Guangyu Cao - Academia.edu (original) (raw)

Papers by Guangyu Cao

Energy and Buildings, 2019

Ventilation and air distribution methods are important for indoor thermal environments and air qu... more Ventilation and air distribution methods are important for indoor thermal environments and air quality. Effective distribution of airflow for indoor built environments with the aim of simultaneously offsetting thermal and ventilation loads in an energy efficient manner has been the research focus in the past several decades. Based on airflow characteristics, ventilation methods can be categorized as fully mixed or non-uniform. Non-uniform methods can be further divided into piston, stratified and task zone ventilation. In this paper, the theory, performance, practical applications, limitations and solutions pertaining to ventilation and air distribution methods are critically reviewed. Since many ventilation methods are buoyancy driving that confines their use for heating mode, some methods suitable for heating are discussed. Furthermore, measuring and evaluating methods for ventilation and air distribution are also discussed to give a comprehensive framework of the review.

E3S Web of Conferences, 2019

The objective of this study is to analyse what conditions may, and may not take place during surg... more The objective of this study is to analyse what conditions may, and may not take place during surgery in a dilution ventilated operating room (OR), to fulfil an ultra-clean requirement (10 CFU/m3). To achieve the objective, literature review and a mock surgery with air sampling was performed. Colony forming unit (CFU) measurements were conducted to estimate the bacterial concentration in the air. During the mock surgery, the following conditions was present: a clean air suit, surgical gowns, double-tie-on masks and surgical hoods was used by all surgical members, except for the non-sterile members whom did not wear surgical gowns. 5 surgical members + 1 patient were present, 0 door openings occurred and a predefined movement and action plan set the activity level. The average CFU/m3 for the mock surgery was 15,4(SD:5,4). The CFU/m3 during a high activity period was about 21,5% higher than in low activity periods. With the conditions simulated in the mock surgery, and the clothing use...

The adverse effect of various indoor pollutants on occupants’ health have been recognized. In pub... more The adverse effect of various indoor pollutants on occupants’ health have been recognized. In public spaces flu viruses may spread from person to person by airflow generated by various traditional ventilation methods, like natural ventilation and mixing ventilation (MV Personalized ventilation (PV) supplies clean air close to the occupant and directly into the breathing zone. Studies show that it improves the inhaled air quality and reduces the risk of airborne cross-infection in comparison with total volume (TV) ventilation. However, it is still challenging for PV and other advanced air distribution methods to reduce the exposure to gaseous and particulate pollutants under disturbed conditions and to ensure thermal comfort at the same time. The objective of this study is to analyse the performance of different advanced airflow distribution methods for protection of occupants from exposure to indoor pollutants. The study shows that due to complex boundary conditions of the indoor en...

Building and Environment, 2021

Infectious diseases have caused significant physical harm to humans as well as enormous economic ... more Infectious diseases have caused significant physical harm to humans as well as enormous economic losses over the years. Effective ventilation and distribution of fresh air could help to reduce indoor cross-infection. The computational fluid dynamics (CFD) method was used in this paper to investigate airborne transmission with seven different air distribution methods. The revised Wells-Riley model, which took into account the non-uniform air distribution generated with the methods, was used to calculate the infection probability in an office room shared by ten occupants for 4 h. One of the occupants was an infector. The significance of the infector's location was studied. The obtained infection probability was compared to that obtained in the case of complete air mixing, which is uncommon in practice. Under specified conditions of this study, personalized ventilation (PV) performed the best in terms of preventing cross-infection, followed by displacement ventilation (DV), impinging jet ventilation (IJV), stratum ventilation (SV) and wall attachment ventilation (WAV). The number of infected occupants was reduced below the number obtained under the complete mixing assumption by using these air distribution methods. Mixing ventilation (MV) and diffuse ceiling ventilation (DCV) exhibited the worst performance. In comparison to the case of complete mixing the infection probability for seven out of nine susceptible occupants was higher with MV and for all occupants in the case of DCV. In SV, the position of the infector had a clear impact on the infection probability of susceptible individuals. WAV may perform better in practice if the system is well designed. The location of the exhaust outlets had a significant impact on the infection probability for DCV.

Journal of Building Engineering, 2021

Ventilation systems are the primary way of eliminating airborne pathogenic particles in an operat... more Ventilation systems are the primary way of eliminating airborne pathogenic particles in an operating room (OR). However, such systems can be complex due to factors such as different surgical instruments, diverse room sizes, various staff counts, types of clothing used, different surgical types and duration, medications, and patient conditions. OR ventilation should provide a thermally comfortable environment for the surgical staff team members while preventing the patient from suffering from any extreme hypothermia. Many technical, logistical, and ethical implications need to be considered in the early stage of designing a ventilation system for an OR. Years of research and a significant number of publications have highlighted the controversy and disagreement among infection specialists, design engineers, and ventilation experts in this context. This review article aims to provide a good understanding of OR ventilation systems in the context of air quality and infection control from existing research and provide multidimensional insights for appropriate design and operation of the OR. To this end, we have conducted a systematic review of the literature, covering 253 articles in this context. Systematic review and meta-analyses were used to map the evidence and identify research gaps in the existing clinical, practical, and engineering knowledge. The present study is categorized into six research focuses: ventilation system, thermal comfort, staff work practice and obstacles, door operation and passage, air cleaning technology, emission rate, and clothing systems. In the conclusion, we summarize the key limitations of the existing studies and insights for future research direction.

Environmental Science and Pollution Research, 2021

The traditional mixing ventilation is not an energy effective approach to remove indoor air pollu... more The traditional mixing ventilation is not an energy effective approach to remove indoor air pollutants, maintain breath zone air quality, and control the airborne transmission. This study investigated the potential of a localized laminar airflow ventilation system to alleviate human exposure to pollutants. Breathing thermal manikins with sitting posture and supine posture were used to simulate the human. N2O was used as the tracer gas to simulate the indoor pollutant emission. The contaminant exposure index (εexp) and intake fraction index (IF) were used to assess the risk of human pollutant exposure for various supply air velocities given different emission source positions. Enhanced pollutant removal efficiency (Eff) (from the result) showed the qualification and desirability of the localized laminar airflow ventilation system in improving the breath zone air quality. The results showed that the CFD results could fit well with the experimental data and found out the interaction between thermal plume and supply air. The results also indicated a low εexp and IF, with over 90%, all of which were highly correlated with the supply velocity. Human’s different breathing methods have little influence on the pollutant exposure so as to the location of the pollution source. This study found that localized laminar airflow ventilation system could efficiently provide fresh air to the breathing zone without sacrificing the thermal environment around human. It can be used for small region air quality control such as that in the bedroom and living room where desired air quality is favored.

Journal of occupational and environmental hygiene, Jan 30, 2017

A cough jet can travel beyond the breathing zone of the source person, and thus, infectious viral... more A cough jet can travel beyond the breathing zone of the source person, and thus, infectious viral- and bacterial-laden particles can be transported from the source person to others in close proximity. To reduce the interpersonal transmission of coughed particles, the objective of this study was to analytically and experimentally investigate the performance of downward plane jets with various discharge velocities. Chamber measurements were conducted to examine the interaction between a transient cough jet (discharge velocities of 12 m/s and 16 m/s) and a steady downward plane jet (discharge velocities from 1.0 m/s to 8.5 m/s) with respect to the transport of and human exposure to coughed particles. The results show that a relatively high-speed cough can easily penetrate a downward plane jet with a discharge velocity of less than 6 m/s. A downward plane jet with a discharge velocity of 8.5 m/s can bend the cough jet to a certain extent. In this study, momentum comparison of the cough ...

Aerosol and Air Quality Research, 2015

The objective of this study is to examine the dynamic interaction of a cough jet with different i... more The objective of this study is to examine the dynamic interaction of a cough jet with different indoor airflow distributions created by linear slot diffusers considering the inter-personal transport of coughed particles. The experimental measurements were performed in a chamber, where the interaction of a cough jet and downward jets with various momentums was visualized by smoke. In this study, parameters related to the dynamic interaction of a transient cough jet and a steady downward jet have been studied: (1) distance between the cough jet source and an exposed dummy (ED); (2) the initial momentum of the downward plane jet. The experimental results indicate that the ceiling-attached horizontal jets that are widely applied in the overhead mixing ventilation systems have difficulties in deflecting the cough jet, and thereby have difficulties in reducing inter-personal transport of the coughed particles. This study found that a downward plane jet could prevent the transport of cough particles from the cough dummy to the ED. When the ED is standing 0.5 meter away from the cough dummy, the personal exposure (PE) level to coughed particles by using a downward plane jet could be two orders of magnitude lower than by using ceiling-attached horizontal jets. In addition, this study quantifies the interaction of a cough jet and a downward plane jet in their ability to reduce exposure to coughed particles. The results may be used in the process of diffuser selection and suggests that ventilation systems employing downward plane jets with high discharge velocities might be useful in public spaces to reduce inter-personal exposure to coughed particles.

Conjunctival geographic ulcer is a rare manifestation of ocular herpes simplex. Geographic ulcers... more Conjunctival geographic ulcer is a rare manifestation of ocular herpes simplex. Geographic ulcers are formed when sloughing of the epithelium occurs in the areas between the dendrite and a broad area of epithelial involvement with irregular angulated borders is formed .We hereby report a case of Primary ocular herpes with blepharitis and geographic ulceration of the conjunctiva in a 8 year old boy with no corneal lesion. To the best of our knowledge only 4 cases of conjunctival herpetic dendritic ulcerations and a single case of herpetic geographical ulcer has been reported in literature till date.

Journal of Genetics and Genomics, 2009

MYB transcription factors compose one of the largest transcription factor families in Arabidopsis... more MYB transcription factors compose one of the largest transcription factor families in Arabidopsis, which play important roles in various developmental processes as well as defense responses against environmental stresses. In this study, we report the characterization of AtMYB17 gene, a putative R2R3 type MYB gene family member in Arabidopsis. AtMYB17 was found exclusively localized in nuclear, with an activation domain at its C-terminus. AtMYB17 was highly expressed in inflorescences and siliques, especially at early flower developmental stages. The level of AtMYB17 transcripts was also found to increase after imbibition during seed germination and gradually concentrate to the shoot apex. Bioinformatics analysis identified several binding sites of LEAFY (LFY) and AGL15 in the promoter region of AtMYB17. Promoter-GUS fusion analysis showed that the LFY binding sites were important in fine-tuning regulation of the spatio-temporal expression of AtMYB17 in transgenic plants. Moreover, AtMYB17 was up-regulated in 35S::AGL15 plants. Taken together, our data suggest that LFY may be involved in the regulation of AtMYB17, possibly together with AGL15, and thereafter in early inflorescence development and seed germination.

International Journal of Heat and Fluid Flow, 2010

The behaviour of an attached plane jet at high turbulence intensity (>20%) is not completely u... more The behaviour of an attached plane jet at high turbulence intensity (>20%) is not completely understood, especially at relatively low Reynolds numbers (

HVAC&R Research, 2009

ABSTRACT Attached plane jets are widely used in room-air distribution solutions. The turbulent at... more ABSTRACT Attached plane jets are widely used in room-air distribution solutions. The turbulent attached plane jet behavior in the transition process that determines the jet behavior in the fully developed region is not completely understood, especially at relative low Reynolds numbers (<6000). This study focuses on obtaining the detailed jet mean flowfield velocity data and jet growing characteristics in the transition region. A virtual origin model was set up to predict the maximum jet velocity decay, and the experiment was carried out to validate the model. In this experiment, three Reynolds numbers—1000, 2000, and 4000—were tested at different distances from 2 to 30 slot heights downstream of the jet slot. The results are significantly different from the known theory for the third and fourth jet zones definition. The experimental data show that after six slot heights downstream distance, most of the data start to fit closely the fully developed turbulent jet velocity profiles and present self-preserving characteristics earlier than in previous studies. The maximum velocity calculated by the models showed good agreement compared with the measured data at distances of 10 to 30 slot heights.

Energy and Buildings, 2014

ABSTRACT

Energy and Buildings, 2013

ABSTRACT The turbulent airflow partner downstream jet slot is determined by the initial turbulent... more ABSTRACT The turbulent airflow partner downstream jet slot is determined by the initial turbulent jet properties, including, turbulence intensity, initial momentum flux and velocity profile. The objective of this experimental study is trying to quantitatively discover the effect of turbulence intensity of supply airflow on the jet flow distribution of an attached plane jet. Our motivation proceeding our measurements is to achieve better understanding of room air flows and the influence of inlet diffusers (turbulence). Eleven conditions were measured in two test chambers where different types of slot diffusers were used to produce an attached air jet with different turbulence intensities. All measurements are under isothermal conditions. The turbulence intensity of the jet discharging from the slot was varying approximately from 1.0% to 14.0%. The results of this study reveal that turbulence intensity of the supplied air will affect significantly the maximum velocity decay of the attached plane jet. Measurement results show that the lower turbulence intensity of supply airflow will result in slower maximum velocity decay. A relatively stable turbulence level of the airflow at local maximum velocity has been found at relatively higher Reynolds numbers of 1333 and 2667, which is about 11% 4 in all measured cases. This study reveals a clear self-similarity characteristic of the turbulent airflow under conditions of different turbulence intensities and different Reynolds number.

Energy and Buildings, 2010

Building and Environment, 2014

ABSTRACT The objective of this article is to review the scientific literature on airflow distribu... more ABSTRACT The objective of this article is to review the scientific literature on airflow distribution systems and ventilation effectiveness to identify and assess the most suitable room air distribution methods for various spaces. In this study, different ventilation systems are classified according to specific requirements and assessment procedures. This study shows that eight ventilation methods have been employed in the built environment for different purposes and tasks. The investigation shows that numerous studies have been carried out on ventilation effectiveness but few studies have been done regarding other aspects of air distribution. Amongst existing types of ventilation systems, the performance of each ventilation methods varies from one case to another due to different usages of the ventilation system in a room and the different assessment indices used. This review shows that the assessment of ventilation effectiveness or efficiency should be determined according to each task of the ventilation system, such as removal of heat, removal of pollutant, supply fresh air to the breathing zone or protecting the occupant from cross infection. The analysis results form a basic framework regarding the application of airflow distribution for the benefit of designers, architects, engineers, installers and building owners.

Building and Environment, 2010

We study the turbulent air flow behaviours of the attached plane jet discharged from an active ch... more We study the turbulent air flow behaviours of the attached plane jet discharged from an active chilled beam in a room using Particle Image Velocimetry (PIV). PIV is an innovative technology to study indoor air flow which began in the eighties of the last century for the measurement of whole air flow fields in fractions of a second. Here an experimental PIV system was built to reveal the structure of a turbulent attached plane jet in the entrainment process of the ambient air downstream from the jet slot. For the particle seeding in the PIV experiments, a few different particles were tested with the attached jet PIV application in a room. The results presented in this paper show the clear structure of the turbulent attached plane jet in the entrainment process after issuing from the chilled beam slot. The PIV visualisation results proved that the jet will attach to the ceiling and become fully turbulent a short distance downstream from the slot. The jet velocity vector fields show that the volume flow rate of the attached plane jet increases because of the large vortex mixing mechanism in the outer region of the jet. In three measurement cases, the air jet grows faster at a Reynolds number of 960 than at Reynolds numbers of 1320 and 1680. The calculated spreading angles in the cases with lower Reynolds numbers have similar values compared with the visualisation results.