Hwataik Han

Double diffusive natural convection in a vertical rectangular enclosure. I, Experimental study

Double diffusive natural convection flows in a two-dimensional rectangular enclosure are investigated using an electrochemical technique with the vertical electrodes maintained at different tem- peratures. Schlieren flow visualization photographs show interesting timewise evolution of multicell flow structures in an enclosure for both aiding and opposing thermal and solutal buoyant forces. Details of the multicell flow characteristics including the temperature and concentration profiles as well as the overall heat and mass transfer characteristics in the cavity are presented.

Double diffusive natural convection in a vertical rectangular enclosure—II. Numerical study

Abstract A numerical study is performed on double diffusive natural convection fluid flow in a vertical rectangular cavity of aspect ratio 4 when the temperature and concentration gradients are imposed in the horizontal direction. A finite difference algorithm is adopted to solve the non-linear momentum equations coupled with the energy and concentration equations. Double diffusive multicell flow structures observed in experiments by the authors are simulated successfully. Different flow structure regimes are obtained as a function of the Grashof number ratio for aiding and opposing buoyancy conditions.

Automated Counting of Airborne Asbestos Fibers by a High-Throughput Microscopy (HTM) Method

Inhalation of airborne asbestos causes serious health problems such as lung cancer and malignant mesothelioma. The phase-contrast microscopy (PCM) method has been widely used for estimating airborne asbestos concentrations because it does not require complicated processes or high-priced equipment. However, the PCM method is time-consuming and laborious as it is manually performed off-site by an expert. We have developed a high-throughput microscopy (HTM) method that can detect fibers distinguishable from other spherical particles in a sample slide by image processing both automatically and quantitatively. A set of parameters for processing and analysis of asbestos fiber images was adjusted for standard asbestos samples with known concentrations. We analyzed sample slides containing airborne asbestos fibers collected at 11 different workplaces following PCM and HTM methods, and found a reasonably good agreement in the asbestos concentration. Image acquisition synchronized with the movement of the robotic sample stages followed by an automated batch processing of a stack of sample images enabled us to count asbestos fibers with greatly reduced time and labors. HTM should be a potential alternative to conventional PCM, moving a step closer to realization of on-site monitoring of asbestos fibers in air.

Selective detection and automated counting of fluorescently-labeled chrysotile asbestos using a dual-mode high-throughput microscopy (DM-HTM) method.

Phase contrast microscopy (PCM) is a widely used analytical method for airborne asbestos, but it is unable to distinguish asbestos from non-asbestos fibers and requires time-consuming and laborious manual counting of fibers. Previously, we developed a high-throughput microscopy (HTM) method that could greatly reduce human intervention and analysis time through automated image acquisition and counting of fibers. In this study, we designed a dual-mode HTM (DM-HTM) device for the combined reflection and fluorescence imaging of asbestos, and automated a series of built-in image processing commands of ImageJ software to test its capabilities. We used DksA, a chrysotile-adhesive protein, for selective detection of chrysotile fibers in the mixed dust-free suspension of crysotile and amosite prepared in the laboratory. We demonstrate that fluorescently-stained chrysotile and total fibers can be identified and enumerated automatically in a high-throughput manner by the DM-HTM system. Combined with more advanced software that can correctly identify overlapping and branching fibers and distinguish between fibers and elongated dust particles, the DM-HTM method should enable fully automated counting of airborne asbestos.

Effect of platform screen doors on the indoor air environment of an underground subway station

Contaminant concentrations in a subway station in Seoul, Korea before (March 2008) and after (March 2009) the installation of platform screen doors (PSDs) were measured to investigate the effect of the PSD system on the subway indoor environment. PM10, CO2 and NO2 concentrations were measured at the platform, concourse and tunnel areas, using an indoor air quality tele-monitoring system (IAQ-TMS) operated by the Korean Ministry of Environment. Spatial correlations of contaminant concentrations at different locations were analysed, to investigate the effect of PSD installation on the movement of contaminants through air passages between zones. The results indicate that PM10 concentrations at the platform were reduced significantly after PSD installation and were within the guideline limit. The R2 value for the platform–tunnel correlation was reduced, indicating that in the absence of PSD, a significant amount of particulate matter was introduced to the platform from the tunnel. Conversely, the CO2 level in the platform was increased slightly after PSD installation, exhibiting a strong correlation with the number of passengers in the station. NO2 was predominantly introduced to the platform from the outdoor environment, on the basis of the source characteristics and their movement through air passages. This paper provides the data to develop a pollution management guide to control air quality contaminants in subway stations.

Shear stress tolerance of Streptococcus mutans aggregates determined by microfluidic funnel device (μFFD)

Dental caries are initiated by the attachment of Streptococcus mutans aggregates to the surface of teeth. Bacterial adhesion to the interproximal space, the space between adjacent teeth, has not been investigated due to the lack of devices that mimic the space. Herein, we describe a method for determining the effect of shear stress and sucrose on the attachment of S. mutans aggregates to the interproximal space using microfluidic funnel device (μFFD). Using μFFD, the shear stress tolerance of sucrose-independent and sucrose-dependent S. mutans aggregates (larger than 50 μm in diameter) trapped in the funnel was tested against various flow rates of saliva solution (5 to 50 μl/min). Sucrose-independent aggregates were completely removed from the funnel walls at a low flow rate (10 μl/min) within 7 min., while sucrose-dependent aggregates were removed from the walls only at higher flow rates (25 and 50 μl/min) within several minutes. These results suggest that sucrose-dependent aggregates are more tolerant of shear stress than sucrose-independent aggregates, and are more likely to remain in the region with the smallest shear stress in the teeth.

EFFECT OF CONDENSATION ON THE EFFICIENCY OF HEAT RECOVERY VENTILATORS FOR BROILER HOUSES

This study experimentally investigates the effect of internal condensation on the performance of a heat recovery ventilator. Experiments were performed using a plate-type sensible heat exchanger element that was designed for very humid and dusty environments such as chicken broiler houses. The results of these experiments show that the temperature efficiency considering condensation is always greater than that without considering latent heat. As outdoor temperature decreases or indoor relative humidity increases, temperature efficiency increases owing to an increase in the rate of condensation. The present polypropylene-based sensible heat exchanger element could be a solution for harsh environments because it can discharge condensate water by gravity and is resistant to moisture and other toxic gases.

Recent Progress in Air-Conditioning and Refrigeration Research : A Review of Papers Published in the Korean Journal of Air-Conditioning and Refrigeration Engineering in 2010

This article reviews the papers published in the Korean Journal of Air-Conditioning and Refrigerating Engineering during 2010. It is intended to understand the status of current research in the areas of heating, cooling, ventilation, sanitation, and indoor environments of buildings and plant facilities. Conclusions are as follows. (1) Research trends of thermal and fluid engineering have been surveyed as groups of general thermal and fluid flow, fluid machinery, and new and renewable energy. Various topics were presented in the field of general thermal and fluid flow. Research issues mainly focused on the thermal reliability of axial fan and compressor in the field of fluid machinery. Studies on the design of ground source heat pump systems and solar chemical reactors were executed in the field of new and renewable energy. (2) Research works on heat transfer area have been reviewed in the categories of heat transfer characteristics and industrial heat exchangers. Researches on heat transfer characteristics included heat transfer in thermoelectric cooling/power generation systems, combined heat and power systems, carbon nano fluid with PVP, channel filled with metal foam and smoke ventilation in a rescue station of a railroad tunnel. Also the studies on flow boiling of R123/oil mixture in a plain tube bundle and R410A charge amount in an air cooled mini-channel condenser were reported. In the area of industrial heat exchangers, researches on plate heat exchanger, shell and tube heat exchanger, enthalpy exchanger, micro channel PCHE were performed. (2) Research works on heat transfer area have been reviewed in the categories of heat transfer characteristics and industrial heat exchangers. Researches on heat transfer characteristics included heat transfer in thermoelectric cooling/power generation systems, combined heat and power systems, carbon nano fluid with PVP, channel filled with metal foam and smoke ventilation in a rescue station of a railroad tunnel. Also the studies on flow boiling of R123/oil mixture in a plain tube bundle and R410A charge amount in an air cooled mini-channel condenser were reported. In the area of industrial heat exchangers, researches on plate heat exchanger, shell and tube heat exchanger, enthalpy exchanger, micro channel PCHE were performed. (3) Refrigeration systems with alternative refrigerants such as hydrocarbons, mixed refrigerants, and CO2 were studied. Performance improvement of refrigeration systems are tried applying various ideas of refrigerant subcooling, dual evaporator with hot gas bypass control and feedforward control. The hybrid solar systems combining the solar collection devices with absorption chillers or compression heat pumps are simulated and studied experimentally as well to improve the understanding and the feasibility for actual applications. (4) Research trend in the field of mechanical building facilities has been found to be mainly focused on field applications rather than performance improvements. Various studies on heating and cooling systems, HVAC facilities, indoor air environments and energy resources were carried to improve the maintenance and management of building service equipments. In the field of heating and cooling systems, papers on a transformer cooling system, a combined heat and power, a slab thermal storage and a heat pump were reported. In the field of HVAC facilities, papers on a cooling load, an ondol and a drying were presented. Also, studies on HVAC systems using unutilized indoor air environments and energy resources such as air curtains, bioviolence, cleanrooms, ventilation, district heating, landfill gas were studied. (5) In the field of architectural environment and energy, studies of various purposes were conducted such as indoor environment, building energy, renewable energy and green building. In particular, renewable energy and building energy-related researches have mainly been studied reflecting the global interest. In addition, many researches which related the domestic green building certification of school building were performed to improve the indoor environment of school.

Measuring OutdoorAir Intake Rates Using Electronic Velocity Sensors at Louvers and Downstream of Airflow Straighteners

Practical and accurate technologies are needed for continuously measuring and controlling outdoor air (OA) intake rates in commercial building heating, ventilating, and air conditioning (HVAC) systems. This project evaluated two new measurement approaches. Laboratory experiments determined that OA flow rates were measurable with errors generally less than 10percent using electronic air velocity probes installed between OA intake louver blades or at the outlet face of louvers. High accuracy was maintained with OA flow rates as low as 15percent of the maximum for the louvers. Thus, with this measurement approach HVAC systems do not need separate OA intakes for minimum OA supply. System calibration parameters are required for each unique combination of louver type and velocity sensor location but calibrations are not necessary for each system installation. The research also determined that the accuracy of measuring OA flow rates with velocity probes located in the duct downstream of the intake louver was not improved by installing honeycomb airflow straighteners upstream of the probes. Errors varied with type of upstream louver, were as high as 100percent, and were often greater than 25percent. In conclusion, use of electronic air velocity probes between the blades of OA intake louvers or at the outlet face of louvers is a highly promising means of accurately measuring rates of OA flow into HVAC systems. The use of electronic velocity probes downstream of airflow straighteners is less promising, at least with the relatively small OA HVAC inlet systems employed in this research.

Occupancy Estimation in a Subway Station Using Bayesian Simulation Based on Carbon Dioxide and Particle Concentrations

Demand controlled ventilation is an energy saving approach used to regulate outdoor air supply to a space according to its demand. The occupancy within a space is a useful parameter reflecting the ventilation requirement. The objective of the present study is to develop a method for estimating the occupancy in a subway station based on CO2 and PM10 concentration data using the Indoor Air Quality Tele-Monitoring System located in the station. A feasibility study has been conducted to investigate the monitoring system can provide occupancy information with satisfactory accuracy for ventilation control purposes. Bayesian inference is used in estimating the occupancy at a platform based on unknown information such as ventilation rate and CO2 generation rate per person using various assumptions. The posterior distribution of the occupancy was simulated using the Markov Chain Monte Carlo sampling method. The results indicate that the dynamic model reduces the effect of the time delay and improves the uncertainty bands in the occupancy inference more than the static model. The inferred occupancy results are within the uncertainty ranges of the actual occupancy in the station. Additional use of the PM10 concentration data improves the accuracy of the inference further.