Exhaust Slot Research Articles

Bleed air CFD modelling in aerodynamic simulation of A heavy duty gas turbine compressor

This study investigates the effects of different bleed air CFD modelling methods on the aerodynamic simulation of a heavy-duty gas turbine multistage compressor with bleed airflow. Two methods, the local source term method and the simplified bleed off-take geometry method, are compared. The results reveal that while overall compressor performance shows minimal variation between the methods, significant differences are observed near the blade tip region. The bleed source term method predicts a more uniform flow field in the bleed cavity, leading to a larger surge margin for the compressor. Therefore, in the analysis of multistage compressors, it is advisable to adopt simplified geometric modeling method for simulating bleed air extraction. Moreover, when utilizing this approach, careful consideration should be given to the choice of the slot inclination angle. This design parameter presents a crucial trade-off between losses within the exhaust structure and those arising from the entry of mainstream flow into the exhaust slot cavity.

Numerical investigation of an inertization system for a radiative coil coating oven

In this work the inertization of a radiative curing oven for coil coating is numerically investigated. Inertization chambers (IC) — comprised by a confined impinging slot jet and an exhaust slot — are applied at the curing oven openings to prevent external air from entering and toxic solvents from exiting the oven, avoiding simultaneously the contamination of the external surroundings and the development of explosive conditions within the oven. The influence of the main IC operating parameters — extracted-to-injected mass flow rate ratio (Ψ), coil plate-to-jet velocity ratio, injection Reynolds number, and oven pressure — on the safety of the sealing process is investigated considering the validated k-kl-ω transition RANS model. To guarantee safety conditions regarding the IC placed at the metal strip entrance, the corresponding range for Ψ was found to be between 0.8 and 1.6 considering oven pressures ranging from −20 to 20Pa. For the IC placed at the metal strip exit and considering high coil velocities, safety conditions can only be observed with negative oven pressures. Overall, this procedure found a Ψ range between 0.8 and 1.2 that complies with the restrictive safety criteria for a realistic oven operation with typical coil velocities and oven pressures ranging from −20 to 10Pa.

Ventilation rate formula for mechanically ventilated broiler houses considering aerodynamics and ventilation operating conditions

Precise ventilation control of broiler houses is essential to effectively exhaust pollutants and attain the required breeding environment. However, the ventilation rate used in practise is always lower than the desired or designed value because of difficulties in measuring the pressure difference between the indoor and outdoor pressure of the facility. In this study, a new formula was developed to estimate the total ventilation rate for mechanically ventilated broiler houses using the number of operating fans and the slot opening rate, both of which are relatively easy to measure in practice. The proposed formula was derived from the in-situ fan performance curve and the discharge coefficient, which represent the ventilation characteristics of the exhaust fans and slot openings respectively. This was evaluated through a field experiment and a computational fluid dynamics (CFD) simulation. The measured ventilation rate was 24.1–26.6% lower than the desired ventilation rate showing that the in-situ fan performance curve was 33.7 Pa lower on average than the designed fan performance curve provided by the manufacturer. The distribution of static pressure in the broiler house was analysed using CFD models and it was found that the new formula could be applied to broiler houses having difference lengths.

Numerical investigation of turbulent mixed convection in an open cavity: Effect of inlet and outlet openings

This paper deals with the numerical investigation of heat transfer by mixed convection inside ventilated cavities with supply and exhaust slots, and filled with air under a steady and turbulent flow regime. Four configurations, rated A, B, C and D are considered here, according to the position of the inlet and outlet air ports: A, the inlet is on the top of the left vertical wall, while the outlet is on the bottom of the right vertical wall; B, the inlet is on the bottom of the left vertical wall and the outlet at the top of the opposite wall; C, the two slots are on the same side, i.e. the inlet is at the bottom and the outlet at the top of the left vertical wall, and D, the inlet is at the top and the outlet at the bottom of the left vertical wall. The bottom of the cavity is kept at a temperature TH and other walls are fixed at a temperature TC, with TH>TC. The cavity is provided with two slots: an inlet slot for introducing fresh air, and an outlet slot to extract hot air. The main aim sought here is to analyze the ventilation efficiency for temperature distribution, and fix the best configuration providing the thermal comfort targeted. We also address the influence of heating on the behavior of flow and thermal comfort, while considering different Rayleigh numbers ranging from 6.4×108 to 3.2×109. Numerical studies have been yet devoted to these configurations, using RANS simulations. The RNG k-ε turbulence model has been adopted for the turbulence closure, and the set of governing equations was then numerically solved via the finite volume method. The SIMPLEC algorithm was associated to ensure the pressure-velocity coupling. In terms of results achieved, the configuration D provides a better ventilation effectiveness for temperature distribution εT and ensures an even temperature in the occupied zone. As for configurations A and C, they maintain an acceptable level of heat and can be used in winter period to ensure good indoor air quality, while configuration B provides an efficiency close to unity and can be used to insure indoor air quality in temperate climate zones.

Surface-Acoustic-Wave-Driven Directional Atomizers Integrated With Pico-Liter Micropumps

In this paper, a surface-acoustic-wave (SAW)-driven atomizer with micropumps was developed. The micropumps consisted of an epoxy-based reservoir with an exhaust slot and a pair of interdigital transducers (IDTs). The liquid supply from the reservoir was controlled by SAW bursts from the IDTs. A microsurge tank was fabricated into the exhaust slot to stabilize the atomization. The transferred liquid was atomized by a pair of arc-shaped IDTs (AS-IDTs). The AS-IDT was optimally designed using optical vibration observations to focus the SAW energy into a single point and enabled high directional atomization. In the operational test of the micropump with water, a transfer rate of 0.24 pl per single burst was confirmed, where the burst signal is operated at 24.1 MHz with a 50% duty cycle, 40-ms period, and 70 Vp_p amplitude. In the water atomization test, we succeeded in ejecting a narrow mist spray from the substrate using a burst signal operating at 23.8 MHz with a 20% duty cycle, 1-ms period, and 50 Vp_p amplitude. The width of the ejected mist spray was 0.7 mm in the vicinity of the substrate, and was maintained at <;1 mm within the ejection height of 8 mm.

Development of the Backflow Model for Simplified Impurity Exhaust in Monte‐Carlo Calculation

AbstractThe Monte‐Carlo (MC) approach has a lot of flexibility in impurity transport modeling in the SOL and divertor region. However, in the divertor plasma simulation with the noble impurity seeding, characteristic time of the impurity transport especially in the sub‐divertor chamber is long because the MC calculation of the impurity gas transport can be finished only by exhaust. The impurity MC calculation for such long exhaust processes is difficult in a series of the iterative calculation of a suite of integrated divertor codes SONIC. In order to overcome such a problem, a backflow model has been developed. Amount of the backflow flux from the sub‐divertor chamber to the divertor region is evaluated in advance, and then simulating impurity flux is injected from the exhaust slot to the divertor region like a backflow. By this model, the MC calculation time is reduced significantly and iterative calculation of SONIC becomes possible within a reasonable calculation time. As a demonstration, the SONIC code with the backflow model has been applied to investigation of power handling in JT‐60SA divertor. The SONIC simulation showed that low divertor heat load (&lt; 10 MW/m2) with the low SOL density (&lt; 1.5 × 1019m–3), which is required in the full non‐inductive current drive scenario, was achieved by the Ar gas puffing of 0.86 Pa m3/s. (© 2014 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Computer-Aided Designs of Die and Thermal Control for Fabrication of A356 Wheels

Horizontal squeeze casting (HSC) is a potential method for casting aluminum alloy wheels. In this study, the process for HSC of an A356 wheel was modeled and simulated. After analysis of the velocity and temperature fields during the casting process, the designs of the die and thermal control were modified and the effects of the design modifications on two key characteristics of HSC were studied: slow filling and squeeze feeding. An increase in the gate size and the use of exhaust slots reduced the tendency for gas to become entrapped. Furthermore, the increase in the gate size and application of thermal control allowed squeeze feeding for the wheel hub to be achieved successfully. Finally, experiments were performed to verify the results of simulation. [doi:10.2320/matertrans.M2013032]

An overview of recent erosion/deposition and hydrogen retention studies in JT-60U

Recent erosion/deposition and hydrogen retention studies in JT-60U have been summarized. Inner divertor tiles were covered by thick redeposited layers, whereas outer divertor tiles eroded, and significant carbon deposition was observed at the outer exhaust slot, i.e. the bottom side of the outer dome wing. The outboard first wall tiles were mostly eroded. The mass balance of carbon erosion and redeposition in the whole vessel is still missing.H+D retention in the redeposited layers on inner divertor tiles correlates well with their thickness, and hydrogen concentration in the layers, (H+D)/C, was uniformly ∼0.03 except for a few μm top surface layers with ∼0.05. Surface D within a few μm in depth was mostly replaced by H owing to H–H (H plasma +H neutral beam injection (NBI)) discharges made for tritium removal, indicating possible T removal by D–D discharges. Rather high D retention was observed on the outer dome wing probably owing to higher energy deuteron implantation originating from NBI.JT-60U seems a good example to reduce carbon deposition as well as tritium retention. Well-aligned tiles with more or less no steps between neighboring tiles in the toroidal and poloidal directions could reduce net erosion and redeposition not only on the plasma-facing surface but also at the plasma-shadowed area. During plasma discharges, the surface temperature in the divertor area becomes higher than the base temperature (600 K), which could reduce tritium retention significantly.

Influence of exhaust hood geometry on the capture efficiency of lateral exhaust and push–pull ventilation systems in surface treatment tanks

AbstractIn a local exhaust ventilation system, where the pollutant or the emitted flows are captured near the generated source, the knowledge of the capture efficiency is necessary to evaluate performance. This article reports a study of the influence of the exhaust hood slot height on the capture efficiency. For this study, the emission of gases and vapors from open surface tanks used in industrial treatments has been simulated in an installation fitted with two ventilation systems: lateral exhaust and push–pull. Several configurations were possible by varying the geometrical and operational conditions. Both qualitative and quantitative evaluations have been performed, the former through observations of the flows using smoke and the latter by using sulfur hexafluoride as tracer gas. The results obtained on capture efficiency for both ventilation systems tested with several exhaust slot height and as a function of the operating flows rates, are presented. It was found that varying the exhaust slot height between 15 and 45 cm had no effect on capture efficiency. The results show that there are no significant differences between the exhaust slots heights tested, although, in the case of 60 cm for lateral exhaust ventilation, the efficiency was slightly lower. © 2008 American Institute of Chemical Engineers Environ Prog, 2008

Analysis of Particle Pumping Using SOLDOR/NEUT2D Code in the JT‐60U Tokamak

AbstractIn order to understand the particle pumping on JT‐60U, we analyze the roles of atomic and molecular processes using SOLDOR/NEUT2D code. A case of short strike point distance shows that most of neutrals produced on the targets go toward the exhaust slot directly. Whereas, neutrals are scattered in the spherically at random for the long distance case by collision processes and a few of them go toward the slot. It is clarified that the incident neutrals to the slot at low ne /high Te divertor plasma condition are dominated by atoms. Those at high ne /low Te condition are dominated by molecules due to elastic collision. (© 2008 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Development of integrated SOL/divertor code and simulation study of the JT-60U/JT-60SA tokamaks

To predict the heat and particle controllability in the divertor of tokamak reactors and to optimize the divertor design, comprehensive simulations by integrated modeling allowing for various physical processes are indispensable. SOL/divertor codes have been developed in the Japan Atomic Energy Agency for the interpretation and the prediction of behaviour of SOL/divertor plasmas, neutrals and impurities. The code system consists of the two-dimensional fluid code SOLDOR, the neutral Monte-Carlo (MC) code NEUT2D and the impurity MC code IMPMC. Their integration code ‘SONIC’ is almost completed and examined to simulate self-consistently the SOL/divertor plasmas in JT-60U. In order to establish the physics modelling used in fluid simulations, the particle simulation code PARASOL has also been developed.Simulation studies using those codes have progressed with the analysis of JT-60U experiments and the divertor designing of JT-60SA (modification program of JT-60U). The X-point multifaceted asymmetric radiation from the edge in the JT-60U experiment is simulated. It is found that the deep penetration of chemically sputtered carbon at the dome causes the large radiation peaking near the X-point. The pumping capability of JT-60SA is evaluated through the simulation. A guideline to enhance the pumping efficiency is obtained in terms of the exhaust slot width and the strike point distance. Transient behaviour of SOL/divertor plasmas after an ELM crash is characterized by the PARASOL simulation; the fast-time-scale heat transport is affected by collisions while the slow-time-scale behaviour is affected by the recycling.

High-beta steady-state research with integrated modeling in the JT-60 Upgrade

Improvement of high-beta performance and its long sustainment was obtained with ferritic steel tiles in the JT-60 Upgrade (JT-60U) [T. Fujita et al., Phys. Plasmas 50, 104 (2005)], which were installed inside the vacuum vessel to reduce fast ion loss by decreasing the toroidal field ripple. When a separation between the plasma surface and the wall was small, high-beta plasmas reached the ideal wall stability limit, i.e., the ideal magnetohydrodynamics stability limit with the wall stabilization. A small rotation velocity of 0.3% of the Alfvén velocity was found to be effective for suppressing the resistive wall mode. Sustainment of the high normalized beta value of βN=2.3 has been extended to 28.6s (∼15 times the current diffusion time) by improvement of the confinement and increase in the net heating power. Based on the research in JT-60U experiments and first-principle simulations, integrated models of core, edge-pedestal, and scrape-off-layer (SOL) divertors were developed, and they clarified complex features of reactor-relevant plasmas. The integrated core plasma model indicated that the small amount of electron cyclotron (EC) current density of about half the bootstrap current density could effectively stabilize the neoclassical tearing mode by the localized EC current accurately aligned to the magnetic island center. The integrated edge-pedestal model clarified that the collisionality dependence of energy loss due to the edge-localized mode was caused by the change in the width of the unstable mode and the SOL transport. The integrated SOL-divertor model clarified the effect of the exhaust slot on the pumping efficiency and the cause of enhanced radiation near the X-point multifaceted asymmetric radiation from edge. Success in these consistent analyses using the integrated code indicates that it is an effective means to investigate complex plasmas and to control the integrated performance.

An Analytical, Numerical, and Experimental Comparison of the Fluid Velocity in the Vicinity of an Open Tank with One and Two Lateral Exhaust Slot Hoods and a Uniform Crossdraft

An Analytical, Numerical, and Experimental Comparison of the Fluid Velocity in the Vicinity of an Open Tank with One and Two Lateral Exhaust Slot Hoods and a Uniform Crossdraft

An analytical, numerical, and experimental comparison of the fluid velocity in the vicinity of an open tank with one and two lateral exhaust slot hoods and a uniform crossdraft

The objective of this research was to compare mathematical models of the fluid velocity in the vicinity of an open tank with lateral slot exhaust. Two approaches were explored: a numerical solution assuming turbulent flow and an analytical solution assuming potential flow. A numerical simulation of the flow field in and around an open surface tank was performed using the commercial software FLUENT. An analytical solution was obtained using two-dimensional potential fluid flow determined using the Schwarz-Christoffel transformation and complex potential theory. The numerical and analytical solutions were compared with numerical solutions and experimental measurements published by others. The numerical solution using FLUENT and the two numerical solutions published by others appear to reflect experimental conditions with equal accuracy. In some regions, the FLUENT solution appears better while in other regions the other two solutions appear better. Differences in geometry and boundary conditions could explain these differences. Greater differences were observed between the FLUENT and CFX-F3D solutions than between the EOL-2D and CFX-F3D solutions. This was unexpected since the geometry, boundary conditions, and turbulence model were more similar in the former case than in the latter. The potential flow solution, while simpler and less computationally intensive than the numerical solutions, resulted in estimates of experimental velocity that were equally as good as those of the numerical solutions. The simplicity and conservative estimates of this model make it useful for estimating exhaust hood flow fields.

A Modified Ventilation Slot Hood for Chemical Drumming Booths

Chemical drumming operations require proper ventilation systems to prevent employee exposure to toxic vapors and aerosols. For a chemical drum filling booth, an inexpensive exhaust slot ventilation system that effectively captures the evolving harmful vapors and aerosols generated during the drum filling operation is described. Rather than the more commonly used open-face slot, an enclosing slot has been designed for emission control. A more than ten-fold reduction in concentration was observed after installing the new control system as compared to that with the dilution ventilation system originally in place. The volumetric exhaust flow rate through the system was one-half that which would have been required for a commonly used slot design. This reduction in exhaust volume was due to partial enclosure of the slot, which reduced the handling of uncontaminated air. This design reduced the capital investment for the fan and operating costs because of reduced energy consumption. Thus, the potential health ha...