Geology topics

Barnaby J. Watten

Publications and source records attributed to Barnaby J. Watten.

24 records · Page 2Linked to original sources

USGS1996

Gas-phase axial dispersion in a spray tower

Gas-phase axial dispersion (mixing of the composition of the gas phase along the longitudinal axis) was characterized in an enclosed spray tower for purposes of establishing reactor type for the solute-solvent pair oxygen and water. Test condition variables were spray tower height (TH), 1·52, 2·03 and 2·54 m; hydraulic loading (HL), 44·2, 66·3 and 88·4 kg/m 2 s; the ratio of volumetric oxygen injection to water flow rate (G/L), 1·0, 2·5 and 5·0%; the ratio of volumetric bulk tower gas recirculation flow rate to water flow rate (BG/L), 0, 500 and 700%; and bulk tower gas recirculation direction, counter-current to and co-current to the water flow. Gas composition measurements (% O 2 ) made across the long axis of the tower under steady-state conditions provided 1020 independent observations and 240 gas composition profiles. Factors showing a significant effect ( P < 0·05) on gas composition were TH, HL, G/L and BG/L. Sample location as a percentage of TH did not have a significant effect on gas composition and accordingly profile slopes were not different from zero ( P > 0·05). Profile data indicate a completely mixed gas phase within the tower. The dispersion observed was attributed to the lack of a significant pressure drop along the axis of the reaction vessel, forces due to nozzle operation, and to bulk tower gas recirculation.

Aquacultural Engineering↗

USGS1995

Influence of tank design and hydraulic loading on the behavior, growth, and metabolism of rainbow trout (Oncorhynchus mykiss)

Subadult rainbow trout ( Oncorhynchus mykiss ) stocked at 48 kg/m 3 (3 lb/ft 3 ) were subjected to treatments of tank design (rectangular plug flow, circular, and cylindrical cross flow) and water exchange rate (1·5 and 2·5 exchanges/h) to determine their effects on fish behavior, growth, and metabolism. Ambient light levels and current velocities were also measured in each of three tank sectors (upstream, middle, and downstream) to determine their relative contributions to behavioral effects. Tank design significantly affected fish orientation to current, contact time with tank surfaces, and frequency of agonistic encounters, though aggression levels were relatively low overall. Gradients in fish distribution by sector were greatest in plug-flow tanks. Effects were either modified or eliminated by increasing the water exchange rate from 1·5 to 2·5/h. Multiple-regression analysis showed the following hieararchy of independent-variable effects on fish distribution: tank type > exchange rate > aggression level > current velocity > light level. Significant effects of tank design were also observed on fish growth in terms of biomass gain (cross flow > plug flow > circular). These results were matched in metabolic studies, where both oxygen consumption and ammonia excretion were highest in circular and lowest in cross-flow tanks. Reduction (cross-flow compared with circular tanks) in oxygen consumption averaged 13·6%, ammonia excretion 17·5%. These results were also modified by an increase in water exchange rate. Tank-design effects on fish metabolism and growth may be mediated, at least partly, through changes in fish behavior.

Aquacultural Engineering↗

USGS1994

Effect of subatmospheric pressure on the performance of an automated packed-column nitrogen desorption system

A portable vacuum degasser was developed to satisfy seasonal hatchery pretreatment needs. Dissolved-gas pressures in water exiting a packed column were regulated automatically with a unique feedback control loop incorporating a gasometer, pressure transducer, electronic (PID) controller and an electrically actuated pump discharge valve. The flow capacity of the system was 160 l/min with a total power requirement of 0·81 kW. Following controller tuning, field tests demonstrated the ability of the feedback loop to set appropriate column vacuum levels quickly in response to varying inlet dissolved-gas pressures or changes in selected controller set points. The degasser's ability to reduce dissolved nitrogen (DN) and increase dissolved oxygen (DO) concentrations was also assessed at four or five pure-oxygen feed rates under each of four column vacuum levels (−4·5, −9·0, −14·6 and −20·0 cm Hg). Performance was then compared with that predicted with a multicomponent gas transfer model. Relative error of model projections averaged just 7·7% for DO and 2·3% for DN (n = 19). Effluent DN ranged between 60·6 and 96·4% of saturation concentrations at 8·8°C with the influent DN at 135% of saturation. The high DN desorption rates achieved allow side-stream pretreatment with blending.

Aquacultural Engineering↗

USGS1990

Gas transfer within a multi-stage packed column oxygen absorber: Model development and application

A packed column oxygen obsorber was developed in which oxygen flow is directed, in serial reuse, through parallel packed column stages receiving equal portions of the liquid being treated. The relative performance of the absorber was established using a computer simulation program employing finite difference-mass transfer calculations. The program was calibrated using packing specific mass transfer coefficients derived from pilot scale test data. A separate series of tests served to verify model assumptions and performance predictions. Simulation data indicated multi-stage operation can substantially reduce the column height required to achieve a selected oxygen absorption efficiency (AE); for example, the column height required to achieve an AE of 76·5% with an inlet volumetric oxygenwater ratio of 0·008 (column packing, 3·81 cm plastic ACTIFIL ® ; water temperature, 20°C; influent dissolved oxygen, 9·08 mg/litre; operating pressure (absolute), 760 mm Hg) was 0·27 m using a 10-stage system versus 1·39 m using a single-stage absorber. Reductions in column height achieved were related to oxygen and water feed rates, number of stages employed, mass transfer characteristics of the column packing used, and concentrations of dissolved gases in the liquid being treated.

Aquacultural Engineering↗

USGS1990

Modeling the effects of serial off-gas reuse on the performance of a hooded surface oxygen obsorption system

A numerical model was used to evaluate the performance of a surface agitation system designed to contact commercial oxygen with water. The modeled system was unique in that oxygen-rich off-gas, normally discharged to the atmosphere, was directed in serial reuse through additional contact stages receiving untreated water. A correlation between the agitator mass-transfer coefficient and power demand, needed to calibrate the model, was established using a single-stage (37 W) contactor of 1·18 m 3 capacity. Additional tests, conducted with both single and three-stage equipment, verified model assumptions and performance predictions. Simulation runs indicated oxygen flow or power input required to meet a given effluent dissolved gas criterion can be substantially reduced by the off-gas reuse step; for example, to achieve an effluent dissolved oxygen of 24·1 mg/litre with a single stage agitator the oxygen feed rate needed was 61·5% greater than that required by a six-stage system receiving the same total power input (standard aeration efficiency, 0·5 kg/kW h; water flow rate, 100 litre/min; influent dissolved oxygen, 9·08 mg/litre at 15°C). The savings achieved increased with (1) greater target effluent dissolved oxygen concentrations, (2) lower oxygen feed rates, (3) higher input power levels, and (4) number of contact stages.

Aquacultural Engineering↗

USGS1990

Design of packed columns for commercial oxygen addition and dissolved nitrogen removal based on effluent criteria

Successful application of the packed column in fish culture requires a design based not only on oxygen supplementation rates (kg/day), or other standard performance indicators such as oxygen absorption efficiency (kg absorbed/kg applied) or transfer efficiency (kg/kWh), bvt also on dissolved nitrogen and total dissolved gas pressure limits and predicted changes across the system. Such a design procedure was developed by applying a mass balance on the gas and liquid phases of the system along with Henry's law and previously published packing-specific mass-transfer correlations. The design approach is unique in that column pressure and oxygen feed rates are calculated for target changes in dissolved oxygen and nitrogen without the use of iterative numerical procedures. An alternative calculation sequence was developed to establish the sensitivity of column performance to changes in oxygen feed rates at a selected column pressure or packed bed depth.

Aquacultural Engineering↗