• 설비공학논문집
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• 제12권5호
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• pp.457-465
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• 2000

An experiment was carried out to evaluate the thermal performance of the wire-coil inserts method. Tested were the smooth tubes with the wire-nil inserts of various pitch and helix angle combinations. Test fluids were the 50%-solution of the ethylene glycol and the Hue water. Heat transfer coefficient and friction factors were deduced from the measured values of temperatures, flowrates and pressure drops. A unified dimensionless correlation for the heat transfer coefficients was developed as a function of the pitch to diameter ratio, the Reynolds number and the Prandtl number. An exergy analysis was performed to evaluate an optimal operating condition with the wire-coil inserts.

• International Journal of Air-Conditioning and Refrigeration
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• 제9권1호
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• pp.11-19
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• 2001

To establish optimum cycle of the inverter-driven heat pump with a variation of frequency, the bypass orifice, which was a short tube haying a bypass hole in the middle, was designed and tested. Flow characteristics of the bypass orifice were measured as a function of orifice geometry and operating conditions. Flow trends with respect to frequency were compared with those of short tube orifices and capillary tubes. Generally, the bypass orifice showed the best flow trends among them. and it would enhance the seasonal energy efficiency ratio of an inverter heat pump system, Based on experimental data, a semi-empirical flow model was developed to predict mass flow rate through bypass orifices. The maximum difference between measured data and model`s prediction was within $\pm$5%.

• 설비공학논문집
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• 제10권1호
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• pp.56-65
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• 1998

In this paper, experimental investigation of capillary tube performance for R-407C is performed. The experimental setup is made of real vapor-compression refrigerating system. In this study, mass flow rate is measured for capillary tubes of various diameter and length as inlet pressure and degree of subcooling are changed. These data are compared with the results of a numerical model. The mass flow rates of the numerical model are less than by 14% compared with the measured mass flow rates. It is found that mass flow rate and length for R-407c are less than those of R-22 under the same condition. Also based on this experimental study and the numerical model, a set of capillary tube selection charts for R-407C is constructed.

• 설비공학논문집
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• 제9권3호
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• pp.376-388
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• 1997

In this study, an experiment was performed to investigate the characteristics of pressure drop and heat transfer of multi-channel tubes for automotive condenser using HFC-134a as an alternative refrigerant. The mass flux and inlet saturation pressure of the refrigerant were controlled, respectively, in the range of 200 to $500kg/m^2s$ and 1.0 to 1.6MPa. Pressure drop and heat transfer coefficient were compared with the previously proposed correlations and new correlations based on Traviss' correlation were suggested. Prediction of pressure drop and heat transfer coefficient based on the new correlations agrees with experimental results within ${\pm}9%$ and -18~+11%, respectively.

• 설비공학논문집
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• 제9권3호
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• pp.333-342
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• 1997

An experimental study has been carried out to investigate the effects of the combination of the different wire mesh number in a regenerator and the tube number in a cooler on the cooling performance of a Vuilleumier cycle heat pump. Effects of operating conditions, such as charging pressure, operating speed, and heat input, on the cooling performance are also studied. The experimental results obtained indicate that the cooling performance could be improved with the proper combination of different wire meshes in a regenerator. More tubes in a cooler are desirable for better cooling performance. It is also found that the cooling capacity is enhanced, whereas COP is reduced with an increase in the heater tube temperature and the revolution speed. Both the cooling capacity and COP are incereased with a higher charging pressure.

• 설비공학논문집
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• 제13권5호
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• pp.333-340
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• 2001

A centrifugal water chiller using alternative refrigerant R134a have been developed. The prototype was designed to have refrigeration capacity of 300RT. Its compressor employs a single high-speed impeller, airfoil diffuser and collector. Newly developed enhanced tubes were installed in the evaporator and the condenser to reduce the required head for the compressor. Off-design characteristics at various conditions, performance test of the compressor and analysis of the refrigeration cycle were performed. So the probability of use in part load condition was checked and the direction for revision was suggested.

• 설비공학논문집
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• 제13권8호
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• pp.730-738
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• 2001

This work discusses the pressure droop, heat and mass transfer of the finned-tube heat exchangers having 7 mm tubes and offset strips in dehumidifying applications. It focuses on the fin material saving and the reduction of pressure drop. The experiment was conducted using three times scaled-up models to simulate the performance of the prototype. Eight kinds of fins having different strips and S shape edges were tested. the area density of the strip was a major factor and its shape and the location were secondary factors on the pressure drop, the heat and mass transfer. The reduced-area fin can almost equal the non-reduced fin in the aspect of heat and mass transfer. The strip fins proposed in the present work can considerably reduce both the pressure drop and the fin material for similar thermal load.

• International Journal of Air-Conditioning and Refrigeration
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• 제9권2호
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• pp.19-27
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• 2001

In the present study, the effects of film Reynolds number (60∼200) and volumetric content of non-absorbable gases (0∼10%) in water vapor on the absorption process of aqueous LiBr solution were investigated experimentally. The formation of solution film on the horizontal tubes of six rows was observed to be complete for Re>100. Transition film Reynolds number was found to exist above which the Nusselt number and Schmidt number diminishes with solution flow rate. As the concentration of non-absorbable gases increased, mass transfer rate decreased more seriously than heat transfer rate did. the degradation effects of non-absorbable gases seemed to be significant especially when small amount of non-absorbable gases was introduced to the pure water vapor.

• 설비공학논문집
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• 제13권8호
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• pp.667-673
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• 2001

As an alternative cooling method to reduce environmental hazard, vortex tubes have been studied for energy separation into cold and hot streams. Hence, the experiments were carried out systematically to find the best ratio of vortex chamber diameter to tube diameter. Also, the work was don to investigate how inlet pressure and geometric ratios of vortex tube affected temperature differences at tow needs as ell as cooling capacity and cooling efficiency. The result showed that the maximum temperature differences at the both ends and the maximum cooling efficiency were obtained when the ratio of vortex chamber diameter was about 1.45, while the inlet pressure ws not higher than 0.7 MPa.

• 설비공학논문집
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• 제11권1호
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• pp.109-116
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• 1999

To establish optimum cycle of the inverter-driven heat pump with a variation of frequency, the bypass orifice, which is a short tube having a bypass hole in the middle, was designed and tested. Flow characteristics of the bypass orifice were measured as a function of orifice geometry and operating conditions. Flow trends with respect to frequency were compared with those of short tube orifices and capillary tubes. Generally, the bypass orifice showed the best flow trends among them, that will enhance the seasonal energy efficiency ratio of an inverter heat pump system. Based on experimental data, the semi-empirical flow model was developed to predict mass flow rate through bypass orifices. The maximum difference between measured data and model's prediction was within ${\pm}5%$.