There is a growing need to expand the upper limit of the operating range of compressors for air-conditioning and refrigeration systems. The expansion of the upper limit causes increasing the load or the rotational speed of the journal bearing that supports the shaft of the compressor. On the other hand, the refrigerant is dissolved in the refrigeration oil, and the refrigerant solubility and the viscosity of the refrigeration oil change depending on the temperature and pressure conditions. In the high load and high speed region, it is considered that changes in viscosity due to frictional heat and refrigerant solubility affect bearing characteristics. The authors have so far analytically clarified the effects of friction heat generation and changes in the refrigerant solubility and viscosity on bearing characteristics. In this report, the validity of the analytical model was experimentally verified by evaluating the characteristics of journal bearings in a refrigerant environment, and we obtained experimental results to support the heat generation caused by the change in refrigerant solubility in the analysis model.
In fish freezing, freshness before freezing is an important factor related to quality after freezing and thawing. In case of fresh condition up to several hours after the killing, however, the effect of differences in freshness on the quality after freezing and thawing has not been well investigated. In this article, we utilized impedance which has been reported to be able to detect the degradation of freshness during several hours after the killing, to evaluate the relationship between the freshness before freezing and the quality of fish meat after freezing and thawing. First, the effect of freezing rate (slow or rapid) on the relationship between the freshness before freezing and the quality after thawing was evaluated without frozen storage. Then a 3-month frozen storage experiment was conducted to simulate actual distribution. As a result, in both non-frozen storage and 3-month frozen storage, the impedance before freezing had relationship with the drip loss after thawing. Furthermore, in such fresh condition as up to several hours after the killing, it was indicated the impedance before freezing was more clearly related with drip loss than freezing rate.
Many air conditioners use fan systems for heat exchange. Vibratory motion and noise in the air conditioner occur when the aerodynamic pressure pulsation by the rotating fan blades act on the cabinet of the air conditioner. On the other hand, reaction force corresponding to the cabinet pressure pulsation occurs, and then the cabinet pressure pulsation transmitted to the motorfeet. Finally, these transmitted forces excite support-structure of the motor. We calculated the cabinet pressure pulsation and pressure fluctuation on fan blades by CFD software “PHOENICS” and we also calculated the reaction force, using the results of CFD analysis. Calculation results of the cabinet pressure pulsation and reaction force were compared with the measured value by the testing system. We found that the calculation result agrees with experimental result.
Among the numerous gas concentration measurement methods, ultrasonic methods are desirable because it can measure a greenhouse or ozone layer-depleting gases that are used as refrigerant gases without extracting the gases and facilitate the measurement of successive gas concentration changes. An ultrasonic gas sensor was successfully fabricated using the difference in sound velocity between polyatomic gases (such as hydrofluorocarbons as refrigerant gases) and base gases. Each gas has its own specific sound velocity; therefore, the traveling time between a transmitter and receiver also has a unique value depending on the type of gas. The gas concentration can be calculated from the difference in the time of flight. The sound velocity in gas is theoretically defined; thus, the gas concentration can be accurately and quickly (in microseconds) calculated from precise sound-traveling-time measurements. Polyatomic gases have specific heat ratios different from those of diatomic gases, such as hydrogen, oxygen, and nitrogen. This paper presents a new algorithm capable of calculating the concentration of polyatomic gases, which have molecular weights and specific heat ratios that differ from those of the base gas. A model-based design was used for this complex gas concentration calculation based on the numerical analysis of nonlinear equations in mixtures of polyatomic molecule gases and diatomic molecule base gases.
We investigated the effect of bubbles on the flow pattern of ice slurry. We observed the ice slurry containing bubbles flowing in the horizontal pipe, changing the flow velocity, IPF, and pipe inner diameter as parameters. As a result, it was found that the flow pattern was homogeneous flow under the high flow velocity and high IPF condition. As the flow velocity and IPF decreased, the flow pattern became heterogeneous flow and intermittent flow. In the flow of ice slurry with bubbles, the transition from heterogeneous flow to homogeneous flow easily occur, comparing with that without bubbles. We suppose that this is the effect of the repulsive force between the bubbles adhering the ice particles in the ice slurry. Moreover, it was found that the effect of bubbles became larger in narrower pipe. It can be said that the flow pattern of ice slurry with bubbles is likely to be homogeneous flow when IPF is high and pipe diameter is small, because the effect of repulsive force becomes larger.