ABSTRACT
Objective Tostudy the influence of pipe structures on the mixing uniformity of airborne effluents from nuclear power plant chimneys. Methods We used the computational fluid dynamics (CFD) method to simulate the velocity distribution and gas mixing in long straight pipes (I type) with square section and circular section, 90° single-bend pipes (L type) with square section and circular section, and 90° double-bend pipes (S type and U type) with square section and circular section. Results For the long straight pipe, due to the lack of flow disturbance caused by structural changes, the mixing effect was not good; when the pipe section was circular, it might take mixing distance 20 times the hydraulic diameter to achieve the uniformity index required by the relevant standard; for the square pipe, the distance might be longer. In the single bend pipe with square section, the velocity uniformity was improved more greatly after the bend, and the tracer gas met the mixing uniformity at a shorter distance (11 times the hydraulic diameter), as compared with the single bend pipe with circular section. For the S-type double-bend pipe, the tracer gas appeared uniformly mixed after a distance 6 times the hydraulic diameter in the square pipe, and 7 times the hydraulic diameter in the circular pipe. For the U-type double-bend pipe, the gas in the square pipe also achieved uniform mixing ata shorter distance downstream, and the airflow showed greater disturbance when passing through the bend. Conclusion The CFD method can make an accurate prediction for the change patterns of gas mixing uniformity in pipes with different structures, and can partially replace physical experiments to study the factors affecting the mixing uniformity of airborne effluents from the chimney of nuclear power plants.
ABSTRACT
Objective To evaluate the technical feasibility and safety of a single-incision technique via axillary vein (AV) for placement of totally implantable venous access port (TIVAP) guided by ultrasound combined with DSA in clinical application. Methods We retrospectively analyzed clinical data of 240 patients who received TIVAP by single incision technique via AV access guided by ultrasound combined with DSA. We observed and recorded operation-related information such as AV width, AV puncture success rate, implantation success rate, ultrasound-guided puncture time, operation time and intraoperative and postoperative complications, etc. Results All 240 patients were successfully implanted with TIVAP, and the success rate was 100%. In 229 cases, TIVAP was implanted through single-incision AV puncture under the guidance of ultrasound combined with DSA, and the success rate of AV puncture was 95.42% (229/240). In 11 cases, TIVAP was implanted through the ipsilateral internal jugular vein (IJV) under the guidance of ultrasound combined with DSA due to the failure of AV puncture. In the 240 patients, the average width of AV of the intended puncture segment was (7.56±1.26) mm measured by preoperative ultrasound exploration and positioning, in which 195 cases were successfully punctured once, 26 cases were successfully punctured twice, and 8 cases were successfully punctured three times, with the success rate of 81.25%, 10.83% and 3.34%, respectively. The average puncture time under ultrasound guidance was (0.85±0.52) min, and the average operation time was (25.9±4.8) min. The incidence of intraoperative complications was 1.67% (4/240). No hemothorax, hemopneumothorax or serious fatal complications occurred. The incidence of complications during TIVAP retention was 2.92% (7/240). No complication such as catheter-related bloodstream infection, catheter-related venous thrombosis, catheter rupture/displacement, clipping syndrome or drug extravasation was observed. Conclusion Ultrasound combined with DSA guided single-incision technique via AV access in the implantation of TIVAP is a feasible and safe implantation method with high technical success rate, short operation time and low risk of complications. It can be used as another choice of TIVAP implantation method.