• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.3
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• pp.255-262
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• 2014

To investigate the effect of oil on evaporation heat transfer of plate heat exchanger, evaporation heat transfer experiment was carried out using experimental apparatus for micro gear pumped R134a-oil circulation. By varying oil circulation rate of POE oil from 0 to 5%, evaporation heat transfer performance of plate heat exchanger was investigated. As OCR(Oil Circulation Ratio) increases, the evaporation heat transfer coefficient of R134a decreases and pressure drop increases. When the evaporating temperature is $30^{\circ}C$ and the refrigerant mass flow rate is 80 g/s, evaporation heat transfer rate decreases by 10 % and pressure drop increases by 10% at 2% of OCR condition.

• Fire Science and Engineering
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• v.27 no.6
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• pp.89-96
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• 2013

The purpose of this study is to check the fire origin and cause of the fire by observing the shape of the flame propagation in air-conditioner indoor unit through the fire tests. We supposed that the flame is spread from the surroundings to the top of the air-conditioner and ignited on top of the air-conditioner with n-heptane. And then repeated this experiment twice under the same conditions. After the ignition, refrigerant filled in air-conditioner and lubricating oil exploded with large explosion and flame having high temperature and pressure belched out rapidly due to bursting refrigerant pipe linked air-conditioner between 734 seconds and 559 seconds. After result of checking the combustion residue we found that almost all of that was lost except a part of the evaporator, motor and metal. The position of short-circuit traces of wiring for the air-conditioner ignited itself is similar to that of fire damage by external flame. Therefore, we verified that it is not certain to determine the ignition cause and point by only the shape of the combustion residues.

• Journal of Advanced Marine Engineering and Technology
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• v.29 no.5
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• pp.526-532
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• 2005

The cooling heat transfer coefficient of $CO_2$(R-744) in a horizontal tube was investigated experimentally. The experiments were conducted without oil in a closed refrigerant loop which was driven by a magnetic gear pump. The main components of the refrigerant loop are a receiver, a variable-speed pump. a mass flow meter. a pre-heater and gas cooler(test section). The test section consists of a smooth, horizontal stainless steel tube of 7.75 mm inner diameter. The experiments were conducted at mass flux of 200 to $400\;kg/m^{2}s$ and the inlet cooling pressure of 7.5 MPa to 10.0 MPa. The variation of heat transfer coefficient tends to decrease as cooling pressure of $CO_2$ increases. The heat transfer coefficient with respect to mass flux increases as mass flux increases. The pressure drop of $CO_2$ in the gas cooler shows a relatively good agreement with that predicted by Blasius's correlation. The local heat transfer coefficient of $CO_2$ agrees well with the correlation by Bringer-Smith.

• Journal of Advanced Marine Engineering and Technology
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• v.29 no.5
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• pp.552-559
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• 2005

The evaporation pressure drop of $CO_2$ (R-744) in a horizontal tube was investigated experimentally. The experiments were conducted without oil in a closed refrigerant loop which was driven by a magnetic gear pump. The main components of the refrigerant loop are a receiver, a variable-speed pump. a mass flow meter, a pre-heater and evaporator (test section). The test section consists of a smooth. horizontal stainless steel tube of 7.75 mm inner diameter. The experiments were conducted at mass flux of 200 to $500\;kg/m^{2}s$, saturation temperature of $-5^{\circ}C\;to\;5^{\circ}C$. and heat flux of 10 to $40\;kW/m^2$. The test results showed the evaporation pressure drop of $CO_2$ are highly dependent on the vapor qualify, heat flux and saturation temperature. The evaporation pressure drop of $CO_2$ is very lower than that of R-22. In comparison with test results and existing correlations. the best fit of the present experimental data is obtained with the correlation of Choi et al. But existing correlations failed to predict the evaporation pressure drop of $CO_2$. Therefore, it is necessary to develop reliable and accurate predictions determining the evaporation pressure drop of $CO_2$ in a horizontal tube.

• 한국태양에너지학회:학술대회논문집
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• 2011.04a
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• pp.199-203
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• 2011

With the improvement of standard of manufacturing process, oil cooling unit for manufacturing machine has been developed. A control system must be designed in order to keep oil temperature of the machine within a very restricted range and also to reduce energy consumption. In order to get the low deviation of the controlled temperature and the low efficiency, the on/off control scheme is gradually being replaced by a variable speed refrigeration system (VSRS) with an inverter driven compressor over recent decades. This paper gives the flowchart to control the compressor speed and also the electronic expansion valve (EEV) aperture in oil cooling unit refrigeration system using R22 as the refrigerant. This control scheme has already tested in experiment apparatus with room temperature condition constant at $25^{\circ}C$ and variable load condition at 4kW, 6kW, 7kW, 8kW and 10kW.

• Journal of Advanced Marine Engineering and Technology
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• v.28 no.3
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• pp.500-508
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• 2004

The heat transfer coefficients during gas cooling process of carbon dioxide in a horizontal tube were investigated. The experiments are conducted without oil in the refrigerant loop. The main components of the refrigerant loop are a receiver, a variable-speed pump, a mass flow meter, a pre-heater, and a gas cooler(test section). The water loop consists of a variable-speed pump, an isothermal tank, and a flow meter. The gas cooler is a counterflow heat exchanger by cooled water flowing in the annulus. The $CO_2$ flows in the horizontal stainless steel tube. which is 9.53mm in O.D. and 7.75mm in I.D. The gas cooler is 6 [m] in length. which is divided into 12 subsections, respectively. The experimental conditions considered in the study are following range of variables : refrigerant temperature is between 20 and $100^{\circ}C$. mass fluxes ranged from 200 to 400kg/($m^2$.s), average pressure varied from 7.5 to 10.0MPa. The main results were summarized as follows : The friction factors of $CO_2$ in the gas cooler show a relatively good agreement with those predicted by Blasius' correlation. The local heat transfer coefficient in the gas cooler has compared with most of correlations, which are the famous ones for forced convection heat transfer of turbulent flow. The results show that the local heat transfer coefficient of gas cooler agrees well with the correlation by Bringer-Smith except that at the region near pseudo critical temperature. while that at the near pseudo critical temperature is higher than the correlation.

• Proceedings of the SAREK Conference
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• 2005.11a
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• pp.262-267
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• 2005

The evaporation heat transfer coefficient of $CO_2$ in a horizontal round tube was investigated experimentally. The experiments were conducted without oil in a closed refrigerant loop which was driven by a magnetic gear pump. The main components of the refrigerant loop are a receiver, a variable-speed pump, a mass flow meter, a pre-heater and evaporator(test section). The test section was made of a horizontal stainless steel tube with the inner diameter of 7.75 mm, and length of 5 m. The experiments were conducted at mass flux of 200 to 500 $kg/m^2s$, saturation temperature of $-5^{\circ}C$ to $5^{\circ}C$, and heat flux of 10 to 40 $kW/m^2$. The test results showed the evaporation heat transfer of $CO_2$ has great effect on more nucleate boiling than convective boiling. The evaporation heat transfer coefficients of $CO_2$ are highly dependent on the vapor quality, heat flux and saturation temperature. In comparison with teat results and existing correlations, correlations failed to predict the evaporation heat transfer coefficient of $CO_2$, therefore, it is necessary to develop reliable and accurate predictions determining the evaporation heat transfer coefficient of $CO_2$ in a horizontal tube.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
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• 2001.11a
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• pp.230-236
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• 2001

We developed a built-in sensor bearing to measure the rotor motion of a rolling piston type compressor for the air conditioner. Because of needs for the high efficiency and long life span of compressor, and the usage of alternative refrigerants, the operating condition of the compressor becomes more severe. The accurate measurement of the rotor motion of the compressor can contribute greatly to the design and analysis of the hydrodynamic bearing. However, it is difficult to measure accurately the shaft behavior of small compressor because of the small space for the sensor mount, high temperature and pressure of compressor, oil mixed with refrigerant, and electromagnetic noise of the motor. To overcome these difficulties, we develop the cylindrical capacitive sensor that is built in the hydrodynamic bearing and calibrate the built-in sensor bearing indirectly through measuring the oil relative permittivity. We measured the rotor motion as well as suction and discharge pressures in various conditions. The several experimental results show that the developed built-in sensor bearing can measure the rotor motion not only in steady state but also in transient state.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.3 no.4
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• pp.297-305
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• 1991

Recently, automotive air conditioning system manufacturers have been made a great efforts on the system compactness and high efficiency. This growing interest comes improvements in evaporator thermal performance, one of the most important factors affecting the performance of air conditioning system. In order to improve design of compact type evaporator, this study executes performs to develop a computer program for evaporator thermal performance prediction of automotive air conditioning system. The brief summaries of this study are as follows: 1) To predict the overall thermal performance of serpentine type evaporator, the new simulating method is developed. 2) The calculations are performed as functions of oil mass concentration and refrigerant two-phase distribution at inlet manifold of evaporator. 3) The validity of this simulating program is confirmed by comparing the predicted thermal performance results to experimental results of practical available evaporator. 4) Based on these results, suggestions are made to improve the thermal performance of evaporator.

• Tribology and Lubricants
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• v.30 no.6
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• pp.370-377
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• 2014

The basic elements in a rotary-type scroll compressor are two identical spiral scrolls containing refrigerant gas. The pressure variations in the compression pockets of a scroll compressor change the forces acting on the orbiting scroll, and these forces affect the dynamic behavior of the compression mechanism parts. To achieve high efficiency, using a self-sealing mechanism as a tip seal mechanism is very effective. Tip seals, which are placed on top of the scroll wraps, accomplish thrust sealing. This study calculates the friction force between the tip seal and the side plate of a scroll compressor using the numerical model considered in the Reynolds equation. The calculated friction force is verified by an experiment using a pin-on-disk apparatus. A hydraulic servo valve that controls the pressure of the oil hydraulic cylinder applies the normal load for the test, and a DC servo motor controls the sliding velocity of the disk. The friction force and normal load are measured by the force sensors attached to the supporting parts. The results show that the theoretical and experimental results are similar and that the friction is influenced by the viscosity of the oil and the sliding velocity of the scroll.