A solid oxide fuel cell (SOFC) needs to be heated to a high temperature to be able to start generating electricity. This study aims to manage the heat-up process of a SOFC by considering the three objectives of time duration, energy consumption, and temperature gradient, simultaneously. Mass flow rate (MFR) and rate of temperature rise (RTR) of the hot air, passing through the cathode channel of the SOFC, are considered as decision variables. The transient heatup process is numerically simulated for six different MFR values (5-50 mg s À1 ) and six different RTR values (0.1-5 K s À1 ). The results indicate that higher RTR leads to lower heat-up duration, lower energy consumption, but higher temperature gradient. Also, higher MFR results in lower heat-up duration, lower temperature gradient, but higher energy consumption. The results also reveal that hot air recycling increases thermal efficiency from below 40% to nearly 100%. Finally, when hot air recycling is employed and all the objectives are considered simultaneously, the heat-up plan with a RTR of 0.5 K s À1 and a MFR of 50 mg s À1 is selected as the best choice by using linear programming technique for multidimensional analysis of preference.
A solid oxide fuel cell (SOFC) needs to be heated to an appropriate temperature (around 600°C) before it is switched to start‐up mode. A fast heat‐up process, which is naturally of interest, can cause high temperature gradients inside the SOFC and the subsequent problems of cracking and delamination. Therefore, in order for the heat‐up process to be efficiently managed, the opposing objectives (heat‐up duration and temperature gradient) have to be considered simultaneously. The present study investigates the influences of the type of temperature rise function and the average rate of temperature rise (ARTR) on each objective (heat‐up duration and temperature gradient). Beside the simple linear temperature rise function of heating fluid considered in previous studies, some innovative nonlinear functions are also introduced and examined in the present study. The results indicate that the rotated‐exponential temperature function with an ARTR of 5 K s−1 and the linear temperature function with an ARTR of 0.1 K s−1 are the best choices in terms of heat‐up duration and temperature gradient, respectively. This study also attempts to make a compromise between the two objectives and introduces the rotated‐quadratic temperature function with an ARTR of 0.4 K s−1 as a representative trade‐off solution.
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