This paper refers to the working fluids selection for Rankine cycle engine driven by the heat source with a small temperature difference. The temperature range of the heat reservoir is from 80oC to 300oC. The heat sink temperature is set at 40oC. Non-fluorocarbon refrigerants are chosen as working fluids. According to the characteristics of the saturated vapor line on T-s diagram, the working fluids are sorted into three groups. Comparing the condensation pressure to the atmospheric pressure, the working fluids are classified into two types. Under some constraints for the reasonable formation of Rankine cycle such as avoiding the condensation in the expansion process, the thermal efficiency and net specific work are calculated by using the database of thermodynamic properties. It is found that the thermal efficiencies are distributed in the range from 10% to 25%, depending on the heat source temperature. The working fluids selection is strongly affected by the heat source temperature, the latent heat around the condensation temperature and the pressure difference between the evaporator and condenser. In addition, the performance evaluation method, based on the irreversible loss in Rankine cycle, is proposed. It is confirmed that the smaller irreversibility brings the higher thermal efficiency.
In recent years, air pollution is one of the big environmental problems. Especially a demand for high quality air is increasing from the view of the living and health life. It is important that we promote effective measures for a bad smell hastily. Various ideas were suggested and have been used, but the decisive solution has not been developed yet. This paper relates to new deodorization system by utilizing condensation phenomenon with photocatalyst. As stable semiconductor which shows a photocatalyst effect, TiO2 is widely used, however, TiO2 needs ultraviolet rays. In order to solve this inconvenience, we showed an effect under the visible ray by using visible ray type photocatalyst and light emitting diodes (LED). Furthermore, for this system, energy saving by the pulse irradiation using high-speed responsiveness of the LED was confirmed experimentally.
We have already developed a Single-Tip Optical fiber Probe (S-TOP): an efficient measurement technique for a velocity and diameter of a bubble or droplet. The objective of the present study is to improve the measurement accuracy of the S-TOP. We use a pre-signal to rationally correct the S-TOP measurement error owing to a random position penetrated by the S-TOP on the bubble surface. Hidden potentials of the pre-signal were revealed through a 3D numerical simulation based on a ray tracing method. The simulator can evaluate the complicated optical signals of the S-TOP by computing the polarization and energy of every incident ray. Based on the numerically simulated result corresponding to the single-bubble measurement, we clarified that the pre-signal was caused by light reflection at the bubble frontal surface. Furthermore, the characteristics of the pre-signal were quantified; the pre-signal intensively appears just before the S-TOP touches the bubble’s central region. Using these characteristic phenomena, we can easily detect the touched position (pre-signal threshold method). This method enables us to achieve an accurate measurement in a bubbly flow. The measured chord lengths via the S-TOP were compared with the lengths of the bubble minor axis obtained from visualization. In consequence, a difference of the results between the pierced chord length and the bubble minor axis was considerably decreased.
Attention has been paid to the enhancement of the performance of CO2 heat pump water heating systems. One of the ways to increase the heat pump coefficient of performance (COP) and system efficiency as well as the volumes of stored and unused hot water is to revise the system by extracting water with middle temperatures from the middle of the storage tank, and the performance of the revised system has been evaluated by numerical simulation. However, the volumes of stored and unused hot water have been evaluated in a conventional method. In this paper, they are evaluated in consideration of hot water supply procedure. An evaluation method by numerical analysis of differential equations is proposed to take account of the discontinuities of the temperature in the storage tank. Through evaluation examples, it turns out that the volumes of stored and unused hot water are evaluated accurately and efficiently in all the cases by the proposed method. In addition, it is clarified how the volumes of stored and unused hot water evaluated by the proposed method differ from those by the conventional method.
In the melting process of ice particle bed in an ice thermal storage tank, water channel is formed due to the local melting of ice particles. Water channel causes some problems such as the decrease of heat transfer performance. In this study, the generating process of water channel was investigated. In experiment and simulation, ice particle bed was melted intentionally by using a line heat source, and water channel was generated in it. As a result, it was found that the melting front becomes longer in the vertical direction as the flow velocity of water increases and the permeability in the ice particle bed decreases. Additionally, the effects of bubble, screen and hole in the ice particle bed, on the shape of melting front were investigated.
A novel two stage compressor for CO2 heat pump water heater was developed. CO2 as a working fluid has high operating pressure and high pressure difference, which brings decrease in efficiency and reliability. Therefore, it is especially important for a development of CO2 compressor to make a proper selection of its basic structure. The developed two stage compressor equips intermediate pressure housing, intermediate gas injection and both rotary and scroll compression chambers as first and second stage respectively. For the efficiency improvement, loss classifications based on the cylinder pressure measurements were conducted and 6% reduction in the indicative efficiency in the second stage was obtained by stiffness enhancement of the fixed scroll. The developed compressor resulted in over 15% improvement of efficiency compared with conventional single stage compressor. Moreover, 25% and 50% improvement of heating capacity and COP respectively is archived on deep frozen condition by employing two stage intermediate gas injection system with the developed compressor.
By having a mechanism to switch-off one of two cylinders, ”Dual Rotary Compressor” has become the best candidate to operate in wide range load condition. But the conventional mechanism still has some problems such as a decrease in efficiency in 2-cylinder operation, space-consuming pipe fittings and difficulties of application to highly-efficient models. We have developed a new mechanism which can solve those problems, and succeeded in commercialization for room air-conditioners. The new space-saving dual rotary compressor is more efficient 3% in APF than conventional model.
A CO2 rotary compressor uses refrigeration oil to lubricate and cool sliding parts and to seal the cylinder. It is difficult to separate the oil in the shell at high pressure from CO2 gas, whose difference in density from the oil is small. It remains an issue to retain high efficiency with the same shell size as a present hydro fluorocarbon (HFC) compressor. We explored improvements in the oil separation by use of computational fluid dynamics (CFD) analysis and identified two effective measures. One measure is to flatten a lower balance weight of the rotor to prevent the oil mist from moving up through the motor flow paths. Another measure is to set up a rotating disc over a protruding balance weight at the top of the rotor to increase the pressure in the upper space and allow the oil over the stator to return to the lower space by gravity. Experiments with an actual compressor verified that oil separation was improved to the target value.
Swashplate compressor is often used for automotive air conditioners. The severest lubrication position in the swashplate compressor is a sliding surface between a swashplate and a shoe. Since metal contact between them sometimes causes lubrication failure, it is important to measure oil film behavior to clarify the lubricating condition between the swashplate and the shoe. In past studies, it was shown that the metal contact between swashplate and shoe occurs during not only compression and discharge processes but also a suction process although contact load on the shoe becomes zero during the suction process. In this paper, the lubricating condition between the swashplate and the shoe in the swashplate compressor is monitored by a capacitance method. In addition, the shoe behavior is observed by optical interferometric fringes between the swashplate and the shoe with a model experimental apparatus which simulates a relative motion of the swashplate and a piston. It is found that the shoe behavior becomes unstable during the suction process. When the contact load on the shoe becomes zero, the wedge angle of the oil film decreases by oil shear force acting on the shoe caused by a precession motion of the piston. Feasibility of an acoustic method for a failure detection is also introduced.
In this study, calculations of the mechanical efficiency of a large reciprocating compressor, developed by Mayekawa MFG. Co., Ltd., with a per cylinder suction volume of 1300 cm3 were carried out. These calculations were used to confirm whether the empirical combination of major design parameters in the Mayekawa compressor delivers optimal mechanical efficiency. Initially, the theoretical equation of motion of the rotating crankshaft is developed. Subsequently, computer calculations are carried out to determine the mechanical efficiency for various combinations of the major design parameters for operating speeds of 800, 1000 and 1200 rpm. From these calculations, the optimal combination parameters yielding the maximum mechanical efficiency could be determined, and then compared with the empirical combination used in the Mayekawa compressor. The maximum mechanical efficiency reaches 91.1% at the operating speed of 1000rpm, with a combination of the piston stroke of 40mm and the piston diameter of 130mm, which agree well with the design values of conventional compressor. An attention should be paid to the characteristics of optimal combination, depending upon the operating speed, where the selection of optimal combination at the average operating speed is recommended.