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Journal articles on the topic 'Inlet Recirculation'

Author: Grafiati

Published: 4 June 2021

Last updated: 16 February 2022

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Elvery, D. G., and K. Bremhorst. "Wall Pressure and Effective Wall Shear Stresses in Heat Exchanger Tube Inlets With Application to Erosion-Corrosion." Journal of Fluids Engineering 119, no. 4 (1997): 948–53. http://dx.doi.org/10.1115/1.2819522.

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Inclined flow into tube inlets is studied in order to identify flow characteristics associated with enhanced erosion-corrosion rates at tube inlets. Measured wall pressures and shear stresses are presented for inlet flow with inclination angles up to 60 deg for a tube Reynolds number of 71,000. These show that the areas with most potential for wear are located near the reattachment point of the recirculation bubble as well as in regions at the downstream side of the tube inlet. The latter are located opposite the recirculation region but away from the symmetry plane due to strong swirl of the flow in that region. The results are related to erosion-corrosion patterns observed in practice.

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Alpan, K., and W. W. Peng. "Suction Reverse Flow in an Axial-Flow Pump." Journal of Fluids Engineering 113, no. 1 (1991): 90–97. http://dx.doi.org/10.1115/1.2926503.

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Experiments are carried out to determine the effects of different inlet geometries on the onset of suction recirculation and its associated power consumption in an axial-flow pump. The critical flow rate is determined by both the “string” visual technique and “pressure” method. The results are correlated with the inlet area and flow velocity distribution upstream of the impeller. Four different conical covers matching the impeller leading edge are employed to cover the impeller inlet completely or partially. Covering the inlet area reduces the critical flowrate corresponding to the onset of suction recirculation and eliminates all recirculation at higher flowrates. The power consumption associated with the suction recirculation flow for the uncovered impeller is determined by comparing the shaft powers with and without inlet covers. At the shut-off condition, the power is estimated from a comparison with the shaft power measured with the impeller inlet completely covered. Experimental studies conclude that the power consumption due to suction recirculation is mainly controlled by the impeller inlet area and is insensitive to the inlet pipe configuration. At shut-off condition, the power coefficient correlates well with the parameter based on the hydraulic radius of inlet area. At a finite through flowrate the analytical model recommended by Tuzson (1983) is adequate, except for a proportionality coefficient determined from the test data.

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Nithesh, N., and S. Prajwal. "Effect of Splitters in Recirculation Channels on Performance of Turbocharger Compressors Used in Gasoline Engines- A CFD Study." International Journal of Automotive and Mechanical Engineering 16, no. 1 (2019): 6214–29. http://dx.doi.org/10.15282/ijame.16.1.2019.10.0472.

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Turbochargers used in gasoline engines have their compressor outlet directly coupled to the engine inlet via the throttle valve. On sudden closing of the throttle, the compressor outlet is blocked, and the compressed air has no path to exit resulting in a compressor surge. Compressor recirculation valves are used to connect the outlet of the compressor to the inlet to recirculate excess air and thus reduce the compressor surge. Under normal operating conditions, when the valve is closed, the channel connecting the compressor inlet and the valve causes an inlet disturbance resulting in the reduction of compressor efficiency. Hence a steady state CFD analysis of a gasoline engine turbocharger compressor modelled with a recirculation channel at the inlet was conducted. The channel connecting the compressor inlet and the recirculation valve was observed to cause inlet aerodynamic disturbance resulting in a drop in compressor efficiency by 1%. To overcome this problem, splitters were used in recirculation channels and 80% recovery of loss was observed with the use of splitters.

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Liu, Yin Li, and Hao Tang. "Numerical Study on the Interaction Mechanism between Swirl and Reverse Flow Rate in a Twin Swirl Combustor." Advanced Materials Research 960-961 (June 2014): 341–48. http://dx.doi.org/10.4028/www.scientific.net/amr.960-961.341.

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An isothermal flow in a Twin Swirl Combustor (TSC) was simulated with the Renormalized Group (RNG) k-ε turbulence model. The swirling and recirculation intensity was studied under different structures and inlet conditions. The results confirmed that there was a significant negative correlation between the trend lines of the swirl number (S) and reversed flow rate (Xr). The gradient of reversed flow rate was larger in the front and middle parts of the combustor than that of swirl number. The end-surface-inlet structure had a better swirl and recirculation enhancement effect. With the end-surface-inlet structure, the internal swirl and reverse intensity could be flexibly adjusted by switching the swirl intensity of the primary air. Under the structure of staggered-inlet, there was a critical distance between primary and secondary air inlets. When exceeded, it would be more difficult to enhance the swirl and reverse flow effect by increasing the swirl intensity of the secondary air.

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Lipej, Andrej, and Dusko Mitrusevski. "Numerical Prediction of Inlet Recirculation in Pumps." International Journal of Fluid Machinery and Systems 9, no. 3 (2016): 277–86. http://dx.doi.org/10.5293/ijfms.2016.9.3.277.

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Zhou, Yu, Yuan Huang, and Zhongqiang Mu. "Large eddy simulation of the influence of synthetic inlet turbulence on a practical aeroengine combustor with counter-rotating swirler." Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 233, no. 3 (2017): 978–90. http://dx.doi.org/10.1177/0954410017745900.

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To study the influence of inlet turbulence on the prediction of flow structure in practical aeroengine combustor, large eddy simulation with dynamic Smagorinsky subgrid model is used to explore the complex unsteady flow field in a single burner of a typical aeroengine combustor with two-stage counter-rotating swirler. The complex geometric configuration including all film cooling holes is fully simulated without any conventional simplification in order to reduce the modeling errors. First, unsteady process that flow developing from static to statistically stationary state is fully simulated under laminar inlet condition to obtain a fundamental understanding of flow characteristics in the combustor. Afterwards, synthetic eddy method is utilized to generate a turbulent inlet condition so that a perturbation with about 5% turbulence intensity is superimposed to the inlet plane. Simulation result shows that for the laminar inflow case, flow separation occurs in the near-wall region of the diffusion section, inducing a boundary layer transition and consequently introducing turbulence with nonuniformity in space before the swirler. In contrast, synthesized inflow generated under turbulent inlet condition by synthetic eddy method is more spatially homogeneous. Time-averaged flow field inside the swirler cup reveals that turbulent inflow ultimately causes the swirling flow with higher rotating speed in central region and more uniform distribution along the circumferential direction. It also enhances the transverse jet flow from primary holes and reverse flow in the central recirculation zone, and makes streamlines corresponding to the recirculation vortices more symmetrical on central profile. Maximum recirculating velocity predicted in central recirculation zone is −27.65 m/s and −17.86 m/s in turbulent and laminar case respectively, and corresponding total pressure recovery coefficient is 96.03% and 96.81%.

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Ali, M., and T. Fujiwara. "A numerical study on the mixing of air and hydrogen in a scramjet combustor." Aeronautical Journal 109, no. 1097 (2005): 325–35. http://dx.doi.org/10.1017/s0001924000000774.

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Abstract A numerical study on mixing of air and hydrogen is performed by solving two-dimensional full Navier-Stokes equations. The main stream is air of Mach 5 entering through the configured inlet of the combustor and gaseous hydrogen is injected from the configured jet on the side wall. Supersonic mixing and diffusion mechanisms of a transverse hydrogen jet in two-dimensional finite air streams have been analyzed and discussed. The computed results are compared with the experimental data and show good agreement. For an otherwise fixed combustor geometry, the air inlet width and injection angle are varied to study the physics of mixing and flow field characteristics. On the effect of inlet width variation, two competing phenomena have been observed: (i) upstream of injector the strength of recirculation is higher for wider inlet and consequently the mixing increases, and (ii) downstream, the diffusion of hydrogen decreases with the increase of inlet width and eventually mixing decreases. As a result, in far downstream the mixing efficiency increases up to certain inlet width and then decreases for further increment of inlet width. For the variation of injection angle results show that upstream of injector the mixing is dominated by recirculation and downstream the mixing is dominated by mass concentration of hydrogen. Upstream recirculation is dominant for injecting angle 60° and 90°. Incorporating the various effects, perpendicular injection shows the maximum mixing efficiency and its large upstream recirculation region has a good flame holding capability.

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Claveau-Mallet, Dominique, Félix Lida, and Yves Comeau. "Improving phosphorus removal of conventional septic tanks by a recirculating steel slag filter." Water Quality Research Journal 50, no. 3 (2015): 211–18. http://dx.doi.org/10.2166/wqrjc.2015.045.

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The objective of this project was to increase the phosphorus (P) retention capacity of a conventional septic tank by adding a recirculating slag filter. Two recirculation modes and recirculation ratios from 5 to 50% were tested in the laboratory with reconstituted domestic wastewater. The best system was recirculation from the end to the inlet of the second compartment of a septic tank with a 50% recirculation ratio in the slag filter, achieving 4.2 and 1.9 mg P/L at the effluent for total phosphorus (TP) and orthophosphate (o-PO4), respectively, and a pH of 8.8. The calculated size of the slag filter for a two-bedroom house application was 1,875 kg for an expected lifetime of 2 years. The 1 mg P/L level goal was not reached, but P precipitation may be favoured by the relatively high effluent pH reaching the infiltration bed.

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Yang, Ce, Yingjun Wang, Dazhong Lao, Ding Tong, Longyu Wei, and Yixiong Liu. "Investigation on inlet recirculation characteristics of double suction centrifugal compressor with unsymmetrical inlet." Journal of Thermal Science 25, no. 4 (2016): 312–24. http://dx.doi.org/10.1007/s11630-016-0866-7.

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Yuan, Jian Ping, Wei Sun, Long Yan Wang, and Yun Liang. "Numerical Simulation Research on Vortex Characteristics of Centrifugal Pump Inlet Recirculation." Advanced Materials Research 468-471 (February 2012): 2235–40. http://dx.doi.org/10.4028/www.scientific.net/amr.468-471.2235.

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The 3-D steady turbulent flow in a centrifugal pump under different conditions was simulated by ANSYS CFX software. The intensity, location and the morphology of the inlet recirculation vortex were analyzed using standard k-ε turbulent model through steady simulation. Based on the results, the turbulent flow in the impeller inlet was simulated by Large Eddy Simulation. The dynamic characters and the whole changing process of the recirculation vortex during the rotation of the impeller were analyzed. The results indicate that the critical flow rate of the recirculation onset is 0.7Qd. As the flow rate decreases, the size and the intensity of the recirculation vortex increase and the vortex partially block the flow passage. The vortex first appears in the passage which passes by the outlet section of the volute. During one rotating, the vortex undergoes a whole process of onset, developing, decreasing and disappearing. As the relative speed and the pressure gradient change under different conditions, the vortices present different morphologies.

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Charles, R. E., and G. S. Samuelsen. "An Experimental Data Base for the Computational Fluid Dynamics of Combustors." Journal of Engineering for Gas Turbines and Power 111, no. 1 (1989): 11–14. http://dx.doi.org/10.1115/1.3240208.

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A model axisymmetric gas-fired can combustor is used to (1) establish the sensitivity of the aerodynamic and thermal structure to inlet boundary conditions, and (2) thereby establish a demanding and comprehensive data base for the computational fluid dynamics of combustors. The parameters varied include fuel injection angle and inlet configuration. Detailed characterizations of the aerodynamic and thermal flowfields are accomplished using two-color laser anemometry and a Type R thermocouple, respectively. Specific results show that the reactor operation is especially sensitive to modest changes in both the inlet geometry and fuel injection angle. For example, the addition of a step expansion significantly alters the size and location of the swirl-induced toroidal recirculation zone. Further, the use of the step expansion, in combination with the injection of fuel matched to the swirl aerodynamics, transforms the recirculation zone to an on-axis structure. The addition of a divergent inlet further enhances the effectiveness of the backmixing by enlarging the recirculation zone. The data base developed for these conditions is carefully documented and provides a comprehensive challenge for the computational fluid dynamics of combustors.

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Janic, Todor, Sasa Igic, Nebojsa Dedovic, Darijan Pavlovic, Jan Turan, and Aleksandar Sedlar. "Thermal power of small scale manually fed boiler." Thermal Science 19, no. 1 (2015): 329–40. http://dx.doi.org/10.2298/tsci130104046j.

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This study reviews test results of the combustion of square soybean straw bales used as fuel in manually fed boiler with nominal thermal power of 120 kWth. The influence of the mass flow rate (180, 265, 350, 435, and 520 kg h-1) of inlet air and flue gas recirculation (0%, 16.5%, and 33%) fed to the boiler furnace was continuously monitored. Direct method was used for determination of the boiler thermal power. Correlation between boiler thermal power and bale residence time has been observed and simple empirical equation has been derived. General conclusions are as follows: the increase of the flow rate of inlet air passing through the boiler furnace results in decrease of the bale residence time and increase of the boiler thermal power. Share of the flue gas recirculation of 16.5% increases bale residence time and decreases average boiler thermal power in all regimes except in the regime with inlet air flow rate of 265 kg h-1. In regime with 0% flue gas recirculation boiler thermal power was higher than nominal in regimes with 435 and 520 kg h-1 inlet air flow rates. In regimes having inlet air mass flow rate of 350 kg h-1 boiler thermal power is equal to the nominal power of 120 kWth.

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Leichtfuß, Sebastian, Johannes Bühler, Heinz-Peter Schiffer, Patrick Peters, and Michael Hanna. "A Casing Treatment with Axial Grooves for Centrifugal Compressors." International Journal of Turbomachinery, Propulsion and Power 4, no. 3 (2019): 27. http://dx.doi.org/10.3390/ijtpp4030027.

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This paper provides an investigation of a casing treatment (CT) approach for pressure ratio improvements of centrifugal compressors between peak efficiency and surge. Results were experimentally verified for a variety of automotive turbocharger compressors and analyzed with 3D CFD. The CT design is an adaptation from an axial high-pressure compressor, which was successfully applied and intensively investigated in recent years. The aerodynamic working principle of the applied CT design and the achievable improvements are shown and described. The demand of operating range for automotive applications typically dictates high inlet shroud to outlet radius ratio (high trim) and past experiences indicate that a recirculation zone is formed in the inducer for those centrifugal compressors. This recirculation at the inlet shroud causes losses, a massive blockage and induces a co-rotating swirl at the inlet of the impeller. The result is a reduced pressure ratio, often leading to flat speed lines between the onset of recirculation and surge. This paper provides an understanding of inducer recirculation, its impacts and suggests countermeasures. The CT design for centrifugal compressors only influences flow locally at the inducer and prevents recirculation. It differs substantially in design and functionality from the classical bleed slot system commonly used to increase operating range. An experimental and CFD comparison between these designs is presented. While the classical bleed slot system often provides a massive increase in operating range, it often fails to increase the pressure ratio between onset of inducer recirculation and surge. In contrast, the CT design achieves a gain in pressure ratio near surge.

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Liśkiewicz, Grzegorz, Kirill Kabalyk, Andrzej Jaeschke, et al. "Unstable Flow Structures Present at Different Rotational Velocities of the Centrifugal Compressor." Energies 13, no. 16 (2020): 4146. http://dx.doi.org/10.3390/en13164146.

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Unstable flow structures cause inevitable energy losses in all power energy systems, including turbomachines. In this study, a set of analyses was conducted with the use of spectral maps on the pressure signals obtained from an industrial centrifugal compressor. The spectral maps provide one a detailed visualization of the flow conditions present in the machine along the performance curve and to distinguish the flow phenomena present prior to the surge. The method accuracy is especially useful in detecting the inlet recirculation. The study was conducted at four impeller rotational speeds with varying loads imposed by a valve at the outlet. At each speed, the machine experienced different stages of unstable flow conditions prior to the surge. Five main frequency peaks that appeared in all cases were identified and discussed. The surge was observed at all impeller speeds. At lower ones, however, it appeared at higher valve closures. At higher speeds, the surge was much more intense. The study has also shown that the inlet recirculation appears also for the closed-type industrial impeller. The phenomenon was present in all conditions. The higher impeller speed, the faster onset of the inlet recirculation was. This structure has a strong potential for an early instability warning because it appears in various types of impellers, has a very particular spectral structure and its positioning is very predictable. This study gives another example of the inlet recirculation universality and potential for efficient anti-surge protection.

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White, Kevin D. "Enhancement of nitrogen removal in subsurface flow constructed wetlands employing a 2-stage configuration, an unsaturated zone, and recirculation." Water Science and Technology 32, no. 3 (1995): 59–67. http://dx.doi.org/10.2166/wst.1995.0126.

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Constructed wetland technology is currently evolving into an acceptable, economically competitive alternative for many wastewater treatment applications. Although showing great promise for removing carbonaceous materials from wastewater, wetland systems have not been as successful at nitrification. This is primarily due to oxygen limitations. Nitrification does occur in conventional wetland treatment systems, but typically requires long hydraulic retention times. This paper describes a study that first evaluated the capability of subsurface flow constructed wetlands to treat a high strength seafood processor wastewater and then evaluated passive aeration configurations and effluent recirculation with respect to nitrogen treatment efficiency. The first stage of a 2-stage wetland treatment system exhibited a relatively short hydraulic retention time and was designed for BOD removal only. The second stage wetland employed an unsaturated inlet zone and effluent recirculation to enhance nitrification. Results indicate that organic loading, and thus BOD removal, in the first stage wetland is key to optimal nitrification. Passive aeration through an unsaturated inlet zone and recirculation achieved up to 65-70 per cent ammonia nitrogen removal at hydraulic retention times of about 3.5 days. Inlet zone configuration and effluent recirculation is shown to enhance the nitrogen removal capability of constructed wetland treatment systems.

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Borghei, Leila, and Ramin Haghighi Khoshkho. "Effects of Wind on Hot Air Recirculation (HAR) Behavior." Applied Mechanics and Materials 110-116 (October 2011): 2067–74. http://dx.doi.org/10.4028/www.scientific.net/amm.110-116.2067.

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The air-cooled condenser system is impacted greatly by many factors such as the wind speed, the direction of wind and arrangement of site equipments. This paper concentrates on the hot air recirculation phenomenon and its dependence on ambient winds are numerically simulated by using the computational fluid dynamics code, FLUENT. In this paper, two different wind directions (case A and case B) and wind speeds are considered: Results show that the hot air recirculation increases with the increment of velocity speed. Case A has a critical wind direction angle. Wind causes an air temperature increase at the fan inlet due to hot air recirculation, resulting in the deterioration of the heat transfer performance. The hot air recirculation is the main factor responsible for the reduction of heat rejection rate. In case A, fan inlet temperature is higher than case B. The peak value of the HAR occurs at 9 m/s in case A.

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Hunt, Martin, Shawn Clark, and Rob Tkach. "Velocity distributions near the inlet of corrugated steel pipe culverts." Canadian Journal of Civil Engineering 39, no. 12 (2012): 1243–51. http://dx.doi.org/10.1139/l2012-112.

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This paper presents the findings of a study examining the velocity field within the inlet region of a corrugated steel pipe (CSP) culvert model with vertical headwall, 45° wingwall, and projecting end inlet treatments. Also examined are the effects of embedding the culvert below the stream bed and backfilling the culvert with granular material. Three-dimensional velocity distributions were measured in an effort to better understand how these inlet treatments may affect fish passage. The study examined velocity structure within a CSP culvert with a diameter of 0.8 m at a flow rate of 0.175 m3/s. Measurements were recorded using acoustic Doppler velocimeters at four locations; 0.25, 0.5, 1, and 2 diameters downstream of the inlet. The velocity field of each inlet configuration was dominated by a central jet of high velocity flow surrounded by a low velocity recirculation zone. Analysis of the percent area less than Uavg for each inlet treatment found that the projecting end configuration contained the largest low velocity zone. The usefulness of the low velocity recirculation zone as a fish passage corridor may however be limited by the presence of significant vertical and spanwise velocities as well as high shear zones.

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Ladommatos, N., S. M. Adelhalim, H. Zhao, and Z. Hu. "The effects of carbon dioxide in exhaust gas recirculation on diesel engine emissions." Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering 212, no. 1 (1998): 25–42. http://dx.doi.org/10.1243/0954407981525777.

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The investigation was conducted on a high-speed direct injection diesel engine and was concerned with the effects of exhaust gas recirculation (EGR) on diesel engine combustion and emissions. In particular, the effects of carbon dioxide (CO2), a principal constituent of EGR, on combustion and emissions were analysed and quantified experimentally. The use of CO2 to displace oxygen (O2) in the inlet air resulted in: reduction in the O2 supplied to the engine (dilution effect), increased inlet charge thermal capacity (thermal effect), and, potentially, participation of the CO2 in the combustion process (chemical effect). In a separate series of tests the temperature of the engine inlet charge was raised gradually in order to simulate the effect of mixing hot EGR with engine inlet air. Finally, tests were carried out during which the CO2 added to the engine air flow increased the charge mass flowrate to the engine, rather than displacing some of the O2 in the inlet air. It was found that when CO2 displaced O2 in the inlet charge, both the chemical and thermal effects on exhaust emissions were small. However, the dilution effect was substantial, and resulted in very large reductions in exhaust oxides of nitrogen (NO x) at the expense of higher particulate and unburned hydrocarbon (uHC) emissions. Higher inlet charge temperature increased exhaust NO x and particulate emissions, but reduced uHC emissions. Finally, when CO2 was additional to the inlet air charge (rather than displacing O2), large reductions in NOx were recorded with little increase in particulate emissions.

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Ladommatos, N., S. Abdelhalim, and H. Zhao. "The effects of exhaust gas recirculation on diesel combustion and emissions." International Journal of Engine Research 1, no. 1 (2000): 107–26. http://dx.doi.org/10.1243/1468087001545290.

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An investigation was conducted with the aim of identifying and quantifying the effects of exhaust gas recirculation (EGR) on diesel engine combustion and exhaust emissions. Five effects of EGR were identified and investigated experimentally: the reduction in oxygen supply to the engine, participation in the combustion process of carbon dioxide and water vapour present in the EGR, increase in the specific heat capacity of the engine inlet charge, increased inlet charge temperature and reduction in the inlet charge mass flowrate arising from the use of hot EGR. The experimental methodology developed allowed each one of these effects to be investigated and quantified separately. The investigation was carried out on a high-speed, direct injection diesel engine, running at an intermediate speed and load. A limited number of tests were also conducted in an optically accessible diesel engine, which established the effects of EGR on local flame temperature. Finally, tests were conducted with simulated EGR being used additionally to the engine air supply. This contrasts with the conventional use of EGR, whereby EGR replaces some of the air supplied to the engine. It was found that the first effect of EGR (reduction in the oxygen flowrate to the engine) was substantial and resulted in very large reductions in exhaust NOx at the expense of higher particulate emissions. The second and third effects (participation of carbon dioxide and water vapour in the combustion process and increase in the charge specific heat capacity) were almost insignificant. The fourth effect (higher inlet charge temperature) increased both exhaust NOx and particulate emissions. The fifth effect (reduction in the inlet charge due to thermal throttling) reduced NOx but raised particulate emission. Finally, when EGR was used additionally to the inlet air charge (rather than displacing air), substantial reductions in NOx were recorded with little increase in particulate emission.

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Yedidiah, S. "Certain Effects of Recirculation on Cavitation in Centrifugal Pumps." Proceedings of the Institution of Mechanical Engineers, Part A: Power and Process Engineering 200, no. 4 (1986): 283–92. http://dx.doi.org/10.1243/pime_proc_1986_200_037_02.

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Ladommatos, N., S. M. Abdelhalim, and H. Zhao. "Effects of exhaust gas recirculation temperature on diesel engine combustion and emissions." Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering 212, no. 6 (1998): 479–500. http://dx.doi.org/10.1243/0954407981526127.

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When hot exhaust gas is mixed with inlet air, the charge to a diesel engine is modified in three ways: the charge temperature increases, the total charge mass is reduced and the charge composition changes. This paper is concerned with the effects on combustion and pollutant emissions of only the first two items. The last item has been investigated by the authors previously and reported in references [1-4]. The investigation was conducted on a high-speed direct-injection diesel engine at about 40 per cent of full load, 2000 r/min and constant fuelling rate. The investigation included in-cylinder heat release and exhaust gas analysis. It was found that increasing inlet charge temperature, at constant inlet charge mass and composition, increased oxides of nitrogen (NO x) and particulate exhaust emissions but reduced unburnt hydrocarbon (UHC) emissions. When the inlet charge mass was reduced at constant inlet temperature, the exhaust particulates and UHC emissions increased substantially, principally because the oxygen available for combustion was reduced. In contrast, NO x emissions increased only slightly, probably because the effects on NO x of a higher combustion peak temperature tended to be offset by substantially lower oxygen availability.

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Shelef, Gedaliah, and Adam Kanarek. "Stabilization ponds with recirculation." Water Science and Technology 31, no. 12 (1995): 389–97. http://dx.doi.org/10.2166/wst.1995.0507.

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The first facultative pond in a series of stabilization ponds, or else the first part of a large pond, is sensitive to organic overloading creating anoxic or anaerobic conditions at the pond's surface, resulting in malodors and nuisances. Such adverse characteristics are usually manifested seasonally when climatic conditions change to lower temperatures and/or reduced solar irradiance. The design organic loadings on such ponds are therefore determined by the critical season and they are lowered accordingly. Introducing recirculation of effluent from a later pond in the series (usually from the second or third pond) back to the inlet of the first one, at a ratio of 1.0 - 2.5 (recirculated effluent) to 1 (raw sewage influent), can be most advantageous, as follows: (1) organic loadings on the first facultative pond in the series can reach 400-600 kg BOD5 per hectare per day (khd) during summer time and 300-400 khd as a yearly average, compared with a yearly average of 60-140 khd on ordinary facultative ponds, while still maintaining odor-free facultative conditions; (2) reseeding the first pond with active adapted algal biomass; (3) mixing the influent (which is often septic) with oxygen-rich recirculated effluent, thus enhancing the biological process in the first pond and suppressing septic odors, and (4) the increased inlet flow (by combining influent flow with the recirculated effluent) increases the area of solids (sludge) settling in the first pond. Altogether, the recirculation is manifested by reduced land requirements, better stability in pond operation, improved pond's performance and reduction or elimination of malodors and nuisances. Step feeding of the ponds further accentuates the effect of recirculation. Obviously, recirculation requires pumping (low head), energy, piping and connection to a power supply. The cost of operation and maintenance amount to US $0.01-0.02 per cubic metre of treated wastes. The advantages of recirculation nevertheless significantly outweigh the added costs. The paper describes the experience and data which have been gathered during the operation of 120 hectares of ponds with recirculation in the Dan Region (Greater Tel-Aviv) over a period of almost 20 years.

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Kao, Hsiao C. "Turbulent Flow in Two-Inlet Channels." Journal of Fluids Engineering 115, no. 4 (1993): 638–45. http://dx.doi.org/10.1115/1.2910192.

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The problem of turbulent flows in two-inlet channels has been studied numerically by solving the Reynolds-averaged Navier-Stokes equations with the k–ε model in a mapped domain. Both the high Reynolds number and the low Reynolds number form were used for this purpose. In general, the former predicts a weaker and smaller recirculation zone than the latter. Comparisons with experimental data, when applicable, were also made. The bulk of the present computations used, however, the high Reynolds number form to correlate different geometries and inflow conditions with the flow properties after turning.

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YANG, Ce. "Inlet Recirculation Influence to the Flow Structure of Centrifugal Impeller." Chinese Journal of Mechanical Engineering 23, no. 05 (2010): 647. http://dx.doi.org/10.3901/cjme.2010.05.647.

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Newburn, E. Ryan, and Ajay K. Agrawal. "Liquid Fuel Combustion Using Heat Recirculation Through Annular Porous Media." Journal of Engineering for Gas Turbines and Power 129, no. 4 (2007): 914–19. http://dx.doi.org/10.1115/1.2719259.

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A counter-flow annular heat recirculating burner was designed for lean prevaporized, premixed combustion. Prior to entering the combustor, the reactants are passed through a porous media-filled preheating annulus surrounding the combustor. Kerosene is dripped by gravity onto the porous media and vaporized by the heat conducted through the combustor wall. Experiments were conducted to evaluate heat transfer and combustion performance at various equivalence ratios, heat release rates, and inlet air temperatures. Results show low CO emissions over a range of equivalence ratios. NOx emissions were high at high heat release rates, indicating inadequate prevaporization and premixing of fuel with air. Heat recirculation and heat loss characteristics are presented at various operating conditions.

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Sakaguchi, D., MT Tun, R. Numakura, and BT Wang. "Global optimization of recirculation flow type casing treatment in centrifugal compressors of turbochargers." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 232, no. 24 (2016): 4461–71. http://dx.doi.org/10.1177/0954406216679435.

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This paper describes a global optimization of a recirculation flow type casing treatment in centrifugal compressors of turbochargers. The global optimization for the recirculating flow type casing treatment has been performed based on the existing casing treatment. The optimization approach to the recirculation flow type casing treatment for the centrifugal compressor, incorporating meta-model assisted evolutionary algorithm, computational fluid dynamics analysis technique, artificial neural network, and genetic algorithms has been presented. For the baseline design of the casing treatment, numerical approach is validated with an experimental result from a test rig. The technical issue of the casing treatment is found to be the dropping of the adiabatic efficiency at smaller flow rate condition. In this study, the objective of the optimization is to improve adiabatic efficiency under multipoint mass flow rate conditions. The shape of the casing treatment has been parameterized by six parameters. The numerical optimization result gives the optimized recirculation casing shape, which has a possibility to improve the efficiency not only at design flow rate but also at smaller flow rate. The improvement in adiabatic efficiency at off-design point is discussed by means of the improved flow incidence at the inlet of the rotating impeller. The influence on adiabatic efficiencies at both design and off-design conditions is discussed by the sensitivity of the recirculation flow rate. It is found that the optimized design of the casing treatment provides optimized recirculation flow rate.

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Omar, Mohd Amal Asrol, Wirachman Wisnoe, and Azman Bakri. "Flow Characteristics of a Servco Fume Cupboard." Applied Mechanics and Materials 393 (September 2013): 753–58. http://dx.doi.org/10.4028/www.scientific.net/amm.393.753.

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A fume cupboard is equipment used to carry out chemical reaction process in its working chamber. A suction fan takes air or gas from the working chamber and releases it outside. When the air or gas is flowing from the inlet to the outlet, some recirculation zones may be formed depending on the internal shape design of the fume cupboard. This recirculation zone may create back flow that can be the cause of leakage. Leakage happens when airborne contaminants escape through inlet of the fume cupboard to the user breathing zone and the surrounding air in the room. To have a good fume cupboard, the recirculation zone needs to be minimised. In this paper, the flow characteristic of a Servco fume cupboard will be presented as a result of computational fluid dynamics (CFD) simulation using κ-ω turbulence model. The results are presented in terms of velocity components at different cross sections of the fume cupboard.

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Ammad ud Din, Syed, Weilin Zhuge, Panpan Song, and Yangjun Zhang. "A method of turbocharger design optimization for a diesel engine with exhaust gas recirculation." Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering 233, no. 10 (2018): 2572–84. http://dx.doi.org/10.1177/0954407018802560.

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Downsizing a diesel engine using turbocharger and coupling it with exhaust gas recirculation is the recent trend to improve engine performance and emission control. For diesel engines, it is important to match a turbocharger that meets both the low-speed torque and high-speed power requirements. This article presents a method of turbocharger design optimization for a turbocharged diesel engine equipped with exhaust gas recirculation, on the basis of parametric study of turbocharger geometry. Turbocharger through-flow model along with one-dimensional engine model is used to study the effect of key geometric parameters of the compressor and turbine on engine brake torque, brake-specific fuel consumption, air flowrate and cylinder peak temperature. For compressor, the research emphasizes on impeller inlet relative diameter, inlet blade tip angle, impeller exit blade angle and exit blade height, while for turbine parameters such as volute throat area, inlet blade height, inlet diameter, outlet diameter and rotor exit blade angle are taken into account. Results show that in case of compressor, engine performance is sensitive to the inlet relative diameter, inlet blade angle and exit blade angle. In case of turbine, volute throat area, inlet blade height and inlet diameter have vital effect on engine performance. On the basis of results, an optimized turbocharger design is developed. Comparison shows prominent improvement in turbocharger maps and engine performance. Compressor maximum efficiency and pressure ratio are increased from 73% to 77% and 3.166 to 3.305, respectively. Most importantly, the area of compressor maximum efficiency zone is increased considerably. Also turbine efficiency is increased from 71.42% to 76.94%. As a result, engine torque and air flowrate are increased up to 5.26% and 8.31%, respectively, while brake-specific fuel consumption and cylinder peak temperature are decreased up to 5.00% and 4.31%, respectively.

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Takahashi, Shirou, Kenichi Nihei, Satoshi Kanno, Shoji Hayashi, Kouji Shiina, and Minoru Ootaka. "ICONE15-10244 DEVELOPMENT OF COOLING TECHNIQUES FOR INDUCTION HEATING STRESS IMPROVEMENT OF REACTOR RECIRCULATION INLET NOZZLE." Proceedings of the International Conference on Nuclear Engineering (ICONE) 2007.15 (2007): _ICONE1510. http://dx.doi.org/10.1299/jsmeicone.2007.15._icone1510_121.

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Azami, Vahid, and Mortaza Yari. "Comparison Between Conventional Design and Cathode Gas Recirculation Design of a Direct-Syngas Solid Oxide Fuel Cell–Gas Turbine Hybrid Systems Part I: Design Performance." International Journal of Renewable Energy Development 6, no. 2 (2017): 127. http://dx.doi.org/10.14710/ijred.6.2.127-136.

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In this paper, a conventional SOFC–GT hybrid system and an SOFC–GT hybrid system with cathode gas recirculation system fuelled with syngas as the main source of energy were analyzed and their performances were compared. In the conventional SOFC–GT hybrid system the incoming air to the cathode is heated at the air recuperator and air preheater to meet the required cathode inlet temperature while in the SOFC–GT hybrid system with cathode gas recirculation, in addition to the air recuperator and air preheater, also the recirculation of the cathode exhaust gas is used to meet the required cathode inlet temperature. The system performances have been analyzed by means of models developed with the computer program Cycle–Tempo. A complete model of the SOFC–GT hybrid system with these two configurations evaluated in terms of energy and exergy efficiencies and their performance characteristics were compared. Simulation results show that the electrical energy and exergy efficiencies achieved in the cathode gas recirculation plant (64.76% and 66.28%, respectively) are significantly higher than those obtained in the conventional plant (54.53% and 55.8%).Keywords: Solid oxide fuel cell, Gas turbine, Cathode gas recirculation, Exergy.Article History: Received Feb 23rd 2017; Received in revised form May 26th 2017; Accepted June 1st 2017; Available onlineHow to Cite This Article: Azami, V, and Yari, M. (2017) Comparison between conventional design and cathode gas recirculation design of a direct-syngas solid oxide fuel cell–gas turbine hybrid systems part I: Design performance. International Journal of Renewable Energy Develeopment, 6(2), 127-136.https://doi.org/10.14710/ijred.6.2.127-136

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Morrison, G. L., R. E. DeOtte, and H. D. Thames. "Turbulence Measurements of High Shear Flow Fields in a Turbomachine Seal Configuration." Journal of Tribology 115, no. 4 (1993): 670–77. http://dx.doi.org/10.1115/1.2921692.

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The mean velocity and Reynolds stress tensor throughout a whirling annular seal are presented. The data were collected with a three-dimensional laser Doppler velocimeter using phase averaging. Two axial flow conditions (Re = 12,000 and 24,000) were studied at one shaft speed (Ta = 6,600). The eccentricity and whirl ratios were 50 percent and 100 percent, respectively. There is a region of high axial momentum at the inlet on the pressure side of the clearance that migrates around the seal to the suction side at the exit. The normalized axial momentum in this region is higher in the low Reynolds number case due to an axial recirculation zone that occurs on the suction side of the rotor at the inlet. The recirculation zone does not occur in the high Reynolds number case. At both Reynolds numbers there is a recirculation zone on the rotor surface in the pressure side of the inlet. This recirculation zone extends from 20 to 200 deg past the rotor zenith in the tangential direction, and is one third of a clearance wide radially. The high Reynolds number circulation zone is 1.5 mean clearances long, while the low Reynolds number zone extends two mean clearances downstream. When compared to previous studies, it is apparent that the tangential momentum is no greater for a seal with whirl than for one without if other parameters are constant. Areas of high tangential momentum occur in the clearance where the axial momentum is low. Average exit plane tangential velocities in the low Reynolds number case are 1.5 times greater than those in the other flow case. These results are in general agreement with predictions made by other investigators.

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Salvage, J. W. "Variable Geometry Pipe Diffusers." Journal of Turbomachinery 119, no. 4 (1997): 831–38. http://dx.doi.org/10.1115/1.2841194.

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Theoretical analyses and experimental results are reported for two unique variable geometry techniques used with pipe diffusers to enhance off-design performance. One technique mechanically closes the diffuser throat in an unusual manner. The other allows flow recirculation to close the throat artificially while attempting to improve diffuser inlet flow characteristics. Results clearly show that surge margin may be significantly improved by either method and that flow recirculation may offer improved efficiency.

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Hu, T.-F., and Y.-Y. Hsu. "On the Turbulent Flow Downstream of a Partly Opened Throttle Valve." Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 208, no. 4 (1994): 213–22. http://dx.doi.org/10.1243/pime_proc_1994_208_122_02.

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Experimental measurements were performed in a model inlet pipe on the turbulent flow downstream of the throttle valve of a commercial motorcycle carburettor. The inlet pipe was made of a section of straight plexiglass tube to facilitate the access of hot-wire and pressure probes. Continuous dry air was drawn into the model to establish the flow. The flow downstream of the partly opened throttle valve is found composed of a recirculation region, a three-dimensional jet stream and a wall boundary layer. Complex turbulent flow interactions among the recirculation region, the jet stream and the boundary layer are observed. This study clearly demonstrates that the jet stream, which includes a major portion of the flow going downstream, shows similarity of axial velocity profiles on planes normal to the angular direction.

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ISHIDA, Masahiro, Taufan SURANA, Tsuyoshi SAKAGUCHI, Tetsuhiro FUKUNAGA, and Hironobu UEKI. "Effect of Inlet Recirculation on Inducer Stall in a Centrifugal Blower." Proceedings of Conference of Kyushu Branch 2003.56 (2003): 127–28. http://dx.doi.org/10.1299/jsmekyushu.2003.56.127.

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Johnson, B. V., S. J. Markowski, and H. M. Craig. "Cold Flow and Combustion Experiments With a New Burner Air Distribution Concept." Journal of Engineering for Gas Turbines and Power 108, no. 2 (1986): 370–75. http://dx.doi.org/10.1115/1.3239913.

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Experiments were conducted with a JT8D-engine sized can combustor modified such that all the combustion and dilution air entered through the burner front face from a single plenum through counter-rotating annular swirlers. Cold flow experiments were conducted to visualize and to develop a mixing and recirculation flow pattern within the combustor which contained annular and central recirculation cells and featured rapid mixing in the downstream section of the combustor. Laser velocimeter measurements, downstream of the air inlet configuration used in the combustion experiments, showed the largest velocity gradients in the radial direction were in the tangential velocity profile. Low-pressure combustion experiments were conducted with three flat spray fuel nozzle orientations and three air inlet geometries to determine the general air inlet and fuel injection characteristics required to produce acceptable combustion characteristics with the selected swirler configuration. The combustion experiments included emission, total pressure and total temperature measurements at the burner exit plane. Low emission levels and temperature pattern factors with relatively low burner pressure losses were demonstrated.

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Krishnamoorthi, M., and R. Malayalamurthi. "Effect of exhaust gas recirculation and charge inlet temperature on performance, combustion, and emission characteristics of diesel engine with bael oil blends." Energy & Environment 29, no. 3 (2018): 372–91. http://dx.doi.org/10.1177/0958305x17748888.

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The threat of fossil fuel depletion and augmented environmental pollution caused by diesel fleets can be curbed by adopting suitable fuel and engine modifications. In the present work, effects of engine speed (r/min), injection timing, injection pressure and compression ratio on performance and emission characteristics of a compression ignition engine were investigated. The ternary test fuel of 65% diesel + 25% bael oil + 10% diethyl ether has been used, where the tests have been conducted at different charge inlet temperature and exhaust gas recirculation. All the experiments were conducted at the trade-off engine load that is 75% engine load. When the diesel engine operating with 320 K charge inlet temperature, brake thermal efficiency has been improved to 28.6%. Meanwhile reduced emission levels of carbon monoxide (0.025%) and hydrocarbon (12.3 ppm) were observed during the engine operation with 320 K charge inlet temperature and compression ratio of 18:1. The oxides of nitrogen have been reduced to 226 ppm at 16:1 compression ratio with 30% exhaust gas recirculation mode.

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Takeuchi, Jinya, Takashi Kurabuchi, Hajime Yoshino, and Sihwan Lee. "Performance comparison of conventional and local computer room air-conditioning systems in data centres by CFD analysis." Indoor and Built Environment 26, no. 2 (2016): 238–47. http://dx.doi.org/10.1177/1420326x16674250.

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The maximum inlet air temperature and air recirculation ratio of information technology machines are important in evaluating the air-conditioning efficiency of data centres. In this study, evaluation models for estimating air and heat distributions were developed based on the thermal equilibrium in data centres, assuming conventional computer room air-conditioning and local computer room air-conditioning systems. The computer room air-conditioning cooling efficiency ( η-index) was defined as the ratio of the effective cooling air volume of an information technology machine to the air volume of the computer room air-conditioning system. The recirculation ratio for an information technology machine ( γ-index) was defined based on the air volume and thermal equilibrium. Several factors affecting air-conditioning efficiency, such as the mounting positions and heat load of the information technology machines and the ratio of the computer room air-conditioning system air volume to that of the information technology machine ( V/Vm-index), were analysed using computational fluid dynamics. A mismatch was confirmed between the heat recirculation ratio ( γm-index) and air recirculation ratio ( γq-index), and the effect of heat transmission by the wall could be ignored in data centres. The mean γ values and inlet air temperatures ( θ0 m-index) could be reduced effectively by increasing the value of V/Vm and mounting the information technology machines at the bottom of each rack.

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Duan, Cuie, Weizhen Lu, Yunwei Zhang, and Zhaolin Gu. "A new urban canopy parameterization scheme for wind environment simulations." Indoor and Built Environment 27, no. 3 (2017): 402–22. http://dx.doi.org/10.1177/1420326x17741338.

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This paper concerns urban canopies populated with tall slender buildings. To clarify the controlling factors of urban canopies, we simulated a series of single high-rise buildings under fully developed turbulence at a realistic scale by large-eddy simulation. We then analysed correlations between the drag force and recirculation area, frontal area, surface area, floor area, porosity and inlet velocity. Our results show that the recirculation length and recirculation area were proportional to the width, height and wind speed, but were inversely proportional to the length of a building. New equations for the recirculation length and area are presented. The maximum error of the recirculation length equation was 6.66%, and the maximum error of the recirculation area equation was 7.49%. The drag source characteristic length was found to be proportional to the recirculation area, frontal area and surface area and inversely proportional to the porosity and height, but was not closely related to floor area. A new local scale drag source model was developed and applied to a complex urban canopy of Xi’an. The model was applied to 7 × 7 buildings and show good agreement with the solid wall simulation results.

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Pordal, H. S., P. K. Khosla, and S. G. Rubin. "A Flux-Split Solution Procedure for Unsteady Inlet Flow Calculations." Journal of Fluids Engineering 114, no. 2 (1992): 198–204. http://dx.doi.org/10.1115/1.2910016.

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The solution of the reduced Navier Stokes (RNS) equations is considered using a flux-split procedure. Unsteady flow in a two dimensional engine inlet is computed. The problems of unstart and restart are investigated. A sparse matrix direct solver combined with a domain decomposition strategy is used to compute the unsteady flow field. Strong shock-boundary layer interaction, time varying shocks, and time varying recirculation regions are efficiently captured.

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Du, Li Ming, and Yi Zhao Gong. "Prediction and Analysis of Performance of a Centrifugal Compressor with Casing Treatment under Multiple Working Conditions." Applied Mechanics and Materials 448-453 (October 2013): 3434–39. http://dx.doi.org/10.4028/www.scientific.net/amm.448-453.3434.

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As an effective and economic technique for flow range enhancement, casing treatment is widely employed to increase stability margin of compressors. In order to explore the effectiveness of casing treatment on performance of centrifugal compressor under multi-working conditions, in the present thesis, numerical analysis of three kinds of inlet recirculation casing treatment and a smooth untreated casing compressor models were carried out. The numerical results coincide well with the experimental data of optimal model and accurately predict the position of surge line, which verifies the reliability of numerical method which applied in this thesis. The results also indicate that, only reasonable configuration of the inlet recirculation casing treatment could significantly enlargement the stable operating range of the compressor at low flow rate under all rotation speeds. In addition, the slot position and front deflector baffle of the casing treatment have a great impact on its performance.

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Ishida, Mashiro, Taufan Surana, Hironobu Ueki, and Daisaku Sakaguchi. "Suppression of Unstable Flow at Small Flow Rates in a Centrifugal Blower by Controlling Tip Leakage Flow and Reverse Flow." Journal of Turbomachinery 127, no. 1 (2005): 76–83. http://dx.doi.org/10.1115/1.1811092.

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The effects of the inlet recirculation arrangement on inducer stall and the diffuser width on diffuser stall in a high-specific-speed-type centrifugal impeller with inducer were analyzed by numerical simulation and also verified experimentally. It was found that the incipient unstable flow occurs due to a rolling-up vortex flow, resulting from an interaction between the tip leakage flow and the reverse flow accumulated at the pressure side immediately downstream of the inducer tip throat, in which a strong streamwise component of vorticity is included. By forming the inlet recirculation flow, the tip leakage vortex is effectively sucked into the suction ring groove, and the flow incidence is decreased simultaneously. The unstable flow range of the test blower was reduced significantly by about 45% without deteriorating the impeller characteristics by implementing optimally both the ring groove arrangement and the narrowed diffuser width.

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Hunziker, R., and G. Gyarmathy. "The Operational Stability of a Centrifugal Compressor and Its Dependence on the Characteristics of the Subcomponents." Journal of Turbomachinery 116, no. 2 (1994): 250–59. http://dx.doi.org/10.1115/1.2928359.

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A centrifugal compressor was tested with three different diffusers with circular-arc vanes. The vane inlet angle was varied from 15 to 30 deg. Detailed static wall pressure measurements show that the pressure field in the diffuser inlet is very sensitive to flow rate. The stability limit regularly occurred at the flow rate giving the maximum pressure rise for the overall stage. Mild surge arises as a dynamic instability of the compression system. The analysis of the pressure rise characteristic of each individual subcomponent (impeller, diffuser inlet, diffuser channel,...) reveals their contribution to the overall pressure rise. The diffuser channels play an inherently destabilizing role while the impeller and the diffuser inlet are typically stabilizing. The stability limit was mainly determined by a change in the characteristic of the diffuser inlet. Further, the stability limit was found to be independent of the development of inducer-tip recirculation.

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Legrand, J., P. Legentilhomme, and G. Lefèbvre. "Analyse de la turbulence pariétale de l'écoulement annulaire tourbillonnaire non entretenu généré par une entrée tangentielle du fluide." Canadian Journal of Physics 78, no. 8 (2000): 779–801. http://dx.doi.org/10.1139/p00-052.

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This work is dedicated to an experimental study of the wall shear stress in a turbulent swirling decaying flow induced by means of a tangential inlet in an annular cell. The flow pattern near both cylinders of the annulus is analyzed by means of measurements of wall velocity gradients using an electrochemical method involving micro-electrodes working in inert wall. The analysis of the axial and circumferential evolutions of the mean wall velocity gradient and of its power spectral density emphasizes the complexity and highly three-dimensional nature of the flow pattern of the annular swirling decaying flow induced by means of a single tangential inlet. Near the inner wall of the annulus, a recirculating zone, consisting of several pairs of contra-rotating cells, develops following the main helical motion of the fluid along the flow path. Near the external wall of the annular cell, high local velocities and energetic turbulent structures are detected in the vicinity of the tangential inlet. These eddies rapidly decay along the flow path because of the decrease of the swirl intensity. The setup of a recirculation bubble near the inner wall induces a quasi-axisymmetric flow behavior at the outer cylinder of the annulus. Near both walls, the power spectral densities of the velocity gradient reveal a superposition of small turbulent eddies having a low energetic level in the high-frequency domain.

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Ljung, Anna-Lena, L. Robin Andersson, Anders G. Andersson, T. Staffan Lundström, and Mats Eriksson. "Modelling the Evaporation Rate in an Impingement Jet Dryer with Multiple Nozzles." International Journal of Chemical Engineering 2017 (2017): 1–9. http://dx.doi.org/10.1155/2017/5784627.

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Impinging jets are often used in industry to dry, cool, or heat items. In this work, a two-dimensional Computational Fluid Dynamics model is created to model an impingement jet dryer with a total of 9 pairs of nozzles that dries sheets of metal. Different methods to model the evaporation rate are studied, as well as the influence of recirculating the outlet air. For the studied conditions, the simulations show that the difference in evaporation rate between single- and two-component treatment of moist air is only around 5%, hence indicating that drying can be predicted with a simplified model where vapor is included as a nonreacting scalar. Furthermore, the humidity of the inlet air, as determined from the degree of recirculating outlet air, has a strong effect on the water evaporation rate. Results show that the metal sheet is dry at the exit if 85% of the air is recirculated, while approximately only 60% of the water has evaporated at a recirculation of 92,5%.

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Hallett, W. L. H. "A Simple Model for the Critical Swirl in a Swirling Sudden Expansion Flow." Journal of Fluids Engineering 110, no. 2 (1988): 155–60. http://dx.doi.org/10.1115/1.3243528.

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A simple momentum integral model for estimating the minimum or “critical” swirl intensity required to produce central recirculation in a swirling sudden expansion flow is presented. An explicit equation is given for the critical swirl as a function of expansion ratio and inlet velocity profile shape, the latter expressed by the radius of the solid body vortex core and a parameter describing an axial velocity maximum or minimum on the axis. The model is tested against experimental data for expansion diameter ratios from 1.25 to 3.0 and a variety of inlet conditions, and found to give good predictions.

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Bortolet, P., E. Merlet, and S. Boverie. "Fuzzy modeling and control of an engine air inlet with exhaust gas recirculation." Control Engineering Practice 7, no. 10 (1999): 1269–77. http://dx.doi.org/10.1016/s0967-0661(99)00092-1.

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Bortolet, P., E. Merlet, and S. Boverie. "Fuzzy Modeling and Control of an Engine Air Inlet with Exhaust Gas Recirculation." IFAC Proceedings Volumes 31, no. 2 (1998): 71–77. http://dx.doi.org/10.1016/s1474-6670(17)44175-9.

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AOKI, Masanori, and Akira GOTO. "Positively Sloped Head-Flow Characteristics and Inlet Recirculation of a Mixed-Flow Pump." Transactions of the Japan Society of Mechanical Engineers Series B 62, no. 596 (1996): 1442–47. http://dx.doi.org/10.1299/kikaib.62.1442.

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Dong, Haotian, Dawei Wan, Minghua Liu, Tiefeng Chen, Shasha Gao, and Yuanbin Zhao. "Evaluation of the Hot Air Recirculation Effect and Relevant Empirical Formulae Applicability for Mechanical Draft Wet Cooling Towers." Energies 13, no. 13 (2020): 3347. http://dx.doi.org/10.3390/en13133347.

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Due to the hot air recirculation, the inlet air enthalpy h1 of mechanical draft wet cooling towers (MCTs) was usually greater than the ambient air enthalpy ha. To realize the cooling performance and accurate design of MCTs, this paper clarified the feasibility of the inlet air enthalpy empirical formula presented by the Cooling Technology Institute (CTI) of the USA. A three-dimensional (3D) numerical model was established for a representative power plant, with full consideration of MCTs and adjacent main workshops, which were validated by design data and published test results. By numerical simulation, the influence of different wind directions and wind speeds on hot air recirculation (HAR) and the influence of HAR on the cooling performance of the MCTs were qualitatively studied based on the concept of hot air recirculation rate (HRR), and the correction value of HRR was compared with the calculated value of the CTI standard. The evaluation coefficient ηh, representing the ratio of the corrected value to the calculated value was introduced to evaluate the applicability of the CTI formula. It was found that HAR was more sensitive to ambient crosswind, and an increase in HRR would deteriorate the tower cooling performance. When the crosswind speed increased from 0 to 15 m/s, ηh, changed from 2.42 to 80.18, and the calculation error increased accordingly. It can be concluded that the CTI empirical HRR formula should be corrected when there are large buildings around the MCTs, especially under high-speed ambient crosswind conditions.

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Budwig, R., D. Elger, H. Hooper, and J. Slippy. "Steady Flow in Abdominal Aortic Aneurysm Models." Journal of Biomechanical Engineering 115, no. 4A (1993): 418–23. http://dx.doi.org/10.1115/1.2895506.

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Steady flow in abdominal aortic aneurysm models has been examined for four aneurysm sizes over Reynolds numbers from 500 to 2600. The Reynolds number is based on entrance tube diameter, and the inlet condition is fully developed flow. Experimental and numerical methods have been used to determine: (i) the overall features of the flow, (ii) the stresses on the aneurysm walls in laminar flow, and (iii) the onset and characteristics of turbulent flow. The laminar flow field is characterized by a jet of fluid (passing directly through the aneurysm) surrounded by a recirculating vortex. The wall shear stress magnitude in the recirculation zone is about ten times less than in the entrance tube. Both wall shear stress and wall normal stress profiles exhibit large magnitude peaks near the reattachment point at the distal end of the aneurysm. The onset of turbulence in the model is intermittent for 2000 < Re < 2500. The results demonstrate that a slug of turbulence in the entrance tube grows much more rapidly in the aneurysm than in a corresponding length of uniform cross section pipe. When turbulence is present in the aneurysm the recirculation zone breaks down and the wall shear stress returns to a magnitude comparable to that in the entrance tube.

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