• Journal of the Korean Solar Energy Society
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• v.32 no.6
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• pp.127-133
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• 2012

This paper is an experimental study on the freezing protection valve used for solar water heating, air-conditioning systems, and plumbing systems. When the phase change occurs from liquid to solid, most of the substances except water volumetrically shrink. And referred to as PCM(Phase Change Material) a substance with such properties, the phase change temperature varies depending on the material. To prevent the freezing of the plumbing system, such as air-conditioning system in the winter season, we developed a several types of freezing protection valve using PCM whose freezing temperature are $2-4^{\circ}C$. The working principle of the freezing protection valve is that the fluid inside the pipe is released to prevent the system-collapse when fluid temperature reaches the freezing temperature of the PCM. And then the valve is closed and returned to the original position automatically when the temperature of the operating fluid rises. In this paper, the operating temperatures, discharge flow rate and the response characteristics of the valve during the operation are tested and investigated. From the results of this research the freezing protection valves employing PCM are expected to be commercialized in the near future.

• Journal of Power System Engineering
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• v.17 no.5
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• pp.58-63
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• 2013

In this study, the effect of deep ocean condenser inlet temperature ($T_{DOI}$), condenser inlet pressure ($P_{cond,in}$), and thermal diffusivity on system efficiency of some selected refrigerants was analyzed using HYSYS. The proposed DOTEC cycle is similar to the reheat Rankine cycle but eliminates irreversibilities by bleeding a fraction of the steam between certain stages of the turbine. The evaporator inlet mass flow rate, inlet temperature of turbine 1, turbine efficiency and inlet and outlet temperature of heat source were imposed. The working fluids considered are sorted in ascending order of their molecular weights as R717, R600a and R152a. Results indicated that a fluid with a lower boiling point temperature like R717 needs a corresponding high heat source and/or evaporator inlet pressure. Also, the response of thermal diffusivity closely follows the change in TDOI as an increase in $T_{DOI}$ increases $P_{cond,in}$ which reduces thermal diffusivity and system efficiency. Furthermore, the fluid with the nominal boiling point temperature has the highest efficiency with efficiency decreasing with an increase in TDOI.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.12
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• pp.1049-1059
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• 2003

R410A is considered as an alternative refrigerant to R22 for air conditioners. An experimental investigation was made to study the characteristics of the heat transfer and pressure drop for R410A flowing in a fin-and-tube heat exchanger used for commercial air-conditioning units. Experiments were carried out under the conditions of inlet refrigerant temperature of 6$0^{\circ}C$ and refrigerant mass flux varying from 150 to 250 kg/$m^2$s for refrigerant side. The inlet air has dry bulb temperature of 35$^{\circ}C$, relative humidity of 40% and air velocity varying from 0.68 to 1.6 m/s. Experiments show that air velocity decreased by 16% is needed for R410A than that of R22 for subcooling temperature of 5$^{\circ}C$, which resulted in air-side pressure drop decrease of 15% for R410A as compared to R22. As a consequence, in order to provide the same design condition of a condenser, the fan requires lower electric-power consumption with R410A than that with R22.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.5 no.2
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• pp.94-101
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• 1993

Recently, efforts of decreasing energy consumption are continously increased and user's preference is also diversified in refrigeration and air conditioning systems. Thus, in order to satisfy these demands, high efficiency, high intelligence, and energy saving for those systems are essential. As the basic study for diverse functions and intelligence of those systems, we investigated the response characteristics through the compressor capacity control concerned with superheat and refrigeration room temperature. And, response characteristics are investigated experimentally by using micro computer based PWM inverter control method. Experimental result of the conventional on-off control method is given in order to be compared to the results of inverter control method. The results obtained through this study are summarized as follows. It is shown from the experimental results of the on-off control method that the range of temperature variation around the steady state ($-18^{\circ}C$) is very large (about $7{\sim}8^{\circ}C$) and the settling time bringing the steady state is not found. In the inverter control method, we can see that the refrigeration room temperature after reaching the setting temperature is very stable without fluctuation and a robust control for disturbance such as opening the door has been realized.

• Transactions of the Korean Society of Automotive Engineers
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• v.23 no.4
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• pp.428-435
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• 2015

This paper presents the experimental study of cabin thermal comfort using a cold storage heat exchanger in a vehicle air-conditioning system. Recent vehicle-applied ISG functions for fuel economy and emission, but when vehicles stop, compressors in the air-conditioning system stop, and the cabin temperature sharply increases, making passengers feel thermal discomfort. This study conducts thermal comfort evaluation in the vehicle, which is applied to a cold storage system for the climate control wind tunnel test and the vehicle fleet road test with various airflow volume rates and ambient temperatures blowing to the cold storage heat exchanger. The experimental results, in the cold storage system, air discharge temperature is $3.1-4.2^{\circ}C$ lower than current air-conditioning system when the compressor stops and provides cold air for at least 38 extra seconds. In addition, the blowing airflow volume to the cold storage heat exchanger with various ambient temperature was examined for the control logic of the cold storage system, and in the results, the airflow volume rate is dominant over the outside temperature. For this study, a cold storage system is economically useful to keep the cabin at a thermally comfortable level during the short period when the engine stops in ISG vehicles.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.12 no.10
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• pp.901-907
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• 2000

The conceptual determination of mixed-refrigerant (MR) for a closed Joule-Thomson cryocooler is described in this paper. The thermodynamic cycle design was mainly considered to develop a cryocooler by using a compressor of domestic air-conditioning unit. The target cooling performance of the designed cryocooler is 10 W around 70 K with less than 5 kJ/kg enthalpy rise. The systematic approach of choosing a proper refrigerant among 20 different kinds of mixture for such cryogenic temperature was introduced in detail. The main components of the cryocooler are compressor, evaporator, oil separator, after-cooler, counterflow heat exchanger, and J-T expansion device. Due to the limitation of the compressor operation range, the temperature after the compression was limited below $117^{\circ}C$ (390 K) and the temperature before compression was restricted above $5^{\circ}C$ (278 K). 20 atm of discharging pressure (high pressure) and less than 3 atm suction pressure (low pressure) were the design conditions. The inlet temperature of a counterflow heat exchanger in the high Pressure side was about 300 K. The proper composition of the mixed refrigerant for the designed J-T cryocooler is 15% mol of$ N_2, 30% mol of $CH_4,\; 30% mol\; of C^2H^ 6,\; 10%\; mol\; of\; C_3H_8\; and \;15%\; mol\; of\; i-C_4H_10$.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.21 no.5
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• pp.291-296
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• 2009

Ice accumulating system patterned ice-an-coil is the way of refrigerating regenerative materials on the surface of copper-tube inserted into the inside of ice-storage. The study experimented to understand ice-an-coil type ice making characteristics according to changing shape of ice making tube. The experiment were carried out under various conditions, that used brine temperature($-l0^{\circ}C$, $-6^{\circ}C$) brine flow rate(l.0m/s, 1.8m/s) and inlet water temperature($6^{\circ}C$, $12^{\circ}C$) etc. Mass of ice per making area increased according to the decrease of the brine temperature and inlet water temperature, but that was increased according to the increase of the brine flow rate. And I set up two hypotheses and compared the capacity of ice-making of the two cases; each had the same thermal area and one had an round-shaped copper tube but the other had an oval-shaped copper tube.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.7
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• pp.595-603
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• 2003

R407C is considered as an alternative refrigerant to R22 for air conditioners. An experimental investigation was made to study the characteristics of the condensation heat transfer and pressure drop for R407C flowing in a fin-and-tube heat exchanger used for commercial air-conditioning units. Experiments were carried out under the conditions of inlet refrigerant temperature of 6$0^{\circ}C$ and refrigerant mass flux varying from 150 to 250 kg/$m^2$s for refrigerant side. The inlet air has dry bulb temperature of 35$^{\circ}C$ , relative humidity of 50% and air velocity varying from 0.8 to 1.6 m/s. Experiments show that air velocity increased by 25% is needed for R407C than that of R22 for subcooling temperature of 5$^{\circ}C$, which resulted in air-side pressure drop increase of 28.8% for R407C as compared to R22. As a consequence, in order to provide the same design condition of a condenser, the fan requires higher electric-power consumption with R407C than that with R22.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.1 no.1
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• pp.82-86
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• 1989

A study has been conducted experimentally on heat transfer characteristics of the heat exchangers with louvered fins in air. The experimental results are as follows; 1. Mean heat transfer coefficient is decreased with increasing temperature difference and model III is the best at constant temperature difference. 2. Pressure drop is increased with increasing air velocity, but it is decreased as the heat transfer area increases. 3. $\bar{h}/^{\Delta}p$ is increased and then decreased as air velocity increases.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.15 no.10
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• pp.795-801
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• 2003

The primary object of this study is to obtain a basic knowledge of heat transfer enhancement mechanism as affected by temperature driven Marangoni convection. Experiments is achieved to visualize the enhanced heat transfer phenomena by the effect of Marangoni convection through the laser holographic interferometry. Also Nusselt Number is introduced for the relation of Marangoni Number.