Condensation induced non-condensables accumulation in a non-vented vertical pipe (original) (raw)
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Nuclear Engineering and Design, 2008
Condensation of steam coming out from the coolant pipe during a loss of coolant accident (LOCA) plays a key role in removing heat from the primary containment of the advanced nuclear reactor (ANR). The presence of large mass fractions of air (W air = 0.25-0.9) and a small mass fraction of helium (W He = 0.017-0.083) reduces the overall heat transfer coefficient (HTC) substantially. The present work emphasizes on the issue that modeling the diffusion of water-vapor through the gas-liquid interface is the key to give good predictions in HTC. In this, condensation conductivity and effective diffusivity plays a key role. Therefore, modifications have been made in the derivation for calculation of condensation conductivity in the case of steam-air mixture and effective diffusivity (in the case of multicomponent mixture). The model validation has been done with the experimental data of Dehbi et al.
International journal of heat and mass …, 2006
Three-dimensional nonlinear breaking acoustic-gravity waves (AGWs) propagating from the Earth's surface to the upper atmosphere are simulated numerically. Horizontally moving periodical structures of vertical velocity on the Earth's surface are used as AGW sources in the model. The 3D algorithm for hydrodynamic equation solution uses finite-difference analogues of basic conservation laws. This approach allows us to select physically correct generalized wave solutions of hydrodynamic equations. The numerical simulation covers altitudes from the ground up to 500 km. Vertical profiles of the mean temperature, density, molecular viscosity, and thermal conductivity are specified from standard models of the atmosphere. Atmospheric waves in a few minutes can propagate to high altitudes above 100 km after activation of the surface wave forcing. Surfaces of constant phases are quasi-vertical first, and then become inclined to the horizon below about 100 km after some transition time interval. Vertical wavelengths decrease with time and tend to theoretically predicted values after times longer than several periods of the wave forcing. Decrease in vertical wavelengths and increase in AGW amplitudes can lead to wave instabilities, accelerations of the mean flow and wave-induced jet streams at altitudes above 100 km. AGWs may transport amplitude modulation of atmospheric wave sources in horizontal directions up to very high levels. Low wave amplitudes in the beginning of transition processes after activation of atmospheric wave sources could be additional reasons for slower amplitude grows with height compared to the nondissipative exponential growth predicted for stationary linear AGWs. Production of wave-induced mean jets and their superposition with nonlinear unstable dissipative AGWs can produce strong narrow peaks of horizontal speed in the upper atmosphere. This may increase the role of transient nonstationary waves in effective energy transport and variations of atmospheric parameters and gas admixtures in a broad altitude range.
The main objective of this work is to study the effect of storage pressure on spontaneous ignition of hydrogen at sudden release from a high pressure vessel and its transient combustion. This paper describes modelling and large eddy simulation (LES) of spontaneous ignition dynamics emerging from a tube into a semi-confined space. The comparison between 147 and 700 bar storage pressures is given in terms of flow velocity, temperature and hydrogen and hydroxyl mole fractions. It is demonstrated that while for the lower pressure the combusting cocoon is broken, for the higher pressure it remains intact. The difference in process dynamics is attributed to the wider high temperature area by the time the mixture reaches the end of the tube.
The advanced Lumped Parameter (LP) and Computational Fluid Dynamics (CFD) codes, which are used for analyzing the nuclear power plant containment thermal-hydraulics under sever accident scenarios require extensive validation against experimental data. The stratification of hydrogen released during a sever accident and the potential destabilization or break-up by the engineered safety systems is of particular concern. An experimental study on the containment hydrodynamics due to the operation of a prototypical hollow cone spray is carried out in the facility, PANDA, at Paul Scherrer Institut (PSI, Switzerland), in the frame of ERCOSAM and SAMARA projects which are supported by EURATOM and ROSATOM, respectively. The test is performed in two vessels, 4 m in diameter and 8 m in height, interconnected by a 1 m diameter bent pipe. Helium is used as a substitute for hydrogen. The test consists of four phases: Injection of steam into an initial air-steam mixture, injection of helium to crea...
Effects of Obstacles on Premixed Hydrogen-Air Mixtures Explosion in Closed Pipe
Jurnal Teknologi, 2015
Results of experiments on explosion premixed hydrogen-air are presented. The data covers a wide range of hydrogen concentration between 13 to 54 % v/v (Ф= 0.4 to 1.8). The experimental work was performed in a closed pipe containing 90 degree bends with a volume of 0.42 m3operating at ambient conditions. This study was carried out to determine the severity of hydrogen explosion in a closed pipe with length over diameter (L/D) ratio of 51. The results indicate that the worst case accident for hydrogen-air mixture occur at concentration slightly above stoichiometric (Ф 1.2) or 36% v/v. It is also found that pressure downstream the bending region experienced an increase of about 2 times, compared to pressure at the bend. It can be said that a strong backflow or retonation reflecting from the end pipe wall influentthe maximum overpressure downstreamof the bend and this phenomenon was highlighted.
A Hydrogen Ignition Mechanism for Explosions in Nuclear Facility Pipe Systems
ASME 2010 Pressure Vessels and Piping Conference: Volume 3, 2010
Hydrogen and oxygen generation due to the radiolysis of water is a recognized hazard in pipe systems used in the nuclear industry, where the accumulation of hydrogen and oxygen at high points in the pipe system is expected, and explosive conditions exist. Pipe ruptures at nuclear facilities were attributed to hydrogen explosions inside pipelines, in nuclear facilities, i.e., Hamaoka, Nuclear Power Station in Japan, and Brunsbuettel in Germany. Prior to these accidents an ignition source for hydrogen was questionable, but these accidents, demonstrated that a mechanism was, in fact, available to initiate combustion and explosion. Hydrogen explosions may occur simultaneously with water hammer accidents in nuclear facilities, and a theoretical mechanism to relate water hammer to hydrogen deflagrations and explosions is presented herein.
Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering 230(1), DOI: 10.1177/0954408914538784, 2016
When a loss of coolant accident occurs in the primary system of a water-cooled nuclear reactor, a large amount of steam is released into the reactor containment. Therefore, there is the possibility of over-pressurization of the reactor containment. In such a condition, the released steam is often condensed using a passive containment cooling system. This system consists of condensing vertical pipes with diameters of 30–50 mm. Thus, condensation inside vertical pipes with annular flow happens, which is usually analyzed using the three-fluid models. In the present work, the effect of variation of condensing vertical pipe diameter on pressure drop predictions in downward condensing annular flow of steam is studied using the new modified three fluid model. In a new pipe diameter, D¼0.03 m, the pressure drops are calculated using the new modified three-fluid model and the correlation of Stevanovic et al. for steam–liquid film interfacial friction coefficient and compared.
The Canadian Journal of Chemical Engineering, 2012
The condensation of pure steam flowing inside a vertical tube has been extensively studied during the last nine decades. Considerable amount of experimental and analytical efforts can be found due to the significance of this subject in practice. In the present work (Part I), experimental investigations have been performed over a range of pressure (0.1 < P < 0.35 MPa) and internal tube diameter (D i = 10, 20 and 43 mm). A twodimensional computational fluid dynamic (CFD) simulations have been carried out commercial software Fluent 6.2 [Fluent 6.2, "User's Manual to FLUENT 6.2," Fluent Inc., Lebanon, USA, 2005]. CFD results were used to predict the temperature profiles, pressure drop and the heat transfer coefficient, which was in close agreement with the experimental values. The film characteristics predicted by the CFD simulations have been compared qualitatively with the photographic images. Further, the CFD model developed in Part I extended for the analysis of all the experimental data reported in the published literature.