Air Volume Flow Rate Research Articles

Modelling of EAF Off‐Gas Post Combustion in Dedusting Systems using CFD Methods

To comply with the increasingly strict environmental regulations, the poisonous off‐gas species, e. g. carbon monoxide (CO), produced in the electric arc furnace (EAF) must be treated in the dedusting system. In this work, gas flow patterns of the off‐gas post combustion in three different dedusting system units were simulated with a computational fluid dynamics (CFD) code: (1) post combustion in a horizontal off‐gas duct, (2) post combustion in a water cooled post combustion chamber without additional energy supply (no gas or air/oxygen injectors) and (3) post combustion in a post combustion chamber with additional energy input (gas, air injectors and ignition burner, case study of VAI‐Fuchs GmbH).All computational results are illustrated with gas velocity, temperature distribution and chemical species concentration fields for the above three cases. In case 1, the effect of different false air volume flow rates at the gap between EAF elbow and exhaust gas duct on the external post combustion of the off‐gas was investigated. For case 2, the computed temperature and chemical composition (CO, CO2 and O2) of the off‐gas at the post chamber exit are in good agreement with additional measurements. Various operating conditions for case 3 have been studied, including different EAF off‐gas temperatures and compositions, i. e. CO content, in order to optimize oxygen and burner gas flow rates. Residence time distributions in the external post combustion chambers have been calculated for cases 2 and 3. Derived temperature fields of the water cooled walls yield valuable information on thermally stressed parts of post combustion units.The results obtained in this work may also gain insight to future investigation of combustion of volatile organic components (VOC) or formation of nitrogenoxide (NOx) and permit the optimization of the operation and design of the off‐gas dedusting system units.

A mathematical model of thermal performance of a solar air heater with slats

A mathematical model for computing the thermal performance of a single pass flat-plate solar air collector is presented. Air channels were formed by providing metal slats running along the circulated air passage linking the absorber plate by the bottom one in an endeavor to enhance the thermal efficiency of the solar air collector. A mathematical model, therefore, is developed by which the influence of the addition of the metal slats on the efficiency of the solar collector is studied. A computer code that employs an iterative solution procedure is constructed to solve for the governing energy equations to estimate the mean temperatures of the collector. The effect of volume airflow rate, collector length, and spacing between the absorber and bottom plates on the thermal performance of the present solar air heater was investigated. Furthermore, a numerical comparison of the present design with the most common type of solar air heaters is conducted. The results of the comparison have indicated that better thermal performance was obtained by the modified system.

The influence of drug type on the release profiles from Surelease-coated pellets

The release of metoclopramide hydrochloride (a water-soluble cationic drug) and diclofenac sodium (a sparingly soluble anionic drug) from pellets coated with ethylcellulose from an aqueous ethylcellulose dispersion (Surelease ®) at different coating loads was investigated. The release rates of each drug decreased as the coating load of Surelease ® increased. However, despite its lower water solubility, diclofenac sodium was released slightly faster than metoclopramide hydrochloride at equivalent coating loads. Changes in the release rates after curing were more pronounced for metoclopramide hydrochloride and the release rates of diclofenac sodium were lower than those of metoclopramide hydrochloride after curing. Differences between the release behaviour of the two drugs were probably due to an interaction between the cationic metoclopramide and the anionic ammonium oleate present in the Surelease ®. The slower release of metoclopramide hydrochloride may be due to an in situ formation of a poorly soluble complex of the drug and the ammonium oleate. This complex, because of its large molecular size, may diffuse more slowly through the film, causing a reduction in the release rate of metoclopramide hydrochloride. This interaction may also account for the differences in release characteristics of the drugs after curing. During curing the surfactant, due to its unstable nature in heat, may be converted to its constituent components. The interaction of drug with the surfactant was reduced as the residue of the ammonium oleate decreased during curing. However, a relatively low volume flow rate of air, and therefore, slower removal of ammonia in the modified side-vented Manesty Accela-cota 10 may also have affected the coating process of the pellets.

PCI at the start of the 21st century

The paper presents a new desiccant cooling cycle to be integrated in residential mechanical ventilation systems. The process shifts the air treatment completely to the return air side, so that the supply air can be cooled by a heat exchanger. Purely sensible cooling is an essential requirement for residential buildings with no maintenance guarantee for supply air humidifiers. As the cooling power is generated on the exhaust air side, the dehumidification process needs to be highly efficient to provide low supply air temperatures. Solid rotating desiccant wheels have been experimentally compared with liquid sorption systems using contact matrix absorbers and cross flow heat exchangers. The best dehumidification performance at no temperature increase was obtained in an evaporatively cooled heat exchanger with sprayed lithium chloride solution. Up to 7 g kg−1 dehumidification could be reached in an isothermal process, although the surface wetting of the first prototype was low. The process then provides inlet air conditions below 20 °C for the summer design conditions of 32 °C, 40% relative humidity. With air volume flow rates of 200 m3 h−1 the system can provide 886 W of cooling power.A theoretical model for both the contact absorber and the cross flow system has been developed and validated against experimental data for a wide range of operating conditions. A simulation study identified the optimisation potential of the system, if for example the surface wetting of the liquid desiccant can be improved.

Positive Pressure Ventilation in Single Medium-Sized Premises

The objective of this study was to investigate the feasibility, for the fire and rescue services, of using mobile fans as a pro-active means of ventilating smoke in medium-sized premises. The efficacy of various types of such fans was therefore tested in two different-sized premises by measuring air pressures and volume flow rates in the premises. Three different types of mobile fans were used. The study was a cold exercise, i.e. the effects of heat and smoke were not considered, in view of the fact that we were primarily interested in the volume flow capacity and pressure. In order better to illustrate and understand the experimental data, simple theoretical models were developed which describe how various parameters affect the results. The parameters considered in the model were the size of the supply and exhaust openings, the primary air flow of the fan, volume flow and static pressure in the building.

Enhancement of turbulent jet diffusion flame blowout limits by annular counterflow

The effects of a proposed combustion technique, named as annular counterflow, on the enhancement of jet diffusion flame blowout limits were investigated by a series of experiments conducted for the present study. Annular counterflow was formed in a concentric annulus, in which fuel jet was ejected from a nozzle and air was sucked into an outer cylinder encompassing the nozzle. Three fuel nozzles and outer cylinders of different sizes were utilized to perform the experiments. Schlieren technique and normal video filming were employed for the visualization of diverse flame morphologies triggered by the said flow. Gas samplings were taken and scrutinized by the use of a gas chromatograph. Results showed that the blowout limits can be enhanced dramatically by an increase in volume flow rates of air-suction. Mixing enhancement is achieved with frequent and strong outward ejection of fluids from the cold jet when this technique is applied. The blowout limits are further extended when the diameter of outer cylinders becomes smaller and/or that of the fuel nozzle becomes larger. The base widths of lifted flames were found to be narrower in the interim of annular counterflow application. The rates of increase in flame lift-off heights and base widths along with an increase in fuel flow velocities become sluggish when the volume flow rates of air are increased. The amount of fuel that was sucked into the outer cylinder was found to be negligible and trivial. A model based on annular and coaxial jet was developed to predict the lifted flame base width and blowout limits. The coincidence between the prediction and experimental results unambiguously validates that the momentum of air-suction dominates the beneficial effect. Copyright © 2001 John Wiley & Sons, Ltd.

A Mathematical Model of Coughing for a Homogeneous Lung

A mathematical model of the homogeneous (healthy) human lung, applicable to the description of coughing, is presented. It is shown that in modeling the cough mechanism, unlike simulation of the forced-expiration maneuver, the inertia of the back trachea wall must be taken into account. The value of the corresponding inertia constant is specified from a comparison of the calculation results and the measured time dependence of the volume flow-rate of air during coughing in a healthy subject.

Volume Flow-Rate Measurements and Scaling Laws for a Transverse-Inlet Multiple-Disk Fan

The air moving capacity of a transverse-inlet multiple-disk fan has been measured experimentally and the results successfully collapsed with a simple scaling law. The disk fan studied was an array of several hundred closely spaced plastic disks that rotated about a common axis inside an approximately semicylindrical housing. A splitter plate lying parallel to the axis of rotation and tangent to the disks separated the inflow and outflow streams. The volume flow rate of air per unit length along the axis of rotation was measured using standard LDV techniques. For disk spacings greater than 1 mm, the volume flow rate was found to be essentially proportional to ωhR3, where ω = radian rotation rate of the disks, h = disk spacing, and R = disk radius. This scaling law was derived from a simple force balance for a small fluid element moving between rotating disks. The Reynolds number of the experiments, ωh3R/ν, was varied from 2 × 102 to 103. In addition, the air-moving capability of the disk fan was found to be nearly independent of the geometrical placement of the rotating disks within the fan housing.

The influence of wind on the performance of forced draught air-cooled heat exchangers

Abstract The influence of wind on fan performance and recirculation in a forced draught air-cooled heat exchanger (ACHE) bank is investigated numerically. Winds blowing across and parallel to the longitudinal axis (long axis) of an ACHE bank are considered. It is found that cross winds significantly reduce the air volume flow rate that is delivered by the up-wind fans, while winds along the longitudinal axis cause increased hot plume air recirculation along the sides of the ACHE bank.

Flow distortions at the fan inlet of forced-draught air-cooled heat exchangers

The effect of inlet flow distortions on fan performance in forced-draught air-cooled heat exchangers (ACHEs) is investigated numerically and experimentally. By varying the distance between the ACHE fan platform and the ground level, significant changes in air volume flow rate are observed. Three different fan inlet shrouds are considered and recommendations towards designing and evaluating the performance of an ACHE are made. The effect of different lengths of a cylindrical fan inlet shroud, as well as the effect of cylindrical sections as part of a conical and a bell-mouth inlet shroud, is also investigated. The results show that a critical length for both the cylindrical inlet shroud and the cylindrical sections of the conical and bell-mouth inlet shrouds can be obtained for optimal fan performance.

Effets thermiques dans la cavitation des fluides cryogéniques

Click to increase image sizeClick to decrease image sizeThe vapour production required to sustain a cavity leads to a temperature reduction at the interface. This temperature reduction, though quite small in the case ofwater, is significant in the case of cryogenic fluids. A method assuming that (i) the vapor production is equal to the volume flow rate of air required to sustain a ventilated cavity and (ii) that heat transfer at the interface is analogous to that over a rough flat plate, gives reasonable estimates of the temperature reduction.

Buoyancy-driven air flow in a stairwell model with through-flow

This paper is concerned with measurement of buoyancy-driven air flows between the two compartments of a half-scale model of a stairwell. The flow was maintained by a heater placed in the lower compartment. The results of earlier investigations are extended by considering a through-flow via two small openings, one in the lower and the other in the upper compartment. The stairwell model and its instrumentation are described. The results include velocity and temperature measurements, volume and mass flow rates of air circulating between the lower and upper compartments and rate of heat loss from the stairwell; all are presented for various heat input rates. For the range of experimental conditions and sizes of the openings considered, the through-flow mass flow was about 15% of the circulation flow rate. The results also include the rate of heat and mass transfer via the openings.

Apparatus for the automated measurement of the responses of humans to odorants

An automated system for the measurement of the psychophysical and physiological responses of humans to odorant stimulation of the nose and eyes is described. All aspects of the generation and production of odor stimuli, the recording of physiological and psychophysical responses of the subjects and the storage of data are managed by an Apple He computer. Both the nasal and ocular olfactometers are based on electronic mass flow controllers which are used to control the ratios of volume flow rates of clean and odorant-saturated air. The output of each olfactometer is measured by a photo-ionization detector. Odor stimuli are delivered to custom-fitted face masks, that allow separate stimulation of the nose and eyes, through Teflon (rtm) flow valves. A video camera records the responses of the eyes and a pneumotachograph, in combination with a pressure transducer, records changes in respiratory behavior. An electronic mouse is used to enter the subject's psychophysical responses directly into the computer. The advantages of this methodology and its current and potential applications are discussed.

Uncontrolled recirculation in auxiliary ventilation with fans in series along the duct

When fans are placed in series at intervals along a duct line it is possible for uncontrolled recirculation of air to take place if there is leakage into or out of the duct. On the assumption that hazardous conditions can develop, many government regulations either forbid the use of auxiliary fans in series along the duct line or specify the installation of auxiliary fans in such a way that uncontrolled recirculation is avoided. The degree of recirculation depends upon the positions of the fans and the leakage characteristic of the duct line. Through an illustrative realistic example, the following advantages of designing auxiliary ventilation systems with recirculation have been determined: (1) the number of fans required becomes less in bad installations, hence reduced capital and power costs; (2) in good installations, the number of fans required may not become less but the fresh airflow at the face improves; (3) the velocity of airflow at the face becomes more, hence the rate of dilution and enhanced mixing; (4) the climatic conditions at the face improve. With the availability of systems for monitoring air volume flow rates and concentrations of pollutants, recirculation can be practised with confidence.

Determination of carbon loss from flue gas analysis in the combustion of methanol

The combustion of methanol was studied in an open system. Quantitative measurement of the unburnt carbon formed during the combustion process was continuously followed by applying a semi-analytical technique based on the composition of the flue gas. The combustion of the alcohol was determined to be zero order under the experimental conditions. The change in the rate of burning, K, was found to correspond in magnitude to the change in the ratio of actual air volume flow-rate, Q a , to the stoichiometric air volume flow-rate, Q s .

Residence time distributions and mass transport in the froth phase of the flotation process

A comprehensive description of some aspects of the physical behaviour of the froth phase of the flotation process has been provided by two mathematical models. Both are formulated in terms of familiar design and control variables (e.g. cell dimensions, froth depth, gas rate) and the froth stability, α, defined as the ratio between the volume flowrate of air in the concentrate stream and the volume flowrate of air in bubbles crossing the froth/slurry interface which have a finite probability of entering the concentrate stream. The first model provides a description of the two-dimensional streamline behaviour of the froth as it moves towards the concentrate weir. The second model is a two-stage approximation of this behaviour and provides a simple and tractable model of froth behaviour which can easily be incorporated in existing models of the flotation process. This model involves two more parameters: the residence time ratio δ, which provides a means for estimating the minimum froth phase residence time (it can be given the value 0.5 unless it is possible and practical to measure it more accurately); and the froth removal efficiency, ε, which is a measure of the efficiency with which the available froth chamber volume is used. RTD measurements using two-phase froths have shown that these models constitute a good description of physical reality, and that ε and α can be obtained as functions of control variables such as gas rate, froth height and frother concentration. Insights obtained from this work have led to the development of a method for froth removal which produces an unambiguous improvement in the performance of the flotation cell. The second model can be used to investigate the effect of control actions and scale-up on cell performance.

Theory of air flow generation by a resonant type PVF2 bimorph cantilever vibrator

A theory is presented for the air flow generation caused by centrifugal forces acting in a vibrating PVF2 multimorph fan in the resonant condition. The vibration system is approximated by a mass acting at the center of inertial force against an elastic plate (the cantilever wing arm). The effect of air was represented by a non-linear dissipative load in the oscillating system. The relevant parameters of this system are then determinable, particularly the vibration amplitude and the wing tip velocity. These parameters determine the generated air flow velocity and volume flow rate. Air flow velocity is predicted to vary inversely as wing length, and the air volume flow rate to remain constant. These predictions agree well with experiment, particularly for larger wing lengths of the fan. Useful design information was obtained.

Design and Performance of an Air Shaker for Citrus Fruit Removal

ABSTRACT AN air shaker for citrus fruit re-moval was designed, constructed, and field tested between 1973 and 1975. The main components of the shaker were three 1.2 m (48 in.) diameter vane-axial fans which were belt driven by two engines and were trailer mounted on a live, steerable axle. The shaker weighed 8,522 kg (18,919 lb) and delivered an air volume flow rate of 85 m3/s (180,000 cfm) with a power input of 242 kW (325 hp). Air pressure measurements are presented to characterize the air shaking pattern. In all field performance tests abscission chemicals were applied to the citrus fruit to reduce the bonding strength of the fruit to the tree. Fruit removal capacities of the air shaker ranged up to 3.4 kg/s (152,856 lb/hr) at 80 to 100 percent removal efficiency. In general, when the fruit bonding strength was uni-formly reduced to 22.4 N (5 lb) or less, the air shaker would remove 90 to 95 percent of the fruit at a rate of not less than 5.7 kg/s (45,000 lb/hr).