The compressors for CO2 refrigerant have a lot of difficulties to achieve high efficiency and reliability because of its very high operating pressure, which causes the deformation for scroll element. The deformations of the fixed scroll during operation fall into the following four categories: (1) pressure deformation due to pressure differences; (2) thermal deformation due to temperature difference; (3) deformation caused by welding for fixing the frame to the shell; and (4) bolt tightening deformation of the compression mechanism. In this study, in order to minimize the deformation during operation, deformations (1) and (2) are grasped by numerical calculations and deformations (3) and (4) are controlled to cancel the deformations (1) and (2) by adjusting the stiffness of fixed scroll. In addition, we measured the deformation under the operation by using the strain gauge in order to confirm that the proper stiffness of fixed scroll can minimize its total amount of deformation.
System performance prediction model for air-cooled air conditioner has been developed, and influences of Grooved tubes on performance of air conditioners with R410A were quantitatively investigated. Calculated results with simulation model correspond approximately to measured results by the authors and other researchers. After that, performances of air conditioners with grooved tubes were predicted. Results show that condensation heat transfer coefficients decrease with the rise of air conditioning load rate, and boiling heat transfer coefficients increase with the rise of air conditioning load rate. On the other hand, pressure drops increase 1.2-1.4 times in evaporator. Then, COPs of air conditioners with the grooved tube are 1.16 times higher than COP of air-conditioners with the smooth tube.
This paper aims to boot up polymer electrolyte fuel cells at subzero temperature without energy from outside and compass the conditions. Visualization tests of water drainage and voltage-current density characteristics provided the selection of a serpentine type as a channel of a fuel cell separator for cold region. The successful start-up of the cell at subzero temperature requires suitable current densities corresponding to the ambient temperature since the lower the temperature is, the lower the cell voltage soon after the start-up is. Suitable amount of exhausted energy is also necessary for the successful self start-up. Humidification using potassium acetate 30 mass% solution provides increased impedance of the cell and inhibits the water freezing owing to its dispersal to the electrode compared to no humidification. A stack laminated 25 sheets of the serpentine type separators enables stabilized power generation at normal temperature. The stack is also bootable with no energy from outside at 263K.
The use of bamboo charcoal, which is one of the carbon from wood, attracts attention from the viewpoint of the environmental protection. Bamboo charcoal has high adsorption removal ability to various substances. In addition Bamboo charcoal is effective also for the filtration of the suspended solid and the bacterium by the macro pore that originates in the plant frame structure. In present paper, a new concept of gas clean technology by bamboo charcoal and TiO2 with UV light irradiation was proposed. Its system is composed of TiO2-coated bamboo charcoal, TiO2-coated silica gel and UV lamp. Water vapor is adsorbed by bamboo charcoal and fine particles and airborne bacterium are trapped on the surface of it. Trapped contaminant is degraded by TiO2 and UV light. In addition, the degradation is promoted by •OH produced by adsorbed water vapor. The air purification sanitization possibility in high efficiency for this system was clarified.
Magnetic refrigeration is a cooling technology based on the magnetocaloric effect (MCE), which is a temperature-changing phenomenon caused under the magnetic field alteration. However, the temperature span caused by MCE is very small at room temperature. Hence Active Magnetic Regenerator (AMR) is developed to enhance temperature span of the system. In this paper, analytical evaluation and projection of cooling performance for magnetic refrigerator with AMR are conducted. An analytical model with bundle of small channels and jet flow and retention region in a test sectional tube is built in order to simulate fluid flow through spherical gadolinium particle packed bed as magneto caloric materials. The evaluation and projection of the AMR magnetic refrigeration system by analytical model showed performance of the temperature, and the existence of optimum operating conditions is shown under the condition of appropriate flow volume and volumetric flow rate.
In this study, pressure drop and local heat transfer characteristics for the condensation process of R744 were measured experimentally in a horizontal multi-port extruded tube of 0.36 mm in hydraulic diameter. Experiments were carried out in the mass velocity range of 470 to 830 kg/(m2 s) at pressure 5, 6 and 7 MPa. The pressure drop was measured between both ends of the test section of approximately 730 mm in length. The local heat transfer was measured in eight subsections of 75 mm in effective heating length. The measured pressure drop was compared with several correlations. The correlations of Friedel and Mishima - Hibiki comparatively show a good agreement at pressure of 5, 6 and 7 MPa. The local heat transfer coefficients were also compared with several correlations. The high vapor quality data agree comparatively with correlations of Moser et al. and Cavallini et al., while other data do not agree with any correlations well. The present experimental results suggest that the condensation in a rectangular mini channel is controlled not only by forced convection effect, but also by surface tension effect.
In this paper,a static analysis of double effect adsorption refrigeration cycle utilizing condensation heat is discussed. Double effect adsorption refrigeration cycle consists of two cycles, High Temperature Cycle (HTC) which is driven from external heat sources, and Low Temperature Cycle (LTC) which is driven by condensation heat from HTC. Both of HTC and LTC are using silica gel and water as working pairs. The effect of heat source temperature on cycle performance was investigated in terms of coefficient of performance (COP) and specific cooling energy (SCE). Results showed that double effect cycle would produce higher COP than single effect cycle for driving temperature observed between 80-150°C with the same operating condition. However, the value of SCE is lower than single effect, despite that the SCE of double effect cycle is improved with heat source temperature higher than 100°C. Further, it was also observed that adsorbent mass ratio of HTC and LTC affected performance of chiller. When adsorbent mass ratio of HTC and LTC was unity, it was found that SCE and COP took the maximum.