Pulsating Air Flow Research Articles

Investigation of food grain drying with pulsating air flows

We investigate experimentally the potential of using pulsating flows for drying of food grains. A Rijke type oscillator with an electrical heater was used to dry batches of soybean grains. Drying temperatures were 60 °C. We observed a decrease on the drying time for pulsating flows when compared with the conventional non-pulsating regime. This decrease depended on sample initial moisture content and weight, and on final sample moisture content

Heat transfer characteristics and Nusselt number correlation of turbulent pulsating pipe air flows

Heat transfer characteristics to turbulent pulsating pipe flows under a wide range of Reynolds number and pulsation frequency were experimentally investigated under uniform heat flux condition. Reynolds number was varied from 8462 to 48540 while the frequency of pulsation ranged from 1 to 29.5 Hz. The results showed that the relative mean Nusselt number is strongly affected by both pulsation frequency and Reynolds number. Enhancements in mean Nusselt number of up to 50% were obtained at medium pulsation frequency between 4.1 and 13.9 Hz for Reynolds number range of 8462 to 14581. An enhancement of up to 50% in mean Nusselt number was obtained at high pulsation frequency range between 13.9 and 29.5 Hz, specially as Reynolds number is close to 15000, while a reduction was observed at higher Reynolds number more than 21200. This reduction, at high Reynolds number, increased as pulsation frequency increased. Also, there was a reduction in mean Nusselt number of up to 20% that obtained at low pulsation frequency range between 1 and 4.1 Hz for Reynolds number range of 8462 to 48543. A significant reduction in mean Nusselt number of up to 40% was obtained at medium pulsation frequency between 4.1 and 13.9 Hz for Reynolds number range of 21208 to 48543. Empirical equations have been developed for the relative mean Nusselt number that related to Reynolds number and dimensionless frequency with about uncertainty of 10% rms.

Studies on Liquid—Gas and Three‐Phase Fluidized Beds with Pulsating Air Flows

AbstractThe effects of air‐flow pulsation and water and air flowrates on the hydrodynamics of liquid—gas and three‐phase fluidized beds containing 3‐mm glass beads have been studied in a 90‐mm i.d. column. Under steady‐flow conditions, both types of bed contained a relatively large number of small bubbles. With a pulsing air flow, however, a smaller number of much larger bubbles or slugs were formed. This was attributed to different mechanisms of bubble formation at the distributor. Variations in phase holdup were explained in terms of the effects of the operating parameters on the bubble characteristics.

Air Photolysis and Recombination Tracking: A New Molecular Tagging Velocimetry Scheme

A new scheme for molecular tagging velocimetry in unseeded airflows is presented. The method, called air photolysis and recombination tracking, is based on the photoinduced formation of nitric oxide (NO) in the waist region of a focused ArF excimer laser beam. The distribution of the formed NO molecules is imaged by planar laser-induced fluorescence in the gamma band, using a frequency-doubled dye laser beam. The role of N-2(+) ions in the NO formation process is discussed, and the lifetime of the NO molecules was determined to be at least 10 ms. The new method has been applied to a laminar and a pulsed airflow and a premixed methane/air flame. Velocities could be determined with an accuracy of 5% in the airflows (on a single-shot basis) and 13% in the flame. By the use of averaging over many laser pulses, velocities as low as 1 cm/s could be measured.

Convective heat transfer characteristics of laminar pulsating pipe air flow

Heat transfer characteristics to laminar pulsating pipe flow under different conditions of Reynolds number and pulsation frequency were experimentally investigated. The tube wall of uniform heat flux condition was considered. Reynolds number was varied from 780 to 1987 while the frequency of pulsation ranged from 1 to 29.5 Hz. The results showed that the relative mean Nusselt number is strongly affected by pulsation frequency while it is slightly affected by Reynolds number. The results showed enhancements in the relative mean Nusselt number. In the frequency range of 1–4 Hz, an enhancement up to 30% (at Reynolds number of 1366 and pulsation frequency of 1.4 Hz) was obtained. In the frequency range of 17–25 Hz, an enhancement up to 9% (at Reynolds number of 1366 and pulsation frequency of 17.5 Hz) was indicated. The rate of enhancement of the relative mean Nusselt number decreased as pulsation frequency increased or as Reynolds number increased. A reduction in relative mean Nusselt number occurred outside these ranges of pulsation frequencies. A reduction in relative mean Nusselt number up to 40% for pulsation frequency range of 4.1–17 Hz and a reduction up to 20% for pulsation frequency range of 25–29.5 Hz for Reynolds numbers range of 780–1987 were considered. This reduction is directly proportional to the pulsation frequency. Empirical dimensionless equations have been developed for the relative mean Nusselt number that related to Reynolds number (750 < Re < 2000) and the dimensionless frequency (3<Ω<18) with about 10% rms.

Intermittent Airblast Atomization and Spray Particle Mixing in Pulsating air Flow

Intermittent Airblast Atomization and Spray Particle Mixing in Pulsating air Flow

Intermittent airblast atomization and spray particle mixing in pulsating air flow

A new twin-fluid injector applicable to a single-point injector for gasoline engine was developed. Using this injector's transient spray characteristics, the mixing mechanism of spray particles and the deposition mechanism on the inner wall of an intake manifold were investigated. The measurements of spray particle sizes, velocities and deposition rates were experimentally conducted in a pulsating air flow. The particle deposition takes place due to the particle inertia at high air flow rates. At low air flow rates it comes due to the recirculation appearing on the inner wall at the entrance of the intake manifold. On the other hand, the deposition rate of spray particles is strongly influenced by air pulsation. The behavior of spray particle is mainly influenced by air pulsation when the velocity of the atomizing air is low and when the velocity of the air flow around the injector is high. Single small particles follow the air flow more easily than large particles, and this causes the spatial particle size distribution in the spray clump. As the spray particles approach to the tip of a spray clump, the size of particles.

Suitable algorithms for calculating air renewal rate by pulsating air flow through a single large opening

Building ventilation of an enclosure with a single opening is affected not only by the steady mean effect of air pressures and temperatures around and within the building, but also by the turbulent nature of the wind. To improve understanding of the physical phenomena causing air exchange through a single opening, models to simulate the indoor pressure resulting from fluctuations of the wind-induced outdoor pressure are analysed and experimental requirements for model validation are discussed. The influence of the dimensions of the opening and the volume of the room on the time constant are discussed and the numerical constraints of the non-linear low-pass filter modelling for infiltration are highlighted. In particular the frequency limits for data logging or simulations are dependent on this time constant. A method is proposed to avoid the oscillation of the simulated indoor pressure for the case of under-sampling which frequently occurs because of the limitation of data acquisition rates. The need for further work on this problem is discussed.

Velocity and Turbulence Intensity Distributions of Developing Turbulent Pulsating Flows in Square Duct.

Turbulent pulsating air flows in the entrance region of a square duct are investigated with a hot-wire anemometer system. The velocity waveforms, the mean and turbulence components of the axial velocity, and the entrance length are obtained as major characteristics of the developing turbulent pulsating flows. An inviscid flow theory coupled with the quasi-steady wall shear stress assumption is presented to describe the developing axial mean velocity profiles. A good agreement is seen between the measured and theoretically predicted values. The propagation of turbulence generated near the entrance of the square duct is satisfactorily approximated by an empirical correlation of the propagation of turbulence proposed previously. The local turbulence intensity is found to be slightly weaker in the accelerating phase than in the decelerating phase. The entrance length is about 60 times as large as the hydraulic diameter.

Groundwater Cleanup by In-Situ Sparging. VIII. Effect of Air Channeling on Dissolved Volatile Organic Compounds Removal Efficiency

Abstract A mathematical model for removal of dissolved volatile organic compounds (VOCs) from contaminated aquifers by in-situ air sparging is described. The model assumes that the sparging air moves through persistent channels in the aquifer, and that VOC transport to the sparging air is by diffusion/dispersion and airinduced circulation of the water in the vicinity of the sparging well. The dependence of model results on the parameters of the model is explored. The use of pulsed air flow in sparging as a means to increase VOC transport by dispersion is suggested. An extension and modification of the Sellers-Schreiber preliminary screening model for in-situ air sparging is also described. The revised model includes an improved method for calculating bubble residence times in the aquifer, and also permits the modeling of nonaqueous phase liquid (NAPL) removal.

Mechanisms of Heat Transfer to Liquid Films in the Manifold of Port-Injected Petrol Engines

Results are presented from flow-rig tests in which water from an automotive engine injector was sprayed on to a small heated surface in the presence of both steady and pulsative air flow. The injection was intermittent and synchronized with the pulsating air flow. The aim of the tests was to improve understanding of some of the basic heat and mass transfer mechanisms that occur in port-injected sparkignition engines where fuel is usually sprayed on to the back of the inlet valve. The main observations focused on the heat transfer to the film and the entrainment of the spray and film by the air stream.

Fuel Atomization and Spray Behavior in an Intake Manifold of Gasoline Engine. 2nd Report. In a Pulsating Air Flow.

The newly developed single-point injector was tested. The spray characteristics of the new twin -fluid injector and the spray behavior in a pulsating air flow were investigated. The mean drop size changes according to the spacial position in the spray clump. The droplet deposition rate is influenced by the pulsation of the air flow in the intake manifold of a gasoline engine. The rate decreases with the increase of the air velocity in the manifold. The temporal changes of the number density of the spray droplets, mean drop size and drop velocity are greatly influenced by the pulsation of the air flow at low atomizing air velocity and at high air velocity in the intake manifold. The smaller droplet follows the air flow more easily, and this difference results in the position change in the spray clump.

オリフィス流量計を用いる気体脈動流の動的測定

オリフィス流量計を用いる気体脈動流の動的測定

A study on the flow and thermal characteristics in a pulse combustor. Time-averaged and fluctuation properties of pulsating air flows in a circular tailpipe.

A study on the flow and thermal characteristics in a pulse combustor. Time-averaged and fluctuation properties of pulsating air flows in a circular tailpipe.

A study on corona discharge air mass flowmeter.

A very quick response air mass flowmeter for accurate measurement of intake air of internal combustion engines was developed. This flowmeter consists of a disk-type anode surrounded by two coaxial cylinders which serve as the first and second cathodes. Steady state flow tests show this flowmeter has sufficient accuracy, linearity, and directivity and no hysteresis is observed. The effects of temperature, pressure and humidity of the air are studied. For pulsating air flow, this flowmeter showed excellent dynamic response. Furthermore, this meter succeeded in measuring the intake air flow rate of a single cylinder spark ignition engine under firing conditions. Therefore, this flowmeter is very useful not only for analyzing transient characteristics of internal combustion engines but also for the accurate control of the fuel injection systems of gasoline engines.

Behavior of droplets in pulsating air flow through an intake manifold.

A numerical calculation supplemented by experimental work was conducted of the behavior of fuel droplets subjected to pulsating air flow in the T-branched duct of a square cross section for a better understanding of fuel supply characteristics in an intake manifold of an automotive spark ignition engine. The Lagrangian approach was adopted to derive simultaneous equations of momentum, heat and mass transfer for computing the locations, temperatures and diameters of moving droplets as a function of spatial coordinates The results were expressed primarily in terms of the location at the impact deposition of droplets relevant to the formation of liquid film on the bottom wall of the duct. It was revealed that the calculated results agreed well with the empirical data. It was also suggested that the undesirable aspects of liquid film might possibly by relieved if small droplets with high volatility and low density are infused at optimum timing into a warm air flow with a short period of pulsation.

Particle Separation in Pulsed Airflow

A theoretical model was developed based on a fluid mechanical force balance to describe the behavior of particles in pulsing airflow. Several attributes distinguished this flow regime from those that have been widely studied: (1) The fluid was a gas; (2) the particles were much larger than aerosol; (3) the airflow was pulsed, as opposed to the more commonly studied oscillatory flow; and (4) the flow was vertical, requiring the inclusion of a body force in the expression. Much effort in the theoretical formulation and calibration was devoted to the acceleration effect, due to its importance in time‐varying flow. Computer models were developed and presented that were used in laboratory calibration of the theoretical expression and in modeling particle separation in rising, pulsing airflow. Theory showed separations based upon density that were not possible in steady rising airstreams. Experimentation with air classifier designs suggested by the model showed greatly increased separation efficiency.

Alternating boundary conditions in drying

The flight-and-soaking movement of granules in a rotary dryer gives rise to intermittent drying conditions. An approximate method is presented here for predicting the influence of alternating conditions on the continuous drying curve for slowly drying materials. It is assumed that the periodicity can be characterized by a continuous mass transfer coefficient, proportional to ▪, where t d and t r are the durations of the drying and resting periods, respectively. The model agrees roughly with rigorous numerical solutions to the diffusion equation. It is also substantiated by experimental results from the drying of fertilizer in a bed with a pulsating air flow. Literature data on intermittent drying of wheat also agree with predictions made by the model.

Experimental Study of Mass Transfer from a Sphere in Pulsating Flow

Mass transfer from a naphthalene sphere in a circular tube under steady and pulsating airflow at room temperature is investigated by measuring the loss in weight or the decrease in dimension of the body after a given time. Because of small mass-transfer rate, there is little difference between the results based on analyses with and without the resistance due to the rate of gas flow. Under the pulsating flow, however, the resistance is taken into consideration, because air and C10H8 gas may be mixed enough. Comparison of these results with theoretical ones reported previously gives the following semi-empirical expression: Sh=2+[(0.58)4+(O.38z0.4)4]1/4Sc1/3Re1/2p where, Sh=2rokf/D, z=(aω/U∞)3/2(a/ro)1/2, Sc=ν/D, Rep=2roU∞/ν (a: amplitude, D: diffusivity, kf: mass-transfer coefficient, ro: radius, U∞: free stream velocity, ν: kinematic viscosity, ω: angular frequency). As z=0, this expression agrees with the experimental one for steady flow mass-transfer, i.e., Sh=2+0.58Sc1/3Re1/2pThe experimental results for half naphthalene-coated sphere and of local mass-transfer show that the acceleration effect of pulsating flow on the mass transfer is remarkable in the dead-water region of the sphere, where the mass transfer is small under steady flow.Pressure and velocity in the pipe and around the sphere are measured by the use of a strain-gauge-type pressure transducer and a hot-wire anemometer, respectively, and the flow behavior is also examined.

Etude des conditions particulieres de frequence favorisant les transferts thermiques en ecoulements pulses en canalisation cylindrique

Experimental results of heat transfer occurring between the wall of a circular duct of large diameter (100 mm) and a turbulent pulsed air flow are presented (mean Reynolds number: 15 × 10 5). They show a significant change of convective transfer mechanisms under condition of the acoustical resonance of the duct, leading to a noticeable increase (until 150%) of local heat transfer rates with respect to those obtained in non-pulsed or pulsed without resonance flows. A theoretical study has been attempted with the hypothesis of a laminar pulsed regime; it confirms that, without resonance condition, the pulsation does not change significantly heat transfer as soon as the frequency overtakes few cycles per second.