• 한국분무공학회지
• /
• 제23권3호
• /
• pp.109-113
• /
• 2018

The critical heat flux of spray cooling were measured on the test surface of 10 mm diameter made by stainless steel. The experiments were carried out for the droplet-flow-rate of $0.00002{\sim}0.003m^3/(m^2s)$ and liquid subcooling temperature of $40{\sim}75^{\circ}C$. Experimental results showed that the critical heat flux of spray cooling increased remarkably with the increase of droplet-flow-rate. Meanwhile, the effect of liquid subcooling on critical heat flux of spray cooling appeared weakly under the present experimental conditions. In additions, correlation between the dimensionless critical heat flux and Weber number based on droplet-floe-rate was developed for experimental results.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2001년도 춘계학술대회논문집D
• /
• pp.175-180
• /
• 2001

In this study, the minimum heat flux conditions are experimentally investigated for the spray cooling of hot plate. The hot plates are cooled down from the initial temperature of about $900^{\circ}C$, and the local heat flux and surface temperatures are calculated from the measured temperature-time history. The results show that the minimum heat flux point temperatures increase linearly resulting from the propagation of wetting front with the increase of the distance from the stagnation point of spray flow. However, in the wall region, the minimum heat flux point temperature becomes independent of the distance. Also, the experimental results show that the velocity of wetting front increases with the increase of the droplet flow rate.

• 전력전자학회:학술대회논문집
• /
• 전력전자학회 2001년도 Proceedings ICPE 01 2001 International Conference on Power Electronics
• /
• pp.418-422
• /
• 2001

To achieve a high performance in direct vector control of induction motor, it is essential to correct estimation of rotor flux. The accuracy of flux observers for induction machines inherently depends on parameter sensitivity. This paper presents an analysis method for conventional flux observers using Parameter Sensitivity. The Parameter sensitivity is defined as the ratio of the percentage change in the system transfer function to the percentage change of the parameter variation. We define the ratio between real flux and estimated flux as the transfer function, and analyzed a parameter sensitivity of this transfer function by simulation.

• 한국환경과학회지
• /
• 제8권3호
• /
• pp.293-297
• /
• 1999

Based on the monthly weather report of Korea Meteorological Administration (KMA) and daily sea surface temperature (SST) in Incheon harbor of National Fisheries Research and Development Institute, heat budget in Incheon coastal area was estimated. The temperature differences between the sea surface and near bottom were nearly within 1$^{\circ}C$. This indicate the mixing from the sea surface and the bottom. The net heat flux through the sea surface and the advection through the inner and outer bay was affected uniformly to the water body in Incheon coastal area. The net heat flux was about 110W/$m^2$ in maximum value on May, about -80W/$m^2$ in minimum on January. The net heat flux through the sea surface from the solar radiation was about 2.35$\times$${10}^5$W during the year. This heat flux flew out the bay through the advection by the same flux.

• Journal of international Conference on Electrical Machines and Systems
• /
• 제1권2호
• /
• pp.38-45
• /
• 2012

A novel kind of switched reluctance motor (SRM) with short flux path is proposed in this paper. Phase excitation in the SRM gives short flux paths, hence reducing the magnetomotive force required to drive the machine, resulting in significant reduction of copper wire and core losses compared to the typical SRM with diametric circulation of magnetic flux. To verify the performance, the characteristics analysis of a double-stator SRM, a 6/5 SRM with C-core structure, and a 4/5 two-phase SRM, which all have short flux paths, and a comparison with conventional SR motors are executed. The comparison demonstrates that the proposed motor offers some advantages in terms of torque and efficiency.

• 설비공학논문집
• /
• 제6권4호
• /
• pp.325-336
• /
• 1994

A numerical simulation of velocity and temperature fields and Nusselt number distributions is performed by using the algebraic stress model (ASM) for the velocity profiles and low Reynolds number ${\kappa}-{\varepsilon}$ model and the algebraic heat flux model(AHFM) for turbulent heat transfer in a $180^{\circ}$ bend with a constant wall heat flux. In the low Reynolds number ${\kappa}-{\varepsilon}$ model, turbulent Prandtl number is modified by considering the streamline curvature effect and the non-equilibrium effect between turbulent kinetic energy production and dissipation rate. Every heat flux term presented in the transport equation of turbulent heat flux is reduced to algebraic expressions in a way similar to algebraic stress model. Also. in the wall region, low Reynods number algebraic heat flux model(AHFM) is applied.

• 동력기계공학회지
• /
• 제11권4호
• /
• pp.92-97
• /
• 2007

This study aims at investigating the wear behavior of thermally sprayed Ni-based self-flux alloy coatings against different counterparts. Ni-based self-flux alloy powders were flame-sprayed onto a carbon steel substrate and then heat-treated at temperature of $1000^{\circ}C$. Dry sliding wear tests were performed using the sliding speeds of 0.2 and 0.8 m/s and the applied loads of 5 and 20 N. AISI 52100, $Al_2O_3$, $Si_3N_4$ and $ZrO_2$ balls were used as counterpart materials. Wear behavior of Ni-based self-flux alloy coatings against different counterparts were studied using a scanning electron microscope(SEM) and energy dispersive X-ray spectroscopy (EDX). It was revealed that wear behavior of Ni-based self-flux alloy coatings were much influenced by counterpart materials.

• KIEE International Transactions on Electrophysics and Applications
• /
• 제5C권5호
• /
• pp.204-210
• /
• 2005

Alternating current (AC) losses of two Bi-2223 ([Bi, Pb]: Sr: Ca: Cu: O = 2:2:2:3) tapes [(Tape I, un-twist-pitch) and the other with a twist-pitch of 10 mm (Tape II)] were measured and compared. These samples, produced by the powder-in-(Ag) tube (PIT) method, are multi-filamentary. Also, it's produced by non-twist and different twist pitch (8, 10, 13, 30, 50 and 70 mm). The critical current measurement was carried out under the environment in liquid Nitrogen and in zero-field by 4-probe method. Susceptibility measurements were conducted while cooling in a magnetic field. Flux loss measurements were conducted as a function of ramping rate, frequency and field direction. The AC flux loss increases as the twist-pitch of the tapes decreased, in agreement with the Norris Equation. Neutron-diffraction measurements have been carried out investigate the crystal structure, magnetic structures, and magnetic phase transitions in Bi-2223([Bi, Pb]:Sr:Ca:Cu:O)

• 설비공학논문집
• /
• 제13권10호
• /
• pp.974-981
• /
• 2001

In this study, the minimum heat flux conditions are experimentally investigated for the spray cooling of hot plate. The hot plates are cooled down from the initial temperature of about$ 900^{\circ}C$, and the local heat flux and surface temperatures are calculated from the measured temperature-time history. The results show that the minimum heat flux point temperatures increase linearly resulting from the propagation of wetting front with the increase of the distance from the stagnation point of spray flow. However, in the wall region, the minimum heat flux point temperature becomes independent of the distance. Also, the velocity of wetting front increases with the increase of the droplet flow rate.

• KSBB Journal
• /
• 제6권3호
• /
• pp.309-319
• /
• 1991

효소를 이용하여 대구피 젤라틴 가수분해물을 연속적으로 생산하기 위해 한외여과막 반응기에서의 젤라틴 가수분해 최적 공정조건 및 한외여과막 반응기를 장시간 작동하였을 때의 효소활성 저하원인을 규명하였다. 효소농도가 0.4mg/ml까지 증가함에 따라 기절의 전환율은 증가하였으나 기질의 경우는 농도가 증가함에 따라 전환율이 감소하였다. 유량(Flux)이 클수록 전환율은 감소되었으며 잔류시간이 길수록 전환율을 증가하였다. 한외여과막 반응기 장치의 작동시 가질의 전환율은 반응시간 1시간 부근에서 최대 전환율을 나타내었으며 시간당(8시간 작동) 평균 전환율 감소는 2.1%였다. 한외여과막을 통한 효소 누출은 반응시간 10~60분 범위에서 최대였으며 6시간 이후에는 거의 누출되지 않았다. 전체 효소량 중 누출량은 $50^{\circ}C$에서 16%인데 비해 $35^{\circ}C$에서는 12%였다. 그러나 효소 누출과 기질 전환율 사이에 명백한 상호관계는 나타나지 않았다. 막에 의한 효소의 활성저하는 작동시간 120분까지 나타났으며, 이때 초기속도의 36%가 저하하였다. 연속식(CSTMR)에서 $K_m$ 값은 회분식의 그것보다 20배 큰 반면 $K_2$ 10.5배 낮았다. 최적 가수분해조건은(기질농도 10%, $50^{\circ}C$, pH 8.0, 유량 7.31ml/min, 잔류시간 82분, S / E = 50w / w) 하에서의 생산량은 효소 mg당 가수분해물이 285mg으로 회분식 44.8mg에 비해 6배 이상이었다.