Increasing Air Flow Rate Research Articles

A numerical investigation of vertical and horizontal laminar airflow ventilation in an operating room

The effectiveness of vertical and horizontal ventilation systems in terms of reducing sedimentation and distribution of bacteria-carrying particles in an operating room is investigated. The exploration is carried out numerically using computational fluid dynamics. Both airborne particle concentration and sedimentation are simulated under different ventilation flow conditions. Model validation is performed through comparisons with experimental data from the literature. Achieved results reveal that the preferred selection between vertical and horizontal ventilation scenario in an operating room is highly depend on internal constellation of obstacles, work practice and supply airflow rate. Improper positioning of operating room personnel may remarkably reduce the ventilation efficiency. Increasing the airflow rate reduces particle concentration in the surgical zone. Efficient ventilation, however, is not only a matter of increasing airflow rate. Inappropriate airflow rates result in flow pattern transition from laminar to less efficient turbulent mixing. A laminar and well- organized (unidirectional) flow pattern is retired for a good result. Innovative further solutions are suggested to be found in cross-disciplinary collaboration.

The use of ducts to improve the control of supply air temperature rise in UFAD systems: CFD and lab study

Cool supply air flowing through the underfloor plenum is exposed to heat gain from both the concrete slab (conducted from the warm return air on the adjacent floor below the slab) and the raised floor panels (conducted from the warmer room above). The magnitude of this heat gain can be quite high, resulting in undesirable loss of control of the supply air temperature from the plenum into the occupied space. These warmer supply air temperatures can make it more difficult to maintain comfort in the occupied space (without increasing airflow rates), particularly in perimeter zones where cooling loads reach their highest levels. How to predict plenum thermal performance is one of the key design issues facing practicing engineers – evidence from completed projects indicates that excessive temperature rise in the plenum can be a problem.One of the recommended strategies for addressing temperature rise in UFAD systems is the use of ductwork (flexible or rigid) within the underfloor plenum to deliver cool air preferentially to perimeter zones or other critical areas of high cooling demand.Several experiments were carried out in a full-scale underfloor plenum test facility, in order to characterize all the phenomena that take place in an underfloor plenum equipped with a fabric or metal duct. Experimental data were collected for validation of a computational fluid dynamics (CFD) model of the plenum. This paper describes the first part of a more comprehensive work, whose aim is to use the validated CFD plenum model to conduct simulations of a broader range of plenum design and operational parameters. This work proves that using ductwork within the underfloor plenum reduce the temperature rise in the plenum.

Testing parameters affecting gas analysis value of particleboard

The gas analysis method according to EN 717 part 2 is a well-known technique to measure the formaldehyde emission of plywood and coated wood-based materials for quality control purposes. There is an increasing interest to apply this method also for uncoated wood-based panels compared to the perforator method (EN 120: 1992) owing to many reasons. As there is still limited experience in testing particleboard with this method, it is the aim of this study to evaluate the effect of some parameters to ensure correct and precise testing using the gas analysis method. Furthermore, the study aimed to show how the m.c. of panels before testing affects the Gm, and to calculate an m.c. correction factor from these results for particleboard with modern bonding systems at a low emission level. Gas analysis value and m.c. show a very good correlation. Based on this correlation an m.c. correction factor can be determined, which facilitates an m.c. correction of Gm data. This may help to improve the quality of Gm data for quality control and data comparison (i.e. for round robin tests). Combining the sampling for hour 3 and 4 as well as 2, 3 and 4 has no significant effect on the level of formaldehyde emission tested. Also the accuracy of testing was not reduced. Consequently, the change in sampling procedure may lead to a reduction on the required number of water analyses needing to be performed in the laboratory, and therefore to a reduction in consumption of chemical consumables and expenditure of human labour. The reduction of overpressure during gas analysis did not have a major effect on the values as such, but increased the coefficient of variation. Also, an increase in air flowrate did not affect the Gm at lower emission levels.

Modelling of particle deposition in a submerged membrane microfiltration system

In this study, microfiltration of a concentrated suspension of kaolin clay was performed in an aerated tank with submerged flat sheet membranes. Particle deposition was correlated with cake resistance based on experimental results. The effects of air flow rate and permeate flux on transmembrane pressure (TMP) and on membrane resistance were studied. The experimental results show that the filtration resistance due to cake formation plays a dominant role in the total filtration resistance. An increase in permeate flux caused higher TMP development due to an increased amount of particle deposition. Conversely, an increase in air flow rate reduced TMP by detaching deposited layers back into suspension. The particle deposition under different filtration flux and air flow rates was correlated to establish an empirical formula. Based on the experimental results, a general relationship between the cake resistance, permeate flux and particle deposition was derived as Rc=1.01×1012J·wc that suggests that the cake resistance is proportional to the multiplication of flux and cake deposition. Moreover, the effect of air flow on cake porosity was observed to be more significant at low permeate flux.

Effect of CO Combustion Promoters on Combustion Air Partition in FCC under Nearly Complete Combustion

With CO combustion promoters, the role of combustion air flow rate for concerns of economics and control is important. The combustion air is conceptually divided to three parts: the air consumed by coke burning, the air consumed by CO combustion and the air unreacted. A mathematical model of a fluid catalytic cracking (FCC) unit, which includes a quantitative correlation of CO heterogeneous combustion and the amount of CO combustion promoters, is introduced to investigate the effects of promoters on the three parts of combustion air. The results show that the air consumed by coke burning is almost linear to combustion air flow rate, while the air consumed by CO combustion promoters tends to saturate as combustion air flow rate increases, indicating that higher air flow rate can only be used as a manipulated variable to control the oxygen content for an economic concern.

Application of response surface methodology to study the biological removal of nitrogen from effluent of cattle slaughterhouse in a sequencing batch reactor

The aim of this study was to evaluate the efficiency of a sequencing batch reactor (SBR) on biological removal of nitrogen from cattle slaughterhouse wastewater by nitrification/denitrification processes. The effects of initial concentration of ammoniacal nitrogen were investigated at 100; 150 and 200 mg L-1 and air flow rate at 0.125; 0.375 and 0.625 L min¹ Lreactor-1 on the nitrogen compounds removal, by a Central Composite Rotational Design (CCRD) configuration. There were variations from 9.2 to 94.9%, 4.0 to 19.6% and 20.8 to 92.0% in the conversion of ammoniacal nitrogen to nitrate and nitrite concentration and removal of total nitrogen, respectively. The increase of air flow rate and decrease of the initial concentration of ammoniacal nitrogen resulted in higher efficiencies of total nitrogen removal, as well as the conversion of ammoniacal nitrogen to nitrate. During the pre-established intervals of this study, the removal and conversion efficiencies of nitrogen compounds above 85% were achieved in air flow rate variations from 0.375 to 0.725 L min-1 Lreactor-1 and initial concentration of ammoniacal nitrogen from 80 to 200 mg L-1. On denitrification process, we obtained efficiencies from 91.5 to 96.9% on the removal of nitrite/nitrate and from 78.3 to 87.9% on the removal of organic matter.

Experiments and modeling of bubble column dehumidifier performance

Humidification–dehumidification is a promising technology for decentralized, small-scale desalination, but conventional dehumidifiers are expensive due to the large surface area required. Direct-contact dehumidification in bubble columns has been shown to significantly decrease dehumidifier size and cost. In this paper, the heat flux and parallel-flow effectiveness of a bubble column dehumidifier are investigated experimentally using significantly smaller cooling coils than in previous work. In addition, a model is developed which predicts the heat transfer rate with an average error of less than 3%. It is found that heat flux rises and effectiveness decreases with decreasing coil area. Increasing air flow rate and air temperature both lead to increased heat flux but decreased effectiveness. Neither bubble-on-coil impact nor column height are found to significantly affect heat flux or effectiveness. The conflicting findings of previous research on bubble-on-coil impact are explained by the other trends identified in this work. Modeling results for salt water temperature and tube diameter are presented. Additional heat transfer in the air gap above the column liquid is explored, but found to be minimal for well-designed columns with low temperature pinch. These findings will inform the design of bubble column dehumidifiers for high heat recovery and low capital cost.

Air Bubble Size Measurement in a Laboratory Flotation Cell

Air bubble size distribution in a laboratory flotation cell was investigated by using of image analysis technology in this paper. Results showed that it was feasible to determine the air bubble size according to image analysis software. For a porous media-aerated flotation cell, bubble size was dependent on poles size of porous media. Furthermore, operating parameters of the cell could affect the size. Mean bubble diameters increased with increasing of air flow rate. In contrast, it decreased when adding deinking agent. Its decreasing with increasing pulp flow rate under given conditions illustrated the fact that proper turbulence strength at the inlet of air bubbles was favorable for reducing bubble size. Gas holdup increased with increasing air flow rate to some extent, but it had a peak value. Gas holdup would rise obviously when deinking agent existed. An efficient approach to enhancing bubble surface area flux was to increase air flow rate and keep small bubble size at the same time.

Theoretical investigation of using a direct contact dehumidifier in humidification–dehumidification desalination unit based on an open air cycle

In the present work, a kind of direct contact dehumidification process used in humidification–dehumidification system is introduced instead of using the conventional indirect condensers. In the purposed system, air is dehumidified by spraying cold water into the hot and humid air stream. The freshwater production, efficiency and effects of various parameters including air flow rate, conditions of inlet cold and hot water and velocity and diameter of droplets on the performance of the system are investigated. Results showed that increasing initial velocity and diameter of water droplets decreases water production. Furthermore, it has been demonstrated that increasing the flow rate and temperature of hot water and reducing the flow rate and temperature of cold water will increase freshwater production and the efficiency. It is found that increasing air flow rate has negative effect on production and energy consumption of the system. Direct contact dehumidifier has a good potential in desalination of seawater which can resolve many operational problems of indirect condensers like: corrosion, salt water leakage, and hydraulic pressure drop.

Dielectric layer equivalent capacitance and loading performance of a coaxial dielectric barrier discharge reactor

Dielectric barrier discharge (DBD) can produce non-equilibrium plasma at atmospheric pressure, and it has become a hot point in recent years. For the DBD excited by pulsed or alternated currents, the effects of the loading performance of power supply, the matching between supply and discharge reactor and the discharge phenomena on its discharge are interesting issues. The studies of these issues are of great importance for understanding the DBD processes and improving the power supply efficiency. In this paper, the Lissajous figures of a DBD reactor with coaxial electrode configuration are measured. The loading performance of the DBD reactor and the dependences of excitation voltage and air flow rate on the dielectric layer equivalent capacitance are studied in atmospheric air. According to the experimental data and circuit modeling analysis, it is proved that the dielectric layer capacitance decreases with the increase of air flow rate, but increases with the increase of excitation voltage. The amplitude-frequency performance of the reactor reveals significant RLC circuit resonance. The resonance frequency of the reactor has the same behavior as its dielectric layer capacitance. Therefore it shows that the dielectric layer capacitance is the main factor for the resonance frequency evolution. A possible mechanism responsible for the dielectric layer capacitance is also presented.

Study of Pre- and Post-Stent Implantation in the Trachea Using Computational Fluid Dynamics

Computational fluid dynamics (CFD) allows the visualization and understanding of physics of flow associated with stent implantation. This study uses patient computed tomography (CT) images to investigate the relationship of pressure drop and air flow rate in the tracheal airway. Moreover, the cross-sectional areas of the patient airway were measured and the area stenosis ratios were calculated. The stenosis ratios were 75.64% and 38.08% without and with stent treatment, respectively. Simulation results show that at an air flow rate of 30 L/min, the pressure drops between the inlet and the outlet before and after central airway stent implantation for the inspiratory phase were 77.23 and 7.05 Pa, respectively. The improvement gain (IG) was 9.95. The IG increased with increasing air flow rate. At an air flow rate of 120 L/min, the value of IG was 11.68. A higher IG value indicates lower airway resistance after an airway stent implantation. The CFD numerical results demonstrate the feasibility of computing airway resistance based on CT images. In clinical practice, it is difficult to assess patients with severe airway obstruction using a symptoms score or a pulmonary function test due to their critical condition. The proposed noninvasive approach for determining airway obstruction severity is helpful for patients who are unable to do pulmonary function tests.

Evaluation of semi-empirical and non-linear drying models by Bayesian inference

Current analysis investigates thin layer drying experiments on passion fruit seeds. Drying characteristics of passion fruit seeds were examined using ambient air for temperature range between 40 and 65oC and air flow velocity range between 0.6 and 1.2 m s -1 . The semi-empirical models were then fitted to the drying data by Bayesian inference, based on the ratios of the difference between the initial and final moisture contents and equilibrium moisture content. The effective diffusivity varied between 1.70 x 10 -10 and 4.68 x 10 -10 m 2 s -1 with temperature and air flow rate increase. Temperature dependence on the diffusivity coefficient was described by an Arrhenius-type relationship. The activation energy for moisture diffusion was 24.36, 35.24 and 13.86 kJ moL -1 for drying air speeds respectively equal to 0.6, 0.9 and 1.2 m s -1 .

Mathematical Model of Compost Pile Temperature Prediction

A mathematical model of heat balance was developed to predict the compost temperature during the maturation stage. The components of the energy balance of the compost pile which include: heat gained (heat generation and solar radiation) and heat lost (radiation, evaporation, convection, and conduction) at different ambient temperatures. The model was able to predict the pile temperature at different ambient temperatures (15, 20, 25, 30 and 35°C) and different airflow rates (0.7, 1.1 and 1.5 mg air s-1 kg-1 dry matter). The results showed that the pile temperature increases with increasing ambient temperature and it decreases with increasing airflow rates, where, as the ambient temperature increased from 15 to 35°C, the pile temperature increased from 33.40 to 37.41°C, and when the airflow rates increased from 0.7 to 1.5 mg air s-1 kg-1 dry matter, the pile temperature decreased from 34.40 to 32.39°C. The pile temperature increased slightly and reached a maximum value at day 14. It indicates that the net energy gained to the pile increases with increasing ambient temperature, meanwhile, the heat lost decreases with increasing ambient temperature. The model results indicated that the predicted daily temperature was in a reasonable agreement with those measured ones and other data in literature (Barrena et al. and Ahn et al.) at different ambient temperatures and airflow rates, where, it ranged from 30.30 to 73.40°C, while it was from 18.0 to 71.0°C experimentally during the whole period of compost maturation.

Using Color Full-Scale Schlieren (CFSS) Technique to Improve Kitchen Exhaust Hood Performance

This article uses color full-scale Schlieren for heat flow visualization of the kitchen exhaust hood. Using grease filters with same percentage of opening but different forms for measurements the heat flow escaping rate, noise, and air velocity of the kitchen exhaust hood under conditions of different percentage masking. The results show that using different grease filters without masking has no escaping heat flow. Employing the rectangular filter with side masking has the worst heat flow escaping. The top masking has also no heat flow escaping and the form with circular opening has the strongest absorbability. In this work, the smallest noise level is 65dB which appears at the situation of top masking. Moreover, kitchen exhaust hood without masking the air flow rate increase 3.17% of the air velocity than side masking.

Increased Natural Ventilation Flow Rates through Ventilation Shafts

Buoyancy-driven natural ventilation in ventilation shafts is investigated with a small scale physical experiment within a duct and CFD simulations of an office building. For a fixed exhaust opening, smaller shafts lead to higher flow rates in upper floors of a multi-storey building with a shared ventilation shaft. These higher flow rates are caused by increased vertical momentum within the smaller shafts that induce flow through upper floors, an effect referred to as the “ejector effect”. In the small scale duct, a 0.5 m by 0.5 m shaft leads to a slight reverse flow of 0.0029 m3/s through the upper floor. Holding all other parameters constant and reducing the shaft to 0.25 m by 0.5 m leads to a positive flow rate of 0.012 m3/s through the upper floor. In the CFD simulations of a three storey office building, this same pattern is observed. A 3 m by 2 m shaft leads to a flow rate of 0.0168 m3/s through the third floor, while the reduced shaft of 2 m by 2 m leads to a flow rate of 0.766 m3/s through the same floor. This increased airflow rate from the ejector effect can allow natural ventilation to be used in buildings where it may otherwise have been deemed inappropriate. Most airflow network models neglect air momentum and fail to account for the ejector effect. To improve these models, an empirical model is incorporated into the airflow network model CoolVent in a manner easily transferable to most airflow network models.

Environmental analysis of present and future fuels in 2D simple model marine gas tubines

Increased worldwide concerns about fossil fuel costs and effects on the environment lead many governments and scientific societies to consider the hydrogen as the fuel of the future. Many researches have been made to assess the suitability of using the hydrogen gas as fuel for internal combustion engines and gas turbines; this suitability was assessed from several viewpoints including the combustion characteristics, the fuel production and storage and also the thermodynamic cycle changes with the application of hydrogen instead of ordinary fossil fuels. This paper introduces the basic environmental differences happening when changing the fuel of a marine gas turbine from marine diesel fuel to gaseous hydrogen for the same power output. Environmentally, the hydrogen is the best when the CO 2 emissions are considered, zero carbon dioxide emissions can be theoretically attained. But when the NO x emissions are considered, the hydrogen is not the best based on the unit heat input. The hydrogen produces 270% more NO x than the diesel case without any control measures. This is primarily due to the increased air flow rate bringing more nitrogen into the combustion chamber and the increased combustion temperature (10% more than the diesel case). Efficient and of course expensive NO x control measures are a must to control these emissions levels.

Operation characteristics of air-cooled proton exchange membrane fuel cell stacks under ambient pressure

Air-cooled proton exchange membrane fuel cells (PEMFC) simplify the traditional cooling and air supply system. Three air-cooled stacks are assembled with different cells to investigate the effect of the polytetrafluoroethylene (PTFE) content in the gas diffusion layer (GDL), air flow rate, as well as the stack temperature on the stack performance. The results show that GDL with appropriate thickness and PTFE content can optimize the stack operation performance. The effect of the cell order on its performance can be neglected. A thermal equilibrium resulting from the heat generation and loss in the stack is achieved near the ambient temperature at low current density of 150 mA cm−2. The output power increases with the increase of air flow rate. However, when the air flow rate exceed 44.7 L min−1 or the stack temperature is higher than 65 °C, the stack performance decreases.

Preparation of ultrafine polyurethane fiber web by laser-electrospinning combined with air blowing

Thermoplastic polyurethane fiber webs were prepared using a laser-heated electrospinning process combined with air blowing. The effect of spinning conditions such as air flow rate and air temperature on fiber diameter and molecular weight was investigated. Although the average fiber diameter decreased with increased air flow rate at each air temperature, the diameter increased when the air flow rate was >15 NL min−1. In addition, the fiber was comparatively thicker with an increase in the air temperature. The variation in the fiber diameter tends to increase with the air flow rate, and a reduction in the molecular weight of the fiber by thermal degradation was suppressed. The thinnest and most uniform fiber with a diameter of 0.9 µm and a diameter coefficient variation of 15% was obtained at an air temperature of 25°C under an air flow rate of 15 NL min−1. This fiber also had a minimum of decreased molecular weight. POLYM. ENG. SCI., 54:2605–2609, 2014. © 2013 Society of Plastics Engineers

Convective Air Drying Characteristics for Thin Layer Carrots

Introduction: Carrot is one of the most commonly used vegetables for human nutrition due to high vitamin and fibre content. Drying is one of the oldest methods of food preservation, and it represents a very important aspect of food processing. Sun drying is the most common method used to preserve agricultural products in most tropical countries; this technique is extremely weather dependent, and has the problems of contamination with dust, soil, sand particles and insects. Also, the required drying time can be quite long. Therefore, using solar and hot-air dryers, which are far more rapid, providing uniformity and hygiene are inevitable for industrial food drying processes. Aim: This paper presents a kinetic study of convective drying without pre-treatment of carrot. The effects of the temperature of the drying agent, the speed of the drying agent and the thickness of the kinetics of drying the sample of carrots were investigated. Materials and methods: The experiments were carried out with the aid of an installation for drying food products, that is capable of ensuring the temperature of the drying agent (air) in the range of +25 ... +125 °C. The drying process was conducted at temperature of 45 °C in first hour of process, 2 hours at 55 °C, and 3 hours at 60 °C. The air velocity was setup at 1.0 - 2.5 m/s. Carrots were divided into segments of a thickness of 0.4 cm. Two mathematical models available in the literature were fitted to the experimental data. Results: The drying rate increases with temperature and decreases with the sample diameter. The Page model is given better prediction than the Henderson and Pabis model and satisfactorily described drying characteristics of carrot slices. Conclusions: The most important characteristics of carrot required for simulation and optimization of the drying were studied. The values of calculated effective diffusivity for drying at 45, 55 and 60oC of air temperature and 1.0, 1.5, 2.0 and 2.5 m/s of air flow velocity. The effective diffusivity increases as air-flow rate and temperature increases. Page’s empirical model showed a good fit curves than the Henderson and Pabis model.

Pottery Evaporative Cooling System: A Novel Approach to Cool Inlet Air With Minimal Change in Relative Humidity and Low Water Consumption

The aim of this research is to investigate the feasibility and potential of using a novel pottery evaporative cooling system. The suggested novel system will be utilized to reduce inlet air temperature in industrial air-conditioning systems, and this reduction will be associated with low water consumption and minimal change in relative humidity. An experimental investigation tested two different unglazed pottery arrangements, aligned and staggered, under dry and wet conditions. The experimental tests were performed using a wind tunnel with an inlet air temperature of 40°C–48°C to simulate the hot summer climate in Kuwait, and different airflow rates from 300 to 1,300 m3/h were used. The average air temperature drop, relative humidity, and pressure drop parameters across the potteries were measured, in addition to water consumption. Tests were performed under dry and wet pottery conditions, and the gap between the potteries were varied during the experimental tests (1, 3, and 5 cm). Results showed that for all arrangements, the staggered case demonstrated a higher air temperature drop compared to the aligned one. For the staggered case at 300 m3/h, the air temperature dropped 6.5°C (5-cm gap) and 11°C (1-cm gap), whereas ata high airflow rate, both aligned and staggered arrangements showed an air temperature drop of 4°C. Results also showed that at the 1-cm gap dry case, a much larger pressure drop is noticed compared to the wet case; as the gap increased, pressure drop became nearly the same for wet and dry conditions. Results also showed that relative humidity increases across the potteries, in the range of 2 to 5%, and tends to be almost constant as airflow rate increases.