Wall Undulations Research Articles

Characteristics and Efficiency of Heat Transfer for Natural Convection by Ag-CuO/H2O Hybrid Nanofluid Inside a Square Cavity with Corrugated Walls

A parametric numerical study is conducted on laminar natural convection and heat transfer in a cavity with opposing undulated walls saturated with a hybrid Ag-CuO/water nanofluid. The two vertical walls of the sinusoidally undulated cavity are maintained at hot and cold temperatures, while the upper and lower walls are thermally insulated. The investigation examines the effects of relevant parameters such as the sinusoidally undulated geometry of the walls for different volumetric fractions of nanoparticles (0% ≤φ≤6%) and Rayleigh numbers (103 ≤ Ra ≤ 106) Thefinite-volumee discretization method is employed to solve the system of governing equations. The results indicate that an increase in the volumetric fraction of nanoparticles enhances the heat exchange rate in the cavity. Additionally, the Rayleigh number, with a significant increase in surface area, strongly influences the dominant heat transfer mode in the cavity. Furthermore, an increase in the number of wall undulations leads to a reduction in the heat transfer rate.

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Anatomy and morphology study of seeds for seven Lathyrus L., 1753 species in Iraq; the species were: L. annuus L.,1753, L. aphaca L., 1753, L. chloranthus Boiss., 1859, L. cicera L., 1753, L. sativus L., 1753, L. inconspicuus L., 1753 and L. sphaericus Retz.,1753. There are 17 species of the Fabaceae family that are distributed throughout the middle and northern regions of Iraq. Using a scanning electron microscope, the study's characteristics were examined to ascertain the taxonomic relationships, interactions, and issues that impeded the species' ability to be separated according to taxa. The seeds were glossy in all species except L. sativus L. and L. sphaericus L. which were matt, the surface cells wall undulation, the wax covered the peak of the conical papillae, the anatomical characteristics determined by cross section in seeds and pointed some trails such us ,Epidermis parenchyma thickness and Palisade, the species L. annus L. and L.aphaca L. were given the highest value of exocarps thickness (5.5) µm while the species L.sativus recorded the Lowest mean (3.8)µm, the seed coat in L. sativus L. is detached from some epidermis in some area with pit aperture, in according the epidermis thickness, the species classification to three groups the L. aphaca L. and L. sphericaus Retz. recorded the highest value (46-49) µm respectively, L. sphaericus Retz. recorded the highest value of palisade thickness which was 61 µm, some unique trails such us present the pit in exocarp, and the pit cavity was along parenchyma layer in L. sativus L., the similar morphology features are considered the evidence for the proximity of the taxa, so the internal structure (anatomy) of the seeds can be used to separate the taxa.

Magneto-nanofluidic thermal transport and irreversibility in semicircular systems with heated wavy bottom under constant fluid volume and cooling surface constraints

PurposeThis study aims to investigate the influence of wall curvature in a semicircular thermal annular system on magneto-nanofluidic flow, heat transfer and entropy generation. The analysis is conducted under constant cooling surface and fluid volume constraints.Design/methodology/approachThe mathematical equations describing the thermo-fluid flow in the semicircular system are solved using the finite element technique. Four different heating wall configurations are considered, varying the undulation numbers of the heated wall. Parametric variations of bottom wall undulation (f), buoyancy force characterized by the Rayleigh number (Ra), magnetic field strength represented by the Hartmann number (Ha) and inclination of the magnetic field (γ) on the overall thermal performance are studied extensively.FindingsThis study reveals that the fluid circulation strength is maximum in the case of a flat bottom wall. The analysis shows that the bottom wall contour and other control parameters significantly influence fluid flow, entropy production and heat transfer. The modified heated wall with a single undulation exhibits the highest entropy production and thermal convection, leading to a heat transfer enhancement of up to 21.85% compared to a flat bottom. The magnetic field intensity and orientation have a significant effect on heat transfer and irreversibility production.Research limitations/implicationsFurther research can explore a wider range of parameter values, alternative heating wall profiles and boundary conditions to expand the understanding of magneto-nanofluidic flow in semicircular thermal systems.Originality/valueThis study introduces a constraint-based analysis of magneto-nanofluidic thermal behavior in a complex semicircular thermal system, providing insights into the impact of wall curvature on heat transfer performance. The findings contribute to the design and optimization of thermal systems in various applications.

A novel strategy of enhanced thermal performance in air cooled lithium-ion battery by wavy walls

Electric vehicles (EVs) with rechargeable lithium-ion batteries are one of the most appealing choices for electrochemical energy storage to address global energy challenges and environmental concerns caused by rising carbon emissions. However, to maintain the performance and longevity of these high power batteries, a well-planned and effective cooling mechanism is required. Here, a novel air-based battery thermal management system (BTMS) is proposed to realize an improved cooling performance. We examined the thermal performance of an air-cooled lithium-ion battery pack of 3x5 Sony 18650 cells by introducing wavy (undulated) sidewalls for the discharge period of the cells. Influence of air inflow velocity (U0) and number of undulations on wavy wall have been delineated at a discharge rate of 2C and 3C. As obvious, the cooling improves with the increasing U0. Interestingly, a significant reduction (∼ 8-10 K) in the average and maximum cell temperature was seen simply by creating an optimal number of undulations on the walls as compared to the results obtained from straight walls. The highest cooling performance was observed when the undulations form a trough above the cells, however, the highest pressure drop was experienced in such cases. A trade-off between the cooling enhancement and power requirement (∼ pressure drop) has been presented by a performance plot. Finally, the efficacy of system was ensured by changing the number of rows and columns of the cell arrangement in the battery pack. An enhanced heat dissipation and thermal uniformity was seen in all the cases when wall undulations are present.

Nanofluid thermo-bio-convection in a horizontal porous wavy-walled annulus: Interaction of phototactic microorganisms and nanoparticles distribution

Transport phenomena related to thermo-bioconvection have recently emerged as an intriguing area of study because of their multi-physical applications such as bio-energy systems, food industries, solar collectors, pollutant dispersion in aquifers, biological wastes processing, chemical catalytic converters, geothermal energy usage, petroleum oil reservoirs, enhanced oil recovery, thermal energy storage, chemical processing equipment, fuel cell technology, medical application, microfluidic devices, and others. In this context, it is highly challenging to design and regulate a system with multi-physical transport in a complex geometry. The goal of the current study is to analyze the thermo-bioconvective heat transfer induced by a gradient of temperature and a motile of phototactic microorganisms with the presence of two types of nanoparticles inside a wavy-walled horizontal cylindrical porous annulus. The originality of this investigation is analyzing the influence of microorganisms, waviness parameters and hybrid nanofluid on thermo-convective instabilities. The effects of the wall waviness parameters, bioconvection Rayleigh number (Rab), thermal Rayleigh number (RaT), nanoparticles volume fraction ϕ and Lewis number (Le) on the flow structure, temperature, and isoconcentrations of microorganisms are investigated and explained in detail. The key findings showed that the Lewis number impacts the onset of thermo-convection and bioconvection and convection phenomena begins rapidly for small values of Lewis number. The nanoparticles enhance the heat transfer in case of thermo-bioconvective flow in a horizontal porous cylindrical system. The average Nusselt number Nu¯ decreases as the wall waviness parameters, amplitude λ, and undulation number η increase. It was also shown that thermo-convective instabilities may develop depending on thermal Rayleigh number, bioconvection Rayleigh number, nanoparticles volume fraction and wall waviness parameters.

Mixed convection within trapezoidal-wavy enclosure filled with nano-encapsulated phase change material: Effect of magnetohydrodynamics and wall waviness

The present work investigates the mixed convection of nano-encapsulated phase change material (NEPCM) inside a trapezoidal-wavy cavity subjected to a magnetic field. The mixed convection results from the movement of the upper lid of the cavity and the temperature difference between the inclined cold side walls and the hot bottom wavy wall. The main goal of this study is to address the impact of wall waviness and the magnetic field on mixed convection on a disclosure filled with NEPCM. The governing equations representing the investigated case were solved by Galerkin finite element method (GFEM). The influences of lid velocity (Re = 1–1000), bottom wall undulation number (N = 1–4), and magnetic field strength (Hartmann number (Ha) = 0–100) on the thermal behavior and the flow patterns were examined and reported. The results revealed that the mean Nusselt number is directly proportional to the lid velocity (Re), whereas it is reverse proportional to the bottom wavy undulation number (N) and the magnetic field strength (Ha). The higher values of Re (e.g., Re = 1000) could lead to a 300% enhancement in local Nu values compared to those of lower Re values (e.g., Re = 1). At Re = 1000, increasing Ha from 0 to 100 and N from 1 to 4 reduced the mean Nusselt number by 53% and 30%, respectively. According to the findings of the present study, it is recommended that heat transfer augmentation should eliminate both the waviness of the bottom wall and the magnetic field since they hinder the free and mixed convection flow.

A novel design of absorber surface of solar chimney power plant (SCPP): Thermal assessment, exergy and regression analysis

Clean and emission-free renewable energy production has attracted more demand. In this context, solar energy, being the most promising renewable energy source with low emission, is utilized for power generation such as solar chimney power plants (SCPP). The present work proposes a modification of the absorber surface with multiple triangular wavy peaks (n) at different amplitudes (h) and analyzes the performance of SCPP of the Manzaranes plant (utilizing velocity, temperature, pressure, different efficiencies, power output, and exergy). For this, a three-dimensional study is conducted by using ANSYS Fluent, RNG k-ε turbulent modeling, discrete ordinates (DO), and solar ray-tracing model. The study reveals the modified wavy ground absorber performs better than the traditional flat ground absorber. An increase in wavy wall amplitude enhances the power generation of SCPP markedly. Maximum gain in power generation and efficiency is noted for a single triangular wavy wall with higher amplitudes (58.61 % and ∼82.5 kW enhanced power and 61.83 % augmented efficiency). The exergy utilization efficiency of the collector rises with wall undulations (n); however, the exergy output drops with amplitude (h). Furthermore, through regression analyses, mathematical correlations are developed for major performance parameters. This novel concept may help the research community to establish a plant either in the hilly area or on any surface wavy nature to supply generated power for the remote area.

Numerical simulation for nanofluid forced/free convection in a partially heated parallelogram enclosure: Effects of wall undulation and inclined Lorentz forces

AbstractThe present study possesses the mathematical computational analysis for mixed convection nanofluid (CuO–water) flow in a lid‐driven parallelogram enclosure with corrugated walls. A partially heated source is located at the bottom corrugated wall. The remaining portions of upper and lower corrugated boundaries are adiabatic. The verticals walls are kept cold. The flow dynamic established with wall undulation and inclined Lorentz forces generate complex mathematical formulation via partial differential equations. Finite element method is implemented to get numerical interpretation of these equations. The simulation is performed against various emerging parameters and the outcomes in terms of isotherms, streamlines and line graphs. The results are recorded against various Richardson numbers , Hartman number , nanoparticles volume fraction , and amplitude of the corrugated horizontal walls . It is observed that against smaller Richardson number streamlines indicate forced convection flow while at higher Richardson number flow divert toward free convection regime. Additionally, heat transportation is maximum when magnetic field is applied in perpendicular direction as well as at maximum amplitude of wall undulations.

Complex neurocysticercosis lesions on imaging: Explained through correlative histomorphology.

Neurocysticercosis, the commonest neuro-parasite, sometimes presents as complex ring enhancing lesion causing diagnostic dilemma. We aim to establish radio-histo-morphological equivalents of early events in degeneration of the parasite to explain such imaging phenotypes. We compared patterns of degeneration in 23 randomly selected complex NCC on MRI with histo-morphology in 30 cysts obtained from an unrelated post mortem brain. The anatomy of the parasite and the degenerative patterns of the scolex (hydropic changes, calcification, evagination, and fragmentation) and the cyst wall (undulation, accessory loculi, and frank disruption) were well demonstrated on both. The intact scolex remarkably resembled head of intestinal Taenia. The complex lesions were conglomeration of multiple communicating cysts with a single parent cyst and multiple daughter cysts. The parent cysts contained a solitary variably degenerated scolex, had thicker walls and associated chronic inflammation. The remaining cysts of the lesion complex contained no scolex, had poorly organized walls, turbid contents, and florid perilesional enhancement with leakage of contrast. Three lesions assumed a multi-cystic pseudo-tumorous pattern, of which two resolved into solitary calcific remnants on follow up. Complex lesion in NCC result from degeneration of solitary parasite with perilesional gliosis, surrounded by multiple non-larval daughter cysts inciting acute intra and perilesional inflammation due to enhanced antigenic challenge. Possibly, attempted abortive asexual reproduction by the cellulose cyst as a preterminal event results in a "limited Racemose like transition." Correct interpretation has diagnostic and therapeutic implications as active lesions and their fibrocalcific residue may have greater epileptogenic potential.

Numerical simulation for mixed convection in a parallelogram enclosure: Magnetohydrodynamic (MHD) and moving wall-undulation effects

The investigation of the interaction between the wall driven fluid stream and the partially heated barriers is a filed of great interest for the researchers. The present analysis aims to evaluate free and forced convection in a corrugated-wall parallelogram cavity. A Heated source is located at the bottom of enclosure and the upper boundary maintained the mixed convection in the enclosure. Flow dynamics and thermal profiles are established with regard to magnetic field. The non-linear partial differential equation obtained from the mathematical interpretation of such complex physical system are solved numerically using finite element method. The outcomes of the simulation towards flow controlling parameters (Richardsonnumber0<Ri≤100,Hartmannnumber0≤Ha≤100,amplitude0.02≤Am≤1.00,magneticfieldinclination0≤φ≤π2) are presented in line graphs and contour maps. It is observed that forced convection dominates at low value of Richardson number and free convection dominates at larger values of Richardson number. Further, the results indicate that increasing wall undulation Am the velocity profile enhances the Nusselt number also possess higher values at maximum Am. It is also reported that heat the transfer rate has maximum behavior at large Ha and φ=π2.

Quantifying the effect of shade on cuticle morphology and carbon isotopes of sycamores: present and past.

PremiseReconstructing the light environment and architecture of the plant canopy from the fossil record requires the use of proxies, such as those derived from cell wall undulation, cell size, and carbon isotopes. All approaches assume that plant taxa will respond predictably to changes in light environments. However, most species‐level studies looking at cell wall undulation only consider “sun” or “shade” leaves; therefore, we need a fully quantitative taxon‐specific method.MethodsWe quantified the response of cell wall undulation, cell size, and carbon isotopes of Platanus occidentalis using two experimental setups: (1) two growth chambers at low and high light and (2) a series of outdoor growth experiments using green and black shade cloth at different densities. We then developed and applied a proxy for daily light integral (DLI) to fossil Platanites leaves from two early Paleocene floras from the San Juan Basin in New Mexico.ResultsAll traits responded to light environment. Cell wall undulation was the most useful trait for reconstructing DLI in the geological record. Median reconstructed DLI from early Paleocene leaves was ~44 mol m−2 d−1, with values from 28 to 54 mol m−2 d−1.ConclusionsCell wall undulation of P. occidentalis is a robust, quantifiable measurement of light environment that can be used to reconstruct the paleo‐light environment from fossil leaves. The distribution of high DLI values from fossil leaves may provide information on canopy architecture; indicating that either (1) most of the canopy mass is within the upper portion of the crown or (2) leaves exposed to more sunlight are preferentially preserved.

Magnetohydrodynamic thermal characteristics of water-based hybrid nanofluid-filled non-Darcian porous wavy enclosure: effect of undulation

PurposeThe aims of this study is to numerically investigate the thermal phenomena during magnetohydrodynamic (MHD) free convection in an oblique enclosure filled with porous media saturated with Cu–Al2O3/water hybrid nanofluid and heated at the left wavy wall. The thermophysical phenomena are explored thoroughly by varying the amplitude (λ) and undulation (n) of the wavy wall and the inclination of the enclosure (γ) along with other pertinent physical parameters. Darcy–Rayleigh number (Ram), Darcy number (Da), Hartmann number (Ha) and nanoparticle volumetric fraction (ϕ). The effect of all parameters has been analyzed and represented by using heatlines, isotherms, streamlines, average Nusselt number and local Nusselt number.Design/methodology/approachThe finite volume method is used to work out the transport equations coupled with velocity, pressure and temperature subjected to non-uniform staggered grid structure after grid-sensitivity analysis by an indigenous computing code and the semi-implicit method for pressure linked equations (SIMPLE) algorithm. The solution process is initiated following an iterative approach through the alternate direction implicit sweep technique and the tridiagonal matrix algorithm (TDMA) algorithm. The iterative process is continued until successive minimization of the residuals (<1e-8) for the governing equations.FindingsThis study reveals that the increase in the heating surface area does not always favor heat transfer. An increase in the undulation amplitude enhances the heat transfer; however, there is an optimum value of undulation of the wavy wall for this. The heat transfer enhancement because of the wall curvature is revealed at higher Ram, lower Da and Ha and lower volume fraction of nanoparticles. In general, this augmentation is optimum for four undulations of the wavy wall with an amplitude of λ = 0.3. The heat transfer enhancement can be more at the cavity inclination γ = 45°.Research limitations/implicationsThe technique of this investigation could be used in other multiphysical areas involving partial porous layers, conducting objects, different heating conditions, wall motion, etc.Practical implicationsThis study is to address MHD thermo-fluid phenomena of Cu–Al2O3/water-based hybrid nanofluid flow through a non-Darcian porous wavy cavity at different inclinations. The amplitude and number of undulations of the wavy wall, permeability of the porous medium, magnetic field intensity, nanoparticle volumetric fraction and inclinations of the enclosure play a significant role in the heat transfer process. This analysis and the findings of this work can be useful for the design and control of similar thermal systems/devices.Originality/valueMany researchers have examined the problem of buoyancy-induced free convection in a wavy-porous cavity packed with regular fluids or nanofluids. However, the effect of magnetic fields along with the amplitude (λ) at different undulations (n) of the heated wavy wall of an inclined enclosure is not attended so far to understand the transport mechanisms. Most often, the evolutions of the thermo-fluid phenomena in such complex geometries invoking different multiphysics are very intricate. Numerical implementations for simulations and subsequent post-processing of the results are also challenging.

Effects of experimental warming on Betula nana epidermal cell growth tested over its maximum climatological growth range.

Numerous long-term, free-air plant growth facilities currently explore vegetation responses to the ongoing climate change in northern latitudes. Open top chamber (OTC) experiments as well as the experimental set-ups with active warming focus on many facets of plant growth and performance, but information on morphological alterations of plant cells is still scarce. Here we compare the effects of in-situ warming on leaf epidermal cell expansion in dwarf birch, Betula nana in Finland, Greenland, and Poland. The localities of the three in-situ warming experiments represent contrasting regions of B. nana distribution, with the sites in Finland and Greenland representing the current main distribution in low and high Arctic, respectively, and the continental site in Poland as a B. nana relict Holocene microrefugium. We quantified the epidermal cell lateral expansion by microscopic analysis of B. nana leaf cuticles. The leaves were produced in paired experimental treatment plots with either artificial warming or ambient temperature. At all localities, the leaves were collected in two years at the end of the growing season to facilitate between-site and within-site comparison. The measured parameters included the epidermal cell area and circumference, and using these, the degree of cell wall undulation was calculated as an Undulation Index (UI). We found enhanced leaf epidermal cell expansion under experimental warming, except for the extremely low temperature Greenland site where no significant difference occurred between the treatments. These results demonstrate a strong response of leaf growth at individual cell level to growing season temperature, but also suggest that in harsh conditions other environmental factors may limit this response. Our results provide evidence of the relevance of climate warming for plant leaf maturation and underpin the importance of studies covering large geographical scales.

Natural convection inside a heat source embedded wavy porous cavity containing an insulated obstacle

In this finite element analysis of natural convection, cooling of a heat source embedded with a wavy porous cavity containing an insulated obstacle is investigated. A heat source is submitted to the left vertical wall, and the wavy right vertical wall is kept at fixed low temperature keeping top and bottom walls as insulated. The insulated obstacle which is placed inside the cavity is either square or circular in shape. The non-dimensional governing equations are solved by Galerkin finite element method and the results are presented in terms of streamlines and isotherms. The parameters considered for the investigation are Rayleigh-Darcy number ([Formula: see text]), amplitude of the wavy wall [Formula: see text], undulation of wavy wall per unit length ( N = 3) and shape of the obstacle. From the obtained results, mathematical correlations to calculate the maximum temperature of the heater and average Nusselt number with governing parameters are presented, and it is observed that the presence of a square insulated body reduces the convection process over a circular body; also, for a fixed Ra, the effect of obstacle at a particular portion of the cavity falls off with increment in a.

Latent Heat Phase Change Heat Transfer of a Nanoliquid with Nano–Encapsulated Phase Change Materials in a Wavy-Wall Enclosure with an Active Rotating Cylinder

A Nano-Encapsulated Phase-Change Material (NEPCM) suspension is made of nanoparticles containing a Phase Change Material in their core and dispersed in a fluid. These particles can contribute to thermal energy storage and heat transfer by their latent heat of phase change as moving with the host fluid. Thus, such novel nanoliquids are promising for applications in waste heat recovery and thermal energy storage systems. In the present research, the mixed convection of NEPCM suspensions was addressed in a wavy wall cavity containing a rotating solid cylinder. As the nanoparticles move with the liquid, they undergo a phase change and transfer the latent heat. The phase change of nanoparticles was considered as temperature-dependent heat capacity. The governing equations of mass, momentum, and energy conservation were presented as partial differential equations. Then, the governing equations were converted to a non-dimensional form to generalize the solution, and solved by the finite element method. The influence of control parameters such as volume concentration of nanoparticles, fusion temperature of nanoparticles, Stefan number, wall undulations number, and as well as the cylinder size, angular rotation, and thermal conductivities was addressed on the heat transfer in the enclosure. The wall undulation number induces a remarkable change in the Nusselt number. There are optimum fusion temperatures for nanoparticles, which could maximize the heat transfer rate. The increase of the latent heat of nanoparticles (a decline of Stefan number) boosts the heat transfer advantage of employing the phase change particles.

Seed morphology and testa ultrastructure in Alliumstipitatum complex (Amaryllidaceae; Allioideae) and their systematic significance

Characteristic features of seed and testa cells in 13 species of Allium, representing its five recognized sections, Compactoprason, Megaloprason, Procerallium, Decipientia and Pseudoprason were studied using both stereomicroscope and scanning electron microscope. The identified characters, such as seed shape, alignment and shape of testa cells, features of outer cell walls, verruca type, density of verrucae and granules, seed size as well as cell wall undulations were evaluated statistically. The our findings indicated the significance level of P ? 0.01 for examined characters using the Kruskal-Wallis and ANOVA analyses.Two principal components of factor analysis revealed the following traits to be most important in distinguishing taxa at various taxonomic ranks within the complex (sections, subsections and species), based on 50.94% of total variance and a correlation coefficient of 0.93: shape and sculpturing of periclinal walls, undulation details of anticlinal walls, verruca type, testa cell alignment, and size of seed and testa cells. The general pattern of testa shared by all taxa of studied complex included convex periclinal walls with verrucate surface and undulated anticlinal walls from S- to U-like, but some taxa differed from each other in the details of testa sculpturing. Exceptionally, the monotypic section, Decipientia revealed adifferent pattern, showing smooth seed surface composed of polygonal testa cells with tightarrangement, flat periclinal surfacebearingsulcate verrucae, and straight anticlinal walls.

Leaf anatomical variation in Desmos Lour. and Dasymaschalon (Hook. f. &amp; Thomson) Dalla Torre &amp; Harms species (Annonaceae)

Abstract. Nikmah IA, Rugayah R, Chikmawati T. 2020. Leaf anatomical variation in Desmos Lour. and Dasymaschalon (Hook. f. &amp; Thomson) Dalla Torre &amp; Harms species (Annonaceae). Biodiversitas 21: 3317-3330. The relationships between Desmos and Dasymaschalon are debated for along time. Those two genera have high morphological similarities, especially in their generative character (moniliform monocarps). Therefore, sterile specimens of Desmos are difficult to be distinguished from Dasymaschalon. Leaf anatomy in paradermal section of 20 taxa (12 species of Desmos, eight species of Dasymaschalon) have been carried out. The data were used to support the interspecific and intergeneric delimitation of Desmos and Dasymaschalon. Desmos and Dasymaschalon are two distinct genera mainly distinguished based on the anticlinal wall undulation of epidermal cells and supported by variation of the crystal type, and size. The anticlinal wall undulation of Desmos is almost straight to slightly wavy, and never sinuous, meanwhile, Dasymaschalon varies from almost straight to deeply sinusoid. The crystals of Desmos consist of rhombohedric, druse type A, and druse type B crystals, whereas Dasymaschalon has prism, druse type A, druse type B, and drue type C crystals.

Effects of undulated wall on the hydrodynamic and thermal transport characteristics of turbulent jet

The present study investigates numerically the effect of wall undulation on the thermo-hydraulic transport characteristics of turbulent jet. In order to explore the influence of position of the nozzle exit from the wall, both wall jet and offset jet are considered. The theoretical model is numerically solved using shear stress transport (SST) model to predict the effects of height of undulation of the wall and the offset jet ratio on the re-attachment length, the velocity profile at different downstream locations, the coefficient of friction and the Nusselt number. The results indicate that the undulation of wall has a strong influence in altering the friction coefficient, Nusselt number and re-attachment length for offset jet. It further reveals that there is an intricate interplay between undulation height and offset ratio in dictating the flow and heat transfer characteristics.

Thermal design optimization of passive cooling capability in a dry-storage system by adding wall undulations or semi-circular fins

Thermal design investigation of a novel liner inner wall surface geometry alteration of a ventilated concrete cask used for spent nuclear fuel storage is carried out through three-dimensional Computational Fluid Dynamics (CFD) simulations. The present study reveals that the new proposal returns values for the convective heat transfer coefficient that are almost three orders of magnitude higher than the base case. Hence, proving that even making such a rather simple alterations to the smooth walls geometry, i.e. adding undulations or semi-circular fins, can result in a significant convective heat transfer enhancement, therefore, further reducing the risks of structural damages caused by the dry-storage system overheating. Before conducting the design optimization study mentioned above, two validation test cases have been considered in order to examine the Reynolds Averaged Navier-Stokes (RANS) models’ capability to predict the flow under buoyancy driven and low turbulence levels such is the case in the passively cooled dry cask system. The test cases considered in the validation study sections are the experimental measurements of Betts and Bokhari for turbulent natural convection in an enclosed tall cavity and the temperature measurements in concrete-shielded spent fuel storage cask system reported by McKinnon. The models selected for the validation study are namely the k-ω SST model, the v2-f model, the low-Reynolds k-ε model, and the recently formulated elliptic blending k-ε model. It has been found that out of these models, the low-Reynolds k-ε model was found to provide a good combination in returning both; physically realistic and conservative solution. The present validation using well-resolved RANS simulations has shown that a more quantitative and detailed comparison of the predictions is required in order to clearly highlight the discrepancies between the models’ predictions in terms of velocity, turbulent kinetic energy and, in particular, convective heat transfer coefficient profiles. The commonly adopted methodology in limiting the validation process to temperature profiles comparison only, would cover up these differences as the temperature variation is affected by the combined effects of the convective and the radiation heat transfer modes.

Shear stress in the microvasculature: influence of red blood cell morphology and endothelial wall undulation.

The effect of red blood cells and the undulation of the endothelium on the shear stress in the microvasculature is studied numerically using the lattice Boltzmann-immersed boundary method. The results demonstrate a significant effect of both the undulation of the endothelium and red blood cells on wall shear stress. Our results also reveal that morphological alterations of red blood cells, as occur in certain pathologies, can significantly affect the values of wall shear stress. The resulting fluctuations in wall shear stress greatly exceed the nominal values, emphasizing the importance of the particulate nature of blood as well as a more realistic description of vessel wall geometry in the study of hemodynamic forces. We find that within the channel widths investigated, which correspond to those found in the microvasculature, the inverse minimum distance normalized to the channel width between the red blood cell and the wall is predictive of the maximum wall shear stress observed in straight channels with a flowing red blood cell. We find that the maximum wall shear stress varies several factors more over a range of capillary numbers (dimensionless number relating strength of flow to membrane elasticity) and reduced areas (measure of deflation of the red blood cell) than the minimum wall shear stress. We see that waviness reduces variation in minimum and maximum shear stresses among different capillary and reduced areas.