Effects of baffles on the performance of model waste stabilization ponds

The performance of three baffled laboratory-scale facultative stabilization ponds were compared with that of an unbaffled control pond. The hydraulic characteristics of the ponds were estimated from the results of tracer tests.The biochemical oxygen demand (BOD₅) removals achieved with the control pond and with the ponds having 3, 6 and 9 baffles were 79, 81, 86 and 89% respectively and the chemical oxygen demand (COD) removals were 81, 84, 84.2 and 84.2%. The reductions in total solids (TS) were respectively 43, 46, 51 and 64%. Dispersion indices of 0.161, 0.126, 0.112 and 0.096 were obtained for the control, 3, 6 and 9 baffle ponds respectively, which indicated a trend of decreasing dispersion index with increasing number of baffles.     

Numerical simulation of baffle effect on the performance of sedimentation basin

Sedimentation basin is an important component of every water treatment process. In order to improve the sedimentation efficiency (SE) of rectangular sedimentation basins, many researchers have proposed various methods. Among the suggested methods, the change of the geometry with installation of baffle in the basin floor is simple and completely economic. In this research, the hydraulic characteristics of the flow with various baffle configurations in the basin floor have been evaluated and the best geometry of the baffle has been presented. The agreement between numerical and experimental results was good. The results showed that the flow in the sedimentation basin is strongly influenced by the baffle. Also, the baffles installed with lower height and closer to the basin inlet and baffles with high height and far from the basin inlet have the greatest effect on the SE.     

Numerical analysis of convective heat transfer in fenestration with between-the-glass louvered shades

A two-dimensional steady laminar natural convection model of a window cavity with between-panes louvers (i.e., slats) was developed by approximating the system as a vertical cavity with isothermal walls at different temperatures, and with rotatable baffles located midway between the walls. The baffles were set to a third temperature so that night-time and day-time conditions could be considered. The effects of wall spacing, baffle angle and temperature, and the wall-to-wall temperature difference were examined. It was found that the system is suited to a traditional one-dimensional analysis, and that the convective heat transfer is largely independent of the Rayleigh number for the conditions of practical interest.     

Steady state theoretical model of fired clay hollow bricks for enhanced external wall thermal insulation

This paper proposes a theoretical model to study the steady state thermal behavior of fired clay hollow bricks for enhanced external wall thermal insulation. The study aims at the development of new materials and structural components with good thermal material properties, with respect to energy saving and ecological design. Thermal insulation capacity of two external walls of different thicknesses, constructed of locally produced bricks, is studied. The basic brick units used for the investigation are small-size bricks with eight equal cavities or recesses and big-size bricks with twelve equal recesses. Their recesses configuration has been varied to perform the assessment. The insulation materials injected within brick recesses during the assessment are granulated cork and expanded polystyrene. The improvement in the thermal performance of the walls will be the result of optimization among the various factors such as brick cavity configurations, integration of insulation within brick recesses and the cavity surface emissivities. So emphasis is given to the study of the impact of these factors singly or in combination on the overall thermal resistance of walls in order to find out the best design solutions to maximize their thermal insulation capacity. Computer modeling and calculations performed, for steady state conditions, show that the increase in hollow brick cavity height contributes to the improvement of the overall thermal resistance of the order of 18–20%. The improvement could significantly increase to the range of 88.64% and 93.33%, if the bricks used are injected with the insulating material. If the cavity surface emissivities are lowered to 0.3, the improvement will be 72.73–78.33%. The results have also shown that replacing the cork by expanded polystyrene (EPS), having lower thermal conductivity, would not improve significantly the overall thermal resistance. This improvement is 9.08% for a wall of small-size bricks having configuration BS2CV and 8.34% for a wall of big-size bricks having configuration BB3CV.     

Computational investigations of baffle configuration effects on the performance of primary sedimentation tanks

To increase the performance of a primary sedimentation tank (clarifier), it is essential to have a uniform and calm flow field. The use of suitable baffle configurations may help forming favourable flow field and increase the efficiency of the primary sedimentation tank. To find the proper position and height of a baffle in a rectangular primary sedimentation tank, computational investigations are performed. Also, laboratory experiments are conducted to verify the numerical results, and the measured velocity fields that were by acoustic Doppler velocimeter (ADV) are used. The results of computational investigations performed in the present study indicate that the favourable flow field (uniform in the settling zone) would be enhanced for the case that the baffle position and height provide small circulation regions volume, or the recirculation region forms a small portion of the flow field and dissipate the kinetic energy in the tank.     

Untersuchung der thermisch‐hygrischen Eigenschaften von Ziegeln mit Hohlraumfüllung aus Recyclingmaterial

Investigation on the thermal‐hygral behaniour of bricks with canity filling by recycling meterials. In the investigation project was examined whether bricks with simple cavity structure have a higher heat resistance by use of a heat insulation material filling in the cavities. The insulation material is a recycled product made of polystyrene and wood covered and bonded with cement. The influence of the configuration and thickness of the perforated bricks with vertical perforations and the geometry of the cavities of the brick on the thermal moisture states was evaluated. For investigation of the thermal resistance and the heat transmission coefficients were used the simulation program THERM, that considered the heat transportation through conduction in the brick fragments and the transport mechanisms conduction, convection and radiation in the airfilled cavities. The software package WUFI 2D was employed for the investigation of moisture transfer in the bricks. The investigations showed that the composite brick insulation stone has a thermal resistance twice as high as the initial brick. The moisture states can be partially in the brick more than 80 % humidity. This load is estimated as uncritical because the wooden particles are covered with cement slime.     

Study of the geometry of a voided clay brick using non-rectangular perforations to optimise its thermal properties

This study seeks to improve the geometrical distribution of bricks to optimise the equivalent thermal transmittance of a wall built of Termoarcilla^® ECO 29 voided clay bricks, using calculations according to Spanish UNE [1], AENOR [10], European EN [6], [7], [8] and [9] and international ISO [11] and [12] standards.The objective is to study improvements in the wall's thermal conductivity, always remembering the limitations imposed by the manufacturing process. Simulations are made using a finite elements application [14].It is concluded that, within the possibilities allowed by the manufacturing process, with non-rectangular voids the heat flux has to cross a higher number of voids, which improves its thermal properties. A rhomboid layout of voids with the longer diagonal at right angles to the heat flux is the best internal void layout. If the internal perforations are also extended to the end of the tongue and groove, the direct thermal bridge in this type of brick is broken.Finally, a 290 mm wide brick with 25 rows is obtained with the geometrical properties described above which shows an improvement of almost 16% over the original ECO 29 brick, performing well in all climatic areas of Spain, with a full-bed mortar joint 30 mm thick.     

Damping enhancement of seismic isolated cylindrical liquid storage tanks using baffles

The effect of baffles in reducing earthquake responses of seismically isolated cylindrical liquid storage tanks is investigated in this study. Seismic isolation is a well-known approach to reduce the earthquake effects on structures by lengthening their fundamental natural periods at the expense of larger displacements in the structural system. To reduce such effects in a system a higher damping ratio is required. In moving liquid containers, baffles play an important role in damping the liquid motion. Thus to study the effects of using baffles in seismically isolated tanks, in the first instance the velocity contours in a cylindrical tank are analysed to determine the most effective shape of baffle. Next, the damping coefficients are analytically determined for horizontal ring shape and vertical blade shape baffles. To estimate the sloshing height level and the damping ratio, a methodology, based on Tank Body Spectra, is developed in which the higher sloshing amplitude and the relative fluid velocity with respect to baffles in base isolated tanks are taken into consideration. A computer program is developed to put all these together and investigate the effect of baffles for different tank dimensions under the effect of four different earthquakes. The results show that the average damping ratio of sloshing mode due to ring baffle increases with a decrease in liquid height and highest damping may be achieved for height to radius ratios of between 1.0 and 1.5. In addition, for reasonable ring baffle dimensions, an average reduction of 6% in base displacement of base isolated tanks and an average reduction of more than 30% in the sloshing height of base isolated and fixed base tanks may be achieved. To study the effect of baffles on the distribution of hydrodynamic and tank body forces with height, a simple dynamic model is proposed. The results of analyses using this model indicate a constant reduction in sloshing forces and different reductions in moment and shear forces for different heights. This happens because contribution of the sloshing force to the total hydrodynamic force varies with height.     

Convective heat transfer in domed skylight cavities

Domed skylights are important architectural design elements that deliver daylight and solar heat into buildings, and connect the building's occupants to the outdoor environment. Despite the widespread use of domed skylights, there is limited information on the convective heat transfer within cavities of multi-glazed domes. This information is required to evaluate the thermal performance of domed skylights for product rating purposes, or to evaluate the heat loss or gain of installed skylights in buildings. This article presents a numerical study on the laminar natural convection in horizontal concentric domed cavities heated from the inside surface. A commercial CFD package is used to solve for the flow and temperature fields. The results show that for large cavity gap spacing-to-radius ratios, the cavity flow is mono-cellular and steady state. For small gap spacing ratios, however, the cavity flow may be multi-cellular and transient periodic. Practical correlations for the heat transfer coefficient as a function of the cavity shape and gap spacing ratio are developed for both flow regimes. The critical gap spacing ratio that yields the maximum Nusselt number is quantified for each cavity shape.     

A novel ensemble model for predicting the performance of a novel vertical slot fishway

We investigate the performance of a novel vertical slot fishway by employing finite volume and surrogate models. Multiple linear regression, multiple log equation regression, gene expression programming, and combinations of these models are employed to predict the maximum turbulence, maximum velocity, resting area, and water depth of the middle pool in the fishway. The statistical parameters and error terms, including the coefficient of determination, root mean square error, normalized square error, maximum positive and negative errors, and mean absolute percentage error were employed to evaluate and compare the accuracy of the models. We also conducted a parametric study. The independent variables include the opening between baffles (OBB), the ratio of the length of the large and small baffles, the volume flow rate, and the angle of the large baffle. The results show that the key parameters of the maximum turbulence and velocity are the volume flow rate and OBB.     

Effects of the configuration of a baffle–avalanche wall system on rock avalanches in Tibet Zhangmu: discrete element analysis

Rock avalanches with a high mobility and kinetic energy pose a potential geological risk to surrounding buildings. Baffles and avalanche walls are effective ways to protect these buildings. However, the primary focus of previous studies has been on baffles or avalanche walls alone, and there have been very few studies investigating the effectiveness of a combination of baffles and avalanche walls as a countermeasure against rock avalanches. In addition, previous studies on lab-scale tests and numerical analyses often did not take the actual topography effects into consideration. In this study we adopted a numerical simulation approach based on an actual project in the town of Zhangmu, Tibet, with the aim to investigate the effect of different configurations of a combined baffle–avalanche wall system on impeding the kinetic energy of rock avalanches. A series of numerical analyses with discrete element methods (DEM) were conducted. First, the effect of three different pile groups on the reduction of the effect of the rock avalanche was studied using the numerical modeling study. Secondly, the influence of the size of the retaining wall on the maximum impact force of the rock avalanche was studied. Finally, a DEM modeling study on the energy dissipation capacity of the baffle–avalanche wall system was conducted. The results demonstrate that an arrangement of different baffle–avalanche wall systems will produce different results in terms of dissipating the energy of rock avalanches: when the wall is long enough to block all rock masses, enhancing baffle density will decrease the maximum impact force exerted on the avalanche wall; however, if the wall is just long enough to protect the target region, reducing baffle density will decrease the maximum impact force exerted on the avalanche wall. The results of this study are significant in terms of providing guidelines for the design of baffle–avalanche wall systems for protection against rock avalanches.

     

排烟口附加组合挡板对隧道火灾排烟效果的模拟研究

建立单孔隧道模型,采用FDS 数值模拟分析不同高度的组合挡板对隧道机械排烟的影响。结果表明,相较于普通排烟口,安装组合挡板可以有效提高隧道机械排烟效率,改善排烟口处气体压力场的分布状态,减小垂直方向的排烟风速,加大水平方向的排烟风速,从而降低吸穿现象发生概率。经模拟验证,发现组合挡板高度是影响吸穿现象发生的重要因素,组合挡板会使排烟口前方烟层厚度变小,当烟层厚度小于挡板高度时就会发生吸穿现象。通过比较挡板高度分别为50、65、80、95、110 cm 几种情况的模拟效果,发现H=50 cm 工况排烟口处的烟气浓度最高,单位时间排烟量最大,排烟效果最好。     

新型机械+折板组合絮凝反应池的试验研究

将机械和水力两类絮凝形式相结合,研发了一种新型机械+折板组合絮凝反应器中试装置.通过絮凝试验对影响反应器絮凝效果的搅拌轴转速、搅拌桨直径、流量及折板等因素进行了研究,并对该絮凝反应池的最佳运行参数进行了试验分析.结果表明,该反应器具有良好的除浊效果,从而为今后实际工程中的应用提供了参考.     

Effect of thermal mass on the thermal performance of various Australian residential constructions systems

The impact of thermal mass on the thermal performance of several types of Australian residential construction, namely: cavity brick (CB), brick veneer (BV), reverse brick veneer (RBV), and light weight (LW) constructions, was examined numerically using the commercial AccuRate energy rating tool developed by the Australian Commonwealth Scientific and Industrial Research Organisation (CSIRO). The performance of each construction type was evaluated using four different hypothetical building envelopes, referred to here as building modules. It was found that the thermal mass had a dramatic impact on the thermal behaviour of the modules studied, particularly in those where the thermal mass was within a protective envelope of insulation. The RBV and CB constructions were found to be the most effective walling systems in this regard.     

蓄能保温砖的制备和保温性能实验

基材砖体以粉煤灰和硅酸钠为主要原料制备,砖体内部填充定量的水合盐相变储能包覆材料后,制备了一种新型复合储能建材——粉煤灰胶体保温蓄能砖(PCM砖)。对该砖体进行了48h的仿真环境热学性能试验,与普通红砖进行了对比,试验结果表明,由于储能的作用,PCM砖起到了调节温度热波动的作用。热流的波动幅度被削弱,作用的时间被推后,将温度变化维持在较小的范围内,可作为保温墙体材料进行应用。     

Defects of non-loadbearing masonry walls due to partial basal supports

The attempts to reduce heat transmission heterogeneity all over the external surface of building envelopes include several recommendations about external protection of concrete structures with thin clay brick walls. This procedure was extensively adopted in Portugal during the last ten years in consequence of the new national thermal code. This practice has generated several defects in consequence of the insufficient technological knowledge in this domain. This work analyses some of those defects adopting an experimental and a numerical approach, using the traditional Portuguese clay brick with a high percentage of horizontal voids.     

Modelling head losses in granular bed anaerobic baffled reactors at high flows during start-up

Anaerobic treatment of low strength, high flow wastewaters can only be effective if the technology employed can meet key hydrodynamic requirements: maximising the contact surface area and contact period between the influent substrate and the biomass solids, minimising solid washout from the reactor and minimising the backpressure across the system. Backpressure or head loss is an important hydrodynamic property of gravity-flow packed bed reactors, where the flow is the resultant of frictional forces between the incoming fluid and the solid packing material through which the wastewater percolates. Excessive backpressure caused by high influent flow-rates can reduce the contact surface area and increase the influent head on the upstream side of the biomass bed leading to overflow spills, unstable performance and process failure. This study investigates the factors affecting backpressure across a Granular bed baffled reactor (GRABBR) with variable baffle positions. Experimental results were used to develop a mathematical model to quantify backpressure based on physical characteristics of the seed biomass, fluid-flow conditions and reactor geometry. Results have shown that for a constant flow rate the anaerobic baffled reactor exhibits the least backpressure characteristics when both the upflow and downflow areas are roughly 50% of the total compartmental width.     

透水性混凝土路面砖材料的正交试验研究

通过正交试验方法配制透水性混凝土路面砖,以混凝土的抗压强度、透水系数、连通孔隙率为指标,分析研究了骨料粒径、水灰比、骨胶比等因素及其不同的水平对透水性混凝土各性能指标的影响.结果表明,正交设计的分析结果与试验结果有良好的一致性,可为透水性混凝土的配合比设计提供方向及定量分析方法.另外,对透水性混凝土的抗冻性也进行了初步研究.     

纤维水泥与硼泥陶粒轻骨料生产内外墙砖

利用快硬早强水泥为胶料,掺入植物纤维、硼泥陶粒、矿物固体材料、陶砂,经挤压电模制作,常温下养护,产品能够保温并能起到限制开裂的作用。     

多孔砖孔洞排布与热阻大小

本文试图从传热的基本原理出发 ,探讨在一定尺寸条件下 ,多孔砖的孔洞排布与孔洞率的变化对砖体热阻的影响作用 ,以此改善砖体的隔热保温性能。