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Air flow exploration of abrasive feed tube

Acta Mechanica Sinica 2009年第6期25卷 761-768页

作者： shijin zhang {2. li yilei gu college of resources and Environmental science,chongqing university, 400044 chongqing, china college of resources and Environmental {2. Chongqing University 400044 Chongqing China

An abrasive water-jet cutting process is one in which water pressure is raised to a very high pressure and forced through a very small orifice to form a very thin high speed jet beam. This thin jet beam is then directed through a chamber and then fed into a secondary nozzle, or mixing tube. During this process, a vacuum is generated in the cham- ber, and garnet abrasives and air are pulled into the chamber, through an abrasive feed tube, and mixes with this high speed stream of water. Because of the restrictions introduced by the abrasive feed tube geometry, a vacuum gradient is generated along the tube. Although this phenomenon has been recog- nized and utilized as a way to monitor nozzle condition and abrasive flowing conditions, yet, until now, conditions inside the abrasive feed line have not been completely understood. A possible reason is that conditions inside the abrasive feed line are complicated. Not only compressible flow but also multi- phase, multi-component flow has been involved in inside of abrasive feed tube. This paper explored various aspects of the vacuum creation process in both the mixing chamber and the abrasive feed tube. Based on an experimental exploration, an analytical framework is presented to allow theoretical calculations of vacuum conditions in the abrasive feed tube.

关键词： Abrasive feed tube- Water jet cutting. Vacuum gradient

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Growth and feeding habits of invasive Pseudorasbora parva in the Chabalang Wetland(Lhasa,china) and its trophic impacts on native fish

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Journal of Oceanology and limnology 2019年第2期37卷 628-639页

作者： DING Huiping gu xiaohong {2. Zhiming HUO Bin li Dapeng XIE Congxin State Key Laboratory of Lake science and Environment Nanjing Institute of Geography & Limnology Chinese Academy of Sciences Nanjing 210008 China university of Chinese Academy of sciences Beijing 100049 China college of Fisheries Huazhong Agricultural University Wuhan 430070 China Institute of Hydroecology MWR & CAS Wuhan 430070 China Key Laboratory of Ecological Impacts of Hydraulic-Projects and Restoration of Aquatic Ecosystem Ministry of Water Resources Wuhan 430070 China

In recent years, fish invasion has become one of the main reasons for the decline of native fish stocks. Pseudorasbora parva is considered one of the major invasive species worldwide. The present study investigated the fish resources of the Chabalang Wetland (Lhasa, Tibet) during diff erent seasons in 2.09 and 2.13. Four hundred and twelve individuals were subsampled to estimate age, growth, and feeding habit of P . parva . Furthermore, food relationships between P . parva and the native Schizothoracinae fish were also examined. The results revealed a significant shift in species composition and community structure characterized by the disappearance of native fish and outbreak of non-native fish. The percentage of nonnative P . parva in the fish collections significantly increased from 33.64% in 2.09 to 64.08% in 2.13. The standard length (SL) ranged from 2..00 to 78.71 mm, and their age was 1–5 a. The von Bertalanff y function was used to model the observed length-at-age data as L t =112.19(1–e^-0.1495 ( t +0.8012.) for females and as L t =12..12.(1–e^-0.1500 ( t +0.7132.) for males. The results indicated that P . parva in Tibet has lower growth and mortality rates compared with that from the native ranges. Ninety-seven prey taxa belonging to 9 prey categories were identified in the gut of 38 P . parva . P . parva can be considered a generalized and opportunistic predator, competing with the native fish, especially Schizothorax o’connori , Schizopygopsis younghusbandi younghusbandi , and Ptychobarbus dipogon , for Bacillariophyta and Chironomid larvae. This is an important reason for the decline in native fish population.

关键词： Pseudorasbora parva growth feeding habits Schizothoracinae fish biological invasion

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