Size distribution impingement

Any refractory material that does not decompose or vaporize can be used for melt spraying. Particles do not coalesce within the spray. The temperature of the particles and the extent to which they melt depend on the flame temperature, which can be controlled by the fueLoxidizer ratio or electrical input, gas flow rate, residence time of the particle in the heat zone, the particle-size distribution of the powders, and the melting point and thermal conductivity of the particle. Quenching rates are very high, and the time required for the molten particle to soHdify after impingement is typically to... 

The constant, K, depends on the target material, particle abrasiveness, and size distribution of the particles. The kinetic energy of the particles is Mp x Vp + 2. This parameter includes the solids loading, or concentration, and velocity of the particle. Alpha is the angle of impingement of the particle on the blade surface. 

Optieal partiele eounters provide information on the partieles present in different size ranges. A beam of light is eollimated and foeused onto a measurement eelL Light impinging on a partiele is seattered and reaehes a photomultiplier tube and eonverted to an output proportional to partiele size. Partiele size distributions are eomputed by appropriate software. 

Impinging jets, which consist of a cylindrical chamber with two spray nozzles that enter from opposite sides of the chamber, provide small particles with narrow size distribution. The solution oi the material is fed through one nozzle and the crystallization agent through the second nozzle. Finasteride has been cry.stallized in this way a solution of the material in acetic acid plus some water was fed from one nozzle and water from the other the average crystal size was 10 to 15 pm. 

Our Chemical Engineering colleagues had developed an elegant impinging jet crystallization which provided excellent particle size control for the finasteride process [13]. In the final pilot plant campaign just before the factory start-up, the crystallization suddenly started producing a different particle size distribution and lower recovery. The problem was traced to a new finasteride solvate which reduced the solubility in the crystallization solvent system. Fortunately, only relatively... 

The importance of chemical-reaction kinetics and the interaction of the latter with transport phenomena is the central theme of the contribution of Fox from Iowa State University. The chapter combines the clarity of a tutorial with the presentation of very recent results. Starting from simple chemistry and singlephase flow the reader is lead towards complex chemistry and two-phase flow. The issue of SGS modeling discussed already in Chapter 2 is now discussed with respect to the concentration fields. A detailed presentation of the joint Probability Density Function (PDF) method is given. The latter allows to account for the interaction between chemistry and physics. Results on impinging jet reactors are shown. When dealing with particulate systems a particle size distribution (PSD) and corresponding population balance equations are intro-... 

The two critical attributes characterizing the performance of DPIs are the imiformity of the delivered dose and the aerodynamie assessment of partiele size distribution. To determine the imiformity of the delivered dose, an apparatus capable of quantitatively retaining the dose leaving the deviee is used. For aerodynamic particle size assessment, a multistage liquid impinger or easeade impaetor is used. All aerosol performance testing must be condueted under defined temperature and humidity conditions. 

JET IMPACTION. A rapidly moving particle, striking a suitably coated surface, will leave an impression whose size is a function of the original drop diameter. Pilcher (7S) illustrates the operation of the jet impactor. The higher the jet velocity, the smaller the particle size which will impinge. An instrument called the cascade impactor consists of a series of these slides. The jet velocity is increased from slide to slide thus, the cascade is useful in determining droplet size distributions. 

The residence time distribution of particles is related to the properties of the particles and the gas flow, including the size distribution, and the velocity of gas flow and its profile. In practically applicable impinging stream devices, the particles being processed usually have relatively narrower size distribution the diameter of the tube to particles size ratio, d Jd,h is normally very large ( 15) while the gas velocity is high... 

In a gas-continuous impinging stream device with liquid as the dispersed phase, the liquid is usually atomized into fine droplets with nozzles of an appropriate type, and ejected into gas flows to form droplets-in-gas suspensions before impingement. This can be called the Primary Atomization, and it defines the primary dispersity of liquids. The mechanism of primary atomization and the methods for predicting size distribution (SD) and mean diameter (MD) of the sprayed droplets have been widely reported and some sources of references may be found, e.g., in Ref. [69]. 

Figure 5.1 Impinging stream device for the measurement of droplet size distribution. 1 critical nozzle 2, 3 rotameter 4 frame 5 guider 6 apron A-A impingement plane.

It is actually very difficult to obtain representative and reproducible data for the size distribution of sprayed droplets, no matter what kind of method is employed for measurement, because the dispersion of liquid by atomization, including re-atomization in impinging streams, is highly random. In the study the following factors are considered carefully in the arrangement of sampling for representative samples and thus statistically trustworthy results ... 

The results of regression analysis of the measured data indicate that the droplet size distributions both before and after the impingement can be expressed by the following equation ... 

It can be seen from the figures that the size distributions of spray droplets become narrower after impingement, or, in other words, the droplet sizes become more uniform than before. Such a variation is observed in most of the runs, although some exceptions also appeared (about 10% in all the runs). As is well known, the uniformity of droplet sizes, or inversely, the scattering of the size distribution can be expressed with the parameter Standard Deviation , a, which is the defined as... 

The larger the value for cr, the greater the scattering of the size distribution, and, correspondingly, the poorer the uniformity of the droplet sizes. Part of the data measured at various air-to-liquid mass flow ratio, m.JmL, are shown in Table 5.1. It can be seen that, normally, the impingement between opposing droplets-in-gas suspension streams makes cr smaller. Only those obtained at in the third column of the... 

Standard deviation of size distribution before and after impingement... 

To an extent, the intensity of impingement is dependent on the impinging distance, S, and smaller S implies stronger impingement. Therefore it is also of interest to understand the effect of the impinging distance on the size distribution of droplets. The... 

Influence of impinging distance on the standard deviation of droplet size distribution... 

Another interesting result observed is that in the case without impingement, i.e., only primary atomization occurred, the scattering of the droplet size distribution, a, decreases, and, consequentially, the droplet sizes become more uniform, as the gas to liquid mass flow rate ratio, increases, as can be seen in the third row of Table... 

The impingement between the two opposing suspension streams makes the sizes of the spray droplets uniform to an extent, yielding narrower size distribution. More intensive impingement favors the uniformization of droplet sizes more effectively. 

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