Circulation Flow Characteristics Research Articles

A review of natural circulation flow in integral effect test facilities

The proposed NCFM map was reviewed using natural circulation data identified in the PWR simulated integral effect test (IET) facility with a height (length) scale ratio of 1/1. Based on this, the characteristics of natural circulation flow in the ATLAS and FESTA facilities, which are major IET facilities in Korea, are compared. It was confirmed that the natural circulation flow characteristics were well maintained within the NCFM area even at the half-height test facility of ATLAS. It was also confirmed that the natural circulation flow characteristics were well maintained within the NCFM area at the full-height test facility of FESTA, and the natural circulation flow characteristics were also maintained outside the NCFM region for a relatively small amount of coolant inventories.

一体化反应堆自然循环流动传热特性分析

一体化反应堆自然循环流动传热特性分析

Inner circulation flow characteristics of coalescence droplets in microchannel

Controllable coalescence of multiple droplets is an important part of droplet manipulation, which is used to add samples to existing droplets, complete multi-step biological and chemical reactions inside droplet. It is of great importance to study the internal circulation characteristics for enhancing heat and mass transfer inside droplets. In this paper, microchannel experiments and volume of fluid method are conducted, and the evolution process of droplet coalescence is analyzed. The velocity distribution inside droplet is used as the main index to study the internal circulation characteristics under different surface velocities conditions. A characterization method of internal circulation strength based on central radial velocity and axial velocity inside the droplet is proposed, which can characterize the internal circulation region inside droplet caused by shearing action of microchannel wall of continuous phase. Results show that with the decrease of droplet length, the velocity distribution inside the droplet changes from being dominated by shearing action of microchannel wall to shearing action of continuous phase. In the process of droplet coalescence, there is a convective trend in the contact area between two droplets, and the maximum radial and axial velocities reach 3.5 times and 7.5 times of the droplet surface velocity respectively. This work can provide a reference for improving droplet control accurancy and mixing efficiency.

Study on seafloor hydrothermal systems circulation flow and heat transfer characteristics

<abstract> <p>In this work, the numerical simulation study of the hydrothermal flow and heat transfer process in the porous rock under 30 MPa pressure was developed. The flow and heat transfer characteristics of hydrothermal in rocks with different porosities are studied by changing the porosity of the rock. The simulation results show that the average flow velocity decreases and the average temperature increases when the porosity decreases. The velocity field and temperature field are coupled due to the nonlinear thermophysical properties of hydrothermal. The velocity field and temperature field have strongly interacted in the range of 400–450 ℃ and the effect of temperature on velocity is gradually diminishing outside the range. Most of the fluid will be "squeezed" into the crevice and the average velocity is almost three times the no-creviced case when a crevice is present. The existence of the crevice makes the total heat flux decrease from an overall perspective, and the crevice makes a large temperature gradient at the entrance and export of the crevice from a local perspective. These results provide theoretical support for the utilization of submarine hydrothermal fluid shallow circulation heat energy.</p> </abstract>

Analysis of Heat Transfer Deterioration and Natural Circulation Flow Characteristics of Supercritical Carbon Dioxide in a Simple Circulation Loop

Analysis of Heat Transfer Deterioration and Natural Circulation Flow Characteristics of Supercritical Carbon Dioxide in a Simple Circulation Loop

The simulation research on the natural circulation operation characteristic of FNPP in rolling and inclined condition

Abstract Recently, the FNPP (Floating Nuclear Power Plant) has got more and more attention and rapid development due to very wide prospect application on remote areas or islands. In general, the IPWR (Integral Pressurized Water Reactor) is adopted to meet the requirements of the limited space, the nuclear safety and the maneuverability in marine. The IPWR could depend on natural circulation operation to remove the residual heat of core under accident or low load operation condition. Because the driving head is low, the natural circulation flow is likely to be influenced by rolling and inclined condition. To clarify the natural circulation flow characteristics of the core in FNPP rolling motion and inclined condition, based on the modified THEATRe code by adding the ocean motion module and spatial coordinate convert module, the main thermal-hydraulic parameters variation in rolling and inclined condition were obtained. The effect of inclined angle, rolling amplitude and period on the natural circulation flow were discussed. The natural circulation flow in the core fluctuates periodically with rolling motion. And the inclination and rolling will also cause the degree of steam superheat of OTSG secondary side fluctuate, which could impact on the stable operation of secondary side system.

CFD analysis on flow and heat transfer characteristic in natural circulation system with subchannels under rolling conditions

The combination of advancement in nuclear technology and ship engineering is a new technology of nuclear application which can not only marine capability and provide power for remote islands, but also help solve the practical issues of high cost, high pollution and high pressure in cutting down emissions in the petroleum exploitation field. The CFD analysis in this paper focuses on the exploration of single-phase natural circulation flow and heat transfer characteristics for rod bundle under rolling conditions. The rolling version CFD tool is developed and compared with the calculated results by system code. The natural circulation system which consists of a 2 by 2 subchannel is established. This paper mainly focuses on the effect of different rolling parameters on natural circulation flow and heat transfer characteristics for rod bundle loop under rolling motion. The thermal–hydraulic performance varies periodically under rolling motion. The variation period equals to rolling period. The stronger the rolling intensity is, the greater the fluctuations of different thermal–hydraulic parameters are. The average values of mass flux and heating section temperature difference under rolling conditions are lower than those under non-rolling conditions, proving that rolling motion may enhance heat transfer. Meanwhile, the inlet temperature of heating section under rolling conditions is lower compared with that under non-rolling conditions. With increasing rolling intensity, the effect of heat transfer enhancement is greater.

The natural circulation flow characteristic of the core in floating nuclear power plant in rolling motion

In recent years, the FNPP (Floating Nuclear Power Plant) has got more and more attention and rapid development due to very wide prospect application on remote areas or islands. In general, the IPWR (Integral Pressurized Water Reactor) is adopted to meet the requirements of the limited space, the nuclear safety and the maneuverability in marine. The IPWR could depend on natural circulation operation to remove the residual heat of core under accident conditions or low load operation condition. Because the driving head is low, the natural circulation flow in many parallel channels is likely to be influenced by ocean motion and thermonuclear coupling effect. Among various kinds of ocean motions, the rolling motion will introduce the additional force pressure drop and change the gravity pressure drop with time, so the force acting on coolant in the assemblies will be more complex. In order to clarify the natural circulation flow characteristics of the core in FNPP in rolling motion, based on the modified RELAP5 code by adding the ocean motion module and spatial coordinate convert module, the neutron physics and thermal-hydraulic coupled model of IPWR was been established. The core three-dimensional distribution, the radial cross-section and axial distribution of main thermal-hydraulic parameters were obtained. The effect of the tangential force pressure drop, the centripetal force pressure drop and the gravity pressure drop on the coolant in the core in rolling motion were discussed. The results showed that the natural circulation flow rate fluctuates periodically with the rolling motion. And the time-varying gravity pressure drop is the main effect factor of fluctuation. Because of the structure of IPWR is compact, the rolling radius is relatively short, the effect of the general rolling motion on the natural circulation flow distribution of the core is not obvious. The coolant temperature and the fuel power distribution of the core periphery fluctuates slightly, and the reactivity feedback introduced by the coolant temperature and the fuel temperature fluctuation is relatively small. In consequence, the FNPP in the movable marine platform in natural circulation mode operation is safety in general rolling motion.

An experimental study on natural circulation flow characteristics under passive IVR-ERVC conditions

In vessel retention (IVR) of molten core debris via water cooling at the external surface of the reactor vessel is an important severe accident management feature of advanced passive plants. During postulated severe accidents, the heat generated by the molten debris relocated to the lower head of reactor pressure vessel needs to be removed continuously to prevent vessel failure.Besides the local critical heat flux (CHF) of outer wall surface which is of the first importance, a stable feature of natural circulation flow and an effective natural circulation capability within the external reactor vessel cooling (ERVC) channel tend to be rather crucial for the success of IVR. Under this circumstance, a full-height ERVC test infrastructure, reactor pressure vessel external cooling II test facility (REPEC-II) was designed and constructed in Shanghai Jiao Tong University (SJTU). During test campaign on the REPEC II facility, the one-dimensional natural circulation boiling flow characteristics with the experimental observation and measurement are investigated under IVR-ERVC conditions.Based on the abundant results acquired in the test campaign, it is attempt to evaluate the ERVC performances and trends under various practical engineered conditions in this paper. From this study, the following conclusions can be made: The influence of different power shapes on the two-phase natural circulation flow is not obvious, while the impact on the resistance characteristics of the outlet section is very significant. Among all the test conditions (power shapes, subcooling, flow path configuration and water level), the resistance characteristics of the outlet section change the most compared with other sections. It is expected that these conclusions may help designers to have a reliable estimate of the impact of some related engineered factors on real IVR-ERVC performance.

Integral effect test on station blackout (SBO) scenario with steam generator tube rupture (SGTR) in ATLAS facility

Station blackout (SBO) is one of the most important design extension conditions (DECs) because a total loss of the heat sink leads to a core uncovery or damage without any proper operator action. During a long transient of an SBO, a steam generator tube rupture (SGTR) accident can occur when a steam generator tube is exposed to a superheated steam flow. In this study, a prolonged SBO with an SGTR occurrence was experimentally investigated by performing an integral effect test with the ATLAS facility. For the transient simulation, the tube rupture was simulated when the core water level became below the top of the active core. As an accident management measure, the auxiliary feedwater was supplied to the intact steam generator when the maximum heater surface temperature started to show an excursion behavior. The experimental results showed that a single tube rupture could not sufficiently reduce the primary system pressure before the injection of the auxiliary feedwater. A delayed supply of the auxiliary feedwater after an excursion of the heater surface temperature successfully cooled the primary system until the end of the transient, where inflow of the coolant from the pressurizer contributed to a recovery of the coolant inventory in the core. The natural circulation flow characteristics in the primary system showed an oscillating behavior depending on the heat removal rate of the steam generators. This integral effect test data can be used to evaluate the prediction capability of safety analysis codes and identify code deficiencies in predicting an SBO transient with an SGTR occurrence.

The Three-Dimensional Dynamic Characteristics on the South of Subei Radiation Shoal Waters

Based on the high precision terrain datas , high resolution FVCOM(Finite-Volume Coastal Ocean Model) numerical model was established to simulation for tide current and study three-dimensional dynamic characteristics of the south of Radiation shoal waters. Result show that transverse circulation was easy to produce in channel and groove. The vorticity and helicity computation method was applied in the area for the frist time. Transverse circulation and helical flow characteristics of typical sections were preliminary studied, and result show the quantitative evidence for the existence of the Spiral flow.Deep groove is not always appear double reverse spiral flow structure, it changes with the main flow velocity. Shoal grooves appear, a main spiral flow structure, and show great adaptability to the terrain, which is the reflection of the spiral flow to the terrain maintain mechanism .

Study theoretically on two-phase circulation flow characteristics under ERVC condition in advanced PWR

For the problem of two-phase natural circulation flow in gap clearance between reactor vessel lower head and insulator in the condition of severe accident, one-dimensional steady-state natural flow analysis code was written by utilizing FORTRAN. Based on the code, the effects of different correlations for friction coefficient and the number of nodes of heating section on mass flow rate of two-phase natural circulation flow were studied. And the results are compared with that of Chinese REPEC experiment and simulation using RELAP5 program so as to verify the rationality and correctness of the code. Based on the experiment data, simulation results and the model, friction coefficient and the void fraction condition under ERVC correlation are obtained by fitting. The results calculated by the model using fitting friction coefficient correlation agree well with ULPU V test data. Furthermore, the effect of power, pressure, inlet area, gap diameter, flooding level and inlet water subcooling on mass flow rate and void fraction of two-phase natural circulation were studied utilizing this code.

C212 沸騰気泡を利用した自然循環冷却システムの開発 : 基礎特性評価(OS-9:沸騰・凝縮伝熱および混相流の最近の展開(3))

In recent years, ebullient cooling and forced-circulation cooling is applied to cooling system for power conversion equipment of high capacity. However, problems of precipitous temperature fluctuation, correspondence to large area, and usage restrictions of the coolant are held in cooling system for the power conversion equipment. This study examined the natural circulation cooling system which canceled the demerit of both the above-mentioned cooling system for the coolant of high environmental performance. The objects of coolant are HFE-7200 and PFK-649. Heat transfer characteristics and natural circulation flow characteristics of the coolant concerned were verified by changing heat flux using an experimental apparatus. Moreover, the effect installed check-valve in the test loop was also made applicable to verification. As a result, we found that flow fluctuation can be reduced from 30 to 50% by the effect of check-valve in any of two kinds of coolants case.

Analytical evaluation of two-phase natural circulation flow characteristics under external reactor vessel cooling

This work proposes an analytical method of evaluating the effects of design and operating parameters on the low-pressure two-phase natural circulation flow through the annular shaped gap at the reactor vessel exterior surface heated by corium (molten core) relocated to the reactor vessel lower plenum after loss of coolant accidents. A natural circulation flow velocity equation derived from steady-state mass, momentum, and energy conservation equations for homogeneous two-phase flow is numerically solved for the core melting conditions of the APR1400 reactor. The solution is compared with existing experiments which measured natural circulation flow through the annular gap slice model. Two kinds of parameters are considered for this analytical method. One is the thermal–hydraulic conditions such as thermal power of corium, pressure and inlet subcooling. The others are those for the thermal insulation system design for the purpose of providing natural circulation flow path outside the reactor vessel: inlet flow area, annular gap clearance and system resistance. A computer program NCIRC is developed for the numerical solution of the implicit flow velocity equation.

재생형 연료펌프의 채널 면적 변화가 성능 특성에 미치는 영향에 대한 수치해석적 연구

The effects of channel area on the performance of regenerative type fuel pump were numerically studied by commercial CFD code (ANSYS CFX-10). To examine the effects of channel area, the shapes of the side channel and blade were simplified. The channel area affected the flow characteristics of the internal recirculation flow between the side channel and the blade groove and also made a difference in the overall performance. These loss mechanism with circulation flow were adopted as a loss coefficient in the performance prediction program. The loss coefficient was newly derived from the results of calculations with different channel area, and compared with the experimental results in the reference paper and used to modify the performance prediction program. The circulation flow characteristics with different channel area, which is related with loss mechanism, were also discussed with the results of 3-dimensional flow calculations.

Mean surface circulation and mesoscale turbulent flow characteristics in the eastern South Pacific from satellite tracked drifters

Circulation of the eastern South Pacific region (10°–34°S, 70°–100°W) was studied using drifting buoy trajectories from 1979 to 2003. Three different current regimes were highlighted: the South Equatorial Current, flowing westward north of 26°S with surface velocities of 7–8 cm s−1; the South Pacific Current, an eastward current of ∼2 cm s−1 south of 25°–30°S; and the Chile‐Peru Current, a northwestward flow of ∼6 cm s−1 found to the east of 82°W and south of 22°S. The velocity variance distribution showed the regional flow to be anisotropic in nature. Maps of eddy kinetic energy obtained from drifter measurements and satellite altimetry data showed similar patterns, with higher energy levels near the South American coast. The Lagrangian time and length scales of the turbulent flow revealed typical values of 5.9 ± 0.6 days and 40.7 ± 5.4 km in the zonal direction and of 3.5 ± 0.4 days and 29 ± 3.4 km in the meridional direction. The estimated diffusivities were (4.9 ± 0.5) × 107 cm2 s−1 and (2.6 ± 0.3) × 107 cm2 s−1 in the eastward and northward directions, respectively. Finally, we estimated the respective role of horizontal advection and lateral diffusion on the mixed layer heat and salt budgets. Near the coast the lateral turbulent fluxes in the surface layer were two times larger than the horizontal transports associated with the large‐scale circulation; mean horizontal heat and salt diffusive fluxes were around 25 W m−2 and 50 g m−2 d−1.

Natural circulation flow behavior at reduced inventory in a VVER geometry

This paper deals with the natural circulation flow characteristics of the VVER-440 geometry at reduced coolant inventory. Special emphasis is on the flow rate of the primary circuits during the two-phase flow regime. For studying two-phase natural circulation flow phenomena in a VVER geometry a series of cold leg small break loss-of-coolant accident (SBLOCA) tests was carried out in the PArallel Channel TEst Loop (PACTEL), a 1/305 volumetrically scaled model of a VVER-440 reactor. The tests were conducted with break areas ranging from 0.1 to 1.5 % of the scaled cold leg cross-sectional area of the reference reactor. A partial failure of the high-pressure injection system (HPIS) was assumed. The tests reveal a trend towards an increasing primary circuit mass flow rate with decreasing inventory. This contradicts the findings of earlier tests in multi-loop VVER geometry. With single-loop facilities, increased mass flow rates at reduced inventories have been reported before. The increase of the two-phase flow rate turns out to be a consequence of the combined effect of break size, pressure range and secondary side feed and bleed procedure. The physical phenomena of flow stagnation in the primary circuits, system pressurization, asymmetric loop flows, and loop seal clearing and refilling take place during the natural circulation cooling process from single-phase into two-phase and boiler–condenser modes. In addition, flow reversal in the undermost tubes of the horizontal steam generators (SG) is observed. These phenomena are discussed briefly while a general insight into the course of the tests is presented.

ＪＴ‐６０粒子入射加熱装置（ＮＢＩ）用クライオポンプ内気液二相ヘリウムの自然循環方式による流動特性

The cryopump for a JT-60 neutral beam injector (NBI) consists of six cryopanels cooled by liquid He below 3.7 K. To evacuate the H2 gas stably, it is necessary to supply liquid He to the six cryopanels sufficiently. Visual experiments were made with a glass model of the JT-60 NBI cryopump in order to confirm usefulness of the natural circulation for cooling the cryopanels. The two-phase He flow was observed to be homogenious flow, liquid and gas mixed uniformly, circulating smoothly through the cryopanels and pipes. The velocities of two-phase He through the channels were measured by means of the tracer introduced in the liquid He. A one-dimensional network calculation model of the cryopump was developed to calculate the flow distributions of the two-phase He into the cryopanels in the natural circulation. The model predicted well the velocities of the two-phase He in the glass model, and was used to predict the natural circulation flow characteristics in the JT-60 NBI cryopump. From the result of the sufficient supply of liquid He to the cryopanels, the natural circulation system was adopted for cooling the JT-60 NBI cryopanels.

The use of wall pressure for recognizing circulation flow characteristics in agitated vessels

To estimate the intensity of secondary circulation flow, the use of pressure on the side wall of an agitated vessel was proposed. The physical significance of the wall pressure and a quantitative relation between the pressure distribution and the axial flow velocity profile near the side wall were deduced and confirmed experimentally. Similarity of the secondary flow field and similarity parameters which have previously been presented by the author were also confirmed by the wall pressure measurements, not only for radial but also for axial discharge types of impellers.