A three-dimensional simulation of an actual 1-kW, 30-cell hydrogen-fueled planar solid oxide fuel cell (SOFC) stack established the steady internal temperature field and its dominant heat-transfer pathways (inlet-manifold gas heating, through-stack gaseous advection, and interconnect conduction) under wet hydrogen at a single operating point. The open problem is to complete this picture into a thermal-management design basis for the same full-scale stack: how the temperature field and pathway hierarchy respond to realistic hydrocarbon (reforming) fueling with its associated reaction heat; how they evolve under load changes, start-up and shut-down transients, and long-term degradation; and which concrete stack design changes acting on the identified levers suppress the thermal stress that drives cracking of unit cells and sealants. Later work by the original group and others has partially advanced the design-lever and hydrocarbon threads at commercial scale, but no published record establishes the transient or degradation-coupled thermal response of this stack or the integrated, stress-quantified design assessment, so the question remains open.

Background

A solid oxide fuel cell (SOFC) is a high-temperature electrochemical device (typically 650-800 degrees Celsius) that converts fuel directly into electricity. Planar SOFC stacks are assembled from tens of thin ceramic repeating units (anode, electrolyte, cathode, plus gas channels) connected in series by metallic interconnect plates, with fuel and air distributed to every layer through internal manifolds, the ducts that carry the gases into and out of the stack. Because the stack operates hot, uneven heat release and heat removal create steep temperature gradients; these gradients impose thermal stress on the ceramic cells and glass-ceramic sealants and are a principal driver of cracking, delamination, and limited lifetime. Thermal management, meaning control over where and how fast heat is removed, is therefore a central constraint on commercial SOFC deployment.

Experimental access to internal temperatures is impossible in a hermetically sealed operating stack, and most simulations before 2020 relied on short stacks or simplified geometries. Kim et al. (2020) closed part of this gap with a three-dimensional computational fluid dynamics (CFD, i.e. numerical solution of the coupled flow and heat-transfer equations) simulation resolving the actual geometry and operating conditions of a commercial 1-kW, 30-cell, cross-flow planar stack (cross-flow meaning the fuel and air streams enter the cell plane at right angles to one another) fueled with humidified (wet) hydrogen. Under the single steady operating condition studied, the stack temperature follows the air flow; the largest temperature gradients fall on the unit cells and sealants near the air inlet, especially in the lower repeating units; and in the stack-height direction the dominant cooling route is advection, heat carried away by the flowing gases, with conduction through the metallic interconnects compensating where advective cooling weakens. The authors inferred that manipulating three levers (heating of the incoming gases near the inlet manifold, advection through the stack, and metallic conduction between repeating units) could redirect the heat-transfer pathways and the internal thermal state.

Three issues fall outside the scope of that analysis and remain unresolved in the published record. First, the model assumes wet hydrogen, so the influence of direct hydrocarbon fueling, including internal steam reforming (the strongly endothermic conversion of hydrocarbon fuel to hydrogen and carbon monoxide over the anode, which acts as a distributed heat sink) and its associated reaction heat on the same full-scale geometry, is unexamined. Second, only one steady operating point is analyzed, leaving the thermal response to load changes, start-up and shut-down transients, and the long-term, degradation-coupled evolution of the temperature field open. Third, the specific design changes needed to control the identified pathways, and the extent to which they suppress thermal stress and improve durability, are undetermined.

Problem Statement

Extend the established steady-state, wet-hydrogen thermal analysis of the actual 1-kW, 30-cell planar SOFC stack into a complete thermal-management design basis. The common objective is to determine how the stack's internal temperature field and its identified heat-transfer pathways (inlet-manifold gas heating, through-stack gaseous advection, interconnect conduction) respond when the assumptions of the original analysis are removed, and which concrete stack design changes suppress the resulting thermal stress. Three interrelated results on the same full-scale stack geometry, all of which are required for the task to count as resolved and each of which is bounded to the minimum coverage stated with it; broader parametric sweeps, additional operating profiles, longer horizons, and their uncertainty refinements are extensions that strengthen the answer without being required:

  1. Hydrocarbon fueling: quantify how direct hydrocarbon operation, with its internal reforming and associated reaction heat, reshapes the steady temperature field and the advective/conductive pathway hierarchy established for wet hydrogen; the required minimum is one steady hydrocarbon operating condition.

  2. Dynamic operation: determine the transient evolution of the temperature field under load changes and start-up and shut-down, and the long-term, degradation-coupled evolution of the thermal field during sustained operation; all four behaviors named here (load change, start-up, shut-down, and long-term degradation-coupled evolution) are required, each by at least one representative case (one load-change transient, one start-up, one shut-down, and one degradation horizon).

  3. Design control: identify specific design changes acting on the three levers (for example manifold and interconnect configuration) and quantify the extent to which they suppress temperature gradients and thermal stress in the vulnerable regions (unit cells and sealants near the air inlet, lower repeating units); for at least one concrete design change the quantification must state the thermal-stress metric used, the baseline condition it is compared against, the quantitative reduction achieved, and the uncertainty in that reduction, and must state explicitly the implications for durability and their uncertainty.

These three results share one geometry, one validated model lineage, and one stress-and-durability objective; together they convert the static thermal diagnosis of the source work into an actionable design basis for the actual device.

References

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