Study of thermal effects on the performance of micro-tubular solid-oxide fuel cells

Abstract

Mathematical modeling of methane-fed anodesupported micro-tubular solid-oxide fuel cell (MT-SOFC) is developed. Steam reforming of methane is considered in two cases of: direct internal reforming (DIR) and gradual internal reforming (GIR). The polarization curves and temperature distribution of a cell fed with three variations of fueling (i.e., DIR and GIR of methane and pure hydrogen) are compared with each other. The simulation results are verified through temperature and performance measurements of a MT-SOFC sample operating on above three variations of fueling. In DIR operating condition, a drop in the anode gas temperature at a short distance after entering the cell takes place which results in high temperature gradient. In GIR operating condition, the temperature distribution in axial direction is steadier. The ohmic loss is lower in the case of pure hydrogen fuel than internal reforming of methane, but the concentration loss is lower in methane-fed operating conditions. Nomenclature A E v Reactive surface area per unit volume of electrode (m 2 m −3 ) c i Concentration of species: i (mol m −3 ) c O 2 Oxygen concentration (mol m −3 ) c H 2 Hydrogen concentration (mol m −3 ) c O 2 ;ref Oxygen reference concentration (mol m −3 ) c H 2 ;ref Hydrogen reference concentration (mol m −3 ) c p Total heat capacity (J kg −1 K −1 ) D eff Effective diffusion coefficient (m 2 s −1 ) E E Apparent activation energy for the electrode reaction (J mol −1 ) F Faraday's constant (96,487 Cmol −1 ) F amb Ambient view factor in radiative heat transfer G m Mutual irradiation arriving from other surfaces in the modeled geometry (W m −2 ) h i Enthalpy of species: i (J mol −1 ) I Cell average current density (A) I Unit 3×3 matrix J E i Electrode normal ionic current flow (A m −2 ) J E e Electrode normal electronic current flow (A m −2 ) J E 0 Electrode reference exchange current density (A m −2 ) J E 0;ref Reference temperature current density (A m −2 ) N D i Species diffusion vector (mol m −2 s −1 ) n CH 4 Molar flow rate of the input fuel (mol s −1 ) n air Molar flow rate of the input air (mol s −1 ) n species Normal flux of species (mol m −2 s −1 ) P Pressure (Pa) P species Partial pressure of species (Pa) Q Volumetric heat generation rate (J m −3 ) q Surface heat transfer (J m −3 ) R Universal gas constant (8.3143 Jmol −1 K −1 ) t E rl

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Design of industrially scalable microtubular solid oxide fuel cells based on an extruded support

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