Thermal Stratification Phenomenon Research Articles

Experimental analysis of steam mixing and thermal stratification phenomena related to small steel containment studies

To study the mixing and thermal stratification caused by the plumes or buoyant jets in the small steel containment during the LOCA or MSLB accidents, temperature was measured experimentally. Using steam as the working medium, the experiments were conducted with various jet inlet temperatures and spray water flow rates to identify their influence on the thermal stratification phenomena. Temperature distributions with height are given to illustrate the thermal stratification in containment. The performed analysis shows that recirculating stratified fluid existed in only lower part of containment while steam mixing and temperature homogenization happened in upper part of containment. Rayleigh-Benard convection, which is often neglected in big steel containment stratification, and convection caused by negatively buoyant jet and plume entrainment are considered to be the major factors causing steam mixing. It is suitable to consider such thermal stratification and steam mixing in developing a more accurate and detailed model for small steel containment and system design of SMRs.

Design and experimental assessment of thermal stratification effects on operational loading of surge line of Unit 5, Novovoronezh NPP

One of the key tasks in substantiating NPP service life extension consists in detailed examination of all factors affecting the remaining lifespan of critical NPP components. Particular attention must be paid to studying the phenomenon of thermal stratification (TS) which is the effect of coolant lamination into the “cold” and “hot” layers in horizontal pipelines when flows with different temperatures propagate at slow velocities. Special importance of this issue is explained by the fact that cyclic loads caused by TS contribute in accumulation of metal damage due to thermal fatigue and can provoke formation and accelerated growth of defects.This study is dedicated to implementing complex analysis of coolant TS observed in horizontal sections of the surge line (SL) on WWER-1000 units from the viewpoint of assessment of TS effects on the stressed-deformed conditions of metal and accumulation of cyclic damages. The experimental data on the distribution of temperature fields in horizontal SL sections, as well as cyclic loading history during several reactor fuel residence campaigns were recorded by the on-line diagnostic monitoring system put into operation on Unit 5 Novovoronezh NPP. Certain distinguishing features of TS in SL of Unit 5 were identified as the result of data analysis depending on operational modes. The most significant TS effects were observed in the control cross-section located within the first horizontal section from the pressurizer.Calculation and experimental assessment of effects of thermal loading factors on the stress-deformed state of SL demonstrated that effects of thermal stratification and thermal fatigue significantly affect the operational loading of the pipeline. It is noted that zones with maximum accumulated damage determined according to the results of calculations coincide with places where factual operational defects were detected. Procedure involving treatment of SL welded joints by the method of surface plastic deformation is suggested as the compensatory measure aimed at extending the SL residual lifespan.

Unsteady-state thermal stress and thermal deformation analysis for a pressurizer surge line subjected to thermal stratification based on a coupled CFD-FEM method

In the pressurizer surge line, the phenomenon of thermal stratification may induce thermal stress and thermal deformation. Excessive thermal stress may result in thermal fatigue of the pipe structure, and excessive thermal deformation may destroy the pipe supports. The phenomenon of thermal stratification, and the induced thermal stress and thermal deformation in the pressurizer surge line would pose a threat on the safe operation of the nuclear power plants (NPPs). Therefore, it is very important to make an analysis to the thermal stratification, thermal stress and thermal deformation of the pressurizer surge line. In this study, a detailed unsteady-state computational fluid dynamics (CFD) analysis involving conjugate heat transfer (CHT) analysis is performed to obtain the transient temperature distributions of the pressurizer surge line under an overall out-surge case, and the thermal loads from the CFD calculations are then transferred to ANSYS Workbench Mechanical as body temperature loads for obtaining the transient thermal stress and the transient thermal deformation. With the coupled computational fluid dynamics-finite element method (CFD-FEM) analysis, the transient response characteristic of the surge line subjected to transient thermal stratification loadings are investigated and analyzed quantitatively. The positions where the maximal thermal stress occurs and where the maximal pipeline displacement occurs are determined, and the method for determining the degree of thermal deformation in the cross-section has been proposed. The coupled CFD-FEM method and the obtained conclusions in this study will be helpful for the design of the pipeline structures and the pipe supports to reduce the structural failure related safety accident.

Numerical communication for MHD thermally stratified dual convection flow of Casson fluid yields by stretching cylinder

This work reports the comparative study of magnetohydrodynamic mixed convection boundary layer flow of Casson fluid brought by both flat and cylindrical stretching surfaces. Flow field analysis is accounted with thermal stratification phenomena. The temperature is assumed to be higher across the surface of cylinder as compared to ambient fluid. The arising mathematically modelled partial differential equations of Casson fluid flow are successfully converted into ordinary differential equations with the source of suitable transformation. The numerical solutions are computed through the application of shooting technique charted with fifth order Runge-Kutta algorithm. The effect logs of an interesting physical parameters namely, magnetic field parameter, mixed convection parameter, thermal stratification parameter, heat generation parameter, curvature parameter and Prandtl number are discussed graphically. Further, the variations of skin friction coefficient and heat transfer rate are identified by way of tables.

Application of shooting method on MHD thermally stratified mixed convection flow of non-Newtonian fluid over an inclined stretching cylinder

An analysis is made to examine the magnetohydrodynamic mixed convection boundary layer flow of Eyring-Powell fluid brought by an inclined stretching cylinder. Flow field analysis is accounted by thermal stratification phenomena. The temperature is assumed to be higher across the surface of cylinder as compared to ambient fluid. The arising mathematical model regarding Eyring-Powell fluid is governed by interesting physical parameters which includes mixed convection parameter, thermal stratification parameter, heat generation/absorption parameter, curvature parameter, fluid parameters, magnetic field parameter and Prandtl number. The numerical solutions are computed through the application of shooting technique conjunction with fifth order Runge-Kutta algorithm. In addition, numeric values for two unlike geometries namely, plate and cylinder for skin friction coefficient and Nusselt number are presented with the aid graphs and some particular cases are discussed. The present study is validated by establishing comparison with previously published works, which sets a benchmark of quality of shooting method.

Squeezed flow of a nanofluid with Cattaneo–Christov heat and mass fluxes

In this article mathematical model is developed for squeezing flow of viscous fluid with heat and mass fluxes using Cattaneo–Christov theory. Characteristics of flow are explored with thermal and solutal stratification phenomena. Disturbance in the fluid is induced by a linear stretching sheet which is characterized by lower plate. The System of arising partial differential equations are reduced to a system of ordinary differential equations by utilizing suitable transformations. The graphical behavior of various parameters on velocity, temperature, and concentration distributions are analyzed and discussed. It is noted that thermal and solutal relaxation parameters result in the reduction of temperature and concentration distribution respectively.

국내원전 배관계통 열성층 연구개발 현황

The thermal stratification phenomenon in the nuclear power plant can cause abnormal deformation of the piping, contact with the support, damage to the support system. Repetition of the thermal stratification phenomenon or variation of the thermal boundary layer can cause thermal fatigue. Thermal stratification phenomenon in nuclear power plants is still an ongoing issue and active research has been carried out. In this paper, the current situation in Korean nuclear power plants is described, followed by the status of research and the future problems on the thermal stratification phenomenon in Korea.

EPRI MAAP5 Fukushima Daiichi Analysis

The study presented in this paper summarizes work conducted as part of the Electric Power Research Institute (EPRI) Fukushima Technical Evaluation project. This effort was designed to develop a representation of the core damage events that occurred at Fukushima Daiichi Units 1, 2, and 3 using the analytical capabilities provided by the EPRI Modular Accident Analysis Program, Version 5 (MAAP5). The analytical investigations of Fukushima Daiichi performed with MAAP5 indicate that core-melt progressions at Units 1, 2, and 3 likely span a range of core damage conditions. The core status at Unit 1 is likely consistent with a large fraction of core debris having relocated into the containment. By contrast, the MAAP5 evaluations indicate that there is a reasonable potential for a significant fraction of core debris to be retained inside the reactor pressure vessel (RPV) at Unit 2. The corresponding Unit 3 simulations, however, highlight the important role that degraded high-pressure coolant injection at low RPV pressure may have played in promoting some relocation of core debris out of the RPV and into containment. The detailed containment evaluations conducted as part of this study also highlight the critical role played by thermal stratification phenomena (either in the suppression pool or in the drywell) in influencing the magnitude of containment pressure and thermal challenges. These simulations highlight the potentially critical role that thermal stratification in the upper drywell may have played in accelerating the onset of leakage through the drywell head flange due to thermal degradation of the drywell head gasket. Finally, these simulations provide good representations of the occurrence of flammable conditions in the Units 1 and 3 reactor buildings, supporting the nature and timing of the observed reactor building combustion events.

Experimental and computational simulation of thermal stratification in large pools with immersed condenser

This paper deals with experimental and numerical investigations on thermal stratification phenomenon conducted in Integral Test Loop (ITL) scaled test facility for Advanced Heavy Water Reactor (AHWR). Experiments at decay power level were designed to simulate thermal hydraulic performance of Isolation Condenser (IC) system of AHWR at prototypical pressure (70bar) and temperature (285°C). The experiments were simulated using the Best Estimate (BE) thermal hydraulic system code RELAP5. Two different pool side nodalizations were tried for simulation of IC-pool. Nodalization, where the IC-pool was simulated with one lumped volume did not simulate the observed thermal stratification behavior appropriately. However, it simulated the Main Heat Transport System (MHTS) behavior well. To simulate pool side stratification a three volume pool nodalization was adopted, which simulated the observed thermal stratification behavior in the pool well apart from simulating MHTS system behavior. Study shows a characteristic thermal stratification behavior in pool, which prevails for the initial few hours of IC functioning. The characteristic curve showing various stages of observed pool thermal stratification development and decay during experiment has been presented in the paper. An interrelation between pressure and water level into the pool has been observed in studies.

CFD Simulations of Selected Steady-State and Transient Experiments in the PLANDTL Test Facility

In Sodium Cooled Fast Neutron Reactors natural convection flow and thermal stratification in the upper plenum may occur under emergency shutdown conditions. Thermal stratification phenomena have been examined experimentally in the PLANDTL facility of the Japan Atomic Energy Agency. This paper presents the results of numerical simulations of selected steady-state and transient experiments in the PLANDTL facility, using TrioCFD/MC2 code developed at CEA. CFD approach for the flow in large volumes and a sub-channel approach for the flow in the core region are used. Calculated results have been validated against experimental values. Validation of the upper plenum modelling has been also made based on CEA Sodium mixed convection experiments.

Experimental investigation on natural convection heat transfer characteristics of C-shape heating rods bundle used in PRHR HX

The heat transfer performance of Passive Residual Heat Removal Heat Exchanger (PRHR HX) immerged in the In-containment Refueling Water Storage Tank (IRWST) is of great importance for the efficient and safe removal of the residual heat in the AP1000 plant. The C-shape heating rods bundle is being used in the PRHR HX, yet the heat transfer characteristics of this special C-shape heat exchanger are not completely clear. The Westinghouse Electric Corporation has performed the PRHR HX experiment using three vertical tubes to validate the design of PRHR HX. However, the horizontal sections of the C-shaped bundle were neglected, and attentions were mainly focused on the local heat transfer effect of the vertical tubes. In the present work, an overall scaled-down IRWST and PRHR HX models are built to simulate the thermal hydraulic process in the residual heat removal accident. The natural convection heat transfer characteristics of both the overall IRWST model and the local C-shaped PRHR HX bundle model are researched in the first stage. For the overall IRWST model, the natural convection flow vectors are qualitatively measured by PIV technique. The velocity and temperature distributions are influenced mutually, then thermal stratification phenomenon develops in the overall IRWST. The existence of the “thermal interface” has great influences on the thermal stratification. For the local PRHR HX heat transfer, traditional natural convection correlations for both horizontal and vertical bundles are compared to the experimental data. For the vertical bundle of the PRHR HX model, a revised Rayleigh number is proposed as a criterion for the slender vertical rod bundles, when the vertical rod bundle outside flow cannot be treated as flat plate. Then revised correlations are proposed to predict the PRHR HX average heat transfer coefficient. Moreover, the analysis shows that the forced convection also plays an important role in enhancing the heat transfer effect of the PRHR HX model upper horizontal bundle, so the modified Numix is recommended for the PRHR HX upper horizontal bundle secondary heat transfer calculation.

Experimental research on the thermal stratification criteria and heat transfer model for the multi-holes steam ejection in IRWST of AP1000 plant

In AP1000 plant, the Automatic Depressurization System (ADS) 1–3 stages operate to discharge the high-temperature and high-pressure steam from the Reactor Coolant System (RCS) primary side to the large heat sink tank In-containment Refueling Water Storage Tank (IRWST) in accidental conditions. The key equipment’s specific shape and arrangement lead to the complicate flow and heat transfer characteristics in IRWST. In the present work, an overall scaled IRWST&ADS sparger experiment has been built up. The thermocouples matrix, flowmeters, pressure transmitters, heat flux sensors, Particle Image Velocimetry (PIV) technique, and high speed camera are employed for the measurements of the key thermal and flow parameters. The local steam jets condensation phenomena as well as the overall flow and thermal behavior are investigated. The experimental results indicate that the thermal stratification phenomenon is obvious in IRWST. The criteria of Richardson Number and Stratification Number are utilized to predict and evaluate the thermal stratification extent, respectively. An improved ADS arrangement design is further proposed to reduce the thermal stratification. Moreover, the multi-holes lumped “steam condensation column” is modeled with characteristic parameters, then the steam condensation heat transfer coefficient range in chugging condensation process is estimated. The experimental results provide practical engineering application reference for the effective operation of the passive safety system in AP1000 plant.

Influence of injection temperature and flow rate on mixing and stratification in small passively cooling enclosures

Thermal mixing and stratification phenomena may occur during the loss of a coolant accident or main steam line break accident in the containment of a Passive Containment Cooling System, or in the suppression pools in BWR. However, the present study pays insufficient attention to the thermal stratification phenomena in the containment of small modular reactors (SMR). In this paper, an investigation on the mixing and thermal stratification phenomena caused by the plumes or buoyant jets in SMR containments was carried out. The experiments were both conducted under non-adiabatic and adiabatic conditions for a steel containment. In each condition, two key parameters, inlet temperature, and flow rate were tested by controlling variables to identify their influence on the thermal stratification phenomenon. The visualization experiments illustrated the jet mixing and stratification development. The experiment results were compared with the numerical computation and they reached a good agreement.

3D CFD simulations to study the effect of inclination of condenser tube on natural convection and thermal stratification in a passive decay heat removal system

Many advanced nuclear reactors adopt methodologies of passive safety systems based on natural forces such as gravity. In one of such system, the decay heat generated from a reactor is removed by isolation condenser (ICs) submerged in a large water pool called the Gravity Driven Water Pool (GDWP). The objective of the present study was to design an IC for the passive decay heat removal system (PDHRS) for advanced nuclear reactor. First, the effect of inclination of IC tube on three dimensional temperature and flow fields was investigated inside a pilot scale (10L) GDWP. Further, the knowledge of these fields has been used for the quantification of heat transfer and thermal stratification phenomenon. In a next step, the knowledge gained from the pilot scale GDWP has been extended to design an IC for real size GDWP (∼10,000m3). Single phase CFD simulation using open source CFD code [OpenFOAM-2.2] was performed for different tube inclination angles (α) (w.r.t. to vertical direction) in the range 0°⩽α⩽90°. The results indicate that the heat transfer coefficient increases with increase in tube inclination angle. The heat transfer was found to be maximum for α=90° and minimum for α=15°. This behavior is due to the interaction between the primary flow (due to pressure gradient) and secondary flow (due to buoyancy force). The primary flow enhanced the fluid sliding motion at the tube top whereas the secondary flow resulted in enhancement in fluid motion along the circumference of tube. As the angle of inclination (α) of the tube was increased, the secondary flow became dominant and resulted into enhanced heat transfer near the tube bottom. Three different heat transfer regimes were identified in the transient period: conduction (0<t<0.4s), quasi-steady (0.4s<t<10s) and fluctuating period (10s<t<100s). The effect of inclination angle (α) was more pronounced in the fluctuating period. The natural convection and heat transfer in the regime of laminar-turbulent transition was studied in the presence of longitudinal vortices. The heat transfer was enhanced in the transition region due to vortices formation and it was reduced in the turbulent regime due to decay of vortices.

Natural circulation characteristics of lead-based reactor under long-term decay heat removal

The natural circulation of primary coolant plays an important role in removing the decay heat in Station-Black-out (SBO) accident from reactor core to decay heat removal systems, such as RVACS and PHXS cooling, for lead-based reactor. In order to study the natural circulation characteristics of primary coolant under Reactor Vessel Air Cooling System (RVACS) and primary heat exchangers (PHXs) cooling, which are crucial to the safety of lead-based reactors. A three-dimensional CFD model for the China Lead-based Research Reactor (CLEAR-I) has been built to analyze the thermal-hydraulics characteristics of primary coolant system and the cooling capability of the two systems. The abilities of the two cooling systems with different decay heat powers were discussed as well. The results demonstrated that the decay heat could be removed effectively only relying on either of the two systems. However, RVACS appeared the obvious thermal stratification phenomenon in the cold pool. Besides, with the increase in decay heat power, the natural circulation capacity of primary coolant between the two systems had a significant difference. The PHXs cooling system was stronger than the RVACS, with respect to the mass flow of primary coolant and the average temperature difference between cold pool and hot pool.

The studies of mixing and thermal stratification in SMR containments

Thermal mixing and stratification, which are common phenomena in the passive containment cooling system, may occur in the containments of the small modular reactors as well during the loss of coolant accidents or the main steam line break accidents. This paper studies the mixing and thermal stratification caused by the plumes or buoyant jets in the small containments. The experiments in a steel containment were conducted with various jet inlet temperatures and flow rates to identify their influence on the thermal stratification phenomena. The temperature distributions with height as well as the contour maps over cross section in the containment are given to illustrate the thermal stratification. The flow visualization was illustrated in a glass simulated containment to obtain detailed understandings of the jet mixing and fluid stratification development. The experiment results agree well with the computation results.

Investigation on thermal stratification and turbulent penetration in a pressurizer surge line with an overall out-surge flow

Excessive thermal stresses caused by temperature fluctuations can result in thermal fatigue in the piping system of a nuclear power plants (NPPs). The phenomenon of thermal stratification and turbulent penetration in a pipe can lead to temperature fluctuations, and have attracted much attention of the researchers who deal with NPPs. In particular, this phenomenon in the pressurizer surge line has been assessed as one of the significant safety and technical issues due to its high rate of occurrence. This work focuses on a fundamental description of the thermal stratification and turbulent penetration in a pressurizer surge line using experiment and computational fluid dynamics (CFD) simulation based on the FLUENT 6.3.26 code. In this study, CFD simulation with the LES turbulence model is proved to be an accurate and effective method of studying thermal stratification in a pressurizer surge line. Details of turbulent penetration have also been studied in this paper. A criterion of determining the depth of turbulent penetration has been proposed, and the main frequency of the velocity fluctuations of turbulent penetration in a surge line is found to be a continuous frequency band, and not a fixed value.

Mixed convection and stratification phenomena in a heavy liquid metal pool

This work deals with an analysis of the first experimental series of tests performed to investigate mixed convection and stratification phenomena in CIRCE HLM large pool. In particular, the tests concern the transition from nominal flow to natural circulation regime, typical of decay heat removal (DHR) regime. To this purpose the CIRCE pool facility has been updated to host a suitable test section in order to reproduce the thermal-hydraulic behaviour of a HLM pool-type reactor. The test section basically consists of an electrical bundle (FPS) made up of 37 pins arranged in a hexagonal wrapped lattice with a pitch diameter ratio of 1.8. Along the FPS active length, three sections were instrumented to monitor the heat transfer coefficient along the bundle as well as the cladding temperatures at different ranks of the sub-channels. This paper reports the experimental data as well as a preliminary analysis and discussion of the results, focusing on the most relevant tests of the campaign, namely Test I (48h) and Test II (97h). Temperatures along three sections of the FPS and at inlet and outlet sections of the main components were reported and the Nusselt number in the FPS sub-channels was investigated together with the void fraction in the riser. Concerning the investigation of in-pool thermal stratification phenomena, the temperatures in the whole LBE pool were monitored at different elevations and radial locations. The analysis of experimental data obtained from Tests I and II underline the occurrence of thermal stratification phenomena in the region placed between the outlet sections of the HX and the DHR, respectively. After the transition to natural circulation, for both tests, this region with temperature stratification moves downwards starting at the exit section of the DHR-system, while upper and lower vessel regions show a uniform temperature.

Numerical investigation of three-dimensional natural circulation phenomenon in passive safety systems for decay heat removal in large pools

Abstract Many advanced designs of nuclear reactors adopt a methodology of passive safety systems in order to avoid the occurence of a severe accident. In one of such systems, the decay heat generated from a reactor is transferred by natural circulation into large pool of water called the Gravity Driven Water Pool (GDWP). Three-dimensional (3D) convection flows develop, which in turn affect the heat transfer process and hence the temperature pattern. The heat transfer process can get compromised by the possible stratification of the temperature. Further, the material of construction of GDWP may have certain temperature limitations and puts bounds on the extent of stratification. The objective of this study is to investigate the 3D natural circulation phenomenon in GDWP. The present work is in continuation of our earlier work Gandhi et al. [1,2] where the natural convection has been analyzed in 0.025 and 0.21 m3 vessels. Now, we have reported the simulation for 9247 m3 GDWP tank. Single phase CFD simulations using open source CFD code [OpenFOAM-1.6] have been performed for a geometry (ID = 12 m, OD = 50 m and height (HT) = 5 m). In order to reduce the thermal stratification, various geometrical modifications have been incorporated on the heat exchanger design, such as (1) distributing the heat transfer area of heat exchanger among single, double and multiple heat sources (2) to optimize the location of heat exchanger inside the GDWP (3) provision of passive elements such as draft tubes (single or concentric multiple) around the heat source at the center, which can act as a chimney. A detailed CFD analysis of three dimensional temperature and velocity distribution in the secondary side of GDWP has confirmed the mitigation of thermal stratification phenomenon by optimizing the distribution and position of heat exchangers. Passive draft tubes also result in significant enhancement in natural circulation and hence reduction in thermal stratification.

典型亚热带热分层水库秋季细菌群落垂直分布

水库在我国东南沿海地区是重要的饮用水水源地,对地区经济发展和社会稳定起到重要作用.选择亚热带地区典型的热分层水库——福建莆田东圳水库,于2011年秋季稳定分层期,以水体温度的垂直变化特征为依据进行分层采样.应用PCR-DGGE和克隆测序的方法研究浮游细菌群落的垂直分布特征,利用多元统计分析揭示细菌群落与热分层水体理化指标之间的关系.结果显示:溶解氧、电导率、叶绿素a、总氮、氨氮及硝氮在上下层水体中的分布有显著差异,下层缺氧区细菌的Shannon-Wiener指数和DGGE条带数明显高于上层好氧区,表明东圳水库热分层水体中存在明显的物理、化学及生物分层现象.测序结果表明β-变形菌可能是东圳水库中占优势的细菌类群,统计结果提示溶解氧是显著影响细菌群落组成的环境因子.热分层水体的物理化学分层与水体细菌群落结构密切相关,提示水库生态学研究应对水体热分层给予重视.;Fujian reservoirs in southeast China are important water resources for economic and social sustainable development, although few have been studied previously. Dongzhen Reservoir, a typical subtropical stratified reservoir in Fujian, was chosen for investigation of bacterial distribution, composition and diversity in autumn 2011. As the only built large reservoir in Putian City, it plays an important role in irrigation, flood control, hydroelectric power, and water supply. Dongzhen Reservoir shows an obvious phenomenon of water thermal stratification during summer and autumn, thus creates a unique gradient of environmental variables along the water column. We investigated the bacterial community and its relation to environmental variables in this study for a better understanding of vertical distribution of bacterial community and the primary environmental drivers in a stratified reservoir. Five water samples were collected from five different depths according to the vertical changes of temperature. Both PCR-DGGE and sequencing were used to investigate the bacterial community and diversity. Moreover, physical and chemical parameters were measured according to the national standard methods. Multivariate statistical techniques were used to examine the relationship between bacterial community and environmental variables. Principal component analysis (PCA) clearly showed that water temperature, dissolved oxygen (DO), chlorophyll a (Chl a), total nitrogen (TN), ammonia nitrogen (NH₄-N), nitrite/nitrate nitrogen (NO_<em>x</em>-N) and electric conductivity of the upper aerobic zone were differed from those of the deeper anoxic zone. Both the number of DGGE bands and the Shannon-Wiener index of the deeper anoxic zone were higher than those of the upper aerobic zone. Further, two groups were distinguished by the cluster analysis of bacterial communities based on the Bray-Curtis similarity. Thus, Dongzhen Reservoir presented an obviously physical, chemical, and biological stratified phenomenon. Seven bands that common to all sampling depths were extracted and sequenced, and among which four were identified as Betaproteobacteria, indicating that Betaproteobacteria were the most dominant taxa in Dongzhen Reservoir in autumn. Bacterial community composition and diversity differed greatly among different sampling depths, and these differences were closely related to the physical and chemical stratification of the water body. Redundancy analysis (RDA) demonstrated DO was the significant environmental variable that shaping the bacterial community and diversity (<em>P</em> < 0.01). Therefore, we should pay more attention to DO and thermal stratification of reservoirs for sustainable reservoir management.