Ambient Steam Research Articles

Coupling effect of phase change heat transfer on free surface in pure steam environment and thermocapillary convection in annular pool

In order to reveal the coupling effect between surface phase change heat transfer in pure steam environment and thermocapillary convection in annular pool, we performed a series of three-dimensional numerical simulations by using the finite volume method based on the statistical evaporation rate theory. The inner and the outer radii of the annular pool are respectively 20 mm and 40 mm, the depth ranges from 1 mm to 20 mm. The selected working fluid is water with Prandtl number of 6.13. Results show that the radial temperature gradient on the free surface near the cylinders increases due to the latent heat absorbed and/or released as a result of phase change heat transfer, which leads to the increase of the thermocapillary force near the cylinders and the enhancement of the flow. Therefore, the isotherms converge to the cylinders. The axial velocity on the free surface caused by surface phase change is much less than the inward radial velocity. Flow pattern depends slightly on Marangoni number. But with the increase of Marangoni number, the flow is enhanced and the flow cells near the cylinders gradually expand to the middle of the annular pool. With the increase of the aspect ratio, thermocapillary convection is enhanced and the evaporation strengthens. With the increase of ambient steam temperature and pressure, the condensation mass flux near the inner cylinder increases, the radial temperature gradient rises, and thermocapillary convection strengthens. However, near the outer cylinder, it is the opposite.

Investigation of steam effect on ignition of dispersed coal particles in O2/N2 and O2/CO2 ambiences

In this paper, we intensively investigate the influence of steam on the hetero-homogeneous joint ignition of dispersed coal particle streams in both O2/N2 and O2/CO2 conditions of an optically accessible flat-flame burner. Two differently ranked coals and one bituminous char were tested for a comparison. The effects of moisture content in the raw coal, steam content or diluents (N2/CO2) in the ambience, and fuel types were systematically examined under isothermal conditions. First, it is seen that the moisture content in raw coal delays its ignition because of endothermic vaporization, which becomes weakened at the high ambient temperature. Secondly, three main mechanisms are categorized to explore the profound effects of ambient steam content on ignition of coal particles, i.e., (i) the promotion effect of OH radical on the oxidation of volatile hydrocarbons, (ii) the inhibition effect of gaseous H2O molecule on the equilibrium of hydrocarbon oxidation, (iii) the negative effect of endothermic surface gasification reaction (C-CO2/C-H2O). In O2/N2 ambience (1500 or 1800 K), as the steam content increases, the ignition delay of coal particles is rapidly reduced in an early stage of 0%–5% due to the positive effect of OH radicals, followed by an inappreciable reduction in 5%–13% stage because of both the steam inhibition effect and the endothermic surface gasification. However, in O2/CO2 ambience with sufficiently high steam content (5%–18%), the ignition delay even becomes longer with the further increment of steam. It is because of the synergistic effect between C-H2O and C-CO2 reaction at high temperatures (1500 K and 1800 K). Finally, for fuel types, the OH radical promotion effect of two lignite samples is obviously higher than that of low-volatile char samples, whereas with steam addition the sodium-rich Zhundong coal exhibits lower ignition delay than Hulunbel lignite due to catalytic effect.

Considerations for post-lethality treatments to reduce Listeria monocytogenes from fully cooked bologna using ambient and pressurized steam

During processing of ready-to-eat (RTE) deli meats, any secondary processing procedures such as peeling and cutting introduce the distinct possibility of cross-contamination between equipment, personnel, and food. To eliminate or reduce pathogens such as Listeria monocytogenes and ensure food safety, RTE deli meats can be pasteurized prior to or after packaging. In this study, ambient steam in-package pasteurization was compared with pressurized steam prepackaging pasteurization to reduce L. monocytogenes from fully cooked RTE bologna. The bologna (14 cm diameter×1.5 cm thickness) samples were surface-inoculated to contain about 8 log 10 of L. monocytogenes. To achieve 2 log reductions for L. monocytogenes, the bologna samples needed to be treated for about 10 s in pressurized steam at 131 °C or for about 2.5 min in ambient steam at 100 °C. The pasteurization time using pressurized steam treatment was about 75–90% shorter than using ambient steam treatment. Pressurized steam treatment may be integrated into a vacuum packaging unit to effectively eradicate L. monocytogenes from RTE meats just prior to sealing the retail packages to further reduce the treatment time, avoid post-treatment recontaminations by pathogens, and improve food safety without detrimentally affecting meat quality.

The calculation of heat transfer to thick metal walls of steam turbine components from ambient steam with time-dependent characteristics

The paper treats non-steady heat conduction, normally through a parallel-sided slab and radially through a cylinder when the rear-side of the slab, or outside of the cylinder, is perfectly insulated, and when the front-side of the slab, or inside of the cylinder, is subjected to a flowing vapour whose pressure, temperature, and mass flow rate vary with time in some prescribed manner. The problem is typical of starting conditions for steam turbines. Formulae are assumed for the vapour-side coefficients (both with and without condensation), and finite-difference approximations are used to obtain solutions to the conduction problem. Certain questions are raised concerning the applicability of the extant vapour-side coefficients, which have been derived empirically under steady-state, one-dimensional conditions, for the solution of non-steady heat conduction problems of the type under consideration.