Shuangfeng Wang

Bio: Shuangfeng Wang is an academic researcher from Chinese Academy of Sciences. The author has contributed to research in topics: Flame spread & Combustion. The author has an hindex of 10, co-authored 26 publications receiving 328 citations. Previous affiliations of Shuangfeng Wang include South China University of Technology.

Space Program SJ-10 of Microgravity Research

Abstract: SJ-10 program provides a mission of space microgravity experiments including both fields of microgravity science and space life science aboard the 24th recoverable satellite of China. Scientific purpose of the program is to promote the scientific research in the space microgravity environment by operating the satellite at lower earth orbit for 2 weeks. There are totally 27 experiments, including 17 ones in the field of microgravity science (microgravity fluid physics 6, microgravity combustion 3, and space materials science 8) and 10 in the field of space life science (radiation biology 3, gravitational biology 3, and space biotechnology 4). These experiments were selected from more than 200 applications. The satellite will be launched in the end of 2015 or a bit later. It is expected that many fruitful scientific results on microgravity science and space life science will be contributed by this program.

Ignition of single coal particle in a hot furnace under normal- and micro-gravity condition

Abstract: An experimental study on ignition and combustion of single particles was conducted at normal gravity (1-g) and microgravity (l-g) for three high volatile coals with initial diameter of 1.5 and 2.0 mm, respectively. The non-intrusive twin-color pyrometry method was used to retrieve the surface temperature of the coal particle through processing the images taken by a color CCD camera. At the same time, a mathematical model considering thermal conduction inside the coal particle was developed to simulate the ignition process. Both experiments and modeling found that ignition occurred homogeneously at the beginning and then heterogeneously for the testing coal particles burning at l-g. Experimental results confirmed that ignition temperature decreased with increasing volatile content and increasing particle size. However, contradicted to previous studies, this study found that for a given coal with certain particle size, ignition temperature was about 50n80 K lower at l-g than that at 1-g. The model predictions agreed well with the l-g experimental data on ignition temperature. The criterion that the temperature gradient in the space away from the particle surface equaled to zero was validated to determine the commence of homogeneous ignition. Thermal conduction inside the particle could have a noticeable effect for determining the ignition temperature. With the consideration of thermal conduction, the critical size for the phase transient from homogeneous to heterogeneous is about 700 lm at ambient temperature 1500 K and oxygen concentration 0.23. 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Bubble Behavior and Heat Transfer in Quasi-Steady Pool Boiling in Microgravity

Abstract: Pool boiling of degassed FC-72 on a plane plate heater has been studied experimentally in microgravity. A quasi-steady heating method is adopted, in which the heating voltage is controlled to increase exponentially with time. Compared with terrestrial experiments, bubble behaviors are very different, and have direct effect on heat transfer. Small, primary bubbles attached on the surface seem to be able to suppress the activation of the cavities in the neighborhoods, resulting in a slow increase of the wall temperature with the heat flux. For the high subcooling, the coalesced bubble has a smooth surface and a small size. It is difficult to cover the whole heater surface, resulting in a special region of gradual transitional boiling in which nucleate boiling and local dry area can co-exist. No turning point corresponding to the transition from nucleate boiling to film boiling can be observed. On the contrary, the surface oscillation of the coalesced bubble at low subcooling may cause more activated nucleate sites, and then the surface temperature may keep constant or even fall down with the increasing heat flux. Furthermore, an abrupt transition to film boiling can also be observed. It is shown that heat transfer coefficient and CHF increase with the subcooling or pressure in microgravity, as observed in normal gravity. But the value of CHF is quite lower in microgravity, which may be only about one third of that at the similar pressure and subcooling in terrestrial condition.

Determination of the maximum effective burning velocity of dust–air mixtures in constant volume combustion

Abstract: The reactivity of a combustible dust cloud is traditionally characterized by the so-called K-St value, defined as the maximum rate of pressure rise measured in constant volume explosion vessels, multiplied with the cube root of the vessel volume. The present paper explores the use of an alternative parameter, called the maximum effective burning velocity (u(eff,max)), which also is derived from pressure-time histories obtained in constant volume explosion experiments. The proposed parameter describes the reactivity of fuel-air mixtures as a function of the dispersion-induced turbulence intensity. Procedures for estimating u(eff,max) from tests in both spherical and cylindrical explosion vessels are outlined, and examples of calculated values for various fuel-air mixtures in closed vessels of different sizes and shapes are presented. Tested fuels include a mixture of 7.5% methane in air, and suspensions of 500 g/m(3) cornstarch in air and 500 g/m(3) coal dust in air. Three different test vessels have been used: a 20-1 spherical vessel and two cylindrical vessels, 7 and 221. The results show that the estimated maximum effective burning velocities are less apparatus dependent than the corresponding K-St values. (C) 2007 Elsevier Ltd. All rights reserved.

Laminar burning velocities and Markstein lengths of premixed methane/air flames near the lean flammability limit in microgravity

Abstract: Effects of flame stretch on the laminar burning velocities of near-limit fuel-lean methane/air flames have been studied experimentally using a microgravity environment to minimize the complications of buoyancy. Outwardly propagating spherical flames were employed to assess the sensitivities of the laminar burning velocity to flame stretch, represented by Markstein lengths, and the fundamental laminar burning velocities of unstretched flames. Resulting data were reported for methane/air mixtures at ambient temperature and pressure, over the specific range of equivalence ratio that extended from 0.512 (the microgravity flammability limit found in the combustion chamber) to 0.601. Present measurements of unstretched laminar burning velocities were in good agreement with the unique existing microgravity data set at all measured equivalence ratios. Most of previous 1-g experiments using a variety of experimental techniques, however, appeared to give significantly higher burning velocities than the microgravity results. Furthermore, the burning velocities predicted by three chemical reaction mechanisms, which have been tuned primarily under off-limit conditions, were also considerably higher than the present experimental data. Additional results of the present investigation were derived for the overall activation energy and corresponding Zeldovich numbers, and the variation of the global flame Lewis numbers with equivalence ratio. The implications of these results were discussed.

On the accuracy of laminar flame speeds measured from outwardly propagating spherical flames: Methane/air at normal temperature and pressure

Abstract: The present work investigates the accuracy of laminar flame speeds measured from outwardly propagating spherical flames. We focus on methane/air mixtures at normal temperature and pressure, for which there is a variety of data sets reported in the literature. It is observed that there are large discrepancies in laminar flame speed measurement, which makes these experimental data unhelpful for restraining the uncertainty of chemical models. Different sources of uncertainty/inaccuracy (including mixture preparation, ignition, buoyancy, instability, confinement, radiation, nonlinear stretch behavior, and extrapolation) are discussed and their contributions to large discrepancies in laminar flame speed measurement are assessed with the help of 1-D simulation. It is found that the uncertainty in equivalence ratio can bring large inconsistency in laminar flame speed measurement, especially for off-stoichiometric mixtures and experiments using pressure gauge with normal or low accuracy. For fuel-rich methane/air mixtures, the large deviations in laminar flame speed measurement could be partly caused by nonlinear stretch behavior and extrapolation. The change of the influence of different sources of uncertainty with initial pressure, initial temperature, and fuel carbon number is also discussed. Furthermore, it is shown that the discrepancy in raw experimental data can be possibly hidden after extrapolation is conducted. Therefore, the data used for extrapolation as well as extracted results should be reported and compared with simulation or other experiments. The recommendations on the laminar flame speeds measurement using the propagating spherical flames are also provided.

Effects of radiation and compression on propagating spherical flames of methane/air mixtures near the lean flammability limit

Abstract: Large discrepancies between the laminar flame speeds and Markstein lengths measured in experiments and those predicted by simulations for ultra-lean methane/air mixtures bring a great concern for kinetic mechanism validation. In order to quantitatively explain these discrepancies, a computational study is performed for propagating spherical flames of lean methane/air mixtures in different spherical chambers using different radiation models. The emphasis is focused on the effects of radiation and compression. It is found that the spherical flame propagation speed is greatly reduced by the coupling between thermal effect (change of flame temperature or unburned gas temperature) and flow effect (inward flow of burned gas) induced by radiation and/or compression. As a result, for methane/air mixtures near the lean flammability limit, the radiation and compression cause large amounts of under-prediction of the laminar flame speeds and Markstein lengths extracted from propagating spherical flames. Since radiation and compression both exist in the experiments on ultra-lean methane/air mixtures reported in the literature, the measured laminar flame speeds and Markstein lengths are much lower than results from simulation and thus cannot be used for kinetic mechanism validation.

Review of flow boiling and critical heat flux in microgravity

Abstract: Space agencies worldwide are actively exploring the implementation of two-phase thermal management systems to support astronaut life onboard future space vehicles and planetary bases. Key motivations for these efforts are to increase the efficiency of power utilization and reduce overall weight and volume. These advantages are realized by orders of magnitude enhancement in heat transfer coefficient achieved with flow boiling and condensation compared to single-phase systems. This study will review published literature concerning two-phase flow and heat transfer in reduced gravity. Discussed are the different methods and platforms dedicated to exploring the influence of reduced gravity, including ground flow boiling experiments performed at different orientations relative to Earth gravity, as well as reduced gravity adiabatic two-phase flow, pool boiling, flow boiling and CHF experiments. Despite the extensive data and flow visualization results available in the literature, it is shown that there is a severe shortage of useful correlations, mechanistic models and computational models, which compromises readiness to adopt flow boiling in future space systems. Key recommendations are provided concerning platform, heater design, and operating conditions for future studies to expedite the deployment of two-phase thermal management in future space missions.

Enhancement of flame development by microwave-assisted spark ignition in constant volume combustion chamber

Abstract: The enhancement of laminar flame development using microwave-assisted spark ignition has been investigated for methane–air mixtures at a range of initial pressures and equivalence ratios in a 1.45 l constant volume combustion chamber. Microwave enhancement was evaluated on the basis of several parameters including flame development time (FDT) (time for 0–10% of total net heat release), flame rise time (FRT) (time for 10–90% of total net heat release), total net heat release, flame kernel growth rate, flame kernel size, and ignitability limit extension. Compared to a capacitive discharge spark, microwave-assisted spark ignition extended the lean and rich ignition limits at all pressures investigated (1.08–7.22 bar). The addition of microwaves to a capacitive discharge spark reduced FDT and increased the flame kernel size for all equivalence ratios tested and resulted in increases in the spatial flame speed for sufficiently lean flames. Flame enhancement is believed to be caused by (1) a non-thermal chemical kinetic enhancement from energy deposition to free electrons in the flame front and (2) induced flame wrinkling from excitation of flame (plasma) instability. The enhancement of flame development by microwaves diminishes as the initial pressure of the mixture increases, with negligible flame enhancement observed above 3 bar.

Suppression of wood dust explosion by ultrafine magnesium hydroxide

Abstract: The suppression effects of ultrafine Mg (OH)2 powders with different particle sizes and mass fractions on explosion flame of wood dust are experimentally studied in a half-closed vertical experimental duct. Flame structures and characteristic parameters, including flame light emission images, propagation velocity, temperature, during the flame propagation of wood dust explosion are recorded by high-speed photography and fine thermocouple. Thermal decomposition behaviors of wood dust and Mg(OH)2 powders are studied using synchronous thermal analyzer. Chemical structures of residual dust samples after the explosion are characterized by Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The experimental results show that explosion flame of wood dust is obviously suppressed by physical and chemical effects of Mg(OH)2 powders, and the suppression effect of nano-Mg(OH)2 is better than that of micron-Mg(OH)2 under same mass fractions. By analyzing multiple characteristics of nano-powders, the advantages of nano-Mg(OH)2 over micron-powders are further investigated.