Young-Chull Ahn

Investigation of pore formation for polystyrene electrospun fiber: Effect of relative humidity

Electrospinning method uses electrical force to produce a polymer nanofiber from a polymer solution. The surface morphology and the pore formation of e-spun fiber have been studied by many variables that are involved in different polymer concentrations and solvent mixing ratios. Another major factor affecting fiber morphology and size distribution is the relative humidity. The interaction between the relative humidity and the solvent evaporation affects the distribution of electric charge on the surface of the e-spun fiber. The higher the electric density, the thinner the fiber that can be produced in low humidity conditions. The relative humidity and solvent evaporation can create pores on the fiber surface. The pores can be formed under the condition of 30% relative humidity using 100% of THF solvent. The boundary of the pores has expanded and becomes formless due to the agglomeration of each pore, which can decrease the evaporating capacity.

The morphology of electrospun polystyrene fibers

Electrospinning is a process of electrostatic fiber formation which uses electrical forces to produce polymer nanofibers from polymer solution. The electrospinning system consists of a syringe feeder system, a collector system, and a high power supplier. The important parameters in the morphology of electrospun polystyrene fibers are concentration, applied voltage, and solvent properties. Higher concentrations of the polymer solution form thicker fibers and fewer beads. When the concentration is 7 wt%, electrospun fibers have an average diameter of 340 nm, but as the concentration of PS increases to 17 wt%, the fiber diameter gradually thickens to 3,610 nm. The fiber morphology under different solvent mixture ratios and solvent mixtures has also been studied.

An Experimental Study of the Air-side Particulate Fouling in Fin-and-Tube Heat Exchangers of Air Conditioners

An experimental study was conducted to investigate the chronological performance variation such as pressure drop across a heat exchanger and cooling capacity due to the air-side particulate fouling of fin-and-tube heat exchangers for air conditioner evaporators used. Thirty samples of air conditioners used in the field such as inns, restaurants, and offices are collected in chronological order of use. This study was intended to provide factual long-term fouling data under actual operating conditions. It was found that the important parameters to influence the fouling of heat exchangers are the concentration and size of indoor pollutants, the filter efficiency, the hydrophilicity of fin surfaces, fin spacing, and the structure of fins. The pressure drop of heat exchangers increases from year to year due to the deposition of indoor pollutants larger than 1 Μm in size and increases up to 44% in the samples used for 7 years. Also, the air-side particulate fouling degrades the cooling capacity by 10-15% in the samples used for 7 years.

Characteristics of Air-Side Particulate Fouling Materials in Finned-Tube Heat Exchangers of Air Conditioners

ABSTRACT Heat exchangers are used widely in residential, commercial, and industrial HVAC applications. Air-side particulate fouling in the heat exchangers of HVAC applications degrades the performance of cooling capacity, pressure drop across a heat exchanger, and indoor air quality. Indoor and outdoor air contaminants foul heat exchangers. The purpose of this study is to investigate the characteristics of the air-side particulate fouling materials in finned-tube heat exchangers of air conditioners. Air conditioners being used in the field such as inns, restaurants, and offices are collected in chronological order of use. The fouling materials attached on the evaporator heat exchangers consist of particulates and fibers. The particulates mainly originate from indoor dusts and the fibers are separated from clothes, bedclothes, papers, fur of pets, and so on. Typical fouling materials on the heat exchangers include fibers and dusts ranging from 6.6 to 20.9 μm in aerodynamic mean diameter.

Measurement of Indoor Air Quality for Ventilation with the Existence of Occupants in Schools

This paper evaluates the performance of ventilation for the removal of indoor pollutants as a function of ventilation rate and the number of occupants in a test room and school classroom. An experimental apparatus consists of a test room, a tracer gas supply system, a gas detector, and a fan for ventilation air supply with a controller. The ventilation performance is evaluated in a step-down method based on ASTM Standard E741-83 using CO2 gas as a tracer gas in the test room of 35 m3. For the ventilation air flow rate of 1.0 ACH, a recommended ventilation flow rate of Korea school standard for acceptable indoor air quality in the case of one person, CO2 gas concentration decreases up to 55% within 50 minutes without occupancy and increases up to 75% in the case of one occupant. Also indoor air quality at the school classroom is investigated experimentally.

An experimental study on the performance of a condensing tumbler dryer with an air-to-air heat exchanger

The performance of energy consumption in the closed-loop tumbler dryer with a condenser for clothes drying is evaluated as a function of the heater capacity, the drying air flow rate inside the dryer, and the cooling air flow rate. The clothes dryer in laundries used in this study consists of a tumbling drum, condenser for condensing the humid and hot air flowing out the rotating drums, and electric heater for heating the circulating drying air. Tests were performed at the heating capacity of 1.9 kW to 2.7 kW, the drying air flow rate of 60 m3/h to 140 m3/h, and the cooling air flow rate of 100 m3/h to 240 m3/h. The total energy consumption, the drying time, and the condensate water rate were also investigated. Parametric results showed that a larger heater power resulted in shorter drying time. With increasing heater power, the air temperature and the condensate rate increased due to the higher humidity ratio in the air. The drying air flow rate and the cooling air flow rate did not have a significant effect on drying performance.

Removal characteristics and distribution of indoor tobacco smoke particles using a room air cleaner

The objective of this study is to analyze the removal characteristics and distribution of indoor air pollutants by a room air cleaner. A pollutant removal effect according to room volume and measurement point was evaluated in an indoor room. A series of filtration efficiency tests were performed on only the electrostatic precipitator of the room air cleaner. The measurements of filter efficiency and pressure drop across the electrostatic precipitator were made using an ASHRAE 52.1-1992 filter test system and an opacity meter to measure the particle concentration upstream and downstream of the test filter. Also the performance of the air cleaner in the room was evaluated by examining tobacco smoke particle concentration. The size distribution of the tobacco smoke particles was 1.27 μm in mass median diameter and a geometric standard deviation of 1.313 μm. The efficiency of the electrostatic filter was measured as 78.6% with dust particles of 1.96 μm in mass median diameter and 1.5m/s face velocity. The tobacco smoke particle concentration as a function of time decayed exponentially. The contaminant removal effect was increased when increasing the effective clean air exchange rate (ηQ/V), which is 0.0780 min−1 for 51 m3 room and 0.0235 min−1 for 149 m3 room. This study clearly shows that a room air cleaner with an electrostatic precipitator is effective in removing tobacco smoke particles. The removal characteristics and distribution of indoor air pollutants in other rooms is predicted based on empirical modeling.

Physical, Chemical and Electrical Analysis of Dust Generated from Cement Plants for Dust Removal with an Electrostatic Precipitator

The physical, chemical and electrical characteristics of cement dust generated from a cement plant have been investigated by using a dust analyzer and a high voltage conductivity cell based on JIS B 9915. Major constituents of raw material cement dust generated from the first grinding process are CaO (41.77%), SiO2 (11.72%), Al2O3 (3.45%), and Fe2O3 (1.47%), while the cement clinker dust generated from the second grinding process consists of mainly CaO (48.09-65.50%), SiO2 (14.02-21.56%), Al2O3 (2.86-3.76%), and Fe2O3 (1.77-2.66%). Size distribution of the raw material cement dust is bi-modal in shape and the mass median diameter (MMD) is 3.68 μm, whereas the cement clinker dust also displays bi-modal distribution and the MMD of the cement clinker dust is in the range of 7.89-58.78 μm. The resistivity of raw material cement dust is so high as 1014 ohm·cm at 300 °C, that cement dust would not precipitate well by the electrostatic precipitator.

A Study on the Dew Condensation According to the Operational Conditions of a Heat-Recovery Ventilator

Heat-recovery ventilators are being adopted in most newly built apartment houses for energy reduction and indoor environment improvement. In winter, however, the dew condensation resulting from the difference between the indoor and outdoor temperatures may reduce the ventilator`s performance and threaten the health of indoor residents. This study analyzes the occurrence of dew condensation according to the ventilator`s operational conditions and the changes of temperature and products. The experimental results show that condensations is formed at and 60%R.H, which is an unfavorable climatic condition, and when the damper is not closed tightly. Therefore it is important to ensure damper performance to prevent back flow.

A Study on The Performance of a Heat Recovery Ventilator According to the Properties of Spacers

ABSTRACT:The importance of ventilation system is being emphasized by interest of indoor air quality. Especially, heat recovery ventilation system has attracted attention as most effective ventilation plan. Because it can reduce hazardous construction materials, indoor air pollutions, and also can reduce air conditioning energy cost. In heat recovery ventilator, the element core is the most important part. The element core is composed of liner and spacer. And liner and spacer are stacked alternately. On the Liner, heat and humidity transfer are made between supply and exhaust air. And spacer plays a role as a tunnel of exhaust and supply. In this study, we investigated and analyzed the efficiency of a heat recovery ventilator, when the spacer’s properties are changed. As a result, difference spacer’s properties affect an efficiency of heat recovery ventilator.Keywords:Heat recovery ventilator(전열교환기), Element core(전열교환 소자), Liner(라이너), Spacer(스페이서) †Corresponding author Tel.: +82-51-510-2492; fax: +82-51-514-2230 E-mail address: ycahn@pusan.ac.kr