Design and peroormance of paddle wheel aerators
ABSTRACT An apparatus was constructed for testing the influence of paddle shape and depth and paddle wheel speed and diameter on oxygen-transfer characteristics of paddle wheel aerators. Paddles triangular in crosssection were more efficient than other paddle shapes. Standard oxygen transfer rate (SOTR) increased with increasing paddle depth and paddle wheel speed while standard aeration efficiency (SAE) declined. For a particular depth and speed, SOTR increased with increasing paddle wheel diameter. The greatest SAE (2·96 kg O2 kWh−1) was achieved with a 91 cm diameter paddle wheel with triangular paddles operated at 77 rev min−1 and 12·5 cm paddle depth. Three companies made floating, 7·5 kW electric paddle wheel aerators according to design specifications developed in this research. These commercial aerators had high values for SOTR (18·8–21·8 kg O2 h−1) and SAE (2·7–2·9 kg O2 kWh−1) and were much more efficient than other aerators used in channel catfish farming.
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ABSTRACT: This study surveyed and simulated paddlewheel-driven circulation in rectangular shrimp culture ponds. Paddlewheels are widely used for highly intensive culture ponds to improve reaeration and circulation. From flow measurements, the major circulation pattern was found to be a single large eddy with strong and weak flows, respectively, along the pond bank and the eddy centre. A two-dimensional depth integrated numerical model was refined to represent the circulation, with acceleration of the paddlewheel given as a shaft force divided by the water mass driven away by paddlewheel blades. The model was applied to a pond F, deploying a single paddlewheel and calibrated for a mass correction factor α in the range 15–20 and for a dimensionless eddy viscosity constant γ of 6. The model was then applied to two ponds A and B, with four paddlewheels deployed at four corners, respectively. The measured and predicted currents were processed using regression analysis to show both the correlation coefficients and gradients; i.e. 0.9067, 1.0393 for direction and 0.6691, 0.8307 for speed in pond A and 0.8269, 1.0075 for direction and 0.7138, 0.9362 for speed in pond B. It was concluded from these results that the model could deal with the paddlewheel-driven jet flow in a simple way to that of using a mass correction factor α, first shown in this study and giving good prediction. Therefore, the model provides a useful tool to predict horizontal circulation and an insight into the circulation-related sedimentation and water quality in shrimp ponds.Aquaculture 03/2004; 231(1):163-179. · 1.83 Impact Factor
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ABSTRACT: An economic engineering approach was used to estimate total aeration cost and to generate average cost curves of aeration. Fixed and variable costs were estimated for 23 different electric and tractor powered aeration devices. Least-cost aeration devices were selected for varying pond sizes. Below about 250 h of aeration per season, tractor-powered aeration devices were more efficient economically. Above approximately 250 h of aeration, electric aerators were more efficient. However, for ponds less than 2 ha in size, the propeller-aspirator-pumps (1–3 hp) were the least-cost system. For pond sizes above 0·4 ha, electric floating paddlewheels generally were the most cost efficient.Aquacultural Engineering - AQUACULT ENG. 01/1989; 8(3):193-207.
Article: Pond water aeration systems[Show abstract] [Hide abstract]
ABSTRACT: During the past decade, pond aeration systems have been developed which will sustain large quantities of fish and invertebrate biomass. These aeration systems are modifications of standard wastewater aeration equipment. Aeration-performance testing has been important in selecting design features to provide cost-effective yet efficient aquaculture pond aerators. Paddlewheel aerators and propeller-aspirator-pumps are probably most widely used. Amounts of aeration vary from as little as 1–2 kW ha−1 in some types of fish culture to as much as 15 or 20 kW ha−1 in intensive culture of marine shrimp. Calculations suggest that about 500 kg additional production of fish or crustaceans can be achieved per kW of aeration. Aerators usually are positioned in ponds to provide maximum water circulation. This practice can result in erosion of pond bottoms and inside slopes of embankments, and accumulation of sediment piles in central areas of ponds where water currents are weaker. Recent studies suggest that the use of heavy aeration to provide the greatest possible production is less profitable than moderate aeration to improve water quality and enhance feed conversion efficiency. Automatic devices to start and stop aerators in response to daily changes in dissolved oxygen (DO) concentrations are improving, but they are expensive and not completely reliable. Augmentation of natural supplies of DO in ponds often is necessary to prevent stress or mortality of fish and crustaceans when DO concentrations are low. Several procedures have been used in attempts to increase DO concentrations in ponds. These methods include exchanging part of the oxygen-depleted pond water with oxygenated water from a well, pond, or other source, application of fertilizer to stimulate oxygen production by photosynthesis of aquatic plants, additions of compounds which release oxygen through chemical reactions, release of pure oxygen gas into pond waters, and aeration with mechanical devices which either splash water into the air or release bubbles of air into the water. Water circulation devices also enhance DO supplies in ponds by mixing DO supersaturated surface waters with deeper waters of lower DO concentration. This reduces the loss of oxygen from ponds by diffusion. Also, when surface waters are not saturated with DO, water circulation causes surface disturbance and enhances oxygen absorption by the water. Mechanical aeration is by far the most common and usually the most effective means of increasing DO concentrations in ponds. In semi-intensive aquaculture, aeration is applied on an emergency basis. Farmers check DO concentrations, and when low concentrations of DO are expected, aeration is applied. In intensive aquaculture, aeration is applied each night or even continuously. The purpose of this article is to summarize the ‘state of the art’ of mechanical aeration of aquaculture ponds.Aquacultural Engineering - AQUACULT ENG. 01/1998; 18(1):9-40.