• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.29 no.6
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• pp.327-340
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• 2017

This article reviews the papers published in the Korean Journal of Air-Conditioning and Refrigeration Engineering during 2016. It is intended to understand the status of current research in the areas of heating, cooling, ventilation, sanitation, and indoor environments of buildings and plant facilities. Conclusions are as follows. (1) The research works on the thermal and fluid engineering have been reviewed as groups of flow, heat and mass transfer, the reduction of pollutant exhaust gas, cooling and heating, the renewable energy system and the flow around buildings. CFD schemes were used more for all research areas. (2) Research works on heat transfer area have been reviewed in the categories of heat transfer characteristics, pool boiling and condensing heat transfer and industrial heat exchangers. Researches on heat transfer characteristics included the results of the long-term performance variation of the plate-type enthalpy exchange element made of paper, design optimization of an extruded-type cooling structure for reducing the weight of LED street lights, and hot plate welding of thermoplastic elastomer packing. In the area of pool boiling and condensing, the heat transfer characteristics of a finned-tube heat exchanger in a PCM (phase change material) thermal energy storage system, influence of flow boiling heat transfer on fouling phenomenon in nanofluids, and PCM at the simultaneous charging and discharging condition were studied. In the area of industrial heat exchangers, one-dimensional flow network model and porous-media model, and R245fa in a plate-shell heat exchanger were studied. (3) Various studies were published in the categories of refrigeration cycle, alternative refrigeration/energy system, system control. In the refrigeration cycle category, subjects include mobile cold storage heat exchanger, compressor reliability, indirect refrigeration system with $CO_2$ as secondary fluid, heat pump for fuel-cell vehicle, heat recovery from hybrid drier and heat exchangers with two-port and flat tubes. In the alternative refrigeration/energy system category, subjects include membrane module for dehumidification refrigeration, desiccant-assisted low-temperature drying, regenerative evaporative cooler and ejector-assisted multi-stage evaporation. In the system control category, subjects include multi-refrigeration system control, emergency cooling of data center and variable-speed compressor control. (4) In building mechanical system research fields, fifteenth studies were reported for achieving effective design of the mechanical systems, and also for maximizing the energy efficiency of buildings. The topics of the studies included energy performance, HVAC system, ventilation, renewable energies, etc. Proposed designs, performance tests using numerical methods and experiments provide useful information and key data which could be help for improving the energy efficiency of the buildings. (5) The field of architectural environment was mostly focused on indoor environment and building energy. The main researches of indoor environment were related to the analyses of indoor thermal environments controlled by portable cooler, the effects of outdoor wind pressure in airflow at high-rise buildings, window air tightness related to the filling piece shapes, stack effect in core type's office building and the development of a movable drawer-type light shelf with adjustable depth of the reflector. The subjects of building energy were worked on the energy consumption analysis in office building, the prediction of exit air temperature of horizontal geothermal heat exchanger, LS-SVM based modeling of hot water supply load for district heating system, the energy saving effect of ERV system using night purge control method and the effect of strengthened insulation level to the building heating and cooling load.

• Journal of the Korean Electrochemical Society
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• v.24 no.3
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• pp.65-75
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• 2021

Coin cell is a basic testing platform for battery research, discovering new materials and concepts, and contributing to fundamental research on next-generation batteries. Li metal batteries (LMBs) are promising since a high energy density (~500 Wh kg^-1) is deliverable far beyond Li-ion. However, Li dendrite-triggered volume fluctuation and high surface cause severe deterioration of performance. Given that such drawbacks are strongly dependent on the cell parameters and structure, such as the amount of electrolyte, Li thickness, and internal pressure, reliable Li metal coin cell testing is challenging. For the LMB-specialized coin cell testing platform, this study suggests the optimal coin cell structure that secures performance and reproducibility of LMBs under stringent conditions, such as lean electrolyte, high mass loading of NMC cathode, and thinner Li use. By controlling the cathode/anode (C/A) area ratio closer to 1.0, the inactive space was minimized, mitigating the cell degradation. The quantification and imaging of inner cell pressure elucidated that the uniformity of the pressure is a crucial matter to improving performance reliability. The LMB coin cells exhibit better cycling retention and reproducibility under higher (0.6 MPa → 2.13 MPa) and uniform (standard deviation: 0.43 → 0.16) stack pressure through the changes in internal parts and introducing a flexible polymer (PDMS) film.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.7 no.3
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• pp.461-467
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• 2003

This paper proposes the method of mobility implementation for location searching in the intelligence wireless ATM networks that expand and apply standard broadband signaling capabilities, and analyze the performance based on the numerical algorithm. The existing B-ISDN UNI protocol stack demands the location search mechanism to determine the location of mobile terminal in the wireless ATM networks because it use single protocol through the fixed PTP interface or PTM interface that don't support terminal mobility. The proposed method make possible the dynamic mobility at a part of wireless access by minimizing the signaling load without a falling-off in system performance by using the intelligence network technology according to the expansion of ATM and B-ISDN signaling integration based on the fixed networks. We implemented the performance analysis by MFC modeling based on numerical algorithm, and realized the efficiency of expenses by carrying out the comparative signaling performance evaluation to measure the relative gains of location search service in the intelligence wireless ATM system. The obtained results have the flexibility to operate in the public B-ISDN network environment without a change of existing B-ISDN/ATM NNI signaling reference to support the wireless ATM access system, and can easily expand to correspond to terminal mobility and various multimedia services in the next broadband PCS.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.36 no.3
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• pp.343-350
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• 2012

A planar solid oxide fuel cell (PSOFC) is studied in its application in a high-temperature stationary power plant. Even though PSOFCs with external reformers are designed for application from the distributed power source to the central power plant, such PSOFCs may sacrifice more system efficiency than internally reformed SOFCs. In this study, modeling of the PSOFC with an external reformer was developed to analyze the feasibility of thermal energy utilization for the external reformer. The PSOFC system model includes the stack, reformer, burner, heat exchanger, blower, pump, PID controller, 3-way valve, reactor, mixer, and steam separator. The model was developed under the Matlab/Simulink environment with Thermolib$^{(R)}$ modules. The model was used to study the system performance according to its configuration. Three configurations of the SOFC system were selected for the comparison of the system performance. The system configuration considered the cathode recirculation, thermal sources for the external reformer, heat-up of operating gases, and condensate anode off-gas for the enhancement of the fuel concentration. The simulation results show that the magnitude of the electric efficiency of the PSOFC system for Case 2 is 12.13% higher than that for Case 1 (reference case), and the thermal efficiency of the PSOFC system for Case 3 is 76.12%, which is the highest of all the cases investigated.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.14 no.11
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• pp.2535-2540
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• 2010

In traditional Publish/Subscribe system, the first procedure to deliver event from publisher to subscriber is that publisher publishes publisher's event to broker. Next step is that broker checks simple binary notion of matching : an event either matches a subscription or it does not. Lastly, broker delivers the event matched with subscriptions to the corresponding subscribers. In this system, information delivery has been accomplished in one way only. However, current some applications require two way delivery between subscriber and publisher. Therefore, we initiate an extended Publish/Subscribe system that supports two way delivery. Extended Publish/Subscribe system requires additional functions of delivering subscription to publisher and especially deciding top-n subscriptions using priority because broker might has a number of subscriptions. In this paper, we propose two priority retrieval techniques based on SIF using IS-List with deciding priority among subscriptions and defining SIF(Specific Interval First). The performance measurements show that RSO(resulting set sorting) technique results in better performance in index creation time and ITS&IS(insertion time sorting and inverse search using stack) technique results in better performance in search time.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2002.09a
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• pp.44-52
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• 2002

Low temperature thermal desorption (LTTD) has become one of the cornerstone technologies used for the treatment of contaminated soils and sediments in the United States. LTTD technology was first used in the mid-1980s for soil treatment on sites managed under the Comprehensive Environmental Respones, Compensation and Liability Act (CERCLA) or Superfund. Implementation was facilitated by CERCLA regulations that require only that spplicable regulations shall be met thus avoiding the need for protracted and expensive permit applications for thermal treatment equipment. The initial equipment designs used typically came from technology transfer sources. Asphalt manufacturing plants were converted to direct-fired LTTD systems, and conventional calciners were adapted for use as indirect-fired LTTD systems. Other innovative designs included hot sand recycle technology (initially developed for synfuels production from tar sand and oil shale), recycle sweep gas, travelling belts and batch-charged vacuum chambers, among others. These systems were used to treat soil contaminated with total petroleum hydrocarbons (TPH), polycyclic aromatic hydrocarbons (PAHs), pesticides, polychlorinated biphenyls (PCBs) and dioxin with varying degrees of success. Ultimately, performance and cost considerations established the suite of systems that are used for LTTD soil treatment applications today. This paper briefly reviews the develpoment of LTTD systems and summarizes the design, performance and cost characteristics of the equipment in use today. Designs reviewed include continuous feed direct-fired and indirect-fired equipment, batch feed systems and in-situ equipment. Performance is compared in terms of before-and-after contaminant levels in the soil and permissible emissions levels in the stack gas vented to the atmosphere. The review of air emissions standards includes a review of regulations in the U.S. and the European Union (EU). Key cost centers for the mobilization and operation of LTTD equipment are identified and compared for the different types of LTTD systems in use today. A work chart is provided for the selection of the optmum LTTD system for site-specific applications. LTTD technology continues to be a cornerstone technology for soil treatment in the U.S. and elsewhere. Examples of leading-edge LTTD technologies developed in the U.S. that are now being delivered locally in global projects are described.

• Proceedings of the Korean Institute of Information and Commucation Sciences Conference
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• 2008.05a
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• pp.55-58
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• 2008

RFID(Radio frequency IDentification) leader is collision of data, when recognizing the multiple tag the inside area. This collision became the cause which delays the tag recognition time of the leader. The protocol which prevents the delay of tag recognition time of the leader the place where representative it uses QT(Query Tree) algorithms, it uses a collision bit position from this paper and are improved QT-MTC(Query Tree with Multi-Tag Cognition) algorithms which it proposes. This algorithm stored the bit position which bit possibility and the collision where the collision happens occurs in the stack and goes round a tree the number of time which, it reduced could be identified two tags simultaneously in order, it was planned. A result of performance analysis, It compared in QT protocols and the this algorithm against the tag bit which is continued a tush efficiency improvement effect was visible.

• Transactions of the Korean Society of Automotive Engineers
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• v.17 no.2
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• pp.150-158
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• 2009

A centrifugal turbo blower is one of the part to generate electric power of fuel cell electric vehicle(FCEV). In order to generate the electric power of FCEV, the centrifugal turbo blower operates at very high speed above 30,000rpm in order to increase the pressure of the air, which supplied to a stack of FCEV, using rotation of its impeller blades. Vibration which originated from the blower is generated by unbalance of mechanical components, rotation of bearings and rotating asymmetry that rotate at high speed. The vibration is transmitted to receiving structure through vibration isolators and it can causes serious problems in the noise, vibration and harshness(NVH) performance. Thus, the study about reducing this kind of vibration is an important task. Quantifying the effectiveness of vibration isolation can be effectively accomplished by using vibrational power flow because relative contributions of each isolator to the total vibration transmission can be easily represented. In this paper, vibrational power flow is applied to the centrifugal turbo blower mounted on FCEV in order to analyze the most dominant vibration transmitting path. As a result, the main contributor among four isolators is a mount #3 of the blower. Also, a 30 percent lowering of the mount #3 stiffness shows 34 percent decrement of vibrational power flow by the simulation.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.28 no.12
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• pp.1914-1922
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• 2004

This paper provides a comprehensive study of optimum design of a helicopter tailrotor driveshaft made of the flexible matrix composites (FMCs). Since the driveshaft transmits power while subjected to large bending deformation due to aerodynamic loadings, the FMCs can be ideal for enhancing the drivetrain performance by absorbing the lateral deformation without shaft segmentation. However, the increased lateral flexibility and high internal damping of the FMCs may induce whirling instability at supercritical operating conditions. Thus, the purpose of optimization in this paper is to find a set of tailored FMC parameters that compromise between the lateral flexibility and the whirling stability while satisfying several criteria such as torsional buckling safety and the maximum shaft temperature at steadystate conditions. At first, the drivetrain was modeled based on the finite element method and the classical laminate theory with complex modulus approach. Then, an objective function was defined as a combination of an allowable bending deformation and external damping and a genetic algorithm was applied to search for an optimum set with respect to ply angles and stack sequences. Results show that an optimum laminate consists of two groups of layers: (i) one has ply angles well below 45$^{\circ}$ and the other far above 45$^{\circ}$ and (ii) the number of layers with low ply angles is much bigger than that with high ply angles. It is also found that a thick FMC shaft is desirable for both lateral flexibility and whirling stability. The genetic algorithm was effective in converging to several local optimums, whose laminates exhibit similar patterns as mentioned above.

• Clean Technology
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• v.3 no.2
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• pp.74-86
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• 1997

Recently the treatment of industrial wastes by membrane processes has drawn much attention due to increasing demands for clean technology. In the process investigated in this study, metal species in the acidic wastes are precipitated as metal hydroxide forms in a neutralization tank, and acid and base solutions are regenerated by water-splitting electrodialysis(WSED) to be reused in the process. Material balances of the processes for treating pickle liquor and mixed wastewater were calculated to explain conceptual design of the process. Experiments for neutralization precipitation with KOH and NaOH for mixed wastewater were carried out to precipitate metal hydroxide and to recover salt solution as supernatant. Also WSED of the salt solutions producing acid and base was tested in 2 or 3 compartment stacks using KCl and NaCl to investigate the effects of stack configurations on the WSED performance.