Kwang-Chul Noh

The Effect of Ventilation Rate and Filter Performance on Indoor Particle Concentration and Fan Power Consumption in a Residential Housing Unit

This paper reports a study of the effect of ventilation rate and filters performance on indoor particle concentration and fan power consumption in a residential housing unit with a mechanical ventilation system. Through an adapted mass-balance model, indoor particle concentrations were calculated for various ventilation rates, filter performances and room sizes. Additionally, the influence of air-exchange effectiveness and cross-contamination around the exterior air vent on the indoor particle concentration was considered. Recirculation of indoor air was not considered. From the results, filters for which the performance was lower than MERV07 were found to be insufficient for reducing indoor particle concentrations below the levels obtained under no ventilation. A higher ventilation rate was needed for the given amount of indoor particle sources for a smaller size residential housing unit in comparison to the larger units. The minimum ventilation rate was less sensitive to variations in the air-exchange effectiveness inside the residential housing unit and the cross-contamination index around the exterior air vents. To satisfy the ventilation requirement for gaseous pollutants and keep the particle concentrations below those under no ventilation, a filter with a performance that would exceed MERV11 should be used when the size of the residential housing unit is in the range of 150—300 m3.

Microscopic energy conversion process in the ion drift region of electrohydrodynamic flow

We theoretically investigated the momentum transfer and energy conversion process of ion-neutral and ensuing neutral-neutral collisions in the ion drift region of electrohydrodynamic flow. Our results are presented in explicit equations with physical interpretations of the phenomena. The unit conversion process was estimated to sustain for 1.0 nano-second in a very tiny 0.5-μm-sized volume in the air. Also, the continuum-based equation formulations are presented according to the microscopic energy conversion phenomena. Numerical simulations reflecting those formulations are performed to verify the theoretical results and experimentally supported by an air corona discharge.

Electric propulsion using an alternating positive/negative corona discharge configuration composed of wire emitters and wire collector arrays in air

We present a study on a corona discharge configuration exclusively composed of thin wires that provides maximal thrust performance and a compact unit staging method. The ion and air flow behaviors were experimentally and numerically investigated. The basic characteristics derived from the experiments are reported for three discharge configurations (positive, negative, and positive/negative alternation). The proposed alternating positive/negative configuration enhanced the thrust (5.4 N/m2 of maximum thrust to air flow area ratio) through the ability to achieve compact staging, compared to a previous study. In addition, two useful equations as criteria in the evaluation of the thrust performance were derived.

Prediction and Evaluation of Cleanliness Levels Inside a Mini-Environment by Measuring Mean Air-Age and Effective Flow Rate

Numerical and experimental studies on the evaluation and prediction of the cleanliness level in a mini-environment system were carried out. The new direct method for estimating the cleanliness of a mini-environment, which involves determining the mean air-age and effective flow rate, is developed and its performance compared with that of the previous performance index based on airflow pattern characteristics. The result shows that the airflow pattern analysis is limited in terms of estimating the real performance of the mini-environment. This is because airflow pattern characteristics, like eddy size or turbulence intensity, can qualitatively show the path of contaminants and the degree of risk, but cannot predict the quantitative variation in the contamination level according to the variation in factors such as the location of the air supply and the exhaust and ventilation rate. In contrast, the mean air-age is capable of predicting quantitative variations in contaminant concentration as well as the effect of the turbulence intensity. Also, computational fluid dynamic (CFD) calculations and experiments show that mean air-age can help predict the relative cleanliness level variation at points in the modified mini-environment when the layout of the mini-environment is changed. It is concluded that mean air-age is a more exact and effective performance index than the previous airflow pattern characteristics like the turbulence intensity or eddy size.

Calculation of Uncertainty in Measuring Heat Release Rate in Room Corner Test

In fire test, accurate heat release rate measurements provide important information to define the fire safety characteristics of products. The calculation of heat release rate depends on the errors of measuring parameters in experimental set-up. In this study, the uncertainty factors of heat release rate in the room corner test facility, which is installed at Korea Railroad Research Institute, were analyzed. Through the fire testings for the KTX interior materials, the uncertainties of heat release rate were calculated. Results showed that uncertainty was high in the initial stage of fire test and gradually decreased with the growth of fire. The oxygen concentration was a major factor contributing to the combined relative standard uncertainty.

Control of Suspended Dust in Various Ventilation Systems of Cement Packaging Process

We performed the experimental study on the control of suspended dust in a cement packaging process for various ventilation systems. To effectively remove the dust generated in the cement packaging process, three different kinds of ventilation system, such as local exhaust ventilation, electrostatic scrubber, and local air supply system, were adopted. Dust concentrations in the packaging process were measured with the variation of the airflow rate of the ventilation systems and then their ventilation performance were evaluated. From the results, we knew that the ventilation performance was the best when the local exhaust ventilation and the electrostatic scrubber were simultaneously operated in the packaging process. In the electrostatic scrubber system, the effect of the airflow rate on the indoor dust removal efficiency was negligible so hat he system ust be operated at for saving power consumption.

Method of Particle Contamination Control for Yield Enhancement in the Cleanroom

The practical studies on the method of particle contamination control for yield enhancement in the cleanroom were carried out. The method of the contamination control was proposed, which are composed of data collection, data analysis, improvement action, verification, and implement control. The partition check method and the composition analysis for data collection and data analysis were respectively used in the main board and the cellular phone module production lines. And these methods were evaluated by the variation of yield loss between before and after improvement action. In case that the partition check method was applied, the critical process step was selected and yield loss reduction through improvement actions was observed. While in case that the composition analysis was applied, the critical sources were selected and yield loss reduction through improvement actions was also investigated. From these results, it is concluded that the partition check and the composition analysis are effective solutions for particle contamination control in the cleanroom production lines.

Study on Thermal Comfort and Indoor Air Quality in the Classroom with System Air-conditioner and Ventilation System for Cooling Loads

The experimental and the numerical study was performed on the comparison of thermal comfort(TC) and indoor air quality(IAQ) in the lecture room for cooling loads when the operating conditions are changed. PMV value and concentration of the lecture room were measured and compared with the numerical results. The numerical results showed a good agreement with the experimental one and then the numerical tool was used to analyze thermal comfort and IAQ for a couple of operating conditions. As a result it was found that the increment of the discharge angle of system air-conditioner makes TC uniformity worse, but rarely affects IAQ. Also TC and IAQ were hardly affected by the variation of the discharge airflow. Finally it turned out that TC is merely affected by the increment of the ventilation airflow, but the average concentration can be satisfied with Japanese IAQ standards of classrooms when the ventilation airflow is more than in this study.

Comparison of Thermal Comfort Performance Indices for Cooling Loads in the Lecture Room - An Correlation of PMV Bnd EDT -

We performed the experimental and the numerical study on the comparison of thermal comfort performance indices for cooling loads in the lecture room for 4 cases: Fan coil unit(FCU) or 4-way cassette air-conditioner is respectively operated with the ventilation system or without. We measured the velocity, the temperature distribution and predicted mean vote(PMV) value in the lecture room for 4 different air-conditioning methods. Effective draft temperature(EDT) and PMV were investigated to analyze the characteristics of two thermal comfort indices in the lecture room and to compare their values each other. From the results we knew that there is the similarity between PMV values and EDTs when the room is air-conditioned for cooling loads. It turned out that definition of the control temperature is very important when the EDT is calculated. Finally EDT should not be used to predict the accurate thermal comfort in case that the temperature and humidity are suddenly varied and the zone affected by the solar and inner wall radiation.

A Study on the 3-D Airflow and Dynamic Cross Contamination in the Photolithography Process Cleanroom

We performed the numerical study on the characteristics of the 3-D airflow and dynamic cross contamination in the photolithography process cleanroom. The nonunifurmity, the deflection angle and the global cross contamination were used for analyzing the characteristics and performances of cleanroom. From the numerical results, we knew that the airflow characteristics of the cleanrooms are largely affected by the porosity of panel and the adjustment of dampers and the global cross contamination varies with the location of source and the passage of time through the concentration ratio.