Multi-junction thermocouple array for in-situ temperature monitoring of SOFC: simulation

Novel multi-junction thermocouple architecture was developed and simulated to in-situ monitor the temperature distribution over a Solid Oxide Fuel Cell (SOFC). This thermocouple architecture requires only {N+1} number of wires for N number of independent temperature measuring points. Therefore, N+1 architecture can independently measure temperature at multiple points simultaneously with much less number of wires than a set of thermocouples require for the same number of independent temperature measurements. Requiring less number of external wires is a distinct advantage, particularly, in constrained environments such as those within SOFC stacks. A thermocouple array having 4 independent temperature measuring points with 5 thermo-elements was simulated in MATLAB. Alumel (Ni:Al:Mn:Si – 95:2:2:1 wt) and Chromel (Ni:Cr – 90:10 wt) were chosen as thermo-element materials because of their wide applicability in the industry as K-type thermocouples. The junctions were considered to be spot welded. Three sets of simulations were performed to investigate two aspects: validation of the multi-junction thermocouple concept and investigation of the effect of the heat affected zone created in spot welding to the temperature measurement. Simulation code generates random temperature values for each junction within a pre-defined range. Temperatures at the boundaries of heat affected zones were also generated randomly according to a pre-defined criterion. The change of Seebeck coefficients within the heat affected zone was set as a percentage change of their corresponding materials Seebeck coefficient. The temperature gradient induced emf values for each sensing point were calculated from Seebeck coefficients. The calculated emf was then mapped back to temperature using ASTM approved inverse conversion function. These mapped temperatures were then compared with the set temperatures for each junction and they were in very good agreement.