Experimental and CFD airflow studies of a cleanroom with special respect to air supply inlets

Investigations were carried out into the airflow in a non-unidirectional airflow cleanroom and its affect on the local airborne particle cleanliness The main influence was the method of air supply A supply inlet with no diffuser gave a pronounced downward jet flow and low levels of contamination below it, but poorer than average conditions in much of the rest of the room A 4-way diffuser gave much better air mixing and a more even airborne particle concentration throughout the cleanroom Other variables such as air inlet supply velocity, temperature difference between air supply and the room, and the release position of contamination also influenced the local airborne cleanliness A CFD analysis of airflow fields in a cleanroom was compared with measured values It was considered that a turbulent intensity of 6%, and a hydraulic diameter based on the actual size of the air inlet, should be used for the inlet boundary conditions and, when combined with a k-epsilon standard turbulence model, a reasonable prediction of the airflow and airborne particle concentration was obtained

Numerical investigation of airborne contaminant transport under different vortex structures in the aircraft cabin.

Airborne contaminants such as pathogens, odors and CO2 released from an individual passenger could spread via air flow in an aircraft cabin and make other passengers unhealthy and uncomfortable. In this study, we introduced the airflow vortex structure to analyze how airflow patterns affected contaminant transport in an aircraft cabin. Experimental data regarding airflow patterns were used to validate a computational fluid dynamics (CFD) model. Using the validated CFD model, we investigated the effects of the airflow vortex structure on contaminant transmission based on quantitative analysis. It was found that the contaminant source located in a vorticity-dominated region was more likely to be "locked" in the vortex, resulting in higher 62% higher average concentration and 14% longer residual time than that when the source was on a deformation dominated location. The contaminant concentrations also differed between the front and rear parts of the cabin because of different airflow structures. Contaminant released close to the heated manikin face was likely to be transported backward according to its distribution mean position. Based on these results, the air flow patterns inside aircraft cabins can potentially be improved to better control the spread of airborne contaminant

Experimental study of the flow field in patient specific lower airways

In this study Particle Image Velocimetry (PIV) is used to visualize and measure airflow in the lower airways. Using Rapid Prototyping Manufacturing (RPM) technology, a hydraulic in vitro model was developed and constructed. Preliminary 2D PIV measurements compared successfully to Computational Fluid Dynamics (CFD) results

Indoor mould growth prediction using coupled computational fluid dynamics and mould growth model

This study investigates, using in-situ and numerical simulation experiments, airflow and hygrothermal distribution in a mechanically ventilated academic research facility with known cases of microbial proliferations. Microclimate parameters were obtained from in-situ experiments and used as boundary conditions and validation of the numerical experiments with a commercial computational fluid dynamics (CFD) analysis tool using the standard k–ε model. Good agreements were obtained with less than 10% deviations between the measured and simulated results. Subsequent upon successful validation, the model was used to investigate hygrothermal and airflow profile within the shelves holding stored components in the facility. The predicted in-shelf hygrothermal profile was superimposed on mould growth limiting curve earlier documented in the literature. Results revealed the growth of xerophilic species in most parts of the shelves. The mould growth prediction was found in correlation with the microbial investigation in the case-studied room reported by the authors elsewhere. Satisfactory prediction of mould growth in the room successfully proved that the CFD simulation can be used to investigate the conditions that lead to microbial growth in the indoor environment

Physical and geometric constraints explain the labyrinth-like shape of the nasal cavity

The nasal cavity is a vital component of the respiratory system that heats and humidifies inhaled air in all vertebrates. Despite this common function, the shapes of nasal cavities vary widely across animals. To understand this variability, we here connect nasal geometry to its function by theoretically studying the airflow and the associated scalar exchange that describes heating and humidification. We find that optimal geometries, which have minimal resistance for a given exchange efficiency, have a constant gap width between their side walls, but their overall shape is restricted only by the geometry of the head. Our theory explains the geometric variations of natural nasal cavities quantitatively and we hypothesize that the trade-off between high exchange efficiency and low resistance to airflow is the main driving force shaping the nasal cavity. Our model further explains why humans, whose nasal cavities evolved to be smaller than expected for their size, become obligate oral breathers in aerobically challenging situations.Comment: 7 pages, 4 figure

Airflow Pattern Similarity Criteria for Ceiling Slot-ventilated Agricultural Enclosures under Isothermal Conditions

The use of a scaled model can be an effective technique to predict ventilation performance of full-scale prototypes. Many criteria have been proposed to predict the behavior of airflow in a scale model and a prototype. Because of inconsistent results of proposed similarity criteria, more validation work is needed to clarify the conflicts. Experiments to study airflow similarity in ceiling slot-ventilated agricultural enclosures using different similarity criteria were conducted on two scale models. The studies focused on the Reynolds number (Re) and inlet jet momentum ratio (Rm) as the similitude criteria for isothermal airflow. The experimental results offer better agreement using Rm as opposed to Re as the similitude criterion for isothermal airflow pattern control

Computer model of a domestic wood burning heater : a thesis presented in fulfilment of the requirements for the degree of Master of Engineering in Chemical Technology at Massey University

Between April 2003 and April 2004 a project, funded by Technology New Zealand, was undertaken to develop a computer model of a wood burning heater for use at Applied Research Services Ltd. Applied Research Services Ltd is a science and engineering research company that specialises in the testing of wood burning heaters. The computer model will be owned by Applied Research Services Ltd and will be used to improve the design of their customers' heaters so that they may pass the particulate emissions and efficiency standards of AS/NZS 4013:1999. The computer model used the software program, Engineering Equation Solver as a platform to solve the model equations. EES was particularly easy to use and more emphasis was able to he placed on the actual modelling. The final model included over eight hundred variables and equations. It included radiant, convective and conductive heat flows, over thirty heat balances, Arrhenious based rate expressions and many empirical equations derived from experiments and data acquired at Applied Research Services Ltd. At the beginning of this project the objective was for the model to match the test results to within 10%. This has been met for the tests on the high airflow setting where the model error is 4% for flue temperature, 8% for heater output and 16% for flue oxygen. Unfortunately on low airflow setting, the model does not reach this target with model errors of 18% for flue temperature, 25% for heat output and 13% for flue temperature. The excellent results for the high flow setting are partially attributed to the use of calibration factors. The calibration factors model the processes in wood combustion that could not be modelled by this project, due to lack of time and resources. Some of these factors are the proportion of air that flows onto the charcoal ember bed or logs, radiation shape factor changes due to firebox geometry, convection heat transfer coefficients changing with turbulence. The calibration of the model only has to be completed once for each heater. The reason why the model does not work as well on low airflow setting is that with less airflow the proportion of air to the charcoal bed opposed to the logs would decrease, therefore decreasing the burn-rate. This model can he used to determine the changes to a heater's performance from changes to air inlet areas, insulation type and thickness, wetback size, baffle size, primary vs secondary air, air bypass ratio and door size. The model provides all the results that are obtained from an emissions test plus extra information such as the amount of excess air, smoke conversion in each combustion zone, flame temperatures and distribution of heat output. The smoke conversions for each combustion zone are particularly helpful in diagnosing where problems with the combustion occur. The reasons for incomplete combustion, lack of temperature or oxygen, can be found and fixed by increasing either insulation or air areas. The model can be used by Applied Research Services Ltd to improve heater designs. For the short term this will involve the author working as a part-time consultant. The project could be built on by another student by using CFD modelling for the sections of the wood burning process not modelled by this model and adding a graphical user interface to make the model easier to use