• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.5 no.3
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• pp.187-197
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• 1993

In this study, the numerical analysis and experiments of the hot water storage using the thermal stratification techniques were carried out. The CPU time for a typical run of the the thermal stratification up to 900 seconds took one week for a $81{\times}31$ mesh size and 10 days for a $118{\times}31$ mesh size, respectively, for a cylindrical shape of the storage. In the initial stage, the numerical results were in favorable agreement with the experimental results, but it showed that the temperature gradients in the storage decreased gradually with time. It was also found that the increase of ${\delta}t$ decreased the convergent speed due to the intensive fluctuation of the velocity field in every iteration. The increase of numbers of grids is projected to forecast a more accurate result, but it made the computing time longer and woul slow down convergence. At the experiments of the flow visualization, it was confirmed that the thermal stratification was apparently built up due to the installation of diffuser at the lower part of the storage. Thus, the thermal performance of the storage could be improved by installing the diffusers at the inlet and outlet.

• Journal of Magnetics
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• v.16 no.4
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• pp.457-460
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• 2011

In this paper, magnetic property and magnetocaloric effect (MCE) in perovskite manganites of the type $La_{(0.75-X)}Ce_XCa_{0.25}MnO_3$ (x = 0.0, 0.2, 0.3 and 0.5) synthesized by using the standard solid state reaction method have been reported. From the magnetic measurements as a function of temperature and applied magnetic field, we have observed that the Curie temperature ($T_C$) of the prepared samples strongly dependent on Ce content and was found to be 255, 213 and 150 K for x = 0.0, 0.2 and 0.3, respectively. A large magnetocaloric effect in vicinity of $T_C$ has been observed with a maximum magnetic entropy change (${\mid}{\Delta}S_M{\mid}_{max}$) of 3.31 and 6.40 J/kgK at 1.5 and 4 T, respectively, for $La_{0.55}Ce_{0.2}Ca_{0.25}MnO_3$. In addition, relative cooling power (RCP) of the sample under the magnetic field variation of 1.5 T reaches 59 J/kg. These results suggest that $La_{0.55}Ce_{0.2}Ca_{0.25}MnO_3$ compound could be a suitable candidate as working substance in magnetic refrigeration at 213 K.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.1 no.4
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• pp.265-275
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• 1989

An experimental study of decaying swirl air flow has been obtained by tangential inlet in a straight tube with Reynolds number range 20,000~40,000. The friction factor, swirl angle, velocity profiles and turbulent intensity are measured by using micro-manometer and hot-wire anemometer. It is found that the swirl flow behaviors depend on the swirl intensity along the test tube.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.2 no.2
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• pp.99-104
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• 1990

A Study has been conducted experimentally on heat transfer characteristics of louvered fin heat exchangers with various louvered positions in air. The experimental results are as follows; 1. Mean heat transfer coefficient is increased with increasing air velocity and decreasing temperature difference. The maximum value of heat transfer coefficient shows at 10㎜ backward louvered fins. 2. Pressure drop is increased with increasing air velocity and apparently depended on the louvered positions at V>10m/sec. 3. $\bar{h}/{\Delta}P$ is decreased with increasing air velocity and its maximum value shows at 10mm forward louvered fins and its minimum value shows at plate fins.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.4 no.2
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• pp.65-71
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• 1992

In most absorption machines, absorption enhancement has been achieved by adding small amount of surfactant additive, which introduced the surface tension difference between absorbent and surfactant droplets in the vapor absorption. The aim of this study is to understand a basic mechanism of Marangoni convection and its effectiveness in the vapor absorption enhancement. In this study, nonflowing aqueous solution of LiBr 60 mass% was exposed to saturated water vapor under the condition that two dropwises surfactant were fixed on the absorbent surface. Our experiments achieved to visualize the enhanced heat and mass transfer phenomena by the effect of Marangoni convection through the laser holographic interferometry. Also, Marangoni convection behavior was obtained by using tracer method.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.9 no.3
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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.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.2 no.4
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• pp.288-294
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• 1990

A study has been conducted experimentally on heat transfer characteristics of louvered fin heat exchangers with various fin spacings in air. The experimental results are as follows; 1. Mean heat transfer coefficient is increased with increasing air velocity and the optimum fin spacing shows at S=5mm. 2. Pressure drop is increased with increasing air velocity and its maximum value shows at S=3.5mm and its minimum value shows at S=6mm. 3. $\bar{h}/{\Delta}P$ is decreased with increasing air velocity and its maximum value shows at S=5mm and its minimum value shows at S=3.5mm.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.7 no.1
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• pp.13-19
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• 1995

An experimental investigation has been made for flow in a circular cylinder with a rotating bottom disk. Flow system considered in this paper is a characteristic model of interior flows of an electric washing machine. Flows in a tub of an electric washing machine are driven by a rotating bottom disk called a pulsator. The simple and characteristic model was composed of a circular cylinder with impulsively rotating endwall disk and a viscous fluid in it. Rotational motion of the pulsator is periodic and alternative in rotation direction. The flow field in the interior region is governed by a horizontal boundary layer forms on the impulsively rotating disk. Experimental approach was accomplished by adopting an image processing technique for velocity measurements. Comprehensive details of the flow structure are presented. Also a meridional circulation is obtained by tracking image particles suspended in the fluid. Flow structure and data are successfully procured for this complex rotating flow field.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.4 no.1
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• pp.1-10
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• 1992

The purpose of this paper is to provide an efficient method of operating and designing HVAC systems for reasonable energy consumption in building. Accroding to the conditions of indoor temperature and humidity, and the methods of dividing and grouping the capacity of boiler and refrigerator, the amount of their annual energy consumptions is simulated by using an energy analysis program which is developed in this paper, and opatimal design methods of HVAC system are suggested as well.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.7 no.1
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• pp.73-80
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• 1995

The object of the present study is to develop a high performance evaporator for automotive air conditioner. The experiment has been conducted on evaporative heat transfer coefficient inside a plate type heat exchanger with a sharp 180-degree turn flow. The test plates have different formed surface, cross-ribbed channel and elliptical-ribbed channel. Also experimental study has been performed to determine optimal design in elliptical-ribbed plate heat exchanger with different turn clearance. In addition to the above experiments, refrigerant behavior and surface temperature distribution in the plate heat exchanger were observed using color thermoviewer(infrared thermometer). In this experiment, working fluid was used R-12 and test conditions were as follows : (1) saturation pressure of $2.116kg/cm^2$, (2) mass fluxes of 40 to $70kg/m^2s$, (3) heat fluxes of 4,500 to $7,300W/m^2$, (4) inlet quality of 0.1 to 0.7. The results indicated that the evaporative heat transfer coefficient of an elliptical-ribbed plate heat exchanger was higher than that of cross-ribbed plate heat exchanger. Also optimal turn clearance in an elliptical-ribbed plate heat exchanger was determined.