scholarly journals A New RANS Correction to Account for Varying Viscosity Effects

2021 ◽  
Author(s):  
Victor Coppo Leite ◽  
Elia Merzari
Keyword(s):  
Reynolds Number ◽  
Numerical Simulations ◽  
National Laboratory ◽  
Argonne National Laboratory ◽  
Design Parameters ◽  
Working Fluid ◽  
Production Term ◽  
High Heat Transfer ◽  
Proposed Model ◽  
Varying Viscosity

Abstract It has previously been shown that by increasing the Reynolds number across a channel by spatially varying the viscosity does not cause an immediate change in the size of turbulent structures and a delay is in fact observed in both wall shear and friction Reynolds number (Coppo Leite, V, & Merzari, E., Proceedings of the ASME 2020 FEDSM, p. V003T05A019). Furthermore, it is also shown that depending on the length in which the flow condition changes, turbulence bursts are observed in the turbulence field. For the present work we propose a new version of the standard Reynolds Averaged Navier Stokes (RANS) k–τ model that includes some modifications in the production term in order to account for these effects. The new proposed model may be useful for many engineering applications as turbulent flows featuring temperature gradients and high heat transfer rates are often seen in heat exchangers, combustion chambers and nuclear reactors. In these applications, thermal and viscous properties of the working fluid are important design parameters that depend on temperature; hence it is likely to observe strong gradients on these scalars’ fields. To accomplish our goal, the modifications for the k–τ model are implemented and tested for a channel flow with spatial varying viscosity in the streamwise direction. The numerical simulations are performed using Nek5000, a spectral-element code developed at Argonne National Laboratory (ANL). Finally, the results considering a turbulence channel using the proposed model are compared against data obtained using Direct Numerical Simulations from the earlier work.

scholarly journals A Novel Analytical Modeling of a Loop Heat Pipe Employing Thin-Film Theory: Part II—Experimental Validation

Energies ◽  
2019 ◽  
Vol 12 (12) ◽  
pp. 2403 ◽  
Author(s):  
Eui Guk Jung ◽  
Joon Hong Boo
Keyword(s):  
Steady State ◽  
Heat Pipe ◽  
Film Theory ◽  
Design Parameters ◽  
Working Fluid ◽  
Coolant Temperature ◽  
Loop Heat Pipe ◽  
Analysis Model ◽  
Proposed Model ◽  
Flat Evaporator

Part I of this study introduced a mathematical model capable of predicting the steady-state performance of a loop heat pipe (LHP) with enhanced rationality and accuracy. Additionally, investigation of the effect of design parameters on the LHP thermal performance was also reported in Part I. The objective of Part II is to experimentally verify the utility of the steady-state analytical model proposed in Part I. To this end, an experimental device comprising a flat-evaporator LHP (FLHP) was designed and fabricated. Methanol was used as the working fluid, and stainless steel as the wall and tubing-system material. The capillary structure in the evaporator was made of polypropylene wick of porosity 47%. To provide vapor removal passages, axial grooves with inverted trapezoidal cross-section were machined at the inner wall of the flat evaporator. Both the evaporator and condenser components measure 40 × 50 mm (W × L). The inner diameters of the tubes constituting the liquid- and vapor-transport lines measure 2 mm and 4 mm, respectively, and the lengths of these lines are 0.5 m. The maximum input thermal load was 90 W in the horizontal alignment with a coolant temperature of 10 °C. Validity of the said steady-state analysis model was verified for both the flat and cylindrical evaporator LHP (CLHP) models in the light of experimental results. The observed difference in temperature values between the proposed model and experiment was less than 4% based on the absolute temperature. Correspondingly, a maximum error of 6% was observed with regard to thermal resistance. The proposed model is considered capable of providing more accurate performance prediction of an LHP.

Implementation of Liquid Metal Properties in RELAP5 MOD3.2 for Safety Analysis of Sodium-Cooled Fast Reactors

2017 ◽  
Author(s):  
Jian Song ◽  
Limin Liu ◽  
Simiao Tang ◽  
Yingwei Wu ◽  
Wenxi Tian ◽  
...  
Keyword(s):  
Experimental Data ◽  
Liquid Metal ◽  
Fast Reactor ◽  
Natural Circulation ◽  
National Laboratory ◽  
Argonne National Laboratory ◽  
Working Fluid ◽  
Primary System ◽  
Steady State Condition ◽  
Design Values

Due to great deal of operation experience and technology accumulation, sodium cooled fast reactor (SFR) is the most promising among the six Generation IV reactors, which has advantages of breeding nuclear fuel, transmuting long-lived actinides and good safety characteristics. Thermal-hydraulic computer codes will have to be developed, verified, and validated to support the conceptual and final designs of new SFRs. However, work on developing thermal hydraulic analysis code for SFR is very limited in China, while the common software RELAP5 MOD3 is unable to analyze liquid metal systems. So the modified RELAP5 MOD3.2 is being considered as the thermal-hydraulic system code to support the development of the SFRs. The thermodynamic and transport properties of sodium liquid and vapor have been implemented into the RELAP5 MOD3.2 code, as well as the specific heat transfer correlations for liquid metal. The sodium liquid properties use polynomial equations based on data obtained from Argonne National Laboratory, and the vapor is assumed to be perfect gas. The property equations are acceptably accurate for analysis of SFR, especially for single-phase liquid. New files are added to the fluids directory to generate property tables for new working fluid, which are similar to the table interpolation subroutines for light and heavy water in the original file directory. The method of code modifications are universal for other working fluids and will not affect the code original performance. Some basic verification work for the modified code are carried out. The steam generator of CEFR is analyzed to verify the modified code. The calculated results show that all the water will boil off in the evaporator and the calculated results are in good agreement with the design values. By using modified RELAP5 to model the primary loop of EBR-II fast reactor, the SHRT-17 PLOF test was analyzed. The results show that the natural circulation can be established in the EBR-II primary system after main pumps off to remove the core decay residual heat effectively, and the peak temperature under the safety limits. Moreover, the results computed in this work compared well with the test experimental data for the steady state condition. During the transients, the changing trends of temperature and pressure are similar to experimental data. The discrepancies between calculation and experiment are considered acceptably which need to be improved in the future work. Our work could demonstrate the capability and reliability of the modified RELAP5 for the analysis of SFRs further.

Extending “Assessment of Tesla Turbine Performance” Model for Sensitivity-Focused Experimental Design

2017 ◽  
Vol 140 (3) ◽  
Author(s):  
Matthew J. Traum ◽  
Fatemeh Hadi ◽  
Muhammad K. Akbar
Keyword(s):  
Reynolds Number ◽  
Power Output ◽  
Performance Model ◽  
Nozzle Geometry ◽  
Design Parameters ◽  
Working Fluid ◽  
Extended Model ◽  
Number Range ◽  
Nozzle Height ◽  
Turbine Performance

The analytical model of Carey is extended and clarified for modeling Tesla turbine performance. The extended model retains differentiability, making it useful for rapid evaluation of engineering design decisions. Several clarifications are provided including a quantitative limitation on the model’s Reynolds number range; a derivation for output shaft torque and power that shows a match to the axial Euler Turbine Equation; eliminating the possibility of tangential disk velocity exceeding inlet working fluid velocity; and introducing a geometric nozzle height parameter. While nozzle geometry is limited to a slot providing identical flow velocity to each channel, variable nozzle height enables this velocity to be controlled by the turbine designer as the flow need not be choked. To illustrate the utility of this improvement, a numerical study of turbine performance with respect to variable nozzle height is provided. Since the extended model is differentiable, power sensitivity to design parameters can be quickly evaluated—a feature important when the main design goal is maximizing measurement sensitivity. The derivatives indicate two important results. First, the derivative of power with respect to Reynolds number for a turbine in the practical design range remains nearly constant over the whole laminar operating range. So, for a given working fluid mass flow rate, Tesla turbine power output is equally sensitive to variation in working fluid physical properties. Second, turbine power sensitivity increases as wetted disk area decreases; there is a design trade-off here between maximizing power output and maximizing power sensitivity.

A Numerical Investigation of Multi-Staged Tesla Valves

2013 ◽  
Author(s):  
Scott M. Thompson ◽  
D. Keith Walters ◽  
Basil J. Paudel ◽  
Tausif Jamal
Keyword(s):  
Reynolds Number ◽  
Numerical Simulations ◽  
Low Reynolds Number ◽  
Three Dimensional ◽  
Check Valve ◽  
Design Parameters ◽  
Optimized Design ◽  
Low Reynolds ◽  
The Individual ◽  
Tesla Valve

The Tesla valve is a passive-type check valve used for flow control/rectification in a variety of micro/mini-channel systems. Previous studies have focused on its optimal design and effectiveness (i.e. diodicity) for the low-Reynolds number regime (Re < 500). Using three-dimensional (3D) CFD, multiple, identically-shaped Tesla valves arranged in-series, i.e.: a Tesla “tree” or multi-staged Tesla valve (MSTV), were investigated. Fully-developed flow at the inlet and complete-laminar conditions throughout the entire valve structure were imposed on all numerical simulations. The number of Tesla valves, valve-to-valve distance and Reynolds number were varied to determine their effect on MSTV diodicity. The individual Tesla valves within each MSTV possessed pre-optimized design parameters as reported from the literature. Results clearly indicate that the MSTV can provide for a significantly higher diodicity than a single Tesla valve and that this MSTV diodicity increases with Reynolds number. Minimizing the distance between adjacent Tesla valves can significantly increase the MSTV diodicity and, for very low Reynolds number (Re < 50), the MSTV diodicity is near-independent of valve-to-valve distance and number of valves used. In general, more Tesla valves are required to maximize the MSTV diodicity as the Reynolds number increases. The current investigation also demonstrates that 3D numerical simulations more accurately predict the diodicity of a single Tesla valve over a wider range of Reynolds numbers.

The Effect of Design Parameters on the Performance of Flagellar Propeller at Low Reynolds Number

2011 ◽  
Author(s):  
Hyejin Jeon ◽  
Yoon-Cheol Kim ◽  
Eun Goh ◽  
Dongwook Yim ◽  
Songwan Jin ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Rotational Speed ◽  
Low Reynolds Number ◽  
Stereoscopic Particle Image Velocimetry ◽  
Macroscopic Model ◽  
Maximum Efficiency ◽  
Design Parameters ◽  
Working Fluid ◽  
Inertia Force ◽  
Low Reynolds

To drive a small object which swims in low Reynolds number situation, we need a new type of propeller which is optimized for low Reynolds number usage since the flow at low Reynolds numbers is dominated by viscous force instead of inertia force. Propeller in a shape of bacterial flagellum can be a strong candidate for propeller of small swimming object. In this paper, we visualized velocity field induced by flagellar shaped propeller using stereoscopic particle image velocimetry. We also have experimentally evaluated the effect of pitch and rotational speeds on the performance of flagellar shaped propeller inspired by flagellum of E.coli using macroscopic model. Silicone oil whose viscosity is 100 times larger than water is used as working fluid to make low Reynolds number situation using macroscopic model. Thrust, torque and velocity were measured as a function of pitch and rotational speed, and efficiency was calculated using measured results. We found that the maximum efficiency of flagellar propeller reaches where the pitch angle is about 40°. However, the effect of rotational speed on the efficiency is relatively smaller than that of pitch. And the flow pattern behind the rotating propeller was altered by pitch of the propeller.

scholarly journals Numerical Investigation of Thermal Hydraulic Performance of Printed Circuit Heat Exchanger of Periodic Diamond Channel Shape

2022 ◽  
Vol 961 (1) ◽  
pp. 012010
Author(s):  
Ali M Aljelawy ◽  
Amer M Aldabbagh ◽  
Falah F Hatem
Keyword(s):  
Reynolds Number ◽  
Heat Exchanger ◽  
Numerical Investigation ◽  
Hydraulic Performance ◽  
Operating Conditions ◽  
Design Parameters ◽  
Working Fluid ◽  
Channel Design ◽  
Printed Circuit ◽  
Pitch Length

Abstract One of the most recently important heat exchangers is the Printed circuit heat exchanger especially in the nuclear power plant and aerospace applications due to its very compact geometry and small print foot. This paper presents a 3D numerical investigation on the thermo-hydraulic performance of PCHE with new non-uniform channel design configuration. The new channel design is a rectangular cross section with repeated converging diverging sections or periodic diamond shape. The influence of three design parameters on the heat exchanger performance was studied and optimized, pitch length (p), length ratio (β) and the converging diverging angle (α). The computational models investigated in this study based on the operating conditions of the intermediate heat exchanger of very high temperature gas cooled reactor with helium as the working fluid under operating pressure of 3Mpa and inlet temperature of 800 K. The Reynolds number varied from 200 to 2000. Different Pitch lengths were used (1.59, 3.18, 6.36, and 12.73) mm, and different C-D angle (0, 4.5, 6, 7.5, 9, 10.5 and 12) and also different length ratios were used (0.2, 0.25 and 0.333). Three performance parameters were studied the Nusselt number, friction factor and the overall performance evaluation factor. Results show that the thermal performance enhanced with decreasing the pitch length and with increasing C-D angle and it was shown that this enhancement was found only at high Reynolds number above 1400. The best performance obtained at p=3.18, α=6 and β=0.25 based on the overall evaluation performance.

scholarly journals Analytical Velocity Study in a Conical Diffuser with Screw Tape Inserts

2018 ◽  
Vol 153 ◽  
pp. 06003
Author(s):  
Ehan Sabah Shukri
Keyword(s):  
Reynolds Number ◽  
Numerical Analysis ◽  
Boundary Conditions ◽  
Velocity Distribution ◽  
Numerical Simulations ◽  
Swirling Flow ◽  
Working Fluid ◽  
Aspect Ratios ◽  
Conical Diffuser ◽  
Better Than

A study is made to enhance the rate of velocity distribution in a conical diffuser. In this work, a numerical analysis on screw tape inserts in a conical diffuser is presented. In the numerical simulations, the swirling flow was introduced by using rectangular screw tape placed inside the inner test wall of the conical diffuser. Screw tape with different aspect ratios (AS) 2.5, 3.5, 4.5, 6.5 and 7.5 was analysed. The simulations were carried out with constant inlet condition considering the flow turbulent and incompressible with inlet Reynolds number 3.2 × 105. The simulations were performed using air as a working fluid. The results obtained from the conical diffuser with screw tape inserts are compared with those without screw tape (plain conical diffuser). On the basis of the same inlet boundary conditions for the screw tape in the conical diffuser and the plain conical diffuser, it was found that the velocity distribution performance of screw tape inserts with different AS is better than plain conical diffuser. It is also observed that the screw tape with AS 3.5 offered the best velocity distribution rate.

Turbulent Channel Flow with Spatially-Dependent Viscosity: A Numerical Study

2021 ◽  
Author(s):  
Victor Coppo Leite ◽  
Elia Merzari
Keyword(s):  
Reynolds Number ◽  
Channel Flow ◽  
Variable Viscosity ◽  
Numerical Study ◽  
Fluid Dynamic ◽  
National Laboratory ◽  
Argonne National Laboratory ◽  
Turbulent Channel Flow ◽  
Viscosity Change ◽  
Dependent Viscosity

Abstract In the present study, we examine in detail the effect of spatially dependent viscosity on wall-bounded flow. For this purpose, Direct Numerical Simulations (DNS) are performed considering a channel flow with a viscosity change along the streamwise direction. The DNS were performed using Nek5000, a computational fluid dynamic code developed at Argonne National Laboratory. The channel is divided in three different regions: in the first one, the flow is at a constant Reynolds number of Re = 5000; in the second region, the Reynolds number is imposed to linearly increase as viscosity decreases through a ramp; finally, in the third region the flow is again at a constant Reynolds number, this time at Re = 10000. Since the temperature field is not evaluated, the proposed set up is a simplification of a heated channel. Nevertheless, the outcomes of this study may be valuable for future works considering variable-viscosity effects, especially for cooling and heating applications. Four test cases with different ramp inclinations were analyzed. The results from the present study were compared with a correlation available in the literature for the friction Reynolds number as a function of the Reynolds number. We observe that in all cases the ramp does not cause an immediate change in the characteristics of turbulent structures and a delay is in fact observed in both wall shear and friction. Finally, in order to characterize and understand these effects, streaks from the viscous region and turbulence statistics for the turbulent kinetic energy budget terms are analyzed.

Electron and ion irradiation-induced dissolution of mechanical twins in the intermetalic U3Si: An in situ HVEM study

1989 ◽  
Vol 47 ◽  
pp. 652-653
Author(s):  
Charles W. Allen ◽  
Robert C. Birtcher
Keyword(s):  
Elevated Temperatures ◽  
Ion Irradiation ◽  
Ion Beam ◽  
National Laboratory ◽  
Argonne National Laboratory ◽  
Heavy Ion ◽  
High Energy ◽  
Mechanical Twinning ◽  
In Situ Experiments

The uranium silicides, including U3Si, are under study as candidate low enrichment nuclear fuels. Ion beam simulations of the in-reactor behavior of such materials are performed because a similar damage structure can be produced in hours by energetic heavy ions which requires years in actual reactor tests. This contribution treats one aspect of the microstructural behavior of U3Si under high energy electron irradiation and low dose energetic heavy ion irradiation and is based on in situ experiments, performed at the HVEM-Tandem User Facility at Argonne National Laboratory. This Facility interfaces a 2 MV Tandem ion accelerator and a 0.6 MV ion implanter to a 1.2 MeV AEI high voltage electron microscope, which allows a wide variety of in situ ion beam experiments to be performed with simultaneous irradiation and electron microscopy or diffraction.At elevated temperatures, U3Si exhibits the ordered AuCu3 structure. On cooling below 1058 K, the intermetallic transforms, evidently martensitically, to a body-centered tetragonal structure (alternatively, the structure may be described as face-centered tetragonal, which would be fcc except for a 1 pet tetragonal distortion). Mechanical twinning accompanies the transformation; however, diferences between electron diffraction patterns from twinned and non-twinned martensite plates could not be distinguished.

Environmental cell studies of deformation and fracture

1990 ◽  
Vol 48 (4) ◽  
pp. 516-517
Author(s):  
H. K. Birnbaum ◽  
I. M. Robertson
Keyword(s):  
National Laboratory ◽  
Argonne National Laboratory ◽  
Damage Threshold ◽  
Chromatic Aberration ◽  
Good Choice ◽  
Point Of View ◽  
Deformation And Fracture ◽  
Environmental Cell ◽  
Gas Molecules ◽  
The University

Studies of the effects of hydrogen environments on the deformation and fracture of fcc, bcc and hep metals and alloys have been carried out in a TEM environmental cell. The initial experiments were performed in the environmental cell of the HVEM facility at Argonne National Laboratory. More recently, a dedicated environmental cell facility has been constructed at the University of Illinois using a JEOL 4000EX and has been used for these studies. In the present paper we will describe the general design features of the JEOL environmental cell and some of the observations we have made on hydrogen effects on deformation and fracture.The JEOL environmental cell is designed to operate at 400 keV and below; in part because of the available accelerating voltage of the microscope and in part because the damage threshold of most materials is below 400 keV. The gas pressure at which chromatic aberration due to electron scattering from the gas molecules becomes excessive does not increase rapidly with with accelerating voltage making 400 keV a good choice from that point of view as well. A series of apertures were placed above and below the cell to control the pressures in various parts of the column.

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