Performance Bounds of Nanoparticles Laden Volumetric Absorption Solar Thermal Platforms in Laminar Flow Regime

TL;DR

This paper develops a comprehensive theoretical framework to evaluate the performance of nanoparticle-laden volumetric absorption solar thermal systems, revealing their potential for higher efficiency in laminar flow regimes at high solar concentrations.

Contribution

It introduces a robust mechanistic model for coupled heat transfer in volumetric absorption systems and compares their performance with surface absorption systems under various conditions.

Findings

Volumetric absorption systems can achieve 35-49% higher efficiency at high solar concentration ratios.

The framework accounts for a wide range of operating parameters and receiver configurations.

Optimal performance domains are identified for laminar flow regimes with specific Reynolds numbers.

Abstract

Recent success in synthesizing thermally stable nanofluids at low costs is a significant breakthrough in the evolution of volumetric absorption based solar thermal systems. However, we have yet not been able to clearly identify the range of operating and design parameters in which volumetric absorption could prove to be beneficial. One of the key reasons being that we have not been able to fully understand the heat transfer mechanisms involved in these novel systems. The present work takes a few steps further in this direction wherein we have developed a comprehensive and mechanistic theoretical framework which is robust enough to account for coupled transport phenomena and orders of magnitudes of operating parameters for host of receiver design configurations. Moreover, we have also modeled equivalent surface absorption based systems to provide a comparison between volumetric and surface absorption processes under similar operating conditions. Performance characteristics reveal that particularly at high solar concentration ratios, volumetric absorption-based receivers could have 35% - 49% higher thermal efficiencies compared to their surface absorption-based counterparts. Finally, the present work serves to define optimal performance domains of these solar thermal systems, particularly in the laminar flow regime (200 < Re < 1600) and over a wide range of solar concentration ratios (5-100) and inlet fluid temperatures (293-593K).