• Proceedings of the KIEE Conference
• /
• 1994.07b
• /
• pp.1559-1561
• /
• 1994

At present, the principle of puffer action in high current interruption is adopted in almost of the EHV(Extra High Voltage) and UHV(Ultra High Voltage) GCB(Gas Circuit Breakers). The thermal interruption capability of these GCBs critically depends on the pressure rise in the puffer cylinder at current zero. The pressure rise in the puffer cylinder depends on the puffer cylinder volume, flow passage and leakage area in the interrupter, stroke curve etc. Recently commercial CFD(Computational Fluid Dynamics ) packages have been widely adopted to calculate the pressure distribution in the interrupter. However, there are still several problems with it, e.g. very expensive price, moving boundary problem, computation time, difficulty in using the package etc. Thus, the calculation of the puffer cylinder pressure in simple and relatively correct method is essential in early stage of GCB design. In these paper, the model ing technique and computed results for EHV class GCB (HICO, 145kV 40kA and 362kV 40kA GCB) are presented and compared with available measured results.

• Journal of the Korean Society of Mechanical Technology
• /
• v.13 no.3
• /
• pp.39-47
• /
• 2011

In a bi-fuel engine using gasoline and LPG fuel, with the current ignition timing for gasoline being used, the optimum performance could not be taken in LPG fuel supply mode. The ignition timing in LPG fuel mode must be advanced much more than that of gasoline mode for the compensation of its higher ignition temperature. The purpose of this study is to investigate how the ignition spark timing conversion influences the engine performance of LPG/Gasoline Bi-Fuel engine. In order to investigate the engine performance during combustion, engine performance are sampled by data acquisition system, for example cylinder pressure, pressure rise rate and heat release rate, while change of the rpm(1500, 2000, 2500) and the ignition timing advance($5^{\circ}$, $10^{\circ}$, $15^{\circ}$, $20^{\circ}$). As the result, between 1500rpm, 2000rpm and 2500rpm, the cylinder pressure and pressure rise rate was increased when the spark ignition was advanced but pressure rise rate at $20^{\circ}$ was smaller value.

• Nuclear Engineering and Technology
• /
• v.36 no.5
• /
• pp.403-414
• /
• 2004

An experimental study of heat transfer characteristics near the critical pressure has been performed with an internally-heated vertical annular channel cooled by R-134a fluid. Two series of tests have been completed: (a) steady-state critical heat flux (CHF) tests, and (b) heat transfer tests for pressure reduction transients through the critical pressure. In the present experimental range, the steady-state CHF decreases with increase of the system pressure for fixed inlet mass flux and subcooling. The CHF falls sharply at about 3.8 MPa and shows a trend towards converging to zero as the pressure approaches the critical point of 4.059 MPa. The CHF phenomenon near the critical pressure does not lead to an abrupt temperature rise of the heated wall, because the CHF occurs at remarkably low power levels. In the pressure reduction transients, as soon as the pressure passes below the critical pressure from the supercritical pressure, the wall temperatures rise rapidly up to very high values due to the departure from nucleate boiling. The wall temperature reaches a maximum at the saturation point of the outlet temperature, and then tends to decrease gradually.

• Journal of the Korean Society of Safety
• /
• v.8 no.4
• /
• pp.114-119
• /
• 1993

The explosion characteristics of nonhomogeneous LPG-Air mixtures was measured in a cylindrical vessel and a pipe. The maximum explosion pressure, the maximum rate of explosion pressure rise, and the flame propagation velocity were measured and compared with that of homogeneous explosion by changing the effective factors on the explosion of nonhomogeneous mixtures such as pressure difference, effusion time and delay time. Explosion was occured even in the lower concentration than the lean flammability limit of mixture. The maximum explosion pressure was increased with increase of LPG concentration, however, the maximum explosion pressure rise was not in the nonhomogeneous explosion. An d the flame propagation velocity was decreased with nonhomogeneity, however, the maximum explosion pressure was always above 0.7kg/$\textrm{cm}^2$.

• Proceedings of the Korean Institute of Building Construction Conference
• /
• 2017.11a
• /
• pp.54-55
• /
• 2017

The High-rise building has a problem the ventilation performance of natural ventilator by stack effect that it occurs by pressure difference. For that reason the study about natural smoke ventilator of High-rise building consistently needs. Therefore on this study does analysis of difference with abroad through investigate of Natrual smoke ventilator's law, it conducts of natural smoke ventilator's research on the actual condition. As a result on this study, in the case of abroad that it states more specific standards than domestic. Also the result of a field study, it shows that the natural smoke ventilator is installed same size and the number regardless of building's pressure difference.

• Fire Science and Engineering
• /
• v.23 no.6
• /
• pp.82-90
• /
• 2009

Natural smoke ventilator is one of domestic prescriptive methods to be used to exhaust smoke in case of fire in a high-rise buildings. The goal of this study is to evaluate the stack effect and the smoke exhaust performance in high-rise buildings with the opening of natural smoke ventilators using computer modeling technology, thus to estimate its effectiveness as a tool of smoke exhaust. For this purpose, the pressure differential in a domestic high-rise building with natural smoke ventilators was experimentally measured to analyze the stack effect with the closure or the opening of natural smoke ventilators and to calculate compensated air leakage of the building. Computer modeling based on experimentally measured data was carried out to estimate effectiveness of natural smoke ventilators in high-rise buildings using CONTAMW network program.

• Proceedings of the KSME Conference
• /
• 2004.04a
• /
• pp.2094-2099
• /
• 2004

An experimental study on heat transfer characteristics near the critical pressure has been performed with an internally-heated vertical annular channel cooled by R-134a fluid. Two series of tests have been completed: (a) steady-state critical heat flux (CHF) and (b) heat transfer tests for pressure reduction transients through the critical pressure. In the present experimental range, the steady-state CHF decreases with the increase of the system pressure For a fixed inlet mass flux and subcooling, the CHF falls sharply at about 3.8 MPa and shows a trend toward converging to zero as the pressure approaches the critical point of 4.059 MPa. The CHF phenomenon near the critical pressure does not lead to an abrupt temperature rise of the heated wall because the CHF occurred at remarkably low power levels. In the pressure reduction transient experiments, as soon as the pressure passed through the critical pressure, the wall temperatures rise rapidly up to a very high value due to the occurrence of the departure from nucleate boiling. The wall temperature reaches a maximum at the saturation point of the outlet temperature, then tends to decrease gradually.

• Journal of Mechanical Science and Technology
• /
• v.18 no.9
• /
• pp.1590-1603
• /
• 2004

In this study the optimization of plate-fin type heat sink with vortex generator for the thermal stability is performed numerically. The optimum solutions in the heat sink are obtained when the temperature rise and the pressure drop are minimized simultaneously. Thermal performance of heat sink is influenced by the heat sink shape such as the base-part fin width, lower-part fin width, and basement thickness. To acquire the optimal design variables automatically, CFD and mathematical optimization are integrated. The flow and thermal fields are predicted using the finite volume method. The optimization is carried out by means of the sequential quadratic programming (SQP) method which is widely used for the constrained nonlinear optimization problem. The results show that the optimal design variables are as follows; B$_1$=2.584 mm, B$_2$=1.741 mm, and t=7.914 mm when the temperature rise is less than 40 K. Comparing with the initial design, the temperature rise is reduced by 4.2 K, while the pressure drop is increased by 9.43 Pa. The relationship between the pressure drop and the temperature rise is also presented to select the heat sink shape for the designers.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.23 no.10
• /
• pp.639-645
• /
• 2011

The object of this study is to analyze and evaluate outdoor wind pressure effect in a high-rise residential building when seasonal wind blow on coast area. The target building consists of 3 tower buildings over 250m in height. For the evaluation of the outdoor wind effect, CFD simulation was performed. The results of the simulations are as follows : 1) In that case of high-rise building, horizontal stream is more affected than vertical stream. 2) In case of summer season northeasterly wind, building pressure distributions are unstable and surface pressures of outside are effected respectively. 3) In case of winter season westerly wind, building preassure differentiations are not so much because of screening effects of the B, and the C buildings. 4) In case of winter season northwesterly wind, front wind affects on the A building directly because of no obstacles.

• Wind and Structures
• /
• v.28 no.6
• /
• pp.389-404
• /
• 2019

In coastal regions, it is common to witness significant damages on low-rise buildings caused by hurricanes and other extreme wind events. These damages start at high pressure zones or weak building components, and then cascade to other building parts. The state-of-the-art in experimental and numerical aerodynamic load evaluation is to assume buildings with intact envelopes where wind acts only on the external walls and correct for internal pressure through separate aerodynamic studies. This approach fails to explain the effect of openings on (i) the external pressure, (ii) internal partition walls; and (iii) the load sharing between internal and external walls. During extreme events, non-structural components (e.g., windows, doors or rooftiles) could fail allowing the wind flow to enter the building, which can subject the internal walls to lateral loads that potentially can exceed their load capacities. Internal walls are typically designed for lower capacities compared to external walls. In the present work, an anticipated damage development scenario is modelled for a four-story building with a stepped gable roof. LES is used to examine the change in the internal and external wind flows for different level of assumed damages (starting from an intact building up to a case with failure in most windows and doors are observed). This study demonstrates that damages in non-structural components can increase the wind risk on the structural elements due to changes in the loading patterns. It also highlights the load sharing mechanisms in low rise buildings.