Safety Instrumented Systems (SIS) are electric/electronic/programmable electronic safety related systems which are intended to achieve or maintain a safe state for the Equipment Under Control (EUC), in respect of a specific hazardous event. A well designed system can increase plant availability by reducing the number of spurious « Trips » caused by an SIS that fails to properly evaluate a safety situation and unnecessarily shut down a process. Data suggest that over 90% of problems in SIS can be attributed to the sensors and final elements. This paper presents the results of a simulation and experimental study based on fault diagnostic of SIS components (especially sensors). The EUC is a furnace in gas process industry. It has been shown that adding a second sensor to the SIS may improve its performance (Safety Integrity Level: SIL).
The Reynolds–averaged Navier–Stokes (RANS) equations were solved along with Reynolds stress model (RSM), to study the fully-developed unsteady and anisotropic single-phase turbulent flow in 90° bend pipe with circular cross-section. Two flow configurations are considered the first is without ribs and the second is with ribs attached to solid walls. The number of ribs is 14 ribs regularly placed along the straight pipe. The pitch ratios is 40 and the rib height e (mm) is 10% of the pipe diameter. Both bends have a curvature radius ratio, of 2.0. The solutions of these flows were obtained using the commercial CFD software Fluent at a Dean number range from 5000 to 40000. In order to validate the turbulence model, numerical simulations were compared with the existing experimental data. The results are found in good agreement with the literature data. After validation of the numerical strategy, the axial velocity distribution and the anisotropy of the Reynolds stresses at several downstream longitudinal locations were obtained in order to investigate the hydrodynamic developments of the analyzed flow. The results show that in the ribbed bend pipe, the maximum velocity value is approximately 47% higher than the corresponding upstream value but it is 9% higher in the case of the bend pipe without ribs. It was also found for both cases that the distribution of the mean axial velocity depends faintly on the Dean number. Finally, it can be seen that the analyzed flow in the bend pipe without ribs appears more anisotropic than in bend pipe with ribs.
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