Multispecies Bhatnagar-Gross-Krook models and the Onsager reciprocal relations

It is shown that most of the existing versions of the Bhatnagar$-$Gross$-$Krook model $-$ those whose coefficient are independent of the molecular velocity $-$ do not satisfy the Onsager relations. This circumstance poses a problem when calibrating these models, making their transport properties match those of a specific fluid.