Experimental and Numerical Study of a Turbulent Multiple Jets Issued from Lobed Diffusers

A combined experimental and computational study of a turbulent multiple jet from lobed diffusers is performed. The main interest of these multiple lobed jets is to come up with the best configuration that improves the thermal and dynamic homogenization in air diffusion units that can be used for ventilation, heating and air conditioning of residential premises. Herein, the configuration of a central lobed jet surrounded by six equidistant peripheral lobed jets has been investigated. On the experimental level, flow velocities and temperatures were measured by a multifunctional thermo-anemometer. In terms of numerical simulation, the conservation equations of mass, momentum and energy are solved while involving four turbulence models, viz., the k-ϵ model, the k-ω, the shear stress transport (SST) k-ω model and the Reynolds Stress Model (RSM). The findings are compared with thermo-anemometer measurements. It turns out that the SST k- ω model is most appropriate for predicting the average flow characteristics

Advanced Methods for Air Distribution in Occupied Spaces for Reduced Risk from Air-Borne Diseases and Improved Air Quality

Denne Ph.d. afhandling beskæftiger sig med nye avancerede metoder til luftfordeling i lokaler. Formålet er at forbedre den inhalerede luftkvalitet og mindske risikoen fra luftbåren krydsinfektion blandt dem der opholder sig i lokalet.De eksisterende ventilationsstrategier nu til dags er ikke i stand til at yde tilstrækkelig ren luft til brugerne og kan endda øge risikoen for krydsinfektion af luftbårne sygdomme indendørs. Det er tydeligt at nye avancerede metoder er nødvendige for at forbedre den nuværende situation. Emnet er særligt vigtigt på grund af spørgsmålet om energiforbrug samt den øgede mulighed for tilfældigemutationer af kendte luftbårne patogener. Truslen fra mulige biologiske terrorangreb i det seneste årti gør emnet meget vigtigt.Hidtil har de eksisterende metoder til indendørs luftrensning bygget på fleregrundlæggende strategier: Fortynding, filtrering og Ultraviolet Bakteriedræbende Bestrålingen (Ultra Violet Germicidal Irradiation – UVGI). Fortynding benytter ventilation ved høje strømningshastigheder til at reducere koncentrationen af forurenende stoffer / patogener til et niveau, der ikke forringer luftkvaliteten eller er til skade for de mennesker der opholder sig i bygningen. Fortynding er også forbundet med visse energimæssige begrænsninger. Filtrering og UVGI er effektive til at beskytte personer, forudsat at kilderne er placeret udendørs. Men disse metoder er ikke særlig effektiv, hvis de forurenende kilder er indendørs, især hvis kilden er en syg person.Afhandlingen fokuserer på to metoder der nedsætter risikoen smittespredning af luftbårne sygdomme ved at yde personlig beskyttelse af den enkelte i et kontormiljø, og ved at beskytte medicinsk personale, patienter og besøgende fra krydsinfektion i sygehusafdelinger.Den første del af afhandlingen fokuserer på forbedring af inhaleret luftkvalitet og mindskelse af risikoen for krydsinfektion gennem et avanceret ventilationsprincip som giver renere luft tæt på brugerne. Princippet er opkaldt personlig ventilation (PV) og anvender kontrol med luftstrømmes interaktion tæt på vejrtrækningszonen. To nye kontrolmetoder, nemlig kontrol over det friekonvektive lag omkring den menneskelige krop og kontrol af det personlige flow er undersøgt, når de anvendes til forskellige PV design. Den første metode har til formål at reducere styrken af det frie konvektive lag via blokering eller lokal udsugning, hvilket dermed muliggør indtrængen af luftstrømninger fra PV med lav hastighed (low flow rate). Den anden metode går ud på at kontrollere måden hvorpå PV strømmen leveres, så denne er mindre påvirket afstrømmeningssamspillet omkring den menneskelige krop: Ved at nedsænke strømningen i den konvektive strømning eller ved blot at udskifte grænselaget med en PV strømning som støder op til kroppen. Begge metoder bidrog i høj grad til at øge effektiviteten af de anvendte PV systemer med hensyn til mængden af ren luft, der leveres i indåndingszonen i forhold til da PV blev anvendt uden nogen form for kontrol. Disse metoder viser også stort potentiale for energibesparelser, som følge af nedsat PV strømningshastighed. De foreslåede design er lette at implementere i rum, hvor folk for det meste sider ned, fx kontorer, teatre, biografer, busser, tog, fly, etc.Den anden del af afhandlingen fokuserer på en ny ventilationsstrategi der reducerer risikoen for krydsinfektion af medicinsk personale, besøgende og patienter på hospitalsafdelinger. Den nye ventilationsstrategi er implementeret ved hjælp af specielt udviklet udstyr, som er opkaldt ’Hospital Bed Integrated Ventilation Cleansing Unit (HBIVCU)’ (udstyret er en del af en patientansøgning i Europa (EP 09165736,1) og i USA (US 61/226, 542). Ved at udsuge den luft som patienten udsender ved host bidrog HBIVCUen til at beskytte læger og andre patienter mod luftbåren smitte. Udover øget beskyttelse fører brugen af HBIVCUen til fald i baggrunden ventilationsraten. Denne teknik til lokal udsugning og rensning af luft fra host kan løse de eksisterende problemer der er relateret til håndtering af spredningsrisiko under behandling af patienter med luftbårne smitsomme sygdomme i et hospital miljø i perioder med epidemier ogpandemier.The current Ph.D. thesis deals with new advanced methods of air distribution in occupied places aimed to improve the inhaled air quality and to reduce the risk from airborne cross infection among the occupants.The existing ventilation strategies nowadays are not able to provide enough clean air to the occupants and can even enhance the risk from cross-infection from airborne diseases indoors. Clearly new advanced methods are needed to improve the current situation. The subject is especially important because of the energy issue as well as the increased possibility of random mutations of known airborne pathogens. The threat from possible bio-terrorist attacks in the lastdecade makes the topic quite important.So far the existing methods of indoor air cleaning rely on several basic strategies: dilution, filtration and Ultra Violet Germicidal Irradiation (UVGI). Dilution utilizes ventilation at high flow rates to reduce the concentration of pollutants/pathogens to levels that would not deteriorate the air quality or be harmful for the occupants. It is also connected to certain energy limitation issues.Filtration and UVGI are efficient in protecting occupants provided the sources are located outdoors. However, these methods are not very efficient, if the contaminant sources are indoors and especially if the source is a sick individual.The current thesis focuses on two ways to provide reduced risk from airborne infections: by providing personal protection of each individual in an office environment and by protecting medical staff, patients and visitors from cross-infection in hospital wards.The first part of the thesis focuses on improvement of inhaled air quality and thus reduction in the risk from cross-infection by advanced ventilation, providing clean air close to the occupants with personalized ventilation (PV) by applying control over the airflow interaction at the breathing zone. Two new control methods, namely control over the free convection layer around the human bodyand control over the personalized flow are studied when applied for different PV designs. The first method aims to reduce the strength of the free convection layer via blocking or local exhausting, and thus make possible its penetration by the personalized flow at low velocity (low flow rate). The second method aims to control the way the PV flow is supplied so that it is less affected by the flowinteraction around the human body: by immersing it within the convection flow or by simply substituting the boundary layer with a PV flow adjacent to the body. Both methods helped greatly increase the performance of the employed PV systems with respect to the amount of clean air supplied into the breathing zone of the occupant compared to the case when the PV was used alone. These methods also show great potential for energy savings, due to the reduced PV flow rate. The suggested designs are easy for implementation in occupied spaces, where people spend most of the time seated, e.g. offices, theaters, cinemas, busses, trains, airplanes, etc.The second part of the thesis focuses on a novel ventilation strategy for reduction the risk of cross-infection for medical staff, visitors, and patients in hospital wards. The novel ventilation strategy is implemented by a specially developed device, named Hospital Bed Integrated Ventilation Cleansing Unit (the device is part of a patient application in Europe (EP 09165736.1) and in the United States of America (US 61/226,542). The HBIVCU helped to provide improved protection to doctor and other patients, present in a space, from a sick individual with highly contagious airborne transferred disease, by locally evacuating the air coughed by the sick patient. Apart of increased protection the use of the HBIVCU leads to decrease of the background ventilation rate. This technique of local exhaust and cleaning of the coughed air can providesolution to the existing problems in a hospital environment related to control and, handling the spread and treating patients with contagious airborne diseases, as well as problems with insufficient space in hospital wards in times of epidemics and pandemics