• Journal of Advanced Marine Engineering and Technology
• /
• 제29권1호
• /
• pp.68-77
• /
• 2005

A transient liquid crystal technique has become one of the most effective ways in measuring the local heat transfer coefficients on the entire surface. The key Point of this technique is to convert the inlet flow temperature into an exponential temperature profile using a mesh heater. In order to verify the validity of this technique. the heat transfer characteristics on the wall surface by a pair of longitudinal vortices is investigated experimently and numerically. A standard ${\kappa}-{\varepsilon}$ is used for the numerical analysis of turbulent flow field. It is found from experiment and numerical analysis that two peak values exist over the whole domain. as the longitudinal vortices move to the farther downstream. these peak values decrease and the dimensionless averaged Nusselt number with the lapse of time is maintained nearly at constant values. The experiment results obtained from the present experiment in terms of the transient liquid crystal technique are in good agreement with the numerical results. Therefore, the transient liquid crystal technique developed for the measurement of heat transfer coefficient is proved to be a valid method.

• 설비공학논문집
• /
• 제18권9호
• /
• pp.729-737
• /
• 2006

Air-side forced convective heat transfer of a plate fin-tube heat exchanger is investigated by experimental measurement and numerical computation. The heat exchanger consists of staggered arrangement of refrigerant pipes of 10.2 m diameter and the pitch of fins is 3.5 m. In the experimental study, the forced convective heat transfer is measured at Reynolds number of 1082, 1397, 1486, 1591 and 1649 based on diameter of refrigerant piping and mean velocity. Average Nusselt number for the convective heat transfer coefficient is also computed for the same Reynolds number by commercial software of STAR-CD with standard $k-{\varepsilon}$ turbulent model. It is found that the relative errors of average Nusselt numbers between experimental and numerical data are less than 6 percentage in Reynolds number of $1082{\sim}1649$. The errors between experiment and other correlations are ranged from 7% to 32.4%. But the correlation of Kim at al is closest to the experimental data within 7% of the relative error.

• 센서학회지
• /
• 제23권4호
• /
• pp.284-289
• /
• 2014

In this paper, modeling of a gate/body-tied (GBT) PMOSFET photodetector with built-in transfer gate is performed. It can control the photocurrent with a high-sensitivity. The GBT photodetector is a hybrid device consisted of a MOSFET, a lateral BJT, and a vertical BJT. This device allows for amplifying the photocurrent gain by $10^3$ due to the GBT structure. However, the operating parameters of this photodetector, including its photocurrent and transfer characteristics, were not known because modeling has not yet been performed. The sophisticated model of GBT photodetector using a process simulator is not compatible with circuit simulator. For this reason, we have performed SPICE modeling of the photodetector with reduced complexity using Cadence's Spectre program. The proposed modeling has been demonstrated by measuring fabricated chip by using 0.35 im 2-poly 4-metal standard CMOS technology.

• 한국멀티미디어학회논문지
• /
• 제4권1호
• /
• pp.75-81
• /
• 2001

EBCOT(Embedded Block Coding with Optimized Truncation)는 현재 개발 중인 JPEG2000의 기본압축 코덱으로 본 논문에서는 EBCOT를 이용하여 하나의 압축 코덱에서 나온 이미지를 밴드 폭이 상이한 여러채널에 전송할 수 있는 방식에 대해 알아보고 이를 바탕으로 동영상에 적용하여 다채널 영상 전송 시스템을 제안한다. 또한 본 논문에서 사용되는 EBCOT가 JPEG에 쓰이는 RLC와 Huffman Coding 통한 VLC보다 압축 성능이 뛰어나다는 것을 실험적 결과를 통해 알 수 있고 JPEG에 적용할 경우 구조적으로 Paralleling의 증가와도 Error Resilience가 높다는 것을 알 수 있다. 다음으로 MPEG구조에 대해 알아보고 다 채널 영상 전송 시스템을 MPEG으로 구현 할 때의 Rate-Control이 힘든 문제와 원하는 Bit-Rate마다 코덱이 각각 있어야 하는 문제점 을 EBCOT를 적용시켜 해결할 수 있는 방법에 대해 제시한다.

• 대한기계학회논문집B
• /
• 제24권10호
• /
• pp.1368-1379
• /
• 2000

A numerical study on swirling pulverized coal combustion in an axisymmetric enclosure is carried out by applying the 2-phase weighted sum of gray gases model (WSGGM) approach with the discrete ordinate method (DOM) to model the radiative heat transfer equation. In the radiative transfer equation, the same polynomial equation and coefficients for weighting factors as those for gas are adopted for the coal/char particles as a function of partial pressure and particle temperature. The Eulerian balance equations for mass, momentum, energy, and species mass fractions are adopted with the standard and RNG k-${\varepsilon}$ turbulence model, whereas the Lagrangian approach is used for the particulate phase. The eddy-dissipation model is employed for the reaction rate for gaseous mixture, and the single-step and two-step first-order reaction model for the devolatilization process for coal. Special attention is given to establish the thermal boundary conditions on radiative transfer equation By comparing the numerical results with experimental ones, the radiation model used here is confirmed and found to provide an alternative for simulating the radiative transfer.

• 한국유체기계학회 논문집
• /
• 제3권4호
• /
• pp.22-29
• /
• 2000

Numerical analysis using three dimensional finite volume method for the discretization, adaptive grid method for the numerical accuracy, multiple rotating frame method for the rotating body and the standard $k-{\epsilon}$ model for the turbulent flow was performed to understand the heat transfer phenomena and to improve the efficiency of the scroll compressor. The temperature measurement was carried out under ARI condition. It was found that the fluid temperature in the compressor was predicted accurately while the temperature of the motor coil showed large discrepancy between the calculation and experiment due to the large anisotropy of the conductivity and non homogeneity. We found that the efficiency of the compressor depends on the inlet temperature of the compressing part and the flow pattern around the inlet region of the compressing part influences the inlet temperature due to high surface temperature of the main frame. The efficiency of the compressor using Coanda effect is higher than the previous one because the smooth suction at the inlet region of the compressing part leads to low heat transfer to the refrigerant of the compressor.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2003년도 춘계학술대회
• /
• pp.1548-1553
• /
• 2003

An experimental study of the absorption process of water vapor into a lithium bromide solution was performed. For the purpose of development of high performance absorption chiller/hater utilizing lithium bromide solution as working fluid, it is the most effective to improve the performance of absorber with the largest heat transfer area of the four heat exchangers. The experimental apparatus was composed of a plate type absorber which can increase the heat exchange area per unit volume to investigate more detail characteristics instead of the conventional type, horizontal tube bundle type. The size of plate absorbers were made for $0.4m{\times}0.6m$ and the design object of a refrigeration capacity was lRT. In this experiment, three kind plate absorbers which were flat plate, dimple plate and groove plate were used. The results were less than the design object values, that is, the refrigeration capacity was about $0.3{\sim}0.4RT$ and the overall heat transfer coefficient was $500{\sim}600kcal/m^2h^{\circ}C$ at the standard conditions.

• 대한기계학회논문집A
• /
• 제24권8호
• /
• pp.1931-1939
• /
• 2000

Operating excitation forces of the linear vibratory system are normally determined by direct measurement techniques using load cells, strain gauges, etc. But, hydraulic forces of the rotating turbomachinery such as centrifugal pumps are exerted on an impeller due to asymmety of the flow by the interaction between pump impeller and volute. So, investigations of wide range of hydraulic designs and geometric deviations are difficult by direct method. This paper presents a hybrid approach for fourier transformed operational excitation forces, which uses pseudo-inverse matrix of the transfer matrix for the system and the measured vibrational data with standard installed pump. The determination of the transfer function matrix is based on a linear rotor/stationary system and steady state harmonic response in finite element analysis. And, vibrational data is collected in both vertical and horizontal directions at inboard and outboard bearing housings. The results of the process may be enhanced by making acceleration measurements at many more locations than there are forces to be determined.

• Structural Engineering and Mechanics
• /
• 제76권1호
• /
• pp.67-81
• /
• 2020

Pretensioned concrete (PC) is widely used in contemporary construction. Bond of prestressing strand is significant for composite-action between the strand and concrete in the transfer and flexural-bond zones of PC members. This study develops a new methodology for quantifying the bond of 18-mm prestressing strand in PC members based on results of a pullout test, the Standard Test for Strand Bond (STSB). The experimental program includes: (a) twenty-four pretensioned concrete beams, using a wide range of concrete compressive strength; and (b) twelve untensioned pullout specimens. By testing beams, the transfer length, flexural-bond length, and development length were all measured. In the STSB, the pullout forces for the strands were measured. Experimental results indicate a significant relationship between the bond of prestressing strand to the code-established design parameters, such as transfer length and development length. However, the code-predictions can be unconservative for the prestressing strands having a low STSB pullout force. Three simplified bond equations are proposed for the design applications of PC members.

• 대한설비공학회:학술대회논문집
• /
• 대한설비공학회 2008년도 하계학술발표대회 논문집
• /
• pp.414-418
• /
• 2008

The effects of paper properties such as density, air permeability, water vapor transmission rate on the thermal performance of plate-type enthalpy exchanger were experimentally investigated. Three enthalpy exchanger samples having different properties were made, and were tested according to the standard test procedure (KS B 6879). Effective efficiencies were defined, which accounted for the air leakage between supply and exhaust streams. Results showed that paper density affected the sensible heat transfer of the samples. Sensible heat transfer increased with density of the paper. It was also shown that water vapor transmission rate alone was not a proper indicator for the efficiency of latent heat transfer. Air permeability should also be considered for adequate evaluation of the latent heat transfer. Best performance was obtained for the sample having highest paper density and moderate water vapor transmission ratio.