Effective use of thermal energy is the key for the energy-efficient processing of materials. A proper understanding of heat flow would be very useful in designing the systems of high energy efficiency with a minimal waste of precious energy resources. In the current study, a distributed heating methodology is proposed for the efficient thermal processing of materials. A detailed investigation on the processing of various fluids of industrial importance (with a Prandtl number of Pr=0.015, 0.7, 10, and 1000) in differentially and discretely heated porous square cavities is presented. Analysis of laminar convective heat flow within a range of Darcy number, Da = 10(-6)-10(-3) and Rayleigh number, Ra = 10(3)-10(6) has been carried out, based on a heatline visualization approach. The effect of Da and the role of distributed heating in enhancing the convection in the cavities is illustrated via heatline distributions, which represent the paths of the heat flow, the magnitude of heat flow, and zones of high heat transfer. It is observed that distributed heating plays an important role in enhancement of thermal mixing and temperature uniformity. Furthermore, the effect of Da for various Pr values on the variation of local Nusselt number (Nu) is analyzed, based on heatline distributions.