Erythritol slurry, which is the mixture of solid erythritol crystal and erythritol aqueous solution, is a promising as slurry heat medium for medium-low temperature application. The flow pattern of slurry heat medium generally depends on the flow velocity and the solid fraction, and erythritol slurry often forms flow with sedimentation, because density difference between solid and liquid is relatively large. In the previous work, we investigated the effect of the flow pattern on the flow and the heat transfer characteristics of erythritol slurry, and proposed the original flow model suitable for flow with sedimentation. In this study, we proposed the modified model, in which the filling rate of solid in the sedimentation bed and the flow velocity of the bed are considered. The pressure drop obtained by the experiment and the model were compared, and it was confirmed we can estimate the pressure drop by using the model in a wide range conditions except for very low solid fraction. Moreover, since the modified model can consider the flow velocity of the bed, the model can be used for the discussion of the heat transfer characteristics of the erythritol slurry flow.

CO2 is a promising refrigerant due to its low environmental impact and low toxicity. In the present study, ultra-low temperature refrigeration technology using CO2 heat pump system is introduced with newly developed cyclone separator-evaporator. In the installation phase of the actual refrigeration system, internal blockage was observed in the flow path of dry ice in a horizontal evaporator, which is modeled after a general-purpose evaporator. It was shown that the blockage phenomena caused to reduce the performance of the system as thermal resistance. In order to solve the problem of internal blockage and to improve the performance of evaporator, we introduced a cyclone separator-evaporator is designed and installed in the actual refrigeration system. The newly developed cyclone separator-evaporator is a combination of a cyclone separator part and an evaporator function part. As a result of evaluating the refrigeration system performance using a cyclone separator-evaporator, it is found that the system achieved high efficiency in the low temperature of -67°C and COPsystem of 1.2. The system performance is expected to be significantly improved compared to the system using a horizontal evaporator.

In recent years, there has been demand for a large-capacity scroll compressor to reduce the size and increase the output power. To increase the capacity of the scroll compressor, technology to increase the stroke volume without increasing the shell size is required. To increase the stroke volume, increasing the wrap height in the axial direction is most effective. However, the higher wrap height raises the stress on the wrap and causes the orbiting scroll to overturn. So, we started to study a new shape of wrap to increase the stroke volume in the horizontal direction. The base plate of an orbiting scroll is usually circular. However, the shape of the sliding surface of the fixed scroll on the base plate of the orbiting scroll is not circular, so wasted space that is not useful for compression exists on the base plate. We devised an oval wrap to make the trajectory of the fixed scroll on the base plate circular and reduce this space. Oval scrolls can increase the stroke volume by 20% compared with the conventional scroll under the conditions evaluated in this paper.

The purpose of this study is to improve the liquid-distribution uniformity of refrigerant gas-liquid flows in parallel-flow type heat exchangers that consist of dividing/combining headers and multiple branch tubes connected to them. The test channel had a vertical header with a height of 81.5mm and 8 horizontal branch tubes connected in parallel at a pitch of 10mm. We tested the refrigerant-supplying method using a pipe with multiple outlet holes installed in the dividing header, i.e., multi-hole inner pipe. Gas-liquid distribution ratios in each branch tube were measured changing an inner diameter and outlet-hole diameters of the inner pipe. It was confirmed that the liquid-distribution uniformity was much improved with the multi-hole inner pipe. Based on the design of experiment with the orthogonal table, we evaluated quantitatively the influence of geometrical parameters of the multi-hole inner pipe on the liquid distribution characteristics. We found that the inner diameter of the inner pipe had the large influence on the maximum reaching height of liquid, while the uniformity of the liquid distribution was influenced by the outlet-hole diameter of the inner pipe. The liquid-distribution uniformity was improved by using the inner pipe with a smaller outlet-hole diameter.

In this paper, an experimental study on the condensation heat transfer coefficient of refrigerant R1234yf was obtained inside a 3.5 mm outside diameter (OD) horizontal microfin tube. Comparison of present work (3.5 mm OD) and previous research (2.5 mm OD) was reported to evaluate the effect of diameter to heat transfer coefficient. Data were obtained over a range of mass velocity from 50 to 200 kg m^-2s^-1, vapor quality 0 to 1, and saturation temperature from 20°C to 30°C. The effect of mass velocity, vapor quality, and saturation temperature on condensation heat transfer coefficient was clarified. The experimental results were compared with some existing correlations in the open literature. Hirose et al. (2018) correlation has good agreement with experimental data.