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The velocity distribution and circulation flow rate in a draft-tube stirred tank of 0.8 m diameter were studied experimentally and were numerically simulated using the FLUENT6.2 computational fluid dynamics (CFD) package. A renormalization group (RNG) k–e turbulent model and multiple reference frame (MRF) were used in the simulation. The circulation flow number and liquid velocity predicted by CFD were in good agreement with experimental values. Both experimental and simulation results show that the axial velocity is far larger than radial and tangential velocities inside and outside the draft tube, and there is a secondary circulation zone close to the outside wall of the draft tube, which could affect the efficiency of the tank. The results are to be of reference for the industrial stirred tank with a draft tube.

Wind-induced cross ventilation is one of the key technologies for saving energy while controlling the indoor environment, and seems to be a crucial element of any sustainable building policy. However, it is sometimes difficult to arrange openings on two sides for cross ventilation of a room. In buildings in built-up areas, many rooms only have openings on a single side. Since the airflow rate for a single-sided opening is much lower than that for two-sided openings, it is important to study how we can increase the airflow rate for a single-sided opening using either passive or active techniques. In this study, the characteristics of wind-induced ventilation with single-sided openings were analysed through wind tunnel experiments. In some experimental cases, a small object was attached to the opening in order to increase the airflow rate. (It was assumed that this object replicated a pivoted window whose vertical axis was in the centre of the window.) In other experimental cases, circulation flow w...

Mixing performances of a new mixing equipment which has a vibrating motor with some fin oscillators on a pair of shafts were investigated. This mixing equipment, which is mainly used for industrial plating processes, was usually operated at the vibrating frequency from 30 Hz to 60 Hz with the amplitude from 1 mm to 10 mm.The mixing time and the circulation time were measured and the flow pattern and the mixing process were visualized. The mixing time and the circulation time took the optimum values (the minimum values) for the equipment design at the frequency range from 40 Hz to 50 Hz irrespective to the configuration of the fins. The complete mixing was achieved in three to four circulations of the liquid in the vessel. From the visualization of the flow pattern and the mixing process it was shown that a primary circulation flow passing through the fins was very important for the mixing operation.

Unstable flow phenomena in a mixing vessel with a marine propeller were investigated experimentally using flow visualization and LDV techniques. It was found that the instantaneous bulk flow profiles were usually asymmetric with respect to the impeller shaft and they fluctuated in the large time scale. The circulation flow patterns in the space between two adjacent baffles were classified into quick-return flow (QR), full-circulation flow (FC) and intermediate-circulation flow (IC), which were replaced randomly one after another with time. Their lifetimes were widely distributed from about half a second to several minutes. Connected with the circulation flow patterns, the impeller stream was directed vertically downward or obliquely outward to the vessel wall and held a high level of angular momentum when pattern FC took place, while the impeller stream was directed obliquely inward to the impeller shaft with a low level of angular momentum when pattern QR took pace.

An experimental investigation was made of the mixing of liquids in a tank where the liquid jet was injected through a nozzle. The mixing time was defined as the time required to reduce the concentration variation within 1% of the mixed mean value and was measured by an impulse response. The circulation time was also obtained from the response curve. It was found that in the circulation flow regime of mixing (Re>3 ×104) there exists an optimum nozzle depth for rapid mixing. It ranges from the liquid surface level to three-quarters of the liquid depth when the liquid depth is equal to the tank diameter, and is the mid-depth of the liquid when the liquid depth is smaller than the tank diameter. When the nozzle height is within one-fourth of the tank diameter, it is efficient for rapid mixing to tilt the nozzle upwards enough to prevent the formation of a wall jet, which induces circulations of small variance of circulation time.

The use of anodic oxidation for the production of acetic acid from a wastewater containing alcohol has been investigated. The initial alcohol concentration and the applied current are found to be the most affecting variables on such conversion. The effect of the circulation flow rate has been also studied. The kinetics of the reaction has been found to be of a second order.