Discussion: “Analysis of Heat Transfer Regulation and Modification Employing Intermittently Emplaced Porous Cavities” (Vafai, K., and Huang, P. C., 1994, ASME J. Heat Transfer, 116, pp. 604–613) and “Analysis of Flow and Heat Transfer Over an External Boundary Covered With a Porous Substrate” (Huang, P. C., and Vafai, K., 1994, ASME J. Heat Transfer, 116, pp. 768–771)