Computational Fluid Dynamics Simulation of a Single-Phase Rectangular Thermosiphon

2020 ◽  
Author(s):  
Tri Nguyen ◽  
Elia Merzari
Keyword(s):  
Single Phase ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Heat Removal ◽  
Spectral Element ◽  
Dynamics Simulation ◽  
Velocity Measurements ◽  
Buoyancy Driven Flows ◽  
The Stability ◽  
Flow Reversals

Abstract Buoyancy-driven flows are widespread in diverse engineering applications. Such flows have been studied in great detail theoretically, experimentally, and numerically. However, the fluid-dynamic instabilities and flow reversals of thermosiphon are still actively investigated. The presence of such instabilities limits the effectiveness of such devices for decay heat removal. Traditionally the stability analysis of natural convection loops has been confined to one-dimensional calculations, on the argument that the flow would be mono-dimensional when the ratio between the radius of the loop and the radius of the pipe is much larger than 1. Nevertheless, accurate velocity measurements of the flow in toroidal loops have shown that the flow presents three-dimensional effects. Previous works of the authors have shown that these structures can be seen in thermosiphons. In this paper, we aim to use modern CFD methods to investigate the three-dimensional flow in thermosiphons. This paper focuses on rectangular thermosiphons. In particular, we perform a series of high-fidelity simulations using the spectral element code Nek5000 to investigate the stability behavior of the flow in a rectangular thermosiphon. We compare the results with available existing experimental data from the L2 facility in Genoa. We examine in detail the flow structures generated. Moreover, in the past various authors have demonstrated that the overall behavior of the thermosiphon depends strongly on the boundary conditions (BCs). The simulation campaign was carried out with different BCs to investigate and confirm this effect. In particular, simulations with Dirichlet, Neumann and Robin BCs for heater and sink were performed.

Numerical Simulation of the Flow in a Toroidal Thermosiphon

2011 ◽  
Author(s):  
Elia Merzari ◽  
Paul Fischer ◽  
Hisashi Ninokata
Keyword(s):  
Three Dimensional ◽  
Heat Removal ◽  
Spectral Element ◽  
Velocity Measurements ◽  
Dimensional Effects ◽  
Buoyancy Driven Flows ◽  
Rans Modeling ◽  
The Stability ◽  
Flow Reversals ◽  
Residual Heat

Buoyancy-driven flows are widespread in diverse engineering applications. Such flows have been studied in great detail theoretically, experimentally, and numerically. The prototype of passive, residual heat removal systems is the toroidal thermosiphon. The stability properties of such systems were first examined in detail by Creveling et al. in the mid-1970s, who reported flow reversals and instability in this geometry. Traditionally, however, the stability analysis of natural convection loops has been confined to one-dimensional calculations, on the argument that the flow would be monodimensional when the ratio between the radius of the loop and the radius of the pipe is much larger than 1. Nevertheless, accurate velocity measurements of the flow in toroidal loops have shown that the flow presents three-dimensional effects. In the present work we analyze the stability problem in a toroidal loop and then use computational fluid dynamics to evaluate the relative importance of these three-dimensional effects with regard to stability. We performed a series of high-fidelity numerical simulations using the spectral element code Nek5000. We compared the results to the available data and calculations performed with the code STAR-CCM+ 5.06. The results show a much richer dynamics than expected from either previous calculations or stability theory. The results also point to some outstanding issues in the RANS modeling of such flows.

Fluid Dynamic Excitation of Centrifugal Compressor Rotor Vibrations

1978 ◽  
Vol 100 (1) ◽  
pp. 73-78
Author(s):  
W. E. Thompson
Keyword(s):  
Fluid Dynamic ◽  
Three Dimensional ◽  
Operating Experience ◽  
Orbital Stability ◽  
Dynamic Force ◽  
Force Coefficient ◽  
Streamline Curvature ◽  
Compressor Rotor ◽  
Pressure Distributions ◽  
The Stability

A mechanism by which compressor rotor lateral vibration perturbs the mass flow-rate, the velocity and the pressure distributions within impeller passages is postulated. Such a perturbation will develop an unbalanced force on the rotor which, if it enhances the rotor vibration, is termed self-exciting. The concepts of rotor orbital velocity, the virtual center of shaft rotation, the reduction of unsteady flow to quasi-steady flow, the fluid dynamic force coefficient, mechanical orbital stability and the stability increment are introduced. The ideas are imposed on the streamline curvature method of quasi-three dimensional analysis of passage flow and a computer program has been assembled to carry out computation. No generalized guidelines have been found as yet but rather individual passage calculations are needed to determine the potentially exciting or damping character of the induced fluid dynamic forces. The average stability increment per stage for nine industrial multistage centrifugal compressors has been determined and compared with known operating experience. Important engineering characteristics of two of the compressors are shown in an example of the analysis. A provisional limit of the stability increment per stage ⩽ 1.85 lbf-s/in. (323.9N-s/m) is suggested, below which unstable nonsynchronous vibration of the compressor rotor can be expected.

scholarly journals Structure elucidation and docking analysis of 5M mutant of T1 lipase Geobacillus zalihae

PLoS ONE ◽  
2021 ◽  
Vol 16 (6) ◽  
pp. e0251751
Author(s):  
Siti Nor Hasmah Ishak ◽  
Nor Hafizah Ahmad Kamarudin ◽  
Mohd Shukuri Mohamad Ali ◽  
Adam Thean Chor Leow ◽  
Fairolniza Mohd Shariff ◽  
...  
Keyword(s):  
Amino Acids ◽  
Hydrogen Bonds ◽  
Three Dimensional ◽  
Substrate Preference ◽  
Dynamics Simulation ◽  
Dimensional Structure ◽  
Docking Analysis ◽  
Three Dimensional Structure ◽  
Ion Interactions ◽  
The Stability

5M mutant lipase was derived through cumulative mutagenesis of amino acid residues (D43E/T118N/E226D/E250L/N304E) of T1 lipase from Geobacillus zalihae. A previous study revealed that cumulative mutations in 5M mutant lipase resulted in decreased thermostability compared to wild-type T1 lipase. Multiple amino acids substitution might cause structural destabilization due to negative cooperation. Hence, the three-dimensional structure of 5M mutant lipase was elucidated to determine the evolution in structural elements caused by amino acids substitution. A suitable crystal for X-ray diffraction was obtained from an optimized formulation containing 0.5 M sodium cacodylate trihydrate, 0.4 M sodium citrate tribasic pH 6.4 and 0.2 M sodium chloride with 2.5 mg/mL protein concentration. The three-dimensional structure of 5M mutant lipase was solved at 2.64 Å with two molecules per asymmetric unit. The detailed analysis of the structure revealed that there was a decrease in the number of molecular interactions, including hydrogen bonds and ion interactions, which are important in maintaining the stability of lipase. This study facilitates understanding of and highlights the importance of hydrogen bonds and ion interactions towards protein stability. Substrate specificity and docking analysis on the open structure of 5M mutant lipase revealed changes in substrate preference. The molecular dynamics simulation of 5M-substrates complexes validated the substrate preference of 5M lipase towards long-chain p-nitrophenyl–esters.

scholarly journals Immunoinformatics-Based Designing of a Multi-Epitope Chimeric Vaccine From Multi-Domain Outer Surface Antigens of Leptospira

2021 ◽  
Vol 12 ◽  
Author(s):  
Pankaj Kumar ◽  
Surabhi Lata ◽  
Umate Nachiket Shankar ◽  
Mohd. Akif
Keyword(s):  
Outer Surface ◽  
Cytotoxic T Lymphocyte ◽  
Three Dimensional ◽  
Dynamics Simulation ◽  
Effective Vaccine ◽  
Accurate Information ◽  
Cell Mediated Immunity ◽  
Heparin Binding ◽  
The Stability ◽  
Chimeric Vaccine

Accurate information on antigenic epitopes within a multi-domain antigen would provide insights into vaccine design and immunotherapy. The multi-domain outer surface Leptospira immunoglobulin-like (Lig) proteins LigA and LigB, consisting of 12–13 homologous bacterial Ig (Big)-like domains, are potential antigens of Leptospira interrogans. Currently, no effective vaccine is available against pathogenic Leptospira. Both the humoral immunity and cell-mediated immunity of the host play critical roles in defending against Leptospira infection. Here, we used immunoinformatics approaches to evaluate antigenic B-cell lymphocyte (BCL) and cytotoxic T-lymphocyte (CTL) epitopes from Lig proteins. Based on certain crucial parameters, potential epitopes that can stimulate both types of adaptive immune responses were selected to design a chimeric vaccine construct. Additionally, an adjuvant, the mycobacterial heparin-binding hemagglutinin adhesin (HBHA), was incorporated into the final multi-epitope vaccine construct with a suitable linker. The final construct was further scored for its antigenicity, allergenicity, and physicochemical parameters. A three-dimensional (3D) modeled construct of the vaccine was implied to interact with Toll-like receptor 4 (TLR4) using molecular docking. The stability of the vaccine construct with TLR4 was predicted with molecular dynamics simulation. Our results demonstrate the application of immunoinformatics and structure biology strategies to develop an epitope-specific chimeric vaccine from multi-domain proteins. The current findings will be useful for future experimental validation to ratify the immunogenicity of the chimera.

An Experimental Study of Natural Convection in a Toroidal Loop

1988 ◽  
Vol 110 (4a) ◽  
pp. 877-884 ◽  
Author(s):  
C. H. Stern ◽  
R. Greif ◽  
J. A. C. Humphrey
Keyword(s):  
Experimental Study ◽  
Three Dimensional ◽  
Secondary Flows ◽  
Laser Doppler Velocimeter ◽  
Temperature Profiles ◽  
Flow Conditions ◽  
Velocity Measurements ◽  
Heating Section ◽  
Thermocouple Probe ◽  
Flow Reversals

Velocity and temperature profiles were measured at the entrance and exit to the heating section of a toroidal thermosyphon loop operating under steady flow conditions for a range of heat inputs. Velocity measurements were made with a laser-Doppler velocimeter and temperature measurements with a small thermocouple probe. Detailed results are presented for the longitudinal and circumferential components of the velocity for four heat inputs. The data for cross-stream secondary flows and streamwise flow reversals emphasize the importance of including three-dimensional effects in analyses of these systems.

A Numerical Investigation on the Influence of Porosity on the Steady-State and Transient Thermal–Hydraulic Behavior of the PBMR

2016 ◽  
Vol 138 (10) ◽  
Author(s):  
Masoumeh Sadat Latifi ◽  
Saeed Setayeshi ◽  
Giuseppe Starace ◽  
Maria Fiorentino
Keyword(s):  
Thermal Conductivity ◽  
Steady State ◽  
Effective Thermal Conductivity ◽  
Fluid Dynamic ◽  
Three Dimensional ◽  
Heat Removal ◽  
Coolant Temperature ◽  
Pebble Bed ◽  
Transient Conditions ◽  
Decay Heat

The thermal–hydraulic phenomena in a pebble bed modular reactor (PBMR) core have been simulated under steady-state and transient conditions. The PBMR core is basically a long right circular cylinder with a fuel effective height of 11 m and a diameter of 3.7 m. It contains approximately 452,000 fuel pebbles. A three-dimensional computational fluid dynamic (CFD) model of the PBMR core has been developed to study the influence of porosity on the core performance after reactor shutdown. The developed model was carried out on a personal computer using ANSYS fluent 14.5. Several important heat transfer and fluid flow parameters have been examined under steady-state and transient conditions, including the coolant temperature, effective thermal conductivity of the pebble bed, and the decay heat. Porosity was found to have a significant influence on the coolant temperature, on the effective thermal conductivity of the pebble bed, on the decay heat, and on the required time for heat removal.

Optimal Disturbances in Three-Dimensional Natural Convection Flows

2012 ◽  
Author(s):  
Elia Merzari ◽  
Paul Fischer ◽  
W. David Pointer
Keyword(s):  
Stability Analysis ◽  
Linear Stability ◽  
Linear Stability Analysis ◽  
Natural Circulation ◽  
Three Dimensional ◽  
Boussinesq Approximation ◽  
Spectral Element ◽  
Base Flow ◽  
The Stability ◽  
Optimal Disturbances

Buoyancy-driven systems are subject to several types of flow instabilities. To evaluate the performance of such systems it is becoming increasingly crucial to be able to predict the stability of a given base flow configuration. Traditional Modal Linear stability Analysis requires the solution of very large eigenvalue systems for three-dimensional flows, which make this problem difficult to tackle. An alternative to modal Linear stability Analysis is the use of adjoint solvers [1] in combination with a power iteration [2]. Such methodology allows for the identification of an optimal disturbance or forcing and has been recently used to evaluate the stability of several isothermal flow systems [2]. In this paper we examine the extension of the methodology to non-isothermal flows driven by buoyancy. The contribution of buoyancy in the momentum equation is modeled through the Boussinesq approximation. The method is implemented in the spectral element code Nek5000. The test case is the flow is a two-dimensional cavity with differential heating and conductive walls and the natural circulation flow in a toroidal thermosiphon.

scholarly journals Three-Dimensional Computation Fluid Dynamics Simulation of CO Methanation Reactor with Immersed Tubes

Energies ◽  
2022 ◽  
Vol 15 (1) ◽  
pp. 321
Author(s):  
Liyan Sun ◽  
Junjie Lin ◽  
Dali Kong ◽  
Kun Luo ◽  
Jianren Fan
Keyword(s):  
Chemical Equilibrium ◽  
Three Dimensional ◽  
Heat Removal ◽  
Dynamics Simulation ◽  
Control Mechanisms ◽  
Reaction Heat ◽  
Co Methanation ◽  
Numerical Studies ◽  
Reaction Characteristics ◽  
Euler Model

CO methanation is an exothermic process, and heat removal is an essential issue for the methanation reactor. Numerical studies were carried out to investigate the performance of a 3D fluidized bed methanation reactor with immersed cooling tubes. The simulations were carried out in the frame of the Euler–Euler model to analyze the performance of the reactor. The influences of operating temperatures were studied to understand the reaction characteristics. The temperature increases rapidly neared the inlet due to the reactions. The immersed tubes were effective at removing the reaction heat. The chemical equilibrium state was achieved with an operating temperature of 682 K for the case with immersed tubes. Different control mechanisms can be found during the process of increasing and decreasing the temperature. The reaction kinetic is the dominate factor for the cases with lower temperatures, while the chemical equilibrium will play a more important role at high temperature conditions. The configuration with staggered tubes is beneficial for heat removal.

scholarly journals Study of the effect of baffles on longitudinal stability of partly filled fuel tanker semi-trailer using CFD

2021 ◽  
Vol 3 (SI2) ◽  
pp. SI13-SI23
Author(s):  
HUYNH PHUOC THIEN ◽  
Hong Duc Thong ◽  
Tran Minh Tai
Keyword(s):  
Fluid Dynamic ◽  
Three Dimensional ◽  
Stability Limit ◽  
Longitudinal Stability ◽  
Fluid Sloshing ◽  
Transient Simulations ◽  
Computational Fluid Dynamics Cfd ◽  
The Stability ◽  
Different Levels ◽  
Simulation Scheme

Sloshing of liquid in partially filled fuel tanker vehicles has a strong effect on the directional stability and safety performance. Under the maneuver of the vehicle, such as steering, braking, or accelerating, the liquid fuel in the tanker tends to oscillate. As a result, hydrodynamic forces and moments raise. It leads to reduce the stability limit and the controllability of the vehicle. To minimize the effect of sloshing, the baffles are usually added to the tanker. This paper presents the study of the effect of baffles on the longitudinal stability of the fuel tanker semi-trailer using the computational fluid dynamics (CFD) approach. A three-dimensional fluid dynamic model of a typical tanker with different baffle configurations is developed. The User Defined Function (UDF) is used to control the acceleration of the tanker according to the simulation scheme. Transient simulations are performed for the cases of constant acceleration longitudinal maneuvers with different levels of fuel in the tanker. The volume of fluid (VOF) and air obtained from the simulation is used to indirectly calculate the center of gravity of the tanker. The post-processing results show that the baffles could provide resistance to the fluid sloshing, resulting in an improvement of the longitudinal stability of the tanker semi-trailer. The results also prove that the benefit of the baffle to the fuel tanker vehicle’s stability depends on the size of the baffle, as well as the number of baffles. The 40% height three baffles model is the proper baffle model to resist the longitudinal sloshing in the partially filled tanker of the studied trailer. By adding baffles, shifting of load on the kingpin and the rear axis are less than 5% and 2% as the tanker is filled with 50% and 70% fluid level respectively.

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