Jianfeng Pan

Microscale combustion research for application to micro thermophotovoltaic systems

Abstract A novel power MEMS concept, a micro thermophotovoltaic (TPV) system, is first described in this work, which would use hydrogen as fuel and would be capable of delivering 3–10 W electrical power in a package less than 1 cubic centimeter in volume. A microcombustor is one of the most important components of a micro TPV system. A high and uniform temperature distribution along the wall of the microcombustor is required to get a high electrical power output. However, sustaining combustion in a MEMS size combustor will be largely affected by the increased heat losses due to the high surface to volume ratio, which tends to suppress ignition and quench the reaction. In order to test the feasibility of combustion in microdevices and determine the relevant factors affecting microcombustion, numerical and experimental work was performed. The results indicated that a high and uniform temperature could be achieved along the wall of the flame tube.

Simultaneous absorption of SO2 and NO from flue gas using ultrasound/Fe2+/heat coactivated persulfate system

A novel process on simultaneous absorption of SO2 and NO from flue gas using ultrasound (US)/Fe2+/heat coactivated persulfate system was proposed. The influencing factors, active species, products and mechanism of SO2 and NO removal were investigated. The results indicate that US enhances NO removal due to enhancement of mass transfer and chemical reaction. US of 28kHz is more effective than that of 40kHz. NO removal efficiency increases with increasing persulfate concentration, ultrasonic power density and Fe2+ concentration (at high persulfate concentration). Solution pH, solution temperature and Fe2+ concentration (at low persulfate concentration) have double effect on NO removal. SO2 is completely removed in most of tested removal systems, except for using water absorption. US, Fe2+ and heat have a synergistic effect for activating persulfate to produce free radicals, and US/Fe2+/heat coactivated persulfate system achieves the highest NO removal efficiency. ·OH and SO4-· play a leading role for NO oxidation, and persulfate only plays a complementary role for NO oxidation.

Micro combustion in sub-millimeter channels for novel modular thermophotovoltaic power generators

The performance of micro combustion-driven power systems is strongly influenced by the combustor structure. A novel modular thermophotovoltaic (TPV) power generator is presented, which is based on the sub-millimeter parallel plate combustor. It has the potential to achieve a high power density because of the high radiation energy per unit volume due to the high surface-to-volume ratio of the micro-combustor. The work experimentally investigated the ignition limitation for two micro-combustors. It also studied the effects of three major parameters on a sub-millimeter combustor, namely hydrogen to oxygen mixing ratio, hydrogen volumetric flow rate and nozzle geometry. The results show that the combustion efficiency decreases with the increase of the hydrogen flow rate, which is caused by reduced residence time. The average wall temperature with the rectangular nozzle is 25 K higher than that with the circle nozzle. The output electrical power and power density of the modular TPV power generator are projected to be 0.175 W and 0.0722 W cm−3 respectively. We experimentally achieve 0.166 W of electrical power, which is in good agreement with the model prediction.

Simultaneous removal of NO and SO2 using vacuum ultraviolet light (VUV)/heat/peroxymonosulfate (PMS)

Simultaneous removal process of SO2 and NO from flue gas using vacuum ultraviolet light (VUV)/heat/peroxymonosulfate (PMS) in a VUV spraying reactor was proposed. The key influencing factors, active species, reaction products and mechanism of SO2 and NO simultaneous removal were investigated. The results show that vacuum ultraviolet light (185xa0nm) achieves the highest NO removal efficiency and yield of and under the same test conditions. NO removal is enhanced at higher PMS concentration, light intensity and oxygen concentration, and is inhibited at higher NO concentration, SO2 concentration and solution pH. Solution temperature has a double impact on NO removal. CO2 concentration has no obvious effect on NO removal. and produced from VUV-activation of PMS play a leading role in NO removal. O3 and ·O produced from VUV-activation of O2 also play an important role in NO removal. SO2 achieves complete removal under all experimental conditions due to its very high solubility in water and good reactivity. The highest simultaneous removal efficiency of SO2 and NO reaches 100% and 91.3%, respectively.

Comparison of cylindrical and modular micro combustor radiators for micro-TPV system application

A modular micro-TPV system was introduced in this work. Compared to the cylindrical structure, the modular TPV system has the advantages of easier fabrication and assembly. A micro combustor is a key component of the micro-TPV system. In order to maximize the power output, higher wall temperature and uniform distribution along the combustor wall is desirable. A micro cylindrical combustor (inner diameter d = 3.56 mm) and three kinds of micro modular combustors with the widths of 1.0 mm, 1.5 mm and 2.0 mm are experimented with. The results indicate that the micro modular combustor with a width of 1 mm has a much higher radiation efficiency than the micro cylindrical combustor. The wall temperature decreases with the increase of width due to the reduced heat transfer between the wall and hot gases. The performance of the micro modular TPV system is also predicted.

Gas-phase elemental mercury removal using ammonium chloride impregnated sargassum chars

ABSTRACT In this article, pyrolyzed bio-chars derived from a kind of macroalgae, sargassum, were modified by ammonium chloride (NH4Cl) impregnation, and were applied to remove Hg0 from flue gas. The characteristics of sorbents were investigated by the Brunauer–Emmett–Teller, X-ray photoelectron spectroscopy, scanning electron microscopy and ultimate and proximate analysis. The key parameters (e.g. loading value, reaction temperature and concentration of O2, NO, SO2 and water vapor), kinetics analysis and reaction mechanism of Hg0 removal were investigated. The results show that increasing loading value, reaction temperature, O2 concentration and NO concentration enhance Hg0 removal. The increase in SO2 concentration or water vapor concentration has a dual effect on Hg0 removal. The C–Cl groups and C=O groups play an important role in the process of Hg0 removal. The Hg0 removal process of modified samples meets the pseudo-second-order kinetic model.

Jet formation of SF6 bubble induced by incident and reflected shock waves

The computational results of two different cases on the evolution of the shock-SF6 heavy bubble interaction are presented. The shock focusing processes and jet formation mechanisms are analyzed by using the high resolution of computation schemes, and the influence of reflected shock waves is also investigated. It is concluded that there are two steps in the shock focusing process behind the incident shock wave, and the density and pressure values increase distinctly when the shock focusing process is completed. The local high pressure and vorticities in the vicinity of the downstream pole can propel the formation of the jet behind the incident shock wave. In addition, the gas is with the rightward velocity before the reflected shock wave impinges on the bubble; therefore, the evolutions of the waves and the bubble are more complicated when the reflected shock wave impinges on the SF6 bubble. Furthermore, the different end wall distances would affect the deformation degree of the bubble before the interact...

Effects of different parameters on the flow field of peripheral ported rotary engines

The performance of rotary engines is significantly influenced by the flow field. In this study, a detailed mathematical model was integrated into the simulation software FLUENT to investigate the gas flow field in a peripheral ported rotary engine by including a dynamic mesh model and a turbulent flow model. The models were also validated by experimental data. The basic flow mechanism in the combustion chamber was numerically studied. Meanwhile, the effects of the three major parameters on the flow field inside the combustion chamber, namely, rotating speed, intake shape, and intake angle, were also investigated. Results showed that a constantly changing swirl was formed in the combustion chamber during the intake and compression strokes as a result of the combined effects of the pocket of the rotor and the swirls in the combustion chamber. The swirl eventually broke into a unidirectional flow near the top dead center because of the significant decrease in combustion chamber volume. Furthermore, with the change in rotating speed, intake shape, and intake angle, significant differences in flow speed, inertia, and distribution were observed when the fluid entered the combustion chamber, which, in turn, led to obvious differences in the flow field, volume coefficient, and average turbulence kinetic energy in the combustion chamber.

Flow Topology of Three-Dimensional Spherical Flame in Shock Accelerated Flows

The flow topologies of compressible large-scale distorted flames are studied by means of the analysis of the invariants of the velocity gradient tensor (VGT). The results indicate that compressibility plays a minor role in the distorted flame zone. And the joint probability density function (p.d.f.) of the diagram appears as a teardrop shape, which is a universal feature of turbulence. Therefore, the distorted flame exhibits the characteristic of large-scale turbulence combustion, especially behind the reflected shock wave, while the p.d.f. of the diagram implies that the dissipation is enhanced in the compression and expansion regions, where it is higher than that when . Furthermore, we identify that the flame evolution is dominated by rotation by means of a quantitative statistical study, and the SFS topology is the predominant flow pattern. Not surprisingly, negative dilatation could suppress the unstable topologies, whereas positive dilatation could suppress the stable topologies.

Design Conceits and Testing of a Prototype Micro Thermophotovoltaic System

The design and testing of micro thermophotovoltaic (micro-TPV) system is described in this paper. The system is made of a SiC emitter, a dielectric filter and a GaSb photovoltaic cell array. The open-circuit voltage and short-circuit current can be measured by a multimeter, and the output power can be calculated. The effect of mass flux and the distance between the PV cell and outer wall of the combustor on the output power is also analyzed. When the flow rate of hydrogen is 4.133 g/hr and the H2/O2 ratio is 1.8, the micro-TPV system is able to deliver an electrical power output of 1.355W in a micro combustor of 0.195 cm3 in volume. The open-circuit electrical voltage and short-circuit current are 1.85 V and 1.032 amp respectively. This work makes it possible for us to replace batteries with micro-TPV systems as the power of micro mechanical devices in near future