Multiple Air Jets Research Articles

Adenosine dry powder inhalation for bronchial challenge testing, part 1: Inhaler and formulation development and in vitro performance testing

Dry powder administration of adenosine by use of an effective inhaler may be an interesting alternative to nebulisation of adenosine 5′-monophosphate in bronchial challenge testing, because of a shorter administration time and more consistent delivered fine particle dose over the entire dose range. In this study, we tested various powder formulations and classifier based dispersion principles and investigated the in vitro performance of the most promising formulation/classifier combination in a new test inhaler system. Spray-dried formulations of either pure adenosine (100%) or adenosine and lactose as diluent (1% and 10% adenosine) were prepared to cover the entire expected dose range for adenosine (0.01–20mg). All three powders, in all 12 suggested doses, dispersed well with the newly developed test inhaler with a multiple air jet classifier disperser, into aerosols with an average volume median diameter of 3.1μm (3.0–3.3μm). For eleven out of 12 dose steps, the fine particle fractions<5μm as percent of the loaded dose varied within the range of 67–80% (mean: 74%). The new test concept allows for more consistent aerosol delivery over the entire dose range with narrower size distributions than nebulisation and thus may improve adenosine administration in bronchial challenge testing.

2P1-E09 複数のエアジェットによる物体の位置と姿勢の非接触制御方式に関する研究 : PWMによる空気噴出法(アクチュエータの機構と制御(3))

2P1-E09 複数のエアジェットによる物体の位置と姿勢の非接触制御方式に関する研究 : PWMによる空気噴出法(アクチュエータの機構と制御(3))

Computational flow and heat transfer of multiple circular jets impinging on a flat surface with effusion

Computational investigations are reported on the local flow and heat transfer characteristics from staggered, multiple circular air jets impinging on a flat surface with effusion holes. The geometrical and flow parameters for the computational study are chosen as per the experimental arrangement of Cho and Rhee J Turbomachinery 123:601–608, (14) so as to explain salient features observed in these experiments. The two peaks in the Nusselt number observed in the case of H/D = 6 and three peaks in the case of H/D = 2 are attributed to the flow characteristics such as primary vortices forming an up-wash region, followed by secondary vortices resulting in a secondary stagnation zone. The magnitude of local peak in heat transfer increases up to 88% with increasing values of D/d from 0.5 to 1.5 at Re = 10,000.

2P2-Q12 複数のエアジェットによる物体の非接触操作 : 平面3自由度制御方式(インフォマティブ・モーションとモーション・メディア-ロボットの身体性と運動-)

We have proposed a technology for manipulating the position and orientation of an object in a contactless manner using multiple air jets. By regulating the air jet directions and flow rates, the object can be actively "force closured" and its position and orientation can be manipulated freely. In this paper, we report an experimental system with 3 DOF (2 translational DOF and 1 rotational DOF) using four air jets on a planar surface.

Influence of Streamwise Pitch on Local Heat Transfer Distribution for In-Line Arrays of Circular Jets with Spent Air Flow in Two Opposite Directions

The effect of streamwise jet-to-jet spacing on local heat transfer distribution due to an in-line rectangular array of confined multiple circular air jets impinging on a surface parallel to the jet plate are experimentally studied. The length-to-diameter ratio of nozzles of the jet plate is 1.0. The flow, after impingement, is constrained to exit in two opposite directions from the confined passage formed between the jet plate and target plate. Mean jet Reynolds numbers based on the nozzle exit diameter (d) covered are 3,000, 5,000, 7,500, and 10,000; jet-to-plate distances studied are d, 2d, and 3d. Streamwise jet-to-jet distances of 3d, 4d, and 5d, and a constant spanwise pitch of 4d, are considered. The jet plates have ten spanwise rows in the streamwise direction and six jets in each spanwise row. The flat heat transfer surface is made of thin stainless-steel metal foil. Local temperature distribution on a target plate is measured using a thermal infrared camera. Wall static pressures in the streamwise direction are measured midway between the spanwise jets to estimate cross-flow velocities and individual jet velocities. The streamwise distribution of the jet flow and the cross flow is found to be least influenced by the streamwise pitch variation for the range of parameters considered during the present study. Heat transfer characteristics are explained partially on the basis of flow distribution. The cooling performance, based on the strip-averaged Nusselt number per unit mass flow rate of coolant per unit area of cooled surface, indicates deterioration for lower streamwise pitch and higher jet-to-plate distance.

1A1-J11 圧縮空気による物体の位置と姿勢の非接触制御方式に関する研究 : 第1報:コンセプト提案

1A1-J11 圧縮空気による物体の位置と姿勢の非接触制御方式に関する研究 : 第1報:コンセプト提案

1A1-J12 圧縮空気による物体の位置と姿勢の非接触制御方式に関する研究 : 第2報:平面1自由度実験システム

1A1-J12 圧縮空気による物体の位置と姿勢の非接触制御方式に関する研究 : 第2報:平面1自由度実験システム

Influence of spanwise pitch on local heat transfer distribution for in-line arrays of circular jets with spent air flow in two opposite directions

Effect of spanwise jet-to-jet spacing on local heat transfer distribution due to an in-line rectangular array of confined multiple circular air jets impinging on a surface parallel to the jet plate are studied experimentally. Length-to-diameter ratio of nozzles of the jet plate is 1.0. The flow, after impingement, is constrained to exit in two opposite directions from the confined passage formed between jet plate and target plate. Mean jet Reynolds numbers based on the nozzle exit diameter ( d) covered are 3000, 5000, 7500 and 10,000 and jet-to-plate spacings studied are d, 2 d and 3 d. Spanwise pitches considered are 2 d, 4 d and 6 d in steps of 2 d keeping the streamwise pitch at 5 d. For all the configurations, the jet-plates have ten spanwise rows in streamwise direction and six jets in each spanwise row. Flat heat transfer surface is made of thin stainless steel metal foil. Local temperature distribution on a target plate is measured using thermal infrared camera. Wall static pressure on the target plate is measured in the streamwise direction to estimate crossflow velocities and individual jet velocities. Heat transfer characteristics are explained on the basis of the flow distribution. A simple correlation to predict streamwise distribution of heat transfer coefficients averaged over each spanwise strip resolved to one jet hole is developed.

Multiple Air-Jet Window Cooling for High-Temperature Pressurized Volumetric Receivers: Testing, Evaluation, and Modeling

High air outlet temperatures increase the solar share of pressurized solar receivers for gas turbines, operated in solar-fossil hybrid mode. However, an increase in outlet temperature over 800°C leads to excessive heating of the receiver window, unless it is actively cooled. This paper describes modeling, testing, and evaluation of a high-temperature receiver with external multiple air-jet window cooling. An asymmetric window-cooling design with pulsating air mass flow rates achieves suitable cooling of the concave fused-silica window. A thermodynamic receiver model, comprising nongray radiative heat transfer, convection, and conduction is the basis of the external window cooling design. In addition to high-temperature testing with window cooling in operation, solar tests at lower temperatures with no window cooling were conducted to verify the thermodynamic receiver model. Temperature distributions on the quartz window and the absorber were determined by an infrared scanner which was specially developed for temperature measurement on the high-temperature module. Comparisons of simulations and measurements show good agreement. With multiple air-jet window cooling, receiver air outlet temperatures over 1000°C could be reached, while window temperatures are kept below 800°C.

Mixing Characteristics of Multijet Modified by Cyclic Perturbation

The effect of cyclic perturbation on the mixing performance of millimeter-sized multiple air jets was investigated using flow visualization, hot-wire anemometry and laser Doppler anemometry techniques. Two types of external perturbation method were used, i.e., adding an acoustic sound and applying a pulsating flow to the jet. External acoustic sounds were found to be an additional dominant factor for the jet mixing, and in the multiple-jet case, the main jet located in the middle between the two same-sized jets was split into two, entrained into the neighboring jets, and eventually merged into one developed flow. For the pulsating-jet case, depending on the phase in one cycle, the jet flow condition alternately changed between laminar and turbulent. This affected the time-mean values of the jet flow profile. An adverse change in the mixing performance at the locations near the nozzle and far downstream was obtained between the pulsating- and steady-jet cases.

Numerical and Experimental Investigation of a Multiple Air Jet Cooling System for Application in a Solar Thermal Receiver

Abstract The transparent quartz glass window of a high temperature solar receiver (1000°C air outlet temperature, 15bars) has to be protected from overheating. The window is an axially symmetric part that can be approximated by a hemisphere with a cylindrical extension (diameter 0.31m, height 0.42m). The cooling is accomplished by impinging several air jets onto the concave window surface. Due to concentrated solar radiation, the air supply nozzles can only be installed at the circumference of the cylindrical extension. Symmetric configurations with six or nine nozzles, equally distributed around the window circumference, are examined. A second configuration generates a swirl in the window cavity by inclining the nozzles. In a third, asymmetric configuration, only nozzles on one side are simultaneously charged with mass flow, while a spatial homogenization of heat transfer is reached by periodically modulating the air flows with time. Computational fluid dynamics (CFD) calculations and laboratory measurements of the heat transfer have been carried out. In the performed 3-D simulations, the realizable k-ε model, the k-ω model, and the SST-k-ω model are compared. For measuring the heat transfer coefficient, a periodic-transient measurement technique with high spatial resolution is used. For the application of cooling of the solar receiver window, the jet cooling system with periodically modulated air flows is identified as the best solution.

MIXING CHARACTERISTICS OF MULTI-JETS MODIFIED BY CYCLIC PERTURBATION(Multiple Jet)

Cyclic perturbation effect on mixing performance of millimeter-sized multiple air jets was investigated using flow visualization, hot wire aneinometry and laser Doppler anemometry techniques. Two types of external perturbation method were used, i.e. adding an acoustic sound and applying a pulsatile flow to the jet itself. External acoustic sounds (St〜0.35) were found to be an additional dominant factor for the jet mixing. Furthermore, the main jet located in the middle between the two same-sized jets was split into two, entrained into the neighboring jets, and eventually merged into one developed-flow, much quicker than the case without the sound. For the pulsatile jet case, depending on the phase in one cycle, a jet flow condition alternately changed between laminar and turbulent. This affected the time-mean values of the jet flow profile. An adverse change of the mixing performance at the location near the nozzle and far downstream was obtained between the pulsatile jet and steady jet cases, namely a better mixing performance was obtained by the pulsatile jet case near the nozzle and vice versa.

Flow and heat transfer from multiple slot air jets impinging on circular cylinders

This study presents flow and heat transfer predictions of multiple slot air jets impinging on circular cylinders using CFD (computational fluid dynamics). The distribution of Nusselt numbers around the cylinders for different Reynolds numbers (23,000–100,000), distances between the jets, and openings between them was determined for two and three jets and compared to simulations of a single jet. The flow characteristics and the heat transfer distribution around the cylinders are found to be dependent on the distance and the opening between the jets. The interaction between two jets is found to be most advantageous. The heat transfer increases for higher Reynolds number in general; for two jets the heat transfer in the stagnation point is Nu s = 0.20 Re 0.68. For three jets, the heat transfer distribution is different on the outer cylinders, as compared to the cylinder in the centre.

A numerical and experimental investigation of the interactions between a non‐uniform planar array of incompressible free jets

AbstractThe interaction between multiple incompressible air jets has been studied numerically and experimentally. The numerical predictions have been first validated using experimental data for a single jet configuration. The spreading features of five unequal jets in the configuration of one larger central jet surrounded by four smaller equi‐distant jets, have been studied, for different lateral spacing ratios of 1.5, 2.0 and 2.5 and a central jet Reynolds number of 1.24×105 (corresponding to a Mach number of 0.16). Flow of five equal jets has also been simulated, for the sake of comparison. The jet interactions commence at an axial distance of about 3–4 diameters and complete by an axial distance of about 10 diameters for the lowest spacing ratio of 1.5. For larger spacing ratios, the length required for the start and completion of jet interaction increase. Peripheral jets bend more towards the central jet and merge at a smaller distance, when their sizes are smaller than that of the central jet. The entrainment ratio for multiple jets is higher than that for a single jet. Excellent agreement is observed between the experimental data and theoretical predictions for both mean flow field and turbulent quantities, at regions away from the jet inlet. The potential core length and initial jet development, however, are not predicted very accurately due to differences in the assumed and actual velocity profiles at the jet inlet. Copyright © 2004 John Wiley &amp; Sons, Ltd.

Local Heat Transfer Distributions in Confined Multiple Air Jet Impingement

Heat transfer from a discrete heat source to multiple, normally impinging, confined air jets was experimentally investigated. The jets issued from short, square-edged orifices with still-developing velocity profiles on to a foil heat source which produced a constant heat flux. The orifice plate and the surface containing the heat source were mounted opposite each other in a parallel-plates arrangement to effect radial outflow of the spent fluid. The local surface temperature was measured in fine increments over the entire heat source. Experiments were conducted for different jet Reynolds numbers (5000&lt;Re&lt;20,000), orifice-to-target spacing 0.5&lt;H/d&lt;4, and multiple-orifice arrangements. The results are compared to those previously obtained for single air jets. A reduction in orifice-to-target spacing was found to increase the heat transfer coefficient in multiple jets, with this effect being stronger at the higher Reynolds numbers. With a nine-jet arrangement, the heat transfer to the central jet was higher than for a corresponding single jet. For a four-jet arrangement, however, each jet was found to have stagnation-region heat transfer coefficients that were comparable to the single-jet values. The effectiveness of single and multiple jets in removing heat from a given heat source is compared at a fixed total flow rate. Predictive correlations are proposed for single and multiple jet impingement heat transfer.

A knowledge based database system for engineering correlations

Engineering design frequently relies on empirical data expressed in the form of non-dimensional correlations. These are almost always governed by applicability limits and the engineer is faced with the problem of choosing the right correlation that would provide design data with acceptable accuracy from a large number which are available. A knowledge based database system (KBDS) has been constructed which assists in the simple formulation of a jet impingement application based on which it retrieves and evaluates the relevant correlation from a database. Where the information in the database does not satisfy this specification the system uses knowledge of the application domain to either select suitable correlations for extrapolation or to modify the database query to select alternative information. The constraints which enable new correlations to be added or the knowledge in the network to be extended to include new geometries and flow conditions whilst maintaining the integrity are described. The operation of the KBDS has been demonstrated with a comprehensive database of correlations for the heat transfer due to the impingement of single and multiple air jets. This application provides typical engineering correlations and hence the techniques described are expected to be widely applicable.

Heat transfer to impinging isothermal gas and flame jets

Heat transfer characteristics of single and multiple isothermal turbulent air and flame jets impinging on surfaces are reviewed. Both circular and slot two-dimensional jets are considered, and the effect of crossflow on impingement heat transfer is included. The emphasis is on physical phenomena and not on comparison of published empirical correlations or comparisons of theory and experiments. The review focuses on applications in the materials or comparisons of theory and experiments. The review focuses on applications in the materials processing field. In spite of the fact that there are many differences in the jet characteristics (ie, axial velocity and turbulence intensity) of isothermal and flame jets, the stagnation point heat transfer of these different jets can be described in a similar way. Areas needing research attention are also identified.

On the rate balance between impingement water evaporation and heat transfer

An experimental investigation of impingement water evaporation under single and multiple air jets was made. Similar studies of impingement heat transfer from solid surfaces were also carried out; the heat transfer areas were nearly the same as those for evaporation. It is established that evaporative fluxes can be calculated from the rate balance between evaporation and heat transfer via heat-mass transfer analogy.

Evaporation of Water With Single and Multiple Impinging Air Jets

An experimental investigation of impingement water evaporation under a single jet and arrays of circular jets was made. The parametric study included the effects of jet Reynolds number and standoff spacing for both single and multiple jets, as well as surface-to-nozzle diameter ratio and fractional nozzle open area for single and multiple jets, respectively. The nozzle exit temperature of the air jet, about the same as that of the laboratory, was 3–6° C higher than that of the evaporating water. Predictive equations are provided for mass transfer coefficient in terms of the flow and geometric conditions.

Impinging cooling of a high temperature flat surface by multiple two-dimensional air jets.

Two-dimensional impinging jets in line have been used for many industrial applications for cooling and heating, but the effectiveness of the heat transfer augmentation has not been well established. The purpose of this study is to clarify the augmented heat transfer performance of impinging air jets in line by means of providing roughnesses on a heat transfer surface. The optimum position of the roughnesses are studied experimentally for the jet Reynolds number of 1×104 when the jet-to-plate spacing is equal to the jet slot width. It is clarified that, even though of no roughness the two jets increases the total heat transfer performance by about 1.4 times that of one jet without roughness regardless of the jet spacing, under the optimum condition the average surface heat transfer coefficient in a semi-enclosed environment increases by about 2.30 times that of one jet without roughness.