Syngas production from methane dry reforming over Ni/SBA-15 catalyst: Effect of operating parameters

The influence of operating conditions including reactant partial pressure and reaction temperature on the catalytic performance of 10%Ni/SBA-15 catalyst for methane dry reforming (MDR) reaction has been investigated in this study. MDR reaction was carried out under atmospheric pressure at varying CH₄/CO₂ volume ratios of 3:1 to 1:3 and 923–1023 K in a tubular fixed-bed reactor. SBA-15 supported Ni catalyst exhibited high specific surface area of 444.96 m² g^?1 and NiO phase with average crystallite size of 27 nm was detected on catalyst surface by X-ray diffraction and Raman measurements. H₂ temperature-programmed reaction shows that NiO particles were reduced to metallic Ni⁰ phase with degree of reduction of about 90.1% and the reduction temperature depended on the extent of metal-support interaction and confinement effect of mesoporous silica support. Catalytic activity appeared to be stable for 4 h on-stream at 973–1023 K whilst a slight drop in activity was observed at 923 K probably due to deposited carbon formed by thermodynamically favored CH₄ decomposition reaction. Both CH₄ and CO₂ conversions increased with rising reaction temperature and reaching about 91% and 94%, respectively at 1023 K with CO₂ and CH₄ partial pressure of 20 kPa. CH₄ conversion improved with increasing CO₂ partial pressure, ${\mathit{P}}_{\mathit{C}{\mathit{O}}_{\mathit{2}}}$ and exhibited an optimum at ${\mathit{P}}_{\mathit{C}{\mathit{O}}_{\mathit{2}}}$ of 30–50 kPa depending on reaction temperature whilst a substantial decline in CO₂ conversion was observed with growing ${\mathit{P}}_{\mathit{C}{\mathit{O}}_{\mathit{2}}}$. Additionally, CH₄ and CO₂ conversions decreased significantly with rising CH₄ partial pressure because of increasing carbon formation rate via CH₄ cracking in CH₄-rich feed. Post-reaction characterization shows that active Ni metal phase was not re-oxidized to inactive metal oxide during MDR reaction. The heterogeneous nature of deposited carbons including carbon nanofilament and graphite was detected on catalyst surface by Raman measurement.     

Drag force acting on bubbles in a subchannel of triangular array of rods

Forces acting on spherical bubbles in a subchannel of a rod bundle with triangular rod arrangement (the pitch to diameter ratio is $P/D=1.34$) have been studied at low bubble Reynolds numbers O(0.1) ? O(1). The bubble motion has been simulated resolving the interface of the bubble by using the lattice Boltzmann method. Steady drag and virtual mass forces have been determined from the simulation results. Based on the simulation data, the relation $C_D=16.375/{\mathit{Re}}_T$ could be established between the steady drag coefficient $C_D$ and the terminal Reynolds number ${\mathit{Re}}_T$ when the diameter ratio $\lambda =d/D$ of the bubble d and the channel D is less than 0.2. It is found that the virtual mass coefficient can achieve as high value as 7.2, which is a consequence of strong wall effects. Considering interactions between bubbles, cooperation in the axial direction and hindering in the lateral direction could be observed. We demonstrate that the relation between the terminal velocity of a bubble and that of the suspension follows a Richardson–Zaki like correlation, but the exponent is not only a function of the Eotvos and Morton numbers, but it also depends on the particle configuration.     

Experimental and kinetic study on ignition delay times of lean n-butane/hydrogen/argon mixtures at elevated pressures

Measurements on ignition delay times of n-butane/hydrogen/oxygen mixtures diluted by argon were conducted using the shock tube at pressures of 2, 10 and 20 atm, temperatures from 1000 to 1600 K and hydrogen fractions (${\mathrm{X}}_{{\mathrm{H}}_2}$) from 0 to 98%. It is found that hydrogen addition has a non-linear promoting effect on ignition delay of n-butane. Results also show that for ${\mathrm{X}}_{{\mathrm{H}}_2}$ less than 95%, ignition delay time shows an Arrhenius type dependence and the increase of pressure and temperature lead to shorter ignition delay times. However, for ${\mathrm{X}}_{{\mathrm{H}}_2}$ = 98% and 100% mixtures, non-monotonic pressure dependence of ignition delay time were observed. The performances of the Aramco2.0 model, San Diego 2016 model and USC2.0 model were evaluated against the experimental data. Only the Aramco2.0 model gives a reasonable agreement with all the measurements, which was conducted in this study to interpret the effect of pressure and hydrogen addition on the ignition chemistry of n-butane.     

Influence of boundary conditions on the structure of laminar boundary layer with hydrogen combustion on a permeable surface

A numerical study was performed to examine how thermal and diffusion boundary conditions affect the structure of laminar diffusion flame in air flow with porous blowing and combustion of hydrogen. Boundary conditions of two types were compared, with lengthwise-constant porous-wall temperature ($T_W=\mathit{const}$ throughout the whole range of blowing ratios), and with lengthwise-constant temperature of the fuel supplied into the main flow ($T^{\prime }=\mathit{const}$). With a liquid fuel having constant evaporating-surface temperature, we deal with boundary conditions of the first type. With a gas fuel, as a rule, we encounter the regime with $T^{\prime }=\mathit{const}$. It is shown that, in spite of the significant difference in velocity and temperature profiles, in both cases the surface friction coefficients have close values. Also, it is found that the wall heat flux exhibits a maximum if considered as a function of fuel supply intensity. Nonetheless, the function of relative heat transfer monotonically decreases with blowing intensity, much like it does in non-reactive flow.     

Heat transfer of a radially rotating furrowed channel with two opposite skewed sinusoidal wavy walls

An experimental study of heat transfer in a radially rotating furrowed channel with two opposite walls enhanced by skewed sinusoidal waves was performed to generate the full-field Nusselt number (Nu) data over two wavy walls. Although the static wavy channel has been proven as an effective heat transfer enhancement (HTE) measure, no previous study examined its heat transfer performances with rotation. As another first-time attempt for turbine cooling researches, the Nu scans over the entire rotational leading (stable) and trailing (unstable) walls were acquired using the infra-red thermography which proved highly advantageous due to its capability to examine the rotating buoyancy effects in details. A selection of experimental data illustrates the full-field Nu variations responding to the changes of Reynolds (Re), rotation (Ro) and buoyancy (Bu) numbers. Parametric analysis is subsequently followed to disclose the individual and interdependent Re, Ro and Bu effects on Nu in the attempt to derive the heat transfer correlations for the area-averaged Nu over the developed flow region $\left({\overline{Nu}}_{\text{FD}}\right)$ on the rotational leading and trailing wavy walls. Within the parametric ranges tested, the rotational leading and trailing ${\overline{Nu}}_{\text{FD}}$ values respectively fall between 3.4–4.3 and 4.2–6.4 times of the Dittus–Boelter datum, which grant the potential applicability of wavy channel as a HTE measure for cooling of gas turbine rotor blades.