Accumulation and transport of microbial-size particles in a pressure protected model burn unit: CFD simulations and experimental evidence

<p>Abstract</p> <p>Background</p> <p>Controlling airborne contamination is of major importance in burn units because of the high susceptibility of burned patients to infections and the unique environmental conditions that can accentuate the infection risk. In particular the required elevated temperatures in the patient room can create thermal convection flows which can transport airborne contaminates throughout the unit. In order to estimate this risk and optimize the design of an intensive care room intended to host severely burned patients, we have relied on a computational fluid dynamic methodology (CFD).</p> <p>Methods</p> <p>The study was carried out in 4 steps: i) patient room design, ii) CFD simulations of patient room design to model air flows throughout the patient room, adjacent anterooms and the corridor, iii) construction of a prototype room and subsequent experimental studies to characterize its performance iv) qualitative comparison of the tendencies between CFD prediction and experimental results. The Electricité De France (EDF) open-source software <it>Code_Saturne</it>^®(<url>http://www.code-saturne.org</url>) was used and CFD simulations were conducted with an hexahedral mesh containing about 300 000 computational cells. The computational domain included the treatment room and two anterooms including equipment, staff and patient. Experiments with inert aerosol particles followed by time-resolved particle counting were conducted in the prototype room for comparison with the CFD observations.</p> <p>Results</p> <p>We found that thermal convection can create contaminated zones near the ceiling of the room, which can subsequently lead to contaminate transfer in adjacent rooms. Experimental confirmation of these phenomena agreed well with CFD predictions and showed that particles greater than one micron (i.e. bacterial or fungal spore sizes) can be influenced by these thermally induced flows. When the temperature difference between rooms was 7°C, a significant contamination transfer was observed to enter into the positive pressure room when the access door was opened, while 2°C had little effect. Based on these findings the constructed burn unit was outfitted with supplemental air exhaust ducts over the doors to compensate for the thermal convective flows.</p> <p>Conclusions</p> <p>CFD simulations proved to be a particularly useful tool for the design and optimization of a burn unit treatment room. Our results, which have been confirmed qualitatively by experimental investigation, stressed that airborne transfer of microbial size particles via thermal convection flows are able to bypass the protective overpressure in the patient room, which can represent a potential risk of cross contamination between rooms in protected environments.</p

Localization and broadband follow-up of the gravitational-wave transient GW150914

A gravitational-wave transient was identified in data recorded by the Advanced LIGO detectors on 2015 September 14. The event candidate, initially designated G184098 and later given the name GW150914, is described in detail elsewhere. By prior arrangement, preliminary estimates of the time, significance, and sky location of the event were shared with 63 teams of observers covering radio, optical, near-infrared, X-ray, and gamma-ray wavelengths with ground- and space-based facilities. In this Letter we describe the low-latency analysis of the gravitational wave data and present the sky localization of the first observed compact binary merger. We summarize the follow-up observations reported by 25 teams via private Gamma-ray Coordinates Network Circulars, giving an overview of the participating facilities, the gravitational wave sky localization coverage, the timeline and depth of the observations. As this event turned out to be a binary black hole merger, there is little expectation of a detectable electromagnetic signature. Nevertheless, this first broadband campaign to search for a counterpart of an Advanced LIGO source represents a milestone and highlights the broad capabilities of the transient astronomy community and the observing strategies that have been developed to pursue neutron star binary merger events. Detailed investigations of the electromagnetic data and results of the electromagnetic follow-up campaign will be disseminated in the papers of the individual teams

Particle interaction with the wall surface in two-phase gas-solid particle flow

Solid-particle impact interaction with material wall surfaces is a problem in many multiphase flow industrial devices. This interaction affected by flows around curved surfaces (aerodynamic effects) is analysed in this paper for generic wall geometry and carrier gas flow. The focus of this paper is to quantify the incidence and reflection of small (near-Stokesian) particles. Particle reflection threshold is found, and depends on both particle Stokes number and carrier gas flow near the wall surface. The analytical results are illustrated and compared with the computational results for cylindrical wall surfaces. The boundary layer theory is employed to predict the key model parameter. The analytical prediction agrees well with the computational results. (C) 1999 Elsevier Science Ltd. All rights reserved

Novel Eulerian formulation for dilute gas-particle flows with an obstruction

A novel Eulerian formulation for dilute gas-particle flows with an obstruction is developed by laking into consideration explicitly incident and reflected particles. Particles in a control volume are separated into two families, incident and reflected, each of which is assumed to move with approximately the same velocity. The drag force over a control volume is split into two components, one for the incident and one for the reflected particles, each of which can be physically consistently calculated using a standard formula. The particulate phase flow can be described equivalently by the composite family, which consists of incident and reflected particles. The particulate flow of incident particles is first evaluated by applying an outflow boundary condition at windward obstruction surfaces, and then the composite particulate flow is computed using the information of the incident particle solution. The novel formulation is implemented in the commercial computation fluid dynamics code, FLUENT, via User Defined Subroutines. The prediction of dilute gas-particle flows past a 45 degrees ramp and a cylinder with afterbody employing our novel Eulerian formulation shows excellent agreement with the results predicted by the Lagrangian approach. The detailed analysis shows that the key mechanism involved in our novel Eulerian formulation is the correctly treated drag force oner each control volume. Our novel Eulerian formulation can provide a useful approach for studying erosion and deposition in coal-fired boilers