Managing temperature uniformity of thermally integrated micro reformers with different axial dimensions: A detailed numerical study

摘要

The behavior of thermally integrated micro reactors is often discussed without considering their non-microscale dimension. However, gradients in the macro length scale may cause undesirable performance decay when scaling up micro reactors to the commercial scale. This paper presents an in-depth numerical study on multilevel operational and structural factors governing the axial temperature uniformity of micro methane reformers. Simulations using a multiscale reactor model show drastic hot spot formed inside micro reformers with a relatively large axial size at given space velocity; meanwhile, methane conversion and product selectivity remain invariant. To provide comprehensive guidelines for improving thermal uniformity, temperature distribution is correlated with axial heat transfer characteristics by utilizing appropriate dimensionless groups for different reactor operation, plate design and catalyst patterning. Increasing the combustion or reforming flowrate leads to intensified convective heat transfer by the gas; as a result, the normalized mean temperature deviation (NMTD) is found to decrease logarithmically with the reciprocal conduction parameter within the normal operation window. When changing the plate thickness, length and conductivity, NMTD is found to vary logarithmically with the Biot number. Furthermore, segmentation of the combustion catalyst allows tuning the combustion behavior without breaking the NMTD - Biot number correlation.