In order to improve the performance of the absorption refrigerator, we investigated the characteristics of horizontal tube-type and vertical plate-type equipments as absorber or generator using water-LiBr system. The horizontal tube-type is used widely as absorber and the vertical plate-type has good performance of heat/mass transfer because of large surface area per unit volume. We examined the effects of heating/cooling water temperatures and the surfactant (1-octanol) concentrations on the efficiencies of two type equipments. The experimental results say that the observed values of the absorption/generation rates for the vertical plate-type used as absorber were much greater than those for the other types. In addition, the observed values of the absorption/generation rates were compared to the calculation values based on heat/mass transfer in LiBr solution film and the observed values were almost equal to the calculation values without the surfactant addition. With surfactant addition, the observed values for the vertical plate-type used as absorber was remarkably increased.
The changes in the antioxidant activity of shredded red and green cabbages during storage, and the effects of packaging, washing and sterilization were investigated. After washing and sterilization of red and green cabbages, radical-scavenging activity, total phenol content, and ascorbic acid content decreased to 70-78%, 68-72%, and 73-83%, respectively. In green cabbage, ascorbic acid content increased for up to 3 days and decreased by 14-day storage in modified atmosphere and aerobic packagings. In red cabbage, radical-scavenging activity and total phenol content also decreased during 7 days but increased by 14-day storage in modified atmosphere and aerobic packagings. The sensory quality of green cabbage was well maintained during 7-day storage. Red cabbage deteriorated on day-3 in modified atmosphere and aerobic packagings, but no quality change was detected in anaerobic packaging. These results demonstrate that modified atmosphere and aerobic packagings seems better than anaerobic packaging in retaining the nutraceutical quality of red and green cabbages.
Dehydro-freezing method with the microwave vacuum drying has been applied to fish tissues in order to reduce cell damages caused by the formation of large ice crystals during freezing. This paper focused on the recovered muscle after thawing, and also investigated the effects of thawing rates on the quality of the tissues. We used two kinds of fish species; i.e., mackerel and sea bream. As for the mackerels, the slow thawing was effective for the re-absorption of water into the tissues, and showed the less drip loss than that by the rapid thawing. Although the sea breams had some damages caused by re-crystallization during the slow thawing, it was found that the damages could be reduced by pre-dehydration. Since the moisture content is different depending on fish species, the best dehydro-freezing needs to understand the moisture transports in the tissues during thawing.
R 1234yf and R 32 are expected as the alternative refrigerants for protection of the global environment. R 1234yf and R 32 have low flammability by comparison with the other HFC refrigerants now in worldwide use. We examined the fire hazard and characteristic of HF generation in the case that a wall mounted type air conditioning system having these alternative refrigerants is used with the fossil-fuel heating systems in the same room (corresponding to 4 pieces and half of tatami mats) at the same time. Both the cases of R 1234yf and R 32, concentration of refrigerant in the room was not more than the lower flammable limit (LFL) of refrigerants even if the all amount of refrigerants leaked from an air conditioning system to the room, so the flame propagation of refrigerants was not confirmed. However, generation of HF over the permissive concentration (3 ppm) was confirmed regardless of the varieties of refrigerants including R 410A due to the contact between refrigerants and heating part in the fossil-fuel heating systems. It was experimentally confirmed that productivity of HF from R 32 per unit time and mass was comparatively larger than that of R 1234yf and R 410A.
The objective of this study is to develop a new prediction method of frictional pressure drop inside horizontal mini-channels for condensation process. Based on the database containing wide range of experimental conditions on the kinds of refrigerants and mini-channels, we developed a new frictional pressure drop correlation of HFC and HFO refrigerants condensing in mini-channels. The present correlation agrees well with experimental data of condensation flow, and it also agrees with the data of two-phase adiabatic flow in mini-channels.
In this study, the condensation process of pure and near-azeotropic refrigerants in a horizontal multi-port tube having 17 rectangular mini-channels is investigated experimentally. The measured heat transfer coefficient is influenced mainly by the vapor shear stress and surface tension. We developed a new prediction model on heat transfer based on the following main assumptions: (1) in the annular flow region, the heat transfer correlation isexpressed as the combination of the vapor shear stress controlled term and the surface tension controlled term, (2) in the plug flow region, the heat transfer characteristic of the vapor plug is the same as the annular flow region, while that of liquid slug is the same as liquid single flow, (3) the annular flow is treated as the plug flow with the long vapor plug and the short liquid slug. The new heat transfer correlation agrees well with the experimental data of R134a, R32, R1234ze(E) and R410A in horizontal rectangular mini-channels within 40 % in deviation.
Thermal energy storage performance of cyclopentane hydrate for air-conditioning use has been researched. In our previous studies, heat of dissociation of this hydrate indicates 284 kJ/kg and thermal energy storage density reaches to 125 MJ/m3 in practical bulky scale using stoichiometrically prepared cyclopentane-in-water emulsion to increase hydrate formation rate. These results show that this hydrate-forming emulsion can be one of the candidates of thermal energy storage media. In this study, heat transfer coefficient of cyclopentane hydrate slurry (suspension state with cyclopentane hydrate particles in emulsion) is focused to be applied to the storage tank design and is investigated with a cooling / heating coil immersed in a cylindrical vessel on several stirred conditions. For this purpose, effective viscosity of this hydrate slurry also has been studied by torque measurement of a plane plate rotator.
Slush nitrogen is a 2-phase coolant of liquid and solid nitrogen. Fine solid particles are contained and dispersed in liquid phase nitrogen. It enables us to utilize the latent heat of fusion resulting in the increase of the volumetric heat capacity of the supplied refrigerant. Consequently, it is expected to be high performance useful and unique refrigerant for high-temperature superconducting devices. The heat transfer characteristics of the slush nitrogen under forced flow condition in pipes were studied in a previous work. It has been still unclear whether the latent heat of fusion of the dispersed solid particles could be efficiently used for cooling.