Reflux Condensation and Transition to Natural Circulation in a Vertical U-Tube

1983 ◽  
Vol 105 (4) ◽  
pp. 719-727 ◽  
Author(s):  
S. Banerjee ◽  
J-S. Chang ◽  
R. Girard ◽  
V. S. Krishnan
Keyword(s):  
Boundary Conditions ◽  
Flow Rate ◽  
Pressure Difference ◽  
Natural Circulation ◽  
Heat Removal ◽  
Liquid Column ◽  
Steam Flow ◽  
Steam Generators ◽  
Cooling Jacket ◽  
Over The Top

Reflux and natural circulation condensation in vertical inverted U-tube steam generators form an important heat removal mechanism for nuclear reactors in certain accidents. As a first step in understanding the behavior of such steam generators, condensation was studied in a single vertical tube with a cooling jacket. Steam was fed into the tube from an inlet plenum and condensed in the jacketed region. The inlet and outlet pressures and cooling jacket conditions were controlled to give well-defined boundary conditions. The amount of steam condensed and the flow patterns obtained were determined. The steam flow rate into the tube initially increased with pressure differences between the inlet and outlet plenums. The condensate ran back to the inlet plenum countercurrent to the steam flow (reflux flow). At a certain pressure difference, no further increase in steam inlet flow rate was observed though pure refluxing was maintained. Instead, a column of liquid formed above the two-phase condensing region. The length of this column increased as the pressure difference was increased. At a sufficiently large pressure difference the liquid column carried over the top of the vertical U-bend and there was a dramatic change in flow regime to natural circulation condensation in which the bulk of the condensate flowed cocurrently with the steam. The behavior of the system was explained by postulating that “flooding” conditions were reached at the inlet when the pressure difference became large enough for a liquid column to form above the condensing region. A small perturbation analysis of the stability of the condensing and liquid column regions was done using a lumped parameter approach and constant pressure boundary conditions. Experimental results on the frequency of oscillations in a single tube followed the qualitative trends predicted by the linear analysis, but the predicted frequencies were about twice as high as those observed.

scholarly journals Modes of Circulation in an Inverted U-Tube Array With Condensation

1982 ◽  
Vol 104 (4) ◽  
pp. 769-773 ◽  
Author(s):  
C. Calia ◽  
P. Griffith
Keyword(s):  
Heat Transfer ◽  
Steam Generator ◽  
Flow Rate ◽  
Pressure Difference ◽  
Operating Conditions ◽  
Steam Generators ◽  
Modes Of Operation ◽  
Glass Tubes ◽  
Abnormal Operating Conditions ◽  
Plenum Pressure

An experiment and analysis was performed on an inverted U-tube steam condenser (similar to a steam generator) to determine the modes of flow that can exist as the rate of steam flow into the condenser is reduced. The condenser consisted of four glass tubes connected to a common inlet plenum and a common exit plenum. Heat-transfer and flow-rate measurements, as well as visual observations were made. Four different modes of operation were identified. Noncondensables were found to substantially alter the plenum to plenum pressure difference and aid flow stability. Satisfactory analytical descriptions of the observations have been developed as well as application of the results to the condensing behavior of nuclear steam generators under abnormal operating conditions.

Analysis of PRHRS for an Integral Pressurized Water Reactor Using RELAP5/MOD3.4

2010 ◽  
Author(s):  
Xuhua Ye ◽  
Minjun Peng ◽  
Jiange Liu
Keyword(s):  
Natural Circulation ◽  
Heat Removal ◽  
Parameter Study ◽  
Pressurized Water Reactor ◽  
Steam Generators ◽  
Primary Coolant ◽  
Pressurized Water ◽  
Water Reactor ◽  
Pressure Peak ◽  
Residual Heat

An investigation on the thermal hydraulic characteristics of the passive residual heat removal system (PRHRS) which is used in an integral pressurized water reactor (INSURE-100) is presented in this paper. The main components of primary coolant system are enclosed in reactor vessel. Primary fluid flow circle is natural circulation. The PRHRS can remove the energy from the primary side as long as the residual heat exchanger (RHE) is submerged in the emergency cooldown tank (ECT). The parameter study is performed by considering the effects of an effective height between the steam generators and the RHE and a valve actuation time, which are useful for the design of the PRHRS. The mass flow in the PRHRS has been affected by the height difference between the steam generators and the RHE. The pressure peak of the primary side and PRHRS has been affected by the valve action time.

An Experimental Study on Open Natural Circulation Flow Characteristics by Air Injection

2017 ◽  
Author(s):  
Pengjiu Cao ◽  
Xiaxin Cao ◽  
Zhongning Sun ◽  
Ming Ding ◽  
Na Li ◽  
...  
Keyword(s):  
Flow Rate ◽  
Driving Force ◽  
Flow Instability ◽  
Natural Circulation ◽  
Heat Removal ◽  
Air Injection ◽  
Circulation System ◽  
Circulation Flow ◽  
Churn Flow ◽  
Circulation Flow Rate

An open natural circulation system has the characteristics of a simple structure, superior safety performance and strong heat removal capability. However, during long-term operation, the flow instability may occur due to the reduction of the driving force, which will have adverse effects on the heat removal capability and safe operation of the system. Thus, injecting air into the riser is designed in this paper to improve the driving force of the circulation flow, reduce the possibility of flow instability, and increase the heat removal capability. In order to investigate the influence of air injection on the evolution of flow pattern, resistance characteristics and circulation flow rate, the method of visual observation and data analysis is used based on different pore sizes porous media, air injection rate and submergence ratios. The ratio of the driving pressure head to the resistance pressure drop is proposed as the basis for assessing the effect of air injection on the ability of natural circulation. It is found that the driving force of natural circulation increases with the increase of air injection rate, and the circulation flow rate increases obviously when the bubbly flow appears in the riser. However, when the transition from bubbly flow to churn flow appears, the growth of the circulation flow rate slows down because the resistance increases faster than the driving force. Therefore, it can be known that the best performance is obtained when bubbly-churn flow appears in the top of the riser. What’s more, the capacity of lifting water will be reduced and churn flow will appear prematurely when the submergence ratio decreases. This means that in the process of open natural circulation system design, the submergence ratio of the system should be increased as much as possible. Finally, in this paper, it is found that the bubble pump with PS = 0.2 μm has better performance.

Theoretical Analysis of a Natural Circulation System Under Rolling Condition Based on RELAP5/MOD3.3 Code

2013 ◽  
Author(s):  
Haibo Lian ◽  
Hongye Zhu ◽  
Xingtuan Yang ◽  
Shengyao Jiang
Keyword(s):  
Flow Rate ◽  
Natural Circulation ◽  
Large Angle ◽  
Heat Removal ◽  
Circulation System ◽  
Ship Motions ◽  
Rolling Angle ◽  
Empirical Formulas ◽  
Body Forces ◽  
Short Period

Natural circulation is an important process for certain advanced reactor’s main loop and passive heat removal systems. However, in marine conditions the thermo-hydraulic characteristics of natural circulation will change because of the ship motions such as inclination, rolling and heaving, which introduces extra body forces in to the system. In this paper, we conducted theoretical studies on the natural circulation behaviors in a symmetrical two-circuit loop under rolling conditions. A RELAP5/MOD3.3 code is developed based on the basic control equations and empirical formulas. Based on this code the natural circulation behavior under a larger range of rolling angle and period is also investigated. It is found that with the increase of rolling angle and decrease of rolling period, the magnitude of flow fluctuation increases. The fluctuation period of mass flow rate do not always consists with the rolling period under the comprehensive actions of complex body forces. Under the rolling with large angle and short period, the fluctuation period of flow rate is only half the rolling period.

Experiment and Analysis on Isolation Condenser Simulator Using Pressurized Steam

2020 ◽  
Author(s):  
Kosuke Ono ◽  
Yasunori Yamamoto ◽  
Masayoshi Mori ◽  
Tetsuya Takada
Keyword(s):  
Heat Transfer ◽  
Temperature Distribution ◽  
Void Fraction ◽  
Flow Rate ◽  
Nuclear Power ◽  
Natural Circulation ◽  
Heat Removal ◽  
Condensation Process ◽  
Heat Transfer Tube ◽  
Transfer Tube

Abstract Isolation condensers (ICs) are important passive cooling systems in BWRs. After the Fukushima Daiichi Nuclear Power Station accident, concerns if the IC was able to restart with the inflow of hydrogen were arose. Because ICs lose heat removal ability when non-condensable gas inflow occurs, accurate evaluation of the effect is necessary. To develop analysis methods, as an initial stage, experiments and analyses considering only high-pressure steam and water were conducted. The experiment was done by an isolation condenser simulator which contains an accumulator with heaters inside, and a heat transfer tube. From the experiment, all steam was condensed at the heat transfer tube and the approximate position of complete condensation was confirmed from the temperature distribution and the observation. The experiment provided data such as temperature distribution, natural circulation flow rate, and pressure to compare with the analysis. The analyses were conducted for 4 cases of void fraction values at the heat transfer tube inlet and found that it has a high sensitivity to condensation. The reason is estimated to be the difference in inflow velocity that strongly depends on the void fraction even if the mass flow rate is constant. And the initial condition of the liquid film also affected condensation process. Heat removal at the section before the heat transfer tube should be considered to adjust void fraction at the inlet of heat transfer tube.

Simulation Model of a Passive Decay Heat Removal System for Lead-Cooled Fast Reactors

2014 ◽  
Vol 137 (3) ◽  
Author(s):  
Lorenzo Damiani ◽  
Alessandro Pini Prato
Keyword(s):  
Fast Reactor ◽  
Natural Circulation ◽  
Heat Removal ◽  
Coolant Temperature ◽  
Feed Water ◽  
Steam Generators ◽  
Fast Reactors ◽  
Primary Coolant ◽  
Reaction Heat ◽  
Decay Heat

The generation IV lead cooled fast reactors are of particular interest for the Italian research: several influential companies (Ansaldo Nucleare, ENEA) are involved in these important European R&D projects. At present, one significant European project in progress is lead cooled European advanced demonstrator reactor (LEADER) which includes, among its goals, the construction of a lead-cooled fast reactor demonstrator, advanced lead fast reactor European demonstrator (ALFRED). The demonstrator has to include technical solutions that simplify the construction phase and assure full safety in operation; according to the latest guidelines, ALFRED final configuration will be characterized by a secondary loop providing bayonet-tube steam generators. The authors have addressed the issue of bayonet-tube steam generators proposing the external boiling bayonet steam generator (EBBSG) system, in which the reaction heat is extracted from the lead by means of coolant under vapor phase. This is possible thanks to an external feed-water boiling, based on the known Loeffler scheme, coupled to the bayonet tube concept. In the present paper, the authors propose a decay heat removal (DHR) system to match the EBBSG scheme. The DHR system is fully passive, exploiting natural circulation phenomena. The performance of the proposed DHR system is investigated through a Matlab-Simulink model. The results are satisfactory since, according to the simulations, the proposed DHR system is able to keep the primary coolant temperature within a safety range for a sufficient time, avoiding the lead freezing or over-heating.

scholarly journals Preliminary Assessment of Decay Heat Removal Systems in the ESFR-SMART Design: The Role of Natural Air Convection Around Steam Generators Outer Shells in Accidental Conditions

2020 ◽  
Author(s):  
Jeremy Bittan ◽  
Clement Bore ◽  
Joel Guidez
Keyword(s):  
Natural Circulation ◽  
Heat Removal ◽  
Steam Generators ◽  
Preliminary Assessment ◽  
Safety Criterion ◽  
Safety Level ◽  
Decay Heat ◽  
Air Convection ◽  
The Impact

Abstract In the frame of the ESFR-SMART European project, aiming at improving the safety level of the European Sodium cooled Fast Reactor (ESFR), this paper presents the preliminary assessment of decay heat removal systems in the ESFR-SMART design: the role of natural air convection around Steam Generators outer shells in accidental conditions. Both theoretical and CATHARE code (Thermal Hydraulics reference code) calculations are presented. The impact of an additional chimney at the top of each casing as well as running primary and secondary pumps on the heat removal capacity are equally evaluated. This paper shows that the evacuation of decay heat thanks to completely passive air natural circulation alone, in case of Fukushima like accident, should lead to temperatures of sodium in the reactor vessel temporarily exceeding the safety criterion of 650°C. The addition of chimneys increase the capacities but is not sufficient to evacuate the decay heat safely. If the primary and secondary side pumps are running, the safety criterion should be met.

scholarly journals Decay Heat Removal and Transient Analysis in Accidental Conditions in the EFIT Reactor

2008 ◽  
Vol 2008 ◽  
pp. 1-8 ◽  
Author(s):  
Giacomino Bandini ◽  
Paride Meloni ◽  
Massimiliano Polidori ◽  
Maddalena Casamirra ◽  
Francesco Castiglia ◽  
...  
Keyword(s):  
Natural Circulation ◽  
Thermal Power ◽  
Heat Removal ◽  
Normal Operation ◽  
Steam Generators ◽  
Flow Paths ◽  
Decay Heat ◽  
Driven System ◽  
Accelerator Driven System ◽  
Relap5 Code

The development of a conceptual design of an industrial-scale transmutation facility (EFIT) of several 100 MW thermal power based on accelerator-driven system (ADS) is addressed in the frame of the European EUROTRANS Integral Project. In normal operation, the core power of EFIT reactor is removed through steam generators by four secondary loops fed by water. A safety-related decay heat removal (DHR) system provided with four independent inherently safe loops is installed in the primary vessel to remove the decay heat by natural convection circulation under accidental conditions which are caused by a loss-of-heat sink (LOHS). In order to confirm the adequacy of the adopted solution for decay heat removal in accidental conditions, some multi-D analyses have been carried out with the SIMMER-III code. The results of the SIMMER-III code have been then used to support the RELAP5 1D representation of the natural circulation flow paths in the reactor vessel. Finally, the thermal-hydraulic RELAP5 code has been employed for the analysis of LOHS accidental scenarios.

Study of fluid flow through a channel deformed by piezoelement

2018 ◽  
Vol 13 (3) ◽  
pp. 1-10 ◽  
Author(s):  
I.Sh. Nasibullayev ◽  
E.Sh Nasibullaeva ◽  
O.V. Darintsev
Keyword(s):  
Fluid Flow ◽  
Pressure Drop ◽  
Boundary Conditions ◽  
Flow Rate ◽  
Contact Surface ◽  
Piezoelectric Element ◽  
Neumann Boundary ◽  
Differential Pressure ◽  
Physical Parameters ◽  
Flow Through

The flow of a liquid through a tube deformed by a piezoelectric cell under a harmonic law is studied in this paper. Linear deformations are compared for the Dirichlet and Neumann boundary conditions on the contact surface of the tube and piezoelectric element. The flow of fluid through a deformed channel for two flow regimes is investigated: in a tube with one closed end due to deformation of the tube; for a tube with two open ends due to deformation of the tube and the differential pressure applied to the channel. The flow rate of the liquid is calculated as a function of the frequency of the deformations, the pressure drop and the physical parameters of the liquid.

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