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Optimal cold sink temperature for thermoelectric dehumidifiers
Kim, Joonoh,Park, Keunhwan,Lee, Duck-Gyu,Chang, Young Soo,Kim, Ho-Young 대한기계학회 2018 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.32 No.2
<P>We propose an optimal cold sink temperature for thermoelectric dehumidifiers based on theoretical and experimental investigations. We show that the optimal condition is such that the latent heat absorption rate per unit power supplied to the dehumidifier is maximized. In consideration of the cooling ability of Peltier pellet and the heat exchange characteristics of the cold sink, we estimate the condensation rate as a function of the cold sink temperature. The theoretical predictions are compared with the results of experiments by using a prototype dehumidifier. We emphasize that the cold sink temperature is a critical parameter that determines the performance of dehumidification. Our study may provide an important insight to the thermoelectric dehumidification system and to designing a cold sink for thermoelectric dehumidifiers with improved energy efficiency.</P>
Kim, Byung Hwan,Jang, Jae Hoon,Seol, Woo-Kyung,Moon, Joonoh,Kim, Sung-Dae,Lee, Tae-Ho,Kim, Hyoung Chan,Lee, Chang-Hoon,Cho, Kyung-Mox Elsevier 2018 Journal of nuclear materials Vol.508 No.-
<P><B>Abstract</B></P> <P>The specificities of hardness change during tempering in Ti-containing reduced activation ferritic/martensitic (RAFM) steels were found while developing new RAFM steels with improved mechanical properties. Hardness decline during tempering of RAFM steel where Ti replaced Ta (Ti-RAFM) and RAFM steel with both Ta and Ti (TaTi-RAFM) was greater than that in conventional RAFM steel with Ta (Ta-RAFM). It is believed that Ti addition tend to accelerate the growth of MX precipitates and thereby accelerated diffusion of carbon from the martensite matrix, leading to a large decrease in hardness of martensite in Ti-containing RAFM steels during tempering.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The hardness decline during tempering in Ti-RAFM or TaTi-RAFM where Ti was added is due to the decrease in carbon remaining in martensite resulting from fast growth of TiC precipitates in Ti containing RAFM compared to TaC precipitates in Ta-RAFM. </LI> </UL> </P>
Kim Sangeun,Jin Hyung-Ha,Kim Hyeongchul,Heo Jungwoo,Cho Seong-Yong,Shin Chansun,Moon Joonoh,Lee Chang-Hoon 한국물리학회 2020 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.77 No.1
Surface swelling caused by He implantation was studied for newly-developed Ti/Ta-added reduced-activation ferritic/martensitic (RAFM) steels. Post-implantation annealing at 623 K for 2 h of He-implanted RAFM-steel samples led to surface-step formation because of surface swelling induced by He bubbles formed inside the samples. Pre-implantation of a small number of H ions was found to cause an increase in the surface-step height, which was not expected. A possible mechanism for this synergistic effect of pre-implanted H is proposed.
Removal of Contaminant Nanoparticles with CO2 Nanobullets at Atmospheric Conditions
Jae Hong Lee,Joonoh Kim,Seungho Kim,Joongha Lee,Jinkyu Kim,Kihoon Choi,Ho-Young Kim 한국정밀공학회 2020 International Journal of Precision Engineering and Vol.7 No.5
As the feature size of semiconductor chips is decreasing down to nanometric scales, cleaning of nanoscale contaminant particles without damaging the fi ne features puts forth severe technological challenges. Here we introduce a design methodology of a nozzle to generate a beam of supersonic CO 2 solid nanobullets into the air at atmospheric pressure, which dislodge the contaminant particles by colliding with them. The dry cleaning scheme proposed here does not resort to the chillers, vacuum chamber, and carrier-gas handling system, which conventional dry cleaning systems often required and thus hampered their practical applications. We provide a theoretical framework to select key design parameters, such as the area ratio of the nozzle throat and exit and the supply gas pressure. We experimentally verify the superior capability of our nozzle in generating a CO 2 aerosol beam under the atmospheric back pressure condition. Additional process parameters including the stand-off distance and the incident angle of the CO 2 beam are optimized to maximize the cleaning efficiency and minimize the pattern damages. Our work suggests a practical nanoparticle cleaning scheme that is faster and simpler than the conventional dry cleaning methods.
양한모,Lee Joo-Eun,Kim Ju-Young,You Jihye,Kim Joonoh,Lee Hak Seung,Yoo Hee Min,Kong Min Gyu,한정규,조현재,Park Kyung Woo,Kang Hyun-Jae,구본권,Park Young-Bae,Kim Hyo-Soo 한국생체재료학회 2023 생체재료학회지 Vol.27 No.00
Background Although vasospastic angina (VSA) is known to be caused by coronary artery spasm, no study has fully elucidated the exact underlying mechanism. Moreover, in order to confirm VSA, patients should undergo invasive coronary angiography with spasm provocation test. Herein, we investigated the pathophysiology of VSA using peripheral blood-derived induced pluripotent stem cells (iPSCs) and developed an ex vivo diagnostic method for VSA. Methods and results With 10 mL of peripheral blood from patients with VSA, we generated iPSCs and differentiated these iPSCs into target cells. As compared with vascular smooth muscle cells (VSMCs) differentiated from iPSCs of normal subjects with negative provocation test, VSA patient-specific iPSCs-derived VSMCs showed very strong contraction in response to stimulants. Moreover, VSA patient-specific VSMCs exhibited a significant increase in stimulation-induced intracellular calcium efflux (Changes in the relative fluorescence unit [ΔF/F]; Control group vs. VSA group, 2.89 ± 0.34 vs. 10.32 ± 0.51, p < 0.01), and exclusively induced a secondary or tertiary peak of calcium efflux, suggesting that those findings could be diagnostic cut-off values for VSA. The observed hyperreactivity of VSA patient-specific VSMCs were caused by the upregulation of sarco/endoplasmic reticulum Ca2+- ATPase 2a (SERCA2a) due to its enhanced small ubiquitin-related modifier (SUMO)ylation. This increased activity of SERCA2a was reversed by treatment with ginkgolic acid, an inhibitor of SUMOylated E1 molecules (pi/μg protein; VSA group vs. VSA + ginkgolic acid, 52.36 ± 0.71 vs. 31.93 ± 1.13, p < 0.01). Conclusions Our findings showed that abnormal calcium handling in sarco/endoplasmic reticulum could be induced by the enhanced SERCA2a activity in patients with VSA, leading to spasm. Such novel mechanisms of coronary artery spasm could be useful for drug development and diagnosis of VSA.
Jung‑Ho Sim,Tae‑Yeong Kim,Jun‑Yeon Kim,Chi‑Won Kim,Jun‑Ho Chung,Joonoh Moon,Chang‑Hoon Lee,Hyun‑Uk Hong 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.2
In the present study, low carbon ferritic and bainitic steels with different contents of Mo, Ti, and Nb were designed for bothseismic and fire-resistant applications. The microstructure of steels containing 0.3 wt% Mo–0.02 wt% Nb (‘A’ hereinafter)was mainly composed of bainite. By contrast, the microstructure of steels with 0.2 wt% Mo–0.13 wt% Ti (‘B’ hereinafter)consisted of ferrite with a high density of nano-sized (Ti,Mo)-rich MX precipitates. The results showed that the bainiticmicrostructure (‘A’ steel) was quite favorable to high-temperature strength and thermal stability. The yield strength of ‘A’ steelat both room and 600 °C temperatures increased consistently with increasing thermal exposure time (600 °C/200–1000 h),since the precipitation of NbC particles occurred while maintaining bainitic ferrite platelets with a high density of dislocationsduring exposure. In the ‘B’ steel, the formation of nano-sized (Ti,Mo)-rich MX particles was effective to impededislocation movement, leading to excellent plasticity (lower yield ratio) at room temperature. However, their contributionto precipitation hardening was not so much at 600 °C, as compared to the bainitic strengthening. During low cycle fatiguetests at room temperature, the main different feature between the two steels is that the ‘A’ steel showed cyclic softeningwhile cyclic hardening was evident in the ‘B’ steel. The bainitic microstructure showed a better fatigue life due to increasedductility manifested by cyclic softening, by which dislocation cell was developed.
Kim, Han Kyu,Lee, Ji Won,Moon, Joonoh,Lee, Chang Hoon,Hong, Hyun Uk Elsevier 2018 JOURNAL OF NUCLEAR MATERIALS Vol.500 No.-
<P><B>Abstract</B></P> <P>The effects of Ti and Ta addition on microstructure stability and tensile properties of a reduced activation ferritic/martensitic (RAFM) steel have been investigated. Ti addition of 0.06 wt% to conventional RAFM reference base steel (Fe-9.3Cr-0.93W-0.22V-0.094Ta-0.1C) was intended to promote the precipitation of nano-sized (Ti,W) carbides with a high resistance to coarsening. In addition, the Ti addition was substituted for 0.094 wt% Ta. The Ti-added RAFM steel (Ti-RAFM) exhibited a higher yield strength (<I>Δ</I>YS = 32 MPa) at 600 °C than the reference base steel due to additional precipitation hardening by (Ti,W)-rich MX with an average size of 6.1 nm and the area fraction of 2.39%. However, after thermal exposure at 600 °C for 1000 h, this Ti-RAFM was more susceptible to degradation than the reference base steel; the block width increased by 77.6% in Ti-RAFM after thermal exposure while the reference base steel showed only 9.1% increase. In order to suppress diffusion rate during thermal exposure, the large-sized Ta element with low activation was added to Ti-RAFM. The Ta-added Ti-RAFM steel exhibited good properties with outstanding microstructure stability. Quantitative comparison in microstructures was discussed with a consideration of Ti and Ta addition.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The Ti addition to RAFM steel without Ta increased the fraction of (Ti,W)-rich MX. </LI> <LI> The Ti-RAFM steel was more susceptible to the degradation during thermal exposure. </LI> <LI> The mutual addition of Ti and Ta accelerated the kinetics of (Ta,Ti)-rich MX precipitation. </LI> <LI> The higher fraction of (Ta,Ti)-rich MX contributed to a higher resistance to the degradation. </LI> </UL> </P>
Joonoh Moon,Chang‑Hoon Lee,Hyo‑Haeng Jo,Sung‑Dae Kim,Hyun‑Uk Hong,Jun‑Ho Chung,Bong Ho Lee 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.4
The microstructural evolution and fire-resistant properties in the weld heat-affected zone (HAZ) of Mo and Mo + Nb-addedfire-resistant steels were investigated. For this purpose, three Fe-0.1 wt%C-1.5 wt%Mn-0.1 wt%Si steels containing variousMo and Nb contents were prepared. HAZ samples were experimentally simulated using a Gleeble simulator at a welding heatinput of 30 and 300 kJ/cm. The yield strength of the HAZ samples was higher than those of base steels at both room temperatureand 600 ℃, whereas a greater decrease in the yield strength at 600 ℃ compared to that at room temperature occurred inthe HAZ samples than in the base steels, indicating that the fire-resistance deteriorated in the HAZs as compared to the basesteels. This is due to the formation of hard phases such as bainite and martensite in the HAZs, i.e., bainite and martensitephase have very high yield strength with high dislocation density at room temperature, while their strengths decrease rapidlyat high temperature due to a great annihilation and recovery of dislocations at high temperature. In addition, the fire-resistanceof the HAZ improved as the heat input was increased. The alloying of Mo and Nb improved the fire-resistance of both the basesteels and the HAZs. Finally, the changes in the microstructures of the base steels and the HAZs upon alloying and the heatinput and corresponding effects on the fire-resistance were carefully explored and discussed through transmission electronmicroscopy analyses, atom probe tomography analyses, and calculations of continuous cooling transformation diagrams.