scholarly journals Modelling of Chlorine Contact Tank and the Combined Applications of Linear Model Predictive Control and Computational Fluid Dynamics

2009 ◽  
Vol 4 (1) ◽  
Author(s):  
Abrar Muslim ◽  
Qin Li ◽  
Moses O. Tadé
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Model Predictive Control ◽  
Linear Model ◽  
Predictive Control ◽  
Mass Flow ◽  
Decay Process ◽  
Flow Rates ◽  
Mass Flow Rates ◽  
Siso System

A dynamic model is developed to present chlorine decay in chlorine contact tank, and a single-input single-output (SISO) model that presents both chlorine dosing and decay process is developed in Simulink of Matlab software with considerations of the process disturbances of temperature and stagnant flow in the tank. A computational fluid dynamics (CFD) model of chlorine transport and decay in the tank is also developed with the use of mixture multiphase model to present the chlorine mixing and decay models in the tank. To optimally control free chlorine residual (FCR) concentration in the SISO system, a linear model predictive control (LMPC) is designed using the SISO system and LMPC control algorithm. The LMPC control objective is to regulate the optimal mass flow rates of gaseous chlorine to control the chlorine decay process inputs/outputs within the constraints. The results on the LMPC simulation using reference data from a real water plant show that the LMPC can control the FCR concentration in the tank within the constraint by regulating the optimal mass flow rates of gaseous chlorine. Commercial CFD software, FluentTM, has been used in this study to simulate the FCR distribution in the CCT channel based on the LMPC result.

Design and analysis of bubble-injected water ramjets with discrete injection configurations by computational fluid dynamics method

2012 ◽  
Vol 227 (9) ◽  
pp. 1945-1955 ◽  
Author(s):  
Arash Nemati Hayati ◽  
Seyed Mohammad Hashemi ◽  
Mehrzad Shams
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Mass Flow ◽  
Operating Conditions ◽  
Flow Rates ◽  
Air Mass ◽  
Mixing Chamber ◽  
Mass Flow Rates ◽  
Dynamics Method ◽  
Water Ramjet

In this study, the performance of a typical bubbly water ramjet was investigated by the application of computational fluid dynamics method at different vessel velocities up to 80 knots for a range of air mass flow rates up to 0.9 kg/s. For this purpose, the validity of presented method was preliminarily examined for a converging–diverging nozzle. Then, a designed ramjet with discrete injection configuration was studied at different operating conditions. It was proved that the injection process significantly increases the amount of generated thrust up to 10 times more than the thrust of a single-phase water ramjet. The results suggest that for optimum operation of the ramjet, specific values should be assigned for both inlet and mixing chamber diameters with respect to outlet diameter. Furthermore, it seems that the modification of mixing chamber profile can effectively improve the performance, as the generated thrust of model with throat-like chamber surpasses that for conventional model up to more than two times. Finally, in order to rectify the contradiction of results obtained in previous literatures on the dependency of thrust on vessel velocity, a meaningful relation was derived between the generated thrust of the ramjet with the advance velocity at different air mass flow rates.

scholarly journals Numerical modelling of twin-screw pumps based on computational fluid dynamics

2016 ◽  
Vol 231 (24) ◽  
pp. 4617-4634 ◽  
Author(s):  
Di Yan ◽  
Ahmed Kovacevic ◽  
Qian Tang ◽  
Sham Rane ◽  
Wenhua Zhang
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Mass Flow ◽  
Dynamics Simulation ◽  
Piping System ◽  
Computational Domain ◽  
Screw Pump ◽  
Flow Rates ◽  
Shaft Power ◽  
Mass Flow Rates

Increasing demands for high-performance screw pumps in oil and gas as well as other applications require deep understanding of the fluid flow field inside the machine. Important effects on the performance such as dynamic losses, influence of the leakage gaps and presence and extent of cavitation are difficult to observe by experiments. However, it is possible to study such effects using well-validated computational fluid dynamics models. The novel-structured numerical mesh consisting of a single-computational domain for moving screw pump rotors was developed to allow three-dimensional computational fluid dynamics simulation of such machine possible. Based on finite volume method, the instantaneous mass flow rates, rotor torque, local pressure field, velocity field and other performance indicators including the indicated power were predicted. A calculation model for the bearing friction losses was introduced to account for mechanical losses. The geometry of the inlet and outlet passages and piping system are taken into consideration to evaluate their influences on the pressure distribution and shaft power. The paper also shows the influence of rotor clearances on the pump performance. The computational fluid dynamics model was validated by comparing the numerical results with the measured performance obtained in the experimental test rig through the comprehensive experiment performed for a set of discharge pressures and rotational speeds. Validation includes comparison of mass flow rates, shaft power and efficiency under variety of speeds and discharge pressure. It has been found that the predicted results match well with the measurements. The results also showed that the radial clearances have larger influence on the mass flow rate than the interlobe clearance. The correct design of the flow passages within the screw pump plays significant role in minimizing required power consumption. The analysis presented in this paper contributes to better understanding of the working process inside the screw pump and offers a good reference to improve design and optimize such machines in terms of clearance selection, shape of the ports, piping system, etc. In future, this model will be used for analysis of cavitating flows and determining performance of other multiphase screw pumps.

Automatic optimization of a centrifugal pump based on impeller–diffuser interaction

2018 ◽  
Vol 232 (8) ◽  
pp. 1004-1018 ◽  
Author(s):  
KM Guleren
Keyword(s):  
Fluid Dynamics ◽  
Genetic Algorithm ◽  
Computational Fluid Dynamics ◽  
Centrifugal Pump ◽  
Mass Flow ◽  
Flow Rate ◽  
Pressure Increase ◽  
Flow Rates ◽  
Automatic Optimization ◽  
Mass Flow Rates

In this study, a centrifugal pump has been optimized using the genetic algorithm coupled with computational fluid dynamics considering the flow physics for various impeller–diffuser configurations. During the automatic optimization process, the population was selected from a pool of pump geometries generated by four design variables; namely the relative diffuser vane angle, number of diffuser vanes, number of impeller blades, and the impeller wrap angle. The genetic algorithm was combined with a flow solver and a computer aided design software which was used also to create the mesh for the generated geometry. Two objective functions were adopted for the optimization: maximum pressure increase and minimum relative flow angle, which is an indication of reverse flow in the impeller. The iteration history of the optimization for the design (2.4 kg/s) and off-design (3.6 kg/s) flow rate showed that the optimization has been converged to an impeller–diffuser configuration within approximately 250 computational fluid dynamics analyses. Three geometries from each optimization with the highest pressure increase were studied for various mass flow rates and the results were compared with those of the original pump. The results show that the first optimization indicates a significant improvement of pressure increase at design flow rate (15.5%) but decrease at larger flow rates. The second optimization which was required after the results of the first optimization enhanced the head for the entire mass flow rates with an average increase of 25.74%.

Using computational fluid dynamics to evaluate a novel venous cannula (Smart canula ®) for use in cardiopulmonary bypass operating procedures

Perfusion ◽  
2007 ◽  
Vol 22 (4) ◽  
pp. 257-265 ◽  
Author(s):  
D. Jegger ◽  
S. Sundaram ◽  
K. Shah ◽  
I. Mallabiabarrena ◽  
G. Mucciolo ◽  
...  
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Cardiopulmonary Bypass ◽  
Pressure Gradient ◽  
Surface Area ◽  
Mass Flow ◽  
Stokes Equations ◽  
Venous Drainage ◽  
Dimensional System ◽  
Flow Rates

Peripheral access cardiopulmonary bypass (CPB) is initiated with percutaneous cannulae (CTRL) and venous drainage is often impeded due to smaller vessel and cannula size. A new cannula (Smartcanula ®, SC) was developed which can change shape in situ and, therefore, may improve venous drainage. Its performance was evaluated using a 2-D computational fluid dynamics (CFD) model. The Navier-Stokes equations could be simplified due to the fact that we use a steady state and a 2-dimensional system while the equation of continuity (ρ constant) was also simplified. We compared the results of the SC to the CTRL using CFDRC® (Version 6.6, CFDRC research corporation, Huntsville, USA) at two preloads (300 and 700 Pa). The SC's mass flow rate outperformed the CTRL by 12.1% and 12.2% at a pressures of 300 and 700 Pa, respectively. At 700 Pa, a pressure gradient of 50% was measured for the CTRL and 11% for the SC. The mean velocity at the 700 Pa for the CTRL was 1.0 m.s-1 at exit while the SC showed an exit velocity of 1.3 m.s-1. Shear rates inside the cannulae were similar between the two cannulae. In conclusion, the prototype shows greater mass flow rates compared to the classic cannula; thus, it is more efficient. This is also advocated by a better pressure gradient and higher average velocities. By reducing cannula-tip surface area or increasing hole surface area, greater flow rates are achieved. Perfusion (2007) 22, 257—265.

scholarly journals Performance Assessment of Double Corrugated Tubes in a Tube-In-Shell Heat Exchanger

Energies ◽  
2021 ◽  
Vol 14 (5) ◽  
pp. 1343
Author(s):  
Kristina Navickaitė ◽  
Michael Penzel ◽  
Christian R. H. Bahl ◽  
Kurt Engelbrecht
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Heat Exchanger ◽  
Pressure Drop ◽  
Heat Exchangers ◽  
Dynamics Analysis ◽  
Flow Rates ◽  
Turbulent Flow Regime ◽  
Computational Fluid Dynamics Analysis ◽  
Mass Flow Rates

In this article, the performance of double corrugated tubes applied in a tube-in-shell heat exchanger is analysed and compared to the performance of a heat exchanger equipped with straight tubes. The CFD (computational fluid dynamics) analysis was performed considering a turbulent flow regime at several mass flow rates. It is observed that the double corrugated geometry does not have a significant impact on the pressure drop inside the analysed heat exchanger, while it has the potential to increase its thermal performance by up to 25%. The ε–NTU (effectiveness–number of transfer units) relation also demonstrates the advantage of using double corrugated tubes in tube-in-shell heat exchangers over straight tubes.

scholarly journals Net-exergetic, hydraulic and thermal optimization of coaxial heat exchangers using fixed flow conditions instead of fixed flow rates

2021 ◽  
Vol 9 (1) ◽  
Author(s):  
Tobias Blanke ◽  
Markus Hagenkamp ◽  
Bernd Döring ◽  
Joachim Göttsche ◽  
Vitali Reger ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Laminar Flow ◽  
Mass Flow ◽  
Flow Rate ◽  
Heat Exchangers ◽  
Circular Ring ◽  
Flow Conditions ◽  
Flow Rates ◽  
Mass Flow Rates ◽  
Pipe Radius

AbstractPrevious studies optimized the dimensions of coaxial heat exchangers using constant mass flow rates as a boundary condition. They show a thermal optimal circular ring width of nearly zero. Hydraulically optimal is an inner to outer pipe radius ratio of 0.65 for turbulent and 0.68 for laminar flow types. In contrast, in this study, flow conditions in the circular ring are kept constant (a set of fixed Reynolds numbers) during optimization. This approach ensures fixed flow conditions and prevents inappropriately high or low mass flow rates. The optimization is carried out for three objectives: Maximum energy gain, minimum hydraulic effort and eventually optimum net-exergy balance. The optimization changes the inner pipe radius and mass flow rate but not the Reynolds number of the circular ring. The thermal calculations base on Hellström’s borehole resistance and the hydraulic optimization on individually calculated linear loss of head coefficients. Increasing the inner pipe radius results in decreased hydraulic losses in the inner pipe but increased losses in the circular ring. The net-exergy difference is a key performance indicator and combines thermal and hydraulic calculations. It is the difference between thermal exergy flux and hydraulic effort. The Reynolds number in the circular ring is instead of the mass flow rate constant during all optimizations. The result from a thermal perspective is an optimal width of the circular ring of nearly zero. The hydraulically optimal inner pipe radius is 54% of the outer pipe radius for laminar flow and 60% for turbulent flow scenarios. Net-exergetic optimization shows a predominant influence of hydraulic losses, especially for small temperature gains. The exact result depends on the earth’s thermal properties and the flow type. Conclusively, coaxial geothermal probes’ design should focus on the hydraulic optimum and take the thermal optimum as a secondary criterion due to the dominating hydraulics.

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