Jae-Keun Lee

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.

Triboelectrostatic separation of pvc materials from mixed plastics for waste plastic recycling

This study covers the triboelectrostatic separation of Polyvinylchloride (PVC) materials from mixed plastics such as polyethylene terephthalate (PET), polyethylene (PE), polypropylene (PP), and polystyrene (PS). The PVC material generates hazardous hydrogen chloride gas resulting from the combustion in the incinerators. The laboratory scale triboelectrostatic separation system consists of a fluidized-bed tribocharger, a separation chamber, a collection chamber and a controller. Negative and positive surface charges can be imparted to the PVC and PET particles, respectively, due to the difference of triboelectric charging series between the particles in the fluidized-bed tribocharger. They can be separated by passing through an external electric field. A highly concentrated PVC (91.9%) can be recovered with a yield of about 96.1% from the mixture of PVC and PET materials in a single stage of processing. For the removal of PVC from the two-component mixed plastics such as PVC/PET, PVC/PP, PVC/PE or PVC/PS, separation results show the recovery of 96–99% with the pure extract content in excess of 90%. The triboelectrostatic separation system using the fluidized-bed tribocharger shows the potential to be an effective method for removing PVC from mixed plastics for waste plastic recycling.

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.

Performance Evaluation of Electrostatically Augmented Air Filters Coupled with a Corona Precharger

An experimental study of electrostatically augmented air (EAA) filters coupled with a corona precharger has been conducted using Arizona road dusts and tobacco smoke. The measurements of filter efficiency and pressure drop across the EAA filter have been 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. The two-stage EAA filter unit consists of the positive corona precharger upstream of a filter, to precharge particles with the electrical strength of 4.7 kV/cm, and an electrified filter collector, which has folded media with meshy metal separators, in the upstream and downstream side gaps. DC voltage of +1,000 V (1.4 kV/cm) is applied between the upstream and downstream separators to produce an electric field between the separators and media as well as across the media in a polarity so that most of the precharged particulates are collected on the upstream filter collector. A conventional filter was measured and had 70.0% efficiency with dusts of 1.96 w m in mass median diameter and 2.5 m/s face velocity, while the EAA filter had 92.9% efficiency. An electrical effect on the EAA filter was evaluated to both improve the filter efficiency and reduce the pressure drop across the filter. Also, the performance evaluation of the EAA filter using an air handling chamber system in occupied space was investigated with tobacco smoke particles.

Performance evaluation of electrodewatering system for sewage sludges

A laboratory-scale electrodewatering system, incorporating an electric field as an additional driving force to conventional pressure dewatering, has been developed to decrease the water content of sludges generated in wastewater treatment. Consisting of a piston-type filter press, a power supply and a data acquisition system, the electrodewatering system’s performance was evaluated as a function of applied pressure, applied voltage, sludge type and filtration time. Experiments were carried out using sewage sludges with the electric field up to 120 V/cm and pressure ranging from 98.1 to 392.4 kPa. Electrodewatering involving a combination of electric field and pressure enhances both the dewatering rate and final dewatered volume. The final water content of sewage sludges in the electrodewatering system can be reduced to 62 wt%, as compared to 78 wt% achieved with the pressure filtration alone. The electrodewatering system shows the potential to be an effective method for reducing the water content in sludges.

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.

Effect of Microbubbles and Particle Size on the Particle Collection in the Column Flotation

Particle-bubble collection characteristics from microbubble behavior in column flotation have been studied theoretically and experimentally. A flotation model taking into account particle collection has been developed by particle-bubble collision followed by the particle sliding over the bubble during which attachment may occur. Bubble size and bubble swarm velocity were measured as a function of frother dosage and superficial gas velocity to estimate the collision and collection efficiency. Separation tests were carried out to compare with theoretical particle recovery. Fly ash particles in the size range of <38, 38-75, 75-125, >125 mm were used as separation test particles. Theoretical collision and collection efficiencies were estimated by experimental data on the bubble behavior such as bubble size, gas holdup and bubble swarm velocity. Collection efficiency improved with an increase of the bubble size and particle size but decreased in the particle size up to 52 mm. Also, flotation rate constants were estimated to predict the optimum separation condition. From the theoretical results on the flotation rate constant, optimum separation condition was estimated as bubble size of 0.3-0.4 mm and superficial gas velocity of 1.5-2.0 cm/s. A decrease of bubble size improved the collection efficiency but did not improve particle recovery.

Round-robin test on thermal conductivity measurement of ZnO nanofluids and comparison of experimental results with theoretical bounds

Ethylene glycol (EG)-based zinc oxide (ZnO) nanofluids containing no surfactant have been manufactured by one-step pulsed wire evaporation (PWE) method. Round-robin tests on thermal conductivity measurements of three samples of EG-based ZnO nanofluids have been conducted by five participating labs, four using accurate measurement apparatuses developed in house and one using a commercial device. The results have been compared with several theoretical bounds on the effective thermal conductivity of heterogeneous systems. This study convincingly demonstrates that the large enhancements in the thermal conductivities of EG-based ZnO nanofluids tested are beyond the lower and upper bounds calculated using the models of the Maxwell and Nan et al. with and without the interfacial thermal resistance.

Performance evaluation of electrocoagulation and electrodewatering system for reduction of water content in sewage sludge

Electrocoagulation is applied to sewage sludge as a pretreatment process of an electrodewatering system to reduce the water content of sludge generated in wastewater treatment. The electrodewatering system, by incorporating an electric field as an additional driving force to the conventional pressure dewatering, has been evaluated as a function of an electrode material, applied voltage and filtration time. Experiments were carried out using sewage sludge with a pressure up to 392.4 kPa and applied electrical field ranging up to 120 V/cm. Mass median diameter of the sewage sludge by the effect of electrocoagulation increases from 34.7 µm to the 41.3 µm. The final water content of sewage sludge in the combination of both electrocoagulation and electrodewatering system can be reduced to 55 wt%, as compared to 78 wt% achieved with pressure dewatering alone. The combination of electrocoagulation and electrodewatering system shows a potential to be an effective method for reducing the water content in sludge.

Effect of bi-modal aerosol mass loading on the pressure drop for gas cleaning industrial filters

The typical size distribution of emission particulates is bi-modal in shape with particles in the fine mode (< 2.0 w m) and the coarse mode. An experimental study of pressure drop across industrial gas cleaning filters has been conducted using a particle mixture of fine alumina and coarse Arizona dusts with a rotating aerosol disperser to generate the bi-modal test aerosol. Pressure drop increased linearly with increasing mass loading. The pressure drop was found to be strongly dependent upon the mass ratio of fine to coarse particles. The measured specific resistances of HEPA filters at a given face velocity of 5 cm/s were 1.18 2 10 6 , 5.89 2 10 5 , 4.67 2 10 5 , 2.65 2 10 5 , and 1.18 2 10 5 s -1 for the mass ratio of fine to coarse particles of fine only, 50%:50%, 25%:75%, 10%:90%, and coarse particles only, respectively. The pressure drop across the loaded filter increased with increasing face velocity. The larger the mass ratio of fine to coarse particles and the higher the face velocity are, the faster pressure drop rises. The fine particles and the greater inertia of the particle moving fast would cause a denser cake formation on the filter surface, resulting in a greater specific resistance to the gas flow.