Apparent viscosity of CWS and TiO2 water slurries which may work between their atomization processes are measured and discussed by means of a capillary viscometer and a rotary viscometer from wide apparent shearing rate of 106s-1 to 10s-1. The apparent viscosity relating of their apparent shearing rate showed a unique flow be-havior so called extended Ostwald's flow regime. As the results the apparent viscosity at the high shearing rate about 105-106s-1 which may appear between atomization was almost nearly as water itself. The apparent viscosity of slurries for the wide range of shearing rate is discussed regarding with their particle size distributions.
In order to study a disintegration mechanism of a high viscous liquid jet issuing from a cylindrical nozzle, a break-up length of the jet was measured. The main parameters in experiments were liquid viscosity, injection speed, diameter and length of a nozzle, and shape of the nozzle entrance. When the viscosity of the liquid was changed widely, the break-up lengths measured by an electrical resistance method were not uniquely expressed with the Reynolds number in the nozzle flows. The smooth jet appared only in low Reynolds number conditions, if the kinematic viscosity increased up to 20×10-6m2/s. However, the high viscosity liquid jet in the wavy flow region showed a smooth surface at the nozzle exit and development of the surface wave suddenly occurred at far away from the nozzle exit. This late development of the wavy flow was predominating on the jet issuing through a long nozzle or a nozzle which had a smooth entarance.
Electrostatic atomization of viscous liquid for liquid-liquid system was investigated. The size of droplet produced by the electrostatic atomization was decreased with increasing applied potential and controlled in the wide range of mm order to several μm. Also, the size distribution was sharp compared with that produced by other atomiza-tion methods using pressure atomizer, twin-fluid atomizer and ultrasonic vibration. In the case of low viscous kerosene, the relatively uniform droplets were regularly produced from the cusp of meniscus which was formed at the tip of the nozzle. At the potential above -3000V, very fine droplets can be produced. On the other hand, in the case of high viscous-castor oil, the liquid thread was drawn out from the meniscus and then disintegrated into small droplets. The liquid viscosity depends on the produced droplet sizes. It was consi-dered that electrostatic atomization was induced by synergistic effects both the transverse vibration and the axial acceleration of the liquid jet issuing from the nozzle.
Although a technique for production of uniform size droplets from a large viscosity liquid is required in industrial field, conventional methods are available for only low viscosity liquid. This work has been done to develop and investigate a new method for easy production of high viscous uniform droplets. In the method, impingement of nozzle by cam mechanism on a stopper with adjustable gap imposes cyclic shocks on high viscous liquid jet. Using a silicone oil with viscosity of 10000mPa ·s, the effects of liquid flow rate, diameter of nozzle and intensity of shocks on producible range of the uniform droplets were examined. Although the flow rate was in relatively low range, following results were obtained: uniform size droplets were obtained with fairly good uniformity, the maximum fre-quency in producible conditions for uniform droplets increased with icrease of liquid flow rate, and the droplet sizes obtained were kept some constant values independently of the change of velocity of the liquid flow, according to the change of the diameter of nozzle and the amplitude of imposed frequency.
The drop formation of emulsions by spinning disks in the ligament mode was experimentally studied for the determination of any difference between the at-omization of emulsions and that of homogeneous liquids. Kerosene/water, water/kerosene and water/ (kerosene+liquid paraffin) emulsions were used. Almost all of them were non-Newtonian fluids and their viscosities were characterized using a power law relationship.To compare the atomization data of emulsions with those of homogenous liquids, the drop formation of aqueous CMC solutions and aqueous glycerol solution containing surfactants were examined. Photographic observations indicated that the atomization of both the O/W and W/O emulsions is similar to that for normal liquid, although ligaments are stably formed even at low flow rates. To apply the stability analysis of a laminar jet to atomiza-tion of emulsions, the apparent viscosity at the disk edge and the dynamic surface tension were used. It was observed that ligament numbers depend on the flow rate, and there is a bend in the relation between the ligament number and the flow rate. The ligament numbers of emulsions are in good agreement with those for normal liquids in the flow rates above this bend. The diametrs of drops formed from ligaments of both the O/W and W/O emul-sions agree with the prediction based on the stability analysis. The drop sizes of emulsions are also in good agreement with the correlation based on the atomization data of normal li-quids, even if the fraction of dispersed phase is rather high. For the non-Newtonian CMC solutions, on the contrary, the drop sizes are larger than that predicted by more than 40%.
Intending the promotion of flash-boiling atomization of coal-water slurry fuel (CWM), an internally mixed twin-fluid atomization combined with flash-boiling was designed and investigated experimentally. CWM heated below the saturated vapor temperature is fed to the mixing chamber through the steam heat exchanger, began to boil by sudden decompression and disturbing effects of flowing air, and is sprayed from the multi-hole nozzle. Main results are as follows: (1) CWM can be easily atomized by flash-boiling at high superheat degrees even at lower air flow rate, because there are a lot of bubble nuclei on the surface of a coal par-ticke. With increasing the air flow rate, fine spray can be obtained at lower superheat de-gree by the promotion of flash-boiling due to violent disturbing of air in the nozzle. (2) Larger spray drops have a tendency to exist near the spray periphery because of their high inertia of motion, while fine drops of high percentage of water content gather near the spray axis.
This paper describes pneumatic atomization test results of Coal-Water-Mixture (CWM) conducted at Babcock-Hitachi K.K. The main purpose of our study is to delineate the effects of CWM properties and the atomizer structure on spray characteris-tics. In order to obtain the necessary data concerning the structure of atomizers and to de-termine the optimum atomizing conditions, numerous experiments have been carried out under various liquid flow rates and air-to-liquid mass ratios using water instead of CWM for various types of internal mixing atomizers. As a result, it has been clarified that ato-mization improves as the liquid flow rate increases provided that the air-to-liquid mass ratio is kept constant. The optimum configurations of the exit ports has been determined ex-perimentally in the aim of reducing spray droplet sizes. The test results achieved in the experiments using various CWMs suggest that pseudo-plastic CWMs are easier to atomize than CWMs of other apparent rheological characteris-tics; that is, pseudo-plastic CWMs reduce the amount of coarser droplets produced by disin-tegration of film-like CWM at the exit ports of the atomizer. The mathematical expression of the spray mean droplet sizes of CWMs and water de-rived from the present study for pneumatic internal mixing atomizers correlated with the test results.
This study aims to clarify a disintegration mechanism and spray char-acteristics of Coal-Water Mixture (CWM) in high speed air stream and to develop an air-blast atomizer of CWM applicable to a boiler. Firstly the model of disintegration mechanism of CWM in high speed air stream was proposed. From the disintegration model, it is sup-posed that the separation-wise disintegration produces relatively small irregular particles and the drop-wise disintegration produces large spherical particles. The certainty of above disintegration model was proved by the observation of disintegration phenomena and the in-fluences of operating conditions on spray drop figures. Secondly an air-blast atomizer with wide spray angle was designed applying the disintegration model. By preparatory experi-ments it was made sure that the prefilming type and internally mixing type of air-blast ato-mizer is suitable for the atomization of CWM. From the investigation of spray characteris-tics of designed atomizer, it was made sure the designed atomizer has good performances for CWM atomization, that is wide spray angle (about 90 degree), small Sauter's mean dia-meter (less than 100μm) under the condition that the flow rate of atomizing air is over 4.5g/s and the air to liquid mass flow rate ratio is over 0.3.
The analysis of spray flow was very important for the spray combus-tion simulation. In this study, the models for the spray pattern and the motion of spray dro-plets in the gas flow were investigated to improve the simulation accuracy. The spray pat-tern was expressed by the random sampling of spray angles from a normal probability de-nsity distribution. The droplet trajectories were calculated by Lagrangian method consider-ing the effect of the velocity fluctuation of turbulent gas flow. At first, the droplet trajectories for the hollow-cone and full-cone types were simulated successfully in the cold air flow. Next, the effect of the two-staged air ratio on the concen-trations of NO and soot in the exhausted gas of PWM (Pitch-Water mixture) spray combus-tion was investigated. As a result, the optimum combustion condition for the reduction of NO and soot concentrations was found out by the three-dimensional spray combustion simulation to estimate clearly the distribution such as gas velocity vectors, temperature, and gas species concentrations within the furnace.