Horizontal Air Research Articles

Nonlinear interaction between two components of motion upon precipitation of a heavy particle in a shear flow

When heavy particles move in a shear flow, the drag depends on the Reynolds number and, hence, on the magnitude of the particle velocity relatively to the medium. This leads to a nonlinear interaction between various components of motion. For example, when a particle precipitates in a horizontal air flow with vertical shear, it also acquires horizontal motion relative to air in addition to vertical motion. These two components of motion contribute to the hydrodynamic drag coefficient by affecting the Reynolds number and thereby influence each other. Steady motion of a particle in a flow with constant vertical shear is analyzed. Dimensionless criterion of significance of the nonlinear effect under consideration is determined. It is demonstrated that this effect can be significant in the near-surface atmospheric layer in the case of storm wind.

Fluid dynamics of horizontal air–water slug flows through a dividing T-junction

Experimental data from horizontal air–water slug flows were obtained in a test facility which was a 34mm internal diameter, 10m long Plexiglas pipe connected to the 90° branch arms from a T-junction. The test points were located on the flow pattern map in the proximity of the transition lines which separates different flow patterns. Capacitive probes with helical and concave plate sensors were used to quantify the dynamic liquid holdup in each branch. They were combined with Venturi nozzles+differential pressure transmitters in each outlet branch for measuring the two-phase mass flow rates. The dynamic characteristics of the slug flow splitting in a T-junction were studied from the acquired signals. Diaphragm straight-through type valves were used in the run and in the lateral branch arms to imitate equipments consuming the two-phase flow after the T-junction. This assembly can also be used as a gas–liquid separation system. The results showed different mechanisms acting on the slug flow division phenomenon. Liquid accumulation into the run branch, between the TJ and the control valve, caused more gas to come to the lateral branch.

Characterization of turbulent airflow over evolving water‐waves in a wind‐wave tank

Results of an experimental investigation of the turbulent boundary layer in airflow over evolving young wind‐waves are presented. The experiments were conducted in a laboratory wind‐wave flume consisting of a closed‐loop wind tunnel capable of generating wind speed that may exceed 15 m/s, atop of a 5 m long wave tank. Simultaneous measurements of mean wind velocity and of instantaneous fluctuations of the horizontal and vertical air velocity components were carried out along the test section at different airflow rates and at numerous heights above the highest wave. Instantaneous surface elevation at the air sensors' location was simultaneously recorded. The friction velocities at all locations and for all airflow rates were determined by two independent methods: by fitting the logarithmic velocity profiles and by extrapolating the measured Reynolds shear stresses to mean water surface level. The variation with height and along the test section of the fluctuations of two velocity components, in the mean flow and in the vertical directions, was also studied and the results compared with flow behavior over rough and smooth plates. Wave‐induced airflow parameters were then investigated by application of cross‐spectral analysis. Results on the vertical extent of wave‐induced boundary layer, on the phase relation between the wave‐induced velocity fluctuations and the surface elevation, as well as on the wave‐induced Reynolds shear stress are reported.

CFD modelling of aerodynamic sealing by vertical and horizontal air curtains

This work presents a comparative study of the aerodynamic sealing of doorways of refrigerated rooms, obtained by vertical and horizontal air curtain devices (ACD). The sealing efficiency is estimated for different situations, with the ACD installed inside, outside or on both sides of the door.For this purpose, a numerical model was developed for the simulation of the turbulent non-isothermal 3D airflow generated by the air curtain in the transient period after the door is opened. The buoyancy-induced airflow field when the ACD is turned off and the door is open was taken as a reference to assess the sealing efficiency.Numerical results are plausible and comply with the physical interpretation of the convective phenomena. In line with previous investigations, the optimum velocity of the air jet was found, corresponding to the highest sealing effect.The advantage of installing the ACD outside the refrigerated room was shown by the present simulations. According to the present study, downward blowing air curtains present better sealing efficiency (over 70%) compared to horizontal jet air curtains (about 55%). Although the direct air recirculation provides a better sealing efficiency (over 80%), the system complexity and the installation and maintenance costs inhibit its common use.

Near ground air temperature calculation model based on heat transfer of vertical turbulent and horizontal air flow

In order to calculate the air temperature of the near surface layer in urban environment, the surface layer air was divided into several sections in the vertical direction, and some energy balance equations were developed for each air layer, in which the heat exchange due to vertical turbulence and horizontal air flow was taken into account. Then, the vertical temperature distribution of the surface layer air was obtained through the coupled calculation using the energy balance equations of underlying surfaces and building walls. Moreover, the measured air temperatures in a small area (with a horizontal scale of less than 500 m) and a large area (with a horizontal scale of more than 1 000 m) in Guangzhou in summer were used to validate the proposed model. The calculated results accord well with the measured ones, with a maximum relative error of 4.18%. It is thus concluded that the proposed model is a high-accuracy method to theoretically analyze the urban heat island and the thermal environment.

Multiscale Performance Characterization of Concrete Formed by Controlled Permeability Formwork Liner

It is well known that the permeation and retention of water with a controlled permeability formwork (CPF) liner directly contribute to discharging superfluous water and minimizing bubble content when fresh concrete is poured and cured. These phenomena considerably improve the properties of concrete. To comprehensively evaluate this technology, an extensive experimental program on evaluating the discharged water, moisture content, water-binder ratio variation during the casting process, and surface quality of specimens formed with the CPF liner and control formwork was conducted. Two types of CPF liners with different parameters in the vertical and horizontal permeability coefficients, weight, nominal thickness, and air permeability coefficient were considered. In addition, multiscale experimental characterization of concrete samples, including chloride ion permeability, abrasion resistance, ultrasonic test, scanning electron microscope, and mercury intrusion porosimetry, was performed. It demonstrated that the compactness, antipermeability, and rebound strength of specimens were increased effectively if the key parameters (e.g., permeability coefficients, weight, and thickness) of the CPF liner were properly chosen. Moreover, the fractal dimension of material porosity, which correlates to the cumulative volume of intruded mercury for the specimens, was computed, and it was capable of quantifying concrete surface densification and revealing the quality-improvement mechanism of concrete formed with the CPF liner.

Observation of Horizontal Air Showers with ARGO-YBJ

A preliminary analysis of Extensive Air Showers reconstructed by ARGO-YBJ with zenith angle greater than 80° is reported. The measurement of the size spectrum and of the azimuthal distribution is discussed. A description of the topology of these events is also provided.

Wavelet analysis on particle dynamics in a horizontal air–solid two-phase pipe flow at low air velocity

High-speed particle image velocimetry (PIV) is first used to measure two components of the fluctuating particle velocities for different particle sizes and solid mass flow rates at low air velocity in a horizontal pipe. Then, the continuous wavelet transform and orthogonal wavelet multi-resolution techniques are employed to analyze and decompose the fluctuating particle velocities to provide both quantitative and qualitative information on the particle fluctuation velocity of various frequencies. It is revealed that the fluctuating energy of axial particle velocity is mainly contributed from the wavelet components of low frequency, accounting for about 84%, near the bottom part of the pipe cross-section. However, the contribution to the fluctuating energy of vertical particle velocity accounts for about 82% from the wavelet components of high frequency. The auto-correlation analysis suggests a quasi-periodical large-scale axial particle fluctuating velocity. On the other hand, the spatial correlation analysis indicates that the low-frequency components of the axial particle velocity exhibit a large correlation near the bottom part of the pipe cross-section. From the probability density function (PDF) distribution, it is found that the low-frequency components of the axial particle velocity exhibit larger fluctuation, and this fluctuation reduces as the frequencies increase near the bottom part of the pipe cross-section. Near the top part of the pipe cross-section, however, a larger fluctuating axial particle velocity appears in the high-frequency range.

Numerical analysis of supersonic gas jets into liquid pools with or without chemical reaction using the SERAPHIM program

Abstract A computer program called SERAPHIM has been developed to calculate multicomponent multiphase flow involving sodium-water chemical reaction in a steam generator of sodium cooled fast reactors. In this study, numerical analyses of supersonic gas jets into liquid pools with or without chemical reaction were performed to validate proposed numerical methods. The SERAPHIM program uses a multi-fluid model and a HSMAC method modified for compressible multiphase flows. An interfacial drag force was calculated from a newly constructed model. A surface reaction model, which has been developed by the authors, was applied to evaluate a mass generation rate by chemical reaction between a gas and liquid phase. As validation for a non-reaction problem, the experiment on horizontal supersonic air jet into water was analyzed. Numerical results showed that velocity of the injected air decreased by the effect of a interfacial drag force, and then the air went upward because of buoyancy. A horizontal penetration length of the air jet agreed with experimental results very well. On the other hand, we analyzed the experiment on vertical supersonic chlorine jet into Na–NaCl mixture. In this analysis, the injected gas disappeared at a certain height from chemical reaction. An estimated plume length showed good agreement with experimental data. The proposed numerical methods were found to be applicable to multiphase flow with supersonic gas jet and chemical reaction.

NOY: a neutrino observatory network project based on stand alone air shower detector arrays

We have developed a self powered stand alone par- ticle detector array dedicated to the observation of horizontal tau air showers induced by high energy neutrinos interacting in mountain rock. Air shower particle detection reaches a 100% duty cycle and is practically free of background when compared to Cherenkov light or radio techniques. It is thus better suited for rare neutrino event search. An appropriate mountain to valley topological configuration has been identi- fied and the first array will be deployed on an inclined slope at an elevation of 1500 m facing Southern Alps near the city of Grenoble (France). A full simulation has been performed. A neutrino energy dependent mountain tomography chart is obtained using a neutrino and tau propagation code together with a detailed cartography and elevation map of the region. The array acceptance is then evaluated between 1 PeV and 100 EeV by simulating decaying tau air showers across the valley. The effective detection surface is determined by the shower lateral extension at array location and is hence much larger than the array geometrical area. The array exposure will be 10 14 cm 2 sr s at 100 PeV. Several independent arrays can be deployed with the aim of constituting a large distributed observatory. Some other sites are already under study. At last, special care is dedicated to the educational and outreach aspects of such a cosmic ray detector.

Evolution to chaotic mixed convection in a multiple ventilated cavity

The characteristics of transition from laminar to chaotic mixed convection in a two-dimensional multiple ventilated cavity is analyzed in this paper. The horizontal air streams enter the cavity from the two inflow-openings near the top of both vertical walls, while the outflow openings are near the bottoms of both vertical walls. The results obtained for a range of the Richardson number, Ri, from 0.01 to 5 at Pr = 0.71, the Reynolds number, Re, from 1000 to 2500 and the inlet flow angle, φ, based on 0°, 20°, 45° and 70°. The results show that, as Ri increases, the solution may exhibit a change from steady-state to periodic oscillation, and then to non-periodic oscillatory state. However, the flow inside the cavity becomes steady-state again as Richardson number increases further. The results also show that the effect of inlet flow angle on the oscillations of mixed convection is evident, the configuration with φ = 0° is the most unstable among the four values of φ. The non-periodic oscillatory solution at Re = 2500 is studied by means of phase portraits, correlation dimension, Kolmogorov entropy and Lyapunov exponents to detect chaos. The phase portraits show the evolution of the attractor from a stable fixed point to a limited cycle to chaos, and finally, to a stable fixed point again, and the correlation dimension, Kolmogorov entropy and the largest Lyapunov numbers all show that the behavior of mixed convection in this dynamical system lies on a low-dimensional chaotic attractor according to the non-periodic oscillatory solution.

Evaporation of methanol droplet on the Teflon surface under different air velocities

Abstract An experiment on the evaporating methanol droplet under different horizontal air velocities on Teflon substrate is presented. The droplet shape evolution was investigated using optical techniques (camera) of DSA100 apparatus. The controlled air velocity is at temperature of 22 °C (ambient and initial droplet). The contact angle, the base line were recorded and the volume time evolution is deduced. It was observed that there were three distinct stages for all air velocities: the constant contact angle stage (CA), the constant contact based line “diameter” stage (CD) corresponding to pinned triple line stage and the transition stage (TS) between CA and CD. In the three stages, the evaporation rate increases with the air velocity increase. And the resulting droplet lifetime is reduced by such increasing of the air velocity. In all different air velocities, it was found that among the three stages, the evaporation rate of the CA stage was largest, the evaporation rate of the CD stage is the least and the evaporation rate of the transition stage is the middle. And the evaporation rate is depended on the energy balance between the latent heat and the sensible heat.

Droplet deposition measurement with high-speed camera and novel high-speed liquid film sensor with high spatial resolution

A sensor based on the electrical conductance method is presented for the measurement of dynamic liquid films in two-phase flow. The so called liquid film sensor consists of a matrix with 64 × 16 measuring points, a spatial resolution of 3.12 mm and a time resolution of 10 kHz. Experiments in a horizontal co-current air–water film flow were conducted to test the capability of the sensor to detect droplet deposition from the gas core onto the liquid film. The experimental setup is equipped with the liquid film sensor and a high speed camera (HSC) recording the droplet deposition with a sampling rate of 10 kHz simultaneously. In some experiments the recognition of droplet deposition on the sensor is enhanced by marking the droplets with higher electrical conductivity. The comparison between the HSC and the sensor shows, that the sensor captures the droplet deposition above a certain droplet diameter. The impacts of droplet deposition can be filtered from the wavy structures respectively conductivity changes of the liquid film using a filter algorithm based on autoregression. The results will be used to locally measure droplet deposition e.g. in the proximity of spacers in a subchannel geometry.

An Cold Experimental Analysis of Draught System with Chain-Grate Stoker

The study of cold state testing and evaluation analysis were carried on the practical running chain-grate stoker, which has an air-supply system with air storehouse and airtrough, to study the air-distribution, air leakage, air tightness and air governing. The result shows that horizontal air distribution across the furnace and the air tightness of the components such as the air port (damper) and airtrough are good. However the air leakage is large because of the complex structure and the high demand of integrated air tightness either in the front or the back of the stoker. The cost of the stoker is high because of large quantity of machine work after casting and high demand of installation, thus the structure should be improved.

Numerical Simulation of Flow and Combustion Characteristics in a 300 MWeDown-Fired Boiler with Different Overfire Air Angles

A computational fluid dynamics (CFD) model of a 300 MWe down-fired furnace equipped with overfire air (OFA) has been developed using Fluent 6.3. A level of confidence in the current CFD model has been established by performing mesh-independence tests and verified by comparing furnace temperature simulations with actual furnace data. The validated CFD model is then applied in the investigation of the effects of several operating conditions at full load with different OFA nozzle angles. In the down-fired furnace, the primary air/fuel was found unable to penetrate the horizontal secondary air flow zone and reach the furnace hopper; thus, no combustion occurs in the furnace hopper zone. The peak-temperature zone appears in the upper furnace, contrary to the original design concept. Simulation results also indicate that an OFA nozzle angle set below 30° moves the mixing point of the OFA flow and the up-flowing gas downward, further aiding combustion in the upper furnace. However, when the angle increases above...

Heat transfer characteristics in a horizontal swirling fluidized bed

An innovative horizontal swirling fluidized bed (HSFB) with a rectangular baffle in the center of an air distributor and three layers of horizontal secondary air nozzles located at each corner of fluidized bed was developed. Experiments on heat transfer characteristics were conducted in a cold HSFB test model. Heat transfer coefficients between immersed tubes and bed materials in the HSBF were measured with the help of a fast response heat transfer probe. The influences of fluidization velocity, particle size of bed materials, measurement height, probe orientation, and secondary air injection, etc. on heat transfer coefficients were intensively investigated. Test results indicated that heat transfer coefficients increase with fluidization velocity, and reach their maximum values at 1.5–3 times of the minimum fluidization velocity. Heat transfer coefficients are variated along the circumference of the probe, and heat transfer coefficients on the leeward side of the probe are larger than that on the windward side of the probe. Heat transfer coefficients decrease with increasing of measurement height; heat transfer coefficients of the longitudinal probe are larger than that of the transverse probe. The proper secondary air injection and particle size of bed materials can generate a preferred hydrodynamics in the dense zone and enhance heat transfer in a HSFB.

Natural convection in a partially open square cavity with internal heat source: An analysis of the opening mass flow

A steady buoyancy-driven flow of air in a partially open square 2D cavity with internal heat source, adiabatic bottom and top walls, and vertical walls maintained at different constant temperatures is investigated numerically in this work. A heat source with 1% of the cavity volume is present in the center of the bottom wall. The cold right wall contains a partial opening occupying 25%, 50% or 75% of the wall. The influence of the temperature gradient between the verticals walls was analyzed for Rae=103–105, while the influence of the heat source was evaluated through the relation R=Rai/Rae, investigated at between 400 and 2000. Interesting results were obtained. For a low Rayleigh number, it is found that the isotherm plots are smooth and follow a parabolic shape indicating the dominance of the heat source. But as the Rae increases, the flow slowly becomes dominated by the temperature difference between the walls. It is also observed that multiple strong secondary circulations are formed for fluids with a small Rae whereas these features are absent at higher Rae. The comprehensive analysis is concluded with horizontal air velocity and temperature plots for the opening. The numerical results show a significant influence of the opening on the heat transfer in the cavity.

Advancement of Sodium-Water Reaction and Compressible Multiphase Flows Analysis Program SERAPHIM (Validation for a Reactive Gas Jet in a Liquid Pool)

A computer program called SERAPHIM has been developed to calculate the multicomponent multiphase flow involving the sodium-water chemical reaction in a steam generator of sodium cooled fast reactors. In this study, numerical analysis of supersonic gas jets into liquid pools with or without chemical reaction was performed to validate the numerical methods. As validation for a non-reaction problem, the visualization experiment on the horizontal supersonic air jet into the water was analyzed. The behavior of the jet and the horizontal penetration length were reproduced very well. On the other hand, the experiment on the vertical supersonic chlorine jet into the Na-NaCl mixture was analyzed. The numerical result showed that the injected gas disappeared at a certain height. The estimated plume length showed good agreement with the experimental data. The numerical methods were found to be applicable to the multiphase flow with the supersonic gas jets and the chemical reaction.

Mixing Time in a Bath in the Presence of Swirl Motion Induced by Horizontal Gas Injection with an L-Shaped Lance

Water model experiments are carried out to understand the mixing behavior of the steel refining processes agitated by horizontal gas injection. Mixing time in a cylindrical water bath agitated by horizontal air injection through an L-shaped top lance is measured with an electric conductivity meter. Several types of bath surface oscillations are induced by the gas injection depending on the operation parameters such as the vessel diameter and gas flow rate. Particular emphasis is placed on the condition that a swirl motion of the deep-water wave type appears in the bath. This is because the swirl motion plays a practically important role for bath mixing. The diameter of the bath, lance exit position, bath depth, and gas flow rate are varied over a wide range. An empirical equation is proposed for the mixing time in the presence of the swirl motion.

Adjusting gap plasmon transmission and intensity in metal-insulator-metal waveguide

A device capable of adjusting gap plasmon (GP) transmission and intensity is proposed. The structure consists of two metallic films: one is etched with a nanoslit, and the other below is movable. Between them is a horizontal air channel. Numerical simulations show that the GP sources can produce alternatively in ports A and B when the film below is moved together with a groove in the center; thus, a sawtooth-like waveform is observed, which is different from the sine-like case without a groove and can be explained well by Fourier series. In addition, with the optimized length of film below, the source intensity can be further enhanced for Fabry–Perot resonance producing in both channels A and B.