Browsing by Author "Tien, Chi-Yu"

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Design and Testing of the NCTU Micro-Orifice Cascade Impactor (NMCI) for the Measurement of Nanoparticle Size Distributions
(2015-01-01)
Chien, Chih-Liang
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Tien, Chi-Yu
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Liu, Chun-Nan
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Ye, Huajun
;
Huang, Wei
The NCTU micro-orifice cascade impactor (NMCI) was redesigned and tested to enable the measurement and adjustment of the jet-to-plate distance (S) of the impactors by using a micrometer. Each stage of the NMCI contains an impaction plate and a nozzle plate which are separated. The bottom casing for impaction plate assembly and the nozzle plate holder of each stage are separated. Calibration results show that the cutoff aerodynamic diameter (d(pa50)) of the three lower stages (d(pa50) = 180, 100, and 56 nm) are close to the nominal values given in Marple et al. (1991). In addition, the S/W (W: nozzle diameter) effects on the d(pa50) for the three lower stages were investigated and an empirical equation was developed to facilitate the prediction of d(pa50) when the nozzle diameters may change slightly from one batch to another. The relationship between the nozzle diameter and pressure drop of the micro-orifice impactors at the fixed operational flow rate of 30 L/min was also established so that the nozzle diameters can be predicted from the pressure drop measurement. An empirical equation was proposed to express the correlation between the dimensionless cutoff size and the S/W ratio when considering isentropic flow to facilitate the design of microorifice impactors for S/W > 4. It is expected that the present NMCI could improve the accuracy of size classification of submicron particles below 180 nm, especially for nanoparticles.
Development of a Novel Shallow Liquid Interface Exposure System for MWCNT Toxicity Assessment
(2019-10-01)
Tien, Chi-Yu
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Li, Jui-Ping
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Han, Ding
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Li, Ziyi
;
Fu, Pin-Kuei
Increasing applications of multiwalled carbon nanotubes (MWCNT) lead to significant occupational exposure and potential health concerns. Toxicity of MWCNT should be carefully elucidated since the conventional (CON) method with fully immersed condition fails to mimic the air-liquid interface (ALI) in airways. Additionally, quantification of MWCNT in cells was a real challenge. Currently available ALI exposure devices are costly, posing problems to conducting in vitro evaluations for emerging nanomaterials. A novel system, consisting of a shaker fluidized-bed atomizer (SFA) and electrostatic shallow liquid interface (ESLI) exposure chamber, has been developed for investigating nanotoxicity of well-dispersed pristine-MWCNT (pMWCNT) and carboxylized-MWCNT (cMWCNT). After 24-h exposure, LDH, MCP-1, IL-1 beta, IL-6, and TNF-alpha releases were determined, and cell uptakes were quantified according to the molybdenum content in cells. Biological responses triggered by SLI exposure are obviously more sensitive compared with those caused by CON exposure at equivalent doses. Exposure dose-dependent release of LDH and IL-6 was highlighted in A549 cells, indicating higher cytotoxicity and inflammatory responses of cMWCNT attributed to its shorter length, smaller size, and higher cell uptake. Cell-associated dose-dependent release of LDH and IL-6 was highlighted in RAW264.7 cells, revealing the higher adverse health risk of pMWCNT due to frustrated phagocytosis and its much higher molybdenum content. These results suggest that inherent characteristics of cells and distinct physicochemical properties of pMWCNT and cMWCNT lead to either exposure dose-dependent or cell-associated dose-dependent responses. Notably, the SLI is superior to the CON exposure method and well suited for nanotoxicity assessment of different MWCNTs.
Development of composite filters with high efficiency, low pressure drop, and high holding capacity PM2.5 filtration
(2019-04-01)
Chang, De-Qiang
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Tien, Chi-Yu
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Peng, Chien-Yuan
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Tang, Min
;
Chen, Sheng-Chieh
Many efforts are being made to develop filters with high efficiency and high holding capacity but remaining a low pressure drop. A two-layer composite filter to achieve the goal was developed, in which the first layer was a charged coarse fibers to provide large void space for particle loading and the second was a thin layer of charged melt-blown with finer fibers to enhance the overall efficiency. Experimental results showed that although the new composite media had a lower initial efficiency than the other two HEPA filters (PTFE and glass fiber filter), its figure of merit (FOM) was the highest. Besides, the composite media had a better holding capacity for PM2.5 than the other two. At a fixed mass load, i.e., 2 g m(-2), the PTFE (Delta P = 380 Pa) and glass fiber (Delta P = 165 Pa) required around 7.6 and 3.3 times more power, respectively, than the composite media (Delta P = 50 Pa). Due to the low charge level of the coarse fiber layer and the fine fiber diameter of the melt-blown layer, resulted in no efficiency reduction along the loading process. Theoretical analysis showed that the charge shielding and the loss of efficiency in the successive top-down layers were timely compensated by the efficiency enhancement caused by the loading effects, which made the composite media a much uniform deposition of PM2.5 in layers. This was the main reason resulting in the high holding capacity and low pressure drop of the current composite media which acted like a perfect depth filtration media.
Experimental and theoretical analysis of loading characteristics of different electret media with various properties toward the design of ideal depth filtration for nanoparticles and fine particles
(2020-02-15)
Tien, Chi-Yu
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Chen, Jiang-Ping
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Li, Shihang
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Li, Ziyi
;
Zheng, Yu-Ming
Loading experiments of four electret fibrous media having various properties, including fiber diameter, porosity, thickness, charging density and fibrous structure, with fine and nanosized particles were conducted for finding out the influencing factors on efficiency decline and particle holding capacity. The four media include a commercial HVAC media rated with the minimum efficiency reporting value of 13 (MERV13), and three home-made media, including a coarse fiber (CF) layer, a melt-blown (MB) layer, and a bead-on-string (BS) layer. A theoretical model for predicting the pressure drop growth along the loading was applied and compared with that of experiments. The experimental results revealed that the charges of electret media did enhance the holding capacity. The decline of efficiency was found to closely relate to the holding capacity of each media. Higher capacity resulted in a higher decline of efficiency. The theoretical calculation illustrated that the ideal holding capacity was significantly higher than the current electret media had achieved, which indicates that it leaves much improvement of media design more desirable. Comparing the theoretical and experimental results of pressure drop growth with respect to mass load, it was found the current electret layers performed different levels of ideal depth filtration, with an order of CF > MERV13 > BS > MB. Beyond the ideal filtration, pressure drop growth raised exponentially. By utilizing their individual ideal filtration stage, three composite media consisting of 3-4 layers of these electrets with a total thickness less than 1 mm were combined and tested. At 1 in-H2O of pressure drop, the composite electret CF + MERV13 + BS achieved the highest holding capacity with 14.1 g m(-2) which was at least 5-10 times higher than the existing commercial HEPA filters. The bead-onstring fibrous structure of BS enhanced the holding capacity of the composite media significantly. The newly developed electret-based composite filters performed an energy efficient filtration for fine and nanosized particles.