Lattice Of Bundles Research Articles

Influence of Micro Ribs Segment on Quasi-periodic Large-scale Vortex Structure in 4 Rod Bundle Lattices

Rod bundle lattices play a crucial role in nuclear reactors, steam generators, and heat exchangers. The inclusion of quasi-periodic large-scale vortex structures (QLVS) can enhance flow mixing between the channels of the rod bundle and improve the lattice’s heat transfer capability. To study the impact of micro-rib segments on flow and heat transfer in the lattice, the Reynolds stress model (RSM) is utilized. Results reveal that the arrangement of micro-ribs on the rod bundle surface promotes the generation of QLVSs. These micro-rib segments modify the flow field within the lattice, thereby influencing the QLVS. The drag coefficient and heat transfer coefficient of the rod bundle lattice with micro-rib segments show a positive correlation with the length of these segments compared with the standard rod bundle lattice.

Quasi-periodic large-scale vortex structure in bod bundle lattice with micro ribs

Quasi-periodic large-scale vortex structure (QLVS) is highly accounted for the local flow and heat transfer and turbulent mixing in rod bundles. The vortex structures between rod bundles with different rib heights are analyzed, and the morphology of QLVS is clarified. The mechanism of the QLVS is studied from the perspective of hydrodynamics, and the formation and development process of the QLVS are analyzed in detail. Combined with the criterion of QLVS, the rotation, deformation and velocity changes of small disturbance are analyzed. With the increase of the height of the micro-rib, QLVS is introduced and gradually enhanced. The velocity gradient between different fluid layers is a key factor in the formation and development of QLVS structures. This research can provide theoretical support for the design and optimization of rod bundle lattices.

Research on coherent structure in 4-rod bundle lattice based on CFD

Coherent structures exist only when the ratio of pitch to rod diameter (P/D) in the rod bundle lattice is less than 1.1. In order to produce coherent structures in large P/D lattices, roughness elements are arranged on the outer surface of the rod bundle. This method can enhance the heat transfer capability of the rod bundle lattice. The whole process of the generation and development of coherent structures are analyzed. The Reynolds stress model (RSM) is used for the numerical calculation of the flow and heat transfer of the working fluid in a 4-rod bundle lattice with a P/D of 1.25. The whole process of the generation and development of the coherent structures in the 4-rod bundle lattice is shown. The influence of different micro-rib size (e) on the coherent structures and the flow and heat transfer of the rod bundle lattice is analyzed. The interaction between the fluid channels in the 4-rod bundle lattice is also analyzed. The results show that with the arrangement of the micro-ribs in the large P/D rod bundle lattice, coherent structures are produced, which enhances the flow mixing between the channels of the 4-rod bundle lattice. The flow and heat transfer characteristics of the rod bundle lattice have been greatly changed, especially when P/(D + 2e) = 1.02, the heat transfer capacity of the rod bundle lattice increases by 44.1% while the flow resistance increases by 3.4 times. This research can provide theoretical support for the design and improvement of reactor fuel elements, heat exchangers and steam generators.

Optimaizing nozzle position on an evaporator of absorbtion system cooling machine

This study examines the refrigerant jet spraying system that has been mounted on the absorption system cooling machine and is optimized using a CFD (Computer Fluid Dynamic). The study was conducted on an absorption system cooling machine that had been built using an arbsorber system in the form of a LiBr-H2O solution. As an efrigerant, water circulated in the tube bundle is used. Refrigran spray patterns greatly affect the performance of the cooling machine. The more evenly distributed refrigran beam in the space between the tube bundle lattice, the more effective the process of water cooling in the tube. The adjustment of the position of the nozzles and the evaporator grille is very influential in this refrigeration cycle. From the results of the initial conditions simulation of the placement of the nozzles with the arrangement of the tube bundle that there is fluid flow in the space between the lattice is not spread evenly. After being modified using the CFD software, an effective formation of tube bundle arrangement, evaporator lattice, and nozzle position is expected so that the refrigeration cycle is expected to go well.

The research on coherent structure in 7-rod bundle lattice

The generation and development of coherent structure in 7-rod bundle lattice are researched by Unsteady Reynolds-Averaged Navier-Stokes (URANS) method with the Reynolds Stress Model (RSM). The influence of the coherent structure on the flow resistance and heat transfer coefficient is also analyzed. It is revealed that the coherent structure is helpful to improve the performance of lattice. Decreasing the pitch-to-diameter (P/D) or properly changing the shape of rod can contribute to the generation of coherent structure. The flow redistribution caused by corner channel has great influence to the coherent structure.

Monte Carlo Few-Group Constant Generation for CANDU 6 Core Analysis

The current neutronics design methodology of CANDU-PHWRs based on the two-step calculations requires determining not only homogenized two-group constants for ordinary fuel bundle lattice cells by the WIMS-AECL lattice cell code but also incremental two-group constants arising from the penetration of control devices into the fuel bundle cells by a supercell analysis code like MULTICELL or DRAGON. As an alternative way to generate the two-group constants necessary for the CANDU-PHWR core analysis, this paper proposes utilizing a B1theory augmented Monte Carlo (MC) few-group constant generation method (B1MC method) which has been devised for the PWR fuel assembly analysis method. To examine the applicability of the B1MC method for the CANDU 6 core analysis, the fuel bundle cell and supercell calculations are performed using it to obtain the two-group constants. By showing that the two-group constants from the B1MC method agree well with those from WIMS-AECL and that core neutronics calculations for hypothetical CANDU 6 cores by a deterministic diffusion theory code SCAN with B1MC method generated two-group constants also agree well with whole core MC analyses, it is concluded that the B1MC method is well qualified for both fuel bundle cell and supercell analyses.

Order from Disorder: The Intrinsically Disordered Protein Tau Facilitates Higher-Order Assembly of Microtubules

Neurofibrillary tangles, the hallmark intracellular symptom of Alzheimer's disease, are aggregations of hyperphosphorylated tau. In its non-diseased state, the microtubule-associated protein tau, a neuronal polyampholyte, promotes assembly of microtubules and serves other critical cell functions. However, characterizing both diseased and non-diseased states have been difficult. Tau is an intrinsically disordered protein, precluding protein crystallography of its structure. Even studying the effects of tau on microtubules is complicated due to the dynamic instability, the cyclic growth and depolymerization of microtubules. While the drug taxol is often used to stabilize microtubules, there is burgeoning evidence that taxol affects microtubule structure and assembly (M.C. Choi et al., BioPhys J., 2009, 97, 519-527).Solution x-ray diffraction, optical microscopy, and EM were used to study the structure of microtubule/tau mixtures near physiological conditions. Surprisingly, in the presence of tau, the microtubules organized into an open bundled structure with a large microtubule-wall-to-wall spacing (approximately 20 to 40 nm), much larger than expected from polyampholyte theory. The bundle lattice parameter was modulated by differences in the projection domain, a little understood segment of tau that gives rise to the different N-termini of tau isoforms. To understand the functional structure of tau, constructs with deleted domains were created to see how specific regions (or lack thereof) affected the packing behavior of the microtubules. It was determined that certain regions of tau are not necessary for bundling (in conflict with existing models), but their presence might give insight into tau's physiological role in the neuron and how it might evolve into its diseased state.

A neutron balance approach in critical parameter determination

The determination of a critical parameter, process known also as criticality or eigenvalue search, is one of the major functionalities in neutronics codes. The determination of the critical boron concentration or the critical control rod position are two examples. Classical procedures used to solve this problem are based on the iterative Newton–Raphson method where the value of the parameter is changed until the eigenvalue matches the target. We present here a different approach where an equation, derived from the neutron balance, is set and the critical parameter is the unknown. Solving this equation is equivalent to solve an eigenvalue problem where the critical parameter is the eigenvalue. It is also shown that this approach can be seen as an application of inverse perturbation theory. This method reduces considerably the computation time in situations where changes on the critical parameter make a high distortion on the flux distribution, as it is the case of the control rods. Some numerical examples illustrate the performances and the gain in stability in cases of simultaneous control of criticality and axial offset of the power distribution. The application to the determination of the critical uranium enrichment in a transport code is also presented. The simplicity of the method makes its implementation in fuel bundle lattice and reactor codes very easy.

Reconstructing masks from markers in non-distributive lattices

In mathematical morphology for sets (binary images), the geodesic reconstruction associates to a set called mask and a subset of it called marker, the union of all connected components of the mask intersected by the marker. It is obtained by iteration of a geodesic dilation applied to the marker inside the mask. This operation extends naturally to numerical functions (grey-level images), where it allows us to reconstruct flat zones. Considering that the family of images constitutes a complete lattice under some partial order relation, a general theory of geodesic dilations and reconstructions in a complete lattice was given in Ronse and Serra [Fundam Inf 46(4):349–395, 2001]. It relies on the assumption that the lattice is infinitely supremum distributive, and it fails for pictorial objects forming a non-distributive lattice. In this paper we give a more general theory of geodesic operations, that can be applied to non-distributive lattices; it is compatible with the previous theory when the lattice is infinitely supremum distributive. We study one particular form of geodesic operator, the impulsive geodesic dilation, which gives good results for images with values in a bundle lattice (e.g., the lattice of labels and the reference lattice). We also briefly discuss geodesy on the lattice of partitions.

Fine modulations in the diffraction pattern of boron nitride nanotubes synthesised by non-ablative laser heating

Non-ablative laser heating has recently turned out to be an efficient synthesis method for boron nitride (BN) nanotubes, offering flexibility in the control of experimental parameters. Long tubes are obtained as a hairy growth on the target around laser impact. Tubes are mostly assembled in bundles and thin. Selected area diffraction diagrams reveal that zigzag and armchair helicities are dominant, without preference. A field emission gun enabled to resolve the fine modulations in the diffraction diagrams for multi-walled nanotubes (MWNT) and for bundles of MWNT. The interpretation of the diffraction pattern of nanotubes is generalised for such modulations, considering the analytical expression of the diffracted amplitude at each graphite reflection. The fine modulations in the pattern are linked to roll diameters, bundle lattice, and interlayer distances. Experimentally, several roll diameter modulations are observed. Unusual modulations corresponding to an interlayer distance of 2 layers are also observed. They show a two-roll period, with an alternative shift along tube axis, in the piling of the rolls of MWNT.

Adsorption of argon on carbon nanotube bundles and its influence on the bundle lattice parameter.

We report experimental studies of the adsorption characteristics and structure of both 36Ar and 40Ar on single-wall carbon nanotube bundles. The structural studies make use of the large difference in coherent neutron scattering cross section for the two Ar isotopes to explore the influence of the adsorbate on the nanotube lattice parameter. We observe no dilation of the nanotube lattice with 40Ar, and explain the apparent expansion of this lattice upon 36Ar adsorption by the location of the adsorbed Ar atoms on the outer bundle surface.

Diffraction by finite-size crystalline bundles of single wall nanotubes

We calculate the diffraction spectrum of finite-size crystalline bundles of single wall carbon nanotubes (SWNT). The general profile of the spectrum as well as the width and position of the (1 0) diffraction peaks of the 2-D lattice of bundles depend on the tubes symmetry, distribution of tubes diameters and diameter of the bundles. Consequently, any attempt to derive the mean-diameter of the tubes from a diffraction spectrum requires to consider the diameters distribution of the tubes and the size of the bundles. Experimental diffraction profiles of various single wall nanotubes samples are well fitted by the calculated spectra.