In this paper, Cooling systems with natural circulation loop of refrigerants are reviewed. The cooling system can largely reduce energy consumption of a cooling system for the telecommunication base site. The cooling system consists of two refrigeration units; vapor compression refrigeration unit and sub-cooling unit with a natural-circulation loop. The experiments and calculations were carried out to evaluate the cycle performance of natural circulation loop with HFCs and CO2. The experimental results showed that the cooling capacity of R410A is approximately 30% larger than that of R407C at the temperature difference of 20K and the cooling capacity of CO2 was approximately 4-13% larger than that of R410A under the two-phase condition. On the other hand, the cooling capacity of CO2 was approximately 11% smaller than that of R410A under the supercritical condition. The cooling capacity took a maximum value at an amount of refrigerant and lineally increased as the temperature difference increases and the slightly increased as the height difference. The air intake temperature profile in the inlet of the heat exchangers makes the reverse circulation under the supercritical state and the driving head difference for the reverse circulation depends on the density change to temperature under the supercritical state. Also, a new fan control method to convert the reverse circulation into the normal circulation was reviewed.
This paper proposes a snow storage system by using a renovated space for the purpose of efficient energy use and cost saving of the utilization of snow and it aims to clarify the effectiveness of this system. First, an outline of snow storage system by using a renovated space is presented, together with a description of a facility for a demonstration test. Second, as a result of long term measurements on snow storage characteristics, the percentage of the energy used for cooling at the end of the space cooling period was 59% of the initially stored snow. And as a result of heat balance analysis, though heat loss from the floor was relatively large due to locating of the underground space, we confirm that this system has possibility of high energy conservation. Finally, as a result of analysis through construction phase and operation phase on the cooling system, payback periods of primary energy were less than 10 years, and initial cost was 96% compared with a conventional system.
Diagnosis of compressor product's malfunctions based on the vibration wave pattern data of the compressor and the FFT analysis data is developed. The feature of the analysis technique is two points. One is "Evaluating the ratio of the FFT integral calculus value of low frequency area and the high frequency area of the vibration wave pattern for the feature of abnormalitys", and the other is "Separating and evaluating the wave pattern region at the time of the start and the steady part as correspondence to the phenomenon that an abnormal tendency appears in the non-steady early start region". The feature of each abnormality is extracted. A diagnosis algorithm that distinguished normality and abnormality is developed. Moreover, the cause is distinguished about abnormality. The verification examination of the scroll compressor is done in the production line. And the effectiveness of this diagnosis algorithm is validated for both the alternating-current motor type scroll compressor and the direct-current motor type scroll compressor.
Cryopreservation of fish eggs and embryos is a highly desired tool to promote aquaculture production and fisheries resource management, but it is still not technically feasible. The failure to develop successful cryopreservation protocols for fish embryos is largely attributed to poor cryoprotectant permeability. The purpose of this study was to test the effectiveness of CaCl2 to enhance cryoprotectant uptake by fish embryos. In this study, embryos (somites and tail elongation stages) of Japanese whiting Sillago japonica were exposed to 10 and 15% dimethyl sulfoxide (DMSO) in artificial sea water (ASW) or a solution of 0.125M CaCl2 in distilled water for 20 min at 24°C. The toxicity of all solutions was estimated from the hatching rates of the embryos and High Performance Liquid Chromatography was used to determine the amount of DMSO taken up during impregnation. The results showed that DMSO incorporation into the embryos was greatly (›50%) enhanced in the presence of CaCl2 compared to ASW. CaCl2 itself was not toxic to the embryos but, probably as a result of the enhanced DMSO uptake, caused decreases in survival of about 14-44% relative to ASW. Somites stage embryos were more tolerant than tail elongation ones to DMSO both as ASW and CaCl2 solutions. The use of CaCl2 as a vehicle for DMSO impregnation could be a promising aid for the successful cryopreservation of fish embryos.
Liquid-liquid direct contact heat transfer can be effectively utilized for the heat transfer between two immiscible liquids of small temperature difference. However, the water droplet in the oil is difficult to start freezing, because the droplet is easy to be supercooled. The charged water-droplet in oil with uniform electric field collides repeatedly with the electrode plate, because it reciprocates between the electrode plates. It is known that the collision is effective for freezing initiation of the supercooling water-droplet. The purpose of this study is to make clear the relation between the collision and the initiation of freezing. The behavior of the droplet is photographed by a high-speed video camera. For the convenience of photographing, transparent electrode plate is used as the lower electrode in the experiment. As a result, the contact behavior between the droplet and the electrode plate, change of contact area with time, position and timing of the freezing initiation, freezing progress in the droplet are clarified. The lower temperature of continuous-phase liquid and the higher electric field strength bring the position of freezing initiation close to the vicinity of three-phase boundary.
Partial dehydration by microwave-vacuum drying has been applied to tuna and strawberry in order to reduce cell-damages caused by the formation of large ice-crystals during freezing. The samples were subjected to microwave vacuum drying at pressure of 5 kPa and temperature less than 27°C to remove small amount of water prior to freezing. The tuna were cooled by using the freezing chamber at temperature -50°C or -150°C, while the strawberries were frozen at temperature -30°C or -80°C, respectively. The temperature transients in tuna showed that removing some water before freezing made the freezing time shorter. The observations of ice crystal clearly indicated that rapid cooling and pre-dehydration prior to freezing were effective in minimizing the size of ice crystal. It is also understood that the formation of large ice crystals has a close relation to the cell damages. After thawing, the observation of microstructure was done on the tuna and strawberry halves. The pre-dehydrated samples showed a better structure than the un-dehydrated one. It is concluded that the pre-dehydration by microwave-vacuum drying is one promising method for the cryo-preservation of foods.