Air Suction Rate Research Articles

Performance Assessment of Venturi-Assisted Confined Tube Aerators with Varying Diameter

A significant amount of energy in wastewater treatment plants is spent on aeration to treat the organic matter with microorganisms in an oxygen-enriched environment. In this study, a novel and simplistic aeration concept known as Confined Tube Aeration (CTA) is proposed, in which the main elements are a Venturi injector and a coiled tube at its outlet. Two Venturi injector diameters were chosen for evaluation in this study, measuring 1 inch (25.4 mm) and 4 inch (101.6 mm). In this study, a relationship was developed between air suction rate and pressure differential across the injector. Then, a numerical model was developed to analyze hydrodynamic conditions and evaluate system performance. The main findings are that the larger diameter aerator performs 20% better than the smaller injector in terms of standard aeration efficiency (SAE), with a maximal value of 0.74 kgO2/kWh found for the larger diameter system. These results suggest that future SAE improvements may be made for larger diameter systems in full-scale wastewater treatment applications with suitably designed injectors.

Numerical study of an infrared suppression (IRS) device with cooling hole configuration on the mixing tube

Hot walls of the infrared suppression (IRS) device intensify the infrared signature of warships, which is detrimental for attaining infrared stealth. In this work, to effectively reduce the wall temperature, hole cooling technology is innovatively adopted on a marine IRS device. Circular holes are arranged on the mixing tube of the device. Numerical simulations are conducted to predict the temperature and flow distribution. The current research comprehensively analyzes the effects of hole position, number of hole rows, and number of holes on the wall temperature of the mixing tube and heat shield. The air suction rate and the exit temperature of the whole device are considered as well. The results indicate that the air suction and exit temperature of the device do not significantly change with the hole arrangement parameters. As the hole position moves towards the mixing tube outlet, the average temperature of the mixing tube continuously increases, while the maximum temperature of the mixing tube exhibits a peak-and-valley pattern. When the holes with large diameters are located near the mixing tube inlet, a backflow occurs between the mixing tube and the heat shield, causing the heat shield temperature to rise appreciably. Increasing the number of hole rows can reduce the mixing tube temperature, but excessive hole rows lead to an elevation in the heat shield temperature. The optimal configuration for the number of hole rows is found to be 2 with a hole diameter of 80 mm. With the increment in hole number, the average temperature of the mixing tube rises due to the accelerated disappearance of the streamwise vortices behind the holes; however, the maximum temperature of the mixing tube shows a decreasing-then-increasing trend owing to that more streamwise vortices are created. This study paves the way for the practical application of hole cooling technology on marine IRS devices. The findings can provide instructive suggestions for the arrangement of cooling holes.

Numerical simulation and application of entrainment dust collector for fully mechanized mining support based on orthogonal test method

In order to alleviate the dust pollution in the fully mechanized mining face, the novel negative pressure entrainment dust collector was optimized by the method of orthogonal experimental design and numerical simulation. The influences of nozzle distance, throat diameter and diffusion angle on the atomization efficiency of the proposed dust collector was investigated. The obtained results showed that the optimum ejection dust removal performance of the developed negative pressure entrainment dust collector was obtained for throat diameter 80 mm, throat distance 60 mm and diffusion angle 20 degrees. Under these conditions, air suction rate at the entrance of contraction section was 17.48 m3/min and the average droplet size and mass concentration were 62.99 μm and 0.034 kg/m3, respectively. Here, we have proposed a local closed atomization control dust removal technology for hydraulic support areas based on the optimized negative pressure entrainment dust collector. After the application of the developed system in 2307 fully mechanized mining face in Tangkou Coal Mine, the average total dust of measuring points was decreased from 337.90 to 49.53 mg/m3 and average exhaust dust was decreased from 271.80 to 41.40 mg/m3. The average dust removal rates of total dust and exhaled dust were 85.17% and 84.74% respectively, and dust removal efficiency of the proposed system was obviously confirmed.

Determination of atmospheric sulphur dioxide and sulphuric acid traces by indirect flame atomic absorption method

A new indirect method has been developed for the determination of sulphuric acid and sulphur dioxide by flame atomic absorption spectrometry, thereby extending the range of application of AAS to some non-metallic substances. Under certain atomization conditions in air-acetylene flame, the absorbance signal of some alkali earth metal salts, such as magnesium shows significant dependence from the anions present. For instance, Mg(ClO4)2 produces almost ten times higher absorbance than MgSO4 in the same concentration, and this phenomenon is due to the thermal differences of these alkali earth salts. When sulphuric acid is added to Mg(ClO4)2 solutions, a continuously decreasing FAAS calibration series is obtained. Using this method unknown sulphuric acid concentration can be determined in samples. The presence of other acids - except phosphoric acid - does not interfere, since they are evaporated during the dry aerosol formation in the flame.The limit of detection for sulphuric acid and sulphur dioxide is 22 µg/m3 and 14 µg/m3. The limit of detection for the obtained solution is 0.11 mg/L and 0.07 mg/L for sulphuric acid and sulphur dioxide using 50 min sampling time at 1 L/min air suction rate into 10 ml appropriate liquid, respectively (enrichment factor = 5000 with respect to volume). The linear range is 0.5 – 5.0 mg/L.The recovery of spiked samples are 98%. The SO2 and SO32− salts can be similarly determined by this method based on the quantitative absorption of SO2 in H2O2, which yields sulphuric acid. The sulphate content of the solutions was determined by turbidimetric and ion chromatographic methods and the results were in good agreement with the developed method.

Investigation of the dust control performance of a new transverse-flow air curtain soft-sealing system

On account of certain technological requirements, it is difficult for some industrial processes that generate dust to be sealed in a fixed pattern and ventilated for dust discharge, mainly automatic welding, pressure casting, wood processing, and crop production, which has become a significant bottleneck in dust control. The present study developed a transverse-flow soft-sealing dust control system, in which four novel air curtain generators were arranged in a square pattern within the region where dust was generated to create end-to-end planar transverse-flow air curtains and achieve soft sealing. The air suction inlet was placed centrally above the area where dust was generated; under the suction airflow, the dusty air was gradually diluted and driven away to effectively suppress dust escape. The flow field characteristics in the area where dust was generated and the performance of the developed sealing system in controlling fine smoke dust were qualitatively analyzed using a tracing experiment with smoke dust. Tracing experimental results on leaf powder qualitatively reveal directional dust control of large dust particles. Moreover, the dust control efficiency was evaluated under different conditions to quantitatively investigate the effects of air curtain outlet velocity, exhaust-to-pressure ratio, and jet angle. The results show that with a greater air supply and air suction rate, the airflow exhibited a more obvious entrainment effect and stronger dust exhaust and discharge, and simultaneously, the formed tracing smoke column had a clearer boundary. At an air curtain outlet velocity of 6.27–8.39 m/s and a corresponding air supply rate of 17.00–22.57 m3/min, a stable air curtain was formed, which achieved remarkable dust control at an exhaust-to-pressure ratio of 0.8–1.0. With an increase in the air curtain jet angle, the dust control efficiency of the system first increased but subsequently decreased. In the present study, the appropriate air curtain jet angle was 10–20° for the developed soft-sealing system. In conclusion, when the air curtain outlet velocity, exhaust-to-pressure ratio, and jet angle were 6.27 m/s, 0.6, and 15°, respectively, the dust control efficiency of the developed soft-sealing system reached 92.6%.

마이크로버블 발생을 위한 벤추리 노즐 형상 연구

Microbubble is a part of advanced water treatment technologies, and there are several ways for microbubble generation. A strategy using Venturi (convergent-divergent) nozzle with air-suction holes has advantage of energy and time saving compared with the others. Here, we used 3D printer to make the various nozzle geometries in order to understand two-phase flow in the Venturi nozzle and air-breaking mechanism. It was evaluated the effects of convergent and divergent angles independently on air-suction rate and pressure drop, and the two-phase flow (air bubbles and liquid water) were observed. The convergent angle strongly affect the air-suction rate corresponding with increase of pressure drop. Meanwhile, as the divergent angle increased, it became dominant the minor loss by sudden enlargement of flow area, so that the air-suction rate and pressure drop showed decreased.

Numerical investigation of maximum air entrainment into cylindrical louvered pipe

The main approach behind the present numerical investigation is to estimate the air flow rate into the pipe through the louvers from the atmosphere. The present numerical investigation has been performed by solving conservation equations of mass, momentum, and energy along with two equation-based k-ɛ models for a louvered horizontal cylindrical pipe by the finite volume method. The existing experimental results of a wall constraint jet have been matched with the numerical results. The numerical computations show that the air suction rate into the pipe increased with the increase in the louvers opening area and number of nozzles used. With all other parameters remain fixed, an optimum protrusion of the nozzle was found where the suction rate was found to be the highest for a given nozzle flow rate. It was also found from the numerical investigation that there exists an optimum pipe diameter corresponding to the three times of nozzle diameter where the maximum air suction rate was achieved.

Performance of Roasted Cocoa Bean Winnower For Small Holder Chocolate Producers

Cocoa bean winnowing has a function to separate cocoa nibs from shell after roasting process of dry bean. Nibs are further processed into fine cocoa liquor by refining process. The aim of this experiment was to evaluate working performance of a home-scale winnower to separate shell from nibs with minimum shell parchment content in cocoa nibs. This experiment was conducted in Postharvest Laboratory at the Indonesian Coffee and Cocoa Research Institute using roasted cocoa bean grade A according to standard of SNI 2323:2008/ Amd1:2010 with shell content of 15% originated from Forastero cocoa. Working performance of the home-scale winnower was evaluated based on shell parchment content in the output, its capacity, energy consumption and power transfer efficiency value by several air suction rates as variable. Data were analyzed using regression and variance analysis to evaluate the influence of the rate and to determine the optimum machine operation. Results of regression and variance analysis from winnowing experiment with air suction rate of 0.54 m/s; 0.63 m/s; 0.72 m/s and 0.90 m/s indicated that shell parchment content in cocoa nibs and power transfer efficiency value were affected by the rate. The optimum machine performance was obtained on 0.72 m/s of air suction rate with total winnowing capacity was 2.615 kg/hour, energy consumption of 132 Watt, power transfer efficiency value of 61.01% and shell parchment content was 1.06%. Shell parchment content in cocoa nibs was appropriate regarding to the SNI standard with maximum content of 1.75%.

Effect of Pipe Configurations on Air Entrainment into a Louvered Cylindrical Pipe: A Comparison between Open and Close Entrance of a Pipe

The present numerical study was performed by solving conservation equations of mass, momentum and energy along with two equation based k-ɛ model for a louvered horizontal cylindrical pipe by finite volume method. It was found that pipe air suction increased with increase in opening area and number of nozzles for both pipe configurations. Increasing the pipe diameter made air suction more effective in pipe configuration B (open entrance of the pipe). o C) directly into the atmosphere is causing various environmental problems like smog formation and constant increase in atmospheric temperature. If the exhaust gases can be cooled, then the environment can be protected from its adverse effects. The cooling of exhaust gases can be done by sucking fresh air from the atmosphere through louvers of the pipe. Some research work was conducted in the past both theoretically and experimentally to overcome the harmful effects of release of hot exhaust gas. Han and Mungal (2001) in their study found that the increase in co-flow speed reduces the entrainment for both reacting and non-reacting jets. They also found that the entrainment in the near field of reacting jets was reduced by a factor of 2.5 due to the heat release effect. Mishra and Dash (2010) in their numerical investigation found that air suction rate is enhanced with increase in louvers opening area but independent of number of louvers per row. Singh et. al. (2010) found in their research that the ratio of tube diameter and inlet jet diameter along with the ratio of free stream air density to density of air at jet inlet condition were the main factors that influenced the entrainment and mixing. Barik et al. (2014) in an experimental and numerical investigation on air entrainment in infra-red suppression device found that the entrainment rate was reduced by 19.2% as the ratio of funnel overlap height and nozzle diameter changed from 0 to 1.6. Singh et al. (2003) in an experimental investigation found that non circular jets provided greater entrainment and mixing with ambient fluid than circular jets. They concluded that by shifting the location of jet, the entrainment was enhanced by 30%. The work found in the literature does not site the use of CFD methods to determine the effect of various parameters on mass suction rate of air into a horizontal louvered pipe for a vehicle, and hence the present work is done to arrive at the optimum design of the pipe by investigating fluid flow and heat transfer characteristics. The study is carried out assuming exhaust pipe as the nozzle and hot air as the nozzle fluid and treated to be incompressible. We have attempted to match the existing experiment results of Singh et. al. (2003) with the present computational methods. II. Mathematical Formulation A cylindrical pipe of diameter DP and length LP was used to carry out the computational investigation. The pipe is closed at the entrance end and its exit end is open to the surrounding atmosphere for Configuration A whereas for Configuration B, both the ends of the pipe are open to the atmosphere. A nozzle of diameter Dn having a protrusion length LPt (into the pipe), is located at the centre of the entrance face of the pipe. A cylindrical computational domain of diameter DCD (about 6 times of DP) and length LCD (about 3 times of LP) is placed around the pipe so that the boundary conditions can be applied on the computational domain for the air to be sucked in by the louvers in the pipe. The louvers are made in circular shape (Dh = 0.03 m). A total of 12 louvers are placed in each stack with a distance of 0.5 m being maintained between each stack. The flow field in the domain is computed by using three- dimensional, incompressible Navier-Stokes equations and a standard two equation k-e turbulence model with energy equation. The two equation k-e turbulence model is believed to give the correct results for such Re flows. The fluid used for simulation is air at 343 K with a mass flow rate of 0.02 kg/s at nozzle outlet for every case and is treated as incompressible. Steel is declared as the solid material used for all the walls used for the present numerical research. Governing Equations

Maximum Air Suction Into a Louvered Funnel Through Optimum Design

The rate of air suction into a louvered cylindrical funnel with lateral openings has been computed numerically by solving the equations of conservation of mass, momentum, and energy along with the two k-z turbulence closure equations. It was found that the air suction rate into a louvered funnel can be maximum for an optimum nozzle protrusion length into the funnel irrespective of the nozzle fluid temperature. There also exists an optimum funnel diameter (irrespective of the nozzle fluid temperature) and funnel height for which the air suction rate can be the maximum. Keeping the volume of the funnel constant, the shape of the funnel was changed to a frustum. It was found that an inverted frustum with a value of r1/r2 = 0.8 could suck the maximum amount of air compared to a cylindrical funnel of the same volume. The cylindrical sucking funnel has interestingly a much shorter entrance length compared to a simple pipe flow case with the same entrance Reynolds number. The entrance length for the sucking funnel is also a function of the nozzle fluid temperature, and a simple relation for the entrance length as a function of Ren and Tn/T∞ could also be developed for a sucking funnel. Numerical experiments were done for an inclined funnel to compute the mass suction into it. It was found that for Gr/Re2 ≤ 0.4 (where Gr is the Grashof number and Re is the Reynolds number) given by the funnel inclination had no effect on the rate of mass suction while for 0.4 < Gr/Re2 < 1 the funnel inclination had marginal influence. As the value of Gr/Re2 increased beyond 1 the influence of the funnel inclination on rate of mass suction was found to be significant.

Numerical investigation of air suction through the louvers of a funnel due to high velocity air jet

The present investigation predicts the suction flow rate from the atmosphere through the louvers of a funnel (used in naval and merchant ships) when the high velocity exhaust comes out from a nozzle or a set of nozzles placed inside the funnel. Conservation equations of mass and momentum have been solved for the funnel with a surrounding computational domain so that the suction can take place at the louvers entry. The resulting equations have been solved numerically using finite volume technique in an unstructured grid employing eddy viscosity based two equation k- ε turbulence model. It has been found from the computation that the air suction rate into the funnel increases with the increase in louvers opening area, nozzle flow rate and height of the funnel. There exists optimum protrusion of the nozzle into the funnel for which maximum suction of air can be achieved with a prescribed nozzle flow rate and all other parameters of the funnel remaining fixed. Similarly there also exists optimum funnel diameter where the suction rate of air becomes the highest with all other parameters remaining fixed. There also exists optimum louver opening area on the funnel where the suction rate becomes the maximum as a function of the funnel diameter. The inclination of the funnel with respect to the vertical has no effect on mass ingress of air into it. An optimum nozzle diameter could be decided for a particular funnel diameter by considering the funnel suction rate and the back pressure developed by the nozzle per meter length of the pipe containing the nozzle (intersection of the two curves gives the optimum point of operation).

Composting of vegetable waste

The effects of the aeration, seeding, and agitation on the composting of vegetable waste were studied in a laboratory-scale reactor. Experimental results showed that the final product at the end of a 4-day composting period met multiple maturity indices suggested by many researchers. The evolution of carbon dioxide during the composting process could be modelled with a modified Gompertz equation that described the bacteria growth successfully. Multivariate regression analysis was used to study the effects of operating parameters on the carbon conversion. The response surface contour plots were constructed using the regression equation for the examination of the dependence of carbon conversion on operating parameters. The maximum carbon conversion of 14.54% was obtained when the percentage of seeding was set at 14.5%, the air suction rate was set at 2.6 L kg(-1) dry-solid min(-1), and the agitator operated half of the time, alternating on and off for every 5 min. Future work will focus on the application of the data and the experience gained in this work to composters of pilot and semi-commercial scales.

Thermophilic composting of food waste

A laboratory reactor was designed to study the effects of operating parameters (air suction rate, seeding and agitation) on the composting process of a synthetic food waste made of dog food. Experimental results showed that the synthetic food waste could be composted within 4 days and the final compost passed the maturity tests. In most cases except those with 32% of seeding, the process involved two major stages of composting. The two peak temperatures between 50 and 60 °C occurred at 8–12th hour and 50–65th hour, respectively. Operating parameters that converted the most volatile solids and carbons in the feedstock were as follows: 1.6 l air/kg dry solid-min of air suction rate, 32% of seeding and 50% of agitation time.

Hydrodynamics and microbial physiology affecting performance of a new MBR, membrane-coupled high-performance compact reactor

In this study, hydrodynamics and physiology of microorganisms were investigated in a new type membrane bioreactor, MHCR, which is a membrane coupled HCR (High performance Compact Reactor) having very high COD removal efficiency. The degree of interference caused by inserting a submerged membrane was evaluated quantitatively by measuring the air suction rate and overall oxygen transfer coefficient ( k L,a ). Despite such interference, MHCR showed greater oxygen transfer efficiency than HCR under particular hydrodynamic conditions. Higher recirculation rate generally resulted in a higher turbulence and thus alleviated membrane fouling. When the recirculation rate was too high however, the microbial flocs were broken by fluid shear and membrane permeability was decreased rapidly. All these results were elucidated through not only physicochemical but also microbiological factors.

Performance of a new micro-bubble generator with a spherical body in a flowing water tube

A new micro-bubble generator with a spherical body in a flowing water tube has been invented, and its trial products have been tested. In the generator, pressurized water is introduced into a pipe with a spherical body in the core. From conservation equations of mass and energy, the water velocity around the body especially in a downstream region becomes higher than the inlet velocity, and thus the pressure there becomes lower. If the pressure becomes less than atmospheric pressure, air is automatically sucked into the water stream through a number of small holes drilled on the pipe wall in the lower pressure region downstream from the center of the body. Since the water flow there is highly-turbulent and shear flow, the air sucked is well broken into a great number of micro-bubbles. In the tests of its trial products, experimental data on air suction rate, hydraulic power needed to introduce water, bubble generation efficiency, and variation of dissolved oxygen in water after bubbling were obtained by changing water supply rate systematically. From the tests, we found an optimum diameter ratio of spherical body to pipe, and confirmed that the generator could generate micro-bubbles with a lesser energy consumption rate within 40 W and raise effectively the dissolved oxygen, etc.

Design and performance of a dynaniic gas flux chamber.

Chambers are commonly used to measure the emission of many trace gases and chemicals from soil. An aerodynamic (flow through) chamber was designed and fabricated to accurately measure the surface flux of trace gases. Flow through the chamber was controlled with a small vacuum at the outlet. Due to the design using fans, a partition plate, and aerodynamic ends, air is forced to sweep parallel and uniform over the entire soil surface. A fraction of the air flowing inside the chamber is sampled in the outlet. The air velocity inside the chamber is controlled by fan speed and outlet suction flow rate. The chamber design resulted in a uniform distribution of air velocity at the soil surface. Steady state flux was attained within 5 min when the outlet air suction rate was 20 L/min or higher. For expected flux rates, the presence of the chamber did not affect the measured fluxes at outlet suction rates of around 20 L/min, except that the chamber caused some cooling of the surface in field experiments. Sensitive measurements of the pressure deficit across the soil layer in conjunction with measured fluxes in the source box and chamber outlet show that the outflow rate must be controlled carefully to minimize errors in the flux measurements. Both over- and underestimation of the fluxes are possible if the outlet flow rate is not controlled carefully. For this design, the chamber accurately measured steady flux at outlet air suction rates of approximately 20 L/min when the pressure deficit within the chamber with respect to the ambient atmosphere ranged between 0.46 and 0.79 Pa.