• 설비공학논문집
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• 제8권2호
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• pp.240-253
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• 1996

The refrigeration cycle of automobile air-conditioners is simulated in an effort to provide a computational tool for optimum thermodynamic design. In the simulation, thermodynamic and heat transfer analysis was performed for the four major components : evaporator, condenser, compressor, and expansion valve. Effectiveness-NTU method was used for modeling both evaporator and condenser. The evaporator was divied into many subgrids and simultaneous cooling and dehumidifying analysis was performed for each grid to predict the performance accurately. Blance equations were used to model the compressor instead of using the compressor map. The performance of each component was checked against the measured data with CFC-12. Then, all the components were combined to yield the total system performance. Predicted cycle points were compared against the measured data with HFC-134a and the deviation was found to be less than 5% for all data. Finally, the system model was used to predict the performance of CFC-12 and HFC-134a for comparison. The results were very reasonable as compared to the trend deduced from the measured data.

• 수산해양기술연구
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• 제23권4호
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• pp.198-203
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• 1987

국내 2개 선박회사로부터 입수한 1978년부터 1986년까지의 중요 기관고장에 관한 자료를 주성분분석법에 의하여 분석한 본 연구의 결과를 요약하면 다음과 같다. 1. 분석결과는 각성분의 인자부하량 크기에 따라 전기.자동제어기기, 보기류, 배관계, 과급기.냉동기류, 주기관계의 5그룹으로 나눌 수 있다. 2. 기기의 고장현상을 발열.소손, 고장원인은 부식.마모 및 오조작, 그리고 기기이상검출의 수단은 누설.혼탁 등이 매우 높은 비중을 차지하고 있다. 3. 주기관의 고장원인은 연료.윤활유 불량이 가장 큰 비중을 차지하며 주로 진동.이음에 의하여 이상을 검출하는 경우가 많다. 4. 전기.자동제어기기 고장은 피해도 비교적 적으며 기계계의 고장 피해는 큰 편이다. 5. 주기관 등은 기기이상의 확실한 사실에 의하여 이상이 검지되는 경향이 매우 강하며 보기류, 과급기.냉동기.에어콘 등은 운전원의 감각적 판단에 의하여 이상이 검지되는 경향이 강하다.

• 한국전기전자재료학회논문지
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• 제25권1호
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• pp.68-75
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• 2012

This paper presents a comparative analysis of the parallel operation of different switches in a DC/DC converter. In high power applications, multi-switch PWM power conditioners may be preferred despite a higher component count, due to the absence of low frequency filters, reduced switching losses and fault tolerance. The paper demonstrates how current sharing (CSH) and time sharing (TSH) lead to the reduction of switching stress in the parallel operation of switches in any converter. The solutions proposed in this study can be applied on different scales to other power conditioners for DC/DC converter systems. Discussions of the concepts, hypotheses and computer simulations are verified by 1 kW experimental results.

• 설비공학논문집
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• 제17권3호
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• pp.262-267
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• 2005

The air-side particulate fouling in the heat exchangers of HVAC applications degrades the performance of cooling capacity, pressure drop across a heat exchanger, and indoor air quality. Indoor and outdoor air contaminants foul heat exchangers. The purpose of this study is to investigate and to model the air-side particulate fouling characteristics of the heat exchangers using accelerated particle loading system. The main variables of the modeling equation are face velocity and dust concentration. The modeling equation shows good agreements with the experimental results at the face velocity of 0.5, 1.0, 1.5 m/s and the dust concentration of 1.28 and $3.84\;g/m^3$. It will be very useful to predict fouling characteristics such as variations of pressure drop and heat transfer capacity in finned-tube heat exchangers of air conditioners.

• 대한설비공학회:학술대회논문집
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• 대한설비공학회 2005년도 동계학술발표대회 논문집
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• pp.433-438
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• 2005

An AHX(Accumulator Heat eXchanger) consists of a commercial accumulator and an inner heat exchanger located inside of the accumulator. The AHX is used in multi air-conditioners to assure the liquid-phase refrigerant entering into the expansion device. This purpose is achieved by heat transfer between the refrigerant leaving the evaporator and the refrigerant leaving the condenser. In this study, the effects of AHX on the performance of a refrigeration system using H-22 were measured and the test results were analyzed. The operating characteristics of the refrigeration system with the installation of AHX were quite different from those without the installation of AHX. Therefore, it is required to find an optimum refrigerant charging amount and optimum operating conditions, when AHX is installed in the refrigeration system with an fixed area expansion device such as a capillary tube.

• 설비공학논문집
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• 제8권1호
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• pp.166-175
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• 1996

In recent years, air-conditioning units designed with higher efficiency and more compactness are required due to emphasis on energy efficiency in home electrical appliances. This trend in the air-conditioning industries has accelerated the development of improved heat exchanger with a better performance in heat transfer aspects. In this study, experiments were performed to investigate the shape and configuration of fins affecting on the performance of the conventional fin-and-tube type heat exchanger equipped in a commercial air conditioners. The geometry similtude method was employed to measure the heat transfer coefficient and pressure drop. Experimental results show that this method is very useful to analyze the heat transfer characteristics of the fin-and-tube type heat exchanger. It is also found that the slit fin has better performance than the conventional fin type in the air conditioners. The present results indicate that heat transfer from the fin si influenced by the parameters such as the forming area of the slit fin, the type of interrupted surfaces like a louver or slit, slit patterns and slit raised direction, and it also affects the overall heat exchanger performance.

• 한국공작기계학회논문집
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• 제10권6호
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• pp.102-108
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• 2001

To prevent green house effect and destruction of an ozone layer, an ozone destruction potential(OBP) must be zero and a refrigerant for low global warming potential(GWP) is needed. HFC-l34a, in which hydrogen is mixed instead of chlorine is a refrigerant used for automobile conditioners and its destruction potential is ecologically zero. However, it is not consid- ered as a perfect substitutive refrigerant as its GWP is high. It is studied refrigerant mixtures in which HFC-l52a and $CF_3 I$ in HFC-l52a with low GWP and zero ODP are mixed by experimentally and concluded as follows: 1) With the variation of speed of compressor outside temperature and flow rate, 7he heat of evaporator and compressor and coefficient of perfor- mance was varied, and influenced the air conditioner. 2) The pressure of evaporator was decreased with increasing the speed of compressor and the pressure of evaporator with the refrigerant HFC-l52a was higher 24% than that of azotrope refrigerant mixed with $CF_3 I$

• 설비공학논문집
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• 제10권3호
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• pp.315-323
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• 1998

This paper contains a verification of simulation program to predict the capacity of a condenser used in car air-conditioners. Verification of simulation program is carried out with the comparison error between experiment and simulation bounds within 3.5%. The present investigation shows the results for heat transfer rates of condenser under different operating conditions, such as velocity and degree of superheat. The range of front velocity of air is 1∼5m/s. As the front velocity is increased, the heat transfer rate of condenser is largely increased at a low velocity range. In a meanwhile, heat transfer rate of condenser is almost constant in a range of velocity over 3m/s. As for the effect of inlet pressure of refrigerant on the heat transfer rate, we obtained the similar trend of heat transfer rates as like varying the front velocity, Also we have calculated the heat transfer rates with varying inlet superheats of refrigerant, the larger the superheat is, the more heat transfer rate is obtained.

• Journal of Power Electronics
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• 제12권6호
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• pp.1003-1010
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• 2012

Recent power electronics and variable-frequency motor drive technologies have been applied to air conditioners to improve efficiency and power density. However, the mechanical vibrations and acoustic noise resulting from the compressor still remain as a serious problem. This paper presents the development and implementation of an online disturbance state-filter for the suppression of multiple unknown and time-varying vibrations of air conditioning systems. The proposed design has a form of the state-filter based on a Luenburger-style closed-loop speed observer. An active vibration decoupling strategy with an estimated disturbance is provided, which manipulates a motor torque command. Since the proposed estimation does not require any additional transducers or hardware for obtaining real-time information upon disturbances, it is suitable for retrofitting industrial air conditioners.

• 전력전자학회논문지
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• 제18권5호
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• pp.448-457
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• 2013

This paper proposes a control method under stand-alone operating mode for distributed-module type photovoltaic power conditioners. In conventional schemes, there are some problems of a controller saturation in the DC-link (or load) voltage controller when overly-heavy load, light load, and the generated PV power reduction occurs, as well as when a transition occurs from an overly-loaded to normal conditions. To overcome these problems, the proposed controller method switches the main control target from DC-link voltage to the maximum power point, which is closer to the stable operating point when it returns to normal operating conditions. For the analysis, a state-plane trajectory was given and the circuit analysis by PSIM simulation was done. For the verification, a prototype hardware with 110[W] and 50[W] dual photovoltaic modules has been implemented. From the results, it can be seen that PV power tracking is successfully done with the proposed method even under a stand-alone operation mode.