Experimental evaluation of low head oxygenators

The overall mass transfer coefficient, G₂₀, for a single hole orifice plate was evaluated in a series of experiments as affected by four geometric variables: orifice plate hole diameter (5, 10, 14, 19, and 22 mm), hydraulic head on the flooded plate (2.5, 5, and 13 cm), water fall height from the orifice to the receiving pool of water (30, 61, 91, and 122 cm), and the collection pool depth (2.5, 8, 13, 25, and 41 cm). This is, in essence, the simplest form of a low head oxygenator (LHO). A regression equation was developed to predict G₂₀ as a function of these variables, their interactions, and squared terms. The hydraulic head above the flooded plate had no significant effect (P<0.10) on the overall mass transfer coefficient. It was determined that the contribution of the orifice hole solely to overall gas transfer was much less than previously assumed, suggesting that a much larger percentage of gas transfer is due to the splashing and subsequent entrainment as water droplets fall into the receiving pool of water. Practical implications of the results are discussed.     

Bubble size distribution in a bubble column applied to aquaculture systems

Bubble size distribution affects the gas-liquid mass transfer rates during aeration and foam fractionation processes employed in recirculating aquacultural systems. The effects of air flow rate, protein concentration and air stone pore size on bubble characterization were investigated. Bubble size was measured photographically in conjunction with image-processing techniques. The study indicated that bubble size increased with air flow rate and air stone pore size, but decreased with protein concentration. Within the tested range of these variables, the geometric diameters of the majority of the bubbles (90%) were within the range of 0·5–3·0 mm, and the bubble sizes followed a normal distribution.     

A mathematical model of low-head oxygenators

A mathematical model is presented that predicts the performance of low-head oxygenators (LHO). Experimentally determined values of G₂₀ for a single hole in a flooded orifice plate were used as the basis to develop a mathematical model that can be used to predict LHO performance under a variety of design and operating conditions. Model predictions were compared to two published studies. The model predicted the published data for dissolved oxygen levels in the departing effluent within 2–3%, oxygen absorption efficiencies within 5–6%, and total gas pressures within 1%. The mathematical model is thoroughly developed including an analysis of numerical stability and necessary restrictions to assure stability and accuracy. Convergence based solely upon effluent values was not sufficient to produce accurate results, but required additional criteria of requiring a minimum number of chamber flushings prior to convergence checking. The model was used to demonstrate its utility in predicting the effects of G/L ratio on gas absorption efficiency, effluent gas conditions and the effects of number of LHO chambers used. This model allows the designer or operator of an LHO to easily make design and operational decisions by modifying the input parameters and observing the exit conditions and performance indicators.     

Numerical analysis of the effects of gas-phase properties on the internal characteristics and wear in a centrifugal pump

Centrifugal pumps are indispensable in aquaculture engineering. The existence of bubbles is inevitable in a centrifugal pump and may affect the performance of the pump which delivers solid-liquid two-phase flow. Thus, this study aims to analyze the effects of gas-phase properties on the internal characteristics of a centrifugal pump by using a computational fluid dynamic code based on Eulerian multiphase mode and a standard k–ε two-equation turbulence model. Results show that gas-phase properties, such as concentration and diameter, affect the absolute pressure and the phase distribution in the centrifugal pump. The gas-phase distribution on the working faces of blades is greater than forces on the back face of the blades. The larger the diameter of the gas-phase is, the easier it is to be concentrated; Thus, the working face of the blades is prone to cavitation and corrosion, and with the increase of the bubble size, the cavitation corrosion of the back surface of the impeller becomes more serious. The solid-phase velocity and static pressure distribution increase with increasing concentration or diameter of gas-phase. The solid-phase is more easily leave the impeller area and enter the volute because of the existence of gas-phase, which may lead to abrasion of volute. The existence of gas makes the solid velocity distribution in the centrifugal pump more uneven, which may cause uneven wear of the centrifugal pump. The obtained results by this method can reveal the effects of gas-phase properties and wear on the internal characteristics in centrifugal pumps and are helpful for improvement and empirical correction in the hydraulic design of centrifugal pumps.     

Mathematical Model of a Foam Fractionator Used in Aquaculture

Water recirculating systems are becoming more prevalent as wild fish supplies and fresh water sources become increasingly scarce. As water recirculating rates increase, the accumulation of fine and dissolved solids can degrade water quality and fish productivity. Foam fractionators have been used with some success to remove these solids, although an understanding of how to best operate such units is currently lacking. The foam enrichment process occurs as bubbles travel from the bottom of a fractionator column to the top of the water column. Factors affecting bubble enrichment include several operating or design parameters under operator control or influence, e.g, water pH, gas bubble size, airflow rates, and fractionator geometry. Predictive relationships were developed to describe these effects and are considered generally applicable to predict the foam enrichment process. Predicting the actual operation of a specific foam fractionator requires additional mathematical expressions to model the foam collection process and removal from the top of the water column. Here, the geometric characteristics and type of foam removal device or geometry of placement become important. Performance data in the literature was used in coajunction with a mathematical model that predicted foam enrichment to model the foam collection process for a typical foam fractionator design. This overall model can be used for foam fractionators that employ glass bonded air diffusers with an inverted funnel at the top of the fractionator column to concentrate and remove the foam being produced. An example problem is given to demonstrate the utility of the mathematical models. Since foam fractionators are typified by erratic performance, the mathematid models presented must be used with some caution and only viewed as providing estimates of average fractionator performance.     

Initial habitat response to incised channel rehabilitation

• 1. Incised stream channel aquatic habitats typically are severely degraded. After the primary knickpoints or knickzones have passed, base flows are limited to shallow channels flanked by sandy berms within the enlarged high-flow channel. Riparian vegetation, woody debris and pool habitat are in short supply, and stream systems become disengaged from their floodplains.
• 2. We hypothesized that habitat recovery might be accelerated in channels that have incised and are regaining equilibrium through deposition of sandy berms by placing rock spurs in the channel and by planting woody vegetation on the berms. On the basis of literature review and a pilot study, planting designs were developed for a large-scale field experiment: 2550 1.5 m long cuttings of native willow (Salix spp.) 2–25 cm in diameter were planted 1–1.2 m deep along the base-flow channel of an incised stream. A ridge of stone was placed on the water side of the plantings, and 17 rock spurs were constructed by extending existing spur dikes from the opposite bank.
• 3. Woody cover along the treated bank increased from 38% to 66% of bankline after one growing season. Survival of individual plantings was reduced from an estimated 60% to an observed 34% by competition from the exotic kudzu vine, Pueraria lobata. Mean depth and mean scour hole depth, corrected for stage variation, increased 44% and 82%, respectively. Mean scour hole width increased 130%. The mean length of fish and the number of fish species approximately doubled, while the total weight of fish captured by a unit of sampling effort increased by an order of magnitude.

     

Fish use of ecohydraulic‐based mesohabitat units in a low‐gradient Illinois stream: implications for stream restoration

• 1. A classification scheme for ecohydraulic‐based mesohabitat units was developed for a summer low‐flow period. Mesohabitat unit designations were based on the integration of three‐dimensional channel hydraulics, geomorphic maintenance processes of bed morphology, and biological resource needs of fish. Ecological relevance of the units was evaluated by a study of fish mesohabitat use patterns, and species relationships to feeding guild. By portraying the stream as a mosaic of hydraulic habitat patches that provide specific biotic resource needs, this study's aim was to advance how ecological information may be incorporated into the stream restoration design process.
• 2. Nine mesohabitat units were designated, including pool‐front, ‐mid, and ‐rear units, scour pool, simple and complex riffles, glide, submerged point bar, and channel expansion marginal deadwater. Physical habitat structure differed among the nine mesohabitat units by length, water depth, and bed slope and complexity. Fish were collected in specific unit volumes by use of prepositioned areal electrofishing devices, in which distinct patterns of fish mesohabitat use were observed.
• 3. A key finding was the differences in fish assemblages among the pool units, in which fish densities were greatest in the pool‐front and scour pool units. Also, fish density in the pool‐front unit was positively correlated with pool entrance slope. Biomass was greatest in the pool‐front and ‐mid units, and it was correlated with maximum mid‐pool depth. Density and biomass were generally lowest in the pool‐rear unit. Other unique relationships were also observed among the mesohabitat units.
• 4. Based on feeding guild, patterns of fish mesohabitat use were observed for this summer low‐flow period; insectivores dominantly used pool‐front and scour pool units, herbivores dominantly used complex riffle units, and piscivores used pool‐front and ‐mid units.
• 5. Useful ecological information was derived from fish species‐habitat relationships observed in this study, linking mesohabitat units with species requirements for food resources. Such findings support advancements to ecological design strategies for stream restoration that promote hydraulic habitat diversity.

Copyright © 2008 John Wiley & Sons, Ltd.     

气泡幕对许氏平鲉的阻拦效果研究

气泡幕可作为海洋牧场鱼群控制的技术手段之一。本研究通过改变气泡幕在水槽中的相对位置和试验许氏平鲉(Sebastes schlegeli)的密度来观察许氏平鲉的行为反应,运用了观察法、对照试验法和控制变量法探究了气泡幕对不同密度下的许氏平鲉的阻拦效果。结果显示:1)试验鱼20尾时,气泡幕的位置分别设置在矩形水槽长的1/4、1/2和3/4处(鱼的密度为12.52、6.26、4.17尾/m2),阻拦率分别达到了98.2%、88.4%和92.9%,阻拦效果明显。2)气泡幕设置在水槽长度方向的1/2处,试验鱼分别为5尾、10尾、15尾和20尾时,气泡幕阻拦率分别达到了100%、85.7%、100%和88.4%(鱼群密度分别为1.56、3.12、4.69、6.26尾/m2),阻拦效果良好。3)由于阻拦率较高,试验鱼群密度和阻拦效率没有明显的关系。本研究结果可为我国投放许氏平鲉的海洋牧场鱼群控制技术以及取水口拦鱼技术提供参考。     

Pathology of gas bubble disease in two air-breathing catfishes (Clarias batrachus Linn. and Heteropneustes fossilis Bloch.)

Gross pathology in Clarias batrachus and Heteropneustes fossilis, and histopathology in the liver, intestine and kidney and abnormalities in erythrocyte count/mm³ and haemoglobin g% of C. batrachus afflicted with gas bubble disease were studied over 96 h. Histopathology and blood abnormalities in H. fossilis could not be observed due to heavy mortality. A tilt in the swimming posture and an upward bend in the tail region were the first signs of the disease. Exophthalmia was noted and blebs containing gas bubbles appeared on the fins and other parts of the body. The blebs burst producing open lesions after 72 h, and the fins became necrotic.Histopathologic changes included, in the liver, vacuolation of cells, necrosis and cordal disarray; in the intestine, lesions in the villi, degeneration of the submucosa, cellular exudate production in the lumen and air bubbles in the villi; and in the kidney, degeneration of tubules and glomeruli and necrosis of haemopoietic tissue. Erythrocyte count and haemoglobin content showed a consistent and significant fall from 12.87 × 10⁶ to 6.91 × 10⁶/mm³ and from 9.33 to 7.00 g%, respectively, up to 72 h. Empty blood vessels were noted in the liver, intestine and kidney. Fish of both species regained normal swimming orientation, and erythrocyte count and haemoglobin content also showed recovery from the disease.     

The effects of dissolved gas supersaturation on larval striped bass, Morone saxatilis (Walbaum)

Abstract. Gas bubble disease in larval striped bass, Morone saxatilis (Walbaum), was characterized by overinflation of the swimbladder and the formation of intestinal bubbles. This accumulation of gas hindered normal swimming of the fish and in extreme cases resulted in floating fish. As gas accumulated in the gut, the inner mucosal lining was compressed down into a cuboidal epithelium and in more advanced cases nearly the entire digestive tract was reduced to a squamous inner epithelium surrounded by a thin serosa. A significant increase in swimbladder volume was observed at total gas pressures as low as 102.9% and mortality was increased at 105.6-106.0%. The older larvae (30-day-old) were less sensitive to gas supersaturation than 10- to 19-day-old larvae.     

Field demonstration of a novel towed,area bubble-plume zooplankton (Calanus sp.) harvester

This paper presents the field testing of a new technology to harvest marine copepods (Calanus sp.) by bubble-induced upwelling. Two large-scale bubble rafts, a 21 m² and a flexible 75 m² bubble raft with tow-parallel and tow-perpendicular sparger elements, respectively, were tested in the sea with high Calanus densities in the upper 25 m. Bubble-driven upwelling velocities (V_up) measured with different air flows (Q) and source depths (z₀), gave V_up ～ Q^0.27 with stratified water, and were in agreement with other results for stratified conditions. Bubble trawls significantly enhanced Calanus concentrations in the upper water column: up to 1416%, with the best results for the transverse sparger raft, which also was tested with weak stratification. Bubble trawl performance also was affected by the stratification, with the highest enhancement for the lowest stratification. Catch species analysis showed reduced bycatch. Thus, this new harvesting technology showed a potential to develop an economically robust, environmentally benign, and sustainable fishery on a renewable resource at lower trophic levels in the food web, within the context of ecosystem-based management.     

不同性别马粪海胆壳形态性状对体质量的影响效果分析

选取大连塔河湾海域马粪海胆260枚,鉴定性别后测量了壳高(L2)、壳径(L1)和体质量(m)等经济性状,采用相关分析和通径分析方法,定量地分析了不同性别马粪海胆壳形态性状与体质量的相关关系。结果表明,塔河湾海域马粪海胆雌雄比例为1∶1,在壳性状、体质量等经济性状和高径比等生物学性状上雌雄差异不显著(P0.05)。雌雄海胆经济性状间的相关系数均较高,其中壳径与体质量的相关系数均为最大(雌雄分别为0.960和0.956)。通径分析表明,雌雄马粪海胆壳径对体质量的直接影响(雌雄分别为0.723和0.645)均大于壳高(雌雄分别为0.280和0.362),雌雄马粪海胆壳形态性状对体质量有较为一致的影响效果。雄性马粪海胆体质量预测模型为m=1.78L1+1.32L2-75.78(r2=0.948),雌性马粪海胆体质量预测模型为m=2.17L1+1.13L2-89.05(r2=0.944),不分性别马粪海胆体质量预测模型为m=1.96L1+1.22L2-81.72(r2=0.944)。     

Tolerance of lake trout, Salvelinus namaycush (Walbaum), sac fry to dissolved gas supersaturation

Abstract. The tolerance of sac fry of lake trout, Salvelinus namaycush (Walbaum), to the acute effects of gas supersaturation, from hatching to swim-up, was tested using six gas levels, ranging from ΔP 8 to 148. Although many fish were moribund by the time the yolk was nearly absorbed, mortality during the 40-day study was negligible; survival to swim-up was 96–99%, including 99% survival at ΔP 148. Of fish examined at ΔP 42, 40% showed bubble formation around the rim of the eye. Signs of trauma were greatest at ΔP 119 and 148, and included intestinal bubbles, a distended abdomen, and bubbles around the eye, in the mouth and in jaw tissues.     

工厂化对虾养殖池管式射流集污水力特性

工厂化养殖池内水体的流场分布特性直接决定了其对残饵、粪便等的排污性能。本实验研究了管式射流驱动模式下,射流角度与射流流速对养殖池内水体流场与污物聚集特性的影响。养殖池流场特性采用点式流速仪进行布点测量,利用MATLAB软件对流场特性进行分析。采用相机采集的养殖池集污效果图像,并利用Photoshop软件与自行开发的不规则图形面积分析软件对图像进行分析。研究表明,流速从池心向外呈"V"型变化,在射流角度固定的情况下,射流速度越大,池心低流速区域越小,污物向池心的聚集效果越好;在流速固定的情况下,存在一个最佳的射流角度,本实验在24 cm/s流速条件下,射流角度为40°时,池内污物聚集效果最优。结论认为在保证养殖对象生长的前提下,可尽量提高射流流速;在24 cm/s流速条件下,最佳射流角度在40°左右。本研究成果可为工厂化养鱼池、养虾池等管式射流水力驱动系统的优化设计提供参考依据。     

竖缝式鱼道桩柱结构过鱼效果探索

竖缝式鱼道作为一种协助鱼类洄游上溯从而缓解提升河流连通性 的设施得到广泛的应用,但是多数鱼道的实际过鱼效能并不理想,尤其 是鱼道的池室结构尚具有一定的提升空间。本研究通过数值模拟和对照性过鱼试验对池室内部未增加和4种方式增加桩柱的池室水流结构进行了比较分析。结果表明在鱼道主流中间增设桩柱结构,可以有效减小回流区面积,减幅达49%;并减小竖缝处紊动能,最大紊动能减小18%;增加鱼类上溯路线分布,提高了池室空间利用率更高 。分析两种结构的上溯轨迹发现,齐口裂腹鱼多选择回流区外侧上溯,避免进入回流区中心,多选择较高的水力应变与紊动能区域调整作为上溯方向 ,且上溯路线中偏好较低水力因子区域上溯,上溯偏好流速范围0.01~0.09m/s,紊动能范围0.001~0.008m2/s2,水力应变范围0.2~3.0s-1     

杂交石斑鱼(斜带石斑鱼♀×赤点石斑鱼♂)与其亲本形态性状比较研究

研究了杂交石斑鱼[斜带石斑鱼(Epinephelus coioides)♀×赤点石斑鱼(E.akaara)♂]与其亲本的生长差异。采用形态学测量方法,分别测定了3种石斑鱼体质量和7个形态性状,对各形态性状对体质量影响进行通径分析,并分析杂交子代杂种优势。结果显示,3种石斑鱼各形态性状与体质量之间均呈极显著相关(P0.01),斜带石斑鱼、赤点石斑鱼体质量与全长的相关性最高,相关系数分别为0.946、0.932,杂交子代体质量与尾柄高的相关性最高(0.955),与全长的相关系数为0.927;形态性状与体质量的多元线性回归方程中,斜带石斑鱼保留体长、体高、尾柄高和体厚,赤点石斑鱼保留全长、体高和尾柄高,杂交子代保留全长、体高、尾柄高和体厚。对杂交子代杂种优势进行分析发现,体质量平均杂种优势为3.43%,体长平均杂种优势为3.02%,杂交子代同时表现出正向超亲优势和负向超亲优势。该研究表明杂交子代(斜带石斑鱼♀×赤点石斑鱼♂)与斜带石斑鱼的差异要小于赤点石斑鱼,杂交子代形态性状更偏向于母本。     

4月龄马口鱼形态性状对体质量的通径分析

为探究马口鱼(Opsariichthys bidens)形态性状与体质量之间的相关程度,对4月龄马口鱼的14个形态性状(全长X1、体长X2、叉长X3、体高X4、体宽X5、头长X6、头宽X7、头高X8、吻长X9、眼后头长X10、眼径X11、眼间距X12、尾柄长X13、尾柄高X14)和体质量(Y)进行了相关分析、通径分析及...     

Gas phase axial dispersion in a packed column oxygen absorber

Gas phase axial dispersion was characterized within an enclosed packed column receiving oxygen and water under counter-current flow conditions. Steady-state gas phase profiles (longitudinal) were measured during a series of 90 column runs in which, at each of three bed depths (0·362, 0·699, and 1·041 m), all combinations of the following independent variables were tested: influent volumetric oxygen-liquid ratio, 0·8, 1·6, 2·6, 4·0, and 8·0%; hydraulic loading, 32·0 and 61·2 kg/m² s; and packing type, 2·54 cm Tri-Pack^®, 3·81 cm Nor-Pac^® and 5·08 cm Nor-Pac^®. Over the range of operating conditions tested, gas phase mixing was extensive and for all practical purposes could be considered complete. A homogeneous gas phase within the column, unlike true counter-current flow, results in an exponential decay in dissolved gas deficits as the liquid passes through the packing. Thus, increases in packed bed depth will result in diminishing increases in gas absorption/desorption.     

官井洋种群网箱养殖大黄鱼的形态特征与生长式型

测定和研究了闽-粤东族官井洋种群养殖大黄鱼群体的形态特征与生长类型,并与文献报道的其亲本野生大黄鱼群体的形态特征进行了比较。结果表明:养殖大黄鱼的眼径/头长和体高/体长的比值普遍大于野生大黄鱼,而吻长/头长和眼后头长/头长的比值普遍小于野生大黄鱼。同时,养殖大黄鱼群体的眼径/头长、吻长/头长和头长/体长三项比值具有随着鱼体体长的增长而逐渐减小的特点。养殖大黄鱼体长与体重、体长生长与养殖时间的关系分别为:W=0.0195L2.9775(R2=0.9959)、y=-0.0259x2+1.7125x+4.1534(R2=0.989),鳔重与体重的比值为0.61%~2.26%,月平均鳔重指数1.08%~1.85%。