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Experimental results are presented for velocity and temperature profiles and for the turbulence quantities vz′ t′ and vzt, for up-flow of air in a vertical pipe with constant heat flux at Reynolds numbers of 5000 to 14,000. The measurements show that, with increasing heat flux, superimposed free convection effects cause marked distortion of the flow structure at low Reynolds numbers, with the velocity maximum moving from the tube center to a position near the wall. The axial turbulence intensity, vz′, is depressed by increasing heat flux while the temperature intensity, t′, first decreases and then rises, with a shift in the position of the peak intensity away from the wall. On the basis of an analysis developed for heated turbulent flow, the turbulent shear stress and heat flux distributions are calculated from the experimental results. As the flow field becomes appreciably distorted on heating, it is found that the turbulent shear stress becomes very small, while the heat flux distribution suggests an increase in the width of the viscous sublayer.

Abstract-Temperature profiles measured in mercury and the NaK eutectic are reported for vertical flow in pipes under conditions of constant heat flux, and it is shown that the mercury profiles are distorted by a superimposed free convection effect up to Reynolds numbers of at least 5000% A correlation is presented whereby the amount of distortion under given conditions may be estimated, and the shape of the undistorted temperature profile may be predicted. These profiles are used to determine the ratio of eddy diffusivities and the Nusseh number for liquid metals in the Reynolds number range 3 x lo4 to 3 x 105.

Measurements were made in mercury, for turbulent flow and constant flux heating in a vertical pipe, in order to determine the extent to which the velocity and temperature distributions are affected by buoyancy forces. With increasing heat flux, velocity profiles at Reynolds numbers of 20,000 to 60,000 were found to be markedly distorted in comparison with the isothermal velocity profile. Even very low heat input caused significant distortion, while at high heat input a limiting profile shape was approached, with the center velocity well below the mean and the maximum occurring in the vicinity of the wall. Eddy diffusivities of heat and momentum calculated from the measured profiles exhibit a considerable variation with heat input, indicating that buoyancy forces not only change the radial shear stress distribution but also alter the nature of the turbulence in the pipe.

Fluctuations in hydraulic and organic loads cause wastewater treatment plant operating problems, necessitating some form of process control to ensure attainment of design objectives. A comparison of in–plant control with equalization control indicates that the latter is more appropriate for the case of long sludge age nutrient removal activated sludge processes which include anaerobic, anoxic and aerobic zones. A microprocessor-based control strategy is presented for the operation of an equalization tank upstream of the process to reduce, optimally, diurnal fluctuations in both flow and organic load rates. Results from implementation on a 150 Mℓ.d−1 plant with an in-line equalization tank (4,5 hour mean retention time) demonstrate the successful performance of the control strategy.

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Treated wastewater offers an excellent source of water for reclamation and reuse. In response to increasing demands for potable water in Southern California, the Orange County Water District and Sanitation District have developed a joint Groundwater Replenishment (GWR) System. This project will treat secondary wastewater effluent, currently discharged to the ocean, to produce high-quality water for recharge of the Orange County groundwater basin and injection into a seawater intrusion barrier.To address the special challenges of the future phases of the 130 mgd GWR project, such as a shortage of land, high costs associated with additional secondary wastewater treatment facilities, and the disposal of additional biosolids, a new treatment approach is being tested. The new approach called the Integrated Membrane Anaerobic Stabilization (IMANS TM ) process utilizes membrane processes in combination with anaerobic biological treatment. The system utilizes the microfiltration (MF) process to treat primary effluent followed by reverse osmosis (RO), or nanofiltration (NF), to concentrate soluble BOD and produce a high-quality effluent for reuse. The RO concentrate, which is free of suspended material, is then treated in a high-rate anaerobic digestion process that eliminates the need for conventional secondary activated sludge treatment.An IMANS TM pilot plant was set up at the Orange County Sanitation District treating 15 gpm of primary effluent. Operation of the MF unit began in August 1999. Preliminary results indicate good performance by the MF and RO processes, with little evidence of permanent membrane fouling occurring. The high rate UASB process is in an acclimation phase. Estimates show that the new process combination has the potential of a lower overall power requirement and substantially less biosolids production. The pilot testing is planned to be complete in October 2000.