PIV-Measurements of Centrifugal Instabilities in a Rectangular Curved Duct with a Small Aspect Ratio

In this study, experimental measurements were undertaken using non-intrusive particle image velocimetry (PIV) to investigate fluid flow within a 180° rectangular, curved duct geometry of a height-to-width aspect ratio of 0.167 and a curvature of 0.54. The duct was constructed from Plexiglas to permit optical access to flow pattern observations and flow velocity field measurements. Silicone oil was used as working fluid because it has a similar refractive index to Plexiglas. The measured velocity fields within the Reynolds number ranged from 116 to 203 and were presented at the curved channel section inlet and outlet, as well as at the mid-channel height over the complete duct length. It was observed from spanwise measurements that the transition to unsteady secondary flows generated the creation of wavy structures linked with the formation of Dean vortices close to the outer channel wall. This flow structure became unsteady with increasing Reynolds number. Simultaneously, the presence of Dean vortices in the spanwise direction influenced the velocity distribution in the streamwise direction. Two distinct regions defined by a higher velocity distribution were observed. Fluid particles were accelerated near the inner wall of the channel bend and subsequently downstream near the outer channel wall.

Double-Wall Natural Draft Heat Exchanger Design for Tritium Control in FHRs

Tritium control is potentially a critical issue for Fluoride salt-cooled High-temperature Reactors (FHRs) and Molten Salt Reactors (MSRs). Tritium production rate in these reactors can be significantly higher compared to that in Light Water Reactors (LWRs). Tritium is highly permeable at high temperatures through reactor structures, especially. Therefore, heat exchangers with large heat transfer areas in FHRs and MSRs provide practical paths for the tritium generated in the primary salt migrating into the surroundings, such as Natural Draft Heat Exchangers (NDHXs) in the direct reactor auxiliary cooling system (DRACS), which are proposed as a passive decay heat removal system for these reactors. A double-wall heat exchanger design was proposed in the literature to significantly minimize the tritium release rate to the environment in FHRs. This unique shell and tube heat exchanger design adopts a three-fluid design concept and each of the heat exchanger tube consists of an inner tube and an outer tube. Each of these tube units forms three flow passages, i.e., the inner channel, annular channel, and outer channel. While this type of heat exchangers was proposed, few such heat exchangers have been designed in the literature, taking into account both heat and tritium mass transfer performance. In this study, a one-dimensional heat and mass transfer model was developed to assist the design of a double-wall NDHX for FHRs. In this model, the molten salt and air flow through the inner and outer channels, respectively. A selected sweep gas acting as a tritium removal medium flows in the annular channel and takes tritium away to minimize tritium leakage to the air flowing in the outer channel. The heat transfer model was benchmarked against a Computational Fluid Dynamics (CFD) code, i.e., ANSYS Fluent. Good agreement was obtained between the model simulation and Fluent analysis. In addition, the heat and mass transfer models combined with non-dominated sorting in generic algorithms (NSGA) were applied to investigate a potential NDHX design in Advanced High-Temperature Reactor (AHTR), a pre-conceptual FHR design developed by the Oak Ridge National Laboratory. A double-wall NDHX design using inner and outer fluted tubes was therefore optimized and compared with a single-wall design in terms of performance and economics.

Numerical Simulation on Sudden Siltation Induced by Winner Storm and Large Waves in Outer Channel of Huanghua Port, China

A multinest storm surge-wave-sediment model is applied to simulate strong storm surge caused by winter storm in Bohai Bay in Oct, 2003. The fields of current and sediment of for- and post- regulating structure are calculated to analysis the effect of regulation. The results show that the alongshore current caused by storm surge strengthen the cross-channel component and that provided the impetus conditions for sediment transport. The siltation in the outer channel of Huanghua port in the second stage is very severe. For example, the thickness of slitting sediment in the area, 3~19 kilometers (away from the entrance of port) is over 2.0 meters. While the third stage dike for debris barrier is completed, the hyper-concentrated silt-laden flow offshore could be eluded, and the maximum deposition area goes out thus the sediment siltation is reduced.

Application Comparison about Sediment Deposition in Outer Channel by Three-Layer Mode and Analog Analysis Mode

Sudden sedimentation is an important subject for building ports in silt-sandy coast. It elaborates calculation methods detailed about three-layer deposition mode and analogy analysis mode. And they are used to predict the deposition in outer channel of Binzhou Port. Comparative results show that they are basically same on the distribution of sudden sedimentation, deposition thickness and volume along the channel. And it is larger from three-layer deposition mode than analogy analysis mode. The formal mode is propitious to project security. By analyzing the characteristics and applicability about two methods, basic law is obtained for sediment movement and predicting methods under strong wind in the outer channel of silt-sandy coast.

Influence of Monsoon on Macrobenthic Assemblage in Outer Channel Area of Chilika Lagoon, East Coast of India

Abundance of macrobenthos in the outer channel area of Chilika lagoon in the east coast of India was studied during Monsoon season of 2007 & 2008. In total 27 species of macrobenthic organisms were collected during the study period season. Crustacea was emerged as the most dominate group representing 9 species followed by polychaetes with 8 species while 5 species belonged to bivalvia and 3 species to gastropoda. The others group in the study area included nematodes and echiurids. The mean density of macrobenthos was 378 organism m-2 and 392 organism m-2 in 2007 & 2008.The biomass was measured as and biomass 0.525 g m-2 and 0.575 g m-2 during 2008 &2007. Mean values of diversity indices like Margalef's richness index was 2.7 in 2007 and 3.0 in 2008. While Shannon's H' was 1.7 of 2008 and 1.8 in 2007. The Evenness J was calculated as 0.76 in 2008 and 0.94 in 2007. The result of the study shows that hydrographical parameters like Temperature (°C), pH and Salinity (psu) parameters had modest relationship with population density and biomass. The preference of macrobenthic organism to any specific parameter couldn't be established clearly and this would be due to the presence of more opportunistic filters feeders than the deposit feeders. The opening of a new outlet connecting with the sea had good influence on species richness and population density. Key words: Chilika lagoon; Macrobenthos; Population density; biomass; diversity indices DOI: 10.3126/jowe.v3i0.2223 Journal of Wetlands Ecology, (2009) Vol. 3, pp 56-67