This paper indicates the effective thermal conductivity of the hydrogen absorbing alloys bed of the passive type hydrogen storing systems for residential energy systems or stand-alone power supplies by experimental measurement. The effective thermal conductivity of the alloys bed depended on the cylinder pressure and the H/M composition of the alloys. Moreover, the conductivity was linear to the H/M composition at Plateau area. The introduction of 15 mass% Cu wires to the bed for improving the heat transfer was effective to raise the effective thermal conductivity of the bed. 50% of void fraction of the bed was also useful. The use of MmNi5 resulted in raising the effective thermal conductivity compared to the use of MmNi4.50Co0.10Al0.15Mn0.25 at the same H/M composition and the void fraction.
The scroll compressor has two leakage passes, which are the gap in an axial direction at the tip of the wrap and the gap in a radial direction between the wraps. Many attempts to reduce the leakage through those gaps have been actively researched and developed. In this study, we grasped the characteristics of the contact force between the wraps of a CO2 scroll compressor with the fixed orbiting radius by measuring the oil-film pressure at the main bearing. In addition, we developed the analytical method to simulate the contact force considering the effect on the formation of oil-film at the bearings and move constrain of the orbiting scroll. As a result, we found that (1) there is a fluctuation of the contact force at one revolution, (2) the contact force increases with rotational speed, (3) the contact force has little change for operating condition and (4) contact force increases with decreasing the wrap clearance.
Authors built an ice making system using water-oil emulsion, which is applicable to dynamic type ice storage system. In order to operate this system, it is important to prevent ice from adhering to cooling wall. In this study, the effects of initial oil content of emulsion and ice making rate were investigated. As the result, it was found that the adhesion of ice is caused by decrease of oil content of the emulsion. The oil content decreases in ice making process, because oil in the emulsion adheres to the ice particles generated in it. It was also found that the decreasing rate of oil content becomes higher as the ice making speed increases. Therefore it was concluded that the initial oil content should be high and ice making rate should be low, in order to produce more amount of ice in this system.
Air-conditioning load takes 30% among the total electricity consumption of a building. It is important to know the electricity consumptions for air-conditioning in detail to each building. However, it is difficult to measure the consumptions of the existing building directly. This report proposed the estimation model for the power consumption of air conditioning. The model uses two hourly data which are user's total electricity consumptions and the ambient temperatures. The hourly electricity consumptions are divided to the air conditioning and the others consumption. The model is written by MINLP, but is easily computed by practical conversion. In the case study, the 13 user's hourly consumptions were estimated. And one of 13 users was compared with the measured consumption for air conditioning. Its coefficient of determination (R2) was 0.84. It means this model is useful for estimating the electricity consumption of the air conditioning.
At present, the combination of aqueous lithium bromide (LiBr) solution as an absorbent and water as a refrigerant have widely been used as the working fluid for absorption refrigerating machines. In order to obtain absorption enhancement of water vapor into the LiBr solution by Marangoni convection, an alcoholic surfactant is being added in the LiBr solution. In that case, the surface tension of the LiBr solution with the surfactant plays an important role for the vapor absorption. In this study, the surface tensions of the LiBr solution with several alcoholic surfactants such as 1-butanol, 1-hexanol, 2-ethyl-1-butanol, 2-methyl-1-pentanol, 1-heptanol, 1-octanol and 2-ethyl-1-hexanol were measured by Wilhelmy plate method. As a result, the surface tensions of 50 wt% LiBr solution with several surfactants were obtained over the LiBr solution temperature range from 298 K to 318 K and the surfactant concentration range from 0 to 104 ppm by mass. The measured surface tension has decreased with the increasing number of carbons included in the surfactant at constant concentration, and the surface tension has increased with the increasing temperature of 50 wt% LiBr solution. The surface tension increase of 1-octanol became greater than any other surfactant used in this work. The effective carbon number of the surfactant for the absorption enhancement was in the range from 7 to 8.
The air cleaning is one of the social problems from the view of the living environment and the health recently. A commercial kitchen and food factory generate the exhaust gas including the odorous components and the oil-mist, but it is difficult to clean this gas without frequent maintenance for disposal of oil. Various ideas have been suggested and used for it, but the decisive solution has not been found yet. This paper is concerning of proposal of the photocatalyst method which used the condensation together to clean the gas including oil-mist and odorous component, and it was clarified experimentally about the influence of operation condition and surface shape of the condensation side for the removal of oil-mist and the odorous components of formaldehyde, amine and ammonia.
An investigation of desiccant air conditioning system is performed to demonstrate its performance in a dispersed desiccant particle systems, based on its higher gas solid contacting efficiency and isothermal dehumidification. Particle dispersion is achieved using the risers of a circulating fluidized bed, CFB, or of a pneumatic conveyer. The risers used for dehumidification are 1390 mm in height and 22 mm in diameter. The former is used to evaluate the overall dehumidification performance and the latter is used to measure the axial humidity distribution under 0.88 m/s of a superficial air velocity. Based on the results of the overall performance by changing solid loading rates, Gs, from 0.4 kg/m2s up to 6 kg/m2s, desiccant particle dispersion shows higher performance in dehumidification, while axial humidity distribution shows very rapid adsorption rate in the entrance zone of the riser. Removal of adsorption heat accelerates dehumidification rate compared to the adiabatic process.
In this study, numerical simulation of a cross fin-tube heat exchanger was conducted to investigate the effects of fin-collar shape on the heat transfer performance and pressure drop. During the making process, two adjacent fin-collars and a tube form a triangular space and the end of fin collar protrude to air side. To investigate these effects on the heat exchanger performance, the form ratio was defined to make an indicator of the triangular space size. Furthermore, the simulation of the models with and without protruded end was conducted. The results indicated that the increase of the form ratio results in the decrease in the heat transfer rate. On the other hand, it contributed to a relatively small increase in the heat transfer coefficient on the air side. A high heat transfer coefficient on the air side was obtained by the protruded fin-collar end. However, the pressure drop was not much different between the models with and without the protruded end. The ratio of the thermal contact resistance to the air side thermal resistance was about 1:5 for the form ratio of 20% to 40%.
This paper has launched a concept of tomographic resistivity distribution measurement in a microchannel for a heat exchanger. With the concept, cross-sectional images of assumed resistivity distribution due to micro bubble in an electrical resistance tomography (ERT) has been simulated by using algorithms of forward and inverse problems. The first step of the algorithm is a forward problem; namely, it is to calculate an electrical potential on electrodes from the assumed resistivity distribution by solving the Maxwell equation. The second step of the algorithm is an inverse problem; namely, it is to calculate the resistivity distribution from the electrical potential on the electrodes calculated by the forward problem. In order to discuss the concept availability in the inverted annular flow and the stratified flow, the simulation results show that the flow condition depends on the correlation. Especially, the stratified flow has a high correlation coefficient as compared to the inverted annular flow.
Optical fiber probing is one of the efficient and reliable measurement methods for gas-liquid two-phase flows. We employed the proving for the measurement of a liquid film inside a two-fluid nozzle. First, we verified the availability of the optical fiber probe in the measurement of the liquid film via calibration experiments and numerical analysis. It was validated that the average film thickness and the amplitude of the thickness fluctuation are measured correctly. Second, we performed two kinds of measurements using a steam-water two-fluid transparent nozzle; the one is the newly developed optical fiber probing stated above and the other is LIF visualization with a high-speed video camera. The following results were obtained from both measurements. The average thickness of the liquid film measured by the optical fiber probe was 61 μm and the amplitude of the liquid film fluctuation was 28 μm. These results were agreed with those obtained by the LIF visualization.
The present paper introduces a numerical study of the particle behaviors under acceleration conditions in the solid-air two-phase flow by means of a combined two-dimensional model of computational fluid dynamics and the discrete element method (CFD-DEM). The simulation model provides information regarding the particle distribution behaviors within the calculation region and the particle run-out rate from the calculation region under different parameter conditions, such as particle size, initial particle loading and particle acceleration condition. The results demonstrate that the particle run-out rate is directly affected by the particle size and the initial loading condition. The particle acceleration in the horizontal direction adversely affects the particle run-out rate when the initial particle loading condition is dispersed and uniform. However, this adverse effect disappears when the initial particle loading condition becomes concentrated and partial.
Carbon dioxide (CO2) is considered to be an alternative to HFC refrigerants due to its non-flammability, non-toxicity and small global warming potential. To improve the performance of the CO2 refrigeration cycle, using an expander as an expansion device to recover a throttling loss has been examined. Since an inlet condition of the expander is supercritical and an exit is subcritical, leakage through a narrow clearance in the expander becomes a transcritical flow where the condition changes from the supercritical to the subcritical. It is necessary to clarify the characteristics of the transcritical leakage flow through the narrow clearance, because the leakage flow has serious influence on the expander performance. In this study, the transcritical leakage flow is modeled analytically and the flow characteristic is examined by the model. The calculated mass flow rate agrees with the experimental one. It is found that frictional loss accounts for a half of pressure drop both in the supercritical and two phase region at any inlet temperature tested in this study. In addition, the sealing effect of oil on the transcritical leakage flow rate is shown to be little.
To clarify the effect of the centrifugal force on phase distribution of gas-liquid two-phase flow, air-water two-phase annular flows in an Archimedes spiral tube were visualized by thermal neutron radiography, and the two-dimensional void fraction distributions were quantitatively measured by an umbra method. An aluminum tube of 8 mm I.D. was coiled in a plane and placed vertically. The cross-sectional averaged void fractions were correlated by the drift flux model for each flow direction. From the two dimensional void fraction distributions, the center of liquid mass under each condition was measured. The condition of inversion whether the liquid phase tends to flow along the inside or outside of spiral tube could be obtained. The condition of the inversion could be correlated by the ratio of body force on the gas and the liquid phases, that is, centrifugal force and gravity.
In pipe lines such as those found in refrigeration cycle, a gas-liquid two-phase flow may occur because of a pressure change in the pipe. This flow causes noise. A vapor phase ratio in a fluid and the behavior of bubbles are related to the outbreak of noise. This experimental study investigated the fluid borne noise caused by gas-liquid two-phase flow passing through a contracted section in horizontal pipe. In the experiment, sound pressure was measured for two purposes: to see the influence of the air-water ratio on sound pressure and to see the change in sound pressure when a single bubble passed through a contracted section in horizontal pipe. The experiment showed that the fluid borne noise of gas-liquid two-phase flow grew louder than that of a liquid single-phase flow. As for the frequency distribution of the fluid borne noise, the sound pressure level was higher in the high frequency band. Furthermore, the fluid borne noise grew louder with increasing bubble diameter.