Outlet Duct Research Articles

Optical investigation on impacts of ambient pressure on macroscopic spray characteristics of ducted fuel injection under non-vaporizing conditions

Ducted fuel injection (DFI) which mimics Bunsen burner, is a cutting-edge technology for reducing the soot formation of heavy-duty diesel engines. In this work, the Mie-scattering optical method was used to visualise impacts of ambient gas pressure on DFI and free spray characteristics with a single-hole injector. Ambient gas pressure varies from 3 to 12 MPa and diesel injection pressure from 40 to 120 MPa. Spray morphology, tip penetration, cone angle and area were discussed. The results indicated that DFI spray has a distinct velocity advantage over free spray, especially under high ambient pressure. As ambient pressure increases, DFI spray has better cone angle and area advantages than those of free spray. Increasing injection pressure helps to promote these advantages. Additionally, when the ambient pressure is high enough, a mushroom-shaped spray appeared at the duct outlet, diffusing actively around and forming a large-scale vortex. All of these characteristics of DFI spray can be interpreted as better serving the fuel-gas mixing as ambient pressure increases.

Study on Dust Diffusion Law and Application of Wet Vibrating Wire Dust Removal Fan in Fully Mechanized Excavation Face

Fully mechanized excavation face is the main place of dust generation in coal mines. Due to the huge dust production and long ventilation distance, the dust concentration is difficult to reach the safety standard. The purpose of this study is to improve the dust removal efficiency of 2410 roadway in Yuhua Coal Mine. Firstly, this paper carried out dust concentration and roadway wind speed measurement on the 2410 fully mechanized excavation face of Yuhua Coal Mine. According to the actual layout of fully mechanized excavation face, the geometric model is established. The distribution of wind field in fully mechanized excavation face is simulated and analyzed by Fluent software. The correctness and feasibility of the model and simulation method are verified by comparing the simulation results with the measured data. Then the paper studies the influence of the air duct outlet installation position on the airflow field and the dust distribution, and analyzes the dust removal effect of the existing wet vibrating wire dust collector dust removal system in Yuhua Coal Mine. The research conclusion is that the wet string vibration dedusting fan has remarkable dedusting effect, and the dedusting efficiency is the highest when the air duct is installed near 10 m from the working face.

Validation and Analysis of Nonlinear System of Centrifugal Compressor using Hot Wire Flow Measurement and Jacobian Matrix

ABSTRACTA mathematical method is developed to predict surge and instability inception in a centrifugal compressor map based on Greitzer and Moore model. The method uses phase plane and Jacobian matrix to determine stable and unstable zone of centrifugal compressor and to extract limit cycle in unstable zone. In order to evaluate accuracy of analytical method, a compressor test rig facility is designed and tested in order to be compared with theoretical results. Accurate Honeywell piezoelectric pressure transducers are used to measure time averaged pressure at inlet and outlet ducts of the compressor. In order to record the flow fluctuation precisely, hot wire sensors are installed in entrance and exit of impeller. The results represent instability inception near true stall point but different from measured data. The discrepancy mostly originates from inlet and outlet ducts which causes measure stall point of compressor deviates from true one. An analytical method which is able to predict surge and instability in a compressor is highly significant for instrumentation and controlling of system.

Modifikacija vazdušnog kanala u cilju smanjenja vibracija i postizanja manjeg pada pritiska

In this work complete methodology for calculation and analysis of fluid flow in air ducts is presented. In order to minimize outlet pressure drop and to reduce the duct vibrations the plates with airfoil cross sections are added to duct critical zones. It was observed that airfoil stream plates efficiently contribute to outlet pressure drop, duct vibration and noise reduction. Modern methods such as CFD and FEA can be efficiently deployed in numerical treatise of flow and vibration analysis in air ducts.

Analysis of heat transfer and flow characteristics in typical cambered ducts

The heat transfer and flow characteristics of the air-water cross flow over cambered ducts were experimental and numerical investigated. The sequence of their Core Volume Goodness Factor (CVGF) is cosinoidal, parabolic, circular, trapezoidal and rectangular ducts successively from superior to inferior. Cambered ducts have more uniform temperature difference distribution than the equal cross section duct, and it has the minimum temperature difference in inlet and outlet of the cosinoidal duct. With the optimal overall heat transfer performance, the cosinoidal duct is superior to that of the rectangular duct by 7.3%–28.1%. In the cosinoidal duct, the smaller the amplitude is, the better the heat transfer performance is. The thickness of the thermal and velocity boundary layers adjacent to the wall surface decreases constantly with increased Reynolds number. In the near wall region, n = 5um, the main heat transfer area is the peak and middle areas, but with weaker heat transfer performance in the trough region. Although gradually expanding cambered duct slows down the flow velocity, the structure form decreases the pressure drop loss during the flow process. While improving the convective heat exchange capability of the upstream, the heat transfer area of the downstream is also improved to boost the overall heat transfer performance.

Study on the Effective Range of Local Ventilation in the Driving Face of Single Head Roadway

The traditional research considers that the effective range of forced local ventilation in single head tunnel is the horizontal distance from the jet exit section to the rotary section, but there is a low wind speed area at the end of the range which can not completely and effectively release toxic and harmful gases. In this area, due to the small jet energy, there is no way to effectively remove the toxic and harmful gases produced in the driving process, which seriously affects the safety of the mine. Therefore, the reasonable definition of the effective range of the forced local ventilation of the single head tunnel can not only improve the theory of the local ventilation of the mine, but also prevent the accumulation of gas and ensure the life safety of the employees. In this paper, the definition of effective range of local ventilation in single head heading face is put forward, and the rationality of the definition of effective range is verified by numerical simulation. On the basis of reasonable definition of effective range, the relationship between wind speed and effective range under different ventilation modes is studied by numerical simulation. The results show that when the wind speed at the outlet of the air duct is less than 20 m/s, the effective range changes rapidly with the outlet wind speed, and after more than 20 m/s, the effect of wind speed on the effective range is gradually weakened. Under the same exit wind speed, the effective range of parallel and coplanar air inlet is much greater than that of single air inlet.

Rotational plating process design with computational fluid analysis

During the semiconductor manufacturing process and equipment development, we designed a face-up type electro-plating process and equipment including technologies of single wafer processing, wafer handling, and cyclic fluid delivery. In this study, with the help of computational fluid dynamics, we presented the flow effect on the wafer from the viewpoint of the coating uniformity. Process and hardware parameters, such as the electrode rotating speed, the gap between the electrode and the wafer, and the electrode shape were considered. The electrode height of 10 mm exhibited the best results, and this may be caused by the shoulder gap location to the outlet duct. A rotating speed of 5 rpm was shown to produce better results than those at other speeds. The butterfly wing and the meshed disk electrode showed a similar tendency in terms of the rotating speed and the gap. However, the butterfly-wing-type might show less uniform results than those of the meshed disk due to its original non-uniformity in the circumferential direction in case of lower rotating speed.

Feasibility analysis for control of bioaerosol concentration at indoor corner via airflow from ventilation outlet with energy optimization

An indoor corner may provide a relatively comfortable environment for bioaerosol growth and propagation, resulting in an increase in health risks for the resident. This paper presents a feasibility analysis for control of bioaerosol concentration at an indoor corner, defined as the area around ceiling edges, through airflow from ventilation outlet with optimized energy consumption. For the proposed approach, a gas-particle flow model with a chaotic moving vortex is developed to simulate the bioaerosol movement at an indoor corner via the Eulerian-Lagrangian method. In this model, the flowrate of the inlet fresh or air-conditioned air is tuned by a flowrate controller, which is installed at ventilation outlet or inside ventilation duct, in order to control the vortex trajectory. A residual concentration is defined as the ratio of the residual number of densely released particles at the corner to the area of the corner, in order to indicate the probability of bioaerosol movement, which is released sparsely and randomly by a microorganism in a real-world situation. The control strategies are then developed to optimize residual bioaerosol concentration and energy consumption by the orthogonal scheme. Based on the simulation results, a small variation of the airflow rate from the ventilation outlet contributes to reducing the residual concentration of bioaerosols that are originally released from the corner, or to increasing the residual concentration of detergents that are released from the ventilation outlet. It is thus concluded that a Pulse Width Modulation controller, with low amplitude, proper duty factor, period and time delay, is more energy efficient to improve the local indoor air quality.

Design optimization of a compressor transition S-shaped duct using a teaching–learning-based optimization algorithm

A high bypass turbofan aero-engine delivers compressed air from the low-pressure to the high-pressure compressor through a compressor transition duct. Weight and design space limitations impel to its S-shaped design. Despite that, the compressor transition duct has to guide the flow very carefully to the high-pressure compressor without disturbances and flow separations. Hence, the present paper is devoted to elaborate on the application of the proposed heuristic optimization technique known as multi-objective teaching–learning-based optimization (MO-TLBO) algorithm in the area of S-shaped transition compressor duct. The present algorithm is applied for obtaining the optimum design of the S-shaped duct while minimizing the total pressure loss coefficient and non-uniformity index at the S-shaped duct outlet. These objectives are also optimized independently and as a multi-objective consideration as well. Because of the conflicting nature of the objective functions, a Pareto-optimal curve is also presented for a successful trade-off between the objectives. Pareto-optimal curve gives flexibility to the designer for selecting the best set of the parameters based on the objectives. Successful execution of the proposed MO-TLBO algorithm is examined by comparing the optimum results acquired by the multi-objective genetic algorithm and comparisons divulge that the TLBO algorithm can be successfully practiced to obtain the optimized design of compressor transition S-shaped duct. Optimized duct shows the reduction in total pressure loss and non-uniformity by 28.80% and 36.67%, respectively, despite the reduction of 14.74% in overall length.

Analysis of The Effects of the Position of the Air Duct Supplying Fresh Air to the Working Face of the Mined Dog Heading on Methane Concentration Levels

Each year, more than one hundred kilometres of new dog headings are mined in underground hard coal mines. Such headings are ventilated by means of an air duct system. A stream of fresh air is supplied to the working face of the mined heading through an air duct with a view to ensuring proper chemical composition and temperature of the mining atmosphere. This is because this heading is being exploited and the ventilation must provide adequate working conditions for the crew. While dog headings are being mined in the body of coal, they are additionally filled with methane, which is released in this process. Due to the risk of its combustion and explosion, methane is a highly dangerous gas. It represents one of the greatest hazards in underground mining. Therefore, a particularly essential issue during the mining of dog headings is to reduce the potential for dangerous methane concentrations to occur. To prevent this from happening, it is necessary to select adequate parameters for the fresh air supplied through the air duct and the position of this air duct. It is the position of the air duct that appears to be a very significant element in the ventilation process of dog headings. Model-based tests were conducted to determine how the position of the air duct affects methane concentration levels. Their results have been presented in the paper. The tests were conducted using Computational Fluid Dynamics (CFD). The related calculations were performed in ANSYS Fluent, based on the finite volume method (FVM). The analyses performed made it possible to identify the concentrations levels of methane and the physical parameters of the flowing gas mixture at each spatial point of the area under examination, for the boundary conditions adopted. The purpose of the tests was to determine whether and to what extent the position of the air duct, which is used to supply fresh air to the mined dog heading, influences methane concentration in this heading. The tests were conducted for an actual mining region in which a dog heading was mined. The input parameters for the model (boundary conditions) were therefore adopted from the actual system. The model-based tests helped to determine the distributions for methane concentration depending on the position of the air duct. The analysis mainly encompassed the distance between the outlet of the air duct and the surface of the mined body of coal. The use of model-based tests which employed numerical methods made it possible to determine a series of significant physical and chemical parameters of the resulting mixture of gases. Their distributions and values in selected points for the variants under analysis have been presented in the paper. The results obtained unambiguously demonstrate that the position of the air duct has a significant impact on the distributions of methane concentration levels in the mined dog heading. In the Authors’ opinion, these results may constitute an essential source of information for service teams responsible for ensuring ventilation-related safety in mines. This is because they allow for predicting the distribution of methane concentration and other parameters of the gas mixture that occurs in dog headings during the mining process.

Calculation of Energy Flow and Carbon Credit Earned in Roof Integrated Photovoltaic Thermal System

In the current paper, analysis has been carried out for a system that has been created on a roof specially designed for semitransparent thermal system. A thermal model has been designed considering quasi-steady state condition to predict the solar cell temperature, tedlar and the temperature at the outlet of duct and room temperature air from room is used as design and electrical parameters. Calculation has been done for electrical and thermal energy outputs at respective places. Finally a comparison has been made between conventional and present system and cost calculation has been calculated. It has been found that for the same system there would be a loss of 6.13 Ton amount of CO2 and a saving of Rs 3,41,390 for 30yrs for the same amount of generation.

Numerical method for prediction of duct break out sound power

The acoustic design of duct systems requires consideration of both the noise propagating within a duct and also of the noise transmitted out through the duct walls into the environment. Control of this breakout noise can form a significant part of a noise control solution, and so understanding this phenomenon can lead to reduced material use. The breakout noise is investigated here using coupled structural-acoustic finite element models. Propagation along a waveguide with constant cross section is represented using a modal expansion of the acoustic pressure in the fluid and displacement in the duct walls. The free-field external environment requires an outer boundary condition, and for this purpose, a perfectly matched layer is applied at some distance from the elastic walls. The finite length of the waveguide is then enforced by coupling the fields to separate infinite length inlet and outlet ducts by the mode matching method. Transmitted power from the finite length duct is investigated when a noise source is placed in the inlet.

Comparison of exhaust duct designs in launch pads for reduction of rocket jet noise

An exhaust duct is commonly installed in a launch pad to reduce the intense noise generated by the rocket exhaust jet at liftoff. In this paper, we investigate the effects of varying the length and shape of the exhaust duct by comparing the noise reduction performance of several different designs. The sub-scale exhaust ducts tested are variations of the original design by Tsutsumi et al. [AIAA Paper 2015-1007], colloquially known as “Seiji’s dog house,” and experiments are performed using cold jets of Mach 1.8 and 3.1, respectively. Linear and semi-circular microphone arrays are employed near the nozzle and at a radial distance of 100 nozzle diameters from the center of the duct outlet. A design guideline as to the length and the outlet shape of the exhaust duct, leading to the best noise reduction performance, is discussed. [This work was conducted at High-Speed Vehicle Research Center of KAIST with the support of the Defense Acquisition Program Administration and the Agency for Defense Development under Contract UD170018CD.]

3D metal printer dust filter structural optimal design and key performance research

To improve the quality of metal 3D printing parts, it is necessary to optimize the structure of the dust collector (guide groove) of the 3D printer. To do this, we applied parametric modeling to design the guide groove, used mold flow simulation to optimize the design of guide groove structure, and finally evaluated guide groove performance by measurement of the contact angles of different materials. The results showed higher modeling efficiency and better guide groove design using parametric modeling combined with mold flow simulation. The turbulence intensity and distribution field were somewhat reduced, the velocity at the outlet was reduced by 3.18%, and the pressure at the inlet was reduced by 38.14% after optimal design. Guide grooves made using PLA or 316L material showed little difference in performance. The outlet of the guide groove was closely fitted with the outlet of the air duct of the 3D printer by tightly attaching the side of the guide groove outlet to the bottom of the printer. This positioning prevented the entry of “solid smoke” and splashed particles, and is an important step towards the improved 3D printing of metal components with high performance.

Distribution Law and Prediction Model of Dust Concentration under Airflow Adjustment in Fully Mechanized Heading Face

The current situation of extensive ventilation management for the fully mechanized heading face cannot dynamically control air velocity and make reasonable dust migration distribution, resulting in serious disaster of dust and environmental pollution in the roadway. In this paper, the fluid mechanics, finite element numerical simulation, and underground measurement were combined to analyze the distribution of dust concentration under the variable airflow state at the duct outlet to obtain the massive correlation data of duct outlet parameters and dust concentration. For the pedestrian breathing-height in the backflow side and driver location, the double-objective BP prediction model for dust concentration under airflow adjustment was established, and the performance parameters and prediction accuracy of the BP prediction model were analyzed by using the relative error and fitting analysis. In Ningtiaota coal mine, located in Northern Shaanxi province of China, the self-developed control device is installed on the duct outlet with underground test and application verification to refine the model. The results indicated the dynamic control of airflow optimizes dust concentration distribution. The dust concentration at the pedestrian breathing-height in the backflow side and driver location was significantly decreased after the installation of adjustment device. Dust concentration at the pedestrian breathing-height and driver location was decreased by 31% and 34%, respectively, compared with the results before adjustment, which achieved the safe, environment-friendly, and energy-saving ventilation and the dust removal function in fully mechanized heading face.

Observational study on the cool breeze effect of a through wall type air conditioner

An air conditioning system has been developed that can select the operation pattern of a through-wall type unit (TWU) according to the air conditioning needs. There is a night-time cool breeze mode like natural ventilation using a fan in modes. The thermal environment and ventilation volume of office buildings can be greatly influenced by outdoor thermal conditions, and it is necessary to grasp the actual conditions. Therefore, in this research, the observational study of thermal environment and ventilation performance was conducted, and was compared and analysed with the simulation result. The cross-section wind velocity distribution was characterized in each area, but the wind velocity in the residential area was about 0.1 to 0.2 m/s, and no draft was seen immediately below the bypass duct outlet. It was almost in agreement with the simulation results. The ventilation performance survey revealed that the windward side was slightly difficult to ventilate. However, there was no big difference in the age of air depending on the location. Moreover, there was no significant difference in the total ventilation volume even if the outdoor thermal conditions were different. It was confirmed that the TWU had expected performance and stable ventilation performance was secured.

Analytical description of the expansion of wall jets of different curvature

The work is devoted to an analytical study of the expansion of wall jets on a convex and concave surfaces (curved semi-limited jets). Such jets have different characteristics depending on the curvature of the surface - from long-range to fast-decay. This makes them one of the most promising areas of increasing the efficiency of air exchange in rooms for various purposes. However, today they have not widespread introduction, which is because of the instability of the development of the jets. The problem is eliminated by using the correct shape of the air outlet duct. To determine the expansion of the jet, an approach has been developed to the analytical description of curved wall jets using the geometric analysis of their turbulent macrostructure. This structure is represented in the form of a sheetof tangent large-scale vortices (puffs). To effectively solve the obtained equations, the Anderson-Björk method was improved. The results show a slight expansion of concave jets and much faster for convex ones. Calculations showed the presence of a critical section with the rapid expansion of a convex jet and the subsequent increased rate of its expansion. Also, a cross section for separation of the jet is obtained. If the slot width is less than 0.15 ... 0.2 of the radius of the wall, then the angle of passage of the jet is significantly reduced, which reduces the expansion of the jet and complicates the design of the multi-slot air distributors developed at the Department of Heat and Gas Supply and Ventilation of Kiev National University of Construction and Architecture.

Coupled characterization and experimental verification of heat transfer and air leakage in a quad-sectional rotary air preheater

Air leakage has a substantial impact on the efficiency of rotary air preheater, and is closely related to their temperature distribution. In this paper, for a quad-sectional rotary air preheater, the coupled model of thermodynamics and air leakage is proposed and verified by the experimental results of a double reheat 1000 MW power generator unit. The air leakage of each chamber, the temperature distribution of the fluid and the matrix can be obtained by using the three-dimensional finite-difference method. On the basis of previous research, the indirect air leakage is considered in the coupled model, as well as the interaction between the heat transfer and the air leakage. The simulation results show that the total air leakage of the quad-sectional air preheater is 33.1% less than that under the tri-sectional preheater condition. Additionally, compared with the experimental results, the difference values of the air leakage rates and the maximum duct outlet temperature are 0.21% and 2.1 °C, respectively, which manifest the model accuracy. The results indicate that, in comparison to previous research methods, this model can accurately obtain the temperature distribution of air preheater.

EVALUATION OF STATIC PRESSURE BEHAVIOR IN AN OSCILLATING WATER COLUMN WAVE ENERGY CONVERTER

The international scenario of non-renewable resources scarcity coupled with increasing energy demand are incentives for the diversification of the world's energy matrix with a focus on renewable energy sources. Among these sources, energy from sea waves is especially attractive because its global resource is estimated around 2 TW, comparable to the average electrical power consumed worldwide each year. There are currently several technologies proposed for the sea wave energy conversion into electricity. Among them it stands out the Oscillating Water Column (OWC) converter, which basically consists of a hydropneumatic chamber and a turbine duct where a turbine is installed. Its chamber is opened below the sea water free surface while the turbine duct outlet is free to atmosphere. Inside the chamber the water free surface oscillating movement produced by the incident waves causes the air to flow through the turbine duct and to activate the turbine, so the OWC principle of operating can be approximated to a cylinder-piston system. Therefore, one of the methodologies used in the computational modeling to simulate the operating principle of this device is the Piston Methodology, which simplifies the problem analysis considering only the air flow through the OWC converter. Among the phenomena that occur within the OWC device, the static pressure behavior is arguably one of the most important because it is through it that it is possible to estimate the hydropneumatic power and the converter efficiency. Thus, the objective of this work is to evaluate the static pressure behavior within the OWC, using the Piston Methodology, by imposing a monochromatic wave boundary condition in an axisymmetric domain. Among the obtained results it was inferred that the static pressure, in this case, depends directly on the flow acceleration and it is strongly influenced by the vorticity generated in domains with a change of area.

Dynamic mode decomposition of the acoustic field in radial compressors

Widely recognized since the beginning of air travel as a major issue, noise reduction remains nowadays a pressing concern for all stakeholders in the aviation industry. While aeroengine compressors, specially at the approach phase, have been historically identified as a leading source of noise, most of the research has been conducted on compressors of the axial type. However, radial compressors are found in a wide array of applications: smaller business jets, helicopters, unmanned aerial vehicles (UAVs), auxiliary power units (APUs), turbochargers for reciprocating engines, etc. Owing to their geometrical particularities, radial compressors feature flow patterns that differ from their axial counterparts, leading to different acoustic performance but also opening the door for different optimization approaches. Yet, classical modal decomposition techniques focused on duct propagation may fail to reveal the complex interactions between geometry and flow features that act as noise sources. In this paper we apply, in addition to the classical approach, a data-driven Dynamic Mode Decomposition (DMD) to pressure data coming from a Detached Eddy Simulation (DES), in which we have experimentally validated the correct reproduction of the modal behaviour of the compressor, thus obtaining in-depth details of the link between flow phenomena and noise generation and transmission across the inlet and outlet ducts.