Experimental investigation on the effect of natural gas composition on performance of autothermal reforming

This paper presents experimental study on catalytic autothermal reforming (ATR) of natural gas (NG) for hydrogen (_H2${\mathrm{H}}_2$) production over sulfide nickel catalyst supported on gamma alumina. The experiments are conducted on a cylindrical reactor of 30 mm in diameter and 200 mm in length with “simulated” NG of different composition under thermal-neutral conditions and fed with different molar air to fuel ratio (A/F$A/F$) and molar water to fuel ratio (W/F)$(W/F)$. The results showed that reforming performance is significantly dependent on A/F$A/F$, W/F$W/F$ and concentration of _C2+${\mathrm{C}}_{2+}$ hydrocarbons in inlet fuel. Fuels containing higher _C2+${\mathrm{C}}_{2+}$ hydrocarbons concentration have optimum performance in terms of more _H2${\mathrm{H}}_2$ at higher A/F$A/F$ and W/F$W/F$ but lower conversion efficiency. Good performance for ATR of fuel containing 15%–20% _C2H6${\mathrm{C}}_2{\mathrm{H}}_6$ can be achieved at A/F=5–7$A/F=5–7$ and W/F=4–6$W/F=4–6$, much higher than that for optimum performance of ATR of methane (A/F=3,W/F=2–2.5$A/F=3,W/F=2–2.5$). _CO2${\mathrm{CO}}_2$ in the inlet fuel does not have significant effect on the reversed water–gas shift reaction. Its effect on reforming performance is mainly due to the dilution of inlet fuel and products.     

Effect of the equivalence ratio,Damköhler number,Lewis number and heat release on the stability of laminar premixed flames in microchannels

The effect of the equivalence ratio on the stability and dynamics of a premixed flame in a planar micro-channel with a step-wise wall temperature profile is numerically investigated using the thermo-diffusive approximation. To characterize the stability behavior of the flame, we construct the stability maps delineating the regions with different flame dynamics in the inlet mass flow rate m   vs. the equivalence ratio ?$?$ parametric space. The flame stability is analyzed for fuels with different diffusivity by changing the Lewis numbers in the range 0.3?_LeF?1.4$0.3?{\mathit{Le}}_F?1.4$. On the other hand, the Lewis number of the oxidizer is kept constant and equal to unity _LeO=1${\mathit{Le}}_O=1$. Our results show that, for very diffusive fuels, the stability of the flame varies significantly with the equivalence ratio, transitioning from stable flames for lean mixtures to highly unstable flames when ?>1$?>1$. As the fuel Lewis number approaches unity, the stability behavior of the flame for lean and rich mixtures becomes more similar to give, in the equidiffusional case _LeF=1${\mathit{Le}}_F=1$, a symmetric stability map around the stoichiometric mixture ?=1$?=1$. In all cases considered, the most stable flames are always found around the stoichiometric mixtures ?=1$?=1$, when the flame instabilities are completely suppressed for very diffusive fuels _LeF<1${\mathit{Le}}_F<1$, or are reduced to a narrow range of inflow velocities for fuel Lewis numbers equal or greater than unity.     

Second law analysis of forced convection in a circular duct for non-Newtonian fluids

The second law characteristics of fluid flow and heat transfer inside a circular duct under fully developed forced convection for non-Newtonian fluids are presented. Heat flux is kept constant at the duct wall. Analytical expressions for dimensionless entropy generation number (_NS$N_{\mathrm{S}}$), irreversibility distribution ratio (Φ  ), and Bejan number (Be$\mathit{Be}$) are obtained as functions of dimensionless radius (R$R$), Peclet number (Pe$\mathit{Pe}$), modified Eckert number (Ec$\mathit{Ec}$), Prandtl number (Pr), dimensionless temperature difference (Ω  ), and fluid index (m$m$ or n$n$). Spatial distributions of local and average entropy generation number, irreversibility ratio, and Bejan number are presented graphically. For a particular value of fluid index, n=1$n=1$ (or m=2$m=2$), the general entropy generation number expression for a non-Newtonian power-law fluid reduces to the expression for Newtonian fluid as expected. Furthermore, entropy generation minimization is applied to calculate an optimum fluid index (_nEGM$n_{\mathrm{EGM}}$). A correlation is proposed that calculates _nEGM$n_{\mathrm{EGM}}$as a function of group parameter (Ec×Pr/Ω$\mathit{Ec}\times \mathit{Pr}/\Omega$) and Peclet number (Pe$\mathit{Pe}$) within ±5% accuracy. Finally, for some selected fluid indices, the governing equations are solved numerically in order to obtain Nusselt number. It is observed that the numerically obtained asymptotic Nusselt number shows excellent agreement with the analytically obtained Nusselt number.