Convection Field Research Articles

Shape optimization considering a rotational body in a unsteady heat convection field

Shape optimization considering a rotational body in a unsteady heat convection field

Diurnal Cycle of Raindrops Size Distribution in a Valley of the Peruvian Central Andes

In the Central Andes of Peru, convective and stratiform rainfall occurs, frequently associated with convective storms. The raindrop size distributions (RSD), measured by a Parsivel-2 optical disdrometer, were characterized by the variation of their normalized parameters. The RSD dataset includes measurements corresponding to 18 months between 2017 and 2019. As a result, it was found that the mass-weighted mean diameter Dm and the Nw parameter present respectively high and low values, in the interval of 15–20 LST (local standard time), wherein deeper and more active clouds appear. The events including convective rainfall contribute 67.5% of the accumulated total, wherein 92% corresponds to the 15–20 LST interval. It is concluded that the spectral variability of the RSD is strongly controlled by the cloudiness configuration field developing over the west (convection over highlands) and east (convection over Amazon) sides of the valley. In the afternoon, clouds develop and drift to the east, over the Andean valleys and towards the Amazon, intensified by local orographic circulation. The opposite happens at night, when the stratiform rainfall is dominant and it is controlled by clouds, located in the Inter-Andean valley, generated by the convection fields formed over the Amazon forest.

ANALISIS KUALITAS PRODUK KONVEKSI BERUPA SERAGAM SEKOLAH DENGAN MENGGUNAKAN METODE SIX SIGMA DI TEMPAT PRAKTIK KETERAMPILAN USAHA (TPKU) BIDANG KONVEKSI TEBUIRENG

The rapid rate of growth of technology and information in the modern era today, encourages companies to further develop their thoughts and views to maximize the goals and objectives set. The Place to Practice Business Skills (TPKU), is a business engaged in the field of convection managed by Tebuireng Boarding School. One of the most widely used convection products is the school uniform. In producing school uniforms, convection also strives to continuously improve quality by pressing the number of defects in the product. Some things that need to be done are identifying the factors that cause disability using the Six Sigma method, calculate the quality of sigma, and propose appropriate actions to control the quality of school uniforms. Six sigma is a tool of quality improvement toward the 3,4 target of failure per a million opportunities for each production. So six sigma is one of the new methods in the field of quality management aimed at quality control and improvement. By using the six sigma method, it can be seen that there are seven types of defects (CTQ) that occur in school uniform products. The two most common types of defects are: seams that are not tidy with a percentage of 51.1% and stain on uniform of 28.4%. For the quality of school uniforms produced by Tebuireng Convection is still low ie 2.95 sigma with a product defect rate as much 74830 products in one million products (DPMO). From the application of these six sigma, it can be concluded that the proposed action to be done convection to reduce the level of product defects is to focus its supervision on improving employee performance, engine performance, applicable work standards, existing facilities and infrastructure, provide motivation to work, and improve time management well.

A stabilized finite element method for inverse problems subject to the convection\u2013diffusion equation. I: diffusion-dominated regime

The numerical approximation of an inverse problem subject to the convection–diffusion equation when diffusion dominates is studied. We derive Carleman estimates that are of a form suitable for use in numerical analysis and with explicit dependence on the Péclet number. A stabilized finite element method is then proposed and analysed. An upper bound on the condition number is first derived. Combining the stability estimates on the continuous problem with the numerical stability of the method, we then obtain error estimates in local H^1- or L^2-norms that are optimal with respect to the approximation order, the problem’s stability and perturbations in data. The convergence order is the same for both norms, but the H^1-estimate requires an additional divergence assumption for the convective field. The theory is illustrated in some computational examples.

Lightning NOx Production in the Tropics as Determined Using OMI NO2 Retrievals and WWLLN Stroke Data

AbstractNitrogen oxide (NOx) production by lightning in the tropics is estimated using tropospheric NOx amounts (LNOx*) over deep convective grid boxes derived from Ozone Monitoring Instrument (OMI) nitrogen dioxide (NO2) slant columns and detection‐efficiency–adjusted World Wide Lightning Location Network (WWLLN) flashes. The lightning NOx production efficiency (LNOx PE) in the tropics is determined for the austral and boreal summers of 2007 to 2011 by regressing regional mean daily values of LNOx* for individual seasons against daily flash totals during flash windows prior to the OMI overpass. LNOx PE is determined to be approximately two times larger over marine locations than over continental locations possibly because marine flashes are more energetic. Overall, the mean LNOx PE for the tropics is calculated to be 170 ± 100 mol per flash with values over the tropical Pacific (low flash rate region) being largest. The main contributors to uncertainties in PE are uncertainties in WWLLN flash detection efficiency, upper tropospheric NOx lifetime in the near field of convection, and air mass factor biases.

Three Different Episodes of Prompt Equatorial Electric Field Perturbations Under Steady Southward IMF Bz During St. Patrick's Day Storm

AbstractThree different episodes of prompt penetration electric field (PPEF) disturbances are observed during the main phase of the St. Patrick's Day storm on 17 March 2015 under steady southward interplanetary magnetic field (IMF) Bz conditions unlike the conventional PPEF associated with southward or northward turnings of IMF Bz. These PPEF events took place during the period when strong disturbance dynamo fields are prevailing in the background. The first event is triggered by a solar wind dynamic pressure pulse that caused a sharp eastward PPEF and strong enhancement of equatorial electrojet current in Brazilian dayside. The second event caused another short but strong westward PPEF on dayside due to the reversal of IMF By from duskward to dawnward under steady IMF Bz. The third event caused a longer eastward PPEF in association with a solar wind dynamic pressure pulse followed by the onset of a substorm, which has led to strong enhancement of equatorial electrojet, quick rejuvenation and symmetric redistribution of equatorial ionization anomaly in the Brazilian sector. The signatures of the PPEF with opposite polarity and smaller magnitudes are also observed in the Asian sector on the nightside. The possible mechanisms for the observed PPEF events under steady IMF Bz are discussed in terms of changes in the high‐latitude field‐aligned currents and reconfiguration of high‐latitude convection fields using Active Magnetosphere and Planetary Electrodynamics Response Experiment and Super Dual Auroral Radar Network high‐frequency radar observations.

Influence of conjugate convective heat transfer on temperature fields in thin walls that organize liquid layers of various orientations

Numerical studies of unsteady conjugate natural convective heat transfer in the model of a thin-walled fuel tank are carried out in the conjugate formulation. The fields of temperature in liquid and in solid walls of the tank are calculated. The evolution of convective flows and temperature fields after a sudden supply of heat to the base of the tank is investigated. Flat layers of liquid enclosed between flat walls of different orientations with inclination angles of 0, 30, 45, 60 and 90 degrees are considered. With the angle of inclination of 0 degrees the outer surface of the side walls is insulated. The outer surface of the lower wall heats up suddenly, the outer surface of the upper wall is isothermally cold. The system of equations of thermogravitation convection in the Boussinesq approximation in dimensionless form, written in terms of temperature, vector potential of the velocity field and velocity vortex, is solved. It is shown that an inhomogeneous temperature field is formed inside the solid walls of the finite thermal conductivity. The thermal conductivity of walls and conditions at the upper boundary of the liquid layer affect significantly the spatial form of convective fuel flows in fuel tanks and laws of conjugated natural convective heat exchange.

Growth of III-V semiconductor crystals under microgravity

The low-gravity environment aboard the space provides a unique platform for both understanding the crystal-growth-related phenomena that are masked by gravity on the earth and exploring new crystal growth techniques. III-V semiconductor crystal growths were carried out under microgravity and the main results include: device-grade semi-insulating GaAs single crystal with improved stoichiometry was grown under microgravity condition, and low noise field-effect transistors and analog switch integrated circuits were fabricated and the performances were better than their terrestrial counterparts; detached Bridgman growth was realized in two model systems of GaSb and InSb by suppressing the hydrostatic pressure of melt, and largely reduced dislocation densities in the materials were observed; the contributions of buoyancy-driven convection, Marangoni convection and rotation magnetic field forced convection on the microscopic segregation were carefully studied; the vertical gradient freezing method was employed to grow semiconductor alloys and chemically homogeneous GaInSb crystal was obtained. In this review, the main progresses in these aspects are summarized and the future challenges are discussed.

Perluasan Pangsa Pasar dan Peningkatan Pendapatan Mina Collection kudus Melalui Online Marketing

Online Marketing is a marketing system that uses internet media as a vehicle for product marketing, a company or an effort to offer new products or to gather information from customers about the results of the products produced requires various forms of marketing. One of them can be by utilizing online marketing for media promotion and marketing of products produced effectively and efficiently. Mina Collection Kudus is a UKM engaged in the field of convection that produces products in the form of fashion. During this time in the promotion and marketing of the resulting product is still done manually only by way of going in and out of the market to offer products and depositing goods as requested. So that the promotion and marketing carried out only in certain areas alone can not reach a wider and broader area coverage, the lack of breadth of the scope of the promotion and marketing carried out causes the income obtained is also less than the maximum. The Muria Kudus University dedication team helps in developing the Online Marketing System at the Holy Mina Collection so that it can expand its Market Share and increase revenue effectively and efficiently.

Three-dimensional analysis of magnetohydrodynamic transverse mixed convection of nanofluid inside a lid-driven enclosure using MRT-LBM

In the current study, an in-house parallel multi-relaxation time lattice Boltzmann method (MRT-LBM) code is developed to resolve and investigate the mixed convection magneto-hydrodynamic (MHD) Cu-water nanofluid flow inside a three-dimensional enclosure with lid-driven walls. The lid-driven walls are moving in different directions with various velocities to form 3D mixed convection (including natural caused by temperature difference and forced convection effects) with a complex mixing within the enclosure. In addition, the magnetic body force effects on the 3D mixed convection flow are observed in terms of the heat transfer and flow characteristics. Accordingly, the complex mixing of flow and heat transfer due to natural convection, moving wall and magnetic field effects is investigated in 3D. In order to scrutinize these three forces effects on the flow characteristics and heat transfer, results are presented and analyzed for various moving wall directions, nanoparticle concentrations (0, 0.2, 0.4, 0.6), Richardson numbers (0.5, 1, 5), Rayleigh numbers (103, 104, 105) and Hartmann numbers (20, 40). It has been shown that the transverse and opposed mixed convection modes have significant negative impacts on the heat transfer. While, the concurrent mixed convection mode remarkably improves the heat transfer. Moreover, the 3D mixing of the transverse mixed convection mode is better than the other cases. Also, though the magnetic field has an undesirable impact on Nusselt, especially in high Ha numbers, but, aligning the MHD force direction and the natural convection circulation plane alleviates this negative impact and makes it ignorable. A comprehensive comparison is made between different cases, and in some situations 30% reduction in heat transfer is observed in comparison with the best case.

The impact of the Marangoni convection and magnetic field versus blood-based carbon nanotube nanofluids

The mutual result of the magnetic field and Marangoni convection against the thin liquid film of Casson fluid, blood-based carbon nanotube nanofluid has been fruitfully discussed in this article. The influence of various model constraints is focused on velocity, heat transfer, pressure distribution, skin friction and Nusselt number through graphical illustration. In addition, we witness that the thermal field of liquid raises with the growing value of [Formula: see text] and this upsurge is more in single-walled carbon nanotubes and is more dominant than multi-walled carbon nanotubes. The controlling approach of the homotopy analysis method has been used for velocity and temperature distribution. For authentication, the achieved results have been associated with the numerical (ND-Solve) method and displayed. This investigation shows that the velocity profile in the case of Casson fluid single-walled carbon nanotube–blood nanofluid is comparatively less affected and the temperature field of single-walled carbon nanotube–blood nanofluid dominates multi-walled carbon nanotube–blood nanofluid.

Global, nonparametric, noniterative optimization of time-averaged quantities under small, time-varying forcing: An application to a thermal convection field

This study demonstrates a global, nonparametric, noniterative optimization of time-mean value of a kind of index vibrated by time-varying forcing. It is based on the fact that the (steady) forced vibration of nonautonomous ordinary differential equation systems is well approximated by an analytical solution when the amplitude of forcing is sufficiently small and its base state without forcing is linearly stable and steady. It is applied to optimize a time-averaged heat-transfer rate on a two-dimensional thermal convection field in a square cavity with horizontal temperature difference, and the globally optimal way of vibrational forcing, i.e. the globally optimal, spatial distribution of vibrational heat and vorticity sources, is first obtained. The maximized vibrational thermal convection corresponds well to the state of internal gravity wave resonance. In contrast, the minimized thermal convection is weak, keeping the boundary layers on both sidewalls thick.

Influence of melt convection on the morphological evolution of seaweed structures: Insights from phase-field simulations

In the present study, the morphological evolution of instabilities in a binary polycrystalline alloy is investigated under the influence of melt convection through phase-field simulations. In the absence of interfacial anisotropy, a grain boundary initiates and amplifies a convex ridge, which sequentially undergoes splitting and generates a random fork like pattern in a supersaturated melt, namely seaweed. Categorized as regimes I and II, degenerate and strongly tilted seaweeds are the two distinguishable structures observed at low and high flow velocities, respectively. In the presence of weak convection fields, the solidification of individual crystallites is driven by the proportional and sideward amplification of the tips across the domain. In regime II, the combined influence of convection and solutal gradients at the grain boundary strikingly generates an oriented pattern. The role of surface energies on the development of perturbations across the two solid grains is studied via comparing the microstructures. For different velocities, we observe that the growth of tip splitting branches along a solidifying interface is restricted with the decrease in the grain boundary energy and the relative grain boundary groove angle. Furthermore, a quantitative image analysis is performed for all the microstructures to study the relation between the local orientation and the liquid phase convection. Symmetric and skewed nature of the distributions demonstrate the preferred local tilt angles for the structures in regimes I and II, respectively. Besides, a power law for the tip splitting frequency f∝Re-0.02 is also established. This relation is consistent with seaweed morphologies, attributed by frequent and inhibited splitting events at various Reynolds numbers.

Deformation of Ionospheric Potential Pattern by Ionospheric Hall Polarization

AbstractThe present study shows that the ionospheric Hall polarization can deform the high‐latitude ionospheric convection field, which is widely considered to be a manifestation of the convection field in the magnetosphere. We perform the Hall polarization field separation with a potential solver by changing the conductance distribution step by step from a uniform one to a more realistic one. We adopt dawn‐dusk and north‐south symmetric distributions of conductance and region 1 (R1) field‐aligned current (FAC). The pair of the primary field of the R1 system and each gradient of off‐diagonal component of conductance tensor (Hall conductance) generates the Hall polarization field and consequently causes potential deformations as follows. (a) The equatorward gradient causes clockwise rotation. (b) The gradient across the terminator, together with the effect of the equatorward gradient, causes the dawn‐dusk asymmetry. (c) The high conductance band in the auroral region causes kink‐type deformations. In particular, a nested structure at the equatorward edge of the band in the midnight sector well resembles the Harang Reversal. Result (a) can explain the clockwise bias inexplicable by the IMF‐By effect alone, the combination of (a) and (b) can explain the clearness and unclearness in the round or crescent shapes of the dawn‐dusk cells depending on the IMF‐By polarity, and (c) suggests that the ionosphere may not need the upward‐FAC for the formation of the Harang Reversal. We suggest that the final structure of the ionospheric potential is established by the combined effects of the magnetospheric requirements (external causes) and ionospheric polarization (internal effect).

CFD Simulation of Convective Heat Transfer on Vernacular Sustainable Architecture: Validation and Application of Methodology

The global background of energy shortages and climate deterioration demands bioclimatic sustainable buildings. Vernacular architecture can provide a useful resource of passive strategies and techniques for creating inner comfort conditions with minimum heating, ventilation, and air conditioning (HVAC) assistance. The identification and verification of such knowledge are essential for climate responsive or energy passive building design. Among the methods, computational fluid dynamics (CFD) is a useful tool for simulating convective heat transfer of vernacular architecture and predicting the convective heat transfer coefficient (CHTC) and flow field. Geometric complexity and diversity of building samples are crucial in the development of an effective simulation methodology in terms of computational cost and accuracy. Therefore, this paper presents high-resolution 3D steady Reynolds-averaged Navier–Stokes (RANS) CFD simulations of convective heat transfer on Japanese vernacular architecture, namely, “machiya.” A CFD validation study on the CHTC is performed based on wind-tunnel experiments on a cube heated by constant heat flux and placed in a turbulent channel flow with a Reynolds number of 3.3 × 104. Three steady RANS models and two boundary layer modeling approaches are compared and discussed. Results show that the SST k-ω model applied with low Reynolds number modeling approach is suitable for CHTC simulations on a simplified building model. The RNG k-ε model applied with wall functions is an appropriate choice for simulating flow field of a complicated building model. Overall, this study develops a methodology involving RANS model selection, boundary layer modeling, and target model fitting to predict the convective heat transfer on vernacular architecture.

On the unsteady Darcy–Forchheimer–Brinkman equation in local and nonlocal tumor growth models

A mathematical analysis of local and nonlocal phase-field models of tumor growth is presented that includes time-dependent Darcy–Forchheimer–Brinkman models of convective velocity fields and models of long-range cell interactions. A complete existence analysis is provided. In addition, a parameter-sensitivity analysis is described that quantifies the sensitivity of key quantities of interest to changes in parameter values. Two sensitivity analyses are examined; one employing statistical variances of model outputs and another employing the notion of active subspaces based on existing observational data. Remarkably, the two approaches yield very similar conclusions on sensitivity for certain quantities of interest. The work concludes with the presentation of numerical approximations of solutions of the governing equations and results of numerical experiments on tumor growth produced using finite element discretizations of the full tumor model for representative cases.

Effect of Uniform Magnetic Field on Melting at Various Rayleigh Numbers

Melting phenomena occurs in various industrial applications, such as metal castings of turbine blades, environmental engineering, PCM-based thermal storage devices, etc. During the design of these devices, they are designed for efficient heat transfer rate. To improve the heat transfer rate, understanding of the important flow processes during the melting (and solidification) is necessary. An objective of the present work is to study the effect of natural convection and magnetic field on interface morphology and thereby on melting rate. In this work, therefore, an effect of uniform transverse magnetic field on the melting inside a cavity, filled initially with solid gallium, at various Rayleigh numbers (Ra=3×105, 6×105, and 9×105) is presented. A 2D unsteady numerical simulation, with the enthalpy-porosity formulation, is performed using ANSYS-Fluent. The magnetic field is characterized by the Hartmann number (Ha) and the results are shown for the Ha = 0, 30 and 50. The horizontal walls of the cavity are considered insulated and vertical walls are respectively considered hot and cold. It is observed that the role of natural convection during the melting is significant on the temperature distribution and solid-liquid interface. The increased magnetic field (Ha = 30 and 50) found to have a suppressing effect on the dominance of natural convection at all Rayleigh numbers (Ra=3×105, 6×105, and 9×105).

Experimental study of heat transfer performance of compact wavy channel with nanofluids as the coolant medium: Real time non-intrusive measurements

Heat transfer performance of nanofluids in the context of corrugated compact channels has been experimentally investigated through real-time, non-intrusive diagnostic technique. The corrugated channel (dimensions: 50 mm (length) × 10 mm (width) × 4 mm (depth); hydraulic diameter of 5.7 mm) comprises of two horizontal wavy plates aligned in an in-phase configuration. Amplitude and period of the wavy plates have been kept constant. Experiments have been performed with varying concentrations of Al2O3/water-based nanofluids for Re = 350–1000. For reference, experiments have also been conducted using water as the base fluid and a plane channel with the same hydraulic diameter as that of the corrugated channel. Convective field has been mapped using a Mach-Zehnder interferometer. Results have been qualitatively as well as quantitatively interpreted to characterize the heat transfer performance of nanofluids as the coolant medium. Interferograms recorded under infinite fringe setting mode captured the phenomena of flow detachment and re-attachment at the wavy sections of the corrugated channel and their dependence on nanofluids concentration. Thermal boundary layer profiles at such sections are seen to be locally perturbed due to flow detachment and its subsequent attachment to the principal wall of the channel. Quantitative data retrieved through the wedge fringe setting interferograms revealed a clear enhancement in heat transfer coefficient for the combination of nanofluids and corrugated channel in comparison with that achieved through water in the plane and/or corrugated channel. For any given Re and channel configuration, the heat transfer coefficient is seen to increase with increasing concentration of dilute nanofluids. For the wavy channel, an enhancement of ≈37% in heat transfer rates with 0.02% volume concentration of nanofluids is achieved at Re = 350 in comparison to the plane channel at the similar levels of nanoparticles volume concentration.

Active acoustic cloaking in a convected flow field.

Acoustic cloaking has mostly been considered within a stationary fluid. The authors herein show that accounting for the effects of convection in the presence of fluid flow is critical for cloaking in the acoustic domain. This work presents active acoustic cloaking in a convected flow field for two different incident fields, corresponding to a plane wave and a single monopole source, impinging on a rigid body. Monopole control sources circumferentially arranged around the rigid body are used to generate a secondary acoustic field to destructively interfere with the primary scattered field arising from the incident excitation cases. The authors show that for sound waves in a moving fluid, active cloaking can only be achieved using a convected cloak, which is dependent on Mach number.

TIV and PIV based natural convection study over a square flat plate under stable stratification

Natural convection over an isolated horizontal plate in a stably stratified background condition is fundamental and challenging in industrial, atmospheric, geographical, and oceanic environmental studies, which, however, is still lack of investigation. In this study, the water tank modelling experiment with two main techniques, Thermal Image Velocimetry (TIV) and Particle Image Velocimetry (PIV), was conducted to investigate large eddy structures, the mean velocity field and heat transfer over an idealized square heated surface under the stable stratification. Shirking, growing and twisting eddy structures were identified in this study. By measuring the velocity fields at different horizontal planes with varied heights, an asymmetric flow structure over a square urban area is suggested by the PIV method to be characterized as the main diagonal inflow at lower levels and as the side outflow (perpendicular to edges) at upper levels. The mean flow speeds measured by TIV and PIV were quantitatively compared and analyzed by using cross-correlation coefficients. The low-level (2 mm or less above) velocity field measured by TIV also well presents the similar characteristics of near-surface diagonal inflow observed in the PIV measurements. Consequently, the reliability of the TIV method in this study is well verified for resolving the near-surface convective flow fields. The stable stratification is found to significantly impair the heat transfer efficiency as results indicated that the heat transfer in a stable environment is significantly weaker than that in a neutral environment by 71%.