Freezing is a valuable technique for food preservation. However, vegetables are known to be softening remarkably after freezing and thawing process. It is expected to find alternative technique instead of freezing. Recently, the application of structured water and/or gas hydrate had been attempted to prolong the preservation of vegetable. In this study, the formation process of structure water and/or gas hydrate in pure water and carrot tissue was investigated by using NMR relaxation times, T1 and T2, of which applying condition was up to 0.4MPa and 0.8MPa at 5oC. Under the pressure of 0.4MPa, no gas hydrate was appeared, however, at 0.8MPa, formation of gas hydrate was recognized in both water and carrot tissue. Once the gas hydrate formation process in carrot tissue started, T1 and T2 increased remarkably. After that, as the gas hydrate developed, then T1 and T2 turned to decrease. Since this phenomenon was not observed in pure water, it is suggested that behavior of NMR relaxation time just after the formation of gas hydrate in carrot tissue may be peculiar to compartment system such as inter and intracellular spaces.
Experimental studies for freeze-concentration of liquid droplet fallen on a horizontal plate located in a cold room have been performed. The ice formed in this method is so called an ice stalagmite. Ethylene glycol aqueous solutions of 5wt% and 10wt% have been frozen to examine the effect of experimental parameters such as droplet temperature and droplet flow rate on concentration phenomena. It is found that the droplet temperature and the droplet flow rate affect ice formation pattern, but they do not affect the degree of concentration of the concentrated liquid. It suggests that the degree of concentration is affected only by cold room temperature. It is also shown that the degree of concentration becomes higher for longer freezing time.
Desiccant air-conditioning system is a promising technology because the exhaust heat can be effectively used in the future. We have reported the proposed system that combines a desiccant rotor with a vapor compression refrigerator. The confirmation experiment of stability and the performance was conducted with the experimental prototype. The result showed that it had the performance that was necessary for dehumidification driving in the summer and the humidification driving in the winter. In this report, we examined the influence on humidity controlling performance of the processing air temperature and humidity. As a result, we got high dehumidification efficiency and clarified the dehumidification characteristic in dehumidification driving in the summer. Dehumidification efficiency about 4.0 kg/kWh and COP of the system about 2.0 in summer driving mode were obtained.
A series of experiments was conducted to estimate the amount of snowfall of dendrite-type crystals produced by an artificial snowfall device that uses the rotary ventilation mesh filter method. An expression is proposed in this paper for the amount of the snowfall. The amount of snowfall (Gs) can be expressed as Gs = ηs VaiΔW , where ΔW is effective water content in the crystal growth, Vai is air mass flow and ηs is snowfall efficiency. The effective water content in the crystal growth (ΔW) is defined as the difference between the specific cloud water content and ice saturation vapor density. The rotary ventilation mesh filter method used in this work had a snowfall efficiency of about 90%. Even for a large amount of cloud water content, we observed only a very few super-cooled cloud droplets on snow crystals. Therefore, we can deduce that the cloud water content should contribute to crystal growth directly. We report here measurements of snowfall as a function of several input parameters and verify the validity of the proposed relationship.
This paper describes the numerical analysis of mixed lubrication and the calculated results for journal bearings in rotary compressors. In this analysis, the modified Reynolds equation and the elastic contact equation, considering the effect of surface roughness, are solved as a coupled problem, and then influences of the elastic deformation of the bearing surface and the motion of the rotating shaft with bending deformation are also considered. The appearance of solid contact in hydrodynamic lubrication can be addressed by the analysis. Influences of the rotating speed and the surface roughness on the lubrication characteristics of the journal bearing were investigated by using the mixed lubrication analysis. As the results, it is made clear that the solid contact on the bearing surface occurs in the discharge process of rotary compressors. Furthermore, the contact pressure and the contact area decrease, even though the oil film thickness decreases, when the surface roughness becomes small.
This paper presents frictional characteristics of thrust bearing in scroll compressor focusing on the behavior of sliding portion which affects the generation of oil film. The coefficient of friction and tilt angle of sliding portion in the thrust bearing are obtained through both elemental friction test and cylinder pressure measurement of actual scroll compressor. Both tests showed that the coefficient of friction in low contact pressure rose with increase of tilt angle of sliding portion. The value of contact pressure which the coefficient of friction turns into increase was in agreement of the value which tilt angle become to increase. Numerical analysis using mixed lubrication theory was also performed. Analytical result indicated the same characteristics as the experiments, and the correlation between the coefficient of friction and the behavior of sliding portion was confirmed. Based on the experimental and the analytical results obtained here, the optimization of thrust bearing for commercial scroll compressor was applied. 2% improvement of total efficiency in rated condition was archived by optimization of thrust bearing.
The previous studies have revealed that the wedge formation at the periphery of the thrust plate, caused by the elastic deformation due to pressure difference across the orbiting thrust plate, is a significant key factor to keep and improve the high performance in lubrication of the thrust-slide bearing. The present study focuses on the effect of the thickness and inner form of the thrust plate upon the lubrication features. A simplified model of cylindrical thrust slide-bearing with thinner thrust plate submerged in a refrigerant oil VG-56 was operated under pressurized conditions using R-22 as the pressurizing gas, where the pressure difference was adjusted from 0 to 1.0 MPa and the friction force and coefficient of friction were measured over a wide range of orbiting speeds, first. The wedge angle by elastic deformation is naturally increased with decreasing the thrust plate thickness, thus resulting in a clear improvement in lubrication at the thrust slide-bearing. On the contrast, secondly, the similar lubrication tests were conducted for the thrust plate with a real inner form, as complicated as in the real scroll compressors, where the thickness of the thrust plate was kept as in the original tests. As a result, no significant change in lubrication features, from those for the simplified cylindrical model, was not addressed, thus confirming that the test results addressed from the simplified cylindrical model tests can be effectively used to examine the basic characteristics in lubrication of thrust slide bearing of scroll compressors.
We have developed a CO2 heat pump water heater compressor with a single-stage rotary mechanism for the first time in the world. Because the rotary compressor has a simple mechanism, it has become the mainstream for air conditioning compressors using R410A. The two-stage rotary and scroll compressors using CO2 have been put into practical use, however the single-stage rotary compressor had not been put to practical use, because the operating pressure of CO2 is more than three times as high as R410A refrigerants. We have applied a processing the DLC-Si (diamond-like-carbon-silicon) to the vane. It is the film of the DLC containing the silicon with a method of the plasma C.V.D. (chemical vapor deposit). The DLC-Si coated vane is hardly worn-out, only the surface roughness is smoothed. This paper describes the relationship between the silicon concentration in the DLC-Si film and their characteristics. Especially the adhesion strength is secured and the internal fracture is prevented by optimizing of the silicon concentration. In applying DLC-Si for practical use of the vane, we controlled the silicon concentration and secured high adhesion strength of the film. We were able to achieve an excellent level of wear durability.
A swing type refrigerant compressor was developed in order to overcome problems related to lubrication of a rotary compressor. However, the lubrication condition of the swing compressor has not been measured quantitatively yet. This paper describes an application of an eddy current displacement sensor to measure oil film thickness of a sliding part between a suction side bush and a blade in the swing compressor, and examined lubrication condition of the sliding part and a motion of the bush against the blade under some operating conditions. The results indicate that the sliding part between the suction side bush and the blade forms a wedge shape in shaft angle from 0° to 180° and forms a negative wedge shape in shaft angle from 180° to 360°. In addition, the results show that the oil film thickness on an upper edge side of the bush and a slope angle of the bush against the blade decrease with an increase of discharge pressure and increase with an increase of operating frequency of the compressor.
In this paper, lubricating conditions between a swashplate and a shoe in a swashplate compressor for automotive air conditioners is investigated experimentally. The conditions are measured with an electric resistance method that utilizes the swash plate and the shoe as electrodes respectively. The instrumented compressor is connected to an experimental cycle with R134a and operated under various operating conditions of pressure and rotational speed. An improved measurement technique and applying a solid contact ratio to the measurement results permit to measure the lubricating condition at high rotational speed (more than 8000 rpm) and to predic an occurrence of scuffing between the swashplate and the shoe, and therefore enables a detailed study of lubricating characteristics. It is shown by the measurement that the voltage of the contact signal decreases, which means better lubricating condition, with the decrease of the compression pressure and with the increase of the rotational speed from 1000 rpm through 5000 rpm. The lubricating condition tends to worsen at more than 5000 rpm. Furthermore, it is confirmed that the lubricating condition under transient operation is worse obviously as compared with that under steady-state operation.
In refrigeration cycles, mixing of refrigeration oil with refrigerant has great influence on the cycle performance, and a concentration measurement of the refrigerant/oil mixture is inevitable. The method of measuring the concentration ratio by detecting density, electric capacity, and refractive index etc. of the mixture has been examined. In this study, a sound speed measurement is applied to measure the concentration of the refrigerant/oil mixture. The sound speed of the mixture is measured by ultrasonic wave, and the relationship between the mixing ratio and the sound speed is obtained experimentally. There is a big difference between the sound speeds of refrigerant and refrigeration oil, and the sound speed can be a suitable physical property for the measurement of the mixing ratio of refrigerant/refrigeration oil mixture. Sound speed of R 410A/PVE mixture and CO2/PAG mixture showed different tendency from calculation values based on a volume fraction. It is found that the change in the sound speed is sufficient to measure the mixing ratio of the refrigerant in the refrigeration oil when the oil mixing ratio is high.