• 설비공학논문집
• /
• 제8권1호
• /
• pp.45-54
• /
• 1996

An experimental investigation on the two-phase flow through tube orifices was performed with the refrigerant mixture of R32/125/134a(30/10/60). A series of tests were conducted to generate wide range of data at varying operation conditions with four short tubes. The tests include both single and two-phase flow conditions at the inlet of the short tube with different oil concentrations. Experimental data were presented as a function of major operating parameters and short tube diameter. Based on test results and data analysis, a semi-empirical flow model was developed to predict the mass flow rate through short tube orifices with a given set of conditions. The flow model was formed to cover both single and two-phase flow at the inlet of short tube with considering the effects of oil concentration.

• 설비공학논문집
• /
• 제20권1호
• /
• pp.49-56
• /
• 2008

When the outdoor air temperature decreased less than the freezing temperature, frost forms at the surface of heat exchangers and it makes the performance degradation of a heat pump system. In this study, a heat pump system has been developed which has a refrigerant heating device as an auxiliarly heating equipment. To reduce power consumptions of the system, a liquid pump, rather than a compressor, was used to drive refrigerant in the heat pump cycle. Ratio of refrigerant mass flow between a refrigerant heating heat exchanger(GHX) and a outdoor plate heat exchanger(PHX) was varied and the system performance was measured and analyzed. As results, when the refrigerant flow rate to the GHX was decreased, the system performance is decreased due to heat absorption capability restriction of the GHX and small variation of the power consumption in the compressor. The effect on the evaporating and condensing pressure by the distribution ratio of the refrigerant to the each heat exchanger is small compare to the effect by the frequency change in the compressor. When the compressor was replaced by the liquid pump, the capacity of the system decreased a little, however the power consumption decrease approximately 80% compare with the power used in the compressor.

• 설비공학논문집
• /
• 제24권8호
• /
• pp.605-611
• /
• 2012

The objective of this study is to investigate the influence of the cooling performance for a water-to-water 10 RT ground source heat pump by using the water switching and refrigerant switching method. The test of water-to-water ground source heat pump was measured by varying the compressor speed, load side inlet temperature, and ground heat source side temperature. The cooling capacity and refrigerant mass flow rate of the heat pump increased with increasing ground heat source temperature. But COP of the heat pump decreased with increasing ground heat source temperature. As a result, the water switching method with counter flow, compared to a refrigerant switching method, improves the cooling capacity and COP by approximately 6~9% in average, respectively.

• 한국자동차공학회논문집
• /
• 제15권2호
• /
• pp.95-100
• /
• 2007

An experimental study was performed to evaluate the in-plate evaporation heat transfer and flow characteristics of a evaporator used in automobile. Two test-cores with different heat transfer area, bead-shape and bead-array were tested, A type and B type. For the heat transfer, Nusselt number for B type test-core reaches a value nearly equal to the one for A type test-core, in the whole range of equivalent Reynolds number. But, for the same mass flow rate of refrigerant, hA for B type test-core becomes higher with the increase of the mass quality of refrigerant than for A type test-core. In a flow visualization experiment, the wake zone of refrigerant circulating at u-turn position of plate is observed.

• 수산해양기술연구
• /
• 제34권3호
• /
• pp.346-351
• /
• 1998

The purpose of this study is analyzing the performance of sea water cooling system under various refrigerant pipe length. In sea water cooling system, the increase of refrigerant pipe length cause increases of pressure drops. These pressure drops cause fresh gas in liquid pipe and increase specific volume in gas pipe outlet, so sea water cooling system capacity is decreased by decrease of refrigerant mass flow rate. Sea water cooling system capacity in refrigerant pipe length 70m is decreased more than 30% when compared with pipe length 10m and the decrease of the coefficient of performance is nearly 20%.

• 한국공작기계학회논문집
• /
• 제10권6호
• /
• pp.102-108
• /
• 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 $CF_3 I$

• 한국가스학회지
• /
• 제17권4호
• /
• pp.51-57
• /
• 2013

천연가스 액화 공정은 상온의 천연가스를 상압 $-160^{\circ}C$ 이하로 냉각해서 액화시키는 공정으로, 안정된 LNG 생산을 위해서는 최적의 제어 전략이 필요하다. 제어 전략을 수립할 때 가장 중요한 작업 중 하나가 공정의 분석인데, 조절 변수의 변화에 따른 제어 변수의 변화를 파악하는 것이다. 본 논문에서는 C3MR(Propane Pre-cooled Mixed Refrigerant) 공정으로 BSU(Bench Scale Unit)를 제작하여 천연가스 액화 공정을 실험하였다. 각 조절변수의 조작에 따른 유량의 변화가 공정에 미치는 영향을 알아보기 위해서 냉매의 유량변화에 따른 냉매 온도 변화 및 천연가스의 온도 변화를 분석하였고, 천연가스 자체의 유량 변화에 따른 냉매의 온도 변화를 분석함으로써 3개의 조절 변수와 공정의 제어변수들과의 관계를 알아보았다. 각 제어변수들은 독립적인 요소들이 아닌 서로 연관되어 유기적인 움직임을 보였으나, 특정 조절 변수의 변화에 따라 큰 반응을 보이는 제어 변수를 확인 할 수 있었다.

• 설비공학논문집
• /
• 제13권11호
• /
• pp.1125-1133
• /
• 2001

Since the surface temperature of the evaporating tube in an ammonia unit cooled is lower than the dew point of atmosphere, the moisture in the atmosphere condenses and the frost grows on the tube. The frost of liquid film decreases the heat transfer rate. The reliable analysis of the heat transfer is required for the prediction of the optimal design of the ammonia unit cooler. For the specific commercial model, the performance was numerical1y estimated for the variation of operating condition and geometric configuration. It is found that there exists an optimum range for the parameters such as mass flow rate of air and refrigerant, humidity, refrigerant quality, fin pitch, the number of step, the number of rows and the pattern of refrigerant path.

• 설비공학논문집
• /
• 제20권7호
• /
• pp.508-516
• /
• 2008

Fault detection and diagnosis(FDD) system is beneficial in equipment management by providing the operator with tools which can help find out a failure of the system. An experimental study has been performed on fault detection and diagnosis method for a water chiller. Bayes classifier, which is one of classical pattern classifiers, is adopted in deciding whether fault occurred or not. Failure modes in this study include refrigerant leakage, decrease in mass flow rate of the chilled water and cooling water, and sensor error of the cooling water inlet temperature. It is possible to detect and diagnose faults in this study by adopting FDD algorithm using only four parameters(compressor outlet temperature, chilled water inlet temperature, cooling water outlet temperature and compressor power consumption). Refrigerant leakage failure is detected at 20% of refrigerant leakage. When mass flow rate of the chilled and cooling water decrease more than 8% or 12%, FDD algorithm can detect the faults. The deviation of temperature sensor over $0.6^{\circ}C$ can be detected as fault.

• 설비공학논문집
• /
• 제13권5호
• /
• pp.422-430
• /
• 2001

In the present study, an evaporative generation process of ammonia-water solution film on the vertical plate was analysed. For the utilization of waste heat, hot water of low temperature was used as the heat source. The continuity, momentum, energy and diffusion equations for the solution film and vapor mixture were formulated in integral forms and solved numerically. Counter-current solution-vapor flow resulted in the refrigerant vapor of the higher ammonia concentration than that of co-current flow. Eve the rectification of refrigerant vapor was observed near the inlet of solution film in counter-current flow. For the optimum operation of generator using hot water, numerical experiments, based on the heat exchange and generation efficiencies. revealed the inter-relationships among the Reynolds number of the solution film and hot water, and the length of generator. Enhancement of heat and mass transport in the solution film was found to be very effective for the improvement of generation performance, especially at high solution flow rate.