Recently, frost formation becomes an more important phenomenon not only in the cryogenic equipment but also in the air conditioner equipped with heat pump systems. When heat pump systems are used to supply thermal energy from air for the purpose of space heating in winter, the surface temperature of the evaporator often falls below 0°C and then frost deposition occurs there because it gains heat from the cold outdoor air.
Frost formation cannot be treated easily as a growth of uniform substances such as ice because of the complicated nature of a frost layer. Accordingly, frost formation has been studied from the various points of view. This paper will give a review of studies on frost fomation and defrosting connected with heat pump systems.

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The performance tests of a plate type condenser for ocean thermal energy conversion (OTEC) plants are carried out under conditions of OTEC. The total plates used in the condenser are 168 in number and the total surface area is 40.7 m². The dimensions of plate used in this condenser are 1450 mm in length, 235 mm in width and 1.0 mm in thickness. Freon 22 is used as working fluid. The overall heat transfer coefficient is about 2500W/(m²K) at the cold water velocity of 1 m/s and the vapor inlet temperature of 22.8~23.2°C. The empirical correlations are proporsed for predicting the average condensation heat transfer coefficients and water side heat transfer coefficients for a plate type condenser. The water side pressure drop is 1 m at the cold water velocity of 1 m/s. The water side friction factor is about 0.25 at Reynolds number of 4×10³.

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A helium compressor is one of the important components comprising a cryogenic refrigerator. The purpous of this investigation is to develop a new small-capacity helium screw compressor. The performance of a single-stage compressor at high compression ratio and the cooling performance of the compressor are investigated. A semi-hermetic screw compressor with new profile screw rotors, with which high performance can be obtained, is utilized in this investigation. Lubricating oil is applied to cool the compressor motor and the compressed gas. As a result, an overall isentropic efficiency of 80% is obtained when helium is compressed to a compression ratio of 19.8 with a single-stage screw compressor. At the same time, the temperature of a compressor motor and discharge gas can be maintained at low levels. Therefore, it is found that a single-stage screw compressor can compress helium to high compression ratio.

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Performance tests on a shell and plate type evaporator (total surface area = 21.95m², length = 1450mm, width = 235mm, plate number = 100) for ocean thermal energy conversion (OTEC) plants. Freon 22 (R22) and ammonia (NH₃) are used as working fluid. The empirical correlations are proporsed in order to predict the boiling heat transfer when using R22 and NH₃ and water side heat transfer coefficients for a shell and plate type evaporator. The water side pressure drop is about 3 m at the warm water velocity of 0.7 m/s. The water side friction factor is obtained.

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Investigation of thermal energy loss in cyclic operation of refrigeration cycle in a refrigerator-freezer were made. The energy loss was found to consist of three parts ; hot gas-refrigerant entering loss, cooling lag loss, and evaporator superheat loss. Hot gas-refrigerant entering loss is occured when high temperature gaseous refrigerant in a condenser flows into an evaporator to heat up the refrigerant in it. Main results are as follows ; 1) Hot gas-refrigerant entering loss, which was the most dominant, was found to be from 7.6 to 12.3% (for reciprocationg compressor) and from 11.9 to 17.4% (for rotary compressor) of the cooling load, respectively. 2) The thermal energy loss was confirmed to be able to be reduced when hot gas-refrigerant was restricted to flow in the evaporator with control valves. It follows to reduce electrical power consumption by 10 and 15%, in the case of reciprocating compressor and of rotary compressor, respectively. 3) Cycle frequency was made to be optimized theoretically and experimentally in the case of with and without valves.

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An efficient numerical method for the multidimensional freezing problems with arbitrary geometries including a multiply connected domain was reported in this report. First, the multilateral element method (MEM), in which the representative point of the element can be placed at the arbitrary point was proposed. Then, a numerical method based on MEM was presented. In this method, the new freezing front positions are calculated by using temperature distribution in the vicinity of the freezing front. Then, adjacent element is enlarged by the same amount as the newly frozen area thus obtained. This procedure is continued until the size of the frozen area reaches the prescribed size.
The present method has such features as (i) applicable to multidimensional problem with arbitrary geometries, (ii) the formulation is simple, (iii) applicable to the combined problem including convection effects, (iv) time reduction is easily possible due to SOR formulation.

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In comparison with conventional refrigerants, the use of non-azeotropic binary mixtures of refrigerants in vapor compression refrigerating systems can result in extension of the application limits, higher reliability, and savings in power consumption. This paper discusses the high temperature heat pump system performance operating with mixed refrigerants.
In order to survey the system performances with various mixtures, six kinds of mixtures are examined : R22-R1l4, R22-R11, R12-R114, R12-R11, R 12-R113, and R22-R12. Thermodynamic properties of the first five mixtures are calculated from the Peng-Robinson equation of state with the mixing rules proposed by Ototake, and R22-R12 mixtures by the BWR type equation of state proposed by Kagawa et al.
When counter-flow heat exchangers with large surface areas are used for the evaporator and the condenser, the temperature differences between the refrigerant and the heat sink / source fluids can be reduced, and so the energy waste resulting from irreversible heat trasfer can be reduced. Comparing the mixed refrigerants with the pure ones by fixing the refrigerant temperature at the evaporator inlet and the dewpoint temperature at the condenser, higher coefficients of performance (COP), lower condensing pressures, and lower pressure ratios in the refrigerant compressor can be realized. But the performances of the mixtures with R114 as a less volatile component are not so good. When the heat transfer surface area is not large, the mean temperature difference becomes large. If the dewpoint temperatures at the evaporator and the condenser fixed, the range of composition for the improvement of the COP is restricted.

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