Effect Of Thermal Stratification Research Articles

Effect of Double Stratification on MHD Williamson Boundary Layer Flow and Heat Transfer across a Shrinking/Stretching Sheet Immersed in a Porous Medium

The present study aims to provide a mathematical model of the Williamson fluid flow via a permeable stretching/shrinking sheet in the MHD boundary layer in the presence of a heat source, chemical reaction, and suction. This study is novel because it investigates the physical effects of thermal and solutal stratification on convective heat and mass transport using thermal radiation. The flow’s PDEs are numerically solved using the BVP4c approach and the pertinent similarity variables until a stable solution is found. Through visual analysis, the effects of dimensionless factors on temperature, velocity, and concentration profiles are examined. This encompasses the mass transfer rate, the heat transfer rate, and the coefficient of friction. The results of the present analysis are found to be consistent with those of previously published studies. The findings demonstrate that enhanced temperature and concentration profiles cause the Williamson, magnetic, and permeability parameters to rise in conjunction with a drop in the dimensionless velocity. In relation to temperature, the thermal stratification parameter exhibits the opposite tendency. Regarding the solutal stratification parameter, concentration profiles are seen to show the opposite trend. Lastly, the current work will have important implications for the removal of dust and viruses from viscoelastic fluid in bioengineering, the medical sciences, and medical equipment.

Aquatic photosynthetic carbon pump driven by periodic temperature variations affects dissolved inorganic carbon and hydrochemical characteristics in a groundwater-fed reservoir

Under the influence of periodic temperature variations, biogeochemical cycling in water bodies is markedly affected by the periodic thermal stratification processes in subtropical reservoirs or lakes. In current studies, there is insufficient research on the influence and mechanism of dissolved inorganic carbon (DIC) distribution in karst carbon-rich groundwater-fed reservoirs under the coupled effects of thermal structure stratification and the biological carbon pump (BCP) effect. To address this issue, the Dalongdong (DLD) reservoir in the subtropical region of southern China was chosen as the site for long-term monitoring and research on relevant physicochemical parameters of water, DIC, and its stable carbon isotope (δ13CDIC), CO2 emission flux, as well as the reservoir's thermal stratification index. The results show that: (1) the DLD reservoir is a typical warm monomictic reservoir, which exhibits regular variations of mixing period-stratification period-mixing period on a yearly scale due to thermal structure changes; (2) DIC was consumed by aquatic photosynthetic organisms in the epilimnion during the stratification period, leading to a decrease in DIC concentration, partial pressure of CO2 (pCO2) and CO2 emission flux, and an increase in stable carbon isotope (δ13CDIC). During the mixing period, the trend was reversed; (3) During the thermal stratification, aquatic photosynthesis and water temperature were the primary factors controlling DIC variations in both the epilimnion and thermocline. Regarding the hypolimnion, calcite dissolution, organic matter decomposition, and water temperature were the dominant controlling factors. These results indicate that although carbon-rich karst groundwater provides a plentiful supply of DIC in the DLD reservoir, its availability is still influenced by variations in the reservoir's thermal structure and the metabolic processes of aquatic photosynthetic organisms. Therefore, to better estimate the regional carbon budget in a reservoir or lake, future studies should especially consider the combined effects of BCP and thermal structure variations on carbon variations.

Thermal structure regulates the dynamics of carbon dioxide flux in alpine saline lake on the Qinghai-Tibet Plateau, China

Thermal stratification and mixing play important roles in the physicochemical composition of lakes and affect the geochemical cycle. However, the regulation of lake carbon exchange at the water-air interface by seasonal thermal structures remains unclear, especially for alpine saline lake on the Qinghai-Tibet Plateau (QTP). Based on continuous field sampling, carbon dioxide flux (FCO2) at the water-air interface in Qinghai Lake during the ice-free period was quantitatively analyzed by thin boundary layer model, as well as the driving factors of the change in FCO2 at the water-air interface. The findings revealed that the FCO2 was −22.16 ± 11.73 mmol m−2d−1 during the stratification period, and − 45.32 ± 29.67 mmol m−2d−1 during the mixing period. We found that thermal stratification limits the matter-energy exchange between the upper and bottom water columns, and carbonate precipitation results in a higher FCO2 than during mixing stage. However, the mixing process reduces the limiting effect of thermal stratification. During the carbonate process, water with higher salinity and pH at the bottom of the water column enters the upper part of the water column, reducing the partial pressure of carbon dioxide (pCO2) in the water column and causing the absorption of CO2 by the lake. Thermal stratification affects the vertical material-energy exchange and atmospheric CO2 uptake of lake. The present study further explains the possible underlying regulation of CO2 uptake in saline lake on the QTP involving the varied thermal structure.

Thermal and mass stratification effects on MHD nanofluid past an exponentially accelerated vertical plate through a porous medium with thermal radiation and heat source

The aim of this research is to investigate the combined effects of thermal and mass stratification on unsteady magnetohydrodynamic nanofluid moving through an exponentially accelerated vertical plate in a porous medium. The governing equations of the problem are solved numerically by using the implicit Crank–Nicolson method. The results of the nanofluid with two different stratification are compared to those obtained without any stratification. The velocity of the nanofluid decreases with both types of stratification, whereas temperature and concentration decrease with thermal stratification and mass stratification, respectively. A variety of parameters, including the volume fraction of nanoparticles, thermal radiation, heat source/sink, and chemical reaction, can be studied using graphs. The important results demonstrate that nanofluids are more thermally conductive than normal fluids. This research holds significant implications in various fields, including power generation, electronic component cooling, and vehicle construction.

Theoretical Study of Thermal and Mass Stratification Effects on MHD Nanofluid Past an Exponentially Accelerated Vertical Plate in a Porous Medium in Presence of Heat Source, Thermal Radiation and Chemical Reaction

Theoretical Study of Thermal and Mass Stratification Effects on MHD Nanofluid Past an Exponentially Accelerated Vertical Plate in a Porous Medium in Presence of Heat Source, Thermal Radiation and Chemical Reaction

Thermal and mass stratification effects on unsteady parabolic flow past an infinite vertical plate with exponential decaying temperature and variable mass diffusion in porous medium

AbstractThis study looks at how thermal and mass stratification affect the unsteady parabolic flow past an infinite vertical plate with exponentially decaying temperature and variable mass diffusion in a porous medium. The Laplace transform method is applied to solve the governing equations for flow, energy, and mass diffusion. The effects of the both stratification on the flow field, temperature, and mass diffusion are then investigated. The research suggests that the existence of thermal and mass stratification has a considerable influence on the profiles of velocity, temperature, and mass diffusion. It is also found that a stable state is reached for the velocity when both stratification parameters are increased, while stable states are reached for the temperature and concentration when the mass stratification is increased but the thermal stratification is decreased.

NUMERICAL INVESTIGATION OF THERMAL STRATIFICATION EFFECTS ON WIND TURBINE WAKE FLOW

Numerical investigation of thermal stratification effects on wind turbine wake flow with and without yawed conditions was conducted in this paper. The three-dimensional wind turbine model from National Renewable Energy Laboratory (NREL) Phase VI experiment was adopted in all the simulations. Model validation was done by using three commonly used turbulence models: realizable <i>k-ε</i> model, shear-stress transport (SST) <i>k-ω</i> model, and large eddy simulation (LES) model. Simulation results were compared with experimental data in the literature. The realizable <i>k-ε</i> model was selected for further simulation as it showed a good balance in achieving accurate results and lowering computational cost. Followed by the validation, wind turbine wake flow with and without yawed effects under different thermal stratification conditions were simulated. Wake flow parameters were discussed and analyzed, followed by suggestions of wind turbine layouts based on different operation conditions to efficiently harness wind energy.

The Effect of Thermal Stratification on Unsteady Parabolic Flow past an Infinite Vertical Plate with Chemical Reaction

This research paper investigates the effects of thermal stratification on unsteady parabolic flow past an infinite vertical plate with chemical reaction. Using the Laplace transform method, analytical solutions are derived to simulate the physical process of the flow. The study considers the effects of thermal stratification on the flow field, as well as the effects of chemical reaction on the velocity, and temperature field. The results of the stratification case are then compared to the case of no stratification of a similar flow field. The results of this research can be used to improve understanding of the unsteady parabolic flow in thermal stratified environments and provide valuable insight into the effects of chemical reactions on the temperature field.

Thermal and Mass Stratification Effects on Unsteady Flow Past an Accelerated Infinite Vertical Plate with Variable Temperature and Exponential Mass Diffusion in Porous Medium

This study looks at how thermal and mass stratification affect the unsteady flow past an infinitely fast-moving vertical plate when the temperature is changing and there is exponential mass diffusion in a porous medium. By applying the Laplace transformation method, we determine the solutions to the equations that govern the system for the case of unitary Prandtl and Schmidt numbers. Graphical representations of the concentration, temperature, and velocity profiles, as well as the Nusselt Number, Sherwood number, and the Skin friction are provided to facilitate discussion of the cause of the different variables. To see the effects of thermal and mass stratification on the fluid flow, we compare the classical solution (Fluid with out stratification) with the primary solution (Fluid with the stratification) by using graph. The combined effects of the two stratification lead to a quicker approach to steady states. The outcomes can be helpful for heat exchange design and other engineering applications.

Stratification and Radiation of Heat in Hybrid Gold-Graphene/Ethylene Glycol Nanofluid Flows Past a Leaning Cylinder

Hybrid gold-graphene/ethylene-glycol (EG) nanofluid past a permeable leaning cylinder is devoted in the current investigation under the effect of thermal radiation and stratification. The governing partial differential equations are reformulated into nonlinear ordinary differential equations by implementing similarity terms. A shooting approach is elected to reformulate the equations into a boundary value problem which is determined by applying a bvp4c code in MATLAB. The effects of selected parameters regarding the recent model on dimensionless velocity and temperature disseminations, reduced skin friction coefficient and reduced Nusselt number are analyzed and presented in graphs and tables. It is perceived that by rising the value of the thermal stratification and radiation parameter, the reduced Nusselt number for the preferred mono and hybrid nanofluids will be declined. The reduced Nusselt number is reported to be the highest value when considering hybrid gold (ϕ s1=0.02)-graphene (ϕ s2 = 0.04)/EG nanofluid.

Analysis of the effect of thermal stratification on the natural circulation decay heat removal of sodium-cooled fast reactor

Thermal stratification is an important phenomenon in the process of natural circulation decay heat removal in sodium-cooled fast reactors (SFR). It affects the establishment of the natural circulation and the flow rate of the natural circulation in a station black out (SBO) accident, and therefore affects the safety of the reactor. In safety evaluation, programs are often required to perform analysis for various conditions and long-term transients. However, it is difficult to meet this requirement by adopting a multi-dimensional method or one-dimensional and multi-dimensional coupling method. Therefore, this paper proposes applying a thermal stratification model to the system analysis program THACS to analyze the thermal stratification phenomenon. First, the thermal stratification model is validated with experimental data. The validated model is applied to analyze a station black out accident in the SFR. The lumped parameter model and thermal stratification model are used respectively for the hot pool. By comparing the calculation results of the two models, the effect of thermal stratification of the hot pool on key parameters such as the natural circulation flow rate of the primary circuit, natural circulation flow rate in the inter-wrapper region, average core outlet temperature, maximum core fluid temperature, and the maximum temperature of cladding was analyzed, and the effect of thermal stratification on natural circulation decay heat removal of the SFR was evaluated. This work can provide a reference for the safety analysis of the reactor and contribute to developing a more conservative safety analysis and evaluation strategy.

Influence of thermal stratification on the transport of polydispersed expiratory particles

The fluid dynamics of expiratory events are complex, and understanding how indoor air conditions affect this and the spread of exhaled material is crucial to the prevention of large-scale spread of diseases. It is known that thermal stratification can trap contaminants in the lower levels of a room; however, there is a lack of studies that investigate the influence of vertical temperature gradients on the transport of expiratory particles at room scale. To this effect, we used Eulerian–Lagrangian large-eddy simulations to investigate the effect of thermal stratification on the transport of polydispersed expiratory particles during speaking in two different sized rooms. Cases with increasing temperature gradient were compared to an isothermal base case, and the influence of stratification on the exhalation jet and the particles suspended within is analyzed. The particle volume fraction was computed to quantify the spatiotemporal evolution of different particle size categories. Our results show that thermal stratification leads to an increased concentration of aerosols in the breathing zone and extends their forward reach. Aerosols up to a size threshold between 12 and 20 μm are locked up at different heights by stratification—beyond this threshold, they fall out continuously. In all cases, aerosols <20 μm traveled up to 4 m from the source, showing that physical distancing guidelines alone may be inadequate for controlling cross-infection risk for long-term exposures. Particles >60 μm are unaffected by stratification and do not follow a ballistic trajectory, falling out within 0.5 m of the infectious individual in all cases.

Large eddy simulation of thermal stratification effects on tracer gas dispersion in a cavity

This paper assesses the effect of thermal stratification on the prediction of inert tracer gas dispersion within a cavity of height (H) 1.0 m, and unity aspect ratio, using large eddy simulation. The Reynolds number of the cavity flow, was 67 000. Thermal stratification was achieved through the heating or cooling of one or more of the walls within the cavity. When compared to an isothermal (neutral) case, unstable stratification from surface heating generally has a weak influence on the primary recirculating cavity vortex, except in the case where the windward wall is heated. For windward wall heating, a large secondary vortex appears at the corner of the windward wall and cavity floor. Unstable stratification has no significant influence on the removal of pollutant mass from the cavity. Stable stratification through surface cooling drastically alters the flow pattern within the cavity, pushing the cavity vortex towards the upper quadrant of the cavity. As a result, large regions of stagnant fluid are present within the cavity, reducing the effectiveness of the shear layer at removing pollutant concentration from the cavity. Some stable stratification configurations can increase the pollutant mass within the cavity by over a factor of five, when compared to the neutral case. Pollutant concentration flux maps show that, in stably stratified cases, the majority of pollutant transport from the cavity is the result of entrainment into the primary cavity vortex. The results show that pollutant concentrations in urban street canyon-type flows are substantially altered by diurnal heating and cooling, which may influence pedestrian management strategies in urban environments.

The Effects of Thermal Stratification on Flow Past an Infinite Vertical Plate in Presence of Chemical Reaction

This study examines how thermal stratification affect the movement of a fluid in presence of first order chemical reaction past an infinite vertical plate. To solve the non-dimensional governing equations in closed form for Pr = 1, the Laplace’s transform system is applied. Significant findings resulting from stratification are compared to the case of no stratification. The effects of many parameters, including S, K, Gr, Gc, Sc and time on velocity, temperature, concentration, skin friction, Nusselt number, and Sherwood number are explored and graphically displayed. It is shown that the steady state is attained at shorter times as a result of the application of stratification on the flow.

Unsteady Flow Past an Accelerated Vertical Plate with Variable Temperature in Presence of Thermal Stratification and Chemical Reaction

This work aims to investigate the effect of thermal stratification on fluid flow past an accelerated vertical plate in the presence of first order chemical reaction. The dimensionless unsteady coupled linear governing equations are solved by Laplace transform technique for the case when the Prandtl number is unity. The important conclusions made in this study the effect of thermal stratification is compared with the scenario in which there was no stratification. The results of numerical computations for different sets of physical parameters, such as velocity, temperature, concentration, skinfriction, Nusselt number and Sherwood number are displayed graphically. It is shown that the steady state is attained more quickly when the flow is stratified.

Effect of Thermal Stratification in Meandering Turbulent Open-Channel Flow with Varying Sinuosity

Effect of Thermal Stratification in Meandering Turbulent Open-Channel Flow with Varying Sinuosity

Hypolimnetic aeration optimization based on reservoir thermal stratification simulation

Hypolimnetic aeration is an effective management strategy for mitigating oxygen deficiency in dam reservoirs caused by thermal stratification (ThS). However, designing an optimal hypolimnetic aeration system based on dissolved oxygen (DO) concentration evaluation has yet to be considered in the literature. This study proposed an innovative optimization model utilizing the non-dominated sorting genetic algorithm-II (NSGA-II) for up to 4 aerators, considering two main objectives: (i) minimizing DO concentration deviation from the standard limit and (ii) minimizing aerator(s) operation energy. This optimization model was developed based on five primary decision variables: the location of the aerator(s) (length and depth), the aeration rate, and the operating time (start and end date). The NSGA-II optimization approach was coupled with the CE-QUAL-W2 simulation model for each identified period of ThS to simulate DO concentrations. To satisfy the conflicting objectives of the primary beneficiaries involving the Ministry of Energy and the Regional Water Organization, a two-step decision-making framework was introduced, utilizing the Nash bargaining (NB) and weighting method (WM) techniques. In order to show the practicality and effectiveness of the suggested framework in enhancing the DO concentration within a dam reservoir, the novel simulation optimization framework was implemented in a real-world case study of the Karkheh dam reservoir (KDR) in Iran. The findings revealed that applying an optimal hypolimnetic aeration system significantly improved the DO concentration, reaching at least twice the level without an aerator. However, the influence of aerators was not long-lasting, gradually diminishing when their operations ceased. Considering the importance of increasing DO concentration to mitigate the adverse effects of ThS, the four-aerators system was chosen as the optimal compromise design for the KDR.

SIMULATION OF FLOW AND HEAT EXCHANGE IN A HEAT ACCUMULATOR TANK

The article deals with the research of thermal energy storage tanks. It is proposed to use a «thermal core» to minimize the effects of thermal stratification and high thermal inertia. The thermal core consists of a binary tube placed along the central axis of the tank, filled with a paraffin mixture with a melting point of 45 to 65oC and a density of 0,880 to 0,915g/cm3 at 15oC. In the study the Fluent software package was used to model the temperature distribution in the tank under free convection conditions, the data was then converted to the Transient Thermal module of the ANSYS software package for further calculations of the unsteady temperature distribution in the thermal core. The study showed that a 1400-liter thermal energy storage device, heated for 1 hour by a heat-transfer fluid at 115oC, cools down to 50oC in 4 hours. The research also revealed the need to improve the tank design based on the analysis of the hydrodynamic structure of the flow in the tank, as evidenced by the trajectory distribution of free convective flows. The authors concluded that the use of a heat core, regardless of the type of paraffin used to form it, helps to reduce temperature stratification by height in the tank and that the type of paraffin used has no significant effect on the overall cooling of the tank. However, using ceresin as a core filler results in a slightly higher average tank temperature. Based on the results of the study, the time of complete cooling of the tank was determined by the non-uniform temperature field of all elements of the tank.

Transient Dynamics in Counter-Rotating Stratified Taylor–Couette Flow

This study focuses on the investigation of stratified Taylor–Couette flow (STCF) using non-modal analysis, which has received relatively limited attention compared to other shear flows. The dynamics of perturbations under different temperature conditions are explored, and their patterns of amplification are analyzed. The study highlights the correlation between flow configurations, emphasizing the similarity in transient dynamics despite different speed ratios. The subcritical effects of thermal stratification on disturbance dynamics are examined, considering the interplay between viscous and buoyancy effects counteracted by strong centrifugal forces. It is found that increasing the wall temperature beyond a critical value leads to buoyancy forces dominating, resulting in a linear increase in the amplification factor. The research reveals significant deviations from previous results, indicating the significant role of temperature stratification.

Experimental investigation in the selection of phase change materials based on thermal stratification effect in thermal energy storage system

AbstractThis study aims to evaluate the effects of thermal stratification on thermal energy storage (TES) systems during the charging process and choose suitable phase change materials (PCMs) for various layers. The research revealed that fiberglass insulation of 60 mm thick significantly decreased natural convection losses and increased the TES system's potential for energy recovery. For constant heat load, the charging time increased with increasing HTF inlet temperature, but remained constant for the first TES layer at a specified flow rate, resulting in increased storage capacity with minimal heat loss to the surroundings. The solar collector efficiency was shown to be dependent on solar radiation and collector efficiency, with peak efficiency seen at specified periods. The lowest melting point of PCMs at each layer 68°C, 62.7°C, 57°C, and 50°C was chosen based on temperature graphs. For comparing stratification behavior, the “MIX” number versus non‐dimensional charging time plot was effective. Additional experiments are needed to assess the selected PCMs' charging and discharging properties.