, four secondary inlet openings each with 5 mm diameter are provided on the suction chamber circumferentially. In the second case, four secondary inlet openings each with 10 mm diameter are provided on the suction chamber circumferentially. These two cases are investigated separately, at all the stagnation pressures. The wall pressure variation is validated based on the k-ω SST turbulent model with experimentally measured wall pressure distribution at 2 bar, without secondary inlet flow. Suction is found to increase with the increase of stagnation pressure in the suction chamber. The inducted mass flow promotes the mixing in the shock-train zone, by triggering the significant momentum exchange between the primary flow and secondary flow. Results show that the pressure recovery takes place as the flow enters the divergent portion of ejector.

Numerical assessment of ejector performance enhancement by means of two-bypass inlets

The pursuit of high efficiency ejectors has been the target of researchers since the invention of these devices. In the present study, numerical work on an ejector with one bypass inlet (with different inlet widths) and two bypass inlets (with different bypass inlet positions) was proposed to enhance performance. The entrainment ratios when the bypass inlet and secondary inlet were under different pressures were also analyzed. In comparison with the original ejector, the ejector with one bypass inlet had better entrainment performance, and an optimal width of the bypass inlet for the highest entrainment ratio was found. In addition, the performance of the ejector with two bypass inlets was superior to that of the ejector with one bypass inlet, when the primary or induced pressure exceeded the designed value. In comparison with the original ejector, the largest increase of entrainment ratio was 48.93% for the ejector with two bypass inlets and 34.88% for the ejector with one bypass inlet. When the bypass inlet pressures differed from the induced pressure, the optimal operational scheme for high entrainment ratio was that the induced pressure should be the maximum value, and the first bypass pressure should be the minimal value.

The optimization of a dust suppression and clean production scheme in a TBM-constructed tunnel based on an orthogonal experiment

This study aims to examine whether clean production can be achieved by using a ventilation dust removal system in a tunnel being constructed using a tunnel boring machine (TBM). The section between the Guizhou-Road Station and the Guipaijing Station on the No. 1 line of the Qingdao Metro was selected as the study area, and the effectiveness of a ventilation dust removal system on the diffusion distance and mean concentration of dust in the excavating area was investigated through the use of a CFD-based numerical simulation. Firstly, it was found that when the first pressure quantity, exhaust quantity, and position of the pressure inlet and exhaust inlet of the ventilation dust removal system all remained unchanged, the secondary pressure quantity corresponding to the optimal dust suppression effect was determined to be 8 m³/s. Next, an orthogonal experiment was performed on the position of the pressure inlet and exhaust inlet and the forced-to-absorbed airflow quantity ratio in order to examine the effect of different combinations on the dust suppression effect in the tunnel. By selecting the dust diffusion distance, mean dust concentration in the tunnel and dust-collecting efficiency as the evaluation indexes, three favorable schemes were determined, from which the optimal scheme was selected. In the optimal combination, the secondary pressure inlet and exhaust inlet were 28 m and 11m away from the tunnel face respectively and the forced-to-absorbed airflow quantity ratio was 1.6. After the scheme’s optimization, the dust diffusion distance in the tunnel was shortened considerably by 53 %, the mean dust concentration was reduced to 1.52E-06 kg/m³, and the dust-collecting efficiency was enhanced by 13.19 %. Under these optimal conditions, a ventilation dust removal system can maximize the operational efficiency and ensure a clean air environment during any production activities.

Simulation of ejector for vacuum generation

Supersonic ejectors are used in a wide range of applications such as compression of refrigerants in cooling systems, pumping of volatile fluids, or vacuum generation. The objective of the present paper is to mesh and simulate, in an OpenFOAM environment with an open access implicit density-based solver HiSA, the physics of the vacuum ejector, and, later, compare the results with experimental measurements. In order to achieve this a 2D axisymmetric mesh made by hexahedral cells has been created. Steady solutions have been obtained, with prescribed total pressure in primary and secondary inlets. Secondary total pressure ranges from 1 to around 0.2 bar in which the secondary flow is zero. Numerical results are compared with experimental measurement, with two flowmeter sizes for small flow rate accuracy. Two regimes are encountered. In supercritic regime the secondary is chocked and sonic flow is reached in the second nozzle. In subcritic regime, the secondary flow is subsonic. The agreement is good, although simulation tends to slightly overestimate flow rate for large values region.

Non-Mechanism Model for Superheater Pollution Diagnosis of Waste Incinerator Based on BP Neural Network

Dust accumulation of boiler heating surface is one of the common problems in power plants, which will affect the unit’s economic and safe operation in serious cases. In this paper, the factors that affect the ash deposition in the superheater of the garbage incinerator are analyzed, and a non-mechanism model for diagnosing the ash deposition pollution in the superheater of the garbage incinerator is established by using 3-layer BP neural network. Parameters such as garbage disposal amount, furnace temperature, primary air flow amount and secondary air flow amount are selected as input vectors, parameters such as secondary superheater inlet smoke temperature and primary superheater inlet temperature are taken as output values, and real-time data of units collected by a power plant DCS system are used as sample sets to train the network after normalization processing. The trained BP network has good effect in superheater pollution diagnosis.

Removal of fine solid particles in aggressive gas flows in a newly designed multi-channel cyclone

A significant proportion of pollutants arise from the heat production equipment in private households. The processes of combustion and product treatment (drying, adding chemical compounds) generate aggressive gas flows containing solid particles (SPs). Common methods employ high-efficiency gas purification to remove SPs, the most popular include electrostatic and sleeve-type filters. However, the operation of these types of filters is complex, and thus their application is very limited. This is especially evident when collecting adhesive and wet FSPs or when purifying aggressive gas flows. New design multi-channel cyclone has a few principal elements of the structure such as secondary inlets, inner slits and convex bottom. These improvements allow to avoid an adhesion of sticky and moist SPs on the inner surfaces of the cyclone. This study focuses on estimating the effect of separating wood and wood ash SPs. The obtained results are presented and the comparison of the advantages and disadvantages of two different design multi-channel cyclone are provided.

Tube inlet orifice design of a once-through steam generator for flow stabilization

A numerical study is conducted on the secondary side screw-type tube inlet orifice design of a once-through steam generator. An orifice length criterion for flow stabilization is derived by introducing the hydraulic resistance ratio of the orifice and the subcooled region to the two-phase and superheated regions. Various tube plugging conditions and power levels are considered, and the secondary coolant pressure at the tube outlet is adjusted to maintain a constant thermal power. Comprehensive numerical solutions are acquired to evaluate the minimum orifice length under various operating conditions. The results obtained show that a constant thermal power is maintained by properly adjusting the secondary coolant outlet pressure with a variation of the superheat degree and secondary coolant pressure drop when the steam generator operates at high power level. The steam generator performance is analyzed according to the tube plugging condition in terms of the degree of superheat, secondary side pressure drop, temperature distribution, and quality distribution. The secondary side outlet pressure curve for the constant thermal power operation is obtained, and the required minimum orifice length to suppress the flow oscillation below the allowable level is evaluated. The lowest power level results in the highest minimum orifice length, and non-plugging condition provides a limiting case for the orifice length criterion except near the 100 % power level.

Experimental Investigation on Ejector Performance Using R134a as Refrigerant

Ejector refrigeration has the advantage of low capital cost, simple design, reliable operation, long lifespan and almost no maintenance. The only weakness is the low efficiency and its intolerance to deviations from design operation condition. R134a used in ejector refrigeration system gives better performance in comparison with many other environmental friendly refrigerants as the generation temperature is from 75°C to 80°C. The present work experimentally investigated the on-design and off-design performance of the ejector with fixed geometry using R134a as refrigerant, and cycle performance of the ejector refrigeration system. The experimental prototype was constructed and the effects of primary flow inlet pressure, secondary flow inlet pressure and ejector back pressure on ejector performance and cycle performance were investigated respectively. The operation conditions are: primary flow inlet pressure from 2.2 MPa to 3.25 MPa, secondary flow inlet pressure from 0.36 MPa to 0.51 MPa, ejector back pressure from 0.45 MPa to 0.67 MPa. Conclusions were drawn from the experimental results, and the experimental data can be used for validation of theoretical model for both critical and subcritical mode.

Numerical CFD Simulations and Indicated Pressure Measurements on a Sliding Vane Expander for Heat to Power Conversion Applications

The paper presents an extensive investigation of a small-scale sliding vane rotary expander operating with R245fa. The key novelty is in an innovative operating layout, which considers a secondary inlet downstream of the conventional inlet port. The additional intake supercharges the expander by increasing the mass of the working fluid in the working chamber during the expansion process; this makes it possible to harvest a greater power output within the same machine. The concept of supercharging is assessed in this paper through numerical computational fluid dynamics (CFD) simulations which are validated against experimental data, including the mass flow rate and indicated pressure measurements. When operating at 1516 rpm and between pressures of 5.4 bar at the inlet and 3.2 bar at the outlet, the supercharged expander provided a power output of 325 W. The specific power output was equal to 3.25 kW/(kg/s) with a mechanical efficiency of 63.1%. The comparison between internal pressure traces obtained by simulation and experimentally is very good. However, the numerical model is not able to account fully for the overfilling of the machine. A comparison between a standard and a supercharged configuration obtained by CFD simulation shows that the specific indicated power increases from 3.41 kW/(kg/s) to 8.30 kW/(kg/s). This large power difference is the result of preventing overexpansion by supercharging. Hence, despite the greater pumping power required for the increased flow through the secondary inlet, a supercharged expander would be the preferred option for applications where the weight of the components is the key issue, for example, in transport applications.