Analyzing Thermal Stratification and Nanoparticle Shapes Influence on an EMHD Ternary Nanofluid Flow amidst Two Spinning Disks

The present study examines the thermal distribution of ternary nanofluid flow amid two spinning disks influenced by electric and magnetic fields. Keeping in view the shape of the particles, the electrically conducting ternary nanofluid is analyzed with variable thermophysical features. Three types of nanoparticles namely Copper, Aluminum Oxide, and Graphene with spherical, cylindrical, and platelet shapes are taken respectively and are immersed in a (50-50)% ratio of water and ethylene glycol mixture which acts as a base fluid. The anticipated problem is addressed by employing a reliable and user-friendly numerical bvp4c built-in collocation scheme. This solution is then showcased through illustrations and tables. Strengthening the radiation results in an enhanced heat transfer rate. Radial and azimuthal velocities once rotation of disks is enhanced. The key findings provide a strong theoretical background in photovoltaic cells, solar collectors, radiators, solar water heaters, and many other applications.

Numerical investigation of variable viscosities and thermal stratification effects on MHD mixed convective heat and mass transfer past a porous wedge in the presence of a chemical reaction

An analysis is presented to investigate the effects of variable viscosities and thermal stratification on the MHD mixed convective heat and mass transfer of a viscous, incompressible, and electrically conducting fluid past a porous wedge in the presence of a chemical reaction. The wall of the wedge is embedded in a uniform nonDarcian porous medium in order to allow for possible fluid wall suction or injection. The governing boundary layer equations are written into a dimensionless form by similarity transformations. The transformed coupled nonlinear ordinary differential equations are solved numerically with finite difference methods. Numerical calculations up to the thirdorder level of truncation are carried out for different values of dimensionless parameters. The results are presented graphically, and show that the flow field and other quantities of physical interest are significantly influenced by these parameters. The results are compared with those available in literature, and show excellent agreement.

Thermal Stratification in Lake Zige Tangco, Central Tibetan Plateau

Lake Zige Tangco is an endorheic saline lake in central Tibetan Plateau.Investigations of 1998 and 1999 revealed that is was a typical stratified lake. The characteristicsof thermal stratification of the lake have been extensively discussed from 4 aspects, i. e.thermocline, hydrochemistry and dissolved oxygen, stable isotope oxygen, and stability. Thethermocline coupled with chemocline was further analyzed.

Diurnal and Seasonal Variations of Thermal Stratification and Vertical Mixing in a Shallow Fresh Water Lake

Among several influential factors, the geographical position and depth of a lake determine its thermal structure. In temperate zones, shallow lakes show significant differences in thermal stratification compared to deep lakes. Here,the variation in thermal stratification in Lake Taihu, a shallow fresh water lake, is studied systematically. Lake Taihu is a warm polymictic lake whose thermal stratification varies in short cycles of one day to a few days. The thermal stratification in Lake Taihu has shallow depths in the upper region and a large amplitude in the temperature gradient,the maximum of which exceeds 5°C m–1. The water temperature in the entire layer changes in a relatively consistent manner. Therefore, compared to a deep lake at similar latitude, the thermal stratification in Lake Taihu exhibits small seasonal differences, but the wide variation in the short term becomes important. Shallow polymictic lakes share the characteristic of diurnal mixing. Prominent differences on the duration and frequency of long-lasting thermal stratification are found in these lakes, which may result from the differences of local climate, lake depth, and fetch. A prominent response of thermal stratification to weather conditions is found, being controlled by the stratifying effect of solar radiation and the mixing effect of wind disturbance. Other than the diurnal stratification and convection, the representative responses of thermal stratification to these two factors with contrary effects are also discussed. When solar radiation increases, stronger wind is required to prevent the lake from becoming stratified. A daily average wind speed greater than 6 m s–1 can maintain the mixed state in Lake Taihu. Moreover, wind-induced convection is detected during thermal stratification. Due to lack of solar radiation, convection occurs more easily in nighttime than in daytime. Convection occurs frequently in fall and winter, whereas long-lasting and stable stratification causes less convection in summer.

Assessment of thermal stratification, stability and characteristics of deep water zone of the southern Caspian Sea

Variations of seawater properties and stratification of water column in the southern deep water zone(470 m depth)of the Caspian Sea were evaluated based on field measured data.Variations of physical characteristics(temperature,salinity,density and sound speed)of seawater mainly were limited to the upper 100 m layers.Below this layer,seasonal changes of seawater parameters were minor.Vertical structure of temperature in the southern Caspian Sea waters was characterized by a significant seasonal thermocline approximately between 20 and 50 m depths in summer with a vertical gradient of around 16℃.Destruction of the thermocline occurred with the general cooling of the sea surface water and deepening of the mixed layer during late of autumn and winter.Frequency of stability in water column often across the upper layers(surface mixed and thermocline)was more than deeper levels.Variations of salinity were around 12.4 PSU in the time of measurements.Structures of thermocline and pycnocline were characterized by a significant homogeneity especially in offshore stations during the year.According to high agreement between density and temperature in the Caspian Seawater,a strong seasonal pycnocline was observed in the position of the thermocline.Furthermore,structure of sound speed variations followed vertical variations of seawater temperature.Variations of chemical characteristics(dissolved oxygen and pH)of seawater mainly were continued from sea surface to near the sea bed in deep water zone.

Transient Behaviors of Thermo-Hydraulic and Thermal Stratification in the Pressurizer Surgeline for the Nuclear Power Plant

In pressurized water reactor(PWR)system,the surgeline plays an important role in bonding the pressurizer and the primary circle.Some considerable problems,including the thermo-hydraulics,the thermal stratification and the accompanying thermal stress under transient conditions,pose risks to the surgeline integrity.Herein,a fully-coupled flow-heat-thermo-elasticity model was developed to investigate the transient behavior of thermo-hydraulic parameters and the thermal stratification phenomenon in PWR.To evaluate the nonuniformity of the stratified flow,a stratification degree indicatorζis introduced.It is found that during the outsurge flow,the increase of temperature variation will enlarge the temperature gradient on the wall,corresponding to a more serious deformation.In the cases of positive temperature variation,the higher temperature variation causes higher stratification degreeζ,and vice versa.The mass flow rate m and the stratification degree are in negative correlation.The local deformation can reach 1.802 cm under a 50 K temperature variation,while its location varies from case to case.More attention should be paid to the regulation between the highest deformation location and the surgeline thermo-hydraulic parameters.

Numerical Analysis of the Mixed Flow of a Non-Newtonian Fluid over a Stretching Sheet with Thermal Radiation

A mathematical model is elaborated for the laminar flow of an Eyring-Powell fluid over a stretching sheet.The considered non-Newtonian fluid has Prandtl number larger than one.The effects of variable fluid properties and heat generation/absorption are also discussed.The balance equations for fluid flow are reduced to a set of ordinary differential equations through a similarity transformation and solved numerically using a Chebyshev spectral scheme.The effect of various parameters on the rate of heat transfer in the thermal boundary regime is investigated,i.e.,thermal conductivity,the heat generation/absorption ratio and the mixed convection parameter.Good agreement appears to exist between theoretical predictions and the existing published results.

Impact of Cattaneo-Christov Heat Flux in the Nanofluid Flow over an Inclined Permeable Surface with Irreversibility Analysis

This study discusses the magnetohydrodynamic nanofluid flow over an inclined permeable surface influenced by mixed convection, and Cattaeo-Christov heat flux. The heat transfer analysis is performed in the presence of a heat source/sink and thermal stratification. To gauge the energy loss during the process, an irreversibility analysis is also performed. A numerical solution to the envisaged problem is obtained using the bvp4c package of MATLAB. Graphs are drawn to assess the consequences of the arising parameters against the associated profiles. The results show that an augmentation in the magnetic field and nanomaterial volume fraction results in an enhancement in the temperature profile. A strong magnetic field can significantly reduce the fluid velocity. The behavior of the Skin friction coefficient against the different estimates of emerging parameters is discussed. .

Investigating the Effects of Injection Pipe Orientation on Mixing and Heat Transfer for Fluid Flow Downstream a T-Junction

At T-junctions, where hot and cold streams flowing in pipes join and mix, significant temperature fluctuations can be created in very close neighborhood of the pipe walls. The wall temperature fluctuations cause cyclical thermal stresses which may induce fatigue cracking. Temperature fluctuation is of crucial importance in many engineering applications and especially in nuclear power plants. This is because the phenomenon leads to thermal fatigue and might subsequently result in failure of structural material. Therefore, the effects of temperature fluctuation in piping structure at mixing junctions in nuclear power systems cannot be neglected. In nuclear power plant, piping structure is exposed to unavoidable temperature differences in a bid to maintain plant operational capacity. Tightly coupled to temperature fluctuation is flow turbulence, which has attracted extensive attention and has been investigated worldwide since several decades. The focus of this study is to investigate the effects of injection pipe orientation on flow mixing and temperature fluctuation for fluid flow downstream a T-junction. Computational fluid dynamics (CFD) approach was applied using STAR CCM+ code. Four inclination angles including 0 (90), 15, 30 and 45 degrees were studied and the mixing intensity and effective mixing zone were investigated. K-omega SST turbulence model was adopted for the simulations. Results of the analysis suggest that, effective mixing of cold and hot fluid which leads to reduced and uniform temperature field at the pipe wall boundary, is achieved at 0 (90) degree inclination of the branch pipe and hence may lower thermal stress levels in the structural material of the pipe. Turbulence mixing, pressure drop and velocity distribution were also found to be more appreciable at 0 (90) degree inclination angle of the branch pipe relative to the other orientations studied.

Computational Analysis of the Oscillatory Mixed Convection Flow along a Horizontal Circular Cylinder in Thermally Stratified Medium

The present work emphasizes the significance of oscillatory mixed convection stratified fluid and heat transfer characteristics at different stations of non-conducting horizontally circular cylinder in the presence of thermally stratified medium.To remove the difficulties in illustrating the coupled PDE’s,the finite-difference scheme with efficient primitive-variable formulation is proposed to transform dimensionless equations.The numerical simulations of coupled non-dimensional equations are computed in terms velocity of fluid,temperature and magnetic field which are computed to examine the fluctuating components of skin friction,heat transfer and current density for various emerging parameters.The governing parameters namely,thermally stratification parameter𝑆𝑆𝑡𝑡,mixed-convection parameter𝜆𝜆,Prandtl number Pr,magnetic force parameter𝜉𝜉and magnetic-Prandtl number𝛾𝛾are displayed graphically at selected values for velocity and heat transfer mechanism.It is computed that heat transfer attains maximum amplitude and good variations in the presence of thermally stratified parameter at each position𝛼𝛼=𝜋𝜋6⁄,𝛼𝛼=𝜋𝜋3⁄and𝛼𝛼=𝜋𝜋around the surface of non-conducting horizontally cylinder.The velocity of fluid attains certain height at station𝛼𝛼=𝜋𝜋6⁄for higher value of stratification parameter.It is also found that the temperature gradient decreases with stratification parameter𝑆𝑆𝑡𝑡,but it increases after a certain distance𝑌𝑌from the cylinder.The novelty of the current work is that due to non-conducting phenomena the magnetic effects are strongly observed far from the surface but exact at the surface are zero for each position.

Simulation of the seasonal thermal structure in the Bobal Sea

The seasonal thermal structure in the Bobal Sea are examined with a three-dimensional boroclinic primitiveequation model for shelf sea. The evolution of the seasonal thermal stratification is well simulated. The stratification ap pears early in April, first in the area off Qinhuangdao and it is well developed in the middle of May. It intensifies withsynoptic and neap-spring nuctuations throughout the summer and reaches its maximum in the middle of July. Eventually,it is destroyed at the end of September. There are cold water belts between well-mixed and stratified regions. They are lo cated on the mixed side of tidal fronts, and coincide with the isolines for a temperature difference of 1-2℃ between surface and bottom. The sea surface temperature(SST)distribution shows local maxima at the head of three bays and to thesouth of Qinhuangdao during the summer. The Bobal Sea responds to the variability in the atmospheric forcing and intides with the synoptic and neap-spring variations of SST, as well as in the stratification and in variable positions of tidalfronts

Homotopy Analysis of MHD Free Convective Micropolar Fluid Flow along a Vertical Surface Embedded in Non-Darcian Thermally-Stratified Medium

The dynamics of steady, two-dimensional magnetohydrodynamics (MHD) free convective flow of micropolar fluid along a vertical porous surface embedded in a thermally stratified medium is investigated. The ratio of pressure drop caused by liquid-solid interactions to that of pressure drop caused by viscous resistance are equal;hence, the non-Darcy effect is properly accounted for in the momentum equation. The temperature at the wall and at the free stream which best accounts for thermal stratification are adopted. Similarity transformations are used to convert the nonlinear partial differential equation to a system of coupled non-linear ordinary differential equation and also to parameterize the governing equations. The approximate analytical solution of the corresponding BVP are obtained using Homotopy Analysis Method (HAM). The effects of stratification parameter, thermal radiation and other pertinent parameters on velocity, angular velocity and temperature profiles are shown graphically. It is observed that increase in the stratification parameter leads to decrease in both velocity and temperature distribution and also makes the microrotation distribution to increase near the plate and decrease away from the plate. The influence of both thermal stratification and exponential space dependent internal heat source on velocity, micro-rotation and temperature profiles are presented. The comparison of the solutions obtained using analytical techniques (HAM) and MATLAB package (bvp4c) is shown and a good agreement is observed.

Simulation and Exploration of the Mechanisms Underlying the Spatiotemporal Distribution of Surface Mixed Layer Depth in a Large Shallow Lake

The aquatic eco-environment is significantly affected by temporal and spatial variation of the mixed layer depth （MLD） in large shallow lakes. In the present study, we simulated the three-dimensional water temperature of Taihu Lake with an unstructured grid with a finite-volume coastal ocean model （FVCOM） using wind speed, wind direction, short-wave radiation and other meteorological data measured during 13-18 August 2008. The simulated results were consistent with the measurements. The temporal and spatial distribution of the MLD and the possible relevant mechanisms were analyzed on the basis of the water temperature profile data of Taihu Lake. The results indicated that diurnal stratification might be established through the combined effect of the hydrodynamic conditions induced by wind and the heat exchange between air and water. Compared with the net heat flux, the changes of the MLD were delayed approximately two hours. Furthermore, there were significant spatial differences of the MLD in Taihu Lake due to the combined impact of thermal and hydrodynamic forces. Briefly, diurnal stratification formed relatively easily in Gonghu Bay, Zhushan Bay, Xukou Bay and East Taihu Bay, and the surface mixed layer was thin. The center of the lake region had the deepest surface mixed layer due to the strong mixing process. In addition, Meiliang Bay showed a medium depth of the surface mixed layer. Our analysis indicated that the spatial difference in the hydrodynamic action was probably the major cause for the spatial variation of the MLD in Taihu Lake.

Development and application of a multi-physics and multi-scale coupling program for lead-cooled fast reactor

In this study,a multi-physics and multi-scale coupling program,Fluent/KMC-sub/NDK,was developed based on the user-defined functions(UDF)of Fluent,in which the KMC-sub-code is a sub-channel thermal-hydraulic code and the NDK code is a neutron diffusion code.The coupling program framework adopts the"master-slave"mode,in which Fluent is the master program while NDK and KMC-sub are coupled internally and compiled into the dynamic link library(DLL)as slave codes.The domain decomposition method was adopted,in which the reactor core was simulated by NDK and KMC-sub,while the rest of the primary loop was simulated using Fluent.A simulation of the reactor shutdown process of M2LFR-1000 was carried out using the coupling program,and the code-to-code verification was performed with ATHLET,demonstrating a good agreement,with absolute deviation was smaller than 0.2%.The results show an obvious thermal stratification phenomenon during the shutdown process,which occurs 10 s after shutdown,and the change in thermal stratification phenomena is also captured by the coupling program.At the same time,the change in the neutron flux density distribution of the reactor was also obtained.

Annual variation in Calanus sinicus abundance and population structure in the northern boundary area of the Yellow Sea Cold Water Mass

The Yellow Sea Cold Water Mass （YSCWM） was suggested as an over-summering site of the dominant copepod species Calanus sinicus in coastal Chinese seas. Population abundance and structure were investigated by monthly sampling along three transects across the northern boundary of the YSCWM during 2009-2010. Results show that thermal stratification existed from June to October and that the vertical thermal difference increased with depth. Generally, total abundance was lowest in October and highest in June, and the female/male sex ratio was highest in February and lowest in August. Evident spatial differences in abundance were observed during the existence of the YSCWM. In June, total abundance averaged 158.8 ind/m~ at well-stratified stations, and 532.1 ind/m3 at other stations. Similarly, high abundances of 322.0 and 324.4 ind/m3 were recorded from July to August inside the YSCWM, while the abundance decreased from 50.4 to 1.9 ind/m3 outside the water mass. C. sinicus distribution tended to even out over the study area in September when the YSCWM disappeared. We believe that the YSCWM may retard population recruitment in spring and preserve abundant cohorts in summer. The summer population was transported to neritic waters in autumn. In addition to low temperatures, stable vertical structure was also an essential condition for preservation of the summer population. C. sinicus can survive the summer in marginal areas in high abundance, but the population structure is completely different in terms of C5 proportion and sex ratio.

Viscous and Ohmic heating effects in doubly stratified free convective flow over vertical plate with radiation and chemical reaction

An analysis is carried out to study the combined effects of viscous and Ohmic heating in the transient, free convective flow of a viscous, incompressible, and doubly stratified fluid past an isothermal vertical plate with radiation and chemical reactions. The governing boundary layer equations are solved numerically by an implicit finite difference scheme of the Crank-Nicolson type. The influence of different parameters on the velocity, the temperature, the concentration, the skin friction, the Nusselt number, and the Sherwood number is discussed with graphical illustrations. It is observed that an increase in either the thermal stratification or the mass stratification parameter decreases the velocity. An increase in the thermal stratification increases the concentration and decreases the temperature while an opposite effect is observed for an increase in the mass stratification. An augmentation in viscous and Ohmic heating increases the velocity and temperature while decreases the concentration. The results are found to be in good agreement with the existing solutions in literature.

Meteorological Data Generation for the Numerical Simulation of Stratified Flow in the Joumine Reservoir, Tunisia

Dynamic numerical simulation of water conditions is useful for reservoir management. In remote semi-arid areas, however, meteorological and hydrological time-series data needed for computation are not frequently measured and must be obtained using other information. This paper presents a case study of data generation for the computation of thermal conditions in the Joumine Reservoir, Tunisia. Data from the Wind Finder web site and daily sunshine duration at the nearest weather stations were utilized to generate cloud cover and solar radiation data based on meteorological correlations obtained in Japan, which is located at the same latitude as Tunisia. A time series of inflow water temperature was estimated from air temperature using a numerical filter expressed as a linear second-order differential equation. A numerical simulation using a vertical 2-D （two-dimensional） turbulent flow model for a stratified water body with generated data successfully reproduced seasonal thermal conditions in the reservoir, which were monitored using a thermistor chain.

Investigation of generalized Fick's and Fourier's laws in the second-grade fluid flow

The second-grade fluid flow due to a rotating porous stretchable disk is modeled and analyzed. A porous medium is characterized by the Darcy relation. The heat and mass transport are characterized through Cattaneo-Christov double diffusions.The thermal and solutal stratifications at the surface are also accounted. The relevant nonlinear ordinary differential systems after using appropriate transformations are solved for the solutions with the homotopy analysis method(HAM). The effects of various involved variables on the temperature, velocity, concentration, skin friction, mass transfer rate, and heat transfer rate are discussed through graphs. From the obtained results,decreasing tendencies for the radial, axial, and tangential velocities are observed. Temperature is a decreasing function of the Reynolds number, thermal relaxation parameter,and Prandtl number. Moreover, the mass diffusivity decreases with the Schmidt number.

Destratification and oxygenation efficiency of a water-lifting aerator system in a deep reservoir:Implications for optimal operation

Thermal stratification is a common phenomenon in lakes and reservoirs and has a significant influence on water quality dynamics. Heihe Reservoir is a canyon-shaped reservoir in Shaanxi Province with strong thermal stratification. Therefore, eight water-lifting aerators （WLAs） were installed in this reservoir, which could overcome thermal stratification and increase oxygenation with gas flows between 20 and 50 m3/hr, and oxygenate the hypolimnion with gas flows less than 20 m3/hr. To examine the destratification efficiency of the WLA system, we used a three- dimensional hydrodynamic module based on MIKE 3 to simulate the thermal structure of Heihe Reservoir and compared the simulations with measured data. Results showed that operation of the WLA system promoted water mixing and effectively oxygenated the hypolimnion. Through the established energy utilization assessment method, the energy utilization efficiency of the WLA system was between 5.36% and 7.30%, indicating the capability of the technique for destratification in such a large reservoir. When the surface water temperature dropped to the theoretical mixed water temperature calculated by the energy utilization assessment method, reducing gas flow could save energy. This would prevent anaerobic conditions from occurring in the bottom water and maintain good water quality in Heihe Reservoir.

Influence of geometry on the thermal performance of water pit seasonal heat storages for solar district heating

The aim of the study is to investigate the influence of geometry on the thermal capacity and stratifications of a water pit heat storage for solar district heating.A TRNSYS component model for a truncated cone water pit was developed based on the coordinate transformation method and validated by experimental results from the water pit heat storage in Huangdicheng in 2018.The thermal performance of 26 water pits with different heights and side wall slopes was calculated for 10 consecutive years.It takes four to six years for the water pit to reach steady-state operation.The operation data from the tenth year was selected to evaluate the thermal performance of each configuration.The results show that because of the thermal insulation on top of the water pit,the height to diameter ratio of a water pit with minimum annual heat loss was always smaller than 1.0.The annual storage efficiency of a water pit increases with side wall slope due to the reduced side wall area.There is an almost linear increase in the thermal stratification number of a water pit with height.With an increase in the height,thermal stratification in water pits with a steeper slope increased more gradually than water pits with a lower slope.The findings in this paper are relevant for the design optimization of water pits as seasonal thermal energy storages.