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Shigeru Takata - One of the best experts on this subject based on the ideXlab platform.
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Vapor flows in the continuum limit in the presence of a small amount of Noncondensable Gas
Physics of Fluids, 2004Co-Authors: Satoshi Taguchi, Kazuo Aoki, Shigeru TakataAbstract:Steady flows of a vapor around its condensed phase of arbitrary shape, on the surface of which evaporation and condensation of the vapor may take place, are considered in the presence of a small amount of a Noncondensable Gas. By a systematic asymptotic analysis of the Boltzmann system, the present authors have derived the fluid-dynamic system describing such flows in the continuum limit in the case where the amount of the Noncondensable Gas is infinitesimal compared with that of the vapor [K. Aoki, S. Takata, and S. Taguchi, Eur. J. Mech. B/Fluids 22, 51 (2003)]. In the present study, the fluid-dynamic system is applied to some physical problems, and it is demonstrated with concrete examples that such a tiny amount of the Noncondensable Gas causes dramatic changes of the overall vapor flows.
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vapor flows condensing at incidence onto a plane condensed phase in the presence of a Noncondensable Gas ii supersonic condensation
Physics of Fluids, 2003Co-Authors: Satoshi Taguchi, Kazuo Aoki, Shigeru TakataAbstract:This paper is the second part of the study of a steady flow of a vapor in a half space condensing onto a plane condensed phase of the vapor at incidence in the presence of a Noncondensable Gas near the condensed phase. The aim of the study is to clarify the behavior of the vapor and Noncondensable Gas on the basis of kinetic theory under the assumption that the molecules of the Noncondensable Gas are mechanically identical with those of the vapor. In the first part [S. Taguchi et al., Phys. Fluids 15, 689 (2003)], the case of subsonic condensation, where the Mach number corresponding to the flow-velocity component perpendicular to the condensed phase at infinity is less than unity, is considered. In the present second part, the case of supersonic condensation is investigated in detail on the same lines as the first part.
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Vapor flows with evaporation and condensation in the continuum limit: effect of a trace of Noncondensable Gas
European Journal of Mechanics - B Fluids, 2003Co-Authors: Kazuo Aoki, Shigeru Takata, Satoshi TaguchiAbstract:Abstract Steady flows of a vapor with evaporation and condensation on the boundary consisting of the condensed phase of the vapor are considered in the following situation: (i) the boundary is of arbitrary smooth shape; (ii) the Knudsen number Kn, the ratio of the typical mean free path of the vapor molecules to the characteristic length of the system, is small; (iii) a small amount of a Noncondensable Gas is contained in the system; more specifically, the amount is such that the average concentration of the Noncondensable Gas is of the order of Kn in the case of a closed domain (the case of an infinite domain is also discussed). The steady behavior of the vapor and the Noncondensable Gas, in particular, that in the continuum limit where Kn vanishes, is investigated by means of a systematic asymptotic analysis based on kinetic theory. In this situation, the average concentration of the Noncondensable Gas becomes infinitely small in the continuum limit in the case of a closed domain. However, it is shown that the Noncondensable Gas accumulates in the infinitely thin Knudsen layer on the boundary where condensation is taking place and has a significant effect on the global vapor flow in the continuum limit. An example demonstrating such an effect is also given.
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Vapor flows caused by evaporation and condensation on two parallel plane surfaces: Effect of the presence of a Noncondensable Gas
Physics of Fluids, 1998Co-Authors: Kazuo Aoki, Shigeru Takata, Shingo KosugeAbstract:A vapor in a gap between two parallel plane surfaces of its condensed phase, on which evaporation or condensation may take place, is considered in the case where another Gas that neither evaporates nor condenses on the surfaces (say, a Noncondensable Gas) is also contained in the gap. The steady flow of the vapor caused by evaporation on one surface and condensation on the other and the behavior of the Noncondensable Gas are investigated on the basis of kinetic theory. First, fundamental features of the flow field are clarified for small values of the Knudsen number (associated with vapor–vapor collisions) by a systematic asymptotic analysis of the Boltzmann equation. Then, the problem is analyzed numerically by means of the direct simulation Monte Carlo method, and the steady behavior of the vapor and of the Noncondensable Gas (e.g., the spatial distributions of the macroscopic quantities) is clarified for a wide range of the Knudsen number. In particular, it is shown that, in the limit as the Knudsen number tends to zero (the continuum limit with respect to the vapor), there are two different types of the limiting behavior depending on the amount of the Noncondensable Gas, and evaporation and condensation can take place only when the average density of the Noncondensable Gas is vanishingly small in comparison with that of the vapor.
Kazuo Aoki - One of the best experts on this subject based on the ideXlab platform.
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Slow evaporation and condensation on a spherical droplet in the presence of a Noncondensable Gas
Physics of Fluids, 2010Co-Authors: Shingo Kosuge, Kazuo Aoki, Masatake HatanoAbstract:A spherical droplet is placed in a binary mixture composed of the vapor of the droplet and another Gas which neither evaporates nor condenses (a Noncondensable Gas). The mixture is in an equilibrium state at rest at infinity. A slow steady flow of the vapor caused by weak evaporation or condensation, under the influence of the Noncondensable Gas, is investigated on the basis of a linearized model Boltzmann equation. Numerical analyses by means of a finite-difference method are carried out for a wide range of the Knudsen number (i.e., from a large to small droplet compared to the molecular mean free path). The numerical results, together with analytical solutions for small and large Knudsen numbers, clarify the behavior the mixture, i.e., the mass- and heat-flow rates from or onto the droplet as well as spatial distributions of the macroscopic quantities, in the entire range of Gas rarefaction. The solution for the steady heat transfer problem between a solid sphere and a binary Gas mixture is also obtaine...
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Vapor Flows Along a Plane Condensed Phase with Weak Condensation in the Presence of a Noncondensable Gas
Journal of Statistical Physics, 2006Co-Authors: Satoshi Taguchi, Kazuo Aoki, Vladimir LatochaAbstract:A steady flow of a vapor in a half space condensing at incidence onto a plane condensed phase is considered in the case where another Gas that does not condense (the Noncondensable Gas) is present near the condensed phase. A systematic asymptotic analysis of the Boltzmann equation for hard-sphere molecules is performed in the case where condensation is weak, and the relation among the parameters of the vapor flow at infinity, those associated with the plane condensed phase, and the amount of the Noncondensable Gas is derived in an analytical form. The result supplements the numerical result for the relation for arbitrarily strong condensation obtained on the basis of a model Boltzmann equation and under the restriction that the vapor molecules are mechanically identical with the Noncondensable-Gas molecules [Taguchi et al ., Phys. Fluids 15 : 689 (2003)].
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Vapor flows in the continuum limit in the presence of a small amount of Noncondensable Gas
Physics of Fluids, 2004Co-Authors: Satoshi Taguchi, Kazuo Aoki, Shigeru TakataAbstract:Steady flows of a vapor around its condensed phase of arbitrary shape, on the surface of which evaporation and condensation of the vapor may take place, are considered in the presence of a small amount of a Noncondensable Gas. By a systematic asymptotic analysis of the Boltzmann system, the present authors have derived the fluid-dynamic system describing such flows in the continuum limit in the case where the amount of the Noncondensable Gas is infinitesimal compared with that of the vapor [K. Aoki, S. Takata, and S. Taguchi, Eur. J. Mech. B/Fluids 22, 51 (2003)]. In the present study, the fluid-dynamic system is applied to some physical problems, and it is demonstrated with concrete examples that such a tiny amount of the Noncondensable Gas causes dramatic changes of the overall vapor flows.
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vapor flows condensing at incidence onto a plane condensed phase in the presence of a Noncondensable Gas ii supersonic condensation
Physics of Fluids, 2003Co-Authors: Satoshi Taguchi, Kazuo Aoki, Shigeru TakataAbstract:This paper is the second part of the study of a steady flow of a vapor in a half space condensing onto a plane condensed phase of the vapor at incidence in the presence of a Noncondensable Gas near the condensed phase. The aim of the study is to clarify the behavior of the vapor and Noncondensable Gas on the basis of kinetic theory under the assumption that the molecules of the Noncondensable Gas are mechanically identical with those of the vapor. In the first part [S. Taguchi et al., Phys. Fluids 15, 689 (2003)], the case of subsonic condensation, where the Mach number corresponding to the flow-velocity component perpendicular to the condensed phase at infinity is less than unity, is considered. In the present second part, the case of supersonic condensation is investigated in detail on the same lines as the first part.
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Vapor flows with evaporation and condensation in the continuum limit: effect of a trace of Noncondensable Gas
European Journal of Mechanics - B Fluids, 2003Co-Authors: Kazuo Aoki, Shigeru Takata, Satoshi TaguchiAbstract:Abstract Steady flows of a vapor with evaporation and condensation on the boundary consisting of the condensed phase of the vapor are considered in the following situation: (i) the boundary is of arbitrary smooth shape; (ii) the Knudsen number Kn, the ratio of the typical mean free path of the vapor molecules to the characteristic length of the system, is small; (iii) a small amount of a Noncondensable Gas is contained in the system; more specifically, the amount is such that the average concentration of the Noncondensable Gas is of the order of Kn in the case of a closed domain (the case of an infinite domain is also discussed). The steady behavior of the vapor and the Noncondensable Gas, in particular, that in the continuum limit where Kn vanishes, is investigated by means of a systematic asymptotic analysis based on kinetic theory. In this situation, the average concentration of the Noncondensable Gas becomes infinitely small in the continuum limit in the case of a closed domain. However, it is shown that the Noncondensable Gas accumulates in the infinitely thin Knudsen layer on the boundary where condensation is taking place and has a significant effect on the global vapor flow in the continuum limit. An example demonstrating such an effect is also given.
A Naviglio - One of the best experts on this subject based on the ideXlab platform.
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film condensation in inclined tubes with Noncondensable Gases an experimental study on the local heat transfer coefficient
International Communications in Heat and Mass Transfer, 2013Co-Authors: Gianfranco Caruso, Damiano Vitale Di Maio, A NaviglioAbstract:Abstract An experimental investigation on the role of Noncondensable Gases during condensation of steam inside inclined tubes is presented. In a condenser, Noncondensable Gases flowing with steam cause reduction of condenser performance and efficiency. Many researchers have investigated in-tube condensation for vertical heat exchangers, but very few works have been performed to study condensation in inclined tubes with Noncondensable Gases. In the paper, experiments dedicated to this situation are described, with reference to the following conditions: tube internal diameter: 12.6 mm, 20 mm and 26.8 mm; tube inclination: 7°, 15°, 30° and 45°; inlet Noncondensable Gas mass fraction ωin = 2%–42%; inlet mixture Reynolds number Rem,in = 5000–20000; local Noncondensable Gas mass fraction ω = 2%–70%; local mixture Reynolds number Rem = 400–21000; local condensate Reynolds number Rel = 10–290; saturated steam at atmospheric pressure; and gravity controlled flow regime. A limited influence of the inclination angle on heat transfer coefficient has been observed. Correlations to evaluate the local heat transfer coefficient along inclined tubes, in a gravity controlled flow regime, have been developed and they are in good agreement with the experimental results.
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condensation heat transfer coefficient with Noncondensable Gases inside near horizontal tubes
Desalination, 2013Co-Authors: Gianfranco Caruso, Damiano Vitale Di Maio, A NaviglioAbstract:Abstract An experimental investigation on the role of Noncondensable Gases during condensation of steam inside horizontal/slightly inclined tubes is presented. In a condenser of a thermal desalination unit, the Noncondensable Gases flowing within the Gas phase cause reduction of performance and efficiency. Many researchers have investigated in-tube condensation for horizontal heat exchangers, but very few works have been performed to study the condensation in slightly inclined tubes with Noncondensable Gases. Inclination of tubes may be requested to achieve suitable and reliable draining. Experiments were conducted in the following conditions: tube internal diameter 12.6 mm, 20 mm and 26.8 mm; tube inclination 7°; inlet Noncondensable Gas mass fraction ωin = 5%–42%; inlet mixture Reynolds number Rem,in = 5000–20,000; local Noncondensable Gas mass fraction ωin = 5%–60%; local mixture Reynolds number Rem = 500–20,000; saturated steam at atmospheric pressure, gravity controlled with stratified flow regime, in which the condensate is collected mainly in the bottom part of the tube due to gravity and it is drawn out by its own momentum. A correlation of mixed Gas heat transfer coefficient along a slightly inclined tube, in a gravity controlled flow regime, has been developed, showing a good agreement with experimental results.
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Film condensation in inclined tubes with Noncondensable Gases: An experimental study on the local heat transfer coefficient
'Elsevier BV', 2013Co-Authors: Gianfranco Caruso, Damiano Vitale Di Maio, A NaviglioAbstract:An experimental investigation on the role of Noncondensable Gases during condensation of steam inside inclined tubes is presented. In a condenser, Noncondensable Gases flowing with steam cause reduction of condenser performance and efficiency. Many researchers have investigated in-tube condensation for vertical heat exchangers, but very few works have been performed to study condensation in inclined tubes with Noncondensable Gases. In the paper, experiments dedicated to this situation are described, with reference to the following conditions: tube internal diameter: 12.6 mm, 20 mm and 26.8 mm; tube inclination: 7 degrees, 15 degrees, 30 degrees and 45 degrees; inlet Noncondensable Gas mass fraction omega(in) = 2%-42%; inlet mixture Reynolds number Re-m,Re-in = 5000-20000; local Noncondensable Gas mass fraction omega = 2%-70%; local mixture Reynolds number Re-m = 400-21000; local condensate Reynolds number Re-l = 10-290; saturated steam at atmospheric pressure; and gravity controlled flow regime. A limited influence of the inclination angle on heat transfer coefficient has been observed. Correlations to evaluate the local heat transfer coefficient along inclined tubes, in a gravity controlled flow regime, have been developed and they are in good agreement with the experimental results. (C) 2013 Elsevier Ltd. All rights reserved
Satoshi Taguchi - One of the best experts on this subject based on the ideXlab platform.
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Vapor Flows Along a Plane Condensed Phase with Weak Condensation in the Presence of a Noncondensable Gas
Journal of Statistical Physics, 2006Co-Authors: Satoshi Taguchi, Kazuo Aoki, Vladimir LatochaAbstract:A steady flow of a vapor in a half space condensing at incidence onto a plane condensed phase is considered in the case where another Gas that does not condense (the Noncondensable Gas) is present near the condensed phase. A systematic asymptotic analysis of the Boltzmann equation for hard-sphere molecules is performed in the case where condensation is weak, and the relation among the parameters of the vapor flow at infinity, those associated with the plane condensed phase, and the amount of the Noncondensable Gas is derived in an analytical form. The result supplements the numerical result for the relation for arbitrarily strong condensation obtained on the basis of a model Boltzmann equation and under the restriction that the vapor molecules are mechanically identical with the Noncondensable-Gas molecules [Taguchi et al ., Phys. Fluids 15 : 689 (2003)].
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Vapor flows in the continuum limit in the presence of a small amount of Noncondensable Gas
Physics of Fluids, 2004Co-Authors: Satoshi Taguchi, Kazuo Aoki, Shigeru TakataAbstract:Steady flows of a vapor around its condensed phase of arbitrary shape, on the surface of which evaporation and condensation of the vapor may take place, are considered in the presence of a small amount of a Noncondensable Gas. By a systematic asymptotic analysis of the Boltzmann system, the present authors have derived the fluid-dynamic system describing such flows in the continuum limit in the case where the amount of the Noncondensable Gas is infinitesimal compared with that of the vapor [K. Aoki, S. Takata, and S. Taguchi, Eur. J. Mech. B/Fluids 22, 51 (2003)]. In the present study, the fluid-dynamic system is applied to some physical problems, and it is demonstrated with concrete examples that such a tiny amount of the Noncondensable Gas causes dramatic changes of the overall vapor flows.
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vapor flows condensing at incidence onto a plane condensed phase in the presence of a Noncondensable Gas ii supersonic condensation
Physics of Fluids, 2003Co-Authors: Satoshi Taguchi, Kazuo Aoki, Shigeru TakataAbstract:This paper is the second part of the study of a steady flow of a vapor in a half space condensing onto a plane condensed phase of the vapor at incidence in the presence of a Noncondensable Gas near the condensed phase. The aim of the study is to clarify the behavior of the vapor and Noncondensable Gas on the basis of kinetic theory under the assumption that the molecules of the Noncondensable Gas are mechanically identical with those of the vapor. In the first part [S. Taguchi et al., Phys. Fluids 15, 689 (2003)], the case of subsonic condensation, where the Mach number corresponding to the flow-velocity component perpendicular to the condensed phase at infinity is less than unity, is considered. In the present second part, the case of supersonic condensation is investigated in detail on the same lines as the first part.
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Vapor flows with evaporation and condensation in the continuum limit: effect of a trace of Noncondensable Gas
European Journal of Mechanics - B Fluids, 2003Co-Authors: Kazuo Aoki, Shigeru Takata, Satoshi TaguchiAbstract:Abstract Steady flows of a vapor with evaporation and condensation on the boundary consisting of the condensed phase of the vapor are considered in the following situation: (i) the boundary is of arbitrary smooth shape; (ii) the Knudsen number Kn, the ratio of the typical mean free path of the vapor molecules to the characteristic length of the system, is small; (iii) a small amount of a Noncondensable Gas is contained in the system; more specifically, the amount is such that the average concentration of the Noncondensable Gas is of the order of Kn in the case of a closed domain (the case of an infinite domain is also discussed). The steady behavior of the vapor and the Noncondensable Gas, in particular, that in the continuum limit where Kn vanishes, is investigated by means of a systematic asymptotic analysis based on kinetic theory. In this situation, the average concentration of the Noncondensable Gas becomes infinitely small in the continuum limit in the case of a closed domain. However, it is shown that the Noncondensable Gas accumulates in the infinitely thin Knudsen layer on the boundary where condensation is taking place and has a significant effect on the global vapor flow in the continuum limit. An example demonstrating such an effect is also given.
Moo Hwan Kim - One of the best experts on this subject based on the ideXlab platform.
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numerical study of gap size ratio effect for Noncondensable Gas ventilation in condensers
Transactions of The Korean Society of Mechanical Engineers B, 2012Co-Authors: Soojea Kim, Chiwoong Choi, Moo Hwan KimAbstract:A numerical analysis was carried out to estimate the effect of the gap size ratio on the performance of condensers under Noncondensable Gas ventilation using the porous medium approach (PMA). In the PMA, the details of the tube bundle in the condenser are considered to be those of a porous medium, and the flow resistance term is added in the momentum equation. Three-dimensional analysis of the condensation for a McAllister condenser was conducted with the PMA using Fluent and user-defined functions (UDFs). The gap size effect on the condensation was negligible under pure steam conditions. However, the gap size effect was dominant in condensation with Noncondensable Gas and external venting. As the gap size decreased, the condensation rate increased for Noncondensable Gas in an external venting system.
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steam condensation in the presence of a Noncondensable Gas in a horizontal tube
2011Co-Authors: Kwon-yeong Lee, Moo Hwan KimAbstract:Perhaps the most common flow configuration in which a convective condensation occurs is a flow in a horizontal circular tube. This configuration is encountered in air-conditioning and refrigeration condensers as well as condensers in Rankine power cycles. Although a convective condensation is also sometimes contrived to occur in a co-current vertical downward flow, a horizontal flow is often preferred because the flow can be repeatedly passed through the heat exchanger core in a serpentine fashion without trapping liquid or vapor in the return bends. (Carey, 1992) Horizontal heat exchangers are also widely used in the nuclear industry. Recently, a horizontal heat exchanger design has been proposed for a passive containment cooling system (PCCS) of future light water reactors. Current PCCS designs typically employ a vertical condenser. The horizontal design is proposed because horizontal heat exchangers have a potentially higher heat removal capability than vertical heat exchangers. (Wu & Vierow, 2006b) As well as, horizontal heat exchangers have less tube fouling, higher structural earthquake resistance which will improve the reliability of the safety system, and a large economic benefit because the shorter coolant pool allows for reduction in the containment height and volume. In spite of these advantages, there is a lack of mechanistic understanding of the heat transfer and fluid flow phenomena occurring in the heat exchanger tubes. This is mainly due to the fact that the phenomena are more complicated compared to the case of vertical heat exchangers. In vertical tubes the phenomena is mainly laminar or turbulent film condensation, whereas in horizontal tubes, the phenomena is complicated by strong asymmetry and flow regime transitions, which causes transitions in heat and mass transfer mechanisms. There is also the need for mechanistic analysis tools that can assess condenser performance. (Wu, 2005) There were many investigations for the condensation phenomena inside horizontal tubes to study the horizontal heat exchangers. However, almost all of them obtained tube sectionaveraged data without a Noncondensable Gas. Recently, Wu and Vierow (2006a, 2006b) studied experimentally the condensation of steam in a horizontal heat exchanger with air present, as shown in Fig. 1. In order to measure the condenser tube inner surface temperatures and to calculate the local heat fluxes, they developed an innovative thermocouple design that allowed for nonintrusive measurements. The experimental results show that the top of the condenser tube is a much better heat transfer surface. At any tube
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Effect of an interfacial shear stress on steam condensation in the presence of a Noncondensable Gas in a vertical tube
International Journal of Heat and Mass Transfer, 2008Co-Authors: Kwon-yeong Lee, Moo Hwan KimAbstract:Experimental and analytical studies were performed to examine local condensation heat transfer coefficients in the presence of a Noncondensable Gas inside a vertical tube. The experimental data for pure steam and steam/nitrogen mixture bypass modes were compared to study the effects of Noncondensable nitrogen Gas on annular film condensation phenomena. The condenser tube had a relatively small inner diameter of 13 mm. The experimental results demonstrated that the local heat transfer coefficients increased as the inlet steam flow rate increased and the inlet nitrogen mass fraction decreased. The results obtained using steam/nitrogen mixtures with a low inlet nitrogen mass fraction were similar to those obtained using pure steam. Therefore, the effects of Noncondensable Gas on steam condensation were weak in the small-diameter condenser tube because of interfacial shear stress. A new correlation based on dimensionless shear stress and Noncondensable Gas mass fraction variables was developed to evaluate the condensation heat transfer coefficient inside a vertical tube with Noncondensable Gas, irrespective of the condenser tube diameter. A theoretical model using a heat and mass transfer analogy and simple models using four empirical correlations were developed and compared with the experimental data obtained under various experimental conditions. The predictions of the theoretical model and the simple model based on a new correlation were in good agreement with the experimental results.
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ANALYSIS OF STEAM CONDENSATION HEAT TRANSFER WITH A Noncondensable Gas IN A VERTICAL CONDENSER TUBE
Nuclear Technology, 2008Co-Authors: Kwon-yeong Lee, Moo Hwan KimAbstract:A theoretical model using a heat and mass transfer analogy was developed to investigate the effects of Noncondensable Gases on the heat transfer coefficient of steam condensing inside a vertical tube. The Nusselt and Sherwood numbers in the Gas phase were modified to incorporate the effects of condensate film roughness, suction, and developing flow. The model predictions showed good agreement with the experimental data obtained for various experimental conditions. A parametric study was conducted using the model with condenser tube diameter as a variable. The results indicated that the effects of Noncondensable Gases become weak as the inlet mixture Reynolds number (Re mix, in = 4m mix, in /πd i μ mix, in ) increases and inlet Noncondensable Gas mass fraction (W nc, in = m nc, in / (m nc, in + m v, in)) decreases. In addition, the effects of Noncondensable Gases also become weak as the condenser tube diameter decreases with the same inlet mixture Reynolds number because of interfacial shear stress.
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experimental and empirical study of steam condensation heat transfer with a Noncondensable Gas in a small diameter vertical tube
Nuclear Engineering and Design, 2008Co-Authors: Kwon-yeong Lee, Moo Hwan KimAbstract:Abstract An experimental study was performed to investigate local condensation heat transfer coefficients in the presence of a Noncondensable Gas inside a vertical tube. The data obtained from pure steam and steam/nitrogen mixture condensation experiments were compared to study the effects of Noncondensable nitrogen Gas on the annular film condensation phenomena. The condenser tube had a relatively small inner diameter of 13 mm (about 1/2-in.). The experimental results demonstrated that the local heat transfer coefficients increased as the inlet steam flow rate increased and the inlet nitrogen Gas mass fraction decreased. The results obtained using pure steam and a steam/nitrogen mixture with a low inlet nitrogen Gas mass fraction were similar. Therefore, the effects of Noncondensable Gas on steam condensation were weak in small-diameter condenser tubes. A new correlation was developed to evaluate the condensation heat transfer coefficient inside a vertical tube with Noncondensable Gas, irrespective of the condenser tube diameter. The new correlation proposed herein is capable of predicting heat transfer rates for tube diameters between 1/2- and 2-in. because of the unique approach of accounting for the heat transfer enhancement via an interfacial shear stress factor.