Oh-Kyung Kwon

Cycle analysis of air-cooled absorption chiller using a new working solution

A cycle analysis was achieved to predict the characteristics by comprehensive modelling and simulation of an air-cooled, double-effect absorption system using the new H2O/LiBr+HO(CH2)3OH solution. The simulation results showed that the new working fluid may provide the crystallisation limit 8% higher than the conventional H2O/LiBr solution. With a crystallisation margin of 3 wt%, the optimal solution distribution ratio was found to be in the range of 37–39%. Variation of cooling air inlet temperature had a sensitive effect on the cooling coefficient of performance (COP) and corrosion problem. The simulation of heat exchangers with UA value revealed that the absorber and evaporator were relatively important for an air-cooled system compared with the condenser and the low temperature generator. The effects of cooling air flow rate, circulation weak solution flow rate and chilled water inlet temperature were also examined. The new working fluid may provide a COP approximately 3% higher than the conventional H2O/LiBr solution in normal conditions of circulation weak solution.

Performance Evaluation of Plate Heat Exchanger with Chevron Angle Variations

The objectives of this paper are to measure the heat transfer and pressure drop of the plate heat exchangers for absorption system applications. Three types of plate heat exchangers with different chevron angles are tested in the present experiment. Heat transfer and pressure drop performance of plate heat exchangers are measured in various operating conditions, and compared each other. The results show that the heat transfer rate of high theta (120°) and mixed theta plate heat exchanger increases about 118% and 98% at the solution flow rate 350 kg/h compared to that of low theta (60°), respectively. The effectiveness of high theta was evaluated about 0.53 ~ 0.85 in this experimental range. The experimental correlations of the Nu and f were developed with error bands of ±7% and ±12%.

Experimental study of heat and mass transfer on an absorber with several enhancement tubes

An experimental study of the absorption process of water vapor into a lithium bromide solution was performed. For the purpose of the development of a high-performance absorption chiller/heater utilizing a lithium bromide solution as the working fluid, it is the most effective way to improve the performance of the absorber with the largest heat transfer area of the four heat exchangers. This paper considers a bare tube, bumping bare tube, floral tube, and twisted floral tube for the absorber of an absorption chiller/heater. The floral and twisted floral tubes have about 40% higher heat and mass transfer performance than the bare tube conventionally used in an absorber. Therefore, floral and twisted floral tubes are expected to realize high heat and mass transfer performance.

A Study on Thermal Performance of Micro Channel Water Block for Computer CPU Cooling

Abstract The object of this paper is to study on the thermal performance of a micro channel water block for computer CPU cooling. The effects of liquid flow rate, micro channel width and height on the thermal performances of water block are investigated experimentally. The water block was fabricated Al and machined with a micro milling. The water block consisted of rectangular micro channels 0.5 to 0.9 mm width and 1.5 to 4.5 mm height. The experiments were conducted using deionized water, over a liquid flow rate ranging from 0.2 to 2.0 kg/min. The base temperature and thermal resistance decrease with increasing of liquid flow rate. The increase of a channel height is more effective on the thermal resistance than the decrease of a channel width. At the flow rate of 0.7 kg/min, input power of 100 W, the base temperature and thermal resistance of sample 6 is 33℃ and 0.13 ℃/W respectively. 기호설명 C p : 비열 [J/kg․℃] D h : 수력직경 [mm] H ch : 채널높이 [mm] I : 전류 [A]△ P : 압력강하 [kPa] Q : 열전달량 [W]

Performance Characteristics of Fin-Tube Heat Exchanger having Large Diameter Oval Tube for Dryer

Abstract The objective of this paper is to provide design data of fin-tube heat exchanger which have a large diameter ovaltube for dryer application. In this study, the heat transfer and pressure drop performance characteristics of the fin-tube heatexchanger were compared with Dittus-Boelter and a new correlation equation using Wilson plot method. The simulationresults based on section by section method were compared with experimental results. These results showed that a new correlationequation using Wilson plot method provided better prediction, about 3 to 12%, than the Dittus-Boelter equation, from theexperiment comparison. Also, the pressure drop of simulation results showed much more deviation with the experimentalresults.. Key words Fin-tube heat exchanger(핀-관 열교환기), Heat transfer coefficient(열전달계수), Oval tube(타원관), Prssure drop(압력강하)†Corresponding author, E-mail: kwonok@kitech.re.kr 기호설명 A ： 면적 [ ㎡ ] C ： 열용량 [W/k] D ： 직경 [m] D h ： 열교환기 수력직경 [m] F p ： 핀간격 [m] h ： 열전달계수 [W/ ㎡․ K] k

Performance Evaluation of a Two-Stage Compression Heat Pump System for District Heating

ABSTRACT:The objective of this study is to investigate the performance of a two-stage com-pression heat pump system for district heating. The experimental setup of heat pump consists of compressor, condenser, evaporator, expansion device, intercooler, flash tank, oil separator and accumulator. The experimental evaluations on the two-stage compression cycle were carried out under various operating conditions which were heat source temperature, the degree of compressor inlet superheat, and intermediate pressure. The temperature ranges of unutilized energy as the heat source were used in the test conditions. As the heat source temperature increased from 10℃ to 30℃, the COP and heating capacity of the heat pump system increased by 22.6% and 45.8%, respectively. The performance of the two-stage heat pump system increased by 5.2% with the variation of the intermediate pressure in the same heat source temperature conditions.Keywords:District heating(지역난방), Intermediate pressure(중간압), Two-stage compression heat pump(2단 압축 히트펌프), Unutilized energy(미활용에너지)

A Study on Heat Transfer and Fluid Flow Characteristics of Radiator for Computer CPU Cooling

The performance of louver-finned flat-tube and fin and tube radiators for computer CPU liquid cooling was experimentally investigated. In this study, 7 samples of radiators with different shape and pass number (1, 2, 10) were tested in a wind tunnel. The experiments were conducted under the different air velocity ranged from 1 to 4 m/s. The water flow rate through a pass was 1.2 LPM. Inlet temperatures of air and water were and respectively. It was found that the best performance was observed in the louver-finned flat-tube sample considering pressure drop and heat transfer coefficient.

An Experimental Study on Beat and Mass Transfer Characteristics of Helical Absorber

In this study, heat and mass transfer characteristics of five components solution (LiBr＋Lil＋LiNO＋LiCl＋) which could be substituted for commonly used LiBr solution are tested using a helical absorber. The arrangement of helical-typed heat exchangers allows to make the system more compact as compared to conventional one. The effects of experimental parameters, such as the solution flow rate, cooling water, solution temperature, solution concentration and surfactant have been investigated in view of the heat and mass transfer. The results of the experiment of heat and mass transfer performance show that five components solution should have 2％ higher concentration fur equal absorption capacity of LiBr solution. But considering that five components solution have higher solubility than LiBr solution about 4％ high concentration, five components solution could be applied to a small sized water cooled or air cooled absorption chiller/heater. The increase of heat and mass transfer coefficient by surfactant addition is about 25∼30％ and 23∼40％ respectively.

Influence of Surfactant on Mass Transfer of Vertical Absorber

This study was concerned with the enhancement of mass transfer by surfactant added to the aqueous solution of LiBr. Different vertical inner tubes were tested with and without an additive of normal octyl alcohol. The test tubes were a bare tube, groove tube, corrugate tube and inserted spring tubes. The additive concentration of normal octyl alcohol as a surfactant is about 0.08mass%. The Sherwood number was measured as a function of film Reynolds number 20~200. The experimental results were compared with those which use no surfactant. The enhancement of mass transfer by Marangoni convection effect which was generated by addition of the surfactant is proved for each testing tube Especially, it is clarified that the tube with the spring has the highest enhancement effect. A correlation of the experimental mass transfer data for the bare, groove, corrugate and insert spring tubes results expressed as the form of Sh

Heat Transfer Enhancement with Surfactants in Horizontal Bundle Tubes on Absorber

This research was concerned with the enhancement of heat transfer by surfactant added to the aqueous solution of LiBr. Different horizontal tubes were tested with and without an additive of normal octyl alcohol. The test tubes were a bare tube, floral tube and hydrophilic tube. The additive mass concentration was about 0.055.5%. The heat transfer coefficient was measured as a function of solution flow rate for the range of 0.010.034 kg/ms. The experimental results were compared with cases without surfactant. The enhancement of heat transfer by Marangoni convection effect generated by the addition of the surfactant is observed in each test tube. The increase of heat transfer coefficient by surfactant addition is about 3590% for bare tube, 4070% for the floral tube, 3050% for the hydrophilic tube and was higher for the cases with smaller a little solution flow rates.