Trends of control technologies about air-conditioning machineries, especially room or packaged air conditioners, are presented in this paper.
Multiple air conditioning systems for office buildings are mainly described as one application of the refrigeration cycle control technologies including sensors for thermal comfort and heating/ cooling loads are also described as one of the system control technologies.
Inverter systems and related technologies for driving variable speed compressors are described in both case of including induction motors and brushless DC motors.
Technologies for more accurate control to meet various kind of regulations such as ozone layer destruction, energy saving and global warming, and for eliminating harmonic distortion of power source current, as a typical EMC problem, will be urgently desired.

View full abstract

An experimental study of the heat and mass transfer within a fibrous porous layer with ventilation air layer is reported. Air layer was a clearance of 20 mm thickness between porous layer and cooling plate. Glasswood of 100 mm in thickness and 16 kg/m³ in density was adopted as a testing fibrous porous layer. Experiments were carried out for a variety of parameters such as flow rate of ventilation air, temperature of ventilation air, temperature of the heating room, and humidity of the heating room. The measurements showed that the heat transfer characteristics within the glasswool are mainly dominated by temperature of ventilation air as well as that of the heating room. An increase in ventilation air rate and a decrease in heating room temperature were found to cause a decrease in moisture accumulation within the glasswool. Moisture migration rate was correlated as a function of the Raynolds number and temperature ratio.

View full abstract

Slurry ice system is desirable as cold heat source for air conditioning, because it requires less conveyance power or less pipe size. On the other hand, recently absorption refrigerator is reevaluated because it can utilize various types of waste heat and it does not use fluorocarbon refrigerant. But it had been regarded to be difficult to make ice by absorption refrigerator because the refrigerant is water. However making slurry ice is possible, of cource, if the slurry ice generated by partial freezing of water is continuously taken away from the evaporator. This method was certified experimentally with a bench scale model. For ice making continuously, ice had not to be frozen stiff at water surface or inside wall of the evaporator. Then refrigerant water in the evaporator was raised swirl flow. And inside wall of the evaporator was finished by water repellent coating, and heated from outside wall. This slurry ice was adaptable to hydraulic transportation, because ice was needle crystal with about 5 mm length and ice temperature was 0°C.

View full abstract

The relationship between the supercooling and the shape of ice dendrite is investigated quantitatively and the quantitative measurement data are compared with calculated data by using the phase field model.
The shape of the ice dendrite tip is approximated by a paraboloid of revolution. The stability criterion of ice dendrite tip is calculated and it is shown that the shape of ice dendrite tip is unstable and side branches have a tendency to grow up.
The fractal dimension of ice dendrite is measured by applying Box-counting method. It is shown that the fractal dimension of ice dendrite is larger at higher supercooling and is also shown that the ice dendrites have fractal structures at lower supercooling.
By fitting the model parameters of the phase field model to the real ice dendrite growth, it is possible to simulate the ice dendrite growth.

View full abstract

The correlation of effect of electric field and environmental parameters on frosting phenomena was studied. The investigation was based on experiments with a forced air stream on the cold plate surface under several frosting conditions. The effect of electric field, defrosting phenomena, was evaluated from frost formation rate and mass transfer coefficient, which was derived from the amount of frost remained on the cold plate surface. The results obtained were as follows ; (1)Under large difference of absolute humidity, the reduction rate of frost formation rate obtained by forming the electric field appeared at nearly constant rate and was independent of the difference of absolute humidity, but it disappeared where the difference of absolute humidity was small. (2)The mass transfer coefficient under the electric field became small as temperature of the cold plate surface became lower. (3)The reduction rate of mass transfer coefficient occured by forming the electric field decreased as air velocity increased. (4)The mass transfer coefficient under the electric field decreased proportionally as the field strength were strength end from 0 k V /cm, but became not to vary beyond a field strength, which depended on temperature of the cold plate surface.

View full abstract

Simulation on melting process of theoretically oriented ice formation was presented using molecular dynamics method under the atmospheric pressure. Two kinds of ice formations were prepared, namely, ferromagnetic and antiferromagnetic orientations. The analysis on melting process of the ice formations were carried out and the results were compared. Number of molecules consisted in ferromagnetic formation was 576 and in antiferromagnetic was 360. Periodic boundary condition was used in both cases to avoid surface effect. If the volume of the cell is fixed, variation of the pressure in the cell during melting process is big and it might influence the characteristics of the melting process, such as melting temperature. Therefore, constant pressure condition was applied in the analysis. Anisotropic variation was adopted for volume change of the cell. It was found that the difference in the melting temperature and the latent heat between the two ice formations were relatively big and the characteristics of ice in nature existed somewhere between them.

View full abstract

Characteristics of two-phase refrigerant flow distribution is experimentally studied in detail. The test section consists of vertical upward main tube and five horizontal evaporator tubes. All the tube has 6mm i.d. A number of tests are made under a constant mixture flow rate at the inlet of header, G_H = 430 kg/m²s, ,where header inlet quality X_H and total heat input Q are varied from 0.07 to 0.3,from 0 to 900 W, respectively. Experimental data indicates that there are some difference in data trend between low X_H and high X_H region. Athigh X_H condition,i. e.,X_H › 0.1, gas phase flow tends to be unevenly distributed to each pass to be the most at pass No. 3,and the variation of Q merely affects the flow distribution profiles. On the other hand, at low X_H region, gas phase flow distribution is relatively equal while Q is small ;by increasing Q the flow distribution profile changes to be similar trend as that at high X_H region. From these results, it is concluded that gas flow distribution is dominated by global conditions of whole system, where liquid flow is affected by local flow state in the vicinity of each junction. On the basis of this concept, a flow model is discussed and obtained correlation shows good agreement with measured data.

View full abstract

The effect of unequal heating load applied to each pass (reffered to as "step heating load" in this paper) on two-phase flow distribution in multipass evaporator was experimentally studied. Four step heating patterns were determined to take into account the flowrate and the flow direction of the air flows outside of the evaporator tube in the actual heat exchanger. Three total heat input conditions were taken as Q = 300,450,600 W. For each heating condition, header inlet quality was varied from 0.07 to 0.3. From the exeperimental result of flow distribution, it was found that step heating load obviously affect the flow distribution. Step heating load causes the difference among the pressure at the inlet of each pass, which affect the liquid division ratio at the junction. But this effect does not clearly appear when the momentum flux of fluid in the main pipe just before the junction is large. It is concluded that liquid phase flow is directed by the kinetic condition in the vicinity of each junction. Together with the results obtained at the authors' first report, the empirical correlation for estimating the liquid division ratio at each junction which was successfully applied to any condition of heating load was derived. Additionally, from the result of pressure drop measurement, it was found that the vapor phase flow distribution had strong relation to the profile of the pressure drop along each pass.

View full abstract

In order to overcome the problem of water supercooling phenomenon for encapsulated ice storage system, ice nucleation effect of some ice nucleating substances is investigated in a bulk supercooled distil1ed water and tap water under various factors. It was understood that a supercooling degree was decreased in an increase in mass ratio of ice nucleating substance in the distil1ed water. The supercooling degree was decreased with increasing vibration frequency for the test sample. Moreover, it was seen that as the repeating number of freezing and thawing increases, supercooling degree for cholesterol as an ice nucleating substance increases, while that for metaldehyde decreases.

View full abstract

On the basis of critically-evaluated thermodynamic property data among those recently published, a new Peng-Robinson equation of state for the HFC refrigerants,R-32,R-125 and R-134a,has be end eveloped so as to represent the VLE properties in the vapor-liquid coexisting phase at temperatures 223K-323K. In accord with a challenge to correlate the binary and/or ternary interatction parameters as functions of temperature, we have also applied the present modified Peng-Robinson equation of state to the promising alternative HFC refrigerant mixtures, i.e., R-32/125,R-32/134a and R-32/125/134a systems. The developed equation of state improves significantly its effectiveness for practical engineering property calculations at refrigerantion and air-conditioning industries in comparison with conventional Peng-Robinson equation.

View full abstract

The authors have studied the phase change process of composite materials containing conductive solids in order to improve the heat transfer characteristics of phase change materials. In this study, experiments for the solidification and melting of water around a spine-fin tube are carried out, and the phase change volume and temperature distribution in the water are measured. As a result, the solidification and melting process are promoted considerably by the heat conduction of the fin and the natural convection in the lower side of the spine-fin tube for the melting process.

View full abstract

This study has been conducted to pursue the relation between microscale behavior and the injury of biological cell during freezing and thawing. As a sample of biological cells, protoplasts isolated from cultured wheat cells were selectively used. As the results of microscopic observation using a cold stage whose cooling and heating velocities were controlled, the recovery of cell by water influx due to osmotic pressure difference, and the fusion of intracellular ice were clarified with heating velocity. It was found that the osmotic stress acting on the ce11 membrane causes the thawing injuries connecting with swell and rupture of cell. The survival of cells was also inspected by dye-exclusion test using Evans Blue. The results suggested rapid temperature-rising is more harmful for slowly-frozen cell.

View full abstract

Heat transfer and simplified physicochemical model for thawing of the frozen biological cell element consisting of cell and extracellular region was proposed. The melting of intra-and extra-cellular ice, the water transport through cell membrane and other microscale behavior during thawing process were discussed as a function of temperature. Recovery of the cell volume and change of osmotic pressure difference during thawing were clarified theortically in connection with heating velocity, initial cell volume and membrane permeability. Extending this model, the thawing of cellular tissue consisted of numerous cell elements was also simulated. There was a position where osmotic pressure difference became maximum during thawing. Summarizing these results, the thawing damage due to osmotic stress was discussed in relation with the heating operation and the size effect of tissue.

View full abstract

The effects of the initial temperature of the solid PCM on a transient direct contact melting were invesigated, analytically. Four types of boundary conditions, that is, the constant temperature at the top, the constant heat flux at the top, the constant heat flux at the bottom, and the constant heat transfer coefficient and the constant temperature of the medium at the bottom of the heating plate, respectively, were examined. The effects of the initial temperature for each boundary condition were investigated through the transient process of the direct contact melting, where the heat transfer phenomena within the liquid film formed between the solid and the heating plate was unsteady, for the case of initial temperature lower than the melting point. It was found, as the results, that the time required until to approach the quasi-steady state and the melting speed at the time depended seriously on the initial temperature. It was understood, at the same time, that the heat flux flowing into the solid was not negligible, even in the quasi-steady state. Then, effects of the non-dimensional parameters, appearing in relation to the initial temperature variation of the solid, were examined, qualitatively.

View full abstract