Airflow Layer Research Articles

Regional PM2.5 pollution confined by atmospheric internal boundaries in the North China Plain: boundary layer structures and numerical simulation

Abstract. This study reveals mesoscale planetary boundary layer (PBL) structures under various pollution categories during autumn and winter in the North China Plain (NCP). The role of the atmospheric internal boundaries (AIBs, referring to the discontinuity of meteorological conditions in the lateral direction) in regulating PBL structures and shaping the PM2.5 pollution patterns is emphasized. The Weather Research and Forecast (WRF) model is used to display the three-dimensional meteorological fields, and its performance is evaluated by surface observations and intensive soundings. The evaluation demonstrates that the model reasonably captures the mesoscale processes and the corresponding PBL structures. Based on the reliable simulations, three typical pollution cases are analyzed. Case 1 and case 2 represent the two main modes of the wind shear category pollution, which is featured with airflow convergence line/zone as AIB, and thus is dominated by dynamical effect. Case 1 presents the west–southwest wind shear mode associated with a trough convergence belt. The convergent airflow layer is comparable to the vertical scale of the PBL, allowing PM2.5 transport to form a high pollution area. Case 2 exhibits another mode with south–north wind shear. A “lying Y-shaped” convergence zone is formed with a thickness of about 3000 m, extending beyond the PBL. It defines a clear edge between the southern polluted air mass and the clean air in the north. Case 3 represents the topographic obstruction category, which is characterized by a cold-air damming AIB in front of the mountains. The PBL at the foothills is thermally stable and dynamically stagnant due to the capping inversion and the convergent winds. It is in sharp contrast to the well-mixed/ventilated PBL in the southern plains, especially in the afternoon. At night, this meteorological discontinuity becomes less pronounced. The diurnal variation of the PBL thermal and dynamical structure causes the pollutants to concentrate at the foot of the mountains during the daytime and locally accumulate throughout the entire plain in the evening. These results provide a more complete mesoscale view of the PBL structure and highlight its spatial heterogeneity, which promotes the understanding of air pollution at the regional scale.

The Impact of a Midlevel Dry Airflow Layer on Deep Convection in the Pre-Gabrielle (2013) Tropical Disturbance on 4–5 September

AbstractOn 4–5 September 2013, a relatively shallow layer of northerly dry airflow was observed just west of the core deep convection associated with the low-level center of the pre-Gabrielle (2013) tropical disturbance. Shortly thereafter, the core deep convection of the disturbance collapsed after having persisted for well over 24 h. The present study provides an in-depth analysis of the interaction between this dry airflow layer and the pre-Gabrielle disturbance core deep convection using a combination of observations, reanalysis fields, and idealized simulations. Based on the analysis, we conclude that the dry airflow layer played an important role in the collapse of the core deep convection in the pre-Gabrielle disturbance. Furthermore, we found that the presence of storm-relative flow was critical to the inhibitive effects of the dry airflow layer on deep convection. The mechanism by which the dry airflow layer inhibited deep convection was found to be enhanced dry air entrainment.

Flow field and cooling capacity in workpiece-tool contact zone during ultra-high speed grinding

Ultra-high speed grinding (UHSG) is a promising machining technology because it can reduce grinding force and greatly increase machining efficiency. However, a mass heat produced in the workpiece-tool contact (WTC) zone risks burning the machined surface during UHSG. Therefore, it is important to ensure timely cooling. The paper studies the flow field of the coolant and cooling capacity of WTC zone under different grinding speeds and coolant velocities by both three-dimensional (3D) finite element (FE) simulation and experiments. Results show that coolant velocity rapidly decreases after a slight initial increase with increasing the distance from the nozzle and little coolant could enter the WTC zone to cool down, which is responsible for the temperature rise in the WTC zone in UHSG. As grinding speed increases, a higher coolant velocity is needed for breaking the barrier of airflow layer to cooling. The critical coolant velocity to break the barrier and enter the WTC zone is obtained by theoretical calculation and experiment. The critical coolant velocity increases with the grinding speed, the coolant velocity needed is 19.2 m/s at the grinding speed of 120 m/s, and it rises to 30 m/s at the grinding speed of 160 m/s. This study could provide a guide to improve the cooling performance in UHSG, which is of great significance to a high-quality surface finish by UHSG.

Effect of a Clean Surgical Airflow Layer on the Incidence of Infection in Total Hip Arthroplasty.

The Center for Health Design estimates that more than 30% of surgical site infections are caused by airborne pathogens. A device that creates a localized clean air field directly adjacent to and surrounding the incision site is meant to shield a surgical site from particulate in the operating room. The purpose of this study was to determine whether the routine use of this device would reduce the rate of infection following total hip arthroplasty (THA). The authors conducted a retrospective review of primary THA cases performed with and without the airflow device. Since July 2013, a total of 1093 primary THA cases were performed with the device at the authors' institution. The incidence of wound dehiscence and deep infection was compared with that of 1171 THA cases performed prior to July 2013 without the airflow device. There were no significant differences between the study groups regarding average patient age, sex, body mass index, or diagnosis. In the airflow group, there were 7 (0.64%) deep infections and 5 (0.46%) cases of wound dehiscence that required a return to the operating room for irrigation and wound revision. In the control group, there were 7 (0.60%) cases of deep infection and 4 (0.34%) wound revisions. The groups were not significantly different in the rates of infection (P=1.0) or wound revision (P=.75). Both groups had a very low incidence of infection and wound revision, with rates below 1%. Despite compelling bench data showing a dramatic reduction of particle load in the wound, the use of the airflow device did not reduce the clinical rate of infection over a large number of cases. [Orthopedics. 2020;43(5):e425-e430.].

Long term examination of thermal management of roof structures with air flow systems or/and polyurethane foams

We have examined the annual, summer, and winter effect of air flow systems to reduce thermal conduction through roof structures and the temperature rise of roof surfaces due to solar absorption. These systems are proposed as replacement for polyurethane foams (PUFs), which are conventionally used for thermal insulation in roof structures and are concerned about the amount of the usage. We prepared six types of roof structures and installed them on experimental cells. The structures consisted of air flow layers and/or PUF layers. We then measured temperatures, evacuated heat, thermal conduction, solar absorption, and thermal radiation every 10 minutes throughout one year. By installing the air flow system in place of or along with PUF, the temperature rise due to solar irradiance of the top roof sheet is suppressed. This suppression is approximately independent of seasons, although it is slightly more effective in winter than summer. Air flow system/PUF combined roof structures control thermal conduction between roof sheets and concrete slabs, though the total thickness is the same or less than those of a single PUF layer. According to heat flow analyses, the air flow systems can evacuate at maximum about 10% of heat that flows into roof structures through the year. In summer, the heat evacuation reduces thermal conduction to concrete slabs, whereas in winter it increases convective heat from concrete slabs. The air flow system is a promising option to allow reduction of the thickness of roof structures and the amount of PUF employed in construction. It is expected to promote improved architectural design, durability, and energy conservation of roofs.

The pseudo-limit problem existing in electromagnetic radiation transmission and its mathematical physics principle analysis

Abstract In the study of electromagnetic radiation transmission for large airflow layers, it is found that not all electromagnetic waves are capable of forming waveguide propagation, and have a limit value problem. This is because whether electromagnetic waves propagating in the atmosphere can be captured by the atmospheric waveguide generated under specific meteorological conditions into the waveguide layer, depending on the wavelength (frequency) of the electromagnetic wave, the relative position of the emission source and the evaporating waveguide. And parameters such as the emission angle of the source. When the angle of incidence of the sun and the angle of observation are at a horizontal level, the amplitude of the electromagnetic radiation reflection is not unique. From a mathematical point of view, the limit value is not unique or the limit value is discontinuous, which is called the pseudo limit problem. This electromagnetic transmission pseudo-limit problem is a mathematical physics principle that ignores the physical principles implied in electromagnetic radiation. Based on this background, the paper studies the influencing factors of the pseudo-limit problem of electromagnetic transmission in large airflow layer, and analyzes the mathematical physics principle in the pseudo-limit problem by using Snell’s optical law.

Analysis of an improved trajectory correction scheme based on mass blocks

In conventional technical trajectory correction schemes, continuous attitude adjusting mechanisms, such as canards, are inferior in terms of response time and efficiency of executing instructions. Discontinuous attitude adjusting mechanisms, such as the lateral pulse jet, have complex impact on the airflow layer of the projectile surface caused by the thrust vector jet flow. An improved two-dimensional trajectory correction mechanism is designed based on the principle of firing mass blocks by a tailor-made propellant. The mechanical properties of the thrust force (namely the correction force) is analyzed. The trajectory correction model is established to analyze the effects of correction starting moment and correction phase angle of a thrust force on the projectile's trajectory. According to the trajectory correction scheme, an improved genetic algorithm is employed to this work. The scheme is tested in the simulation. The results show that the correction scheme is effective to reduce target dispersion and increase the precision of the impact point.

Generation of wind waves by vortices in a retarding flow of air

It is shown that stable waves are generated on a water surface induced by a horizontal airflow whose speed falls along the flux under certain conditions: the period of chain of vortices generated in a viscous layer of airflow coincides with that of a group of waves with a length corresponding to the distance between the vortices. The dependence of a stable wave on the speed and drop in speed of a slowing airflow is obtained.

Investigation of Airflow Field in Grinding Zone Based on FLUENT

It is necessary to supply enough grinding fluid during grinding process to lower grinding temperature. But, there is little grinding fluid into the contact area actually due to the airflow layer with high pressure around grinding wheel. In this paper, the finite element analysis and simulation on airflow field in the grinding zone is performed based on hydrodynamics. The performance and the influencing mechanism of the airflow field on effective grinding fluid are analyzed further. The research works show that it is important to design the grinding wheel and fluid jet parameters reasonably for increasing the proportion of effective grinding fluid.

Rapid point-of-care concentration of bacteria in a disposable microfluidic device using meniscus dragging effect.

We report a low cost, disposable polymer microfluidic sample preparation device to perform rapid concentration of bacteria from liquid samples using enhanced evaporation targeted at downstream detection using surface enhanced Raman spectroscopy (SERS). The device is composed of a poly(dimethylsiloxane) (PDMS) liquid sample flow layer, a reusable metal airflow layer, and a porous PTFE (Teflon™) membrane sandwiched in between the liquid and air layers. The concentration capacity of the device was successfully demonstrated with fluorescently tagged Escherichia coli (E. coli). The recovery concentration was above 85% for all initial concentrations lower than 1 × 10(4) CFU mL(-1). In the lowest initial concentration cases, 100 µL initial volumes of bacteria solution at 100 CFU mL(-1) were concentrated into 500 nL droplets with greater than 90% efficiency in 15 min. Subsequent tests with SERS on clinically relevant Methicillin-Sensitive Staphylococcus aureus (MSSA) after concentration in this device proved more than 100-fold enhancement in SERS signal intensity compared to the signal obtained from the unconcentrated sample. The concentration device is straightforward to design and use, and as such could be used in conjunction with a number of detection technologies.

Experimental Study on Point Grinding Technical Parameters Affecting Coolant Jet Parameters

Point grinding is a new type of high and super-high speed grinding process with a point contact zone and less grinding force. Because of the lower grinding power, the grinding heat in point grinding process is much less than that of the conventional grinding process. Therefore, the less grinding coolant jet parameters can be used during point grinding process. That is very propitious to the environment and resource, as well as the green manufacturing. Based on the mathematic model of the edge contact area of point grinding, the simulations of the edge contact area with point grinding angles and depth of cut was performed to study the grinding power. In addition, the relations between the grinding power and the depth of cut and vertical grinding angle were investigated. The dynamic pressure and velocity distributions in the airflow layer around the wheel edge were analyzed more by means of experiment. The point grinding experiment for grinding coolant jet parameters was performed.

Study on Effect of Grinding Fluid Supply Parameters on Surface Integrity in Quick-Point Grinding for Green Manufacturing

In high and super-high speed grinding process, there is an airflow layer with high speed around the circle edge of the grinding wheel that hinders the grinding fluid into contact layer, namely, the air barrier effect. The speed of airflow layer is directly proportional to the square of the wheel speed. Quick-point grinding is a new type of high and super-high speed grinding process with a point contact zone and less grinding power. The edge effect of the air barrier is weakened because the thin CBN wheel is applied in the process. By the analysis of dynamic pressure and velocity distributions in the airflow layer around the wheel edge, the mathematic models of the flow and jet pressure of grinding fluid for effective supply in the process were established and the process of optimization calculation of the jet nozzle diameter for green manufacturing was also analyzed based on the thermodynamics and the technical character of quick-point grinding process. The quick-point grinding experiment for surface integrity influenced by grinding fluid supply parameters was performed.

Physical principle of wind erosion on sandy land surface in southern Beijing

The endangerment of aeolian sand is one of the most serious eco-environmental problems facing the southern suburb of Beijing. To control wind erosion is thus a matter of great urgency. This paper chooses typical land-use types, i.e., cultivated land, wild grassland, drifting sandy land, etc. based on the fixed experimental observation and quantitative analysis, to conduct studies on the principles and characteristics of aeolian activities and measures controlling wind erosion in Daxing District of Beijing. The results show that: the near ground wind velocity yielded the logarithmic distribution with height; there are significant differences among different ground cover roughness; there are significant differences in the corresponding friction velocities caused by different properties of the underlying surface; there are differences in the threshold wind velocities speed in different land use types; and there are minus exponential relations between the sediment discharge percentage and the height at a range of 0–20 cm air flow layer. Different land use types result in various degrees of coarse component. There is a significant exponential relation between sediment transport concentration and wind velocity.

転がり軸受の冷風潤滑に関する研究 ２ 軸受に供給された冷却エアの挙動

Continued to the first report, this paper deals with the behavior of cooling generated by vortex tube leading to a set of angular contact ball bearings operated which are high speed in machine tool spindle. The main purpose is to make clear the bearing cooling mechanism by measuring the temperature and flow situation of cooling air, which are exerted by the air flow layer produced from the rotation of bearing retainer, and the bearing circumference temperature distribution. As a result of the experiment, the followings are clarified. (1) If the distance between bearing and cooling air nozzle is 25 mm or less, cooling effect is obtained almost the same. (2) The temperature of cooling air has a little change by arrangement angle between rotating directions of bearing and the cooling air nozzle. (3) As for the cooling air, the temperature can rise immediately after jetted from a nozzle and keep 0 degree or less to the location where is around 15 mm apart from the nozzle. (4) The cooling air supplied to bearing does not reach at the inside of bearing, and revolves around perimeter of bearing.

Multiple Radon Entry Modeling in a House with a Cellar

ABSTRACT Combining a computational fluid dynamics (CFD) model and a multi-zonal model, a study was carried out on radon entry through the complex substructure of a house with a cellar. The uniqueness of the radon entry problem in this type of house was due to the involvement of two radon entry routes to two chambers: the cellar and the living area of the house. Soil gas carrying radon was driven through the two routes by two coupled disturbance pressures in the chambers. The effects of temperature differences were considered as another driving force for the radon entry. Examined in this study were the effects of the geometry of the substructure, air permeability of the soil, air-tightness of the cellar shell, and cellar ventilation on radon entry to both the cellar and the living area. The ground floor covering on top of the soil outside a cellar wall increased radon entry through this wall by about 68%, as radon built up to a very high level under the covering. The effect of cellar ventilation was found as follows: the cellar ventilation created a layer of airflow in the soil under the ground floor; the flow passed over a crack in the ground floor, the entry route to the living area, diluting the radon in the area. Hence, the soil gas entering the living area carried less radon. Cellar ventilation seems more effective in reducing radon entry to the living area in a more permeable soil and leaky cellar shell; a moderate cellar ventilation condition achieved 77% reduction in radon entry to the area. When permeability of these two materials was lower and soil radon content remained the same, the chances of radon entry was also lower; hence, the indoor radon level was lower and no radon control was needed. When such soil contains high radon concentration, other mitigation measures must be sought.

Cooling action of grinding fluid in shallow grinding

A new method is proposed for measuring the heat transfer coefficient in the vicinity of the wheel-workpiece contact zone. The accuracy of measurement is estimated by using a finite element method and the factor for correcting the measured results is derived. The experiments are performed in a number of conditions where grinding fluid is supplied and the following measures are consequently recommended for increasing the cooling efficiency: (1) set the velocity of coolant to more than the critical value to penetrate the air flow layer formed around the wheel periphery; (2) use a nozzle with a thin throat, about 1 mm in height, and attach a scraper plate above the nozzle outlet; (3) choose a wheel of large grain size and dress roughly, or form shallow grooves on the wheel periphery; and (4) set a higher wheel speed.