Vaporization droplet

The impact process of a 3.8 mm water droplet under the conditions experimentally studied by Chen and Hsu (1995) is simulated and the simulation results are shown in Figs. 16 and 17. Their experiments involve water-droplet impact on a heated Inconel plate with Ni coating. The surface temperature in this simulation is set as 400 °C with the initial temperature of the droplet given as 20 °C. The impact velocity is lOOcm/s, which gives a Weber number of 54. Fig. 16 shows the calculated temperature distributions within the droplet and within the solid surface. The isotherm corresponding to 21 °C is plotted inside the droplet to represent the extent of the thermal boundary layer of the droplet that is affected by the heating of the solid surface. It can be seen that, in the droplet spreading process (0-7.0 ms), the bulk of the liquid droplet remains at its initial temperature and the thermal boundary layer is very thin. As the liquid film spreads on the solid surface, the heat-transfer rate on the liquid side of the droplet-vapor interface can be evaluated by... 

In a supersonic gas flow, the convective heat transfer coefficient is not only a function of the Reynolds and Prandtl numbers, but also depends on the droplet surface temperature and the Mach number (compressibility of gas). 154 156 However, the effects of the surface temperature and the Mach number may be substantially eliminated if all properties are evaluated at a film temperature defined in Ref. 623. Thus, the convective heat transfer coefficient may still be estimated using the experimental correlation proposed by Ranz and Marshall 505 with appropriate modifications to account for various effects such as turbulence,[587] droplet oscillation and distortion,[5851 and droplet vaporization and mass transfer. 555 It has been demonstrated 1561 that using the modified Newton s law of cooling and evaluating the heat transfer coefficient at the film temperature allow numerical calculations of droplet cooling and solidification histories in both subsonic and supersonic gas flows in the spray. 

Sirignano, W. A. 1983. Fuel droplet vaporization and spray combustion theory. Progress Energy Combustion Science 9 291-322. 

Law, C. K. 1982. Recent advances in droplet vaporization and combustion. Progress Energy Combustion Science 8 171-201. 

Photographs of the spray under nonburning conditions with steam, preheated air, and normal unheated air as the atomization fluids are shown in Fig. 16.2. The addition of enthalpy to the fuel for the steam and preheated-air cases enhanced initial droplet vaporization under nonburning conditions, as compared to the normal-air case (compare the spray pattern shown in Figs. 16.2a and 16.26 with Fig. 16.2c near to the nozzle exit). Further downstream, the general spray features for the two air cases are essentially the same except for the significantly reduced number of droplets in the preheated-air case. Droplets appear to be smaller for steam than for the two air cases, with few larger size droplets. The presence of a mist of droplets for the steam case, Fig. 16.2a, is attributed to the finer droplet atomization. Fuel viscosity is reduced as a result of enthalpy transfer from the steam to the fuel, and viscosity of the steam increases relative to the normal or preheated air. 

These results show that droplet vaporization must be different between the three flames. Droplet and fuel vapor transport must be significantly different for these flames and must affect combustion efficiency. The solid-cone nature of the spray flame was found to be preserved irrespective of the atomization gas. 

Chemical composition and reactivity of the atomization air, therefore, affects droplet vaporization and transport in spray flames. In order to determine quantitatively the extent of this variation, information was obtained on the spatial distribution of droplet size and velocity, as well as their temporal distributions at various spatial positions in the spray flames. 

An increase in droplet size with axial position is observed for all three gases. However, the relative trend of smallest droplet mean size with steam and largest with normal (unheated) air remains unchanged. As an example, at 50 mm downstream from the nozzle exit at r = 0, droplet mean size for steam, preheated air, and normal air were found to be 69, 86, and 107 pm, respectively see Fig 16.3. The droplet size with steam is also significantly smaller than air at all radial positions see Fig. 16.3. The droplet size with preheated air is somewhat smaller than normal air due to the decreased effect of preheated air at this location and increased effect of combustion. Early ignition of the mixture with preheated air (see Fig. 16.1) must provide a longer droplet residence time which results in a smaller droplet size. In addition, the increased flame radiation with preheated air increased droplet vaporization at greater distances downstream from the nozzle exit. Indeed, the results indicate that the measured droplet sizes with preheated atomization air are smaller than normal air in the center... 

Gregory, C. A., Jr., Calcote, H. F., Combustion Studies of Droplet-Vapor Systems, ... 

Linear Range The concentration range where increasing concentrations of an analyte have a proportional increase in LC-MS response. Overall QqQ-type mass spectrometers (triple quadmpoles, Q-TRAPS) are superior in terms of linearity. Most common causes for nonlinear response include MS detector saturation, dimmer/adduct formation, API droplet/vapor saturation at high concentrations, and space charge effects. 

A quantitative understanding of certain primary combustion phenomena, e.g., liquid fuel-droplet vaporization and burning, gas phase chemical reaction kinetics, radiation heat transfer from combustion products, and mixing of reactants and combustion products, is required to develop a rational approach for the effective utilization of synfuels in industrial boiler/furnace systems. Those processes are defined by the interaction of a number of mechanisms which are conveniently described in terms of physical and chemical related processes. The physical processes are ... 

The evolution of a particular compound is determined by the rate of droplet vaporization, the relative volatility and diffusi-vity in the liquid phase of the compound in question. Because of the complex composition of fuel oils, it is difficult to separate the relative importance of these effects since the measured nitrogen evolution is a summation of many fractions, each of which is influenced to a different extent. In order to reveal the role of diffusion and relative volatility in the evolution of fuel nitrogen, a complementary set of experiments were performed using n-dodecane doped with pyridine, quinoline or acridine. 

The equilibrium distillation behavior of the model fuels is adequately covered in the fuel oil discussion. However, the case for the rapid droplet vaporization, which was not clearly seen for fuel oils, is more amenable to analysis for a binary system. The surface gradients are given by the following relationship,... 

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