Last decade has seen tremendous progress in the development of nanoparticle dispersion based volumetrically absorbing solar thermal systems. However, for these systems to compete with their surface absorption counterparts, it is imperative to reach an optimum receiver design. Optimization in turn necessitates accurate modeling of highly coupled transport phenomena involved in these systems. The present work represents a significant step ahead in this direction, wherein, a comprehensive and mechanistic theoretical framework is developed which is robust enough to account for coupled transport phenomena and orders of magnitude of operating parameters for a host of receiver design configurations. Moreover, equivalent surface absorption based systems are also modeled to provide a comparison between volumetric and surface absorption processes under similar operating conditions. Finally, the present work serves to define optimal performance domains of these solar thermal systems, particularly in the laminar flow regime (100 < Re < 1600) and over a wide range of solar concentration ratios (5-100) and inlet fluid temperatures (293 K-593 K). Performance characteristics reveal that particularly at high solar concentration ratios, volumetric absorption-based receivers could have 45%-51% higher thermal efficiencies compared to their surface absorption-based counterparts. Further, this could translate into a significant increase (by 15%-18%) in overall energy conversion efficiency of concentrated solar power plants.