Jen-Shih Chang

The role of H2O and NH3 on the formation of NH4NO3 aerosol particles and De-NOx under the corona discharge treatment of combustion flue gases

Abstract In this paper, mechanisms of NO x removal by streamer corona discharges are proposed and the role played by H 2 O and NH 3 in the system is discussed in detail. The results show that: (1) The ion-molecule reactions play an important role in the De-NO x processes as well as the radicals reactions. (2) The effects of gas temperature and electron energy cannot be neglected in current processes. (3) The effect of H 2 O and NH 3 concentrations and external electric field becomes a significant influence on the current processes due to the importance of the ion-molecule reactions and volume recombinations. (4) Ion induced aerosol formation plays an important role in the formation of NH 4 NO 3 ultrafine particles.

Characterization of the Soot Deposition Profiles in Diesel Engine Exhaust Gas Recirculation (EGR) Cooling Devices Using a Digital Neutron Radiography Imaging Technique

A non-destructive neutron radiography technique was used to measure the thickness of diesel soot deposited in the tubes of exhaust gas recirculation (EGR) cooling devices. Measurements were performed to characterize the fouling in single-tube and three-tube devices for laminar and turbulent flows. Measurements were also performed to characterize the effect that the design of the inlet header had on the deposition characteristics in the device. The analysis of the neutron images showed that the soot deposition in the single-tube device occurred at a faster rate for a turbulent flow than for a laminar flow. The deposition thickness decreased along the tubes for both flow regimes. More soot deposited in the center tube of the three-tube bundle for the expansion angle 45° inlet header suggesting there was an uneven distribution of the exhaust gas flow in the tube bundle. For the device with the expansion angle 60° inlet header the soot was approximately more evenly distributed along the tubes.

The effect of molecular ions on the plasma parameters in a medium pressure rare gas radio frequency discharge positive column

A rare gas positive column plasma theory that takes into account the effect of various chemical processes on the production, loss, and interconversion of metastable and ion species is developed and compared with experimental results. The experimental measurements have been made in a 4 cm i.d. radio frequency (rf) discharge tube for He, Ne, and Ar. An electrostatic triple probe was used to monitor the electron temperature and plasma density, and a mass spectrometer was used to analyze the ion species. The results show that the molecular ion becomes important when gas pressure is above 1 Torr in the Ar and Ne plasmas. For a He plasma, the molecular ion always plays an important role in the plasma process. Good agreement has been observed between present model and experiments.

Mechanisms of electrohydrodynamic flow boiling heat transfer in coaxial flow channels of dielectric refrigerant R-134a

Experimental and numerical investigations have been conducted to study the mechanisms involved in dielectric refrigerant R-134a electrohydrodynamic (EHD) flow boiling in a concentric horizontal flow channel. Numerical calculations of the electric field distribution in two-phase flow with different gas-liquid distributions and interfacial geometries in a concentric electrode arrangement are conducted by a finite element method. The experiments conducted are performed at inlet qualities from 0 to 20%, mass fluxes from 100 to 500 kg/m/sup 2/s, heat flux from 10 kW/m/sup 2/ to 20 kW/m/sup 2/ and applied voltage from 0 to 10 kV. It was found that the application of an electrohydrodynamic body force to an R-134a evaporator can result in a significant augmentation of heat transfer that may be partially explained by the numerically simulated electric field profiles near gas-liquid interfaces.

Dissociative recombination of Ne2+ at elevated electron and gas temperatures

The rate coefficients for the dissociative recombination of Ne2+ at elevated electron, Te, and gas, Tg, temperatures have been measured using a shock-heated pulsed-flow-RF-discharge-pulsed afterglow with an external microwave beam for electron heating. The result shows that the temperature dependence of the recombination coefficient of Ne2+ is approximately T-3/2 when Tg=Te, and Te-(0.6-1.0) for elevated gas temperature. These results confirm the theoretical prediction of Cunningham et al (1981) for noble-gas diatomic molecular ions.

Electrohydrodynamically enhanced flow boiling in an eccentric horizontal cylindrical channel

Experimental and numerical investigations have been conducted to study the effect of electrode position in a 10.92 cm i.d. cylindrical flow channel on the electrohydrodynamically (EHD) enhanced flow boiling. The experiments were conducted for tube-side boiling of HFC-134a at dc voltage from 0 to 8 kV, liquid mass flux from 0 to 500 kg/m2s, inlet quality from 0 to 50%, and 3 vertical electrode positions within the tube (0 mm and 2.73 mm from centreline). Numerical simulation of electrical field profiles was conducted by finite element methods for various flow regimes. The results show that the heat transfer was enhanced up to 160% by EHD forces while only 20% pressure drop increase was observed. The results also show that the EHD heat transfer enhancement increases with increasing applied voltage and decreases with increasing mass flux. The effects of electrode vertical position on the EHD heat transfer enhancement will be discussed in detail based on numerical results.

Numerical and experimental simulations of diffusion charging of non-spherical aerosol particles by dense bipolar ions

Abstract Numerical and experimental simulations have been conducted for the time history of the diffusion charging process on the surface of aerosol particles by dense bipolar ions under continuum conditions. The range of conditions treated in the numerical simulations include positive-negative ion diffusion coefficient ratio from 0 to 1, aerosol particle radius from 0.1 to 10 μm, Debye ratio R p/ λ D from 0 to 1 (equivalent to maximum charge density up to N 1 = 10 12 cm −3 for an ion temperature of 300 K), the major-to minor axis ratios of prolate spheroids, L, from 1 to 100. The experimental simulation was conducted by using a conductive dummy particle suspended by a thin shielded wire, and the charged particle deposition current flux was measured and the bipolar environments. Then the effect of particle surface charges was simulated by imposing an electric potential on the dummy particles. The results show that, (1) for small ion density ( R p/ λD ⩽ 10 −2 ); the present results are in good agreement with model of Chang et al. (1978, 1983). (2) the aeroso particle charging speed and charging limit increase with increasing Debye ratio; (3) for larger Debye ratio, bipolar charging is faster than unipolar charging; (4) the effect of particle shape L is observed to be significantly influenced by Debye ratios: (5) the charging limit of the aerosol particle increases with L.

Experimental simulation of field charging of ultrafine nonspherical particles

Abstract The experimental simulations have been conducted for field charging of ultrafine nonspherical particles under external electric field conditions. The results show that the effect of external electric field decreases with increasing major-to-minor axis length ratio of spheroids.