scholarly journals Computational fluid dynamics simulation of spray dryers: transient or steady state simulation?

2018 ◽  
Author(s):  
M. W. Woo ◽  
S. Afshar ◽  
H. Jubaer ◽  
B. Chen ◽  
J. Xiao ◽  
...  
Keyword(s):  
Steady State ◽  
Spray Drying ◽  
Cfd Simulation ◽  
Computation Time ◽  
Transient Simulation ◽  
Dynamics Simulation ◽  
Simulation Approach ◽  
Simulation Framework ◽  
Cfd Simulations ◽  
Steady State Simulation

Self-sustained fluctuating airflow behaviour in spray drying chambers is in essence an unsteady phenomenon requiring the transient CFD simulation framework. There is currently, however, a mixture of steady state and transient CFD simulations of spray dryers practised and reported in the literature. The choice between steady state and transient approach significantly affects the computation time of the simulation and subsequently the adoption of this approach by industry. This paper firstly examines in detail the bottleneck in computation time of the transient simulation approach. Based on past reports, this review paper then presents a discussion and provides several recommendations on the use of steady state and transient simulation approach for spray dryers. Keywords: CFD simulation, spray drying, transient, steady state, fluctuation 

Cyclic Breathing Simulations in Large Scale Models of the Lung Airway From the Oronasal Opening to the Terminal Bronchioles

2012 ◽  
Author(s):  
D. Keith Walters ◽  
Greg W. Burgreen ◽  
Robert L. Hester ◽  
David S. Thompson ◽  
David M. Lavallee ◽  
...  
Keyword(s):  
Steady State ◽  
Boundary Conditions ◽  
Large Scale ◽  
Whole Body ◽  
Patient Specific ◽  
Cfd Simulations ◽  
Reduced Order ◽  
Scale Models ◽  
Steady State Simulation ◽  
Conducting Zone

Computational fluid dynamics (CFD) simulations were performed for unsteady periodic breathing conditions, using large-scale models of the human lung airway. The computational domain included fully coupled representations of the orotracheal region and large conducting zone up to generation four (G4) obtained from patient-specific CT data, and the small conducting zone (to G16) obtained from a stochastically generated airway tree with statistically realistic geometrical characteristics. A reduced-order geometry was used, in which several airway branches in each generation were truncated, and only select flow paths were retained to G16. The inlet and outlet flow boundaries corresponded to the oronasal opening (superior), the inlet/outlet planes in terminal bronchioles (distal), and the unresolved airway boundaries arising from the truncation procedure (intermediate). The cyclic flow was specified according to the predicted ventilation patterns for a healthy adult male at three different activity levels, supplied by the whole-body modeling software HumMod. The CFD simulations were performed using Ansys FLUENT. The mass flow distribution at the distal boundaries was prescribed using a previously documented methodology, in which the percentage of the total flow for each boundary was first determined from a steady-state simulation with an applied flow rate equal to the average during the inhalation phase of the breathing cycle. The distal pressure boundary conditions for the steady-state simulation were set using a stochastic coupling procedure to ensure physiologically realistic flow conditions. The results show that: 1) physiologically realistic flow is obtained in the model, in terms of cyclic mass conservation and approximately uniform pressure distribution in the distal airways; 2) the predicted alveolar pressure is in good agreement with previously documented values; and 3) the use of reduced-order geometry modeling allows accurate and efficient simulation of large-scale breathing lung flow, provided care is taken to use a physiologically realistic geometry and to properly address the unsteady boundary conditions.

scholarly journals A Simulation Study of Drying Chamber for Marine Product

2021 ◽  
Vol 13 (6) ◽  
Author(s):  
Mohd Afzanizam Mohd Rosli ◽  
◽  
Hiew Sit Jing ◽  
Nur Izzati Mohd Azhar ◽  
Maidi Saputra ◽  
...  
Keyword(s):  
Steady State ◽  
Cfd Simulation ◽  
Air Flow ◽  
Flow Distribution ◽  
Cfd Simulations ◽  
High Quality ◽  
Steady State Condition ◽  
Temperature Distributions ◽  
Marine Product ◽  
Drying Chamber

Drying chamber is a drying application for agriculture product to produce high quality and hygiene product. The purpose of this paper is to propose best configuration trays arrangement in drying chamber for better distribution of velocity and temperature. Therefore, five configurations of trays are analyzed to obtain the best performance of uniformity air flow distribution within drying chamber. CFD simulation studied the uniform air flow in the drying chamber in steady state condition. A validation is performed by comparing the data obtained from the literature review CFD simulation to ensure the methodology is correct. Then, the drying chamber with different trays arrangements are simulated using CFD simulations to obtain velocity and temperature distributions at nine plotted points on trays. From the results obtained, it concluded that design (A) and (D) are selected as the best designs for uniformity because there is less discrepancy for each point contributed the more uniformity of distribution.

A Study of the Development of an Analytical Wall Function for LES

2014 ◽  
Author(s):  
R. S. Amano ◽  
Takahiko Hasegawa ◽  
Shaohua Shen
Keyword(s):  
Boundary Layer ◽  
Steady State ◽  
Cfd Simulation ◽  
The Other ◽  
Unsteady State ◽  
Wall Function ◽  
Other Hand ◽  
Log Law ◽  
Complicated Geometry ◽  
Steady State Simulation

In order to invent a new near-wall treatment for turbulence in Computational Fluid Dynamics (CFD) simulation, an Analytical Wall Function (AWF) has been studied and shown that it is possible to work accurately with Reynolds Averaged Navier-Stokes (RANS) Simulation even for complicated geometry such as impinging jet flow or separation and reattachment flow. One of the most common wall functions is the Standard Wall Function (SWF) which assumes log-law inside the boundary layer. However, there is a problem that SWF has been used for industrial applications even though it is difficult to analyze the turbulence phenomenon in a complicated geometry accurately because log-law is not applicable in that geometry. On the other hand, since AWF derives the boundary condition on the wall by integrating analytically the boundary layer equation in wall adjacent cells, it can analyze the turbulence accurately even in complicated geometry. AWF has an advantage over SWF from this point of view. In this study, AWF was improved and optimized for Large Eddy Simulation (LES) by changing the way of modeling of eddy viscosity inside the boundary layer for steady state simulation to that for unsteady state simulation. This is because RANS is a steady state simulation; on the other hand, LES is unsteady state simulation, which is one of the largest differences between them. The accuracy of the new AWF for LES (LES-AWF) was validated by both of experimental results and CFD simulation results. Both of the experiment and CFD simulation are conducted in the wind tunnel.

CFD Performance Analysis of a Stirred Tank Flowmaker

2006 ◽  
Author(s):  
Lasse A. Rosendahl ◽  
Xiaopeng Wang ◽  
Christian B. Jacobsen
Keyword(s):  
Steady State ◽  
Turbulence Model ◽  
Cfd Simulation ◽  
Flow Characteristics ◽  
Stirred Tank ◽  
Mean Flow ◽  
Solution Quality ◽  
Transient Simulations ◽  
Multiple Frame ◽  
Steady State Simulation

In the present work, the mean flow field in a stirred tank equipped with a commercially available Grundfos AFG.40.230.35 flowmaker is investigated using both steady-state and transient CFD simulation, in order to provide information on the interaction between flow, propeller and wall proximity as well as information on aspects of using numerical tools for this type of fluid machinery. The simulations, carried out with Ansys CFX 10, used a multiple frame of reference (MFR) approach to include a full representation of the flowmaker blade and motor geometry, in order to fully include the effects of the blade shape and variable pitch for both stationary and transient simulations. The influence of grid type, turbulence model and steady vs transient setup on solution quality has been investigated, and the steady state calculations are compared with LDA measurements. The results show that for the steady state calculations, the choice of grid type is decisive in terms of quality of results, and that the transient simulations using the SST turbulence model yields a superior prediction of flow characteristics; however, the computational expenses for transient simulation is around 10 times than steady-state simulation.

TRANSIENT SIMULATION VIA EMPIRICALLY BASED COUPLING

1999 ◽  
Vol 13 (2) ◽  
pp. 147-167 ◽  
Author(s):  
Eugene W. Wong ◽  
Peter W. Glynn ◽  
Donald L. Iglehart
Keyword(s):  
Steady State ◽  
Confidence Interval ◽  
Stationary Distribution ◽  
Performance Measures ◽  
Empirical Data ◽  
Transient Simulation ◽  
Transient Performance ◽  
Steady State Simulation

In this paper we consider the use of coupling ideas in efficiently computing a certain class of transient performance measures. Specifically, we consider the setting in which the stationary distribution is unknown, and for which no exact means of generating stationary versions of the process is known. In this context, we can approximate the stationary distribution from empirical data obtained from a first-stage steady-state simulation. This empirical approximation is then used in place of the stationary distribution in implementing our coupling-based estimator. In addition to the empirically based coupling estimator itself, we also develop an associated confidence interval procedure.

Fast and Accurate Evaluation of Cooling in Data Centers

2014 ◽  
Vol 137 (1) ◽  
Author(s):  
Harshad Bhagwat ◽  
Umesh Singh ◽  
Anirudh Deodhar ◽  
Amarendra Singh ◽  
Anand Sivasubramaniam
Keyword(s):  
Data Center ◽  
Data Centers ◽  
Cfd Simulation ◽  
Computation Time ◽  
Production Data ◽  
Real Time Control ◽  
Cfd Simulations ◽  
Accurate Evaluation ◽  
Time Control ◽  
Data Center Cooling

Cooling is a major component in the enormous energy consumption in data centers. Accurate evaluation of cooling inside a data center forms the backbone of all the attempts for improving cooling efficiency. Models based on computational fluid dynamics (CFD) are typically used for accurate evaluation, but have a drawback of high computation time. This paper presents a novel thermal predictor to evaluate data center cooling in seconds. The key idea is to extract information from a single instance of CFD simulation using metrics called as influence indices to build the fast thermal predictor. Then, this predictor can evaluate the cooling for altered operation of data center with comparable accuracy in seconds without the need for repetitive CFD simulations. This paper demonstrates the accuracy of the thermal predictor by comparing with CFD simulations for a sample, but realistic data center. The fast thermal predictor then successfully passed more challenging tests in a real production data center and proved its practical utility. The results of the thermal predictor compared with measurements carried out in the production data center are also presented. This fast thermal predictor is an important milestone in the development of a method for model-based real time control of data center cooling.

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