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Highlights • Pressure profile in submerged venturi scrubber has been predicted. • Injection characteristics of submerged venturi scrubber are discussed. • Iodine retention in venturi scrubber is evaluated. Abstract Post Fukushima, many utilities are planning to install the Filtered Containment Venting System (FCVS) to protect the nuclear reactor containment under severe accident scenarios. FCVS aims at depressurizing the reactor containment and filtering the radioactive gas leaving the containment boundary under such scenarios. A key component of FCVS is the venturi scrubber. The hydrodynamics of the fluid flow inside the FCVS is complex involving multi-phase and multi-component systems with droplets formed by entrainment of high velocity gas stream with liquid jet. The size of droplets and their trajectories are critical with regard to decontamination of iodine which combines with the droplets inside the venturi. Thus, understanding the injection characteristics, hydrodynamics and absorption of iodine vapour with the droplets in the venturi scrubber is very important. There are very limited studies on this aspect. In view of this, a CFD simulation study has been performed in this work for understanding of venturi scrubber operation and performance in self-priming mode. The interaction of the continuous gas phase and droplets is assumed to occur through drag force. The gas flow rate is varied from 1700 to 3400 lpm for two submergence heights of 3 m and 4 m. The liquid loading is estimated from pressure drop at the nozzles observed in the experiments. The retention of iodine in venturi scrubber is calculated assuming instantaneous mass transfer at gas droplet interface. The mass transfer coefficient is evaluated from Steinberg and Treybal correlation. Our results indicate that the liquid loading to the scrubber increases at lower flow rates of 1700 lpm gas flow and further decreases with the increase in gas flow. The two phase pressure profile predicted is close to measured values for each case. The pressure decreases in the converging section; decreases sharply in the throat section due to liquid injection as droplets and shows negligible recovery in the diverging section of the venturi scrubber. The retention of iodine in the venturi scrubber increases with the increase in gas flow rate in the venturi scrubber. This indicates that the participation of venturi scrubber in the iodine retention increases as the air flow rate increases. [ABSTRACT FROM AUTHOR]

The objective of this study is to investigate the transient 3D numerical simulations of natural convection of air around a circular finned tube (24.9 mm OD ) kept in a small chimney. The annular plain fins are considered in this study. The effects of fin spacing to fin diameter ratio (0.057 mm ⩽ S / D f ⩽ 0.24 mm), chimney height (400–1000 mm) and ambient to surface temperature difference (10 K ⩽ T s ⩽ 65 K) on the heat transfer and the driving force have been investigated. The results are presented in terms of the temperature contours, velocity vectors, heat transfer and the driving force. It has been found that the heat transfer coefficient increases with an increase in the fin spacing upto an optimum value ( S = 8 mm) for all the fin geometries, and beyond S = 8 mm, the heat transfer coefficient decreases. The separation of the thermal boundary layer with a variation in the fin spacing and its effects on the heat transfer and driving force has been shown. For a fixed fin spacing, the heat transfer rate, heat transfer coefficient and the driving force increases with an increase in the fin diameter, however, for D f > 41 mm, the rate of increase in the heat transfer coefficient reduces. The heat transfer coefficient increases with an increase in the chimney height and it has been found that the effect of chimney height on the heat transfer coefficient is a resultant effect of the air outlet temperature and the driving force generated by the chimney. The base to ambient temperature difference has been varied to observe the temperature sensitivity on the heat transfer coefficient and flow patterns. In the last section, various circular and elliptical tube designs have been investigated, and it is found that, the elliptical tube with minimum ellipticity ( b / a = 0.33) and circular tube with smallest diameter (7 mm) provides better heat transfer coefficient than the other circular and elliptical designs. [ABSTRACT FROM AUTHOR]

In this paper, a review is presented on the experimental investigations and the numerical simulations performed to analyze the thermal-hydraulic performance of the air-cooled heat exchangers. The air-cooled heat exchangers mostly consist of the finned-tube bundles. The primary role of the extended surfaces (fins) is to provide more heat transfer area to enhance the rate of heat transfer on the air side. The secondary role of the fins is to generate vortices, which help in enhancing the mixing and the heat transfer coefficient. In this study, the annular and plate fins are considered, the annular fins are further divided into four categories: (1) plane annular fins, (2) serrated fins, (3) crimped spiral fins, (4) perforated fins, and similarly for the plate fins, the fin types are: (1) plain plate fins, (2)wavy plate fins, (3) plate fins withDWP, and (4) slit and strip fins. In Section 4, the performance of the various types of fins is presented with respect to the parameters: (1) Reynolds number, (2) fin pitch, (3) fin height, (4) fin thickness, (5) tube diameter, (6) tube pitch, (7) tube type, (8) number of tube rows, and (9) effect of dehumidifying conditions. In Section 5, the conclusions and the recommendations for the future work have been given. [ABSTRACT FROM AUTHOR]

The objective of this work is to investigate the transient 3D numerical simulations of natural convection of air around a circular cylinder (76.2 mm OD ) enclosed in a box of 1000 mm × 600 mm × 1200 mm for a Rayleigh number of 1.3 × 10 6 . The 2D numerical simulations have also been performed and the comparison between the 2D and 3D simulations has been presented in terms of the Nusselt number. The effect of clearance between the top wall and the cylinder (0.2 ⩽ H ∗ / D ⩽ 2.3) on the flow pattern has also been investigated for the case of conducting ceiling. The flow becomes 3D, unstable and oscillating when the H ∗ / D ratio is 0.2, and as the H ∗ / D ratio is increased to 0.4, 1 and then to 2.3; the flow becomes 2D and stable. The studies of Cesini et al. (1999) [5] and Newport et al. (2001) [7] have also been analyzed by 2D and 3D numerical simulations. The flow shows 3D, unstable and oscillatory behavior in the case of Cesini et al. (1999) [5] due to the wall-cylinder interaction. However, the flow was found to be 2D and stable for the case of Newport et al. (2001) [7]. A comparison between our results and their numerical and experimental results has been presented. The time varying behavior of the surface averaged Nusselt number has been estimated, and it was found that, the time to reach the steady state for the flow depends on the aspect ratio of the geometry and 3D nature of the natural convection. [ABSTRACT FROM AUTHOR]