Open Area Ratio Research Articles

Field measurements on thermal stratification and cooling potential of natural ventilation for large space buildings

Large space buildings often have high HVAC energy consumption, and the thermal pressure ventilation can be utilized to reduce the using of chiller. Temperatures were tested on two naturally ventilated large spaces, and it increased linearly towards the ceiling with its gradients α being in range of 0.1–0.4 °C/m. The traditional stack effect model is modified by introducing thermal stratification. For three hot and humid cities in China, the acceptable indoor air temperatures are discussed and determined based on its monthly outdoor air temperatures. Investigations are done to find out parameters’ influences on the indoor thermal environment. It is known that both the dimensionless neutral plane height Hn/H and the volumetric flow rate per unit floor area l are not sensitive to outdoor climate, but decrease with increasing of the lower-upper opening area ratio Rab; the occupied air temperature tn increases with the increase of Rab or q but with the decrease of α or H; under case of 0.2 °C/m and 150 W/m2, Nanjing has the maximum scopes of available upper opening areas in transition season to achieve natural ventilation cooling potential. Such results would be useful in design and management of upper openings for large spaces.

Study on downward flame spread over extruded polystyrene foam in a vertical channel: Influence of opening area

SummaryExperimental methods and theoretical analysis are employed to investigate effects of channel opening area on downward flame spread characteristics of extruded polystyrene (XPS) thermal insulation materials on building facade. The average flame height first drops and then rises as dimensionless opening area (the ratio of sidewall opening area to sidewall area, ie, S*) increases. As S* rises, both the average and maximum temperature of the curtain wall decrease, and the decreasing of the average temperature is linear. XPS surface temperature history can be divided into four stages, ie, inapparent rising stage (preheating), significant rising stage (melting), dropping stage (pyrolysis), and rerising stage (ignition). The preheating length first rises and then drops as S* increases. The XPS flame spreads steadily at the early period while acceleration occurs at the later period. For different opening areas, the difference in spread distance history is not apparent in the early stage while this difference is significant in the later stage. The flame spread rate (Vf) first increases and then decreases as S* rises. A downward flame spread model for XPS in vertical channel with openings is built. The varied trend of Vf predicted using this model corresponds to the experimental result.

Experimental study on thermal buoyancy-induced natural ventilation

It is well known that natural ventilation is caused by the outdoor wind velocity and the indoor-outdoor temperature difference. Generally, natural ventilation is rarely caused by one effect alone, but by the coupled form of two effects. However, only the indoor-outdoor temperature difference (ΔT) was considered to evaluate the characteristic of thermal buoyancy-induced natural ventilation in this experimental study. The indoor-outdoor temperature differences were set to 5, 10, 20 and 30 °C. The measured ventilation rates by changing ΔT were compared to the calculation results based on the hydrostatic theory. From the experimental results, it was found that the ventilation rate is exponentially proportional to ΔT and the area ratio (AR) of the inlet opening to the outlet opening is an important factor to affect natural ventilation. However, the influence on a ventilation rate by AR nearly disappeared when AR exceeds over 5.0. In addition to it, it was identified that AR and a flow resistance coefficient of Cd for ventilation can be correlated as an exponential function and its form is exp(−3.6AR).

Prediction of natural and hybrid ventilation performance used for fire-induced smoke control in a large single space

This paper deals with a large single space building for smoke control when a fire happens. Two hybrid ventilations are investigated, i.e. natural ventilation through a roof opening combined with mechanical suction flow, and with mechanical jet flow. Pure natural ventilation is used as a benchmark. An experimental model was reproduced as 1/10 of the prototype. Under pure natural ventilation, the roof opening played an important role in exhausting but the smoke layer height descended rapidly. Influences of mechanical flows from sidewalls on the smoke distributions were found to be evident. Large eddy full-scale simulations were performed in which grid size of the fire-domain was determined to be 0.125 m being one half of the non-fire domain. The simulation results agreed well with the experimental ones. A total of 63 ventilation cases are further simulated, and it reveals that mass flow rates of the roof opening increase with the increase of opening area ratio or discharge velocity of inlets or heat release rate but with the decrease of exhaust velocity of outlets; under hybrid ventilation of mode 4, back-flow occurs under the roof opening when the exhaust velocity reaches up to 6 m/s, and the maximum smoke temperature and the CO concentration near the door is of the lowest indicating its best advantage in controlling the fire smoke; the smoke plume is more easily disrupted by jet flow than by suction flow. This study helps to promote the design and operation of ventilation system for large and high spaces when firing.

Performance comparison of jet pumps with round and sharp edge of small opening in oscillatory flow

Owing to the capability to induce a time-averaged pressure drop in oscillatory flow, a jet pump has been used to suppress the Gedeon streaming in a looped thermoacoustic engine. The suppression capacity originates from the asymmetric pressure drop through the jet pump, and could be enhanced by rounding the edge of the jet pump in traditional view. This paper systematically probes the rounding effect on a jet pump and compares the performance of jet pumps with round and with sharp edge on small opening. The performance dependences on the taper angle and the cross-sectional area ratios, including the big-to-small opening area ratio of the jet pump and the small opening-to-pipe cross sectional area ratio, are analyzed and compared for the two types of jet pump. The results reveal a reversed and higher time-averaged pressure drop in the shape edge jet pump in contrast to that in the rounded jet pump. However, the round edge of the small opening can improve working efficiency of a jet pump.

On the simultaneous inversion of micro-perforated panels' parameters: Application to single and double air-cavity backed systems

This study deals with the deduction of parameters of Micro-Perforated Panel (MPP) systems from impedance tube data. It is shown that there is an ambiguity problem that exists between the MPP thickness and its open area ratio. This problem makes it difficult to invert the reflection coefficient data fitting and therefore to deduct the MPP parameters. A technique is proposed to reduce this ambiguity by using an equation that links the hole diameter to the open area ratio. Reflection coefficient data obtained for two specimens with different characteristics is employed for searching the MPP parameters using a simulated annealing algorithm. The results obtained demonstrate the effectiveness of this technique.

Physical modeling of vortical cross-step flow in the American paddlefish, Polyodon spathula.

Vortical cross-step filtration in suspension-feeding fish has been reported recently as a novel mechanism, distinct from other biological and industrial filtration processes. Although crossflow passing over backward-facing steps generates vortices that can suspend, concentrate, and transport particles, the morphological factors affecting this vortical flow have not been identified previously. In our 3D-printed models of the oral cavity for ram suspension-feeding fish, the angle of the backward-facing step with respect to the model’s dorsal midline affected vortex parameters significantly, including rotational, tangential, and axial speed. These vortices were comparable to those quantified downstream of the backward-facing steps that were formed by the branchial arches of preserved American paddlefish in a recirculating flow tank. Our data indicate that vortices in cross-step filtration have the characteristics of forced vortices, as the flow of water inside the oral cavity provides the external torque required to sustain forced vortices. Additionally, we quantified a new variable for ram suspension feeding termed the fluid exit ratio. This is defined as the ratio of the total open pore area for water leaving the oral cavity via spaces between branchial arches that are not blocked by gill rakers, divided by the total area for water entering through the gape during ram suspension feeding. Our experiments demonstrated that the fluid exit ratio in preserved paddlefish was a significant predictor of the flow speeds that were quantified anterior of the rostrum, at the gape, directly dorsal of the first ceratobranchial, and in the forced vortex generated by the first ceratobranchial. Physical modeling of vortical cross-step filtration offers future opportunities to explore the complex interactions between structural features of the oral cavity, vortex parameters, motile particle behavior, and particle morphology that determine the suspension, concentration, and transport of particles within the oral cavity of ram suspension-feeding fish.

Aerothermal Characteristics of Solid and Slitted Pentagonal Rib Turbulators

This work is an experimental study of detailed aerothermal characteristics inside a duct carrying an array of solid and permeable pentagonal ribs with a parallel and inclined slit, mounted on the bottom wall. The rib height-to-hydraulic diameter ratio, the rib pitch-to-height ratio, and the open area ratio fixed during experiments are 0.125%, 12%, and 25%, respectively. The heat transfer coefficient (HTC) distribution is mapped by using transient liquid crystal thermography (LCT), while the detailed flow measurements are performed by using particle image velocimetry (PIV). The primary focus of the study is to assess the influence of inter-rib region flow characteristics on the local heat transfer fields. The heat transfer and friction factor measurements are evaluated along with thermohydraulic performances at different Reynolds numbers, i.e., 26,160, 42,500, and 58,850. Performance indexes show that the pentagonal ribs with the inclined-slit are superior to other configurations from both perspective. Aerothermal features within inter-rib region were elucidated by analyzing the time-averaged streamlines, mean velocities, fluctuation statistics, vorticity, turbulent kinetic energy (TKE) budget terms, and local and spanwise-averaged Nusselt number as well as augmentation Nusselt numbers. Critical flow structures and coherent structures were identified, which illustrate about different flow dynamic processes. The flow emanating out of the inclined-slit pentagonal rib significantly affects the magnitude of streamwise velocity, fluctuation statistics, vorticity, and TKE budget terms at the downstream corner, whereas the dissipation term of TKE budget correlates well with the surface heat transfer distribution.

Impact of Tile Design on the Thermal Performance of Open and Enclosed Aisles

In raised floor data centers, tiles with high open area ratio or complex understructure are used to fulfill the demand of today's high-density computing. Using more open tiles reduces the pressure drop across the raised floor with the potential advantages of increased airflow and lower noise. However, it introduces the disadvantage of increased nonuniformity of airflow distribution. In addition, there are various tile designs available on the market with different opening shapes or understructures. Furthermore, a physical separation of cold and hot aisles (containment) has been introduced to minimize the mixing of cold and hot air. In this study, three types of floor tiles with different open area, opening geometry, and understructure are considered. Experimentally validated detail models of tiles were implemented in computational fluid dynamics (CFD) simulations to address the impact of tile design on the cooling of information technology (IT) equipment in both open and enclosed aisle configurations. Also, impacts of under-cabinet leakage on the IT equipment inlet temperature in the provisioned and under-provisioned scenarios are studied. In addition, a predictive equation for the critical under-provisioning point that can lead to a no-flow condition in IT equipment with weaker airflow systems is presented. Finally, the impact of tile design on thermal performance in a partially enclosed aisle with entrance doors is studied and discussed.

Performance studies of atomic layer deposited microchannel plate electron multipliers

Microchannel plate (MCP) photon counting, event timing, imaging detectors have found wide use in astronomical, remote sensing, and biological imaging applications. Novel MCP technology using borosilicate glass microcapillary array substrates functionalized by the application of resistive and secondary emissive layers using atomic layer deposition (ALD) techniques has the potential to outperform traditional MCP technology. Using ALD techniques to functionalize the MCPs allow customization of parameters like gain and resistance independently from the glass substrate. Borosilicate substrates have many advantages over traditional micro-capillary arrays, including low radioactive content, higher open area ratios, low outgassing, and high operational stability. These ALD MCPs can be manufactured in large areas (400 cm2) providing a unique solution for many timing/imaging applications. ALD MCPs can withstand the processing temperatures required for high temperature deposition of III–V materials, such as Gallium Nitride, for UV photocathodes with high quantum efficiencies (QE) in the Near-UV (∼100–380 nm). We present the effects of different ALD configurations on the gain (magnitude and uniformity), resistance, imaging, background and detection efficiency, and how these parameters change during lifetime testing. We also present the QE of ALD MCPs and various QE enhancement techniques.

UV-Grade Silicon Photomultipliers for Direct Counting of Low-Energy Electrons and Protons

This paper reports a novel application of silicon photomultipliers (SiPMs) for directly counting kiloelectron-volt-range electrons and protons. Current instruments for measuring low-energy ions and neutral atoms ( keV particles replacing conventional detectors for certain applications in this paper. Our results demonstrated that the VUV-SiPM was sensitive above 1 keV both for electron pulses and protons. Using absolute beam monitor system, the proton detection efficiency of these SiPMs was evaluated. The efficiency was ~1% for 1-keV protons and plateaued above 5–6 keV at the expected 75% efficiency that agreed reasonably with the Monte Carlo numerical simulation results. The 75% plateau level was matching the open area ratio of the SiPM structure. The electron-pulse efficiency was also estimated by applying the same model, which shows ~1-keV detection limit and plateau above 3–4 keV. The agreement between the simulation and measurement shows that the dominating mechanism to trigger SiPM signals is the ionization loss of primary electrons and protons in the active volume of the pixel. An analytic investigation shows that the dark count rate can be significantly reduced with a double (or quadruple) coincidence measurement if multiple electrons can be produced from a single event.

Optimization of a rectangular pin fin using elliptical perforations with different inclination angles

An innovative form of a perforated fin (with inclination angles) was considered. In most previous studies, pin fins were perforated in a straight direction to improve the thermal performance of the heat sink. The present rectangular pin fin consisted of an elliptical perforation with two models and two cases. The signum function was used to model the opposite and mutable approach of the heat-transfer area. The degenerate hypergeometric equation was used as a new derivative method to determine a general solution and solved by Kummer’s series. Two validation methods (previous work and Ansys 16.0 steady-state thermal analysis) were considered. The strong agreement of the validation results (0.31 %-0.52 %) showed the reliability of the presented model. The use of the perforated fin reduced the thermal resistance and improved the thermal performance of the pin fin by enhancing heat transfer and increasing the Nusselt number. Moreover, increasing the inclination angle, size, and number of perforations can optimize the present model by maximizing heat transfer and minimizing the weight and length of the pin fins. Increasing the open-area ratio minimizes entropy generation at a certain Rayleigh number and constant heat flux.

The Formation of Vortex Structures in a Screen Cylinder Wake

The formation of vortex structures in a screen cylinder wake was investigated in a wind tunnel at a Reynolds number of 7000. The screen cylinder was made of a stainless steel wire mesh with an open area ratio of 67%. The results showed that the screen cylinder wake could be classified into two distinct regions. The first region was characterised by the development of the shear layer vortices which resulted from Kelvin-Helmholtz instability. At about x/d = 2 0 (where d is the diameter of the cylinder) the shear layer vortices started to interact with each other across the centreline, and evolved downstream to form the alternately arranged ‘large-scale’ coherent structures. These structures were most pronounced at x/d = 40. The vortex formation region was therefore extended significantly downstream compared with that of the solid cylinder wake. The second region involved a gradual decay of the fully-formed large-scale structures, evidenced by the weak vorticity exchange across the wake centreline.

Efficacy of sellar opening in the pituitary adenoma resection of transsphenoidal surgery influences the degree of tumor resection

BackgroundEndonasal transsphenoidal microsurgery is often adopted in the resection of pituitary adenoma, and has showed satisfactory treatment and minor injuries. It is important to accurately localize sellar floor and properly incise the bone and dura matter.MethodsFifty-one patients with pituitary adenoma undergoing endonasal transsphenoidal microsurgery were included in the present study. To identify the scope of sellar floor opening, CT scan of the paranasal sinus and MRI scan of the pituitary gland were performed for each subject. Intraoperatively, internal carotid artery injury, leakage of cerebrospinal fluid, and tumor texture were recorded, and postoperative complications and residual tumors were identified.ResultThe relative size of sellar floor opening significantly differed among the pituitary micro-, macro- and giant adenoma groups, and between the total and partial tumor resection groups. The ratio of sellar floor opening area to maximal tumor area was significantly different between the total and partial resection groups. Logistic regression analysis revealed that the ratio of sellar floor opening area to the largest tumor area, tumor texture, tumor invasion and age were independent prognostic factors. The vertical distance between the top point of sellar floor opening and planum sphenoidale significantly differed between the patients with and without leakage of cerebrospinal fluid.ConclusionThese results together indicated that relatively insufficient sellar floor opening is a cause of leading to residual tumor, and the higher position of the opening and closer to the planum sphenoidale are likely to induce the occurrence of leakage of cerebrospinal fluid.

On the prediction of uniformity of air flow out from manifold distribution

AbstractComputational fluid dynamics (CFD) was used to simulate a closed‐end multiple outlet pipe to examine the effect of different exit port geometry and size of perforation on performance of manifold distribution. To obtain an optimum design, the amount of fluid discharging from any opening in a pipe is greatly concern in engineering applications because uniform flow distribution has significant influence on the performance of manifold distribution. In this investigation, the vertical manifold system was used to study the hydrodynamics of air flow and simulate with computational fluid dynamics (CFD). Firstly, three different exit port geometry (circular, rectangular and square) are chosen to investigate the effect of exit port on mass flow rate uniformity effusing from distribution manifold. The best performance, which most closely approximating uniform outflow was achieved by the rectangle exit ports. Secondly, three different perforation size (3, 4 and 5 mm) of circular exit port were selected to reach to the finding of uniformity. Results show the 5 mm diameter orifices exit port achieve the uniform outflow of all. The ratio of the total opening area for all cases to the cross‐sectional area of the cylindrical pipe is identical for these two cases. Thirdly, the effect of perforation diameter with variable pipe ratio for equal number of orifices was investigated. The analysis for investigating the changes in the discharge angle of the stream between the orifices of multi‐perforated pipes perform for all cases. Standard k–ϵ turbulence model was considered for the numerical simulation, the finding results of numerical simulation were evaluated by the laboratory experiments.

A new sound quality metric for the design of engine exhaust mufflers

In this paper, a study is made to determine the critical dimensions in the design of a family of reactive mufflers which significantly affect the sound quality of the tailpipe radiated noise. The sound quality parameters of the tailpipe noise such as the loudness level, the roughness and the tonality are measured, and a new sound quality metric is developed which can be used as an index to predict the performance of a muffler. The new sound quality metric was based on the evaluations of the synthesized tailpipe noise by a jury consisting of a few undergraduate and postgraduate students at the Indian Institute of Technology Kharagpur. Using the new sound quality metric, the parameters with the most influence on the design of the muffler can be determined. It was found that the length and the open area ratio of a concentric-tube resonator muffler have the highest impact on the tailpipe noise sound quality.

Pressure Drop Through Orifices for Single- and Two-Phase Vertically Upward Flow—Implication for Metering

Pressure drop has been measured for upward single- and two-phase gas–liquid flow across an orifice in a vertical pipe. A conductance probe provided average void fraction upstream of the orifice. Six orifices with different apertures/thickness were mounted in turn in a 34 mm diameter transparent acrylic resin pipe. Gas and liquid superficial velocities of 0–4 m/s and 0.3–0.91 m/s, respectively, were studied. For single-phase flow, pressure drop, expressed as an Euler number, was seen to be independent of Reynolds number in turbulent region. The Euler number increased with decreasing the open area ratio/orifice thickness and increasing velocity. The pressure drop was well predicted by the correlation of Idel'chik et al. (1994, Handbook of Hydraulic Resistances, 3rd ed., CRC Press, Boca, Raton, FL.), which uses a form of Euler number. The corresponding two-phase flow pressure drop depends on the flow pattern. Decreasing open area ratio/orifice thickness increased the pressure drop. For a given liquid superficial velocity, the pressure drop increases with gas superficial velocity except for low open area ratio where this increase is followed by a decrease beyond a critical superficial gas velocity for the high liquid superficial velocities. Relevant correlations were assessed using the present data via a systematic statistical approach. The two-phase multiplier equations of Morris (1985, “Two-Phase Pressure Drop Across Valves and Orifice Plates,” European Two Phase Flow Group Meeting, Marchwood Engineering Laboratories, Southampton, UK.) and Simpson et al. (1983, “Two-Phase Flow Through Gate Valves and Orifice Plates,” International Conference on Physical Modelling of Multiphase Flow, Coventry, UK.) are the most reliable ones.

Design and characterisation of external orifice semi-active suspension system for armoured vehicle application

The objective of this paper is to investigate the force-velocity characteristics of a new design of external orifice semi-active suspension system (EOSASS). EOSASS is a class of semi-active system where the orifice area is controlled electronically using an electric motor. The idea of EOSASS is to modify the internal fixed orifice of the existing passive damper into externally controllable using hydraulic unit. The behaviour of the EOSASS is tested in terms of its force-velocity and force-displacement characteristics using Instron 8801 Servohydraulic fatigue testing system and WaveMatrix dynamic testing software. The ratio of the orifice opening area for the compression and extension on the hydraulic unit is varied in order to study the hysteresis behaviour of the damper. From the experimental results, the relationship between the damping force and the ratio of orifice opening during extension and compression are obtained. It was verified that decreasing the ratio of orifice opening will produce higher damping force in both compression and extension stages.

Effects of the lattice leg on cavities and bearing capacity of deeply embedded spudcans in clay

This paper examines the effect of the lattice leg on the cavities of deeply embedded spudcans in clays using centrifuge model tests and finite-element analyses. The lattice legs are characterised by two parameters, namely the opening ratio and area ratio. Both centrifuge and numerical results show that, in the presence of lattice legs, the cavities consist of two zones: a deep inner cavity within the cross-sections of the lattice legs and a much shallower outer cavity beyond the periphery of the lattice legs. The latter can be attributed to cavity wall collapse around the rim. The volume contributed by the outer cavity is much smaller than that contributed by the inner cavity. Hence, the latter is the focus of this study. The findings show that the lattice leg affects the cavity in two ways. First, it restricts soil back-flow to the region outside the lattice leg. Second, it enhances the stability of the soil on the walls of the cavity, thereby limiting the wall collapse zone to the topmost portion of the cavity. Both of these effects contribute to an increase in the cavity depth. Based on the centrifuge model test results and finite-element analyses, relations are proposed to predict the inner cavity depth which incorporates the opening and area ratios of the lattice leg, spudcan diameter and undrained shear strength of the soil. The effect of the lattice leg on bearing capacity is also illustrated using centrifuge results. Finally, the possibility of cavity wall collapse and spudcan settlement due to consolidation of soil and cyclic loading are briefly discussed using centrifuge data.

Transient analysis of passive vapor-feed DMFC fed with neat methanol

A transient model is presented to investigate the transport phenomena for passive vapor-feed direct methanol fuel cell (DMFC). The pervaporation membrane and vapor transport layer are considered for the formation and transport of methanol vapor, respectively. We attempt to provide insight into the transient mass transport characteristics of DMFCs by testing different operation conditions, including current density, open area ratio of the vaporizer, and membrane thickness. The results show that the methanol crossover rate and water transport from the cathode to the anode are the key factors for improving the cell performance, and indicate that fuel efficiency, energy efficiency and energy density of the DMFCs are improved by increasing current density, decreasing open ratio of the vaporizer or increasing membrane thickness due to the reduced methanol crossover rate. The cathode micro-porous layer (MPL) is useful in enhancing water recovery flux and decreasing water losses.