Open Area Ratio Research Articles

Hydrodynamics of a Multisized Particle Mixture in Shallow Fluidized Bed With Immersed Tubes

Abstract Inert solid particles have made the integration of more efficient power cycles with super high operating temperatures into the concentrated solar power (CSP) station feasible. Fluidized bed heat exchangers with feature of high heat transfer coefficient have great application potential in the particle-based CSP. However, the parasitic loads of the additional fluidizing gas loop and the finely sieved monosized particles may deteriorate the economic efficiency of the integrated system. In order to cope with this problem, a conceptual design of a shallow fluidized bed (SFB) heat exchanger is proposed for the new generation CSP technology. Fluidization characteristics of bauxite particles with a nonuniform particle size distribution in SFB with immersed tubes are investigated with a combination of experimental measurements and computational fluid dynamics simulations. Results show that the static bed height and opening area ratio of the distributor has insignificant influence on the range of semifluidized region and the minimum fluidization velocity Umf. The standard deviation of bed pressure drop σ in the grid region can be used as an alternative criterion for identifying the fluidization state. A range of superficial velocity that distinguishes two different solid circulation patterns exists, with its boundary values being four times and eight times the Umf, respectively. The immersed tubes can inhibit the asymmetric particle circulation patterns from developing in the SFB, but cause a substantial increase in the σ within the grid region.

Experimental Study of Thermal Hydraulic Performance Improvement in Solar Air Heater Channel With V-Shaped Porous Baffles

Abstract Experiments have been conducted to determine how several geometrical parameters of V-shaped porous baffles influence flow characteristics and heat transfer in a rectangular channel. Experiments were conducted on geometric parameters, namely, a relative baffle height (e/H) of 0.4–1, a relative baffle pitch (P/e) of 3–6, open area ratio values of 21–34%, and a single attack angle (α) of 60 deg. Using Reynolds numbers ranging from 2500 to 12,000, V-shaped porous baffles have been examined. Based on a relative baffle pitch of 5, a relative baffle height of 1, and an open area ratio of 21%, the maximum increases in the Nusselt number (Nu) and friction factor (f) were 2.84 and 7 times, respectively. A maximum value of 1.69 is found at e/H = 0.40, P/e = 6, and b = 34% for the thermo-hydraulic performance parameter. Correlations for (Nu) and (f) are developed as functions of P/e, e/H, and Re.

Development of Nusselt number and friction factor correlations for double-pass solar air heater duct

A solar air heater exhibits a low heat transfer rate due to the formation of a laminar thermal boundary layer across the absorber plate. Furthermore, the artificial roughness contributes to the intensification of turbulence along the absorber plate, which interrupts and breaks the thermal boundary layer. Keeping in this view, a three-dimensional simulation is performed to investigate the heat transfer and frictional characteristics of a double-pass solar air heater with semicircular tubes and perforated baffles as artificial roughness. This numerical investigation is performed for the parameters considered in the study: tube amplitude ratios (a/H) from 0.2 to 0.5, baffle height ratios (e/H) from 0.4 to 0.8, open area ratios (β) from 13 % to 30 % and Reynolds number (Re) from 3000 to 19000. The experimental testing rig is designed to validate numerical results corresponding to e/H of 0.4, an open area ratio of 30 %, a/H of 0.3, and Reynolds number varying from 3000 to 15000. Numerical results are found to be in good agreement with the experimental results, with a maximum absolute percentage error of 1.82 % and 5.28 % for the Nusselt number (Nur) and friction factor (fr), respectively. The maximum Nusselt number is observed as 274.29 at Reynolds number of 19,000 and e/H of 0.8; however, the maximum friction factor is observed as 0.6290 at Reynolds number of 3000 and e/H of 0.8 at a constant value of open area ratio of 30 % and a/H of 0.3. Within the range parameters studied, the maximum THPP value is reported to be 2.51 at Reynolds number of 3000, β of 30 %, e/H of 0.4, and a/H of 0.3. Further, correlations for the Nusselt number and friction factor in the function of a/H, e/H, open area ratio, and Reynolds number have been derived based on simulation results.

Acquisition of field ion microscope image using deflector during atom probe analysis

Atom probe (AP) is an elemental analysis technique that ionizes surface atoms by a strong field formed by a sharp needle-shaped sample and identifies ions in an atom-by-atom manner by the time of flight mass spectrometer. The detection efficiency of AP has been estimated to be extremely high by the correlation to field ion microscopy (FIM) observations, which show the surface morphology change in atomic scale during the field evaporation of the surface layer. The estimation of detection efficiency has been indirectly done by the comparison of AP data and FIM observation. We evaluated the detection efficiency of AP directly from ion data and counting spot change in FIM images by repeating two measurements sequentially in this work. The experimentally obtained ratio between the detected count over disappeared spots was 10/33 ≈ 0.30, which was ca. 1/2 of the optimal value expected from the opening area ratio of the microchannel plate (∼0.60).

The potential of a retractable roof of the natatorium on the indoor environmental improvement: Taking Jiading natatorium of Tongji University as an example

The Star-ccm + multiphysics simulation software was used to perform Computer Fluid Dynamic (CFD) simulation on the five operating conditions of a swimming pool at the Jiading Swimming Hall of Tongji University in Shanghai, to determine the energy efficiency of these operations. The indoor environment of each working condition was evaluated. The relationship between the opening and closing area ratio and the indoor environment was also evaluated and obtained the optimal opening area ratio for the Jiading Swimming Hall. The simulation research of the open–closed roof further confirmed that the open–closed roof technology can effectively adjust the internal environment of the swimming pool in summer. The open–closed roof could improve the indoor comfort and reduce the summer energy consumption of the swimming pool and could also provide an organically integrate architectural art feature and technology to create a new stadium design.

High-strength steel beams with hexagonal web openings under impact load

A drop-weight impact testing machine was used to conduct an impact test on 15 specimens in order to examine the impact resistance of high-strength (HS) steel beams with hexagonal web openings (SBHWO). The test findings demonstrate that as steel strength increases, maximal impact force and impact platform value rise, while maximum displacement, residual displacement, beam-end rotation, reduction ratio of opening area, and energy absorption ratio decrease. The use of high-strength steel can significantly improve the impact resistance of the SBHWO. When steel Q235 was lifted to steel Q550, the average increase of impact peak and impact platform value was 17.94% and 90.80%, respectively, and the average reduction range of maximum displacement and residual displacement in the span was 45.36% and 55.30%, respectively. After steel Q550 was upgraded to steel Q690, the improvement effect of impact resistance is small. Empirical equations of the relationship between impact energy，steel strength and dynamic responses were established.

Drag reduction by means of an array of staggered circular cavities at moderate Reynolds numbers

Further insight into the physics of boundary layers developing over an array of circular cavities at moderate Reynolds numbers (Reθ up to 3400) is gained from hot wire boundary layer surveys on a range of parameters. The findings are consistent with literature as to the possibility of reducing skin friction drag with circular perforations. The results evidence a modification of the mean velocity profile, an increase of the wake parameter and the shape factor associated to a decrease of the skin friction. The modifications of the boundary layer as well as the skin friction reduction are more pronounced when the open area ratio is increased, which is achieved by increasing the cavity diameter or equivalently by decreasing the inter-cavity spacing. The turbulent activity is shifted in the upward direction, the burst intensity decreases in the buffer layer (10<Y+<35) and increases in the upper part of the logarithmic region/beginning of outer layer (80<Y+<200) with the formation of an outer peak in the turbulence intensity profile. The premultiplied spectra and the streamwise shear stress profiles evidence an energy surplus in the same part of the boundary layer and for the highest open area ratios a “bi-hump” behaviour. The formation of outer quasi-streamwise rollers is believed to be the cause of this energy hump in the spectrum. The turbulence statistics show a striking similarity with the turbulent boundary layer in presence of wall-normal blowing. It is believed that the cavities promote a vertical velocity component that displaces the turbulent activity towards the outer region. Different hypotheses to explain the modification of the flow statistics are detailed in the paper.

Influence of winter natural ventilation on thermal environment of university dormitories under central heating mode in severe cold regions of China

The indoor thermal environment impacts people’s health, while it can be adjusted by natural ventilation. However, studies on the effects of winter natural ventilation on the thermal environment in severe cold regions are minimal. Through field measurements in university dormitories in winter in Shenyang, China, this study explored, under the central heating mode, the thermal environment differences in different orientations of the dormitory and its different indoor positions under natural ventilation and the influence of window opening area and duration on the thermal environment. The results show that under winter natural ventilation, the air temperature, mean radiation temperature, and adaptive predicted mean vote (APMV) of dormitories facing different orientations were mainly affected by the direct solar radiation reception. When the ventilation duration reached 15mins, with the ratio of window opening area to a ground area of 0.05, 0.11, and 0.16, the APMV decreased by about 0.35, 0.5, and 1, respectively.

Experimental uncertainty assessment of meso- and microplastic concentrations in rivers based on net sampling

Meso- and microplastics have been collected via net sampling in marine and freshwater environments, but the effect of net clogging on evaluations of their concentrations (mPC) remains uncertain. We experimentally investigated the mPC uncertainties resulting from net clogging in the Ohori and Tone-unga Rivers, typical urban rivers in Japan, throughout 16 samplings with five filtration durations in one day. The weighted mean concentration in the Ohori River was significantly lower than that in the Tone-unga River, allowing us to examine the effect of clogging in rivers with different contamination levels. The variances in both rivers consistently tended to increase with increasing filtration duration, which can be expressed by applying the integral form of the Weibull reliability function (WRF).Furthermore, application of the WRF successfully revealed the optimal filtration durations in the Ohori and Tone-unga Rivers, which depended on the plastic abundance and sample volume. Since it could be difficult to obtain the plastic contamination level in advance, our suggestion is to predict the time sustained above 85 % filtration efficiency by applying a WRF-based model. In actuality, the sustained time in the Ohori (Tone-unga) River varied between 2.6 and 6.2 min (3.2 and 7.1 min) throughout the experiment, which permitted low mPC uncertainties of 12 % and 9.5 %, respectively. If notable uncertainty exists due to a low contamination level, a net with a high open area ratio should be used to increase the filtration duration. Hence, our results emphasize the importance of considering the open area ratio of nets used for sampling in studies. Our study provides insights into the occurrence of uncertainty due to net clogging to establish a standardized methodology for meso- and microplastic monitoring in aquatic environments via net sampling and consequently contributes to improving the sampling accuracy.

Thermo-hydraulic performance of double pass solar air heater duct having semi-circular tubes and perforated blocks as artificial roughness

Solar air heaters (SAH) are used to collect and convert the solar radiations into thermal energy for various thermal applications. Its thermo-hydraulic performance can be improved by using various geometries of artificial roughness that breaks the laminar sublayer on absorber plate. In view of the same, a 3-dimensional computational investigation is conducted to study the heat transfer and friction characteristics of a double pass SAH having transverse semi-circular tubes with rectangular perforated blocks as artificial roughness and its outcomes are reported under the present paper. The investigation is carried out for different parameters such as Reynolds number (Re), tube amplitude to duct-height ratio (a/H), relative blockage-height ratio (e/H) and open area ratio (β) within a range of 3000–19,000, 0.2 to 0.5, 0.4 to 0.8 and 13%–30%, respectively. The results obtained through CFD simulations are also compared with the experimental results for a typical set of parameters and a maximum percentage deviation for Nusselt number and friction factor are found as 1.82% and 5.28% respectively. For a considered range of parameters, the maximum value of thermo-hydraulic performance parameter is achieved as 2.51 corresponds to Re of 3000, a/H of 0.3, e/H of 0.4, and β of 30%. Based on the obtained results, it is found that the perforated blocks having maximum value of β and minimum value of e/H results in improved thermo-hydraulic performance of a double pass SAH. The research output of the present study may be useful for designing and optimize the parameters of a double pass SAH for the low temperature applications such as space heating, solar drying and solar air conditioning.

Effect of Open Area Ratio on Vortex Behavior of Turbulent Grid Wake

Effect of Open Area Ratio on Vortex Behavior of Turbulent Grid Wake

Experimental Assessment of Variation in Open Area Ratio on Thermohydraulic Performance of Parallel Flow Solar Air Heater

Experimental Assessment of Variation in Open Area Ratio on Thermohydraulic Performance of Parallel Flow Solar Air Heater

Effect of Window Openable Area and Shading on Indoor Thermal Comfort and Energy Efficiency in Residential Buildings with Various Operating Modes

Solar heat gain and natural ventilation cooling of the indoor environment in buildings are highly influenced by the shading and openable area of windows. In addition to the ambient condition, the Heating, ventilation and air conditioning (HVAC) system’s mode of use can affect the windows’ performance, especially when multiple modes are used in combination (mixed-mode). Although many studies have investigated the mixed-mode application, their conditions for starting/shutting down HVAC equipment and controlling window ventilation are inconsistent with the relevant codes. Here, we propose a mixed-mode operation that resolves the gap between the air conditioning operation temperature and the adaptive comfort upper temperature. It investigates residential buildings’ indoor thermal environment and energy efficiency by combining the effective ventilation opening area ratio (REV) and shading design. Simulation results show that our mixed-mode can reduce the indoor overheating hours by about 50% and the building’s energy consumption by about 50%. We thereby conclude that the openable area of exterior windows in residential buildings in Chongqing should not be less than 10% of the room’s floor axis area where the exterior windows are located. In general, our study expands the existing knowledge of passive energy-saving measures and provides a method for further research on building energy design in hot summer and cold winter regions.

A Study on the Resolution and Depth of Focus of ArF Immersion Photolithography.

In this study, the resolution and depth of focus (DOF) of the ArF immersion scanner are measured experimentally according to numerical aperture (NA). Based on the experiment, the theoretical trade-off relationship between the resolution and depth of focus can be confirmed and k1 and k2 are extracted to be about 0.288 and 0.745, respectively. Another observation for a problem in small critical dimension realization is the increase in line width roughness (LWR) according to mask open area ratio. To mitigate the trade-off problem and critical dimension variation, the photoresist thickness effect on depth of focus is analyzed. Generally, the photoresist thickness is chosen considering depth of focus, which is decided by NA. In practice, the depth of focus is found to be influenced by the photoresist thickness, which can be caused by the intensity change of the reflected ArF light. This means that photoresist thickness can be optimized under a fixed NA in ArF immersion photolithography technology according to the critical dimension and pattern density of the target layer.

Flexural biomimetic responsive building façade using a hybrid soft robot actuator and fabric membrane

The geometrical inflexibility of rigid-body kinetic building façades is disadvantageous in free-form architecture. To address this problem, a gearless, lightweight, and geometrically flexible daylight-adaptive shading façade module is proposed by hybridizing gripper-shaped pneumatic elastomer and shape memory alloy (SMA) actuators. The compliant inflation mechanism and thermomechanical response of the bias SMA actuation achieved flexural morphology of the stretchable fabric skin and a maximum opening area ratio of ∼20%. Design feasibility, stable mobility, and structural endurance were identified through performance simulation and material testing, followed by operation tests with full-scale prototyping. This paper presents an advanced architectural application of soft robotics technology and smart material. Our findings expand the knowledge on bio-inspired designs and construction processes in climate-responsive building.

Numerical investigation of the particle circulation characteristics in a tapered fluidized bed

PurposeThe objective of this study is to investigate several issues related to particle circulation within the TFB, including exploring an appropriate method to quantify particle circulation time, the effects of different operational parameters on particle circulation time, and the relationship between particle mixing and particle circulation.Design/methodology/approachThe computational fluid dynamics coupled with the discrete element method (CFD-DEM) is applied to investigate the particle circulation characteristics of a tapered fluidized bed (TFB). An approach for defining particle circulation, which accounts for the horizontal motion of each particle, is proposed to estimate particle circulation time.FindingsIt is found that the overall particle circulation in a TFB could be accelerated by increasing air velocity and wall inclination angle, while an increase in particle size and an increase in inter-particle cohesive forces decelerate particle circulation; the increase in the open area ratio of the central region of the air distributor would decelerate the particle circulation. Moreover, the particle circulation time and mixing rate are independent variables that describe the flow dynamics of particles from different perspectives.Practical implicationsA large part of fluidized beds in industrial applications can be classified as TFB. This study presents a numerical method to obtain detailed knowledge about particle circulation in a TFB, which is essential for the design, optimization, and control of related processes.Originality/valueThe particle circulation in a TFB is important but rarely investigated, and it is hard to be quantified using existing experimental approaches. The proposed numerical workflow reveals the characteristics of particle circulation from a particle-scale perspective.

Water and heat management of vapor-fed direct methanol fuel cells with a non-isothermal triple-phase mass transfer model

Direct methanol fuel cells (DMFCs) operating with methanol vapor tends to operate under higher temperature, which contributes to improve cell performance and specific energy. However, the design of vapor-fed DMFCs with high performance and adaptability are still hindered by the complex water and heat management. To provide a comprehensive understanding of the critical multiphase heat and mass transfer, we develop a two-dimensional non-isothermal triple-phase mass transfer model for a passive vapor-fed DMFC. Effects of the electrochemical reactions and related thermal effect are fully investigated. Increasing the current density raises the operating temperature, thus enhancing the generation rate of methanol vapor and reducing concentration polarization under high current densities. With the enlargement of the open area ratio (from 0.1 to 0.3), an excessive methanol supply rate may cause deteriorated methanol crossover rates and excessively high temperatures, resulting in severe dehydration of polymer electrolytes and a degraded cathode overpotential (from −0.48V to −0.54V). For the DMFC with Nafion 112 membrane, the maximum current density and peak power density are 33.3% and 36.0% greater than that of Nafion 117 membrane. The simulation work will provide an exhaustive theoretical guidance for the efficient management of water and heat in DMFCs fed with neat methanol.

Heat transfer and friction factor correlations development for double pass solar air heater artificially roughened with perforated multi-V ribs

Thermo-hydraulic performance of a Double Pass Parallel Flow Solar Air Heater (DPPFSAH) roughened with perforated multi-V ribs has been studied experimentally in a prior study and the effect of variation in open area ratio and change in relative roughness width has been analysed and reported. The current work builds upon the aforementioned earlier study by discussing in detail the methodology and various steps involved in the development of a correlation for variable parameters with Nusselt number and friction factor for DPPFSAH. The outcomes show that perforations in the multi-V ribs lead to a considerable rise in the Nusselt number, a 9.66 times increase in the thermo-hydraulic performance parameter and nearly a four times increase in friction factor compared to multi-V ribs with smoothed walls. Empirical correlations for the Nusselt number and friction factor were obtained for the double pass parallel flow solar air heater with perforated multi-V ribs established with ±14% and ±7%.

Perforation effects on the wake dynamics of normal flat plates

The effect of perforation on the wake of a thin flat plate placed normal to the free stream at Reynolds number ( $Re$ ) 250 (based on plate width $d$ , and inflow velocity $U_o$ ) is studied by means of direct numerical simulation. The perforated plate of length $6d$ consist of six equidistant square holes of varying sizes corresponding to porosity $\beta$ (ratio of open area to total plate area) of 0 %, 4 %, 9 %, 12.25 %, 16 %, 20.25 % and 25 %. It is observed that the bleed or jet flow through perforations pushes the shear layer interaction farther downstream with increasing $\beta$ . This causes a monotonic decrease in the drag coefficient with increasing porosity, and a sharp fall seeming to begin at $\beta \approx 4\,\%$ . On the other hand, the Strouhal number increases with $\beta$ up to 16 % (at $\beta =16\,\%$ , loss of flow three-dimensionality leads to a ‘quasi-laminar’ state of flow). This is followed by a sharp fall in the Strouhal number at $\beta \approx 20\,\%$ . The behaviour of the large-scale vortical structures in the far wake is influenced by the near-wake behaviour of the bleed flow, where the local $Re$ based on the perforation hole size determines the overall flow three-dimensionality. It is also observed that the jet or bleed flow undergoes meandering instability when pitch separation is equivalent to the hole size (at $\beta =25\,\%$ ). The low- $Re$ turbulent flow for a non-perforated plate is altered to a transitional state by the presence of perforation. The streamwise vortex pairs (secondary instabilities) become fairly organized as $\beta$ is increased from 0 % to 16 %. The secondary instability at $\beta =16\,\%$ appears similar to mode-B with wavelength ${\approx }1d$ . On the contrary, the secondary instability at $\beta =25\,\%$ appears similar to mode-A with a wavelength of ${\approx }2d$ .

Experimental Analysis of Pressure Shielding Mechanisms in Bioinspired Unidirectional Canopies

Previous studies have demonstrated that treatments such as a canopy or finlets placed within a boundary layer can shield surfaces from unsteady pressure fluctuations without substantially compromising the aerodynamic performance. This paper describes research into fundamental mechanisms of this phenomenon known as pressure shielding. Unidirectional canopy is an idealized surface treatment which consists of a streamwise array of rods cantilevered at the downstream end, inspired from the downy coating on owls’ wings. Experiments show that such a canopy attenuates the surface pressure in two distinct frequency ranges. At low frequencies associated with convective scales much greater than the canopy height, the attenuation spectra show scaling on the Strouhal number based on canopy height. At high frequencies, associated with convective scales of the order of the canopy height or lower, a dissipation-type frequency scaling appears more appropriate. The ratio of streamwise distance over the height is an important parameter at the low-frequency regions of attenuation, while the open-area ratio controls the broadband magnitude of attenuation spectra. Spatial and temporal correlations further shed light on the effects of the canopy in reducing the larger, energetic turbulent structures associated with the wall jet unsteady surface pressure fluctuations.