Aeration high velocity

Horizontally Mixing Aspirator Aerators. An aerator using a horizontally mixing aspirator has a marine propeller, submerged under water, attached to a soHd or a hoUow shaft. The other end of the shaft is out of the water and attached to an electric motor. When the propeller is rotated at high velocity, at either 1800 or 3600 rpm, a pressure drop develops around the propeller. Air is then aspirated under the water and mixed with the water, and moved out. This type of aerator, shown ia Figure 3g, is very efficient ia mixing wastewater. 

In static air-free sea water the potential of iron or steel reaches a steady-statevalueof —0-75 V (v5. S.C.E., = 0-246 V) which should be compared with the more noble potential of —0-61 V observed under conditions of high velocity and aeration (Table 2.16). This potential of —0-75 V for iron in sea water is important in the practice of cathodic protection. 

Example 5 A stainless steel pipe is to be used to convey an aerated reducing acid at high velocity. If the concentration of dissolved Oj is 10 mol dm (10 mol cm ) calculate whether or not the steel will corrode when (a) the acid is static, (b) the acid is moving at high velocity. Assume that the critical current density for passivation of the steel in the acid is 200/iAcm the thickness of the diffusion layer is 0-05 cm when the acid is static and 0-005 cm when the acid flows at a high velocity assume the diffusion coeffi-... 

Figure 9 illustrates the adiabatic hp/1000 scfin in fermenters. Important features of using high velocity aeration are the following ... 

Feed velocities leaving the feed pipe or feed sparger should not exceed 10 ft/s (305) and preferably be less than 4 to 5 ft/s (111). High velocities may disturb the liquid surface or cause excessive aeration in the distributor or parting box. 

Anderson combined his love for teaching and interest in students with an active research program. In addition to sediment transport, he was also active in research in such areas as flow in bends, culvert hydraulics, air entrainment by high-velocity flow, or hydraulic structures. He was further active as a consultant for both national and international projects. He also took interest in professional associations, including the International Association for Hydraulic Research lAHR, the American Society of Civil Engineers ASCE, or AWRA. He was the recipient of the 1961 ASCE Norman Medal for the benchmark paper Self-aerated flow, co-authored by Lorenz G. Straub (1901-1963), and the 1965 ASCE J.C. Stevens Award for discussing Sediment transportation mechanics. 

Anderson, A.G. (1965). Influence of channel roughness on the aeration of high-velocity, open channel flow. 1 lAHR Congress Leningrad 1(37) 1-13. 

Carbon steels corrode in aerated seawater conditions. Their corrosion rate decreases with time as protective barrier films are formed on the carbon steel surfaces. These protective films may be a rust layer, calcareous deposits, or biofouling. The corrosion rate of carbon steels increases in high velocity seawater because the protective barrier layer is either not allowed to form or is stripped away under the flow conditions. Also, the available oxygen at the metal surface is increased in flowing seawater, which promotes a higher carbon steel corrosion rate. 

High-velocity aerated waters and aqueous solutions... 

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