Drop Number Density Research Articles

An experimental study of air-assist atomizer spray flames

Spray flames have, in the past, been modeled and treated as homogeneous turbulent gas diffusion flames based upon the similarities in flame structure. Air-assisted atomizer spray flames, as commonly used in industrial furnaces, boilers, and gas turbine combustors, are shown, in this paper, to have a more complex structure. The swirling motion introduced into the fuel and air flows for the control of flame stability, flame length, combustion intensity and efficiency, causes the structure of air-assist atomizer spray flames to be different from that of turbulent gas diffusion flames. Detailed measurements in air-assist atomizer spray flames have been made using a newly developed non-intrusive light scattering Phase/Doppler detection technique. Based upon the measurements and observations, a physical model of the air-assist atomizer spray flames has been constructed. Detailed comparison of the spray structures in burning and non-burning conditions is presented. The presence of the flame has very little effect on the large drops in the outer edges of the spray, outside the flame zone. The spray structure is, however, drastically changed inside the flame reaction zone, as shown by changes in both the magnitude and shape of the radial distributions of drop number density, liquid flux, mean drop size diameter, and drop mean axial velocity.

A study on the mechanism of dropwise condensation. 2nd report Condensation coefficient of water at low pressures.

Though an apparent difference in the number density of microscopic drops existed between gold and chromium condenser surfaces used, the heat-transfer coefficient was found to be almost of the same value. Then the distributions of drops by sizes down to 1μm in radius were experimentally determined. For the gold condenser surface on which small drops seemed to be densely populated, the measured drop-size distribution showed a satisfactory agreement with the theoretical prediction in the so-called equilibrium region of small drops. On the other hand, for the chromium surface, the number density of drops smaller than 7μm deviated clealy downward. Integrating the measured drop-size distribution weighted with the substantial condensation rate onto each droplet yields a heat-transfer coefficient, which should coincide with the actually measured one. From the comparison of the data for the both condenser surfaces, it is concluded that the condensation coefficient of water at pressures 1 and 3 kPa is 0.4.

A fast, approximative method for integrating the stochastic coalescence equation

The use of mean values of the drop number density in the coalescence equation is shown to lead to a system of ordinary differential equations that provide good approximative solutions with a minimum of computational effort. The coefficients in this system of equations are functions of the kernel and can be obtained by simple quadrature. Comparisons are made between numerical and analytic solutions for two types of kernels (constant and sum of arguments), using a Gaussian initial distribution of cloud droplets. Systematic deviations of the numerical results from corresponding analytic solutions are shown to depend on the choice of variables, and methods to suppress these deviations are discussed.