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Wheels and wheelhouses are a significant source of aerodynamic drag on passenger cars. The use of air jets, in the form of an air curtain, to smooth the airflow around front wheel housings on cars has become common practice, as it produces a small drag benefit. This paper reports an initial small-scale wind tunnel study of an air jet employed as an effective wheel spoiler to reduce the drag produced by the front wheels and wheel housings of passenger cars. For this investigation, the air jet was created using an external compressed-air supply and was applied to a highly simplified car body shape. The data presented suggest that the air jet has some potential as a drag-reduction device. [ABSTRACT FROM AUTHOR]

This article is related to investigations of the capture hoods of the local exhaust ventilation. The purpose of the research: to increase the zone of action of local exhaust hoods and reduce the amount of air removed. It is equipped with two barriers for air: ring and cylindrical. The empirical dependences for air velocity determination near the suction zone are obtained. Graphs, chart and three-dimensional image visualizations of removed air jet velocity near capture hood with barriers for air are designed. The reduction of production energy consumption, material, and ventilation system maintenance costs due to the correction of the design of the capture hood are the main benefits of the new solution. [ABSTRACT FROM AUTHOR]

Flexible, continuum-type robots can access narrow spaces in debris areas during search-and-rescue missions. However, their current problem is the lifting capability of the head, which is necessary to surmount the rubble. This study proposes a passive-thrust vectoring method to stabilize head levitation for air-jet-actuated, long, continuum robots, and thus enhance their step-climbing abilities. An air jet can generate a thrust force that is sufficient for head levitation. A critical issue in levitation involves the backward bending of the head without using any air-jet control; however, thrust control is inappropriate because of the delay caused by the long channel. Therefore, the proposed method maintains the thrust direction constant. Sufficient conditions for global stability are derived and confirmed via dynamic simulations. The proposed method is simple and can be mechanically realized with a passive head-bending mechanism, thus contributing to a lightweight design. Experiments demonstrated that the developed air-floating-type, 7-m long robot, can achieve stabilized head levitation, and that the robot can climb a step with a height of 250 mm. Robot demonstrations in rubble justify the robot’s capacity to surmount the rubble. This passive-thrust vectoring method is expected to contribute to the future enhancement of the mobility of continuum robots owing to its simplicity and practicality. [ABSTRACT FROM AUTHOR]

This article is directed on increase of the premise ventilation efficiency by using linear diffusers. The aim of the work was to carry out theoretical research, experimental investigations and numerical modeling of the linear diffuser air dynamic characteristics, to obtain the graphs and analytical equations for determination of the linear diffuser necessary parameters and to encrease of efficiency air distribution in the room. Graphs of air velocity dependence on current coordinate and plates angle have been created and approximated by empirical equations. There was established that air velocity decreases intensively with increasing current coordinate and decreases with increasing of the plates angle. [ABSTRACT FROM AUTHOR]

This paper focused on the investigation of the slub yarn parameters and the relationships of the aerodynamic friction along the surface of the slub yarn. The calculation of the frictional drag force was analyzed for spun yarns, which proves it has an irregular surface due to the irregularity of the yarn diameter along its length. In the case of slub yarns, the main descriptive parameters such as slub length, slub distance, slub multiplier, and base yarn count, will affect the air drag coefficient. A methodology for the calculation of the coefficient of air drag along the yarn in an airstream was developed for both regular and slub yarns under different conditions. The air frictional drag coefficients of yarn samples were calculated accordingly. Finally, empirical equations were developed. Calculations of the air friction drag coefficient of slub yarn were determined. The experimental results agreed well with the model predictions and showed that the present model had a high prediction accuracy. [ABSTRACT FROM AUTHOR]

The underexpanded jet induced by loss of vacuum accidents (LOVA) can significantly impact the fusion reactor management, since it poses safety problems associated with hydrogen risks and radioactivity to the environment. To characterize the air ingress process into the high vacuum environment, simulations were performed with OpenFOAM modelling in a representative small-scale fusion facility. The general features of the thermodynamic parameters, such as density, pressure, velocity, and temperature, were analyzed, and also characterized the wall friction velocity and the formation of the Mach disk within the underexpanded jet. Proper orthogonal decomposition (POD) method was applied to compare the fluid dynamic behaviors of the jet subjected to different thermodynamic conditions. The results show that the rapid expansion and acceleration of the jet leads to a decrease in density and an accumulation of the gas along the centerline. The high jet velocity will result in a lower jet temperature and raise the temperature of the surroundings, which also triggers the formation of recirculation zones, and the gradual development of Mach disk structure, also, the higher wall friction velocity will further contribute to the complex air ingress dynamics. Moreover, it is observed that the ideal gas and real gas model appear similar fluid dynamic structures and energy modes during the pressure and velocity development, and only subtle differences appear in the low energy contribution POD modes. The main differences of the energy modes are captured in the momentum field between these different thermodynamic conditions. The observations can contribute to fusion safety management and appropriate thermodynamic modelling selection in such applications. [ABSTRACT FROM AUTHOR]

Wheels and wheelhouses are a significant source of aerodynamic drag on passenger cars. The use of air jets, in the form of an air curtain, to smooth the airflow around front wheel housings on cars has become common practice, as it produces a small drag benefit. This paper reports an initial small-scale wind tunnel study of an air jet employed as an effective wheel spoiler to reduce the drag produced by the front wheels and wheel housings of passenger cars. For this investigation, the air jet was created using an external compressed-air supply and was applied to a highly simplified car body shape. The data presented suggest that the air jet has some potential as a drag-reduction device.

A ring-type nozzle combining a jet of air and water was employed in this study for improving the quality of laser-cut channel and limiting thermal damage along the cut. A nanosecond pulse laser equipped with the water–air jet nozzle was used for producing a microgroove on the surface of commercially pure titanium. The influences of average laser power, air pressure, and water flow rate on groove dimensions and size of damage region were experimentally investigated. The results revealed that using high air jet pressure together with high water flow rate provided a narrow and deep groove with little recast deposition. The selections of air jet pressure and water flow rate were also found to be nonlinearly dependent to each other for creating a microgroove with high aspect ratio. With the aid of weighted sum method, an optimum condition of the coaxial water and air jet–assisted laser micromachining of titanium was 30-W average laser power, 2-bar air jet pressure, and 2.5-l/min water flow rate. Under this condition, a high aspect ratio groove with negligible recast and no heat-affected zone was achievable by using the proposed technique. [ABSTRACT FROM AUTHOR]

Monitoring the tool condition of machining processes is important but challenging. Several automated tool condition monitoring solutions are available, but often not used due to existing restrictions or disadvantages. A new approach can be the detection and measurement of tool conditions analyzing the sound of an air jet impingement on tools. Due to the availability of compressed air as a working and cleaning medium for many processes, this approach can be used for various condition monitoring and measuring tasks. In this paper the procedure and its functionality are first presented on simple shapes and then tested on the tool wear of inserts. [ABSTRACT FROM AUTHOR]

We propose the mechanism and control method of the air jet based parallel link actuator with 6 degrees of freedom. The rotor of the actuator is called a platform which is constructed by connecting multiple spheres that are located in vertex of a regular polygon with high rigid wires. Each sphere is spatially levitated using coanda effect and its 3D position is feedback controlled by the dedicated air jet driven by a pan-tilt motor on the stator of the actuator. First, we discuss the platform structure in which n spheres are arranged at the vertices of a regular polygon, and the kinematics and control of the parallel link mechanism in which each sphere is operated by one of n air jet nozzles arranged in the same structure as the platform. Then we created an experimental system using the case of the minimum number n = 3, implemented a control system based on the inverse kinematics, and conducted operation experiments. The basic validity of the proposed method was confirmed by evaluating the experimental results obtained from an external measuring system which can accurately calculate the position and the orientation of the platform.

To effectively reduce shock wave loss at the trailing edge of a supersonic cascade under high back-pressure, a shock wave control method based on air jets is proposed. The air jet was arranged on the pressure side of the blade in the upstream of the trailing-edge shock. The flow control mechanism and effects of parameters were analyzed by computational methods. The results show that the air jet formed an oblique shock wave in the cascade passage which decelerated and pressurized the airflow. The resulting expansion wave downstream of the jet slot weakened the strength of the trailing-edge shock. This could effectively change the normal shock into oblique shock and thus weaken the shock loss. Optimal control effect was achieved when the mass flow rate ratio of the jet to the passage airflow remained 0.35–1.11% and the distance from the jet slot to the shock foot of the trailing-edge shock was about five times the thickness of the boundary layer. The proposed method can reduce the total pressure loss of a supersonic cascade, with the maximum improvement effect reaching 7.29% compared to the no-control state.

A computational study on the performance of mixed compression supersonic air intake has been carried out with and without air jet at various operating conditions. Commercially available software ANSYS was used and K-ω SST turbulence model was selected to capture the turbulent flow inside the air intake. All the simulations were simulated at a design Mach number of 2.2. Two Air jet of 1 mm diameter each and perpendicular to the local ramp surface have been placed in longitudinal direction at 0.47 times the total length of the air intake. Effect of variation of injection pressure on the flow field of air intake has been studied. Injection pressure has been varied with respect to the free stream pressure. Four different cases of injection pressure have been investigated. Three different positions (1.far away before the air jet, 2. immediately after the air jet and 3. far away behind the air jet) of normal shock were simulated to study the effect of air jet by varying the back pressure of the supersonic air intake. Significant reduction in the flow separation due the normal shock wave was noticed for all the cases of injection pressure, which further helps in improving the performance of the supersonic air intake. Important performance parameters such as flow distortion, mass flow ratio and total pressure recovery were calculated to measure the efficacy of supersonic air intake with air jet at various operating conditions. [ABSTRACT FROM AUTHOR]

A novel noncontact indentation system with the combination of an air jet and optical coherence tomography (OCT) was presented in this paper for the quantitative measurement of the mechanical properties of soft tissues. The key idea of this method is to use a pressure-controlled air jet as an indenter to compress the soft tissue in a noncontact way and utilize the OCT signals to extract the deformation induced. This indentation system provides measurement and mapping of tissue elasticity for small specimens with high scanning speed. Experiments were performed on 27 silicone tissue-mimicking phantoms with different Young's moduli, which were also measured by uniaxial compression tests. The regression coefficient of the indentation force to the indentation depth (N mm(-1)) was used as an indicator of the stiffness of tissue under air jet indentation. Results showed that the stiffness coefficients measured by the current system correlated well with the corresponding Young's moduli obtained by conventional mechanical testing (r = 0.89, p < 0.001). Preliminary in vivo tests also showed that the change of soft tissue stiffness with and without the contraction of the underlying muscles in the hand could be differentiated by the current measurement. This system may have broad applications in tissue assessment and characterization where alterations of mechanical properties are involved, in particular with the potential of noncontact micro-indentation for tissues.

Introduction Iran is a frontier of pomegranate fruit production in the world (with almost 40 % of the world`s production). However due to traditional processing operations is not ranked as the largest pomegranate exporter. Saveh, Neyriz and Ferdows are the top pomegranate producing cities in Iran. Pomegranate is consumed as a fresh fruit as well as processed product as food additive, paste, syrup, jelly, pectin, jam, beverage, essence, vinegar and concentrate. Aril extraction is the first and essential postharvest operation for pomegranate processing. Arils are mostly extracted manually even in large scales for fresh and processed consumption. This labor intensive operation is rational when aril quality is an important index for consumer. But whenever pomegranate juice is desired, the aril quality has no priority for consumer, and therefore arils can be extracted with less care. Sarig (1985) was the first inventor of a pomegranate aril extractor who employed air jet force to extract the arils. Later, other researchers employed the same method as well as water jet to extract fruit juice and sac. In the present study, fabrication and evaluation of vibratory aril extractor augmented with air system was conducted. Materials and Methods The study was conducted using Rabab cultivar samples which were manually harvested from an orchard in Neyriz town, Fars province. Samples were kept in refrigerator at 5 0C till experimental trials. Initial moisture content of fruit skin, arils and internal fleshes were measured by gravimetric method as 31.7±2.6 %, 61.5±1.8 % and 42.8±1.4 %, respectively and for a whole fruit was measured 45.3±11.5 % (w.b.). For conducting laboratory tests, an aril extraction unit was designed and fabricated. It comprised a steel main frame, a 746 W electric motor, drive mechanism (eccentric and shaft), sample retentive unit, air jet unit, aril tank, and an air compressor-tank assembly. Sample retentive unit was designed in such a manner to hold a halved fruit. This unit was made from four elements, a hemisphere bowel, four pressure (spring) arms to apply force on skin of the sample, and four tension (spring) arms for fixing the sample in the bowel by applying pressure on the edges of the halved sample. Such configuration helped sample to open more and more while extracting the arils to expose trapped aril for easier extraction. Sample retentive assembly was vibrated by the electric motor and drive mechanism. Electric motor was equipped with an electric convertor to create different levels of vibration frequency. Also, the drive mechanism was designed in such a manner to create different levels of vibration amplitudes. According to the previous studies, 2 nozzles with 3.5 mm diameter were selected for air jet unit. Nozzles were spaced at 8 cm apart according to the measured mean diameter of samples. Outlet air jet from nozzles covered the cross sectional area of the halved fruit. Nozzles assembly was rotated 180 degrees clockwise and counterclockwise with an electronically controlled stepper motor. Pressurized air (from air tank) was transferred to nozzles assembly by flexible pipes. Air pressure was controlled at 500 kPa level by air regulator. To conduct experimental trials, samples halved at three different cutting directions (horizontal (equatorial), vertical and oblique) by a sharp cutter and halved samples were used for tests. Halved sample was fixed in bowel and then the unit was excited by the electric motor. The assembly was vibrated for 60 seconds before blowing the air jet for extra 30 seconds. Tests for air jet alone were conducted for 90 seconds and percentage of detached and damaged arils were calculated. Damaged aril during cutting process was subtracted from total damaged arils for each trial. Collected data were analyzed according to factorial experiments based on completely randomized design, and means were compared by Duncan post-hoc test. Data of combined and air jet alone systems were analyzed by two independent sample t tests. Results and Discussion ANOVA results revealed that cutting type, frequency and amplitude, significantly influenced the percentage of aril extraction at 5 % level of significance. The highest amount of extraction was obtained at 30 Hz frequency and 4 mm amplitude for diagonal cutting by 87 %. At this condition, 13.9 % of arils were damaged by air jet pressure. A significant difference in percentage of extracted and damaged arils was observed between vibratory-air and air systems at 5 % level of significance. The highest amount of aril extraction as well as damage was observed for vibratory-air system with the means of 80.1 % and 9.9 %, respectively. Conclusions Maximum percentages of extraction and aril damage were achieved by applying the combined system with as compared to air jet system alone, so that combined system increased aril extraction by 7.1 % with 2.2 % extra damages.

Computations of entrainment of air into a pipe were performed by placing an air jet at the bottom of the pipe. An experiment was performed with cylindrical mixing pipe having different diameter, length and jet location. A flow meter was used to measure the flow through the nozzle and velocity at the mixing pipe exit was measured by anemometer. CFD analyses were performed using Ansys-Fluent 16 to match the experimental results for exit velocity and amount of air sucked into the pipe. Further numerical investigations were performed for a mixing pipe with hot jet to estimate the amount of air entrained as a function pipe diameter, pipe length, nozzle protrusion and pipe shape. It was found from the numerical simulations there exists an optimum pipe length and nozzle protrusion for highest entrainment of air. Also a particular frustum shaped pipe could suck highest air compared to cylindrical shaped pipe. [ABSTRACT FROM AUTHOR]

Highlights • Mixing augmentation mechanisms of three devices were analyzed and compared. • Streamwise vorticity induced by additional vorticity is the main reason for mixing enhancement. • Stagnation pressure loss induced by the pulsed jet is small. • Air jet enhances mixing and reduces the hydrogen distribution on the bottom. • Ramp has a highly remarkable improvement on mixing efficiency and penetration depth. Abstract Numerical investigation of some mixing enhancement strategies based on the traditional transverse injection technique proposed in recent years was carried out by means of the three-dimensional Reynolds-average Navier–Stokes (RANS) equations coupled with the two equation k-ω shear stress transport (SST) turbulence model. The numerical approaches employed in the current study were validated against the available two- and three-dimensional data in the open literature, and they can be used with confidence to achieve a better understanding of mixing augmentation mechanisms in transverse injection flow fields with various mixing enhancement strategies, namely the pulsed jet, the air jet and the ramp. Results obtained in this study provide important insight into complex flow phenomena. Various fundamental mechanisms dictating the intricate flow characteristics for the transverse injection flow field with various mixing enhancement strategies, including the circulation, vertical structures, velocity vectors and shock wave systems, have been analyzed systematically. The performance parameters of the transverse injection flow fields, such as the mixing length, the fuel penetration depth and the stagnation pressure loss have been compared. Different mixing enhancement strategies have their advantages and disadvantages, and the combination of various mixing enhancement strategies may be a promising injection strategy for better mixing performance of the transverse injection flow field. A stronger streamwise vorticity is the main reason for the mixing enhancement. However, the mixing length and the stagnation pressure loss of the transverse injection flow field show opposite trends from each other with a variance in the intensity of streamwise vorticity. [ABSTRACT FROM AUTHOR]

The purpose of this work was to determine, in the Wistar male rats, the role of the stress system in the control of cerebral hemodynamics induced by emotional stress (air jet). Blood flow rates in the internal carotid arteries have been obtained using chronically implanted Doppler probes. In this investigation, air-jet stress provokes a rapid and substantial elevation of blood pressure combined with hyperemia and vasodilation. Spectral analysis reveals an increase in the variability of carotid blood flow and carotid vascular conductance during stress compared to the baseline state. The coherence between the two carotid blood flow, which provides a linear correlation index in the frequency domain, was calculated before (ordinary coherence) and after mathematical elimination of the influence of blood pressure (partial coherence). The main advantages of the technique are as follows:• It allows the measurement of cerebral blood flow while comparing them with the physiological parameters of the animal such as blood pressure.• Air-jet stress is a psychological rather than physical stress that generates hyperemia in a non-pharmacological way (no side effects) without injuring the animal or damaging the experimental installation during the recording sessions.• A simple method for tracing a kinetic path before and at the moment of stress initiation.• The presence of a catheter facilitates the administration of drug substances if required.• Laboratory-developed software, based on the Lab VIEW 5.1, allows real-time monitoring of blood pressure and carotid flow rates signals using fast Fourier transform. [ABSTRACT FROM AUTHOR]

For transplanting vegetables plug seedlings, it is difficult to directly pick up seedlings from the tray cells. Damages of root lumps of plug seedling happen all the time in extracting. In this paper, a root lump loosening mechanism using air jets to eject vegetable plug seedlings making for transplanting was designed and evaluated. It consisted of air jets, a linear module, a double-rod cylinder, a control system and some other supporting parts. The step transmission of the air jet along the horizontal direction was performed using the linear module, which was a synchronous belt system. The air jet′ motion along the vertical direction up and down for ejecting plug seedlings was moved by the double-rod cylinder. For high blowing rates, wholes rows of air jets aiming for each drain hole was designed. In this arrangement, the seedlings could be loosened row by row. With a row of air jets blowing the seedling plugs from the drain holes of the tray cells, air pressures along with the force of the plungers effectively loosened seedlings. It would be good for manual pulling seedlings or automatically picking up seedlings from the tray cells. Based on the integrated design and analysis, the air pressure range of succeeding in loosening seedling plugs was 0.098-0.235 MPa using the air jet at the diameter of 5 mm. Under this condition, the seedlings appeared to be most effective in the loosening and not in destroy of the root soil. Meanwhile, the air jet could eject each drain hole at the bottom of the 128-cell tray. Being the first prototype, its optimal machine parameters were examined under various conditions. In the optimum tests, it was found that the air pressure of the air jet plungers exerted the greatest effect on the integrated ratio in loosening seedling plugs, and followed by the moisture content. Other factors such as the seedling age, the air flow rate and the air jet with sponges or not had no significant effects on the integrated ratio in loosening seedling plugs. In reality, it would probably be a moderate air blast for blowing of the plug seedlings from the tray. If the moisture content of root lumps of the plug seedlings was less than 55%, the cohesion forces between the roots and the tray cell walls would increase. In this case, wetting the roots might serve to reduce the adhesion making for blowing. For cucumbers seedlings, when the air pressure of the air jet plungers was 0.2 MPa, the root zone moisture was 55%-60%, the seedling age was 25 d, the airflow circuit was fully open at the outlet of 4 mm, and the air jet had no sponges, the best intact rate succeeding in loosening root lumps of plug seedlings was achieved. Finally, the overall loosening performance test was carried out. The intact rate of seedling and root lump in loosening root lumps by blowing was more than 96%. It needed about 48 s for finishing loosening the whole tray of plug seedling. The loosening mechanism using air jets to eject vegetable plug seedlings has a good performance, which can meet the actual requirements. [ABSTRACT FROM AUTHOR]

As an important actuator of the dual parallel jet, the porous nozzle has some non-structural parameters (such as inlet pressure, nozzle spacing ratio, etc.) which have a significant influence on energy transport, chemical combustion and pollutant generation. The research on the microfluidic state of the porous nozzle dual parallel jet, however, remains insufficient because of its microjet pattern and complex intersection process. In this paper, the authors used numerical simulation and an experimental method to clarify the influence of porous nozzles’ non-structural parameters on dual parallel jet characteristics. The results show that the inlet pressure only changes the pressure peak value on the parallel jet axis; the starting point (SP) and peak point (PP) on the parallel jet axis, which are located at Xsp = 22 mm and Xpp = 75 mm, respectively, are not changed; and with the increase in the nozzle spacing ratio, the merging points (MPs) on the parallel jet axis are Xmp = 25 mm, 32 mm and 59 mm, respectively. The merging point and the combined point move to a farther distance and the inner deflection angle of the jet is weakened.

The present study aims to numerically analyze the cooling characteristics of the air-jet array in designing more efficient air-cooling system. Heat transfer and flow characteristics are also examined under different operating conditions and air-jet arrangements. The commercial CFD program (FLUENT V. 17) is used for the designed configuration where 10 specimens are cooled by the air-jet arrangement. From the result, it is found that the inner jet arrangement can make the cooling performance higher because of substantial interaction between them in the flow direction. When inner jets are installed for cooling, there is a fluid mixing zone before the specimen by short jet-to-jet distance, leading to a decrease in heat transfer. Also, the fluid mixing zones are concentrated near to the specimen because of similar flow rate between outer and inner jets. Therefore, we suggest the appropriate configuration showing the best cooling efficiency when considered the air temperature, the heat transfer coefficient, and the flow usage. The number of nozzles of inner jets is 44, but highvelocity jet is used for preventing flow mixing among the inner jets. Consequently, cooling with the outer jets effectively occurs around the specimen. This result would be helpful in determining the jet velocity and its configuration between inner and outer jets that are essential for multiple specimens cooling. [ABSTRACT FROM AUTHOR]

Large space building using side wall nozzle air-conditioning system may result in poor ventilation effectiveness for positions out of the reach of primary supply air. A secondary airflow device is proposed to be applied in such system to improve the uniformity of temperature and velocity distribution in the occupied zone under cooling condition. The characteristics of the secondary airflow device, including central-line velocity decay and jet trajectory model were investigated through experiments to provide fundamental data for the system design. The indoor thermal environment parameters were measured and compared between with and without the secondary airflow device system in a large space factory workshop conditioned by side wall air supply nozzles. Experimental results with the secondary airflow device showed that the vertical thermal stratification height slightly changed, with lower air temperature in unoccupied zone and higher temperature in occupied zone comparing to the cases without secondary airflow device. At occupied level, air diffusion performance index (ADPI) significantly improved, while the percentage dissatisfied (PD) due to draught decreased in the occupied zone. Air velocity uniformity at occupied level also significantly increased. The results of this study provide an exemplary reference for the design of the air distribution system in large-space buildings. [ABSTRACT FROM AUTHOR]

A heavy pendulum oscillating in a vertical air jet is studied in this short communication. Different jet Reynolds number and initial inclination angle of the pendulum are considered. As the jet Reynolds number increases, it is always observed that the time taken by the pendulum to reach the final equilibrium vertical state reduces. The suction pressure induced by the streamlines of the air jet deflected by the pendulum aids the gravitational restoring force. The subsequent increase in the frictional damping force from the pivot of the pendulum is shown to be responsible for this behavior. A theoretical model along with numerical results corroborate this conclusion. • Dynamic behaviour of a heavy pendulum oscillating in a vertical air jet is studied. • A higher jet velocity reduces the decay time of the freely oscillating pendulum. • The pressure force on the bob interacting with the jet aids the gravity force. • The dynamics is captured by a theoretical model with enhanced gravity. [ABSTRACT FROM AUTHOR]

Energy saving is one of the most important research directions in the building sector. Personalized ventilation systems are energy conscious solutions providing fresh air for the occupants. As a side effect, cooling energy can be saved due to higher convective heat removal. Using the data gathered from previous experiments performed with the developed personalized ventilation system, a ±1.408 °C accurate simulation model was created in ANSYS 19.2 Academic version in order to determine the temperature distribution on the face. In this paper, the method and the first results are presented. It was clearly demonstrated by measurements and simulations that the personalized ventilation equipment used has a considerable effect on the skin temperature of the face. The developed model can be used to analyze the skin temperature on the faces of people using the novel, personalized ventilation equipment. This way the time spent on examination can be reduced considerably.

Heat transfer using air jet impingement technique is one of the conspicuous tasks in the looming world of electronic packaging system. Here, the material selection of heat sink becomes one of the prior and important assignments to construct a heat sink with desired characteristic cooling rate. In order to study the material effect of heat sink over the cooling characteristic, the present work takes an initiative in plotting the Nusselt magnitude over the radial distance for different material of heat sink. This is done by computing the flow regime and heat transfer characteristic of a 2D axis symmetric geometry in commercial simulating software, ANSYS CFX. The computation of cooling characteristic in form of Nusselt profile is done using SST + Gamma-theta turbulence model. Since the prediction of heat interaction due to the intermediacy and transition in the flow regime is a unique issue of this problem. The results for Nusselt curve signifies a tangible elevation in local Nusselt value (nonuniformity) with decrease in thermal diffusivity of target surface. Also the nonuniformity is observed to vanish above a critical range (66.76mm2/s) of thermal diffusivity. This happens due to presences of abnormal turbulence of heat flow which occurs inside the target surface. Since the variation in thermal diffusivity causes some imbalance competition between the heat storage and dissipation capabilities. Above all the target surface carrying thermal diffusivity less than 66.76mm2/s possesses a dominating heat storage capability, on behalf of which some heat transfer occurring in near jet and far jet regions are being restricted. These are transferred towards stagnation region in radial direction. [ABSTRACT FROM AUTHOR]

The influence on the turbulent wake of a generic space launcher model due to the presence of an under-expanded jet is investigated experimentally. Wake flow phenomena represent a significant source of uncertainties in the design of a space launcher. Especially critical are dynamic loads on the structure. The wake flow is investigated at supersonic ( $$M=2.9$$ ) and hypersonic ( $$M=5.9$$ ) flow regimes. The jet flow is simulated using air and helium as working gas. Due to the lower molar mass of helium, higher jet velocities are realized, and therefore, velocity ratios similar to space launchers can be simulated. The degree of under-expansion of the jet is moderate for the supersonic case ( $$p_\mathrm{e}/p_\infty \approx 5$$ ) and high for the hypersonic case ( $$p_\mathrm{e}/p_\infty \approx 90$$ ). The flow topology is described by Schlieren visualization and mean-pressure measurements. Unsteady pressure measurements are performed to describe the dynamic wake flow. The influences of the under-expanded jet and different jet velocities are reported. On the base fluctuations at a Strouhal number, around $$\mathrm{St}_D \approx 0.25$$ dominate for supersonic free-stream flows. With air jet, a fluctuation-level increase on the base is observed for Strouhal numbers above $$\mathrm{St}_D \approx 0.75$$ in hypersonic flow regime. With helium jet, distinct peaks at higher frequencies are found. This is attributed to the interactions of wake flow and jet. [ABSTRACT FROM AUTHOR]

This paper presents a new three-dimensional model for the distribution of air speed in the secondary zone of a displacement ventilation jet, combining both physical analysis and correlations-based models. For this purpose the measurements on two wall-mounted DV diffusers are used along with other published data. The maximum air speed at the end of primary zone is predicted by using the supplying conditions at the outlet, the thickness of air jet at the end of the primary zone, and the air entrainment in the jet. The longitudinal profile of maximum air speed in secondary zone is modeled using a new normalization and a generalized profile developed using correlation-based models obtained from experimental data. The vertical and transversal air speed profiles are also presented and analyzed. Finally all air speed profiles in the secondary zone are combined into a three-dimensional air speed model in the DV jet. [ABSTRACT FROM AUTHOR]

A computational fluid dynamics (CFD) procedure is presented for the prediction of the erosive footprint size in abrasive jet micro-machining (AJM). The CFD-obtained footprints were in good agreement with those measured experimentally. The footprint was found to be due to both primary particle impacts in the conical plume emanating from the nozzle, and secondary particle impacts driven by the flow. The footprint depended on target curvature because the spread in lateral particle rebounds differed, depending on the target radius. It thus follows that footprints obtained from shallow channels machined on flat targets cannot be used to predict channel shape on curved surfaces. Since the footprint must consider secondary impacts, this has important implications for surface profile modeling of curved surfaces. [ABSTRACT FROM AUTHOR]

In the context of obligations to reduce greenhouse gas emissions to which EU countries have pledged, reducing energy consumption is a necessity of the current period. Thus, within Energy Strategy, Romania was among the first countries that have approved targets for the years 2012, 2015 and 2020. In this respect, the article presents a study regarding the assessment to an industrial consumer of the energy potential of the evacuated air jets through the exhaust systems with which technological facilities are equipped. In order to assess the possibility of utilizing the kinetic energy of the air jets evacuated by the exhaust systems, the calculation of the nominal power and power generated by a 600M2 wind turbine was performed. Based on the results obtained during the air jet speeds recording and of the recovered energy potential, it can be concluded that the evacuated air jet kinetic energy is a source that can be converted into electricity for the economic agent own consumption (insularised system). [ABSTRACT FROM AUTHOR]

The porous layer subjected to air jet is set above fluid passing through heating surface to control its thickness and avoid drying up, as well as ultrasound is introduced at upstream to enhance convection in flowing channel, in which heat flux can be dispersed in convection between fluid and heating surface as well as evaporation on the outside surface of porous cover to the outside. Local thermal equilibrium (LTE) occurs in porous cover, and the effect of sound pressure from ultrasound on liquid fluid is introduced according to acoustic theory. Brinkman–Forchheimer extended Darcy equations and k-ε turbulent model together with the above formulas are employed to describe the heat transfer in fluid covered by porous media subjected to ultrasound and air jet impingement. The effects of ultrasound power and frequency, fluid layer thickness as well as porosity and particle size in porous cover on heat transfer are investigated. The performance evaluation criteria (PEC) is defined to evaluate thermal characteristics in the cases with ultrasound than those without. The 35.7% rise ratio of heat transfer coefficient in the mode with ultrasound power of 50 W happens than that without. The higher ultrasound power and lower frequency of ultrasound cause lower heating surface temperature and larger heat transfer coefficient. The simulations agree with available published experiment data. All results of this study can be considered into utilization of ultrasound and porous layer to enhance heat transfer in flowing channel. • Low frequency and high power of ultrasound benefit thermal-hydraulic behaviors. • More evaporation and convection in the cases with thicker fluid under ultrasound. • Large porosity and particle in porous cover favor thermal behaviors under ultrasound. [ABSTRACT FROM AUTHOR]

Calcium looping is a potential energy-efficient post-combustion CO 2 capture process that is competitive with existing commercially available technology like oxy-combustion. The attrition of CaO-based sorbents during alternating calcination/carbonation cycling in calcium looping (CaL) has the potential to escalate operation cost and contribute to environmental emisssions. Here, we measure jet mill attrition rates of four commercial limestones from Ghana and Canada and compare them with fluid catalytic cracking catalyst (FCC) and commercial vanadyl pyrophosphate (VPP) in a jet mill. We assessed the effect of orifice velocity, attrition time and calcination on particle attrition resistance. The attrition rates of the limestones increased exponentially from as low as 2.4 mg h−1, which is an acceptable rate for industrial applications, up to 38 mg h−1, which is prohibitively high as the orifice velocity increased from 180 m s−1 to 230 m s−1. The attrition rates of the FCC and VPP catalyst were somewhat higher at the low orifice velocity (5 5 mg h−1 and 8 mg h−1, respectively) but lower at the high orifice velocity (21 mg h−1−1 and 26 mg h−1, respectively). Within 3 h, Bui and Nauli limestones reached a steady attrition rate of 19 mg h−1 and 21 mg h−1, respectively whereas Oterpklu limestone reached a steady rate of 17 mg h−1 after 4 h. The calcined limestones attrition rate was twice as high as their carbonated counterpart. The limestones attrited predominantly throgh fragmentation. [Display omitted] • I TPG and d p,max attrition ranking is more reliable compared to the Gwyn model. • The attrition rates increased exponentially with increase in orifice velocity. • Fragmentation dominated the attrition process of the limestones. [ABSTRACT FROM AUTHOR]

The 2D numerical model to simulate the pollutant dispersion and evaporation, when the air jet is used, was proposed. The results of numerical experiment are presented.

Convective heat transfer to an impinging air jet is known to yield high local and area-average Nusselt numbers. We simulate this heat transfer over a wide range of study parameters, including Reynolds number and mist mass fraction, and three jet shapes: circular, half circuit, and quarter circuit. Simulations show that when compared with air only, mist provides higher heat-transfer enhancements for the first two shapes but is insignificant for the third. The area-average Nusselt number is higher by ∼100% for the half-circuit jet than for the circular jet for both single-phase air and mist. With 0.5% mist, the area-average Nusselt number of the circular jet is enhanced by 41% at Reynolds number 10000. [ABSTRACT FROM AUTHOR]

Particle attrition is a prevalent problem in fluidized beds due to continuous moving of catalyst particles. It is always operated at high temperature either for lab- or industrial-scale fluidized beds. The influence of temperature on the attrition behavior of commercial methanol-to-olefins (MTO) and fluid catalytic cracking (FCC) catalysts is analyzed in a three-orifice lab-scale fluidized bed device from room temperature to 600 °C. The two catalysts are found to be alike in attrition mode. Both change from a combination of abrasion and fragmentation to main abrasion with increasing temperature, but differ greatly in the variation of attrition index with temperature which may be attributed to the difference of material and particle properties. An empirical correlation of attrition index to attrition temperature for all test samples is proposed. [ABSTRACT FROM AUTHOR]

Abrasive slurry jet micro-machining (ASJM) in combination with abrasive air jet micro-machining (AJM) was used to mill micro-pockets in three different ceramic wafers: sintered alumina, aluminum nitride, and zirconium tin titanate. A composite substrate of aluminum nitride with an array of copper-filled through-holes was also machined using a hybrid process of AJM and ASJM that capitalized on the significant differences in the erosive characteristics of each method. The objective was to investigate an alternative to laser micro-milling. The sintered ceramics were found to erode in a brittle manner by the dislodgment of grains upon abrasive particle impact. The eroded profiles produced by ASJM and AJM were modeled analytically. ASJM could make 100 μm deep flat pockets, 500 μm wide with 60° sidewall angles in the sintered ceramics using overlapping parallel channels. The shapes of the pockets could be predicted accurately as long as the depth of each machined pass was less than 50 μm. Pockets of the same size and roughness ( R a = 0.4 μm) could also be machined and modeled accurately using masked AJM. The surface roughness of the sintered ceramics was found to be insensitive to particle size, being controlled by the size of the sintered grains. Similar pockets could be machined in the aluminum nitride containing 180 μm diameter copper through-holes using ASJM provided that the maximum depth was about 25 μm. Beyond that, the secondary slurry flow away from the jet footprint created unwanted etching of the copper-filled through-holes leading to a lack of flatness. Deeper pockets in these substrates were machined using a hybrid AJM–ASJM methodology, in which AJM was used to selectively erode the brittle sintered ceramic without etching the ductile copper, followed by the leveling of the protruding copper pillars to the depth of the ceramic using ASJM. Computational fluid dynamics models were used to explain the results in terms of the large differences in the local particle impact angles and velocities in ASJM and AJM. [ABSTRACT FROM AUTHOR]

The jet impingement heat transfer is a well-established technique for obtaining high heat transfer rates for many cooling and heating applications. Impingement heat transfer methods are widely used in domestic and industrial appliances. The impinging isothermal gas jets are used for both heating and cooling. However, premixed flame jets are used for heating the target surface. Present study is an attempt to compare the heat transfer characteristics of the isothermal air jets and premixed flame jets. The isothermal air jet having jet temperature of 30 °C (cold jet or ambient temperature jet), 100 °C (hot jet), and premixed methane–air flame jet (stoichiometric mixture) with Reynolds numbers of 500, 750, 1000, 1250 and 1500 and nozzle or burner to plate spacings of 2 d , 4 d and 6 d are experimentally investigated for heat transfer characterisation. Thin metal foil technique is used for characterising isothermal air jets. For a fixed jet Reynolds number, the Nusselt number of isothermal air jet is found independent of the temperature difference between jet and surrounding fluid. A steady state technique is proposed for characterisation of premixed flame jets. The outcome of the present study reveals that the heat transfer characteristics of isothermal air jet and the premixed flame jet are almost same. The higher thermal entrainment in premixed flame jet in comparison with isothermal air jet results in a lower effectiveness. The present heat transfer data can be directly utilised for many practical applications. [ABSTRACT FROM AUTHOR]

We propose a technology for manipulating the position and attitude of an object on a planar surface in a contactless manner. This technology involves multiple ejectors that stream jets of compressed air onto an object from various directions. By regulating air jet directions and volumes, the object can be actively "force closured" and its position and attitude can be manipulated freely. As the first step of this research, we discuss the fundamental ideas and the technological challenges as a manipulation method. Next we provide a preliminary investigation with one degree-of-freedom experimental system. Based on this, we examine two DOF system with three air jets and finally three DOF system with four air jets.

We investigated the mechanism for the removal of fine particles from a solid wall using a high-speed impinging air jet. In general, it is difficult to remove fine particles of the order of micrometers by the impingement of simple air flow because they strongly adhere to the surface by van der Waals forces and remain immersed in the viscous sublayer. To overcome this, we developed high-speed air jet nozzles with triangular cavities that add strong velocity and pressure fluctuations to the high-speed air flow. The experimental results showed that the cavity nozzle enhances the removal performance for particles larger than 1 μm. The effect of the pressure fluctuation induced in the jet flow on the removal performance is discussed from the experimental results. First, the adhesive force was measured experimentally from the centrifugal force acting on particles with 5-25 μm diameters set on a rotating disk. Based on a simple theoretical consideration regarding the balance of moments acting on a particle, we estimated the effects of hydrodynamic removal forces such as drag, lift, and pressure gradient fluctuation against measured adhesive forces. The theoretical estimation showed that drag plays a major role, and the force of the pressure gradient could be effective for the removal of large particles. The proposed model is able to explain the experimental results indicating that the removal rates for 3-μm-sized particles are improved by the air flow velocity fluctuations generated by the cavity nozzle.

Many previous studies have mentioned the critical effect of natural convection caused by passengers heat transfer on the air distribution inside the air cabins, but No study focused on it to make a further experimental or numerical analysis. In fact, the air flow field inside the air cabin with narrow interior space and passengers seated intensively is the result of interaction between natural convection from the passengers and forced convection from the supply air diffusers, including the air jet which plays the most essential part on the flow pattern. This study has measured the air flow jet in a 7-row cabin mockup with 2D-PIV (two dimension Particle Image Velocity) measurement system, and to make comparison of the air jet under isothermal and cooling conditions to analyze qualitatively the impact of natural convection inside the cabin mockup, which is to increase the air jet entrainment and weaken the attaching effect which can also enhance the velocity distribution uniformity. With the variety of air flow volume in a reasonable range of design parameters, we measured the different air velocity fields to quantify the effects of natural convection on the air jet. It can be concluded that the air jet decay rate becomes slower with the enhancement of natural convection. [ABSTRACT FROM AUTHOR]