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Bypass Flow

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J Bouma – 1st expert on this subject based on the ideXlab platform

  • Aluminum-contaminant transport by surface runoff and Bypass Flow from an acid sulphate soil
    Agricultural Water Management, 2002
    Co-Authors: L Q Minh, To Phuc Tuong, Martinus E F Van Mensvoort, J Bouma

    Abstract:

    Abstract Quantifying the process and the amount of acid-contaminant released to the surroundings is important in assessing the environmental hazards associated with reclaiming acid sulphate soils (ASS). The roles of surface runoff and Bypass Flow (i.e. the rapid downward Flow of free water along macropores through an unsaturated soil matrix) in transporting aluminum from three types of raised beds (soil ridges formed by piling up soil materials excavated from adjacent ditches) were studied in a Typic Sulfaquept in Can Tho, Vietnam. During the month of April, 1 h cumulative infiltration of the low raised beds (made only of the topsoil materials) and high raised beds (made of topsoil and jarositic layers) was significantly higher than that of the traditional raised beds (made of topsoil, jarositic and pyritic materials). As the rainfall season progressed, infiltration in July decreased four to seven-fold from the initial values in April, resulting in an increase in runoff. Due to surface crusting, the traditional raised beds yielded the highest runoff (110 versus 50–60 mm in the other types in July). Aluminum concentrations in the Bypass Flow (6–22 mmol l −1 ) associated with each of the three bed types were higher than in the runoff (3–14 mmol l −1 ). In low and high raised beds, the amounts of aluminum transported by Bypass Flow (15–16 kmol ha −1 ) was higher than in the runoff (4–6.5 kmol ha −1 ), while in the traditional type, the two components were similar (11–12 kmol ha −1 ). The total amount of aluminum released from the low raised beds was lowest. Low raised beds thus pose less environmental hazards to the surroundings compared to the other two types. Interventions that affect the amount of aluminum transport in runoff and in Bypass Flow are important in balancing agricultural production and environmental protection in ASS areas.

  • Bypass Flow and its role in leaching of raised beds under different land use types on an acid sulphate soil
    Agricultural Water Management, 1997
    Co-Authors: L Q Minh, To Phuc Tuong, H W G Booltink, Martinus E F Van Mensvoort, J Bouma

    Abstract:

    Abstract A better understanding of leaching processes in raised beds is useful in assessing management options for acid sulphate soils. Field and laboratory studies were carried out to quantify the effects of soil physical properties and Bypass Flow on leaching processes of new, 1-year-old and 2-year-old raised beds for yam and pineapple cultivation in a Typic Sulfaquept in Tien Giang, Vietnam. The methylene blue staining technique was used to characterize the water-conducting pores in terms of number, stained area, and total pore perimeter at 10 cm depth intervals of six 1 × 1 m subplots. Undisturbed 20 cm X 25 cm soil cores taken from the raised beds were subjected to three 30 mm h −1 rains. Volume, aluminum and sulphate concentration of the outFlows were monitored. Consolidation with time decreased the area and perimeter of water-conducting pores in 2-year-old pineapple beds to about a third, and Bypass Flow rate to about 80% of those in newly constructed beds. Consolidation did not affect macropore network geometry in yam beds because they were subjected to annual tillage and yam tubers were uprooted regularly. A13 + and SO 4 2− concentrations in the outFlows of the newly constructed and 1-year-old raised beds were higher in pineapple, while those in 2-year raised beds were higher in yam.

  • Sensitivity analysis on processes affecting Bypass Flow.
    Hydrological Processes, 1993
    Co-Authors: H W G Booltink, J Bouma

    Abstract:

    Bypass Flow in structured soils is dominated by soil hydrological processes, such as rain intensity, initial pressure head of the soil, surface storage of rain, horizontal contact area and absorption rate, and hydraulic conductivity of the soil matrix. This study was conducted to determine the relative impact of these processes in different soil types. A quasi 3-dimensional simulation model was used to calculate the effects of these soil hydrological input parameters on surface infiltration, macropore Flow (with related horizontal absorption) and drainage. For light textured soils, surface infiltration was the most important term in the water balance. Heavy textured soils, in contrast, had drainage as the main term. In the latter soils Bypass Flow, when occurring, was almost equal to the amount of rain applied, indicating that absorption processes were strongly reduced. Lateral absorption on macropore walls was a minor fraction in the total mass balances, due to limited contact area and relatively weak diffusivity forces. Surface infiltration is a crucial parameter in Bypass Flow and is mainly dependent on rain intensity, initial pressure head and conductivity of the soil matrix. This requires measurement methods for hydraulic conductivity that specifically consider the effect of macropores.

Eisuke Tatsumi – 2nd expert on this subject based on the ideXlab platform

  • Impact of Bypass Flow rate and catheter position in veno-venous extracorporeal membrane oxygenation on gas exchange in vivo
    Journal of Artificial Organs, 2014
    Co-Authors: Konomi Togo, Yoshiaki Takewa, Nobumasa Katagiri, Yutaka Fujii, Satoru Kishimoto, Kazuma Date, Yuji Miyamoto, Eisuke Tatsumi

    Abstract:

    The clinical use of veno-venous extracorporeal membrane oxygenation (VVECMO) in adult patients with respiratory failure is rapidly increasing. However, recirculation of blood oxygenated by ECMO back into the circuit may occur in VVECMO, resulting in insufficient oxygenation. The cannula position and Bypass Flow rate are two major factors influencing recirculation, but the relationship and ideal configuration of these factors are not fully understood. In the present study, we attempted to clarify these parameters for effective gas exchange. VVECMO was performed in eight adult goats under general anesthesia. The position of the drainage cannula was fixed in the inferior vena cava (IVC), but the return cannula position was varied between the IVC, right atrium (RA), and superior vena cava (SVC). At each position, the recirculation rates calculated, and the adequacy of oxygen delivery by ECMO in supplying systemic oxygen demand was assessed by measuring the arterial oxygen saturation (SaO2) and pressure (PaO2). Although the recirculation rates increased as the Bypass Flow rates increased, SaO2 and PaO2 also increased in any position of return cannula. The recirculation rates and PaO2 were 27 ± 2 % and 162 ± 16 mmHg, 36 ± 6 % and 139 ± 11 mmHg, and 63 ± 6 % and 77 ± 9 mmHg in the SVC, RA and IVC position at 4 L/min respectively. In conclusion, the best return cannula position was the SVC, and a high Bypass Flow rate was advantageous for effective oxygenation. Both the Bypass Flow rates and cannula position must be considered to achieve effective oxygenation.

  • development and hydrodynamic evaluation of a novel inFlow cannula in a mechanical circulatory support system for bridge to decision
    Artificial Organs, 2011
    Co-Authors: Hirohito Sumikura, Koichi Toda, Yoshiaki Takewa, Tomonori Tsukiya, Kentaro Ohnuma, Mitsuo Sasagawa, Fumikazu Watanabe, Junichi Ugawa, Yoshiyuki Taenaka, Eisuke Tatsumi

    Abstract:

    : Recent progress in the development of implantable rotary blood pumps realized long-term mechanical circulatory support (MCS) for bridge to transplant, bridge to recovery, or a destination therapy. Meanwhile, a short-term MCS system is becoming necessary for bridge to decision. We developed a novel inFlow cannula for the short-term MCS system, which gives sufficient Bypass Flow with minimal invasion at insertion, and evaluated its hydrodynamic characteristics. The novel inFlow cannula, named the Lantern cannula, is made of elastic silicone reinforced with metal wires. The cannula tip has six slits on the side. This cannula tip can be extended to the axial direction by using an introducer and can be reduced in diameter, and the Lantern cannula enables easy insertion into the left ventricle apex with minimal invasion. The sufficient Bypass Flow rate can be obtained due to low pressure loss. Moreover, this Lantern shape also resists suction complication around the cannula tip. The pressure loss through the Lantern cannula was measured using a mock circulation and compared with two commercially available venous cannulae (Sarns4882, Terumo, Tokyo, Japan and Stockert V122-28, Sorin Group, Tokyo, Japan), which have almost same diameter as the Lantern cannula. Moreover, the Flow patterns around the cannula tip were numerically analyzed by computational fluid dynamics (CFD). Acute animal experiment was also performed to confirm the practical effectiveness of the Lantern cannula. The pressure loss of the Lantern cannula was the lowest compared with those of the commercially available venous cannulae in in vitro experiment. CFD analysis results demonstrated that the Lantern cannula has low pressure loss because of wide inFlow orifice area and a bell mouth, which were formed via Lantern shape. The highest Bypass Flow was obtained in the Lantern cannula because of the low pressure loss under pulsatile condition in in vivo experiments. The Lantern cannula demonstrated superior hydrodynamic characteristics as the inFlow cannula in terms of pressure loss due to its specially designed Lantern shape.

  • Oxygen metabolism under various Bypass Flow conditions during cardiopulmonary support in awake goats.
    International Journal of Artificial Organs, 2001
    Co-Authors: Yoshiaki Takewa, Eisuke Tatsumi, Yoshiyuki Taenaka, Hisateru Takano

    Abstract:

    : Despite its wide clinical application, patient recovery from cardiopulmonary support (CPS) is not necessarily satisfactory. To clarify what influence CPS has on organ perfusion, we investigated the oxygen metabolism under various Bypass Flow (BF) conditions in a series of chronic animal CPS experiments. The CPS system, which consists of a pulsatile ventricular assist device and a compact artificial lung was installed without anesthesia in 6 adult goats weighing 49-51 kg. BF was adjusted stepwise from 0% to 50%, 75%, 90%, and 100% of total systemic blood Flow (TSF) by balancing the pulmonary arterial Flow. The animals’ TSF and oxygen delivery (DO2) were sufficiently maintained throughout the experiments. The oxygen consumption (VO2) and the oxygen extraction rate (ExO2) increased from 178+/-14 to 342+/-19 ml/min, and from 28+/-2% to 64+/-1%, respectively, in proportion to the increase of CPBF dependency from 0% to 100%. The blood lactate level did not change appreciably even at 90% BF from 5.7+/-0.3 to 11.2+/-1.2 mg/dl, but drastically elevated to 23.5+/-4.6 mg/dl at the total Bypass. This indicates that CPS leads to a relative lack of oxygen and can induce organ dysfunction due to increasing VO2 and ExO2 in proportion to the increase of BF dependence even if TSF and DO2 are sufficiently maintained.

Richard W. Johnson – 3rd expert on this subject based on the ideXlab platform

  • Bypass Flow Resistance in Prismatic Gas-Cooled Nuclear Reactors
    Journal of Nuclear Engineering and Radiation Science, 2016
    Co-Authors: Donald M. Mceligot, Richard W. Johnson

    Abstract:

    Available computational fluid dynamics (CFD) predictions of pressure distributions in the vertical Bypass Flow between blocks in a prismatic gas-cooled reactor (GCR) have been analyzed to deduce apparent friction factors and loss coefficients for nuclear engineering systems and network codes. Calculations were performed for vertical gap spacings “s” of 2, 6, and 10 mm — representing 1, 3, and 5 mm in a GCR design, horizontal gaps between the blocks of 2 mm and two Flow rates, giving a range of vertical gap Reynolds numbers ReDh of about 40–5300. The present focus is on the examination of the Flow in the vertical gaps. Horizontal gaps are treated in CFD calculations but their Flows are not examined. Laminar predictions of the fully developed friction factor ffd were about 3–10% lower than the classical infinitely wide channel. In the entry region, the local apparent friction factor was slightly higher than the classic idealized case, but the hydraulic entry length Lhy was approximately the same. The per cent reduction in Flow resistance was greater than the per cent increase in Flow area at the vertical corners of the blocks. The standard k–ϵ turbulence model was employed for Flows expected to be turbulent. Its predictions of ffd and Flow resistance were significantly higher than direct numerical simulations (DNS) for the classic case; the value of Lhy was about 30 gap spacings. Initial quantitative information for entry coefficients and loss coefficients for the expansion–contraction junctions between blocks is also presented. The present study demonstrates how CFD predictions can be employed to provide integral quantities needed in systems and network codes.

  • Bypass Flow computations on the LOFA transient in a VHTR
    Applied Thermal Engineering, 2014
    Co-Authors: Yu-hsin Tung, Richard W. Johnson, Yuh-ming Ferng, Ching-chang Chieng

    Abstract:

    Abstract Bypass Flow in the prismatic gas-cooled very high temperature reactor (VHTR) is not intentionally designed to occur, but is present in the gaps between graphite blocks. Previous studies of the Bypass Flow in the core indicated that the cooling provided by Flow in the Bypass gaps had a significant effect on temperature and Flow distributions for normal operating conditions. However, the Flow and heat transports in the core are changed significantly after a Loss of Flow Accident (LOFA). This study aims to study the effect and role of the Bypass Flow after a LOFA in terms of the temperature and Flow distributions and for the heat transport out of the core by natural convection of the coolant for a 1/12 symmetric section of the active core which is composed of images and mirror images of two sub-region models. The two sub-region models, 9 × 1/12 and 15 × 1/12 symmetric sectors of the active core, are employed as the CFD Flow models using computational grid systems of 70.2 million and 117 million nodes, respectively. It is concluded that the effect of Bypass Flow is significant for the initial conditions and the beginning of LOFA, but the Bypass Flow has little effect after a long period of time in the transient computation of natural circulation.

  • Effects of Bypass Flow on the LOFA Transient Computations in a VHTR
    Volume 3: Nuclear Safety and Security; Codes Standards Licensing and Regulatory Issues; Computational Fluid Dynamics and Coupled Codes, 2013
    Co-Authors: Yu-hsin Tung, Richard W. Johnson, Yuh-ming Ferng, Ching-chang Chieng

    Abstract:

    The prismatic gas-cooled very high temperature reactor (VHTR) is one possible option for the generation IV nuclear power plant. The prismatic VHTR basically involves stacks of hexagonal graphite blocks that are drilled to accept cylindrical fuel compacts and provide coolant channels for the helium coolant. Between the hexagonal blocks, there are gaps, which allow the coolant Flow to Bypass the coolant channels. The gaps are not intentionally designed to occur in the core, but are present because of tolerances in machining the blocks, imperfect installation and expansion and shrinkage from heating and irradiation. Based on previous studies of a loss of Flow accident (LOFA), the cooling provided by Flow in the Bypass gaps has a significant effect on the nature and strength of the attendant natural circulation. One of the mechanisms that occurs after a LOFA for the transport of heat out of the core is by the natural convection of the coolant. It is of interest to know if there are problems for the core associated with the natural circulation and what is the role played by the Bypass Flow in such an event.The distribution of heat generation and the separation of the partial columns included in the CFD model of the heated core have a strong effect on the natural circulation. In the present paper, a 1/12 symmetric section of the active core is considered for the CFD model. Two regions of the 1/12 section are employed to perform the LOFA transient calculations. Several scenarios are investigated including with and without the Bypass gap in the model. The present study also reports the effects of Bypass Flow on the natural circulation with time for these cases.Copyright © 2013 by ASME