To understand the abnormal flow conditions caused by the presence of stenoses in arteries, an analytical solution is obtained for the steady laminar flow of an incompressible Newtonian fluid in an axisymmetric conduit with irregular surface where the spread of the surface roughness is large compared with the mean radius of the conduit. Numerical results are presented for the streamlines, the distributions of velocity, vorticity, and pressure, the energy dissipation, and the separation and reattachment points for conduits with sinusoidal wall variations. The analysis is also applicable to a locally constricted conduit, provided the separation zone does not extend into the straight wall portion of the conduit.
To understand the abnormal flow conditions caused by the boundary irregularities in diseased vessels, an analytical solution is obtained for the steady laminar flow of an incompressible Newtonian fluid in a channel with irregular surfaces where the spread of the surface roughness is large compared to the mean width of the channel. The hydrodynamic solution is then used to obtain the effects of wall roughness upon the blood oxygenation in a membrane oxygenator. The effects of various pertinent parameters upon the flow field, energy loss, and oxygen concentration, and possible occurrence of separation and reattachment are examined for symmetric and nonsymmetric channels with sinusoidal variation. It is found that when the blood is assumed to behave like a homogeneous fluid the wall irregularity has a strong effect on local oxygen concentration distribution, but has little effect on the saturation length. The saturation length is found to be of the order of 3/2 (1 + FS0/P0)ReScd for a channel with, or without, wall irregularity. Therefore, the secondary flows induced by the cell-plasma and cell-cell interaction is more likely the primary mechanism for a vast increase in oxygenation efficiency using wavy channels reported by Kolobow, et al.
During a station blackout of PWR. the pump seal will fail due to loss of the seal cooling. This particular transient-LOCA sequence designated as S3-TMLB' analyzed by SNL with MELPROG/TRAC for Surry plant showed that the depressurization due to the pump seal LOCA would result in early accumulator injection and subsequent core cooling which lead to the delay of reactor pressure vessel (RPV) meltthrough. The present analysis was performed with SCDAP/RELAP5 to evaluate this scenario shown in the MELPROG/TRAC analyses. Additionally. the calculated results were compared with the similar experimental studies of JAERI's ROSA-IV program.The present analyses showed t h a t : (1) During S3-TMLB', the loop seal clearing would occur and cause a slight delay of accident progression. (2) It is unlikely that the accumulator injection, which leads to the delay of RPV meltthrough by approximately 60min, is initiated automatically during S3-TMLB'. Accordingly, an intentional depressurization using PORVs is recommended for the mitigation of the accident consequences. (3) The present SCDAP/RELAP5 analyses did not show significant delay of accident progression. It was found that non-realistic lower heat generation and higher core cooling models used in the MELPROG/TRAC analysis are attributed to this discrepancy.
Analytical solutions are obtained on the effects of boundary constriction on heat or mass transfer at the entrance region in a well-developed steady laminar flow in symmetric and axisymmetric conduits subjected to uniform wall temperature or mass concentration. The solutions are limited to the fluids of constant properties with negligible viscous dissipation, moderate Reynolds number, and large Peclet or Schmidt number, and the spread of the wall constriction is large compared to the mean width or radius of the conduits. It is found that both the bulk temperature and heat transfer rate at the wall are oscillatory in nature, and their amplitudes decrease drastically as the fluid moves away from the entrance. Near thermal entry length, the bulk fluid temperature approaches its mean value with vanishing oscillation, but the heat transfer rate at the wall stays oscillatory in nature due to the irregularity of the wall. The thermal entry length changes very little from the corresponding straight-wall conduits. These results are also true for the mass transfer.
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