• 한국지열·수열에너지학회논문집
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• 제14권4호
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• pp.20-26
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• 2018

In this study, the performance characteristics of a welded plate heat exchanger was investigated experimentally. Performance tests were carried out according to the flow rate and inlet temperature of working fluid. As a result, the heat transfer capacity increased by 335.5 kW with an increasing the flow rate and temperature difference between hot and cold side. However, the overall heat transfer coefficient was increased with the increase of flow rate, and it was not effected significantly from inlet temperature difference between hot and cold working fluid. The pressure drop was increased by 55.78 kPa with an increasing the frow rate when the flow rate ratio between hot and cold side 1:1. However, the tendency of pressure drop was difference when flow rate ratio wasn't 1:1. In case that the flow rate ratio between hot and cold side was not 1:1, the pressure drop at the low flow rate side was higher than that when the flow rate ratio was 1:1, while pressure drop of the other side was decreased compared to that when the flow rate ratio was 1:1.

• 전자공학회논문지S
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• 제36S권6호
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• pp.17-29
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• 1999

이 논문에서는 CDMA (Code Division Multiple Access) 셀룰러시스템에서 우선순위 Queue를 이용한 핸드오프(Handoff)의 채널항당기법을 제안하였다. 또한 제안한 기법에 대한 해석적 분석과 아울러 컴퓨터시뮬레이션을 통해 제안한 기법의 성능을 비 우선순위기법 및 FIFO(First In First Out) Quene기법의 성능과 비교하였다. 제안하는 기법의 핸드오프 채널할당방식은 새로운 파이롯(Pilot)에 대한 전력세기가 T-ADD 임계치 보다 크게 되는 시점부터 현재 사용중인 파일롯의 전력세기가 T-DROP 임계치 보다 낮고 T-DROP 타이머가 종료되는 시점까지를 핸드오프 처리가능 영역으로 정의하고 이를 최대 Queue 대기시간으로 결정하였다. 제안된 기법의 성능을 분석하기 위한 성능평가 척도는 강제 종료 확률 (Forced Termination Probability), 호 블럭킹 확률(Call Blocking Probability), 전체 제공 트래픽에 대한 수행 트래픽 비율(Carried Traffic to Total Offered Traffic), 평균 Queue크기(Average Queue Size) 및 핸드오프 시 Queue의 평균 지연시간(Average Handoff Delay Time in Prioritized Queue)등이다. 성능 시뮬레이션 결과, 제안된 기법이 전체 시스템 용량면에서 약간의 단점은 발생하지만 핸드오프 처리에 있어서 높은 성능을 유지함을 알 수 있었다.

• 설비공학논문집
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• 제15권12호
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• pp.1049-1059
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• 2003

R410A is considered as an alternative refrigerant to R22 for air conditioners. An experimental investigation was made to study the characteristics of the heat transfer and pressure drop for R410A flowing in a fin-and-tube heat exchanger used for commercial air-conditioning units. Experiments were carried out under the conditions of inlet refrigerant temperature of 6$0^{\circ}C$ and refrigerant mass flux varying from 150 to 250 kg/$m^2$s for refrigerant side. The inlet air has dry bulb temperature of 35$^{\circ}C$, relative humidity of 40% and air velocity varying from 0.68 to 1.6 m/s. Experiments show that air velocity decreased by 16% is needed for R410A than that of R22 for subcooling temperature of 5$^{\circ}C$, which resulted in air-side pressure drop decrease of 15% for R410A as compared to R22. As a consequence, in order to provide the same design condition of a condenser, the fan requires lower electric-power consumption with R410A than that with R22.

• 설비공학논문집
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• 제16권5호
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• pp.397-407
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• 2004

It is well known that some key parameters, such as evaporating temperature, refrigerant mass flow rate, face velocity and inlet air temperature, have significant influence on the evaporator performance. However performance studies related to a humid environment have been very scarce. It is demonstrated that the refrigerant mass flow rate, heat flux, water condensing rate and air outlet temperature of the evaporator significantly increase with air inlet relative humidity. As the air inlet relative humidity increases, the latent and total heat transfer rates increase, but the sensible heat transfer rate decreases. The purpose of this study is to provide experimental data on the effect of air inlet relative humidity on the air and refrigerant side pressure drop characteristics for a slit fin-tube heat exchanger. Experiments were carried out under the conditions of inlet refrigerant saturation temperature of 7 $^{\circ}C$ and mass flux varied from 150 to 250 kg/$m^2$s. The condition of air was dry bulb temperature of 27$^{\circ}C$, air Velocity Varied from 0.38 to 1.6 m/s. Experiments Showed that air Velocity decreased 8.7% on 50% of relative humidity 40% of that at degree of superheat of 5$^{\circ}C$, which resulted that pressure drop of air and refrigerant was decreased 20.8 and 8.3% for 50% of relative humidity as compared to 40%, respectively.

• Journal of Mechanical Science and Technology
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• 제18권9호
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• pp.1590-1603
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• 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.

• International Journal of Ocean System Engineering
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• 제2권3호
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• pp.151-159
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• 2012

The characteristics of an impact load and pressure were experimentally investigated. Drop tests were carried out using a modified Wigley with CB = 0.56. The vertical force, pressures, and vertical accelerations were measured. A 6-component load cell was used to measure the forces, piezo-electric sensors were used to capture the impact pressure, and strain-gauge type accelerometers were used to measure the vertical accelerations. A 50-kHz sampling rate was applied to capture the peak values. The repeatability of the measured data was confirmed and the basic characteristics of the impact load and pressure such as the linearity to the falling height were observed for all of the measurements. A simple formula was derived to extract the physical impact load from the measured force based on a simple mass-sensor-mass diagram, which was validated by comparing impact forces with existing data using the mathematical model of Faltinsen and Chezhian (2005). The effects of the elasticity of the model and change in acceleration during the water entry were investigated. It is interesting to observe that the impact loads occurred and reached peak values at the same time duration after water entry for all drop heights.

• 동력기계공학회지
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• 제8권2호
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• pp.31-38
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• 2004

The main purpose of this study is to investigate the characteristics of hybrid collection system combined with centrifugal force of cyclone and filtration of bag filter in one unit system. The experiment and numerical simulation are executed for the analysis of collection efficiency and pressure drop characteristics of hybrid system in comparison with those of a general fabric bag filter with the various experimental parameters such as inlet velocity(filtration velocity), dust concentration and dust type, etc.. In present system, dust particles tangentially coming into the system body are controlled by the centrifugal force effect, and the next collection is made out by the filtration mechanism in the fabric filter media. Therefore, the effective first collection causes the decrease of dust loading on the fabric filter, and it presents quite a lower pressure drop of fabric filter than that of a general fabric filter. At the inlet velocity, $21{\sim}27m/sec$ and inlet concentration(fly ash) $300mg/m^3$, pressure drops through the filter media of hybrid system are shown lower as $10{\sim}22mmH_2O$ comparing to those($17{\sim}33mmH_2O$) of a general fabric bag filter.

• 동력기계공학회지
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• 제17권6호
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• pp.63-72
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• 2013

The main purpose of this study is to analyze the collection characteristics of multi-layer multi-stage porous plate system with ionizer and dielectric-substance experimentally. The experiment is carried out to analyze the characteristics of pressure drop and collection efficiency for the present system with experimental parameters such as applied voltage, inlet velocity, stage number and inlet particle concentration, etc. In results, for multi-layer multi-stage porous plate system of inflow type, at 5 stage and $v_{in}$=2.58 m/s, the pressure drop becomes lower 15 $mmH_2O$ as 95 $mmH_2O$ than that of non-inflow type system. It is estimated that for the present system with ionizer and dielectric-substance, the collection efficiency represents 98.5% showing higher 5.2% comparing to that of multi-layer multi-stage porous plate system without ionizer and dielectric-substance at 5 stage, $v_{in}$=2.58 m/s and inlet concentration $3g/m^3$(fly ash).

• Journal of Welding and Joining
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• 제28권6호
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• pp.28-34
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• 2010

This paper was described on investigation to prevent porosity in high speed MIG Welding of Al 6082-T6. Porosity measurement was carried out by using image analysis of micrographs with the help of an analysis software. The main parameter was arc length and torch progressive angle. The porosity ratio was increased as arc length was increased. The arc length was increased depending upon the output voltage. By proper selection of pulse waveform parameter, the stable arc of one pulse one drop was generated. The porosity ratio of optimum condition in one pulse one drop was lower than high voltage condition. When torch progressive angle was an angle of advance $10^{\circ}$, porosity ratio was minium.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.1491-1498
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• 2003

Droplet evaporation can be used to transfer large amounts of energy since heat is transferred across a thin liquid film. Spreading the drop over a larger area can enhance this heat transfer. One method of accomplishing this is to dissolve gas into the liquid. When the drop strikes the surface, a gas bubble nucleates and can grow and merge within the liquid, resulting in an increase in the droplet diameter. In this study, time and space resolved heat transfer characteristics for a single droplet striking a heated surface were experimentally investigated. The local wall heat flux and temperature measurements were provided by a novel experimental technique in which 96 individually controlled heaters were used to map the heat transfer coefficient contour on the surface. A high-speed digital video camera was used to simultaneously record images of the drop from below. The measurements to date indicate that significantly smaller droplet evaporation times can be achieved. The splat diameter was observed to increase with time just after the initial transient dies out due to the growth of the bubble, in contrast to a monotonically decreasing splat diameter for the case of no bubbles. Bursting of the bubble corresponded to a sudden decrease in droplet heat transfer.