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Kang, Min Su,Joh, Hyungmok,Kim, Haneun,Yun, Hye-Won,Kim, Donggyu,Woo, Ho Kun,Lee, Woo Seok,Hong, Sung-Hoon,Oh, Soong Ju The Royal Society of Chemistry 2018 Nanoscale Vol.10 No.38
<P>In this work, we introduce a low cost, room-temperature and atmospheric pressure based chemical method to produce highly transparent, conductive, and flexible nano-mesh structured electrodes using Ag nanocrystals (NCs). Sequential treatments of ligand exchange and reduction processes were developed to engineer the optoelectronic properties of Ag NC thin films. Combinatorial analysis indicates that the origin of the relatively low conductivity comes from the non-metallic compounds that are introduced during ligand exchange. The reduction process successfully removed these non-metallic compounds, yielding structurally uniform, optically more transparent, dispersive, and electrically more conductive thin films. We optimized the design of Ag NC thin film mesh structures, and achieved low sheet resistance (9.12 Ω □<SUP>−1</SUP>), high optical transmittance (94.7%), and the highest figure of merit (FOM) of 6.37 × 10<SUP>−2</SUP>. Solution processed flexible transparent heaters, touch pads, and wearable sensors are demonstrated, emphasizing the potential applications of Ag NC transparent electrodes in multifunctional sensors and devices.</P>
Evaluation of heat storage and release in a double shell and tube heat exchanger with a PCM layer
Donggyu Lee,CHAEDONG KANG 대한기계학회 2020 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.34 No.8
In this study, a thermal storage type heat exchanger that combines heat storage and heat exchange functions has proposed and the heat transfer characteristics of the new type of heat exchanger were analyzed through experiments. The proposed thermal storage type heat exchanger has a shell and tube structure and allows mutual heat transfer between three or more mediums, including a phase change material (PCM). This thermal storage type heat exchanger contains 52.2 kg of a PCM with a phase change temperature of 68.8 °C to provide heat storage function. The heat transfer experiment of the heat exchanger confirmed the effect of the temperature change of the heating medium under the same flow conditions. Furthermore, due to the structural characteristics of the thermal storage type double shell and tube heat exchanger (TSDHE), the phenomenon of three-medium heat exchange (hot watercold water, hot water-PCM, additional water-PCM) was verified during the experimental process. In particular, due to the PCM filled inside the heat exchanger, the cold water received a heat transfer of 3 kW or higher from the PCM for at least 5 min (maximum 33 min), even when the hot water supply (heat source) was stopped. The results of this study will be used as basic data for applying a thermal storage type evaporator to a high temperature heat pump that generates steam using industrial waste heat.
이동규(Donggyu Lee),서재경(Jae-Kyoung Suh),오영택(Youngtaig Oh),강채동(Chaedong Kang) 한국자동차공학회 2005 한국자동차공학회 춘 추계 학술대회 논문집 Vol.2005 No.5_1
In advance of energy crisis in recent future, the development of energy conversion system has been increased rapidly to practical use of renewable energy. The stirling engine which was invented by Rev Robert Stirling in 1816 is one of the efficient and practical machines. The engine has been commonly used in some very specialized applications, such as in submarines or auxiliary power generator for vehicles, where quiet operation is required. A γ -type stirling engine, one of the stirling engine consists of two cylinders, a piston and a displacer. In this study, a stirling engine which is based on the design and data of Moriya stirling engine(1938), was developed in laboratory scale. The geometry of the engine was scaled up with 1.5 times to the original one. All the parts were made by self-manufacturing, except raw material, axial bearing and fly wheel. From the partial test of the performance, rotational speed of axle was obtained to 270 rpm when the temperature of the heating and cooling zone was 120℃ , 50℃, respectively.
동시 축ㆍ방열 조건에서 PCM의 열전달 특성에 관한 연구
이동규(Donggyu Lee),박세창(Sechang Park),정동열(Dong-yeol Chung),강채동(Cheadong Kang) 대한설비공학회 2016 설비공학 논문집 Vol.28 No.8
A thermal storage systems was designed to correspond to the temporal or quantitative variation in the thermal energy demand, and most of its heat is stored using the latent and sensible heat of the heat storage material. The heat storage method using latent heat has a very complex phenomenon for heat transfer and thermal behavior because it is accompanied by a phase change in the course of heating/cooling of the heat storage material. Therefore, many studies have been conducted to produce an experimentally accessible as well as numerical approach to confirm the heat transfer and thermal behavior of phase change materials. The purpose of this study was to investigate the problems encountered during the actual heat transfer from an internal storage tank through simulation of the process of storing and utilizing thermal energy from the thermal storage tank containing charged PCM. This study used analysis methods to investigate the heat transfer characteristics of the PCM with simultaneous heating/cooling conditions in the rectangular space simulating the thermal storage tank. A numerical analysis was carried out in a state considering natural convection using the ANSYS FLUENT® program. The result indicates that the slope of the liquid-solid interface in the analysis field changed according to the temperature difference between the heating surface and cooling surface.
이동규(Donggyu Lee),정근면(Geunmyon Jeong),강채동(Chaedong Kang) 대한설비공학회 2016 대한설비공학회 학술발표대회논문집 Vol.2016 No.6
Recently, the interest has been increased to the efficient use for unutilized energy and the emission reduction of carbon dioxide. In particular, waste water on middle temperature is recognized to one of the representative unutilized energy, which occurs on manufacturing processes in the many manufacturers such as power, food and textile industry. The unutilized energy have a disadvantage such as the low energy utility because low energy density. Therefore, a lot of research about the system improvement combined with a heat pump were reported for the production of heat energy of high temperature of utility. However, It is important to maintain steadily heat supply from the system. A heat storage and heat exchanger is applied to the system in order to increase utilization because the heated waste water which occurred in the industry process has various flow according to time. In this article, we designed an thermal storage type heat exchanger which has a thermal storage tank and heat exchanger function as an evaporator of heat pump system. The designed thermal storage type heat exchanger has a double shell and tube structure. Moreover, it is structured to the purpose of conducting stored heat and transferring to four heat medium including a phase change material(PCM). In this article, a basic experiment was conducted in order to measure the heat transfer characteristics of the each three heat medium between PCM. And experimental results will be used as the design data for thermal storage type heat exchanger.
판형 열교환기에서 유동 과냉도 및 냉각속도가 연속제빙에 미치는 영향
이동규(Donggyu Lee),백종현(JongHyun Peck),홍희기(Hiki Hong),강채동(Chaedong Kang) 대한설비공학회 2006 대한설비공학회 학술발표대회논문집 Vol.2006 No.6
The peculiarity of ice slurry, such as liquidity, high heat transfer rate and easy storage can also find to supercooled type dynamic ice storage system(DISS) which is one of the DISS. However, in order to accomplish continuous ice formation in the system without mechanical moving parts, supercooled aqueous solutionshould be formed stable through cooling heat exchanger and be dissoluted in storage tank. In previous research, the time of ice slurry increased as the pressure of the cooling heat exchanger(PHX) increased. In this study, a cooling experiment of an ethylene glycol 7mass% solution was performed with various inlet temperature of the PHX, which has constant brine inlet temperature of -7 ℃. The temperature in the storage tank maintained to freezing point of the solution. At results, the time of ice slurry formation increased as the supercooling degree decreased and the cooling rate increased.