scholarly journals CFD Study of Gas Holdup and Frictional Pressure Drop of Vertical Riser Inside IC Reactor

Processes ◽  
2019 ◽  
Vol 7 (12) ◽  
pp. 936 ◽  
Author(s):  
Sheng Wang ◽  
He Dong ◽  
Zhongfeng Geng ◽  
Xiuqin Dong
Keyword(s):  
Pressure Drop ◽  
Flow Rate ◽  
Phase Interface ◽  
Gas Holdup ◽  
Circulation System ◽  
Circulation Flow ◽  
Internal Circulation ◽  
Frictional Pressure Drop ◽  
Volumetric Loading ◽  
Circulation Flow Rate

The internal circulation system in Internal Circulation (IC) reactor plays an important role in increasing volumetric loading rate and promoting the mixing between sludge and wastewater. In order to design the internal circulation system, the flow behaviors of gas-liquid inside vertical riser should be studied in detail. In the present study, the Multiple Flow Regimes model is adopted to capture the phase interface for different flow conditions. The flow patterns, internal circulation flow rate, gas holdup, and frictional pressure drop of vertical riser are investigated. The results show that the bubble flow inside a vertical riser is in a stable flow condition. There exists a maximum value for internal circulation flow rate with the increasing superficial gas velocity. The parameters of Martinelli models for gas holdup and frictional pressure drop are improved based on Computational Fluid Dynamics (CFD) results. The deviations between the calculated gas holdup and frictional pressure drop by improved model and experimental value are reduced to 14% and 13.2%, respectively. The improved gas holdup and frictional pressure drop model can be used for the optimal design of internal circulation system.

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.

Gas Holdup and Frictional Pressure Drop In a Modified Slurry Bubble Column

2012 ◽  
Vol 10 (1) ◽  
Author(s):  
Mekala Sivaiah ◽  
Subrata Kumar Majumder
Keyword(s):  
Pressure Drop ◽  
Flow Rate ◽  
Bubble Column ◽  
Gas Holdup ◽  
Phase Flow ◽  
Frictional Pressure Drop ◽  
Operating Variables ◽  
Slurry Bubble Column ◽  
Three Phase ◽  
Three Phase Flow

Abstract This article presents the analysis of gas holdup, pressure drop and bubble size of gas-liquid-solid flow in a modified downflow slurry bubble column. The analysis is done based on the Lockhart-Martinelli principle. The Lockhart-Martinelli model is modified and incorporate to predict the frictional pressure drop and gas holdup of three-phase flow in the modified bubble column. The effects of operating variables such as slurry flow rate, gas flow rate, slurry concentration and particle diameter on frictional pressure drop and gas holdup are investigated. To predict the gas holdup, Sauter mean bubble diameter and pressure drop, correlations have also been developed as function of different dimensionless groups by introducing the operating variables and physical properties. The studies of the pressure drop in the downflow slurry bubble column may give insight into a further understanding and modeling of the three-phase flow characteristics in industrial applications.

Analysis of Flow Instabilities in Two-Phase Natural Circulation

2009 ◽  
Author(s):  
Geping Wu
Keyword(s):  
Heat Flux ◽  
Pressure Drop ◽  
Flow Rate ◽  
Natural Circulation ◽  
Flow Instabilities ◽  
High Heat Flux ◽  
Circulation Flow ◽  
Two Phase ◽  
Drift Flux Model ◽  
Circulation Flow Rate

Safety concerns of nuclear reactors have attracted the attention of researchers on flow instabilities in natural circulation boiling loops. In this theoretical study, a drift flux model which solves the conservation equations of mass, momentum and energy applicable to boiling two-phase natural circulation systems is adopted. The influence of two-phase flow parameters such as drift velocity and void distribution parameter on the loop flow rate is weak. The model is used to analysis the effects of heat flux and inlet subcooling on steady circulation flow rate. High circulation flow rate is accompanied by high heat flux and low inlet subcooling. According to the region and number of meeting points which connects the resistance pressure drop curve and the driving pressure drop curve, flow excursion and density-wave instability sometimes may occur. Further, investigations are carried out to study the effect of heat flux and system pressure on the instabilities region in natural circulation.

Aqua-Ammonia as an Environmentally Acceptable Low Temperature Brine

2011 ◽  
Author(s):  
Alan A. Kornhauser
Keyword(s):  
Energy Efficiency ◽  
Pressure Drop ◽  
Calcium Chloride ◽  
Flow Rate ◽  
Methylene Chloride ◽  
Volume Flow Rate ◽  
Environmental Safety ◽  
High Viscosity ◽  
Frictional Pressure Drop ◽  
Aqua Ammonia

In many industrial processes, cooling with brines is preferable to cooling with an evaporating refrigerant. For medium and high temperatures (above about −35°C/−30°F), aqueous solutions of calcium chloride, sodium chloride, ethylene glycol, propylene glycol, and methanol have typically been used. For very low temperatures (down to about −80°C/-110°F) halocarbon refrigerants methylene chloride and trichloroethylene have generally been used. In recent years, both methylene chloride and trichloroethylene have come under increasingly strict regulation because of their toxicity. While many plants continue to use these brines, most are searching for alternates. This study was begun in response to the needs of a plant that was replacing methylene chloride with aqueous calcium chloride. The high viscosity of the calcium chloride brine caused design and operational problems. The above-mentioned brines, as well as aqua-ammonia, polydimethylsiloxane, and d-limonene, were compared for cost, toxicity, flammability, environmental safety, and energy efficiency. The energy efficiency comparison included comparisons of heat transfer coefficient, mass flow rate, volume flow rate, frictional pressure drop, inertial pressure drop, and pumping power. The comparisons indicated that aqua-ammonia was the best choice as a replacement for methylene chloride and trichloroethylene in some temperature ranges.

Modeling of Gas Holdup and Pressure Drop Using ANN for Gas-Non-Newtonian Liquid Flow in Vertical Pipe

2014 ◽  
Vol 917 ◽  
pp. 244-256 ◽  
Author(s):  
Nirjhar Bar ◽  
Sudip Kumar Das
Keyword(s):  
Pressure Drop ◽  
Liquid Flow ◽  
Multilayer Perceptron ◽  
Transfer Functions ◽  
Gas Holdup ◽  
Newtonian Liquid ◽  
Training Algorithms ◽  
Vertical Pipe ◽  
Frictional Pressure Drop ◽  
Hidden Layer

This paper is an attempt to compare the the performance of the three different Multilayer Perceptron training algorithms namely Backpropagation, Scaled Conjugate Gradient and Levenberg-Marquardt for the prediction of the gas hold up and frictional pressure drop across the vertical pipe for gas non-Newtonian liquid flow from our earlier experimental data. The Multilayer Perceptron consists of a single hidden layer. Four different transfer functions were used in the hidden layer. All three algorithms were useful to predict the gas holdup and frictional pressure drop across the vertical pipe. Statistical analysis using Chi-square test (χ2) confirms that the Backpropagation training algorithm gives the best predictability for both cases.

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.

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