• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2002.05b
• /
• pp.47-50
• /
• 2002

The displacemant current measuring system used for detecting the dynamic behavior of monolayers at the air-water interface is described. It basically consists of a film balance, a pair of electrodes connected to each other through a sensitive ammeter. Here, one electrode is suspended in air and the other electrode is placed in the water. With Maxwell-displacement-current-measuring method, the phase transitons of $Poly-{\gamma}-benzyl_{L}$ -glutamate (PBLG) and $Poly-{\gamma}-benzyl_{D}$-glutamate(PBDG) on a water surface were detected. Measured surface pressure, displacement current and dipole moment of monolayers of PBLG and PBDG on the water surface. Also, we measured that compression velocity (30, 40, 50[mm/min]) when the sample spread volume was about 370[ul]-400[ul] and displacement current that occur when differed temperature. From the result, it is known that current is generated in the range of high surface pressures as compression velocity become faster and increase of temperature.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.15 no.6
• /
• pp.461-470
• /
• 2003

The purpose of this study is to investigate the performance of a transcritical cycle for hot water heating using $CO_2$ as a working fluid. Some of the main parameters that affect the practical performance of the $CO_2$ system are discussed; the performance on the variation of refrigerant charge, changes in flow conditions of secondary fluids, and that with or without internal heat exchanger, The experimental results show that the optimum charge is approximately the same for various mass flow rates of the secondary fluid at gas cooler. The experimental results on the effect of secondary fluids are in general agreement with the experimental results of transcritical cycle in the open literature and show similar trend for conventional subcritical vapor compression cycles. The heat exchanger effectiveness increases with an increase of the heat exchange area of the internal heat exchanger regardless of the mass flow rate at the gas cooler.

• Proceedings of the KIEE Conference
• /
• 2001.07c
• /
• pp.1530-1532
• /
• 2001

The displacement current measuring system used for detecting the dynamic behavior of monolayers at the air-water interface is described. It basically consists of a film balance, a pair of electrodes connected to each other through a sensitive ammeter. Here, one electrode is suspended in air and the other electrode is placed in the water. With Maxwell-displacement-current-measuring method, the phase transitons of Poly-$\gamma$-benzyl p-glutamate (PBDG) on a water surface were detected. Measured surface pressure, displacement current and dipole moment of monolayers of PBDG on the water surface. Also, we measured that compression velocity(30, 40, 50[mm/min]) when the sample spread volume was about 400[ul]. From the result, it is known that current is generated in the range of high surface pressures as compression velocity become faster.

• Proceedings of the KIEE Conference
• /
• 2002.07c
• /
• pp.1413-1415
• /
• 2002

The Displacement current measurement system used in this experiment because detecting the dynamic behavior of monolayers at the air-water interface is possible. It basically consists of a film balance, a pair of electrodes connected to each other through a sensitive ammeter. Here, one electrode is suspended in air and the other electrode is placed in the water. PBLG phase transformation measured by Maxwell-displacement-current-measurement method in surface of the water. Measured (surfacc pressure, displacement current and dipole moment) of monolayers of PBLG on the water surface. We measured displacement current that occur when changed temperature(15, 20, 25$^{\circ}$ ) and the compression speed(30, 40, 50(mm/min)). From the result, it is known that curren generated in the range of high surface pressur compression velocity and temperature become faste.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.16 no.2
• /
• pp.158-166
• /
• 2004

The performance of a heat pump using $CO_2$ is predicted and analyzed by using a cycle simulation model developed in this study. Cycle simulations are conducted by varying design parameters and operating conditions with the applications of advanced techniques to improve system performance. The applied systems in the simulations are internal heat exchanger, expander, and 2-stage compression with intercooling. As a result, the applications of advanced techniques improve the heating and cooling performances of the transcritical $CO_2$ cycle by 8∼26％ and 20∼30％, respectively, over the basic cycle.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.7 no.1
• /
• pp.30-41
• /
• 1995

The present paper investigated irreversibilities and energy flow of a vapor compression refrigerator. The entropy generation and the available energy dissipation in components of the system were analyzed by using experimental data. It was shown that the dissipated available energy in the compressor including electric motor was much more than those in other components. The effects of the pressure drop and heat loss on irreversibilities in the condenser and the evaporator were small in comparison with heat transfer.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.28 no.9
• /
• pp.367-372
• /
• 2016

Gas diffusion layer (GDL) of PEMFCs plays a role that it diffuses the reactant gases to the catalyst layer on the membrane and discharge water from the catalyst layer to the channel. Physical parameters related to the mass transport of GDL are mostly from the uncompressed GDLs while actual GDLs in the assembled stacks are compressed. In this study, the relation of compression and strain of GDLs with various Polytetrafluoroethylene (PTFE) loading is measured experimentally and In-plane gas permeability is measured at the condition that the GDLs are in compressive strain. The gas permeability decreased with the loading of PTFE and the presentation of gas permeability under compressive stain is expected to improve the accuracy of modeling work of mass transport in the GDL.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.21 no.11
• /
• pp.1403-1412
• /
• 1997

When a high-speed railway train enters a tunnel, a compression wave is generated ahead of the train and propagates through the tunnel, compressing and accelerating the rest air in front of the wave. At the exit of the tunnel, an impulsive wave is emitted outward toward the surrounding, which causes a positive impulsive noise like a kind of sonic boom produced by a supersonic aircraft. With the advent of high-speed train, such an impulsive noise can be large enough to cause the noise problem, unless some attempts are made to alleviate its pressure levels. In the purpose of the impulsive noise reduction, the present study calculated the effect of porous walls on the compression wave propagating into a model tunnel. Two-dimensional unsteady compressible equations were differenced by using a Piecewise Linear Method. Calculation results show that the cavity/porous wall system is very effective for a compression wave with a large nonlinear effect. The porosity of 30% is most effective for the reduction of the maximum pressure gradient of the compression wave front. The present calculation results are in a good agreement with experimental ones obtained previously.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.30 no.6 s.249
• /
• pp.538-545
• /
• 2006

Stratified charge compression ignition (SCCI) combustion, also known as HCCI(homogeneous charge compression ignition), offers the potential to improve fuel economy and reduce emission. In this study, SCCI combustion was studied in a single cylinder gasoline DI engine, with a direct injection system. We investigated the effects of air-fuel ratio, intake temperature and injection timing such as early injection and late injection on the attainable SCCI combustion region. Injection timing during the intake process was found to be an important parameter that affects the SCCI region width. We also find it. The effects of mixture stratification and fuel reformation can be utilized to reduce the required intake temperature for suitable SCCI combustion under each set of engine speed and compression ratio conditions.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.19 no.9
• /
• pp.630-639
• /
• 2007

A $CO_2$ cycle shows large throttling loss during the expansion process. The application of an expander into the $CO_2$ cycle can reduce the throttling loss and then improve system performance. In this study, the performance of a transcritical $CO_2$ cycle with an expander was analytically investigated in order to improve the cooling performance of the system. The expander was applied to the single-stage and two-stage compression cycles. The performance was analyzed with the variations of compressor frequency, outdoor temperature, and expander efficiency. The single-stage and two-stage compression cycles with the expander showed COP improvement of 25% and 32%, respectively, over the single-stage cycle with an EEV.