Quantifying the effects of spectral and directional distribution of radiation on its propagation in saline water

Abstract

The interactions of radiation with saline water facilitate various energy-related applications, such as radiative evaporation at the air–water interface, radiation-driven underwater vapor generation, and underwater photovoltaic systems. However, these applications require a comprehensive understanding of radiation propagation through saline water, considering both its spectral and directional characteristics, which are often inadequately explored. This study introduces a three-dimensional Monte Carlo radiative transfer model equipped with fine spectral resolution and detailed angular considerations. The model simulates the transfer of radiation from the air to the air–water interface and throughout the saline water body to thoroughly examine the effects of spectral and directional properties of incident radiation on its propagation across different depths of saline water. The findings reveal that within the solar spectrum, radiation entering the water at a 62.7-degree angle of incidence and completely diffuse radiation exhibit similar absorption effects in water layers less than 2 meters deep. In addition, the incident angle has little impact on the absorption rate of both the water surface and the water body when the angle is below 62.7◦. Spectrally, radiation wavelengths longer than 1.4 μm, 1.14 μm, and 1 μm are fully absorbed within the first 1, 8, and 50 centimeters of saline water, respectively, representing approximately 20%, 30%, and 50% of incident solar radiation. Additionally, radiation from blackbody sources below 1300 Kelvin is absorbed entirely within the top 1 centimeter of saline water. Empirical correlations are then developed to easily estimate the absorption rate based on the depth of the water and the temperature of the blackbody heat source. The findings elucidate the influence of the spectral and directional characteristics of incident radiation on its underwater propagation, offering essential guidance for the design and performance evaluation of various energy-centric applications.