Water spray is used for cooling suction air of gas turbine. The aim of this study is to investigate the spraying properties and the influence of secular change in the spray nozzle.
PDA measurements are conducted in wind tunnel. Four types of nozzle are tested. Same type nozzles with different using period are also tested. The nozzles are new one and old one which is used hours. The spray properties in high spatial-temporal resolution are provided by the PDA. On the other hand, the velocity and flow rate decrease after hours. In experiments, transition from mixture A to B and B to A were performed for a stagnation flow premixed flame.
The transition time changes from 1 sec to 10 sec, keeping flow velocity and equivalence ratio constant at 0. The flame position was measured by a picture taken by high speed video camera with fps. Experimental results show overshoot of flame position during the transition. The overshoot was much significant for shooter transition time. Presently, hybrid hydrogen-gasoline fueling stations are being constructed at every region of Japan. The hybrid station is more dangerous than a simple hydrogen station, especially in the case of a fire in the gasoline tank.
The fire increases the temperaute of the hydrogen storage tank via thermal radiation. In order to simulate the thermal radiation arising from such a heat source, we first estimate its shape factor. We clarified the thermal radiation from the fire and the temperature rise in each tank using Monte Carlo method. A desiccant air conditioning system which can handle the sensible and latent heats in the air separately is generally composed of a dehumidifying rotor with desiccant material, a heat source for regeneration of the material and a heat exchanger controlling the dehumidified air temperature.
We proposed a desiccant rotor heated by solar irradiation, concentrated by Fresnel lens, impinging the rotor directly.
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The irradiation has a distribution along the channel on the wall in a rotor. This study presents local heat transfer coefficient on the wall by performing a CFD simulation assuming laminar forced convection heat transfer in a circular channel. The results showed that the coefficients decreased along the channel. Comparing with the result considering uniform heat flux condition, the decreasing rate was large, and it didn't reach a constant value obtained at the fully developed flow region.
This study describes a heat transfer characteristic of pulsating airflow around heating obstruction mounted in a rectangular duct. Several researchers have reported the possibility of the heat transfer enhancement by pulsating flow. Our study is trying to apply pulsating flow to the heat transfer enhancement method in thermal equipment such as heat exchangers and electronic equipment.
It is found that pulsating flow can enhance heat transfer around the obstruction except in the case of extremely narrow flow passage. This paper suggests that there is equality in physics between coaxial cylinder and pipe flow on the friction force per unit area. Among rotational machinery, electric motors and turbines for example are common industry which may have concentric shell structure. As the speed of rotating cylinder ascend, particular flow will occur known as Taylor-vortex flow regime beyond certain rotating speed. The major circulation of which has distance at least between coaxial cylinders.
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This means mass-flow is stirred enough to transport between inner and outer cylinder to emerge universal turbulence representation. It is investigated that stress force within concentric structure is almost the same as of the pipe flow even if the boundaries have various roughness. Consequently, complex behavior of frictional force including bumped surface can be estimated algebraically using Moody diagram. Therefore, the improvement of heat removal capacity needs to know the internal flow and heat transfer characteristics. The internal structure of the rotating machine has coaxial cylinders consisting of the inner cylinder and outer cylinder.
This study produced three shapes of the rotating coaxial cylinders. By performing a visualization using Kalliroscope flakes, the effect of the shape variation on flow characteristics was investigated. Toward the improvement of performance of an electrical rotating machine such as a motor and a generator, an appropriate design for heat removal is important.
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A typical motor is composed of the pair of coaxial cylinders with the fixed outer cylinder i. The present study numerically clarifies the influence of inner shape on heat transfer characteristics in the electrical rotating machine.
The heat transfer coefficient of the gap region between the rotor and stator was obtained. As a result, a vortex structure was observed in the slit on the stator wall, and the heat transfer coefficient of with-slit case in the high rotational speed was increased compared with that of without-slit case.
Hence, it was implied that the heat flux was increased by the presence of the vortex of the internal slits. This study investigated pressure drop for gas and non-Newtonian liquid two-phase flows in a horizontal circular microchannel. The microchannel was a fused silica tube with 0. Polyacrylamide aqueous solutions with different mass concentration, which exhibit pseudo plastic behavior, were used as non-Newtonian liquid, while the nitrogen gas was used as the test gas.
Pressure drop was measured with a calibrated differential pressure transducer.
As the comparison results, the data have been correlated with separated flow model by using a newly developed equation of two-phase friction factor as well as homogenous flow model with an effective viscosity accounting for non-Newtonian effects. The Lockhart-Martinelli model also predicted well the present data if an appropriate C -value in two-phase friction multiplier was adopted. In this study, we performed to observe horizontal vapor-liquid two phase flow of refrigerant R a in the rectangular glass channel which hydraulic diameter is 0.
The test glass tube was added the oscillation to the gravity direction for slug and stratified flow under low mass flux and heat flux. When the channel was oscillated of certain frequency and amplitude, the liquid of the corner part of rectangular channel waved up and down. In slug flow, dry surface of central was supplied the liquid by the oscillation and was formed the thin liquid. In stratified flow, dry surface of top was supplied the liquid and flow pattern changed to annular from stratified flow.
The oscillation influences were investigated in a quantitative way. Experiments were performed to explore the conditions for the onset of secondary droplet formation during single drop impact onto a liquid film splashing. It was found that there were two types of splashing: the prompt splash and the late splash.
In the prompt splash, small droplets were scattered with high velocity immediately after the impact. Whilst, in the late splash, larger droplets of lower velocity were produced after the development of liquid crown. The condition for the onset of splashing was expressed using the two dimensionless numbers: the Weber number, the Ohnesorge number. The correlations were given separately for the prompt and late splashes. Moreover new correlations were developed about prediction of the secondary droplet diameter and velocity.
The coalescence of horizontally approaching twin bubbles is experimentally studied in isothermal system at room temperature. The bubbles are generated at the outlets of two tubes facing each other horizontally. Liquid film thickness formed between approaching bubbles were measured by simultaneous measurement of laser extinction method and laser interference method.
This study investigates the rupture location in liquid film and the distribution of the liquid film thickness for water. The variable of the experiment are the air flow rate and the transmitted laser position. The effects of bubble approach velocity and the contact duration were investigated. Experimental databases and knowledge of turbulent flows in rod bundles are required for validation and improvement of numerical prediction methods for two-phase flow in rod bundles.
In this study, we therefore measure liquid velocity in single-phase and bubbly flows by installing a small LDV probe into a rod in a 2x2 rod bundle. The diameter and the pitch of the rods are 10 and 13 mm, respectively. The liquid volume flux is 0. There are several methods for heat transfer enhancement. For example, one can attach various fins on the heat transfer surface, process the surface roughly, insert twisted tape, and so on. These methods increase the heat transfer coefficient or area by manufacturing changes to the heat transfer surface.
However it is necessary to consider the problem on account of processing heat transfer area. In this study, heat transfer and flow characteristics performance of air-water heat exchanger by under the condition inserting metallic wire was evaluated, and compared the case of the fin.
Pressure drop as compared with the case of the fins is significantly reduced. This study deals with condensing heat transfer in a quadrilobed tube.
HFCa was used as the working fluid. The effect of the tube configuration on the heat transfer coefficient was evaluated in horizontal flow. Superheated vapor or wet vapor was supplied to the condenser, and heated in water.
A straight and twisted quadrilobed tubes were used. The local heat transfer coefficient at the center in the length was evaluated from the wall temperature measured by mounted thermocouples. As the result, for low refrigerant mass flux in the straight tube, deterioration in local heat transfer coefficient under low quality condition was suppressed, because condensate might be accumulated along the center by surface tension. For the twisted tube, on the other hand, heat transfer coefficient was lower than the straight one. In this experiment, since the twist tube improved the water heat transfer, the twist tube produced higher heat transfer rate than the straight one.
Experiments were carried out to investigate the characteristics of high-heat-flux heat removal using a porous-micro-channel a small rectangular channel filled with a porous-metal plate. The working fluid was water and the main experimental parameters were the inlet liquid subcooling, mass flux, and channel size.
It was shown that nucleate boiling heat transfer is enhanced in the porous-micro-channel in comparison with the normal rectangular channel. Another important finding was that as in the normal channel, the micro-bubble emission boiling MEB occurs in the porous-micro-channel if the mass flux and liquid subcooling are high enough. In addition, the flow oscillation and noise production that often accompany with the MEB in the normal channel were mitigated significantly in the porous-micro-channel. This indicates that the porous-micro-channel enables the stable and high-heat-flux heat removal by the MEB.
Dropwise condensation DWC has high heat transfer coefficient. However, It is difficult to maintain DWC for long time. In order to maintain DWC long enough, it is important to understand the effect of the surface condition.