P.A. Sleigh

An unstructured finite-volume algorithm for predicting flow in rivers and estuaries

Abstract A numerical algorithm is presented for the solution of geometrically challenging two-dimensional river and estuary flows, based on an adaptive triangular tessellation of the flow domains of interest. The governing, shallow water, equations are discretised using a finite volume approach embodying variable step time integrators, to yield a method that is second order accurate in both space and time. An approximate Riemann solver is used to determine flow directionality in conjunction with an effective means of dealing with wetting and drying at the boundaries. The approach is capable of handling complex flow domains and yielding solutions for which errors are controlled automatically by the use of spatial re-gridding and time stepping based on local error estimates. Its range of applicability is demonstrated through considering several problems involving super/sub-critical flow, wetting/drying, culminating in the solution of a complete estuary problem.

The use of solar desiccant cooling in the UK: a feasibility study

The desiccant cooling cycle is a novel open heat driven cycle which can be used both to cool and dehumidify air. Being a heat driven cycle, desiccant cooling affords an opportunity to utilise heat which might otherwise be wasted. It can therefore be coupled to solar collectors to produce a cooling system which, in theory, should be environmentally friendly. This paper discusses the feasibility of using solar energy to power the desiccant cooling cycle and also presents a study, in which a solar desiccant cooling model is used to evaluate installations located in the southeast and east midlands of England, and in central Scotland. The paper demonstrates that solar powered desiccant cooling is a feasible solution for cooling and heating buildings in the United Kingdom.

The potential for solar powered single-stage desiccant cooling in southern Europe

Desiccant cooling is an environmentally friendly technology which can be used to condition the internal environment of buildings. Unlike conventional air conditioning systems, which rely on electrical energy to drive the cooling cycle, desiccant cooling is a heat driven cycle. Desiccant cooling systems have been used successfully in northern Europe and a number of studies have demonstrated that solar energy can be used to drive the system in this region. However, to date, desiccant cooling has not been used in southern European. This paper presents the results of a study, in which a solar desiccant cooling model was used to evaluate the potential for using solar power to drive a single-stage desiccant cooling system in various locations in southern Europe. The study demonstrates that solar desiccant cooling is feasible in parts of southern Europe, provided that the latent heat gains experienced are not excessive. However, if the relative humidities experienced are too high then desiccant cooling becomes impracticable simply because the regeneration temperatures required are excessive.

A theoretical study of the thermal performance of the TermoDeck hollow core slab system

The TermoDeck hollow core slab system is a versatile energy storage technique for controlling the environment within large and medium sized buildings. It utilises the hollow cores within pre-cast concrete floor slabs as ventilation ducts to produce an environment which is thermally stable. Although many TermoDeck systems have successfully been installed in Scandinavia, the United Kingdom and in other northern European countries, the thermal performance of the system is not fully understood. This paper presents the results of a theoretical study, using a numerical model, into the thermal performance of the TermoDeck system. In particular, the role of the bends in the system is investigated and the conclusion reached that their impact on overall heat transfer is minimal. It is also concluded that greater thermal attenuation is achieved by using a five-core pass system in comparison with a three-core system.

Bioaerosol Production on a Respiratory Ward

Although much hospital acquired infection is associated with person-to-person contact, there is increasing evidence that some nosocomial infections may be transmitted via the airborne route. However, the knowledge base concerning airborne microflora in hospitals is poor. In particular, there is a need for good quality data relating bioaerosol production to clinical activity in hospital wards. A short aerobiological survey was therefore undertaken by the authors on a respiratory ward at St James’s University Hospital in Leeds in order to gain an understanding of the relationship between activity and bioaerosol production. This survey involved regular microbiological and particulate (0.3–5 m) sampling of the ward air, together with an observational study of ward activity. Two identical four-bed ward bays were surveyed, one containing high dependency patients who regularly used noninvasive ventilators (NIVs), and the other containing patients who did not require mechanical ventilation. The survey found a correlation between activity and aerosol production.

A quantitative method for evaluating the germicidal effect of upper room UV fields.

With the general increase in the worldwide incidence of tuberculosis there is increasing interest in the use of upper room ultraviolet germicidal irradiation (UVGI) systems to disinfect air. A number of researchers have demonstrated experimentally the ability of such systems to inactivate airborne microorganisms. However, relatively little theoretical work has been done to explain the results observed and few models exist to describe the performance of upper room UVGI systems. This paper presents a new model, which can be used both to design such systems and to evaluate their germicidal effectiveness. A theoretical study is undertaken, which indicates that although upper room UVGI systems work well at lower ventilation rates, they are of limited benefit in highly ventilated applications. The paper also demonstrates and quantifies the relationship between inter-zonal air velocity and room ventilation rate. In particular, the paper shows that under steady-state conditions the number of passes made by bioaerosol particles through an upper room UV field is independent of the ventilation rate.

CFD simulation of airborne pathogen transport due to human activities

Abstract Computational Fluid Dynamics (CFD) is an increasingly popular tool for studying the impact of design interventions on the transport of infectious microorganisms. While much of the focus is on respiratory infections, there is substantial evidence that certain pathogens, such as those which colonise the skin, can be released into, and transported through the air through routine activities. In these situations the bacteria is released over a volume of space, with different intensities and locations varying in time rather than being released at a single point. This paper considers the application of CFD modelling to the evaluation of risk from this type of bioaerosol generation. An experimental validation study provides a direct comparison between CFD simulations and bioaerosol distribution, showing that passive scalar and particle tracking approaches are both appropriate for small particle bioaerosols. The study introduces a zonal source, which aims to represent the time averaged release of bacteria from an activity within a zone around the entire location the release takes place. This approach is shown to perform well when validated numerically though comparison with the time averaged dispersion patterns from a transient source. However, the ability of a point source to represent such dispersion is dependent on airflow regime. The applicability of the model is demonstrated using a simulation of an isolation room representing the release of bacteria from bedmaking.

Modelling the Performance of Upper Room Ultraviolet Germicidal Irradiation Devices in Ventilated Rooms: Comparison of Analytical and CFD Methods

Models to evaluate upper room ultraviolet germicidal irradiation (UVGI) devices can be used to improve the understanding of the behaviour of UV devices in ventilated rooms and so enable more confident predictions to be made of their performance. This paper presents two- and three-zone mixing models for investigating the effect of upper room UVGI devices in a typical ventilated room. The results from these analytical models are compared to a CFD simulation of the same room that incorporates the biological inactivation of micro-organisms in the presence of an ultraviolet field. The study demonstrates that analytical mixing models give reasonably good average zone concentrations and are therefore useful in estimating overall performance. However, the CFD simulations are necessary to fully examine the interaction of the room airflow with the inactivation of micro-organisms due to the UV field.

Use of CFD modelling to optimise the design of upper-room UVGI disinfection systems for ventilated rooms

The installation of upper-room ultraviolet germicidal irradiation (UVGI) devices in ventilated rooms has the potential to reduce transmission of infections by an airborne route. However, the performance of such devices is dependant on several factors including the location of the lamp and the ventilation airflow in the room. This study uses a CFD model to evaluate the performance of UVGI devices by considering the cumulative UV-C dose received by the bulk room air in a ventilated room. By evaluating the UV dose rather than the resulting micro-organism inactivation the methodology can be used to optimise UVGI systems at the design stage, particularly when the source location of bioaerosol contaminants is not known. The study investigates the relationships between the lamp location, lamp power, ventilation system and room heating in a small, ventilated room. The results show that with ventilation air supplied at low level and extracted at high level the UVGI system performs better than with the air supplied at high level and extracted close to the floor. In addition the results show the presence of a heater in the room is unlikely to have a detrimental effect on performance and may promote mixing to increase the extent of disinfection.

Use of CFD Analysis in Modifying a TB Ward in Lima, Peru

The high world-wide prevalence of tuberculosis (TB) and the increase in multi-drug resistant strains (MDRTB) have prompted increased interest in engineering control solutions such as ventilation system design and the use of ultraviolet germicidal irradiation (UVGI). This study considers the contribution of the ventilation airflow to the transmission of TB, and uses computational fluid dynamics (CFD) simulations to examine how changes in the design of a ward, in Hospital Nacional Dos de Mayo, Lima, Peru may reduce the transmission of TB from patients to health-care workers, visitors and other patients. The results of this study were used to advise the architects and engineers in the remodelling of the ward.