A Computational Study of the Evaporation Characteristics of an Air-Blast Atomized, Kerosene Spray in Porous Media

The evaporation characteristics of an air-blast atomized kerosene spray in porous media in a 2D-axisymmetric coflow environment were studied numerically. A swirling primary air stream with varying intensity was used to aid the atomization process. The effects of non-Darcy flow in porous medium were modeled using a modified form of Ergun equation. Local thermal equilibrium between the fluid mixture and porous medium was assumed. Conductive and transient heat flux terms in the energy equation were modified to include the effective thermal conductivity and thermal inertia of the solid region respectively. The effective thermal conductivity was defined as the volumetric average between solid and fluid media. First, the temperature characteristics of the porous medium, arising from different source terms, were obtained. Complete vaporization of kerosene was achieved when the maximum temperature of the porous medium was at 590 K. The effects of porous medium temperature, primary air swirl number, fuel flow rate, and secondary (coflow) air inlet temperature on vaporization were analyzed. For all cases, kerosene vapor concentration profiles at five different axial locations in the domain (0.08, 0.12, 0.13, 0.14, and 0.19m from the nozzle) were obtained. An increase in secondary air inlet temperature from 373 K to 473 K increased the completeness of evaporation from 94% to 97%. When the swirl number was increased from 0.14 to 0.34, the peak vapor concentration was reduced by 31% and more vapor spread radially. The porous medium temperature was found to be a crucial factor in obtaining the complete vaporization of the spray.

NOX as a Function of Fuel Type: C1-to-C16 Hydrocarbons and Methanol

The response of NOX to fuel type is determined for lean-prevaporized-premixed combustion in on atmospheric pressure jet-stirred reactor (JSR). Pure, straight chain, alkane fuels from C1 (methane) to C16 (hexadecane) and methanol are tested. Testing is conducted under three conditions, each of which is obtained using a particular inlet-jet nozzle for the JSR. For a selected condition, the fuels are burned under nearly identical macroscopic thermal and fluid mechanical fields in the JSR. A constant mixture inlet total temperature is used that provides for complete vaporization of all of the fuels tested without causing pre-flame reactions in the premixer. Two of the nozzles used have single, centered jets and provide a nominal combustion temperature of 1790 K. The third nozzle has eight diverging jets. In this case, the fuel-air equivalence ratio is increased, providing a nominal combustion temperature of 1850 K. Lowest levels of NOX are measured when methanol is burned. Upon switching to methane, the NOX concentration increases by 62±10%. For the alkane fuels, methane combustion yields the least amount of NOX. Upon switching from methane to ethane, the NOX increases by 22±2%. Further increases in the size of the alkane fuel molecule (from C2 to C16) show small increases (8±5%) in the NOX concentration. Although the JSR-condition selected affects the absolute NOX concentration, the trends in NOX concentration with respect to fuel-type are the same for the three conditions used. The JSR is modeled as a single perfectly stirred reactor (PSR) operating at the experimental residence time and combustion temperature. This modeling shows that the increase in the NOX measured for the alkane fuels may be explained in terms of the increase in O-atom concentration with increasing C/H ratio. In order to explore the effect of Fenimore prompt NOX, a two-PSRs-in-series model is used. The first PSR is assigned a residence time equal to 5% the total residence time of the reactor. The second PSR accounts for the remaining 95% of the reactor residence time. Because of its short lifetime, the CH radical is effectively restricted to the first PSR, and prompt NOX mainly forms in this zone. Mechanisms directly dependent on the O-atom form NOX throughout the reactor. The modeling suggests that prompt NOX is responsible for the greater concentration of NOX found in the methane combustion compared to the methanol combustion.

Vaporization of Isoflurane by Liquid Infusion

We investigated the vaporization of liquid isoflurane when infused directly into a circuit. Pooling of isoflurane occurred within the circuit tubing at infusion rates used during clinical practice when constant gas flows were used. Despite pooling, the concentration of isoflurane was linearly related to infusion rate. Cyclical gas flow, such as that seen in a circle system, increased vaporization so that pooling occurred only at the higher infusion rates used during the first five minutes of totally closed circuit anaesthesia. There were no major differences in pooling or the maximum concentration of isoflurane reached between 26 gauge needle and droplet administration of isoflurane: however the maximum concentration was reached more quickly by droplet administration. We conclude that direct infusion of liquid isoflurane into an anaesthetic circuit will result in complete vaporization during maintenance anaesthesia.

Premixing and Flash Vaporization in a Two-Stage Combustor

A double recirculation zone two-stage combustor fitted with airblast atomizers has been investigated in a previous work. The present paper describes further tests with premixing tubes in the secondary combustion zone. Flash vaporization was employed to ensure complete vaporization of the secondary fuel, which was heated to 600K by the combustor inlet air. The combustor was run at conditions corresponding to four different engine power settings, and the effect of primary/secondary fuel flow split on emissions was investigated. Tests were also performed with unheated secondary fuel, and comparisons were made with flash vaporization data. The best configuration reduced the oxides of nitrogen by 54 percent, carbon monoxide by 59 percent and unburned hydrocarbons by 97 percent as compared to emission levels for the standard JT8D combustor, which was used as a reference.

A Generalization of the System Mean Void Fraction Model for Transient Two-Phase Evaporating Flows

The system mean void fraction model has been successful in the prediction of a variety of transient evaporating and condensing flow phenomena; however, applications of the model have been restricted to physical situations involving complete vaporization or condensation. The major contribution of this paper is the development of a generalization of the existing system mean void fraction model, applicable to the broader class of transient two-phase flow problems involving incomplete vaporization. Present applications of the generalized system mean void fraction model to transient evaporating flows indicate good agreement with experimental void fraction and mass flux response data available in the literature. These data represent a variety of different flow geometries, types of fluids, and a wide range of operating conditions.

The Influence of Matrix Anion on Characteristics of the Arc Plasma and on Spectrochemical Determinations

The influence of the matrix anion in CdO and CdCl2 was studied. Radial distributions of temperature and electron density in the arc plasma were measured. For CdCl2 matrix, a higher arc temperature and electron density as well as higher radial gradients of these values have been observed. Spectral line intensities (with background corrections) of trace elements were investigated in both matrices. Elements evaporate faster from chloride matrix. This causes in the beginning an intensity increase of lines compared with CdO matrix. But in determinations with exposure time long enough to ensure complete vaporization of traces from oxide matrix, an enhancement of integral line intensities of traces in CdO, compared with CdCl2 matrix, has been observed.

Theoretical Model of the Mixture-Vapor Transition Point Oscillations Associated With Two-Phase Evaporating Flow Instabilities

A horizontal tube evaporator in which complete vaporization takes place can be divided into three distinct regions—a subcooled, a two-phase, and a superheat region. The mixture-vapor transition point corresponds to the liquid film dryout point, and when entrainment is negligible, it represents the boundary between the two-phase and superheat regions. Experimental evidence indicates that during what is conventionally accepted as steady flow conditions, the motion of the mixture-vapor transition point is of an oscillatory nature. Furthermore, not only are the oscillations random, but their statistical characteristics can be represented by a modified Rayleigh distribution. This paper presents the formulation of a theoretical model which incorporates various deterministic mechanisms, while at the same time includes the existence of a random phenomenon. The model has the capability of predicting the influence of evaporator heat flux and inlet flow quality on the statistical characteristics of the transition point oscillations. Perhaps, the most significant potential of the proposed model is that it represents a first step toward the formulation of some of the fundamental mechanisms associated with two-phase evaporating flow instabilities on a statistical basis; a basis which appears to be consistent with many of the experimental observations currently available.

An Experimental Investigation Into the Oscillatory Motion of the Mixture-Vapor Transition Point in Horizontal Evaporating Flow

A horizontal tube evaporator in which complete vaporization takes place can be divided into two distinct regions: a two-phase region and a super heat region. The mixture-vapor transition point refers to the boundary between these two regions. Experimental evidence indicates that, during steady as well as transient flow conditions, the motion of the mixture-vapor transition point is of an oscillatory nature. This study is concerned with the statistical characteristics of these oscillations, the physical mechanisms causing them, and the influence of various evaporator parameters. Experimental data are presented which indicate that the statistical characteristics of the transition point oscillations can be described by a transformed Rayleigh distribution, and that the inlet flow quality and evaporator heat flux have a considerable influence on this distribution.