The purpose of this research and investigation is to confirm and clarify the performance characteristics of the vapor compression refrigeration cycle based on the Ericsson Cycle (referred to hereinafter as "this cycle" in this paper). The theoretical analysis and comparison in performance of the conventional refrigeration cycle with this cycle using 12 different but typical refrigerants, produced the following essential and interesting results, i.e., (1) there are conditions for maximizing the COP of this cycle using the expansion valve, (2)both the COP and refrigeration capacity using this cycle showed improvement for all refrigerants other than R717 and R32, (3)the improvement rate for the COP and the refrigeration capacity becomes larger as the specific heat ratio at the gas outlet point of the regenerative heat exchanger becomes smaller, with the rate value differing according to the type of refrigerant.
Tuna is the most favorite marine products for Japanese people. Most of them are consumed as Sashimi in Japan, and a half of them are imported. Cold transportation technology is essential to keep freshness of tuna during the oversea transportation. In the case of transporting tuna, ship transportation in ultra low temperature such as -60 °C is applied and also high speed transportation even by using airplane is practically used. On the other hand, it is a fact that such transportation processes of tuna are giving huge environmental load, though it has not been so much focused. Evaluation of cold transportation technologies from this environmental viewpoint must be important in the future. In this article, we compared CO2 emission during cold transportations of frozen tuna (marine transportation) and non-frozen tuna (air transportation) by using LCI analysis. As a result, CO2 emission of non-frozen tuna is found to be about four times greater than that of frozen tuna. This is due to the difference in the amount of freight per transportation of the airplane and the ship.
This paper deals with the experimental study on cooling heat transfer of supercritical carbon dioxide inside micro-fin tubes. The geometrical parameters in micro-fin tubes used in the present study are 6.02 mm in outer diameter, 4.76 mm to 5.11 mm in average inner diameter, 0.15 mm to 0.24 mm in fin height, 5 to 25 in helix angle, 46 to 52 in number of fins and 1.4 to 2.3 in area expansion ratio. Heat transfer coefficients were measured at 8-10 MPa in pressure, 360-690 kg/(m2•s) in mass velocity and 20-75 °C in CO2 temperature. The measured heat transfer coefficients of micro-fin tubes were 1.4 to 2 times higher than those of the smooth tube having 4.42 in inner diameter. The predicted heat transfer coefficients using the correlation equation, which was developed for single-phase turbulent fluid flow inside micro-fin-tubes, showed large deviations to the measured values. The new correlation to predict cooling heat transfer coefficient of supercritical carbon dioxide inside micro-fin tubes was developed taking into account the shape of fins based on experimental data empirically. This correlation equation agreed within ±20% of almost all of the experimental data.
Cryosurgery and hyperthermia treatment are used as a treatment method for malignant tumors. Since liquid nitrogen is used as the cryogens, it is difficult to control the freezing rate and thawing rate. In hyperthermia, there are problems of thermotolerance acquisition by heat shock protein (HSP) and only a few studies regarding hyperthermia with cryosurgery have been investigated. The aims of this study are to produce cryosurgery-hyperthermia system utilizing Stirling Cooler and Peltier device and evaluate hyperthermia after cryosurgery by comparing cryosurgery and hyperthermia on the mouse liver. Normal living liver tissues of mice are divided into 3 groups (cryosurgery and cryosurgery-hyperthermia, hyperthermia), then performed cryosurgery, hyperthermia and hyperthermia followed cryosurgery, applying a 1 cycle rapid freezing and slow thawing method for cryosurgery. The temperatures of the tissue surface and probe were measured during operation, the liver was stained by Hematoxylin-Eosin (HE) after operation and observed under an optical microscope. The results showed measured temperature of rapid freezing and slow thawing. HE stained tissue showed stasis, pyknosis, nucleus disappearance and decreasing stainability in cryosurgery and cryosurgery-hyperthermia group, stasis, pyknosis and degreasing stainability in hyperthermia group. The results suggested cryosurgery-hyperthermia was the most effective to destroy the tissue.
This paper presents the performance estimation of hybrid absorption/compression heat pump cycle, which use dimethyl ether (DME) and methanol pair as a working fluid. The disadvantage of the DME as a refrigerant is that it is flammable. But it has several advantages from the environmental aspects; toxicity is very low, and GWP is small. The first purpose of this study is to estimate the reduction of the loss of the heat exchangers, by use of absorption/compression cycle. And the second purpose is to lower the working pressure to reduce the possibility of the leakage of the working fluids. Two hybrid systems are supposed as models; one is absorption/compression system with single stage solution circuit, and another is an absorption/compression system with generator/absorber heat exchange cycle. The former cycle exceeds the cooling and heating COPs of pure DME cycle, reducing the maximum pressure about 130 kPa. And the latter system increases the heating COP by 6 to 36% with the working pressure range about 150-260 kPa.
Adsorption / desorption behavior of water vapor onto desiccant rotor has been investigated to improve the desiccant cooling system by means of computer simulation. In this paper, we paid attention to the relationship between the equilibrium amount of water adsorbed onto the desiccant material and the relative humidity, that is adsorption isotherm as a principal characteristic feature of adsorbent. Considering actual adsorbents, five types of adsorption isotherms were assumed to clarify the influence of adsorption isotherm on the dehumidifying performance. After the investigation on the influences of some operating conditions on the dehumidifying performance at each selected adsorption isotherm, it was found that higher dehumidifying performance and reduction of length of desiccant rotor could be achieved by selecting appropriate adsorption isotherm. It was also predicted that S-shaped adsorption isotherm which is raised sharply at relative humidity around 15 % could produce the lowest air humidity at regeneration air temperature 80 °C. Moreover influence of the intraparticle diffusion coefficient which significantly influence on the adsorption / desorption rate was discussed choosing two adsorption isotherm from the above five isotherms. It seems that effective range of the intraparticle diffusion coefficient for the significant improvement of the dehumidifying performance was strongly influenced by the shape of adsorption isotherm.
In the present study, the fundamental experiments that investigate characteristics of local heat transfer in forced convective boiling on vertical flat plate with 2-mm channel height are taken to realize plate type compact evaporator for OTEC or STEC. The experiments are performed with ammonia as the working fluid. The experiments are also carried out with the following test conditions; saturated pressure = 0.7, 0.8, 0.9 MPa, mass flux = 7.5, 10, 15 kg/(m2•s), heat flux = 15, 20, 25 kW/m2 and inlet quality = 0.1 ~ 0.4 [-]. The result shows that the wall superheated temperature of forced convective boiling is lower than that of pool boiling. And the heat transfer coefficient increases with an increase in quality and the decrease in the local heat flux and saturated pressure for prescribed experimental conditions. However, local heat transfer coefficients are not affected by mass fluxes in the prescribed experimental conditions. An empirical correlation that can predict the local heat transfer coefficient on vertical flat plate within experimental conditions is also proposed.
Formation of metmyoglobin (metMb) in frozen tuna meat stored at -90, -60, -40, -30, -20, and -10°C for approximately 6 months was investigated. The reaction rate of metMB formation was estimated from a linear plot of ln ([M∞ . Mt] /[M∞ . Mo]) and storage time (t) for each storage temperature (Ts) (M∞, Mt, and Mo are metMb contents at times t = t∞, t, and 0, respectively). When M∞ was assumed to be 100%, the rate of metMb formation followed the first-order reaction only during the early stage of storage period. MetMb formation, however obeyed the first-order reaction for all test temperatures even during long-term storage when M∞ was assumed to be dependent on storage temperature (M∞(Ts)). A discontinuity was observed in the temperature dependence of M∞(Ts) at storage temperature range between -60 and -40°C, which was attributed to the glass transition of protein system. On the other hand, the temperature dependence of metMb formation did not show a significant change over all storage temperatures.
Formation process of hydrate was studied experimentally using propane gas, where ice particles were set in a container and then filled with propane gas. In order to improve the hydrate production rate and conversion rate, the temperature in the container was raised over 0 °C after an initial formation process. The experiments were carried out under various temperatures in the container, using two mean diameters of ice particles. Effect of the time interval of the initial formation process on the hydrate production rate was investigated. It was found that a higher hydrate production rate and higher conversion rate were obtained by raising the temperature in the container over 0 °C and by using smaller ice particles and also found that there was a suitable time interval of the initial formation process. Moreover, the formation process of hydrate was observed by taking microscopic pictures of the hydrate in order to understand the phenomena of hydrate formation with melting ice particles.
A water droplet injected into silicone oil, to which uniform electric field is applied by use of a pair of electrode plate, reciprocates colliding alternately with each electrode plate. This paper proposes to use the collision to augment initiation of freezing nucleation of super-cooling water droplet, and deals with the characteristics of the phenomena. The shuttle migration of a droplet between electrodes and initiation of freezing is photographed by use of a video camera, and the phenomena are analyzed on a monitor. As a result, the freezing initiation of the droplet is observed while the droplet is touched to the negative electrode plate. Relative frequency of the initiation is shown by the super-cooling degree and the electric field strength. The upper limitation of the temperature at which all sample droplets initiate to freeze is -3°C. Characteristics of the initiation are clarified and the effectiveness of this method is shown.
This study presents an establishment of optimal design method for lubrication at the thrust slide-bearing of scroll compressors, where, the analysis method using the average Reynolds equation by Patir & Cheng and the solid contact theory by Greenwood & Williamson were applied to calculate the resultant lubrication performance. For given values of friction area, thrust load and orbiting speed, the oil film pressure, the solid contact force and the friction forces were calculated to determine the friction coefficient. The friction coefficient decreased gradually with decreasing the friction area, because of decreased oil viscous force. When the friction area became quite small, however, the influence of the effect of surface roughness became large, thus resulting in increased friction coefficient. Thereby, the optimum performance appeared, which changes according to the friction area. In addition, the optimal friction area changed with the orbiting speed, the thrust load, the oil viscosity and the wedge angle. It was concluded that the optimal design values of the thrust slide-bearing can be calculated for given working conditions of the compressor.
In scroll compressors, an increase in oil flow rate into thecompression chamber improves sealing effectsand decreases refrigerant leakage. On the other hand, as the oil supplies the heat energy, the suction refrigerantis heated and the volumetric efficiency degreases. In the present study, we made an apparatus which suppliesthe oil into the compression chamber while measuring the mass flow rate, thus investigating the relationshipbetween the oil flow rate and the compressor performance. Experimental results indicated that the presentR410A scroll compressor provided higher performance as the oil flow rate decreased under the rated conditionof the air-conditioner. In addition, based on the experimental results, we discussed that the oil flow in thecapillary installed in the orbiting scroll was considered to be a laminar flow, and the volumetric efficiencywould degrease by the effect of a quarter of the oil heat energy.
This study presents an evaluation method of leakage flow through small axial and radial clearances between the orbiting and fixed scrolls of scroll compressors, where empirical friction factors were addressed. Leakage flow experiments were conducted for two refrigerants, CO2 and R22, flowing through the small axial and radial clearance models with a thin rectangular cross-sectional opening. The pressure drop in a pressurized closed vessel, due to leakage, was measured at a variety of initial pressure up to 3 MPa for CO2 and 0.6 MPa for R22. Darcy-Weisbach equation for the incompressible viscous fluid flow through the circular pipe was successfully applied to calculate the pressure drop due to leakage through the thin rectangular cross-section, where the empirical friction factors were determined and plotted on a Moody diagram. It was concluded that the working fluids are compressible and the leakage flow through the small clearances can be treated as the incompressible viscous fluid, where both the axial and radial clearance leakage flows can be represented by the same friction factor for both CO2 and R22 refrigerants, despite the significantly different working pressures. In addition it was addressed that the empirical friction factors were strongly dependent on the relative roughness of leakage channel surface.
An expander can improve the performance of CO2 refrigeration cycles by recovering a throttling loss. One way to utilize the recovered work is to drive an additional compressor by the expander, and it is effective to use an intercooler between a first-stage compressor and a second-stage compressor. An expander/compressor combination, in which the second-stage compressor is driven by the expander autonomously, is developed and the operating characteristics of the achine are discussed. It is operated at a balance point of mass flow rate and shaft torque between the compressor and the expander, and the balance point can be estimated using performance data of the compressor and expander. Although the expander/compressor combination improves the cycle performance, a heat rejection pressure is not maintained at an optimum pressure under off-design operating conditions. A control that keeps the heat rejection pressure optimum by a pre-expansion or a bypass is effective to obtain good performance of the CO2 refrigeration cycle with the expander/compressor combination.
Vane type compressors pressurize a back-pressure chamber of the vane with discharge pressure to keep a contact between a vane tip and a stator wall in a steady-state operation. At a start-up operation, however, the discharge pressure has not increased yet and chattering phenomenon sometimes occurs. In this study, a mathematical model to analyze the vane behavior at the start-up operation is developed. The equation of motion is applied to each vane, and the back-pressure of each vane and pressure in a plate groove which is connected to the back-pressure chambers are calculated simultaneously. Then changes of suction and discharge pressure are calculated according to the flow rate through the compressor corresponding to the vane behavior. It is found that when the vane back-pressure becomes less than the suction pressure by a volume increase of the vane back-pressure chamber, the vane hardly comes out from the vane slot, because a negative force caused by the pressure difference is dominant to the vane behavior during the start-up operation. The size of plate groove, i.e. connection area between the back-pressure chamber and the plate groove and the existence of a pressure supply hole also influence the start-up characteristics. Although the start-up operation has irregular characteristics, the calculating results agree qualitatively with the experimental results.