This article concerns freeze concentration and its recent development. Freeze concentration enables to remove water from aqueous solutions including volatile and heat-sensitive components with less damage to the concentrated solution because of the operation at lower temperature near the freezing point with possibly no gas-liquid boundary. Moreover, the lower latent heat accompanied with ice crystallization provides a possibility of the operation with lower energy consumption. Recently freeze concentration has been applied to the wastewater treatment field. First the principle of freeze concentration will be addressed. Second applications of freeze concentration to the wastewater treatment field will be reviewed, including our recent works. Finally prospective views of freeze concentration will be given.

View full abstract

The performance of scroll compressors using the new back-pressure control system is much better than that of conventional compressors, especially under the cooling half-load condition at a higher suction pressure and a lower discharge pressure. Optimum performance is obtained under all operating conditions by varying the backpr-pessure at a level that is a constant amount above the suction pressure. This reduces friction at the thrust bearing between the orbiting and fixed scrolls. In this paper, we discuss the theoretical analysis of backpressure control method.

View full abstract

The measurement of the effective thermal conductivity of corrugated insulating materials, the evaluation of heat transfer mechanism in these materials and the improvement of insulating effect of them are studied in this paper. It is recognized that the contribution of radiative heat transfer to effective thermal conductivity is almost equal to the heat rate by conduction. The fairly good improvement are obtained by attaching Al foils to upper and lower surfaces of air space of specimen.

View full abstract

A new prediction method for evaporation pressure drop inside horizontal smooth and grooved tubes is proposed. These tubes had an outer diameter of 7mm, and the working fluids were R407C (HFC-32/HFC-125/HFC-134a, 23/25/52 mass%) and R410A (HFC-32/HFC-125, 50/50 mass%). The previous and present experimental data were correlated by Lockhart-Martinelli method, where Colburn and Carnavos equations were utilized for predicting single phase pressure drop of smooth and grooved tubes, respectively. Different numerical constants were adopted for smooth and grooved tubes to calculate the L-M pressure parameter φ _L.Inorder to express the gravitational effect, a damping function for φ _L was introduced. The proposed damping function was expressed as a function of Froude number for both smooth and grooved tubes. It is confirmed that 95% of the predicted results are within the accuracy of ±30% for both smooth and grooved tubes.

View full abstract

As regards the supercooling phenomena which is important matter in encapsulated ice system, we studied the supercooling release agent using the microorganism. Though the nucleation active bacteria had the high super cooling release ability, it was proved that the performance gradually lowered in long terms continuous use, when the live microorganism was used. In order to solve this problem, the sterilization treatment of the microorganism was examined and it was clariiied that there was the high effect in the ultraviolet irradiation. In addition, the persistence of the supercooling release ability is improved by freeze-drying treatment.

View full abstract

Ice formation phenomena of ethylene-glycol solution flow in a cooled vertical pipe have been examined experimentally. As a cooled pipe, polyvinyl chloride has been used. The concentrations of the ethylene-glycol solution are 2,6,10 wt%. It is shown that the crystal ice formed in the pipe is removed from the pipe surface and drift away downstream with the solution flow. It suggests the possibility of “liquid-like ice” formation by this method. It is found that the heat transfer coefficient in the pipe is strongly affected by ice formation and ice removal phenomena, and that the ice formation rate increases with decreasing Reynolds number. The ice removal phenomenon becomes not to occur for smaller Reynolds numbers and for larger cooling heat fluxes.

View full abstract

We have been studying on a suspension as a new thermal storage material. The suspension is made from silicone oil-water mixture with some additive or water with that by cooling with stirring. When designing the ice storage system using this suspension, the thermal conductivity of the suspension is essential. The purpose of this study is to measure a thermal conductivity of the ice-oil or ice-water suspension with good fluidity. The thermal conductivity was measured by at ransient hot wire method. In this study, the relationship between thermal conductivity and IPF was clarified, and thermal conductivity was expressed as a function of IPF. Moreover, the uncertainty of measurement of the thermal conductivity was estimated.

View full abstract

The liquid density of CFC and HCFC alternatives is an important property which is necessary in designing the heat exchange system of a refrigerating equipment.Seven fluorinated ethers and four fluorinated ketones which are expected as promising candidates of CFC and HCFC alternatives were measured at temperatures from 278K to 323K and at atmospheric pressure within an uncertainty of 0.2%, using the vibrating tube densitometer (ANTON PARR, DMA602) which has excellent performance of measurement speed, accuracy, and small sample quantity for a various type of a spescimen.The samples used in this study are 1, 1, 2-trifluoro-1-(2, 2, 2-trifluoroethoxy) ethane, 1;1, 2, 2-tetrafluoro-1-(2, 2-difluoroethoxy) ethane;1, 1, 2, 3, 3, 3-heptafluoro-1-methoxypropane;2, 2, 3, 4, 4, 4-hexafluoro-1-(monofluoromethoxy) butane;2, 2, 3, 3, 3-pentafluoro-1-(1, 1, 2, 2- tetrafluoroethoxy) propane; 1, 1, 2, 2, 3, 3, 3-heptafluoro-1-(1, 2, 2 -trifluoroethoxy) propane1;1, 1, 2, 2, 3, 3, 4, 4, 4-nonafluoro-1-ethoxybutane ; 3, 4, 4, 4-tetrafluoro-3-trifluoromethylbutane-2-ketone; 3, 3, 4, 4, 5, 5, 5-heptafluoropentane-2-ketone; 3, 3, 4, 4, 5, 5, 6, 6, 6-nonafluorohexane-2-ketone; 3, 3, 4, 4, 5, 5, 6, 6, 7, 7, 7-undecafluoroheptane-2-ketone.The liquid densities decrease monotonically with increase of temperature. The measurement value can be predicted within ±0.3% deviation using the HBT method or the Rackette equation if one point measurement was performed in case of the unknown critical values of the sample. The density of each structural isomer is shown to have ad ifferent value, which indicates that the composition of isomers should be determined in applying the density values of a isomer mixture.

View full abstract

Water ethanol mixture has a liquidus line (or crystallizing line) and a solidus line (or melting line) that are separated, and therefore it can have both liquid and solid phases existing together. As a result, with advances in low temperature technology in recent days, water ethanol mixture is attracting more and more attention as an environment friendly coolant or as a thermal storage material. In this study, we investigated the mechanism of mushy crystal formation and the state of am ushy layer formed on ac ooling surface, with the objective of utilizing water ethanol mixture as ac oolant or at hermal energy storage material. Two types of experiments were done in this work in order to study the mechanisms of crystal formation and growth. In one experiment, we studied the mechanism of crystal formation within a minute droplet of water ethanol mixture, and in the other, the mechanism of the crystal growth in the mushy layer formed in a liquid pool in contact with a cooling surface.

View full abstract

We experimentally examined the characteristics of a heat transfer plate during ice and chilled water making. The stainless steal heat transfer plate was developed for dynamic ice harvesting thermal storage systems. We obtained the following results:(1) The range 1.2×10^-4 to 1.7×10^-4m3<3/sup>/(s⋅m) volume flow rate is the optimum value to obtain the maximum amount of ice during ice making. (2) The estimated history of the ice thickness, which is obtained from the accumulated latent heat, is 0.8 to 0.85 times that of the semi-theoretical value. This is because the weld lines on the heat transfer plate don't contribute ice making plate. (3) The measured surface heat transfer coefficient during chilled water making is about 1.2 times of the calculated value when the volume flow rate is up to 1.6×10^-4m³/(s⋅m). This is because the falling film on the heat transfer plate is uniform and the heat transfer plate surface with wave contributes to increasing the heat transfer coefficient.

View full abstract

The effect of chitin hydrolysate made from shell of crustaceans and cartilage of cephalopods on the denaturation and the state of water of lizard fish myofibrillar protein (Mf) during frozen storage at -250°C for 120 days were investigated. 5.0% chitin hydrolysate (dried matter) added Mf samples were frozen at -25°C and storage for 120 days, and the change of inactivation of Mf Ca-ATPase and the change of unfrozen water in Mf were examined during the frozen storage. The decrease of Mf Ca-ATPase during frozen storage were slow by addition of chitin hydrolysate. The amount of unfrozen water in Mf were increased by addition of chitin hydrolysate, and decreaced gradually during frozen storage. On the other hand, the amount of unfrozen water of the control were decreaced suddenly during frozen storage. Above results suggest that chitin hydrolysate has cryoprotective effect on Mf. It is guessed that the mechanism of cryoprotective effect of chitin hydrolysate may be caused by an interaction between hydration sphere of Mf and equatorial OH groups in the molecular structure of chitin hydrolysate.

View full abstract

Experiments of in-tube condensation of R410A have been carried out for as mooth tube, a h elical micro fin tube and five types of herringbone micro fin tubes. In the herringbone micro fin tube, the micro fins work to remove liquid at fin-diverging parts and collect liquid at fin-converging parts. In the high mass velocity region, heat transfer coefficient of all the herringbone tubes is about 2-4 times higher than that of the helical micro fin tube. In the low mass velocity region, however, the heat transfer coefficients of the herringbone micro fin tubes are equal to or smaller than those of the helical micro fin tube. Up to the fin height of 0.18 mm, the heat transfer coefficient is higher for higher fin, whereas that of ah igher fin tube is saturated. The pressure drop increases with increasing fin height. The helix angle strongly affects the heat transfer and pressure drop. Higher helix angle causes higher heat transfer coefficient and higher pressure drop. In the case of the herringbone tube which has shorter fin and/or smaller helix angle, pressure drops are equal to or lower than that of the helical micro fin tube, whereas those of other tubes are higher.

View full abstract