Yuhiro Iwamoto

Performance study of supercritical CO2-based solar Rankine cycle system with a novel-concept thermally driven pump

In this article, a supercritical CO2-based solar Rankine cycle system (SRCS) with a novel-concept thermally driven pump is studied. The thermally driven pump is a refrigerant-circulating pump composed of two expansion tanks and having merits of low power consumption and high reliability in comparison with conventional mechanical pump. The application of the present thermally driven pump in the supercritical CO2-based SRCS shows that an oscillatory flow is realized in the system and the system thermal efficiency is enhanced compared to the SRCS using the mechanical feed pump.

Study on a supercritical CO2 solar water heater system induced by the natural circulation

This article proposes a solar water heater system induced by natural convective flow using supercritical CO2 as a working fluid. In order to investigate the characteristics of the system, the dynamic characteristics and heat transfer property of the supercritical CO2 flow are measured under variable ambient conditions. The performance parameters such as the heat recovery efficiency, effective energy efficiency ratio, effective energy efficiency, highest temperature of the water, and the amount of hot water supplied by this heater system are presented and analyzed in detail. The effects of weather and season on the system performance are respectively examined. Furthermore, the methods to obtain higher efficiency of the system are also studied. The current results indicate that the circulation of supercritical CO2 flow in this solar heater system can be easily induced by natural convection. Without a driving pump, the highest heat recovery efficiency can be up to 90.4%, which is higher than the efficiencies of other conventional solar water heater systems. It is also found that the natural convection in the system is mainly affected by the intensity, stability, and continuity of solar radiation in a day. Furthermore, the amount of hot water supplied by this system is adequate for an ordinary house-hold usage with the highest temperature of the hot water in summer being 78°C.

Measurement of vapor void fraction in binary magnetic fluid using electromagnetic induction method

When an external magnetic field is applied to boiling two-phase flow in a magnetic fluid, it is known to effectively increase the heat transfer of magnetic fluid. In particular, void fraction of vapor two-phase flow plays a important role in understanding the heat transfer characteristics of magnetic fluid. However, there are a few studies to measure the void fraction of magnetic fluid because several conventional measurement techniques are difficult to apply to a magnetic fluid. In the present study, electromagnetic induction method was installed to measure the vapor void fraction and this measurement technique was proved to be valid for measuring void fraction of vapor bubbles. As a result, the present measurement was able to confirm the reduction of vapor void fraction under the influence of an external magnetic field.