This paper focuses on the scroll compressor and traces the history of technology developments that leads from its initial development to the present, and also describes future prospect. Almost 40 years after commercialization, in order to cope with the replacement of refrigerants and further energy saving to reduce environmental impact, the performance and reliability of the scroll compressor has been greatly improved, and it has been widely adopted for air conditioning and refrigeration systems. This is due to the development of new scroll profiles and driving mechanisms, reduction of gas leakage and mechanical loss, adoption of high-speed high-precision scroll processing technology, and the advancement of analysis and measurement technologies. We expected to continue to lead the world in active research and development that will contribute to improving social life and the environmental impact reduction.

To develop a highly efficient compressor, it is necessary to reduce friction loss of the sliding surfaces. The sliding surfaces of the crank shaft have rotational sliding mode that has good lubricated condition. On the other hand, the sliding surfaces of the piston surface and small end of the connecting rod have bad lubricated condition because these sliding surfaces have reciprocating motion and swing motion. In this study, we evaluated the friction characteristics of the small end of the connecting rod. The structure of small end of the connecting rod are two types,a ball joint type and piston pin type. The result showed that the friction coefficient is independent from the joint structure, the diameter of the piston pin. The friction coefficient is saturated to 0.16 with increasing load. These results mean that the friction loss is proportional to the diameter of the sliding surface. The piston pin with side-relief grooves was evaluated using friction torque test and electrical resistance method. The results showed that side-relief grooves had effect of improving the lubrication condition and making friction torque lower.

A Tip seal is used to prevent a radial leakage at a tip of scroll tooth. In order to improve an efficiency of the scroll compressor, it is necessary to reduce both gas leakage across the tip seal and friction at the tip seal. However, there are many parameters regarding the gas leakage and the friction, and influences of the parameters on the gas leakage and the friction have not been clarified. In this study, test apparatus which can measure the leakage and friction at sliding surface of the tip seal simultaneously was developed. Influences of a waviness and Young’s modulus of the tip seal on the seal effect and the friction were examined with the test apparatus. Although the leakage increases when the tip seal has large waviness on the surface, it is expected that the tip seal in actual compressor is pressed uniformly to base plate. Furthermore, when Young’s modulus of the tip seal is small, frictional force at the tip seal increases compared to a tip seal having high Young’s modulus.

This paper describes leakage loss reduction of three-dimensional scroll for the purpose of further efficiency improvement of scroll compressor. The shape of three-dimensional scroll, which leads to reduction of loss in step clearances peculiar to the conventional three-dimensional scroll, was examined, and a new structure was proposed in which the wrap height can be continuously changed by inclining scroll tip and end plate in a slope shape. The new three-dimensional scroll realizes high efficiency by eliminating leakage from the step clearances, and inherits advantages of the conventional three-dimensional scroll, high compression ratio, high strength, large capacity and small size. As a result of performance and cylinder pressure measurement of the prototype new three-dimensional compressor, it was confirmed that an appropriate range of slope angle exists in order for maintaining high efficiency, and that adiabatic efficiency was improved by up to 4.8% by reduction of leakage loss.

In most scroll compressors, the Oldham ring is a prevalently used mechanism to realize orbital motion. When the scroll compressor is operated at higher speed, the Oldham ring may be severely damaged. This damage is apparently due to inherent characteristics of the Oldham ring. The reciprocating motion of the Oldham ring becomes unstable due to the increased inertia force of the Oldham ring itself, resulting in what is here denoted as the slap behavior of the Oldham ring keys in their key slots. In this paper, a theoretical analysis of the Oldham ring key slap behavior during reciprocating motion of the Oldham ring is developed. The dynamics of the Oldham ring in reciprocating motion is re-examined with inclusion of the small clearance gaps. The analysis considers the constraint forces acting on the key slot surfaces to determine the speed limitations to avoid the key slap behavior. In addition, the key slap behavior was qualitatively confirmed by model experiment.

To reduce the energy consumption of household refrigerators, we focused on leakage loss, one of the main losses, with the aim of improving the efficiency of reciprocating compressors. Since there are few reports on the measurement of leakage from the compression chamber during operation, the method of measuring leakage during operation was first examined, and the relationship between the piston diametral gap and leakage, and relation between the oil viscosity and leakage were investigated. After that, the relationship between groove specifications and leakage was experimentally investigated for oil grooves provided on the piston surface. As a result, the oil groove on the piston surface was effective in reducing leakage, and the oil groove specification to reduce leakage was clarified.

For conventional air conditioning systems, the efficiency degradation caused by sub cooling dehumidification in summer and air drying due to no humidification function in winter are two important issues in terms of energy efficiency and thermal comfort. Desiccant is considered to be one of options to humidity control with high efficiency instead of sub cooling dehumidification method adopted in conventional air conditioning systems. In this study, experiments were conducted to measure the dehumidification and humidification performance of a desiccant module consisting of a desiccant-coated heat exchanger and a novel slide type air flow switching device. Experimental results show that the desiccant module under the size of 500 (Height) x 700 (Width) x 1100 (Length) mm can satisfy 90% of the dehumidification and humidification demand (1050 g·hour^-1 for summer and 750 g·hour^-1 for winter) of a detached house at the floor space of 90m², ceiling height of 2.4m, ventilation frequency of 0.7 times per hour.

An experimental study was conducted on gas-liquid distributions of the refrigerant flow in a multi-pass channel with vertical headers and horizontal multiport flat tubes that simulated the parallel-flow type evaporator. In particular, the influence of protrusion of branch tubes into the dividing header on gas-liquid distributions and pressure loss of the channel was examined. The refrigerant (R410A) was supplied from the bottom of the header, and experiments were conducted under an adiabatic condition. It was found that the maximum height of the liquid distribution was increased by protruding branch tubes into the header at high mass flow rates. The pressure loss of the channel increased as the mass flow rate and/or quality of the refrigerant were increased, and the pressure loss in branch tubes occupied 60-70% of the pressure loss of the channel. The pressure in the dividing header decreased gradually in the upward direction, while that in the combining header was almost constant. Based on experimental data, we made clear pressure distributions in channels. The pressure in the channel showed quite a uniform distribution in the vertical direction under a high quality condition, while the uniformity of the liquid distribution was deteriorated as the quality was increased.