scholarly journals Parameters to characterize the internal recirculation of an oxidation ditch

Water SA ◽  
2021 ◽  
Vol 47 (2 April) ◽  
Author(s):  
Shao Po Wang ◽  
Jing Jie Yu ◽  
Hua Ji Ma
Keyword(s):  
Flow Rate ◽  
Dilution Effect ◽  
Circulation Flow ◽  
Oxidation Ditch ◽  
Mixed Liquor ◽  
Treatment Processes ◽  
Formula Derivation ◽  
Recirculation Frequency ◽  
Better Than ◽  
Circulation Flow Rate

Mixed liquor circulates ceaselessly in the closed-loop corridor in an oxidation ditch (OD), which is significantly different from other wastewater treatment processes. The internal recirculation ratio (IRR), i.e., the ratio between circulation flow rate (QCC) and influent flow rate (QIn), and the circulatory period (T), i.e. the time consumed for the mixed liquor to complete one lap in the circular corridor, was used to quantify the internal recirculation characteristics of the OD system. In order to elucidate the characteristics and applicability of IRR and T, this study obtained the numerical relationship between IRR and T by formula derivation. It also discusses the factors influencing IRR and analyses the applications of IRR and T. The results showed that IRR = QCC/QIn = HRT/T = HRT ž IRF (HRT = hydraulic retention time of the mixed liquor in the circular corridor; IRF = internal recirculation frequency). Moreover, three kinds of parameters had an effect on IRR: QIn; reactor dimensions, i.e., length (Lmid), width (B), and height (H) of the circular corridor; and horizontal velocity of the mixed liquor in the circular corridor (v). QIn changed IRR by altering HRT. However, B, H, Lmid, and v changed IRR by altering IRF and T. Furthermore, the same IRR corresponded to many different HRT and IRF. Therefore, when QIn and QCC varied in the OD system, using HRT and IRF to evaluate the variation of QIn and QCC, respectively, was better than using IRR to evaluate their synthetical variation. IRF and T were useful for directly and precisely characterizing the circulation speed and circulation flow rate in the circular corridor, while IRR was more useful for evaluating the dilution effect of reflux on influent.

A Theoretical and Experimental Procedure for Designing of Oil Circulation Ratio Reduction

2003 ◽  
Author(s):  
Toshiyuki Toyama ◽  
Takashi Uekawa ◽  
Susumu Hiodoshi ◽  
Shigeki Hagiwara
Keyword(s):  
Flow Rate ◽  
High Speed ◽  
Structural Changes ◽  
Separation Efficiency ◽  
Analysis Tool ◽  
Circulation Flow ◽  
Oil Droplets ◽  
Substantial Impact ◽  
Circulation Ratio ◽  
Circulation Flow Rate

This report demonstrates the successful development of a design method reducing oil circulation ratio (hereafter OCR) in swing compressors, based on calculations from a simplified model and an actual experiment. The developed OCR analysis tool features the addition of oil circulation flow rate circuit to the oil supply circuit that diagnoses the pump, the oil feeding passage, and the bearings by electrical circuit. The oil circulation flow rate is affected by refrigerant flow. In consideration of the complementary effects of refrigerant gas and oil circulation flow rate, including wall impingement of oil droplets, the gravity of oil droplets, and buoyancy, calculations can be conducted as separation efficiency ratio. In the experiment, the behavior of oil droplets in refrigerant in a compressor outfitted with pressure-proof glass was observed with a high-speed camera. It was thereby ascertained that the predicted speed of oil droplets and the actual speed in the compressor were almost the same. The effects of a drop in oil level during operation due to the oil circulation flow rate can be taken into account, something previously impossible with conventional circuits. The conclusive analytical precision of OCR is a range of 30–115Hz with a margin of error of ±0.3wt%. Using this method, design points that have substantial impact on OCR reduction can be clarified. With structural changes to the motor-rotor as suggested from the analysis, OCR can be reduced. Consequently, a significant reduction in the period necessary for compressor development has been achieved.

Two-Phase Natural Circulation Cooling Performance Assessment and Safety Analysis for APR1400 Core Catcher System

2014 ◽  
Author(s):  
Ki Won Song ◽  
Shripad T. Revankar ◽  
Hyun Sun Park ◽  
Bo Rhee ◽  
Kwang Soon Ha ◽  
...  
Keyword(s):  
Void Fraction ◽  
Flow Rate ◽  
Natural Circulation ◽  
Scaling Analysis ◽  
Circulation Flow ◽  
Two Phase ◽  
Cooling Performance ◽  
The Core ◽  
Core Catcher ◽  
Circulation Flow Rate

The two-phase natural circulation cooling performance of the APR1400 core catcher system is studied utilizing a drift flux flow model developed via scaling analysis and with an air-water experimental facility. Scaling analysis was carried out to identify key parameters, so that model facility could simulates two-phase natural circulation. In the experimental apparatus, instead of steam, air is injected into the top wall of the test channel to simulate bubble formation and void distribution due to boiling water in the core catcher channel. Measurement of void fraction critical to the heat transfer between the wall and coolant is carried out at certain key position using double-sensor conductivity probes. Results from the model provide expected natural circulation flow rate in the cooling channel of the core catcher system. The observed flow regimes and the data on void fraction are presented. For a given design of the down comer piping entrance condition bubble entrainment was observed that significantly reduced the natural circulation flow rate.

An Experimental Study on Open Natural Circulation Flow Characteristics by Air Injection

2017 ◽  
Author(s):  
Pengjiu Cao ◽  
Xiaxin Cao ◽  
Zhongning Sun ◽  
Ming Ding ◽  
Na Li ◽  
...  
Keyword(s):  
Flow Rate ◽  
Driving Force ◽  
Flow Instability ◽  
Natural Circulation ◽  
Heat Removal ◽  
Air Injection ◽  
Circulation System ◽  
Circulation Flow ◽  
Churn Flow ◽  
Circulation Flow Rate

An open natural circulation system has the characteristics of a simple structure, superior safety performance and strong heat removal capability. However, during long-term operation, the flow instability may occur due to the reduction of the driving force, which will have adverse effects on the heat removal capability and safe operation of the system. Thus, injecting air into the riser is designed in this paper to improve the driving force of the circulation flow, reduce the possibility of flow instability, and increase the heat removal capability. In order to investigate the influence of air injection on the evolution of flow pattern, resistance characteristics and circulation flow rate, the method of visual observation and data analysis is used based on different pore sizes porous media, air injection rate and submergence ratios. The ratio of the driving pressure head to the resistance pressure drop is proposed as the basis for assessing the effect of air injection on the ability of natural circulation. It is found that the driving force of natural circulation increases with the increase of air injection rate, and the circulation flow rate increases obviously when the bubbly flow appears in the riser. However, when the transition from bubbly flow to churn flow appears, the growth of the circulation flow rate slows down because the resistance increases faster than the driving force. Therefore, it can be known that the best performance is obtained when bubbly-churn flow appears in the top of the riser. What’s more, the capacity of lifting water will be reduced and churn flow will appear prematurely when the submergence ratio decreases. This means that in the process of open natural circulation system design, the submergence ratio of the system should be increased as much as possible. Finally, in this paper, it is found that the bubble pump with PS = 0.2 μm has better performance.

scholarly journals On the Circulation Flow Rate and the Desulphurization of Molten Pig Iron on the Gas-Lift Mixing Reactor Process Used for an External Desulphurization

1976 ◽  
Vol 62 (8) ◽  
pp. 962-970 ◽  
Author(s):  
Kiichi NARITA ◽  
Yoshitomo SATOH ◽  
Takasuke MORI ◽  
Takamichi ITO ◽  
Akira KUJIME
Keyword(s):  
Flow Rate ◽  
Pig Iron ◽  
Circulation Flow ◽  
Gas Lift ◽  
Circulation Flow Rate
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