Trends of compressor technologies for air conditioners are presented in this paper. HFC refrigerants such is R410A and R407C are promising candidates as an alternative for R22. Performance of rotary and scroll compressors in the operation with R410A and R407C are described. In addition, compressor technologies such as efficiency improvement, reliability and simulation methods are described in both cases of rotary and scroll compressors.
Advanced compressor technologies developed for air conditioners are desired in the field of the global environment protection and the energy saving.

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When a pipe is cut off to repair fuel oil pipelines, the oil has to be drained from the pipelines. If the oil inside the pipe is frozen at both sides of a cutting plane, it is not necessary to drain the oil from the pipelines. In the present paper, such a freezing method is studied analytically and experimentally to establish a suitable construction method, where liquid-nitrogen (LN₂) is used as a coolant and fuel oil-C is used as a typical example. From the result, thermal conductivity and thermal diffusivity of the fuel oil-C in a low temperature range were measured as a function of temperature in addition to the pour point and glass transition point. Furthermore, in order to compare the agreement between analysis and experiment, an analytical method was performed under various conditions. Finally, temperatures in analytical values were agreed well with experimental ones, and suitable position and time for cutting are clarified.

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An apparatus for measuring the vapor-pressures was newly designed and constructed in order to make the basic thermodynamic properties for environmentally acceptable refrigerants clear. The temperature of sample fluid was measured with 100Ω platinum resistance thermometer calibrated against ITS-90 using a 25Ω standard platinum resistance thermometer. With respect to the pressure measurement, two kinds of presure transducer were adopted. One is a diaphragm semi-conductor strain pressure transducer with the uncertainty of ±0.09%. This pressure transducer was calibrated against quartz crystal pressure transducer with the uncertainty of ±0.01% after every series of experiments. Another is a quartz crystal pressure transducer with the uncertainty of ±0.01%. A quartz crystal pressure transducer was calibrated against the dead weight pressure gauge and barometer.
The vapor-pressures for R-32, R-134a, R-290 (propane), R-600a (iso-butane) and n-pentane were measured in the temperature range between273.15 and 323.15K. As the results of vapor-pressure measurements, the reliability of the experimental apparatus as well as the reproducibility of the experimental data were confirmed. In addition, coefficients of Antoine vapor pressure equation were determined from the experimental data. Normal boiling points for environmentally acceptable refrigerants were also determined with high accuracy.

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Stirling engine-driven vapor compression systems have many unique advantages including higher thermal efficiencies, preferable exhaust gas characteristics, multi-fuel usage, and low noise and vibration which can play an important role in alleviating environmental and energy problems. This paper introduces a design method for the systems based on reliable mathematical methods for Stirling and Rankin cycles using reliable thermophysical information for refrigerants. The model deals with a combination of a kinematic Stirling engine and a scroll compressor. Some experimental coefficients are used to formulate the model. The obtained results show the performance behavior in detail. The measured performance of the actual system coincides with the calculated results. Furthermore, the calculated results clarify the performance using alternative refrigerants for R-22.

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A method which is generally applicable to predict the axially local (circumferentially averaged) heat transfer coefficient for refrigerant with oil contained flowing in horizontal evaporator tubes was developed by modifying a prediction method for pure refrigerants. The dimensionless correlation for an annular flow regime takes account of the influence of oil on an improvement or a reduction in the heat transfer, in addition to the change of the properties due to the addition of oil. For a separated flow regime, the correlations of the average heat transfer coefficients in the top part and the bottom part and their boundary angle were developed by modifying each correlation for pure refrigerants. The circumferentially averaged heat transfer coefficient for the separated flow regime can be obtained by using the solution of the steady heat conduction equation in the tube wall, to which the values calculated from the above correlations are applied as the boundary conditions at the inside surface of the tube. Which flow regime, annular or separated, prevails can be determined by the correlation of the boundary angle. The present prediction method was confirmed to be applicable to various kinds of refrigerant-oil mixture.

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Motors that occupy the most part of refrigerating hermetic compressors must be small sized, lightened, high efficient and reducted costs.
To achieve these objects, we need to investigate torque of compressors at the starting time and develop new motors with torque adapt to it.
In this report, we research on high temperature reciprocating compressors that begin to rotate in the condition of pressure balanced and that torque of one rotation sharply fluctuates. We measure pressure fluctuation inside the cylinder and rotational speed of motors from beginning to rotate to full speed. After that we calculate torque of compressors that is, torque necessary to motors.
As a result, we put to use condenser run motors useless starting condenser and voltage relay. Eventually we could develop compressors with better starting performance, high efficiency, small size, light weight and cost reduction.

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In this paper, experimental analysis was performed for ammonia-water falling film absorption process in a plate heat exchanger with enhanced surfaces such as offset strip fin. This paper examined the effect of vapor flow characteristics, inlet subcooling of the liquid flow and inlet concentration difference on heat and mass transfer performance. The inlet liquid concentration was kept constant at 0% while the inlet vapor concentration was varied from70. 36 to 77.31% It was found that before absorption started there was rectification process at the top of the test section by the inlet subcooling effect. Water desorption phenomenon was found near the bottom of test section. The lower inlet liquid temperature, the higher Nusselt and Sherwood numbers were obtained. NusseIt and Sherwood correlations were developed as functions of vapor Reynolds number Re_V, inlet subcooling and inlet concentration difference with ±10% and ±5% error bands, respectively.

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The dynamic characteristics of ammonia refrigerator system are observed when the expansion valve's opening is slightly changed. The refrigerator system is constructed with the reciprocal compressor, the plate type heat exchanger for the condenser and the evaporator, and the expansion valve. A simple simulation model for this refrigerator system is proposed to develop the computer-simulator of this ammonia refrigerator system and those simulation results are compared to above experimental results. For the development of the computer-simulator, simple but useful models, which can represent the dynamic characteristics of the refrigerator, are adopted for each components of the refrigerator system. The simulation shows the overall good agreement with experiment, without the time constant in the variation of the temperature at the evaporator outlet.

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In a refrigerator and an air conditioner, it is a well-known fact that the contamination of lubricant into a pure refrigerant has a great influence on the heat transfer characteristics and two-phase flow behavior at the condenser and evaporator. However, up to now, in the most of heat exchanger design, the refrigerant has been regarded as a pure one.
On the other hand, a recent condenser tube diameter tends to be fine to overcome the various demands on the compactness and the high performance, especially required for the alternative refrigerant. Unfortunately, quantitative studies of the tube less than 6 mm in diameter were insufficient, moreover, only few studies have been made including the effect of the oil contamination on the condensation heat transfer.
In this study, we employed HFC134a as a refrigerant and PAG-oil as a lubricant and experiments with a flat tube and three kinds of circular tube which has different diameters were made. By using the flow visualization data, a new flow pattern map being applicable both of a pure and oil-lubricant mixture was proposed. Moreover, by examining the local heat transfer coefficient and pressure drop, the most sensitive flow pattern affected by contamination of lubricant was specified and the detailed discussion on the quantitative effect of oil contamination on condensation heat transfer including the effect of tube geometry was carried out.
Finally, based on these results, new correlation for heat transfer and pressure drop was suggested, and it predicted our data successfully well up to a mass flux of 150kg/(m²•s.)

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This paper presents experimental results of the concentration dependence of heat transfer coefficients for mixtures of R134a and polyolester (POE) oil under the conditions of pool nuc1eateboiling. The experiments are conducted by means of ah horizontal platinum wire at saturation tel11peraturesof 9, 19, and 29°C and at oil concentrations from 0 to 8 mass%. The present results show that the boiling heat transfer coefficient for the system concerned decreases with increasing oil concentration as a whole but increases slightly at a low oil concentration of about 4 mass%. A correlation equation is also given as a function of heat flux, temperature and oil concentration to reproduce the experimental boiling heat transfer coefficient within an uncertainly of about±15%.

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