Open Area Ratio Research Articles

Experimental investigation of thermo hydraulic performance due to angle of attack in solar air heater duct equipped with V-shaped perforated blockages

An experimental investigation has been performed to study the effect on thermo hydraulic performance parameter of V–shaped perforated blockages attached on one broad heated wall of a rectangular solar air heater duct. The rectangular duct was equipped with V–shaped perforated blockages having aspect ratio of 12. The geometrical parameters of blockage were taken as relative blockages height value of 0.8, relative pitch ratio value of 8, open area ratio value of 20%. An angle of attack was varied from 30° to 75°. The experiment encompassed with Reynolds number from 2,000 to 20,000. Experimental data has been collected to calculate Nusselt number, friction factor and thermo–hydraulic performance parameter. It was observed that there was a significant effect on Nusselt number, friction factor and thermo hydraulic performance parameter due to angle of attack.

開口を有するカバーの防音特性の開口率依存性（内側吸音単層壁と吸音材内封二重壁の比較）

開口を有するカバーの防音特性の開口率依存性（内側吸音単層壁と吸音材内封二重壁の比較）

Interaction of vortex rings with multiple permeable screens

Interaction of a vortex ring impinging on multiple permeable screens orthogonal to the ring axis was studied to experimentally investigate the persistence and decay of vortical structures inside the screen array using digital particle image velocimetry in a refractive index matched environment. The permeable screens had porosities (open area ratios) of 83.8%, 69.0%, and 55.7% and were held by a transparent frame that allowed the screen spacing to be changed. Vortex rings were generated using a piston-cylinder mechanism at nominal jet Reynolds numbers of 1000, 2000, and 3000 with piston stroke length-to-diameter ratios of 2 and 3. The interaction of vortex rings with the porous medium showed a strong dependence of the overall flow evolution on the screen porosity, with a central flow being preserved and vortex ring-like structures (with smaller diameter than the primary vortex ring) being generated near the centerline. Due to the large rod size used in the screens, immediate reformation of the transmitted vortex ring with size comparable to the primary ring (as has been observed with thin screens) was not observed in most cases. Since the screens have lower complexity and high open area ratios, centerline vortex ring-like flow structures formed with comparable size to the screen pore size and penetrated through the screens. In the case of low porosity screens (55.7%) with large screen spacing, re-emergence of large scale (large separation), weak vortical structures/pairs (analogous to a transmitted vortex ring) was observed downstream of the first screen. Additional smaller scale vortical structures were generated by the interaction of the vortex ring with subsequent screens. The size distribution of the generated vortical structures were shown to be strongly affected by porosity, with smaller vortical structures playing a stronger role as porosity decreased. Finally, porosity significantly affected the decay of total energy, but the effect of screen spacing decreased as porosity decreased.

Thermal Behavior in Rectangular Channel Duct Fitted With V-Shaped Perforated Baffles

An experimental investigation has been carried out to study the heat transfer and friction factor characteristics of a V-down-perforated baffled roughened solar air heater duct. The roughened wall was uniformly heated and the rest three walls of the duct were kept insulated. Measurements have been carried out for the duct aspect ratio of 10, Reynolds number range of 3800–19,000, relative hole position range of 0.429–0.571, relative roughness pitch range of 2–4, and open area ratio range of 12–44%. The relative roughness height of 0.4 and angle of attack of 60° are kept constant during the entire experimentation. The heat transfer and friction factor data obtained were compared with the data obtained from a smooth duct under similar operating conditions. In comparison to the smooth duct the V-shaped perforated baffle roughened duct enhanced the Nusselt number and friction factor by 2.57 and 5.96 times, respectively. The thermohydraulic performance parameter is found superior for the open area ratio of 24% and relative roughness pitch of 2.5.

Study on a Generic Nonlocally Reacting Liner

For many applications (e.g., in aircraft engines), the cells of Helmholtz resonator liners are not solely locally reacting because drainage slots are cut into the side walls. However, for the design of liners, the resulting effects of such drainage slots are currently not taken into account. Therefore, this paper presents a study on the effects of liner-cell interaction. In the first part, experimental results for different slot configurations of a generic test object (the scaled liner cavity) are shown and discussed. The major result is an additional dissipation maximum caused by the cell interaction. Based on these findings, an empirical relation is derived incorporating geometrical parameters like the percentage open area ratio to predict the appearance of the additional maximum.

A numerical study of a vortex ring impacting a permeable wall

In this paper, we numerically simulate a vortex ring impacting a permeable wall by using a lattice Boltzmann method. The study is motivated by recent publications on vortex ring/permeable wall interaction and our desire to address some of the unanswered questions such as evolution of core vorticity, kinetic energy, and enstrophy of the flow field during the interaction. The simulation was conducted for a wide range of parameters, namely, wall open-area ratios (ϕ) (0 ≤ ϕ ≤ 1), wire structure dimensions (A) (0.015 ≤ A ≤ 0.1), wall-thicknesses (H) (0.015 ≤ H ≤ 1), and Reynolds numbers (\documentclass[12pt]{minimal}\begin{document}$Re_\Gamma$\end{document}ReΓ) (\documentclass[12pt]{minimal}\begin{document}$500 \le Re_\Gamma \le 5000$\end{document}500≤ReΓ≤5000). Results show that the flow characteristics upstream and downstream of the permeable wall depends on these parameters. Specifically, increasing ϕ or \documentclass[12pt]{minimal}\begin{document}$Re_\Gamma$\end{document}ReΓ enhances vorticity transport across the permeable wall, leading to a regenerated vortex ring, while increasing H impedes vorticity transportation and the formation of regenerated vortex ring. Moreover, larger A promotes vortex shedding from wire grids and generates fine-scale flow structures in the wake region. The study further shows a strong correlation between the attainment of maximum enstrophy and the lifting of the secondary vortex ring from the wall by the induced velocity of the primary vortex ring. While increasing ϕ causes the peak enstrophy to decrease in the upstream region and increase in the downstream region, increasing wall thickness has the opposite effect on the peak enstrophy. On the other hand, increasing wire dimension reduces peak enstrophy in both the upstream and downstream regions, while increasing Reynolds number has the opposite effect on the peak enstrophy.

Theoretical predictions and field measurements for potential natural ventilation in urban vehicular tunnels with roof openings

Naturally ventilated urban vehicular tunnels with multiple roof openings have emerged in China; thus, the ventilation strategy needs to be studied and validated. The safety standards for CO concentration depend on people's exposure time: 125 mg/m3 for 5 min, 100 mg/m3 for 15 min, and 35–44 mg/m3 for 1 h. Airflow and contaminant equations were established and solved based on one-dimensional and steady state assumptions. Three naturally ventilated and two mechanically ventilated urban vehicular tunnels were investigated from 11/2013 to 1/2014 using TSI7575-X and KIMO-VT200 for continuous and single-point measurements during congested periods. The survey reveals that piston winds existed in each tunnel but the effect in mechanically ventilated tunnels was more apparent compared to that in naturally ventilated tunnels. Furthermore, all temperature as well as CO and CO2 concentrations increased from inlets to outlets. The theory model was validated by comparing the analytical air velocity and CO concentration of the XIANMEN Tunnel to that of the field measurement. Further theoretical analyses indicate that under a constant traffic flow of 1700 veh/h.lane, the air velocities depend largely on the vehicle speed vt and the opening area ratio Rf; moreover, the maximum CO concentrations increase with a decrease in vt and an increase in tunnel length L but are minimally affected by Rf. At 20 km/h, drivers are exposed for different times based on the tunnel length, and they are always safe against CO exposure in tunnels up to 3000 m.

Influence of open area ratio on microstructure shape in Cu–Ni alloy electrodeposition

This research experimentally analyzed the influence of the open area ratio (OAR) on the formation and growth of the microstructure in Cu–Ni alloy electrodeposition. The OAR was controlled by changing the pitch of circular patterns with a diameter of 20 µm. For an OAR higher than 20 %, the electrodeposited structures grew vertically in pillar-like formations. As the OAR was decreased from 100 to 20 %, the density, height, and width of the structures increased. In addition, in this OAR range, the structures formed along the edge area of the circular patterns. In contrast, for an OAR lower than 10 %, dendrite structures were generated. The electrodeposited structures were coated with a hydrophobic plasma-polymerized fluorocarbon (PPFC) layer. In the electrodeposited sample without circular patterns (OAR = 100 %) with an OAR smaller than 1.25 %, the measured contact angles were almost the same as the contact angle (107°) measured from the flat surface without electrodeposition. In contrast, the samples with an OAR range of 2.5–50 % were modified to be superhydrophobic, and they demonstrated an excellent self-cleaning ability.

INFLUENCE OF SOME GEOMETRICAL PARAMETERS ON THE CHARACTERISTICS OF PREFILMING TWIN-FLUID ATOMIZATION

Geometries are considered to have a great influence on the spray characteristics of atomizers. In the present study, we studied a prefilming twin-fluid atomizer patented by Sadatomi and Kawahara (2012), in which liquid atomization is implemented by supplying compressed air alone into an internal mixing chamber, and water is automatically sucked by the negative pressure induced by an orifice. In the experiments, we studied spray characteristics influenced by the geometrical parameters, such as orifices in different opening area ratios and different shapes, porous rings with different porous diameters, and different atomizer sizes. Higher spray performance can be obtained by a small sized atomizer with a circular orifice in opening area ratio of 0.429 and a porous fiber ring with porosity of 25 μm. The present results provide a significant guidance for practical applications with different requirements of spray characteristics.

Heat Transfer Enhancement due to V-Shaped Perforated Blocks in a Solar Air Heater Duct

An experimental study of enhancement of heat transfer due to V-shaped perforated blockages attached to the heated surface has been presented in this paper. The duct equipped with perforated V-blocks had an aspect ratio (W/H) of 12, relative blockage height ratio (e/H) of 0.8, angle of attack (α) of 60° and open area ratio (β) of 20%, while relative pitch ratio (P/e) was varied from 4 to 12. The values of Nusselt number and friction factor of the duct with blockages were compared with values of Nusselt number and friction factor of the smooth duct operating under similar experimental conditions. It was found that there was a significant effect on the Nusselt number ratio and friction factor ratio when the pitch ratio was changed and there was exist an optimum value of pitch ratio. Thermal hydraulic performance was found to be maximum corresponding to relative pitch value of 8.

Note: Absolute detection efficiency of a tapered microchannel plate for Ne⁺ ions.

The absolute detection efficiency of a tapered microchannel plate with an open-area ratio of 90% was measured for Ne(+) with energies up to 5 keV, and comparison with the results for Xe(+) was made. As in the case of Xe(+), the maximum detection efficiency was 90%. The energy dependence of the efficiency curves normalized with respect to the open-area ratios was examined based on the scaling law proposed previously.

Parameters measurement of hydrodynamics and CFD simulation in multi‐stage bubble columns

The effect of superficial gas velocity and structural parameters of plate (perforated plate and tongue plate) on the hydrodynamics parameters of column are studied in a multi‐stage bubble column, with 2000 mm height and 282 mm diameter of the multi‐stage bubble column, by using the electrical resistance tomography (ERT) technique and computational fluid dynamics (CFD). According to the results, ERT and CFD techniques can be well applied to the measurement and estimation of gas–liquid two‐phase processes. The gas holdups, the radial distribution of gas holdup and gas cap height strongly depend on the operating condition and tray structure. By increasing the superficial gas velocity, the gas holdup in the multi‐stage bubble column increases. With a decrease of the open area ratio, the hole diameter and tongue angle, the gas holdups and gas cap height below the perforated plate increase. The addition of the perforated plate enhances the flow behaviour of gas–liquid in bubble column. The CFD can then aid the prediction of gas cap height and gas holdup in a multi‐stage bubble column.

Effect of circularity of perforation holes in V-shaped blockages on heat transfer and friction characteristics of rectangular solar air heater duct

The effect of non-circular perforation holes in term of circularity of V-shaped blockages attached to one heated wall of a rectangular duct of solar air heater. Five different hole shapes ranging from circular to square to rectangular in the circularity range of 1–0.6 have been used with varying relative pitch of 4–12, relative blockage height of 0.4–1.0, open area ratio of 5–25% and angle of attack of 30–75° and Reynolds number of flow was varied between 2000 and 20,000. It has been found that there exists an optimum non-circular shape of perforation holes that yields maximum value of Nusselt number; a perfectly circular hole performs substantially inferior as compared to a non-circular hole of considerable non-circularity (ψ=0.69). An improvement of Nusselt number value in the ratio of 1.13 has been found when circular perforation holes are replaced by rectangular holes of circularity of 0.69. Correlations of Nusselt number as well of friction factor are established in term of Reynolds number and geometrical parameters of blockages which can be used to predict the values of Nusselt number and friction factor with considerably good accuracy.

Hydrodynamic characteristics of gas–solid fluidized beds with shroud nozzle distributors for hydrochlorination of metallurgical-grade silicon

The hydrodynamic characteristics of a gas–solid fluidized bed for the hydrochlorination of metallurgical-grade Si were compared by analyzing the distributor configuration at similar opening area ratios, and using a superficial gas velocity (U0) ranging from 0.02 to 0.17m/s. A perforated plate with a similar opening area ratio to those of the shroud nozzle distributors was also used as a reference. Metallurgical-grade silicon (MG-Si) and air were used as the bed material and the fluidizing gas, respectively. To evaluate the stability of gas distribution, the pressure drop across each distributor was measured, and the coefficient of variation (CV) of the pressure drop was compared between distributors, according to the number of nozzles and the superficial gas velocity. The CV for distributors decreased with an increasing modified Froude number. The CV was significantly increased in 1 and 2 shroud nozzle distributors when the modified Froude number was under 50. The bed expansion ratio was also found to increase with an increasing number of nozzles in the distributors. In addition, the drop in bed pressure increased with an increasing number of nozzles. Bed pressure drops of the 1, 2, and 3-shroud nozzle distributors were lower than those of 7-shroud or the perforated plate. In the case of a 1 shroud nozzle, high dead zone occurred, causing poor gas distribution. The standard deviation of the bed pressure drop was measured to evaluate fluctuations in the drop. The fluctuation was found to be proportional to the superficial gas velocity. The CV of the distributor and the bed pressure drop fluctuation were not directly proportional; however, the pressure fluctuation of a 1 shroud nozzle distributor was higher than those of other distributors, due to a non-uniform gas distribution.

Theory of Compressor Stability Enhancement Using Novel Casing Treatment, Part II: Experiment

A stall precursor-suppressed casing treatment is designed to enhance stall margin for both subsonic and transonic compressors. It is noted that the open area ratio of the stall precursor-suppressed casing treatment is only 4–10%, far smaller than conventional casing treatments, with over 50% open area ratio. The effect of the novel casing treatment on the stall margin and efficiency of compressors has been investigated experimentally. The results show that the stall precursor-suppressed casing treatment can improve the stall margin by about 8–18% without significantly decreasing the efficiency of the related fan/compressors. Meanwhile, the present investigation has also attempted to reveal the mechanism of stall margin improvement with such casing treatment. It is found that the stall precursor-suppressed casing treatment will delay the nonlinear development of the stall process by suppressing the propagation of the stall precursor waves, as compared with the evolution of the precursors without casing treatment. This is consistent with the design strategy of the stall precursor-suppressed casing treatment.

Theory of Compressor Stability Enhancement Using Novel Casing Treatment, Part I: Methodology

This paper proposes a novel casing treatment, designated a stall precursor-suppressed casing treatment. It is designed to suppress stall precursors to realize stall margin enhancement in turbomachinery. This paper first presents a physical and mathematical model to describe the casing treatment configuration as a wall boundary condition and then establishes the stability equation with its effect. The sensitivity of stall inception to different boundary conditions is considered numerically for both subsonic and transonic axial flow fan/compressors. One important finding from this numerical prediction and analysis is that such a casing treatment can be used to change stall inception even when using a casing treatment configuration with low open area ratio. Thus, a reduction of momentum loss due to recirculating flow can be realized, in comparison with a conventional recessed casing treatment with more than 50% open area ratio. It is thus theoretically possible to design an advanced casing treatment to affect the evolution of stall precursors and finally change stall inception without significantly changing the efficiency of the fan and compressors.

Experimental validation of numerical simulations for an acoustic liner in grazing flow: Self-noise and added drag

Abstract A coordinated experimental and numerical simulation effort is carried out to improve our understanding of the physics of acoustic liners in a grazing flow as well our computational aeroacoustics (CAA) method prediction capability. A numerical simulation code based on advanced CAA methods is developed. In a parallel effort, experiments are performed using the Grazing Flow Impedance Tube at the NASA Langley Research Center. In the experiment, a liner is installed in the upper wall of a rectangular flow duct with a 2 in. by 2.5 in. cross section. Spatial distribution of sound pressure levels and relative phases are measured on the wall opposite the liner in the presence of a Mach 0.3 grazing flow. The computer code is validated by comparing computed results with experimental measurements. Good agreements are found. The numerical simulation code is then used to investigate the physical properties of the acoustic liner. It is shown that an acoustic liner can produce self-noise in the presence of a grazing flow and that a feedback acoustic resonance mechanism is responsible for the generation of this liner self-noise. In addition, the same mechanism also creates additional liner drag. An estimate, based on numerical simulation data, indicates that for a resonant liner with a 10 percent open area ratio, the drag increase would be about 4 percent of the turbulent boundary layer drag over a flat wall.

Experimental investigation on heat transfer enhancement due to V-shaped perforated blocks in a rectangular duct of solar air heater

In this work, the effect of geometrical parameters of the V-shaped perforated blocks on heat transfer and flow characteristics of rectangular duct, has been investigated experimentally. The experimental investigation encompassed the geometrical parameter namely, relative blockage height (e/H) of 0.4–1.0, relative pitch ratio (P/e) of 4–12 and open area ratio (β) of 5–25% at a fixed angle of attack (α) of 60°. The effect of V-shaped perforated blockages has been investigated for the range of Reynolds number from 2000 to 20,000. The maximum enhancement in Nusselt and friction factor has been found to be 6.76 and 28.84 times to that of smooth duct, respectively. Thermohydraulic performance of V-shaped perforated blockages is also compared to that of V-shaped solid blockages for same geometrical parameters.

Model-Based Approach To Predict and Control Hydraulic Gradient on Slotted Sieve Trays

The hydraulic gradients of the small-hole sieve trays with and without slots were experimentally determined. On the basis of the experimental results, a semitheoretical two-layer model was proposed to describe the gradient of clear liquid height on these trays. The model takes into account both the resistance and the driven forces of gases coming from the sieve holes and the slots, respectively. Two model parameters were identified by comparing the calculated results with the experimental data. By applying the model, the open area ratio of the slots on the sieve trays was optimized to give a minimum clear liquid height gradient for various sets of values of design and operating parameters, and the optimum slot open area ratio was correlated with the parameters. The approach developed in this paper can help to manipulate the hydraulic gradient by changing the slot open area ratio.

스파크점화기관에서 흡기제어 방식이 부분부하 성능에 미치는 영향(1) - 스로틀링과 마스킹의 비교

Abstract : This paper is the first investigation on the effect of flow control methods on the part load performance in a spark ignition engine. For comparison of the methods, two control devices, port throttling and masking, were applied to a conventional engine without any design change of the intake port. Steady flow evaluation shows that steady flow rates per unit opening area and swirl ratio are very low compared with the port throttling and saturated from mid-stage valve lift, however, swirl increases slightly as the lift is higher in case of 1/4 masking control. In the part load performance, the effect of simple port throttling on lean misfire limit expansion is limited and insufficient; on the other hand a masking improves the limit considerably without any port modification for increasing swirl. Also the results show that the intake flow control improves the combustion with following two mechanisms: stratification induced by the combination of the flow pattern and the fuel injection timing attribute to ignition ability and the intensified flow ensure fast burn. In addition fuel consumption reduces under the flow controls and the reduction rate is different according to the operation conditions and control methods. At the Stoichiometric and/or low speed and low load the throttling method is more advantageous; however vice versa at lean and high load condition. Finally, the throttling is more efficient for HC reduction than masking, on the other side the NOx emissions increase under the masking and decrease under the port throttling compared with conventional port scheme.