Investigation of Steady-State Characteristics of Natural Circulation Loop

2013 ◽  
Author(s):  
Zheng Huang
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Two Phase Flow ◽  
Flow Instability ◽  
Natural Circulation ◽  
Circulation Loop ◽  
Phase Flow ◽  
Two Phase ◽  
Natural Circulation Loop ◽  
Flow Case

Natural circulation is one of the most important mechanisms of passive safety systems in the advanced NPP design. By using RELAP5, steady-state behaviors of a typical natural circulation loop (NCL) were investigated. The Influences of various system parameters, such as pressure, cooling heat transfer area and loop height were studied. The results show that the heat transfer power of the NCL (i.e. the heat transferred from the heater to the tank by NCL) is linear with respect to the temperatures of boundary heat source and sink, excluding the phase transition region. The NCL operation mode (i.e. two-phase flow or one-phase flow) is mainly determined by the loop pressure. It is found that with the decrease of the pressure, the two-phase flow operation range is widened. The heat transfer power of two-phase flow case is always higher, and varies more substantially with pressure, than that of one-phase flow case under the same boundary temperatures. However, flow instability may occur for two-phase flow case. By increasing the area of heat transfer surface between loop cooling section and tank, the temperature difference between the inlet and the outlet of loop heating section as well as the heat transfer power of the NCL will increase. But the influence is insignificant when the tank temperature is relatively high. It is also observed that for both one-phase flow and two-phase flow, the change of loop height has little effect upon the heat transfer power of the NCL under the given boundary condition in this study.

Analytical Study of Two-Phase Flow Instability in a Natural Circulation PWR Auxiliary Feedwater System

2013 ◽  
Author(s):  
Jong Chull Jo ◽  
Frederick J. Moody ◽  
Kyu Sik Do
Keyword(s):  
Water Level ◽  
Two Phase Flow ◽  
Flow Instability ◽  
Natural Circulation ◽  
Circulation Loop ◽  
Phase Flow ◽  
Vertical Pipe ◽  
Two Phase ◽  
Pipe Section ◽  
Natural Circulation Loop

A PWR incorporates a passive auxiliary feedwater system (PAFS), a closed natural circulation loop which is aligned to feed condensed water to its corresponding steam generator (SG). During its operation, saturated steam in the SG secondary side moves up due to buoyancy force and passes through a steam line, and then flows into a tube-tank type passive condensation heat exchanger where steam is condensed inside the tubes while the tube outer surfaces are cooled by the pool water. The condensate water is passively fed into the SG economizer by gravity. Because a natural circulation loop is susceptible to two-phase flow instability, it is requisite to confirm the system is designed adequately to avoid the potential challenges to its operational safety due to the instability. This paper presents an analytical approach for assessing if the PAFS has possible thermal and fluid mechanical characteristics which could lead to an undesirable unstable or oscillating condensate water level in the vertical pipe section. Both steady and unsteady analytical solutions for a simplified natural circulation loop model of the PAFS were derived in terms of the condensate water level and velocity in the vertical pipe section. From the solutions, the criteria for determining a potential for two-phase instability in the system were obtained.

Steady-State Behavior of a Two-Phase Natural Circulation Loop With Thermodynamic Nonequilibrium

2009 ◽  
Vol 131 (2) ◽  
Author(s):  
Dipankar N. Basu ◽  
Souvik Bhattacharyya ◽  
P. K. Das
Keyword(s):  
Heat Transfer ◽  
Steady State ◽  
Natural Circulation ◽  
Circulation Loop ◽  
Control Parameters ◽  
Subcooled Boiling ◽  
Two Phase ◽  
State Behavior ◽  
Natural Circulation Loop ◽  
Steady State Behavior

A model to predict the steady-state behavior of a rectangular two-phase natural circulation loop has been proposed. The analysis employs a one-dimensional two-fluid model to identify various system parameters, with particular emphasis on the subcooled boiling region. The onset of two-phase region and point of net vapor generation and associated liquid temperatures and vapor qualities have been estimated using a few widely recognized correlations. Predicted results demonstrate that the consideration of subcooled boiling may have significant effect on system behavior, particularly around the transition regions. The interaction of saturated bubbles and subcooled liquid and associated change in heat transfer and frictional forces has been discussed in detail. Fluid stream has been observed to have different combinations of flow stream conditions at boiler exit and condenser inlet. Five probable combinations have been identified and a generalized working-regime map has been proposed on Nsub−NZu plane. Attempts have been made to identify the influence of various control parameters. A favorable sink condition (higher coolant flow rate or lower coolant entry temperature) has been found to be of particular importance to attain a wider operating range of wall heat flux and better heat transfer characteristics. A design map has been proposed to identify favorable operating condition in terms of control parameters to ensure complete condensation.

Measurement of Natural Circulation Two-Phase Flow by Hybrid Doppler Contrapropagating and Pulse Echo Ultrasonic Techniques

2009 ◽  
Author(s):  
Jose´ L. H. Faccini ◽  
Jen-Shih Chang ◽  
Glenn D. Harvel ◽  
Paulo A. B. De Sampaio ◽  
Jian Su
Keyword(s):  
Flow Rate ◽  
Single Phase ◽  
Two Phase Flow ◽  
Natural Circulation ◽  
Circulation Loop ◽  
Phase Flow ◽  
Two Phase ◽  
Flow Rates ◽  
Natural Circulation Loop ◽  
Pulse Echo

In this work, a hybrid ultrasonic technique for diagnostic natural circulation gas-liquid two-phase flow is experimentally investigated. The method is applied on a two-phase natural circulation loop using a contrapropagating transmission flow rate measurement technique in the single phase section and a Doppler velocity measurement and single transducer pulse echo technique in the two-phase region. The two-phase natural circulation loop used in this work consists of a two-phase vertical section where the liquid has an induced flow rate by an air-lift pumping technique. Gas is injected into the lower region of the two-phase test section, and rises to a separation tank causing the liquid to circulate naturally about the loop. The liquid slug velocities, the air flow rates, and the liquid flow rates are measured, respectively, in the two-phase and single-phase section of the loop as well as two-phase interfaces and time averaged void fraction. A comparison with available results from other investigators is given, in terms of liquid superficial velocity and bubble velocity for two flow patterns generated in the loop; bubbly flow and slug flow. The results show that the present hybrid system can be used to identify not only flow regime but also key two-phase flow parameters for natural circulation conditions.

EXPERIMENTAL STUDY OF TWO-PHASE FLOW OSCILLATIONS IN A NATURAL CIRCULATION LOOP

2016 ◽  
Author(s):  
André Luiz Braucks Vianna ◽  
Su Jian ◽  
José Luiz Horacio Faccini ◽  
André Luiz Braucks Vianna
Keyword(s):  
Experimental Study ◽  
Two Phase Flow ◽  
Natural Circulation ◽  
Circulation Loop ◽  
Phase Flow ◽  
Two Phase ◽  
Natural Circulation Loop ◽  
Flow Oscillations
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