CFD simulations of a semi-transverse ventilation system in a long tunnel

In the present work,a semi-transverse ventilation system in a long tunnel with a length of 4.9 km,as a complex case study,is numer-ically studied by performing a set of three-dimensional steady incompressible computational fluid dynamics(CFD)simulations.The ven-tilation system consisted of a ceiling duct connected to two axial fans at the ending portals,and a series of jet fans in the main tunnel for supporting airflow in the desired direction.To focus on what can and cannot be achieved in commissioning tests,the ventilation system’s performance in various scenarios is numerically evaluated with two different tunnel states;empty tunnel and complete traffic congestion with 1176 stationary vehicles–which is almost impossible to evaluate during a commissioning test.By considering two hypothetical loca-tions for the extraction zone from the main tunnel(in a distance of 450 and 1000 m from one portal),it is shown that the required number of jet fans in a traffic condition drops from 57 for the first extraction location to 43(25%decrease)when the ventilation system extracts from the second zone.We show that if only the close axial fan to the extraction zone is activated,the required number of jet fans reduces by 56%and 72%for the first and second extraction locations,respectively.This finding can provide a cheaper and easier controlling scenario for emergency ventilation.

Effect of a portable ultra-clean exponential airflow unit on the particle distribution in an operating room

The effects of a mobile laminar airflow unit on the concentration, deposition and distribution of bacteria- carrying particles in an operating room are investigated. The exploration is carried out using numerical calculation schemes （computational fluid dynamics approach）. The model validation was performed through result comparisons with published measurement data from literature. Two types of mobile screen units were evaluated as an extension of turbulent-mixing operating-room ventilation. Airborne particle concentration/sedimentation was recorded with and without a screen unit on the operating table and two instrument tables. Both active and passive air sampling were examined and the results are compared. It was found that the additional mobile ultra-clean laminar airflow unit reduces the counts of airborne bacteria and surface contamination to a level acceptable for infection-prone surgeries.

Influence of staff number and internal constellation on surgical site infection in an operating room

Prediction of bacteria-carrying particle （BCP） dispersion and particle distribution released from staffmem- bers in an operating room （OR） is very important for creating and sustaining a safe indoor environment. Postoperative wound infections cause significant morbidity and mortality, and contribute to increased hospitalization time. Increasing the number of personnel within the OR disrupts the ventilation airflow pattern and causes enhanced contamination risk in the area of an open wound. Whether the amount of staffwithin the OR influences the BCP distribution in the surgical zone has rarely been investigated. This study was conducted to explore the influence of the number of personnel in the OR on the airflow field and the BCP distribution. This was performed by applying a numerical calculation to map the airflow field and Lagrangian particle tracking （LPT） for the BCP phase. The results are reported both for active sampling and passive monitoring approaches. Not surprisingly, a growing trend in the BCP concentration （cfu/ms） was observed as the amount of staff in the OR increased. Passive sampling shows unpredictable results due to the sedimentation rate, especially for small particles （5-10 i^m）. Risk factors for surgical site infections （SSls） must be well understood to develop more effective prevention programs.