Session: 05-04 Solar Receiver Design 2

Paper Number: 106936

106936 - Numerical Study of Solar Receiver Tube With Modified Surface Roughness for Enhanced and Selective Absorptivity in Concentrated Solar Power Tower 

Concentrated solar power (CSP) has become one of the most beneficial renewable energy sources on the market because of the scalability of its power production and ability to store excess thermal energy. Concentrated solar power towers (CSPT) are becoming more desirable because of their ability to reach higher temperatures which correlate with higher thermal efficiencies. Within CSPTs there are three different types of solar receivers: gas based, liquid based, and solid based. Depending on the operating temperatures, the tubes that flow heat transfer media (also called receiver tubes) usually will experience uneven external temperature distribution and significant heat loss due to radiative heat loss (i.e., reflective, and emissive heat loss).

There are several solar selective coatings which can achieve the goal of reducing radiative heat loss, however their performances deteriorate at high temperatures, particularly for CSPT above 600C. In this study, instead of looking for various selective coating materials, we propose to mitigate the heat loss by modifying the receiver tubes' surface roughness, therefore solar selective surfaces on the receiver tubes can be manufactured for the enhanced and selective solar optical properties, such as maximizing absorption from UV to near-infrared spectrum and minimizing emission in the infrared range. Light trapping is when the reflected and emitted radiation is absorbed by a neighboring surface to be reabsorbed on the surface. The more light trapping that occurs the more efficient the surface becomes. 3D printing parameters can be critiqued to optimize surface topography such as hatch distance and laser power. Also, the size of the powder chosen to be used can affect the surfaces (i.e., larger powder size leads to rougher surfaces).

In our previous efforts, additive manufacturing (AM) was adopted to 3D print advanced solar absorber tubes with internal fins, therefore the induced helical fluid flow inside the tube can lead to uniform external temperature distribution, thus significantly extend the life cycle of receiver tubes. In this study, we anticipate to utilize previously 3D printed samples to develop a data base of surface profiles for roughness, then numerical simulations will be conducted to simulate the solar absorptivity in the range from UV to near-infrared, it is expected that the simulation can provide guidance for the 3D printing parameters to build a surface to allow for more light trapping. We intend to use COMSOL Multiphysics to simulate the effect of light trapping by building a multiphysics model with surfaces that range in roughness height to prove that absorption can be enhanced. The simulation will have a wavelength range from 0.4μm to 3.5μm and assume an incident solar flux comparable to CSPT systems. The material chosen is Inconel 718 which has an absorptivity coefficient of 0.54. Preliminary simulation results show that rougher surfaces tend to have more absorption (i.e., greater than 0.54). We will modify the surface roughness profile from the scanned samples, and rerun the simulations with the same input solar flux conditions, to demonstrate the possible technical approach to enhance the selective solar absorption. Comparisons will be made between the original and modified surfaces, and we will also recommend methods and parameters of controlling the AM process. We expect this work to transform how solar absorber tubes are manufactured without using solar selective coating and supplement the 2030 SunShot initiative.

Presenting Author: Ben Xu Mississippi State University

Presenting Author Biography: Dr. Ben Xu is currently an Assistant Professor, Presidential Frontier Faculty Fellow at University of Houston. When this work was completed, Dr. Xu was an Assistant Professor at Mississippi State University.