Secondary Inlet Research Articles

Stability and combustion characteristics of dual annular counter-rotating swirl oxy-methane flames: Effects of equivalence and velocity ratios

An experimental study was carried out to investigate flow/flame interactions, stability, combustion, and emissions properties of CH4/O2/CO2 stratified flames stabilized on a dual annular counter-rotating swirl (DACRS) burner for gas turbine combustion applications. The effects of two targeted parameters, namely equivalence ratios (for primary - ϕp, secondary - ϕs, and global - ϕg streams) and velocity ratio (Vr = Vp/Vs: primary to secondary stream inlet velocity ratio), are studied at fixed volumetric oxygen fraction (OF) in the oxidizer mixture (O2 + CO2) of both primary and secondary streams of 34 % at fixed Vp of 5 m/s. The experimental results indicated that no flame flashback was recorded in the domain of any operational ϕp up to stoichiometric operation of the secondary stream (ϕs = 1.0). At near stoichiometric operation of the primary stream, the main secondary flame can persist in extremely lean conditions (ϕs = 0.45 @ Vr = 3), thereby extending the thresholds of flame blowout. Moreover, raising ϕp from 0.4 to 1.0 results in significant reduction of ϕs at blowout from 0.595 to 0.456, corresponding to reducing the combustor ϕg at blowout from 0.577 to 0.499. At lower ϕp, the oxy-methane flame tends to lift and extinguish earlier.

Effect of inlet diameter on the flow structure and performance for aluminum-based water-jet engine

Abstract In this study, the flow field and performance for the aluminum based water ramjet was analyzed through numerical simulation. The time decrease in evaporation heat absorption process expands the range of aluminum/water combustion and increase the specific impulse. If the diameter of atomized water droplets from the primary inlet is large, the evaporation efficiency will be further reduced, which is not conducive to the further propagation of the reaction. However, if the diameter is small, the flow field temperature will be rapidly dropped due to rapid evaporation, and a large range of low-temperature areas will appear in the reaction area of the combustor. The diameter reduction of atomized water droplets from the secondary water inlet is conducive to the diffusion of the reaction area downstream, further and makes the combustion range be expanded. This effect is benefit for increasing the specific impulse and can reduce the temperature near the wall.

Influence of cyclone combustor structure on the motion behaviors of solid fuel particles

A coarse-grained computational fluid dynamics-discrete element method (CFD-DEM) was established to investigate the influence of cyclone combustor structure on the motion behaviors of solid fuel particles. Four structural parameters, i.e., primary inlet number (Pn), secondary inlet number (Sn), secondary inlet location (SL), and guide blade angle (α), were examined. Compared to the base structure with a single primary inlet, the addition of extra primary inlet, secondary inlet, or diversion structure elevates the global parcel location. Increasing Pn and Sn decreases the average parcel residence time, while augmenting SL and α generally lengthens it. Meanwhile, increasing Pn, Sn, and SL or decreasing α broadly reduces the wall parcel-hold ratio. Furthermore, the inclusion of secondary inlet and diversion structure increases the probability of small parcels occurring in the near-wall zone. These observations are helpful for optimizing the design and operation of cyclone combustors.

Cavitation and Pulsation Reduction for External Gear Pumps Using Novel Core-Feed Inlets and Outlets: An Integrated Experimental and Numerical Study

Abstract Fluid starvation and congestion at the meshing area of external gear pumps (EGP) happen inevitably as an intrinsic nature of these pumps. As a result, cavitation and excessive pressure pulsation are the two significant issues suffering the pump performance at almost any pump speed. Increasing speed or differential pressure exacerbates the situation, resulting in excessive noise, vibration, and damage to the pump or the hydraulic circuit, plus a significant reduction of pump efficiency. External gear pumps have tiny decompression grooves on the bearing blocks to alleviate these issues. However, these grooves cannot handle sufficient flow to prevent pressure drop at the intake side and pressure rise at the discharge side of the meshing area. This study presents analysis of an innovative Core-Feed inlets/outlets which effectively reduce cavitation and excessive pressure pulsation, even at extremely high speeds, by connecting the closed volumes of fluid at the gears meshing area to the main inlet/outlet through the center of gears. A computational fluid dynamics (CFD) analysis was performed to study the dynamic behavior of the pump. A fully functional prototype with secondary inlets and transparent components was built to validate the flow rate calculation against the experimental data and visualize the cavitation phenomena. The numerical results were in an excellent agreement with experimental data. The results show that the new pump can operate at much higher speeds with higher efficiency than a typical gear pump.

Enhancing the efficiency of two‐stage cyclones without increasing pressure drop by optimizing inlet and outlet dimensions

AbstractEfforts to enhance cyclone separators aim to minimize gas energy consumption while improving separation efficiency. This study attempts to achieve this goal for cyclones arranged in series using straightforward methods. Experimental and numerical simulation analyses were performed to study the effect of matching inlet and outlet diameters on the performance of a two‐stage tandem cyclone separator. The results show that the matching method, in which the inlet gas velocities of both stages are higher than the outlet gas velocity, has a better separation efficiency. The efficiency and pressure drop models of the two‐stage cyclones in series were constructed using the response surface methodology (RSM) to obtain the optimal combination of inlet size and exhaust pipe diameter. Experimental tests showed that the accuracy of this model was reasonable. At different permitted pressure drops, the optimized structure revealed that: (1) The inlet area should be smaller than the outlet area for each cyclone stage. (2) The secondary inlet size (KA) should be as large as possible. (3) dr decreases while KA increases in each step.

Optimizing R152a/R600 and R290/R600 mixtures for superior energy performance in vapor compression systems: Promising alternatives to Isobutane (R600a)

This study presents an experimental investigation into the optimal composition of R152a/R600 and R290/R600 mixtures as potential alternatives to isobutane (R600a) in a single-stage vapor compression cycle. The research involved testing eight different mass compositions for R152a/R600 and ten mass compositions for R290/R600, comparing their performance with that of R600a. After careful analysis, the “optimum” mass compositions were identified as (10/90)% for both R152a/R600 and R290/R600, achieving a balanced trade-off among coefficient of performance (COP), volumetric cooling capacity (VCC), and cooling output (Q̇o). Further tests were conducted on the “optimum” compositions at nine different secondary fluid temperature inlets. The results indicated an average COP increase of + 7.3 % for the R152a/R600 mixture, with decreases of −11.4 % in VCC and −9.7 % in Q̇o. Similarly, the R290/R600 (10/90)% mixture showed a COP increase of + 10.3 %, accompanied by VCC and Q̇o decreases of −8.8 % and −6.6 %, respectively. Notably, both mixtures exhibited superior energy performance compared to isobutane while maintaining similar thermodynamic properties, particularly the R290/R600 (10/90)% mixture. These findings suggest that the R152a/R600 and R290/R600 mixtures could serve as long-term, high-efficiency alternatives to R600a in vapor compression cycles.

Direct numerical simulation of a pressurized thermal shock scenario at higher reynolds number

Direct Numerical Simulation (DNS) is performed for a pressurized thermal shock scenario in a reactor downcomer geometry. In the present work, a simplified representative geometry is adopted where cold fluid injected from a square duct is injected in a planar downcomer. A secondary hot inlet at the top of the downcomer is employed to enforce a downward flow of the injected emergency core cooling water, to mimic the effect of density driven flow. The Reynolds number of the impinging flow, based on bulk velocity and duct height, equals 12,500, while a unity Prandtl number fluid is used. The simulation is performed for two thermal boundary conditions, namely an isotemperature condition and an adiabatic condition, representing the two extreme scenarios of a conjugate heat transfer problem. The instantaneous and mean fields are first analysed in order to study the flow pattern and formation of vortical structures within the downcomer. The impinging flow is deflected radially outwards in the vicinity of the barrel wall, which then interacts with the surrounding hot fluid forming large vortical structures and bringing the cold fluid back to the vessel wall. The mixing of flow and penetration of colder temperatures in the downcomer is observed to be greatly influenced by interaction of these vortical structures. The descending cold plume in the downcomer is observed to form three branches separated by low-speed regions. The maximum values of turbulent kinetic energy are observed only in the vicinity of flow impingement, while high values of its production and dissipation are also observed within the shear layers of the descending plume. The maximum values of temperature fluctuations are found at the interface of the descending cold plume and surrounding hot fluid, while relatively high values are also seen at the locations of large vortical strucutres. Anisotropy in turbulence is also analysed using the componentality contour approach and a modified barycentric colour mapping scheme. Also reported herein is a comparison of mean and statistical profiles with those at lower Reynolds number reported in the literature. At higher Reynolds number, the cold impinging jet is deflected farther outwards in the downcomer. The locations of peak fluctuations in velocity and temperature are also farther away from the impingement. The magnitudes of fluctuating temperature and turbulent kinetic energy are observed to be higher for the present higher Reynolds number case. The peak Nusselt number at the barrel wall is observed to scale with a factor of Re1/2 in the present configuration.

Investigation and numerical simulation of two-phase ejectors for use in the water desalination cycle

This study investigates enhancing energy efficiency in desalination by introducing a novel combined ejector-solar vacuum tube collector cycle. The cycle utilizes a two-phase state and lower-temperature saturated steam generation to overcome the energy consumption hurdle, particularly by compressors. Water enters the ejector's primary nozzle in a liquid phase, while steam from the solar collector aids in separation, yielding desalinated water in a variable phase. Fluent software's computational fluid dynamics assesses the ejector's performance, considering primary and secondary inlet pressures' impact on hydrodynamic characteristics. TRNSYS software models the cycle transiently over a year in Tehran, exploring different pressures' effects on fluid behavior. Results indicate that increasing secondary nozzle pressure at constant primary pressure significantly boosts steam flow rate and inlet velocity. The investigation covers secondary inlet pressures ranging from 7000 Pa to 39,000 Pa and primary nozzle pressures between 200,000 Pa and 500,000 Pa, studying their impact on fluid behavior. Under Tehran's climatic conditions, the proposed cycle achieves a peak output rate of 1.35 kg/m2/h, a maximum daily yield of 8.47 kg/m2, and a total annual output of 767 kg/m2 for desalinated water. This innovative approach showcases promise for energy-efficient desalination, especially in regions with solar potential like Tehran.

Experimental evaluation of CO2/R-152a mixtures in a refrigeration plant with and without IHX

In recent years, CO2-based mixtures have been considered as a way to improve the performance of refrigerating plants using pure CO2 as refrigerant. Combining CO2 with a fluid with higher critical temperature generates a blend which allows to run a refrigeration plant in subcritical conditions at higher heat rejection temperature when compared to pure carbon dioxide, and consequently reach higher COP. This work evaluates from an experimental point of view two CO2/R-152a mixtures, ([90/10 %] and [95/5 %]), used as refrigerants in a single-stage refrigeration plant with and without internal heat exchanger, and compares the results to those obtained using pure CO2. The work analyses the main energy parameters of the plant for secondary fluid inlet temperature of 2.5 °C at the evaporator, and in the range from 20 °C to 40 °C with 5 °C step at the condenser/gas-cooler. The use of such mixtures, compared to the use of pure CO2, allowed to obtain a higher COP in the base cycle for heat rejection temperature above 25 °C, reaching the largest increment at the highest temperature while, when working with IHX cycle, no improvements in the COP were measured.

Effect of temperature, geometric parameters, and surface conditions on fluid mixing in a vertical port static mixer

This study comprehensively investigates how elevated temperature and surface roughness affect vertical liquid jet mixing in a multi-port nozzle, using both experimental and computational methods. It explores various geometrical parameters and precise nozzle positioning. Experiments, conducted across different temperature and surface roughness conditions, involve adjusting convergent nozzle angles, driving nozzle distance from the throat, and insert presence. Conductivity probes, turbidity meters, and pH meters quantify fluid mixing under diverse conditions. Optimal mixing conditions for vertical flow secondary fluid inlets are determined, along with corresponding mixing efficiencies for each port. Computational fluid dynamics (CFD) simulations with ANSYS Fluent R2 2001 confirm that the highest mixing efficiency of nearly 98% is achieved with an elevated temperature of 50 °C, a rough-surfaced convergent nozzle, a helical insert, and a 45 mm driving nozzle distance, when all vertical ports are open simultaneously. These findings advance understanding of optimizing vertical-flow mixing in multi-port static mixers under varying conditions.

Monitoring and fault detection: a comparative study using computational intelligence techniques

In this work, two different Computational Intelligence Techniques were used to provide a comparative study by using Neural Networks and Neuro-fuzzy applied in Monitoring and Fault Detection in sensor of an experimental reactor. Both methodologies were developed and tested using a model composed by 9 variables: N2 (% power), T3 (pool water temperature), T4 (decay tank inlet temperature), T7 (primary loop outlet temperature), T8 (secondary loop inlet temperature), T9 (secondary loop outlet temperature), F1M3 (primary loop flowrate), F2M3 (secondary loop flow rate) and R1M3 (nuclear dose rate). It was used data from the first week experimental reactor IEA-R1 operation from October 2012 in both Monitoring Systems, which was divided in subsets in a following way: 60% for training, 20% for tens and 20% for validation. The results obtained using Neuro-fuzzy were better than the ones with Neural Networks.

Effect of mixing chamber structure on the performance of adjustable ejector

The study employs numerical simulation method to analyze performance of an adjustable ejector, with a specific focus on the influence of the structure dimension of mixing chamber. R41/R1234yf refrigerant is used as the working medium in the study. The primary and secondary flow inlets are set at the pressure of 1.4 MPa and 0.2 MPa, respectively, along with temperature of 353.15 K and 288.15 K corresponding. The outlet pressure of the ejector is 0.3 MPa. The simulation results show that optimal mixing chamber diameter within a range from 14.7mm to 18.7mm exists for obtaining peak adjustable ejector performance. Maximum entrainment ratio of 0.59 is obtained when cone diameter ratio is 65% and diameter of the mixing chamber is 15.7mm. Furthermore, the optimal mixing chamber length within range from 24mm to 220mm exists for obtaining peak adjustable ejector performance. Maximum entrainment ratio of 0.624 is obtained when cone diameter ratio is 76% and length of the mixing chamber is 88 mm. Therefore, it is crucial during designing process of the mixing chamber to ensure the complete fluid mixture and minimal flow resistance.

Influence of inlet structure on combustion flow structure in magnesium powder fueled water ramjet engine

Abstract Different inlet structures have a significant impact on the internal flow characteristics of a solid-magnesium powder water ramjet engine. Based on the magnesium-water reaction model, a computational fluid dynamics (CFD) method is applied to establish a numerical simulation method for the internal flow field of the engine, and the internal flow characteristics of the engine under different inlet structure conditions are studied. The simulation results show that high-temperature gas can effectively promote the ignition of magnesium powder at the top of the combustion chamber, while accelerating the evaporation of the first inlet water and increasing the combustion rate of magnesium powder. The secondary inlet has the most significant effect on the temperature inside the combustion chamber. When the secondary inlet flow rate increases towards the top of the combustion chamber, it increases the amount of heat absorbed by the evaporating water at the top of the chamber, thereby reducing the temperature at the top of the combustion chamber. However, when the flow rate is low, it results in insufficient oxidizer at the top of the combustion chamber, which is unfavorable for the combustion of magnesium powder.

A counter-swirl design concept for dry powder inhalers

A swirling airflow is incorporated in several dry powder inhalers (DPIs) for effective powder de-agglomeration. This commonly requires the use of a flow-straightening grid in the DPI to reduce drug deposition loss caused by large lateral spreading of the emerging aerosol. Here, we propose a novel grid-free DPI design concept that improves the aerosol flow characteristics and reduces the aforementioned drug loss. The basis of this design is the implementation of a secondary airflow that swirls in the opposite direction (counter-swirl) to that of a primary swirling airflow. In-vitro deposition, computational fluid dynamics simulations and particle image velocimetry measurements are used to evaluate the counter-swirl DPI aerosol performance and flow characteristics.In comparison with a baseline-DPI that has only a primary swirling airflow, the counter-swirl DPI has 20% less deposition of the emitted drug dose in the induction port and pre-separator of a next generation impactor (NGI). This occurs as a result of the lower flow-swirl generated from the counter-swirl DPI which eliminates the axial reverse flow outside of the mouthpiece and substantially reduces lateral spreading in the exiting aerosol.Modifications to the counter-swirl DPI design were made to prevent drug loss from the secondary airflow tangential inlets, which involved the addition of wall perforations in the tangential inlets and the separation of the primary and secondary swirling airflows by an annular channel. These modified DPI devices were successful in that aspect but had higher flow-swirl than that in the counter-swirl DPI and thus had higher drug mass retained in the device and deposited in the induction port and pre-separator of the NGI. The fine particle fraction in the aerosols generated from all the counter-swirl-based DPIs and the baseline-DPI are found to be statistically similar to each other.

Self-cleaning effect and secondary swirling clean gas for suppressing particle deposition on vortex finder of gas cyclones

In order to suppressing the particle deposition on vortex finder, a series of gas cyclones with the secondary swirling clean gas were developed inspired by the gas purge effect. Effects of the width and extension length of the flow channel as well as the secondary inlet velocity and running time on the particle deposition pattern, the deposited particle mass and the cyclones’ performance were experimentally investigated, respectively. The results show that the ultrafine particles (Stokes number Stk < 0.0358) are mainly loose deposited on the walls under the secondary gas. Compare to the conventional cyclone with single tangential inlet, the total deposited particle mass of the improved cyclone has a maximum reduction more than 60%, and the collecting efficiency is increased up to 97.5% under the basically same pressure drop. The corresponding no-deposition area is increased by about 13%, and remains constant in spite of extending the running time. Moreover, an interesting phenomenon named “self-cleaning effect” of the vortex finder was captured for the gas cyclones, and mechanism of the secondary clean gas on the particle deposition is preliminarily analyzed. The results can deepen the understanding of the particle deposition on the vortex finder and guide the design of the anti-coking gas cyclones.

Investigation of aerodynamics in combustion of vegetative waste on isothermal models

Modern agricultural vehicles contain a large number of components, which include micro Abstract. Conventional furnaces using alternative fuels, such as vegetable waste (VW), are widely used instead of furnaces operating on conventional fuels. The furnaces aggregated with dryers of SZT and SP type are widely used in agriculture and food industry. Two models with a suspended bed were investigated: with flare-vortex and cyclone-vortex modes. The first model assumes the presence of an inclined grate in a rectangular chamber with a concentrated supply of secondary blast, primary blast with material is supplied above the grate in its lower part, and the second model assumes a cylindrical-shaped chamber with primary air inlet in the center and cyclonic secondary blast inlet at a certain height. This scheme is close to the first, only in the lower part of the model concentrated input of primary blast with material. The methodology of aerodynamics studies included: feeding of material from the hopper; material cutoff after steady-state mode; collection and weighing of fallen particles from the model; determination of the time of material presence in the model by labeled particles. Modeling of aerodynamics for different schemes of furnace process organization showed the possibility of creating two-span or single-span furnace blocks depending on the required operating mode. The results of comparative studies of aerodynamics of flare-vortex and cyclone-vortex modes are given. The results of comparative studies of aerodynamics of flare-vortex and cyclone-vortex modes are given. Optimal blowing parameters, secondary and primary air ratio, furnace design parameters contributing to the maximum specific volume heat stress are determined.

Simulation and Optimization of the Operation Efficiency of Heat Exchange Units in Intelligent Heating Systems Based on Entransy Dissipation Thermal Resistance

So as to investigate heat exchange efficiency of heat exchange units under different operating conditions, this paper builds a simulation analysis model for heat exchange units in the framework of intelligent district heating systems based on the Modelica unified modeling language and the MWorks platform. Analyze the real-time operating efficiency of heat exchange units using entransy dissipation thermal resistance as an evaluation indicator of heat exchange efficiency. This paper analyzes the trend of heat exchange efficiency changes of heat exchange units when the primary side flow rate, secondary side flow rate, primary side inlet temperature, secondary side inlet temperature, and secondary side bypass pipeline valve opening change. The simulation results verify that when the primary side and the secondary side flow match, the entransy dissipation thermal resistance is the smallest, and its heat transfer efficiency is the highest. Under the simulation condition where the convective heat transfer coefficient is constant, the entransy dissipation thermal resistance is independent of the inlet temperature changes on the primary and secondary sides. The minimum entransy dissipation thermal resistance could be achieved, which represents the optimal real-time heat exchange efficiency state, when the valve opening of the mixed water heat exchange unit is 45% under the specific flow conditions.

Performance analysis of the cyclone separator with a novel clean air inlet installed on the roof surface

The study investigated the impact of implementing a new method of injecting clean air axially through the roof of the cylindrical section on the performance of cyclone separators. This secondary inlet was confined to a region common to both the vortex finder tube and the cylindrical section. The Stairmand high-efficiency cyclone was used as a reference model for comparison against the proposed design. For analysis, we made the potential use of CFD methods (based on LES and DPM models), along with the experimental and stereo-PIV research. Comparative analysis was carried out based on performance parameters (viz. the collection efficiency and pressure losses) and exploring flow physics inside the separator. Furthermore, six different values of clean gas inlet velocities were also considered to measure the relative performance. Conclusive results indicate that the new model increased the separation efficiency for all inlet velocities of the clean gas.

Thermal Performance Optimization of Integrated Microchannel Cooling Plate for IGBT Power Module.

In high-integration electronic components, the insulated-gate bipolar transistor (IGBT) power module has a high working temperature, which requires reasonable thermal analysis and a cooling process to improve the reliability of the IGBT module. This paper presents an investigation into the heat dissipation of the integrated microchannel cooling plate in the silicon carbide IGBT power module and reports the impact of the BL series micropump on the efficiency of the cooling plate. The IGBT power module was first simplified as an equivalent-mass block with a mass of 62.64 g, a volume of 15.27 cm3, a density of 4.10 g/cm3, and a specific heat capacity of 512.53 J/(kg·K), through an equivalent method. Then, the thermal performance of the microchannel cooling plate with a main channel and a secondary channel was analyzed and the design of experiment (DOE) method was used to provide three factors and three levels of orthogonal simulation experiments. The three factors included microchannel width, number of secondary inlets, and inlet diameter. The results show that the microchannel cooling plate significantly reduces the temperature of IGBT chips and, as the microchannel width, number of secondary inlets, and inlet diameter increase, the junction temperature of chips gradually decreases. The optimal structure of the cooling plate is a microchannel width of 0.58 mm, 13 secondary inlets, and an inlet diameter of 3.8 mm, and the chip-junction temperature of this structure is decreased from 677 °C to 77.7 °C. In addition, the BL series micropump was connected to the inlet of the cooling plate and the thermal performance of the microchannel cooling plate with a micropump was analyzed. The micropump increases the frictional resistance of fluid flow, resulting in an increase in chip-junction temperature to 110 °C. This work demonstrates the impact of micropumps on the heat dissipation of cooling plates and provides a foundation for the design of cooling plates for IGBT power modules.

Hydraulic Performance and Energy Dissipation Mechanism Analysis of the Tesla-Shaped Emitter

In this paper, a tesla-shaped emitter is proposed based on the structure of the “tesla valve” as the source of inspiration, so that the water flow in the channel would produce a variety of energy dissipation phenomena, such as diversion, hedging, and mixing, to explore the hydraulic performance and energy dissipation mechanism of the tesla-shaped emitter. The channel structure parameters were taken as factors, and 16 groups of orthogonal tests were arranged. Based on CFD technology, the pressure–flow relationship curve slope, flow ratio between the main channel and secondary channel, flow field, and head loss of the emitter were calculated and analyzed for different combinations of structural parameters. Based on a significance level α = 0.05 test, the main channel inlet section length (L3) had a significant impact on the curve slope, and the secondary channel length (L1) and main channel inlet section length (L3) had a significant impact on the flow. The multiple linear regression mathematical models between the channel structure parameters and the curve slope and the flow were constructed. The larger the ratio between the main channel and the secondary channel flow, the better the hydraulic performance of the emitter. The channel unit loss coefficient increased linearly with the increase of the emitter inlet pressure, and its value ranged from 4.5769 to 8.1716, with an excellent energy dissipation effect. The hedge mixing of the water flow was the core of the energy dissipation of the tesla-shaped emitter. By appropriately increasing the inlet size of the main channel and other elements to increase the main channel flow and optimize the flow ratio between the main channel and the secondary channel, the mixing was improved, which consequently improved the hydraulic performance of the emitter.