• 대한기계학회논문집B
• /
• 제27권4호
• /
• pp.511-517
• /
• 2003

An experiment is conducted to investigate the effect of air and water mass flow rates on cooling characteristics of mist impinging jet on a flat plate. The air mass flow rate ranges from 0.0 to 3.0 g/s, and water mass flow rates from 5.0 to 20.0 g/s. An air-atomizing nozzle is used fur the purpose of controlling air and water mass flow rates. The test section is designed distinctively from previous works to obtain local heat transfer coefficient distributions. Heat transfer characteristics of the mist impinging jet are explained with the aid of flow visualization. Surface temperature and heat transfer coefficient distributions become more uniform as air mass flow rate increases. The water flow rate provides substantial contribution to enhancement of cooling performance. On the other hand, The air mass flow rate weakly influences the averaged heat transfer rate when the water mass flow rate is low, but the averaged heat transfer rate Increases remarkably with the air mass flow rate in case of the high water mass flow rate.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2001년도 춘계학술대회논문집D
• /
• pp.528-533
• /
• 2001

An experimental study is carried out to investigate the effects of air and water mass flow rates on cooling characteristics of mist impinging jet on a flat plate. Experiments are conducted with air mass flow rates from 0.0 to 3.0 g/s, and water mass flow rates from 5.0 to 20.0 g/s. An air-atomizing nozzle is used for the purpose of controlling air and water mass flow rates. In this study, a new test section is designed to obtain local heat transfer coefficient distributions. Heat transfer characteristics of the mist impinging jet are explained with the aid of flow visualization. Surface temperature and heat transfer coefficient distributions become more uniform as air mass flow rate increases, and that the increases in water flow rate mainly enhance cooling performance. Air mass flow rate weakly influences averaged heat transfer coefficient when water mass flow rate is low, but averaged heat transfer coefficient increases remarkably as air mass flow rate in case of high water mass flow rate.

• 설비공학논문집
• /
• 제15권8호
• /
• pp.690-696
• /
• 2003

This paper presents the heat recovery performance of water fluidized-bed heat exchanger. Temperature and humidity ratio of waste gas are considered as important parameters in this study. Therefore, the heat recovery rate through water fluidized-bed heat exchanger for exhaust gases with various temperatures and humidity ratios can be estimated from the results of this study. Mass flow ratio (the ratio of mass flow rate of water to that of gas) and temperature of inlet water are also considered as important operating variables. Increase of heat recovery rate can be obtained through either high mass flow ratio or low temperature of inlet water with resultant low recovered temperature. The heat recovery performance with the mass flow ratio of about up to 10 has been investigated. The effect of number of stages of water fluidized-bed on the heat recovery performance has been also examined in this study.

• 생물환경조절학회지
• /
• 제18권3호
• /
• pp.200-207
• /
• 2009

This study was conducted to analyze the variations of air temperature, relative humidity and pressure in a low pressure chamber for plant growth. The low pressure chamber was composed of an acrylic cylinder, a stainless plate, a mass flow controller, an elastomer pressure controller, a read-out-box, a vacuum pump, and sensors of air temperature, relative humidity, and pressure. The pressure leakage in the low pressure chamber was greatly affected by the material and connection method of tubes. The leakage rate in the low pressure chamber with the welding of the stainless tubes and a plate decreased by $0.21kPa{\cdot}h^{-1}$, whereas the leakage in the low pressure chamber with teflon tube and rubber O-ring was given by $1.03kPa{\cdot}h^{-1}$. Pressure in the low pressure chamber was sensitively fluctuated by the air temperature inside the chamber. An elastomer pressure controller was installed to keep the pressure in the low pressure chamber at a setting value. However, inside relative humidity at dark period increased to saturation level.. Two levels (25 and 50kPa) of pressure and two levels (500 and 1,000sccm) of mass flow rate were provided to investigate the effect of low pressure and mass flow rate on relative humidity inside the chamber. It was concluded that low setting value of pressure and high mass flow rate of mixed gas were the effective methods to control the pressure and to suppress the excessive rise of relative humidity inside the chamber.

• Bulletin of the Korean Chemical Society
• /
• 제18권7호
• /
• pp.706-710
• /
• 1997

Isotope ratios of K, Ca, Cr and Fe are measured at cool plasma condition generated using high carrier flow rate and relatively low RF power of 900 W. Background molecular ions are suppressed to below 100 counts which give isobaric interference to the analytes. The background ions show different attenuation characteristics at increased carrier flow rate and hence for each element different carrier flow rate should be used to measure isotope ratios without isobaric interference. Isotope ratios are measured at both scan and peak-hopping modes and compared with certified or accepted ratios. The measured isotope ratios show some mass discrimination against low mass due to low ion energy induced from a copper shield to eliminate capacitive coupling of plasma with load coil.

• 한국추진공학회지
• /
• 제23권5호
• /
• pp.43-52
• /
• 2019

극저온 유체를 사용하는 발사체는 극저온 유체의 자연순환회로를 이용하여 발사체의 엔진 입구를 냉각한다. 자연순환회로의 질량유량은 순환시스템을 구성하는 배관의 길이 및 직경과 시스템으로 들어오는 열유입에 의하여 결정된다. 극저온 유체의 자연순환회로의 순환 검증 및 질량유량 측정을 위하여 실험을 진행하였으며, 이론적 계산 결과와 비교하였다. 비교 결과 12%의 오차가 있음을 확인하였다. 이 결과를 바탕으로 발사체 상단에서 저중력 구간 및 가속 구간에서의 자연순환 질량유량을 예측한 내용을 포함한다. 가속구간에서는 산화제탱크가 100 kPa 내외로 유지하는 것이 자연순환유량 증가에 이로웠으며, 저중력구간에서는 중력가속도의 크기에 따른 최적 압력으로 조절해야 자연순환유량의 최고값을 유지할 수 있었다.

• 대한기계학회논문집B
• /
• 제24권8호
• /
• pp.1085-1096
• /
• 2000

An experimental study was performed to examine the heat and mass transfer characteristics of $LiBr-H_2O$ solution flowing over a single horizontal tube with the water vapor absorption. Effects of the flow rate and the temperature of the solution at the top of the tube, the absorber pressure and the drainage pattern were considered. The absorption rate depends highly on the absorber pressure at the low flow rate condition while on the solution inlet temperature at the high flow rate condition. Also, when the flow rate is low, the absorption performance with the sheet flow drainage appeared to be higher than that with the dripping/jet drainage. However, at the high flow rate condition, the case became reversed. The liquid film became wavy with the higher absorption rate. The waves were more probable to form with the lower flow rate and temperature of the solution, and with the higher absorber pressure.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2004년도 춘계학술대회
• /
• pp.1783-1788
• /
• 2004

In the present paper, a micro flow sensor, which can be used at bio-delivery systems and micro heat pumps, is developed. For this, the micro flow sensor is integrated on a quartz wafer ($SiO_2$) and is manufactured by simple and convenient microfabrication processes. The micro flow sensor aims for measuring mass flow rates in the low range of about $0{\sim}20$ SCCM. The micro flow sensor is composed of temperature sensors, a heater, and a flow microchannel. The temperature sensors and the heater are manufactured by the sputtering processes in this study. In the microfabrication processes, stainless steel masks with different patterns are used to deposit alumel and chromel for temperature sensors and nichrome for the heater on the quartz wafer. The microchannel is made of Polydimethylsiloxane(PDMS) easily. A deposited quartz wafer is bonded to the PDMS microchannel by using the air plasma. Finally, we confirmed the good operation of the present micro flow sensor by measuring flow rate.

• 전기학회논문지P
• /
• 제58권4호
• /
• pp.563-567
• /
• 2009

The polymer electrolyte membrane fuel cell(PEMFC) with the advantages of low-operating temperature, high current density, low cost and volume, fast start-up ability, and suitability for discontinuous operation becomes the most reasonable and attractive power system for transportation vehicle and micro-grid power plant in a household. 200W PEM-type FCs system was integrated by this study, then the electrical characteristics and diagnosis of the fuel cell were analyzed with variations on mass flow rate and stack temperature. The ranges of the variations are 1~8L/min on $H_2$ volume and $20{\sim}70^{\circ}C$ on stack temperature.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2008년도 춘계학술대회논문집
• /
• pp.240-243
• /
• 2008

In this paper, the design of Centrifugal Compressor which is used in sizes 50 horse power has 8 pressure ratio and numerical analysis of the flow within compressor varying tip clearance length are performed. To get high pressure ratio with low power the exit height of impellers is low but compressor has very high speed of revolution. So compressor has high specific speed although mass flow rate is very small. The shape of impellers at the first stage is carried out. Flow and performance characteristics of impellers has been analyzed by using a commercial CFD program, $Fine^{TM}$/turbo. The result shows that loss coefficient is affected by tip clearance length and compressor has proper tip clearance length. It is possible to decrease loss by selecting apt tip clearance length.