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A Study on Improvement of Ventilation Efficiency of Multi-Stage Slot Hood (외부식 다단형 슬로트 후드의 효율 향상에 관한 연구)

  • Kim, Hyun Seok;Paik, Nam Won
    • Journal of Korean Society of Occupational and Environmental Hygiene
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    • v.3 no.2
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    • pp.204-212
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    • 1993
  • This study was conducted to evaluate ventilation efficiency of 4-stage slot hood by variation of slot width, flow rate, hood size and baffle size. The slot velocity, control velocity and plenum velocity were related to slot width and the distance between source of contamination and hood. The results obtained from laboratory experiment for local exhaust ventilation systems were as follows ; 1. When slot widths were constant(equally changed) and the velocity was 6-10 m/s, the slot velocity from 1st slot to 4th slot gradually decreased. As the slot width-to-slot length ratio(WLR) decreased, the slot velocity of each stage increased. But if WLR value was less than 0.04, the slot velocity decreased. 2. When slot velocity exceeded 10 m/s with constant slot widths, the slot velocity of each stage was uniform. 3. When the slot velocity was uniform within 10 m/s and the first slot width was 14-20 mm, the slot width ratio between 1st slot and each of three other slots were 1, 1.25, 1.5 and 3.0, respectively. 4. The slot and plenum velocity were uniform when exhaust flow rate changed from 14 to $19m^3/min$ and there were no hood splitter vanes. 5. When the slot velocity at each stage was uniform, the control velocity at site 30 cm away from hood No.2 increased from 0.15-0.30 to 0.25-0.45 m/s and the control distance from 20 to 30 cm(about 1.5 times).

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A Study on the Time-slot Allocation Methods for the Multi-slot Calls on ATM Telephone Network (ATM 통화로 망에서의 다중호 배치방법에 대한 연구)

  • 박경태
    • Journal of the Institute of Convergence Signal Processing
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    • v.5 no.1
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    • pp.73-78
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    • 2004
  • There are random, continuous, and periodic allocation methods in the time slot sequence integrity for the multi-slot call. In the T-S-T switch, there are 2 time switch and the 2*2 space switch. Three time-slot allocation methods are suggested for the simulation. In the simulation, the searching times for time-slots on a multi-slot call is chosen to 32, and the simulation time is chosen to 100,000 seconds. Three kinds of calls are supposed for a multi-slot call : one time-slot call, two time-slot call, and 6 time-slot call. In the simulation, the carried traffic and the blocking probability are calculated on the 3 different traffic cases of 8:1:1, 6:2:2, 4:3:3(one time-slot : two time-slot : 6 time-slot) multi slot calls. It is shown that the blocking probability for the periodic time slot allocation method is best. As a result, the periodic time-slot allocation method is the proper one for the multi-slot ATM switch.

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Effects of bracket slot size during en-masse retraction of the six maxillary anterior teeth using an induction-heating typodont simulation system

  • Kim, Ji-Yong;Yu, Won-Jae;Koteswaracc, Prasad N.K.;Kyung, Hee-Moon
    • The korean journal of orthodontics
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    • v.47 no.3
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    • pp.158-166
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    • 2017
  • Objective: To investigate how bracket slot size affects the direction of maxillary anterior tooth movement when en-masse retraction is performed in sliding mechanics using an induction-heating typodont simulation system. Methods: An induction-heating typodont simulation system was designed based on the Calorific Machine system. The typodont included metal anterior and resin posterior teeth embedded in a sticky wax arch. Three bracket slot groups (0.018, 0.020, and 0.022 inch [in]) were tested. A retraction force of 250 g was applied in the posterior-superior direction. Results: In the anteroposterior direction, the cusp tip of the canine in the 0.020-in slot group moved more distally than in the 0.018-in slot group. In the vertical direction, all six anterior teeth were intruded in the 0.018-in slot group and extruded in the 0.020- and 0.022-in slot groups. The lateral incisor was significantly extruded in the 0.020- and 0.022-in slot groups. Significant differences in the crown linguoversion were found between the 0.018- and 0.020-in slot groups and 0.018- and 0.022-in slot groups for the central incisor and between the 0.018- and 0.022-in slot groups and 0.020- and 0.022-in slot groups for the canine. In the 0.018-in slot group, all anterior teeth showed crown mesial angulation. Significant differences were found between the 0.018- and 0.022-in slot groups for the lateral incisor and between the 0.018- and 0.020-in slot groups and 0.018- and 0.022-in slot groups for the canine. Conclusions: Use of 0.018-in slot brackets was effective for preventing extrusion and crown linguoversion of anterior teeth in sliding mechanics.

Geometric Effects of Compartment Opening on Fuel-Air Mixing and Backdraft Behavior (개구부의 기하학적 형상이 구획실의 연료-공기 혼합특성 및 백드래프트 거동에 미치는 영향)

  • Ha, Suim;Oh, Chang Bo
    • Fire Science and Engineering
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    • v.33 no.1
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    • pp.30-38
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    • 2019
  • Mixing characteristics and backdraft dynamics were investigated using large eddy simulation for compartments initially filled with methane fuel. Four different opening geometries, i.e. conventional door opening case (Door) and the cases where horizontal door was implemented on the upper ($Slot_U$), middle ($Slot_M$) and lower part ($Slot_L$) of side wall, were considered in the simulations. For cases without ignition, the amounts of inflow oxygen and outflow fuel from the compartment opening were, from largest to smallest, Door > $Slot_U$ ~ $Slot_M$ > $Slot_L$. However, the fuel and oxygen were the best mixed for the $Slot_U$ case while the fuel and oxygen were not well mixed and in relatively separated two layers for the $Slot_L$ case. The global equivalence ratio defined by the amounts of fuel and oxygen in the compartment was not correlated reasonably with the peak pressure of backdraft. The peak pressure during backdraft was the highest for the $Slot_U$ case, a well mixed condition of fuel and air, and backdraft was not found for the $Slot_L$ where the pressure rise was not so high due to the mixing status. The peak pressures for the Door and $Slot_M$ cases were in between Door and $Slot_L$ cases. The peak pressure during backdraft was well correlated with the total amount of heat release until the instance of backdraft occurrence.

Effect of Pole to Slot Ratio on Cogging Torque and EMF Waveform in Permanent Magnet Motor with Fractional-Slot (분수슬롯을 가진 영구자석 전동기에서 극당 슬롯 비율이 코깅토크와 역기전력에 미치는 영향)

  • Lee, Kab-Jae;Lee, Ju
    • The Transactions of the Korean Institute of Electrical Engineers B
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    • v.52 no.9
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    • pp.454-459
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    • 2003
  • Conventional integral-slot design in permanent magnet(PM) motor tends to have a high cogging torque and large end turns, which contribute to copper losses. The fractional-slot design is effective compared to integral-slot design in the cogging torque and electromotive force(EMF) waveform. The effectiveness of fractional slot can be maximized by selecting optimal pole to slot ratio. This paper presents the effect of pole to slot ratio on the cogging torque and EMF waveform in the PM motor with fractional-slot. The effectiveness of the proposed designs has been confirmed by comparing waveform of EMF. cogging torque and torque ripple between conventional and new models.

Flow and Combustion Characteristic in an Array of Multiple Pre-Mixed Methane/Air Flame Jets (메탄/공기 다중 제트 예혼합 화염에서의 유동과 연소특성)

  • Kim, Young-Su;Lee, Dae-Rae;Ha, Man-Yeong;Chang, Young-June;Jeon, Chung-Hwan;Cho, Seung-Wan;Kang, Kil-Young;Yu, Jae-Hyun
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.31 no.6
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    • pp.547-557
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    • 2007
  • This study was conducted to investigate the flow and combustion characteristic of the experimental burner which was manufactured for the reflection of the oven and broil burner features. As slot shape, spacing between slots, and slot arrangement of the exit area which emits the mixing gas are different in case of oven burners and broil turners, the purpose of this study is to know the affection of the flame interaction and combustion characteristic according to the change of shape factors such as slot shape, slot arrangement, and slot-to-slot spacing. With no relation of the slot shape, as the spacing between slots became narrow, the occurrence of a lift-flame was delayed. So the combustion was possible in the leaner region, but the appearance of yellow-tip became a little fast. Slit slot port had the broadest operating range among the other slot shapes. Specially, from the side of lift-flame, as the jet that spreads downstream in the longitudinal slot was nearly circular just a few slot lengths away from the orifice, slot-to-slot spacing of the Slit port was closer than the other ports. These results could be expected through the computer numerical method and had a good agreement. As the spacing between slots increased, in case of Slit and Mix port, NOx emission rate was constant or decreased, but the NOx emission of Hole port was increased. CO emission rate of Slit and Hole port was increased as the slot-to-slot spacing was broadened.

A Study on Balanced Airport Slot Allocation Model Applying AIP Model -Focused on Incheon International Airport- (AIP 모델을 응용한 균형적 공항 슬롯 배정 모델에 관한 연구 -인천국제공항 사례 연구-)

  • Park, Hak-Soon;Kim, Kee-Woong
    • Journal of the Korean Society for Aviation and Aeronautics
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    • v.26 no.1
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    • pp.25-36
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    • 2018
  • This paper presents a new airport slot allocation model that uses AIP model to balance the use of airport slots within existing capacity based on the limitation of capacity expansion of airport slots. This new model is called a 'balanced airport slot allocation model', which integrates the airport facility usage system, which is applied independently without linkage, with the airport slot allocation system, introducing the market logical characteristic of 'administered incentive pricing. In this paper, we propose a new proposal to dramatically change the airport slot allocation system in the current situation where the expansion of facilities is limited in the urgent problem of the airport slot shortage, and it is necessary to balance the airport slot allocation. Airline paying for the use of an airport slot can determine the slot of the desired time slot based on the costs incurred by differentiating in the new airport slot allocation model. This is a system that allows the airlines that are willing to pay a lot of money in the market to use preferred airport slots.

Hydrualic Model Test for Siphon Spillway Capable of Controlling Discharge (유량조절이 가능한 사이펀 여수로 수리모형실험)

  • Jung, Jae-Sang;Jang, Eun-Cheol;Lee, Changhoon
    • Proceedings of the Korea Water Resources Association Conference
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    • pp.43-47
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    • 2019
  • In this study, capability of an air slot in a siphon spillway for controlling outflow discharge is investigated through hydraulic experiments. Arc and rectangular shapes of air slot are considered and the open area of air slot can be varied. Complex air-regulated flow occurs inside the the siphon spillway when the air slot is installed on it. The same discharge is measured at the same water level inside the reservoir when the water level rises or falls. Nondimensional discharge through the siphon spillway increases slowly as nondimensional open area of the air slot increases. The hydraulic experiments show that the control of outflow discharge of siphon spillway is possible by controlling the open area of the air slot.

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Analysis of Resonant Slots in the Narrow Wall of a Rectangular Waveguide (구형 도파관 측벽 공진 슬랏의 특성 해석)

  • 박정호;김민준
    • Journal of the Korea Institute of Information and Communication Engineering
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    • v.3 no.1
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    • pp.23-28
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    • 1999
  • Rectangular waveguide slot antenna which has simple structure, high efficiency, high trust and small size, is extending in a field of application such as many Radar and Microwave communication. A slot cut into a wall of waveguide is propagated electromagnetic wave to free space it interrtupts the flow of current inner conductor of waveguide. Therefore incident of slot, cutdepth, width, length, i.e. are important parameter of characteristic change of the slot antenna. Result from difficulty of theoretical analysis about slot frequently experimental measured data useful design and manufacture have been accomplished. In this paper, we find the suitable method of analysis that compare two analysis results with measured result of established literature - admittance of slot be solved by propagated power from electric field distribution of slot and mode current computation and accomplishment of computable chart which hasresonant length and cutdepth, incident of slot, i.e. and use the HFSS which applyed finite-element method obtain equal slot analyed method.

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5 GHz Bow-tie-shaped Meander Slot Antenna

  • Wi, Sang-Hyuk;Kim, Jung-Min;Yoo, Tae-Hoon;Park, Jae-Yeong;Yook, Jong-Gwan;Park, Han-Kyu
    • Journal of electromagnetic engineering and science
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    • v.2 no.1
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    • pp.50-55
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    • 2002
  • In this paper, Ive propose a bow-tie-shaped meander slot antenna find by a microstrip line to achieve compact size as well as wideband characteristic. While conventional bow-tie slot antennas exhibit wide band characteristic, they have relatively large size. On the other hand, the meander slot antennas are very small, but they reveal quite narrow bandwidth (typically less than 1 %). To realize miniaturized antennas balling large bandwidth, combination of the bow-tie slot and the meander slot geometries is proposed in this paper. Theoretical results show that the proposed antenna with uniform slot width is 65.5 % smaller than that of the conventional bow-tie antenna in size, while the bandwidth is 3 times larger than that of the meander slot antenna. Moreover, the non-uniform slot width antenna shows 60 % smaller in size and about 3.5 times wider in bandwidth than the previous antennas. Measured antenna performance reveals excellent agreement with the predicted values.