Room-temperature magnetic refrigeration is attracting attention as a next-generation CFC-free refrigeration technology. However, the magnetic refrigeration is not put into practical use because of a low cooling capacity. The aim of this work is to increase the cooling capacity of the magnetic refrigerator by focusing on an improvement of the refrigeration cycle based on the Active Magnetic Regenerator (AMR). By using the hill-climbing method, we searched for the optimum refrigeration cycle depending on the temperature span and the AMR aspect ratio. The cooling capacity is calculated by the one-dimensional model of the AMR. The results of this study show that there are better cycles in obtaining high cooling capacity than conventional ones such as Brayton cycle. These cycles are constructed by the combination of Brayton and Ericsson cycles.

In the industry, chicken egg white is used to improve physical property of fish meat gel. However, there are no detailed investigations regarding to the effect of egg white on the fish meat gel. In the present study, the effect of ovalbumin and its derivatives, which is a main protein of egg white, on the gel forming ability of Alaska pollack Theragra chalcogramma surimi was clarified. S-ovalbumin and I-ovalbumin were successfully prepared from N-ovalbumin. The ovalbumins reduced the physical property of surimi gel when heated at 40 ºC, whereas promoted when heated at 60 or 90 ºC, regardless of ovalbumin type. The ovalbumins showed no inhibitory effect toward trypsin activity. From the results, it is suggested that the improving effect of ovalbumins on physical property of heat-induced surimi gel is not due to its inhibitory effect of protease, but to its gel forming ability.

Transient two-dimensional numerical computations are carried out to examine the laminar flow forced convective heat transfer characteristics of Al2O3-water nanofluids in a horizontal tube. A tube with the length of 50 times of a diameter is insulated from the inlet to the central part and is cooled isothermally from the central part to the outlet. The high-temperature Al2O3-water nanofluids flowing into a tube is assumed to be Hagen-Poiseuille flow. The thermophysical properties of Al2O3-water nanofluids are estimated by either the experimental correlation equations reported by Khanafer and Vafai or the conventional prediction equations for solid-liquid dispersed system. The numerical conditions are Re = 1700 or 2300, Pr = 5.85, and the volume fraction of nanoparticles is in the range of 0.00 to 0.04. The ratios of average Nusselt number of Al2O3-water nanofluids computed by applying the experimental correlation equations and the conventional prediction equations to that of water denoted less than unity. On the contrary, the ratios of average heat transfer coefficient of Al2O3-water nanofluids to that of water denoted more than unity. Specifically, the average heat transfer coefficient ratio of Al2O3-water nanofluids with 50 nm diameter particles computed by applying the experimental correlation equations took a maximum value (= 1.041) when the volume fraction of nanoparticles was 0.03. That of Al2O3-water nanofluids with 100 nm diameter particles took a maximum value (= 1.016) when the volume fraction of nanoparticles was 0.01. That of Al2O3-water nanofluids computed by applying the conventional prediction equations took a maximum value (= 1.071) when the volume fraction of nanoparticles was 0.04. The enlargement of the average heat transfer coefficient of nanofluids is due to the enlargement of effective thermal conductivity of nanofluids.

Risk assessment of lower GWP refrigerants assuming explosion accidents of compressor during pump-down of air conditioner was experimentally investigated. Penetration of air into refrigerant tube was experimentally simulated by adiabatic compression of refrigerant, air and lubricating oil for the compressor. Lower GWP refrigerants; R 1234yf and R32, and conventional refrigerants; R 410A and R 22 were tested for comparison. PAG oil and POE oil were used. The effect of the oils for the combustion was studied by comparing the results with different oils and amount of oil. It was revealed that the upper flammability limit of refrigerant became higher and the maximum pressure at combustion was higher with lager amount of oil. The flammable range with POE oil was significantly smaller than that with PAG oil. Thus, the accidents during pump-down are greatly affected by burning characteristic of the lubricating oils as well as that of refrigerants.

The effect of pre-treatment at subzero temperature of grains on the grinding process was investigated in respect of physical properties of particle. The average particle size of ground soybean and black soybean powders decreased as pre-treatment temperature decreased. The theoretical model that described grinding characteristics revealed that the freezing as pre-treatment is effective on grinding process. In all grain samples, the Bond’s constant and work index showed lower values as the pretreatment temperature decreased. The scanning electron microscopy was used for observation of surface damages on the particles by grinding process. Some cracks were seen on the surface of particles of soybean powder ground with freezing pretreatment. On the other hand, the particles of black soybean powder showed no fractures. The freezing as pre-treatment of grains prior to grinding process is effective to controlling their grinding characteristics and microstructure damages.

We developed a new type of quadruple thread spiral tube in order to improve the heat transfer coefficient on the liquid side of the gas cooler. The COP of the heat pump water heater can be well improved by optimizing the performance of the CO2- water heat exchanger. In this paper, the improvement of heat transfer performance has been analyzed based on numerical and experimental verifications. As a result, the quadruple thread spiral tube can provide higher heat transfer performance by 12% compared with the current triple thread spiral tube. A correlation equation of the heat transfer coefficient is made on the basis of the measurement data. It has a prediction accuracy at ±20% compared with the experimental data.

This study was conducted to investigate the characteristics of condensation heat transfer and frictional pressure drop of non-azeotropic mixture R32/R152a inside a horizontal internally helical-grooved small-diameter tube with equivalent inner diameter of 3.48 mm. The condensation heat transfer coefficients and frictional pressure drops were measured in the range of mass velocities from 100 to 400 kg/(m²s), and at an average saturation temperature of 35 °C. In order to study the effect of grooves on the condensation characteristics of non-azeotropic refrigerant mixture, the heat transfer coefficients and frictional pressure drops inside the helically grooved small-diameter tube were compared with those of a smooth small-diameter tube of same diameter. The frictional pressure drop was not affected by non-azeotropy, and it could be estimated from the previous correlation. And the heat transfer coefficient of R32/R152a was greatly decreasing compared with that of R32 and R152a at the lowest mass velocity. The enhancement ratio of heat transfer by the internally helical-grooves was large at low wetness region, and it is small at high wetness region.

The purpose of this research is to evaluate the performance characteristics of two-stage compressed gas injection cycle with respect to the pressure pulsation experimentally. The pressure pulsation is generated by the cyclic flow between two compressor chambers. It has been thought that pressure pulsation affect not only the pressure difference between both ends of the injection pipe but also flow rate in this pipe. However, these effects and performance characteristics caused by pressure pulsation are not clear. This paper shows that the pressure wave is transmitted from the injection port of the compressor to the gas-liquid separator through the injection pipe and COP is varied by the length of injection pipe cyclically. Appropriate injection pipe length can be calculated using the resonance wavelength caused by compressor rotational speed.

Low global warming potential refrigerants such as HFO (hydro fluoro olefin) -1234yf are attractive as alternative working fluids in air-conditioning and cooling systems to address global warming. However, larger compressor sizes were required due to the lower fluid density compared with conventional refrigerants such as R 410A. Thus, a new wing-vane compressor which has no contact between the vane and cylinder has been developed to prevent on increase in size without performance degradation. In this paper, the compression characteristics and the load characteristics were investigated by creating a dynamic model of the wing-vane type. The results are as follows: (1) The striking feature of the wing-vane type is that there is no friction loss at the vane tip. (2) Like the conventional sliding vane type, the torque and rotor load fluctuate with the same number of peaks as the number of vanes.

Low global warming potential refrigerants such as R 1234yf are attractive as alternative refrigerants in air-conditioning and cooling systems. However, larger compressor sizes were required due to the lower fluid density compared with R 410A. Thus, a new wing-vane compressor which has no contact between the vane and the cylinder has been developed to prevent an increase in the size without performance degradation. The rotary motion of the vane is supported by the arc vane guide on the upper and lower ends of the vane. Discovering the lubrication properties and the stability of the vane guide was one of the issues required in development. So we analyzed the friction coefficient between the vane guide and the guide bearing with numerical analysis, and measured the friction coefficient by experiment. We confirmed that the friction coefficient of the analysis and experiment result are in good agreement, and can be organized in a Stribeck curve as well as full journal bearing in the fluid lubrication region. And we solved motion equation to clarify the behavior of the vane guide.

Low global warming potential refrigerants such as HFO (hydro fluoro olefin) -1234yf are attractive as alternative working fluids in air-conditioning and cooling systems to address global warming. However, larger compressor sizes were required due to the lower fluid density compared with conventional refrigerants such as R 410A. Thus, a new wing-vane compressor which has no contact between the vane and cylinder has been developed to prevent on increase in size without performance degradation. In this paper, a prototype of the wing-vane compressor was operated using R 134a refrigerant to simulate HFO-1234yf refrigerant. The results are as follows: (1) the APF (annual performance factor) ratio of the prototype of the wing-vane compressor was 100.2% with respect to the twin-rotary compressor. (2) Stable operation was confirmed without problems in the process from suction to discharge. (3) There were no serious abrasions and scratches in the friction parts of the wing-vane compressor after 100 hours of operation under high load operating conditions. (4) The vane-guide, whose arc angle is over 60 degrees, operates stably in low load conditions which are the most worrying conditions for instability of a vane-guide.

The authors studied elemental technologies that realize large capacity and high efficiency in rotary compressors in order to achieve energy and resource savings and weight reduction of the heat pump systems. These technologies are the optimization of cylinder dimensions, the development of a new discharge structure, the compatibility between sliding loss reduction and securing of reliability in the sliding parts, the newly developed motor, and the use of PWM converter. We developed and commercialized a model that increased maximum refrigeration capacity by about 1.7 times compared to our conventional large model and improved the COP ratio by about 6% in the full capacity range compared to that conventional one. We also worked on reducing the amount of rare earth magnet usage and improving PWR (Power Weight Ratio), and obtained the effects of resource saving and weight reduction by increasing the capacity of the rotary compressor.

The reciprocating compressor is mainly used in household refrigerators, and the lubricating oil is supplied to the compression mechanism by the oil pump system, which consists mainly of the oil viscous pump. The performance and reliability of the refrigerant compressors are influenced by the lubricating oil. Recently, we examined the flow characteristics of the oil viscous pump provided with a spiral groove on the shaft surface, in theoretical and experimental study. When the oil flow in the spiral groove was assumed to be fully developed and steady laminar flow, it became clear that relationship between the pump head and the discharge flow rate of the oil viscous pump becomes in theoretically linear function. Also by the experiments, it was found that if the oil groove length is greater than a certain value, the error between the experimental flow characteristics and the theoretical flow characteristic was small.

It is very important to reduce the friction loss of the compressor for developing the refrigeration and air conditioning equipment with high efficiency. In this study, we focused on the low friction technology with the surface texturing on the crank shaft for reciprocating compressor. The characteristic of the crank shaft with the micro grooves was evaluated using calculation and experimental method. Compared to the crank shaft with smooth surface, the crank shaft with the micro grooves showed low friction characteristics. The performance of the reciprocating compressor with the textured crank shaft was also evaluated using the refrigeration cycle. The result of the performance test showed that the surface texturing on the crank shaft has the effect of decreasing the power consumption of the compressor and the coefficient of performance was improved.

Vane type compressor are widely used in automotive air-conditioner system. The vane type compressor driven by an engine via an electromagnetic clutch causes a large torque peak at a start-up operation. It may result in deterioration of drive feeling and inducing noise. Therefore, the cause of the peak torque occurrence and a torque transferred to the engine side at the start-up operation should be clarified. In this study, an analytical model which can examine the peak torque generation and characteristics of torque transfer to the engine side is developed. It is found that the peak torque under the start-up operation is caused by an over compression in compressor chambers during a discharge process due to sudden acceleration of the compressor and characteristics of the torque transfer by the electromagnetic clutch. The change of clutch torque induces the peak torque and fluctuation of the driving torque at the engine side by a torsional vibration of a driving train.

Linear compressor is a reciprocating compressor, in which a piston is driven directly by a linear motor with linear motion. The linear compressor has an advantage that contact force between the piston and a cylinder is small compared with conventional reciprocating compressors because the linear compressor doesn’t have a crank mechanism. However, the influence of the mechanical loss on the performance becomes large in a miniature size linear compressor, and the mechanical loss in the small linear compressor was not investigated in detail. In this study, measurement of the mechanical loss in the linear compressor is examined by measuring the side contact force between the piston and the cylinder. As a result, it is found that when a support spring shrinks around BDC, the piston leans in a certain direction and makes contact with the cylinder. The frictional force by the contact between the piston and the cylinder is smaller than a viscous force by lubricant in the linear compressor used in this study.