• 대한기계학회논문집B
• /
• 제21권5호
• /
• pp.713-723
• /
• 1997

Performance and heat transfer characteristics of an air conditioning system filled with hydro- carbon refrigerants are experimentally investigated. Single component hydrocarbon refrigerants (propane, isobutane, butane and propylene) and binary mixtures of propane/isobutane and propane/butane are considered as working fluids in the air conditioning system. Performances of each refrigerant are obtained at several compressor speeds and temperature levels of secondary heat transfer fluids. The cooling capacity and the coefficient of performance are obtained as test results. Heat transfer data of selected refrigerants are achieved from overall conductance measurement. Average heat transfer coefficients at different mass fluxes are shown and they are also displayed for different heat capacities of the system. Experimental results show that some hydrocarbon refrigerants have better characteristics than R22.

• 설비공학논문집
• /
• 제3권3호
• /
• pp.168-175
• /
• 1991

Experiments have been conducted to measure the overall heat transfer coefficient for gas-solid fluidized double pipe heat exchanger with finned tube. The average particle diameters of alumina are used in 0.4, 0.5, 0.6 and 0.9mm. And the effects of average particle diameter, static bed height and flow velocity on overall heat transfer coefficient have been investigated. Also the heat transfer effect of fluidized bed was compared with that of single phase forced convection and that of heat exchanger with smooth tube.

• 한국환경과학회지
• /
• 제6권1호
• /
• pp.25-31
• /
• 1997

The variations of gas hold-up, overall volumetric oxygen mass transfer coefficients and liquid circulation velocity in an internal loop reactor were investigated to manifest scale-up effect. The relationship between superficial gas velocity and gas hold-up were found as Ugr = 0.045 $\varepsilon$r in the pilot-scale and Ugr = 0.056 $\varepsilon$r in the bench-scale reactor. The overall volumetric oxygen mass tractsfer coefficient, KLa was slightly increased in the pilot-scale than in the bench-scale reactor. Flow regime was changed from the bubble flow to the churn-turbulent flow when the superficial gas velocity reached to 3.5 - 4 cm/sec in the pilot-scale.

• 동력기계공학회지
• /
• 제18권1호
• /
• pp.14-21
• /
• 2014

Piezoelectric fans are thin elastic beams whose vibratory motion is actuated by means of a piezoelectric material bonded to the beam. These fans have found use as a means to enhance convective heat transfer while requiring only small amounts of power. This study presents new types of models with heat sink having air passage and investigates experimentally their heat transfer characteristics. From the comparison results for four models, the heat transfer coefficients of model 1 are approximately 44~66% higher than those of the reference model 0. The model 1 show the best overall performance about heat transfer and cooling capability. As shown in above results, it is necessary to design the heat sink with air pass for cooling of electronic devices, in order to increase the convective heat transfer coefficient of a piezoelectric fan for electronic cooling.

• 수산해양교육연구
• /
• 제16권2호
• /
• pp.257-270
• /
• 2004

The two-phase closed thermosyphon is a heat transfer device capable of transfer large quantities of heat from a source to a sink by taking advantage of the high heat transfer rates associated with the evaporation and condensation of a working fluid within the device. A study was carried out with the performance of the heat transfer of the thermosyphon having 50, 60, 70, 80, 90 internal micro grooves in which boiling and condensation occur. A plain thermosyphon having the same inner and outer diameter as the grooved thermosyphon is also tested for comparison. Water, methanol and ethanol have been used as the working fluids. The liquid filling as the ratio of working fluid volume to total volume of thermosyphon, the inclination angle, micro grooves and operating temperature have been used as the experimental parameters. The heat flux and the boiling and the condensation heat transfer coefficient and overall heat transfer coefficient at the condenser and evaporator zone are estimated from the experimental results. The experimental results have been assessed and compared with existing correlations. Imura's and Kusuda's correlation for boiling showed in good agreement with experimental results within ${\pm}20$％ in plain thermosyphon. The maximum heat transfer rate was obtained when the liquid fill ratio was about 25%. The high heat transfer coefficient was found between 25o and 30o of inclination angle for water and between 20o and 25o for methanol and ethanol. The relatively high rates of heat transfer have been achieved in the thermosyphon with internal micro grooves. The micro grooved thermosyphon having 60 grooves shows the best heat transfer coefficient in both condensation and boiling. The maximum enhancement (i.e. the ratio of the heat transfer coefficients of the micro grooved thermosyphon to plain thermosyphon) is 2.5 for condensation and 2.3 for boiling.

• 대한기계학회논문집
• /
• 제12권4호
• /
• pp.833-846
• /
• 1988

본 연구에서는 후래시현상과 가열이 동시에 존재하면서 증발을 일으키는 수직 증발관내에서의 유동양식에 대해서, 우선 전기 프로우브를 이용하여 관내의 유동양식 에 따른 전기적 신호를 얻고, 시진실험 방법(photographic experimental method)을 통 하여 이를 확인한다. 또한, 전기 프로우브를 통하여 얻은 신호는 적절한 해석과정을 통해 수직 증발관내의 유동에 따른 기공률을 측정하는데 적용된다.

• 대한설비공학회:학술대회논문집
• /
• 대한설비공학회 2008년도 하계학술발표대회 논문집
• /
• pp.419-424
• /
• 2008

Heat transfer and pressure drop characteristics of welded plate heat exchanger are studied to apply it for the solution heat exchanger of 210RT absorption system. This study quantifies the effect of mass flow rate and strong solution concentration on the heat transfer coefficient and pressure drop in the plate heat exchanger. The concentration of weak solution is fixed at 55% and the strong solution varies 55%, 57%, and 59% in mass. The results show that the overall heat transfer coefficient and pressure drop increase linearly with increasing Reynolds number. It is also found that the heat transfer coefficient of hot side increases with increasing the concentration of strong solution while the strong solution concentration has no effect on heat transfer coefficient of cold side.

• 대한기계학회논문집
• /
• 제16권6호
• /
• pp.1171-1178
• /
• 1992

본 연구에서는 직접접촉식 열교환기를 이용한 실험을 통하여 열교환기 설계에 가장 중요한 열교환기 단위 체적당 총괄 열전달 계수를 시스템의 작동조건에 따라 구 하여 실제 설계자료로 이용하는 데 그 목적이 있다.

• 동력기계공학회지
• /
• 제11권2호
• /
• pp.20-25
• /
• 2007

The performance of air-to-air heat exchanger has been investigated with rotating porous plates newly developed in this study. With an equal interval of 18 mm, the rotating porous plates are installed inside the heat exchanger where the hot and cold airs enter at opposite ends. When flowing in opposite directions by the separating plate installed in the center of the rotating porous plates, the airs give and receive the heat each other. Dry bulb temperature is set by adjusting heat supply at heater. In order to measure the temperature distribution of the hot air side inside heat exchanger, the thermocouples are inserted between the plates. The first location of thermocouple is 10mm downstream from the inlet of heat exchanger, and succeeding ten locations are aligned at an equal interval of 18mm. From the experiment of air-to-air heat exchanger with the rotating porous plates, the heat transfer rate increased as both air flow rate and RPM of the rotating porous plate increased. It was found that the overall heat transfer coefficient increased with the increase in RPM of porous plate at the conditions of the same air flow rate.

• 한국추진공학회지
• /
• 제14권6호
• /
• pp.60-68
• /
• 2010

본 연구에서는 팁 형상이 가스터빈 블레이드의 팁 열전달에 미치는 영향을 알아보기 위하여 선형 캐스케이드의 블레이드에 설치된 평면 팁, 스퀼러 팁, Groove 팁들에 대하여 열전달 계수가 측정되었다. 블레이드 팁에서의 열전달 계수는 색상검출방식에 기반을 둔 천이액정법을 이용하여 측정되었으며 각각의 팁 형상에 대하여 팁 간극은 블레이드 스팬의 1.5%와 2.3% 두 조건에서 실험을 수행하였다. 캐스케이드 출구 속도와 블레이드 코드길이에 기초를 둔 Reynolds 수는 $2.48{\times}10^5$ 이다. Groove 팁 표면에서의 열전달 계수는 평면 팁보다 낮게 측정되었으며, 특히 흡입면을 따라 경사진 홈이 파인 팁에서는 스퀼러 팁보다 낮은 열전달 계수가 측정되었다.