Study on evaporation characteristics of water droplet array under heating of thermal irradiation: Monte Carlo method

• Published in: Applied thermal engineering 2025-03, Vol.262, Article 125247
• Main Authors: Zhang, Dan, Zhou, Wenbo, Liu, Shuoqiao, Zhao, Bingchao, Gao, Dan, Zhang, Liangye
• Format: Article
• Language: English
• Subjects: Absorptivity; Droplet array; Evaporation; Evaporation rate; Monte Carlo method; Thermal irradiation
• ISSN: 1359-4311
• DOI: 10.1016/j.applthermaleng.2024.125247

•Evaporation of water droplet array heated by thermal irradiation are studied.•Calculation model for absorption and evaporation is built by Monte Carlo method.•Evaporation in size control is ideal working state to evaporate water droplet array.•Reasonable irradiation waveband includes 1430–1466, 1877–2099, 2324–2500 nm.•Absorptivity reaches 70% by reducing droplet size or increasing volume fraction. Directly evaporating droplet array by thermal irradiation is the core process to integrate solar energy in desalination, energy storage, carbon capture and so on. On the basis of Monte Carlo method, a calculation model for this evaporation was built, verified by experiments, and then was used to investigate the evaporation characteristics and dependence on external irradiation, geometrical characteristics and radiative properties. All droplets were uniform randomly distributed in a 10 × 10 × 10 mm cubic domain with initial diameter of 0.5–1.5 mm, initial volume fraction of 0.01–0.15, absorption coefficient of 100–15000 m−1. The external irradiation was cylindrical in shape with diameter of 3–8 mm, power of 1–20 W. The droplet whose absorption was no less than 0.1 % of total absorption of the array was defined as primary irradiated droplet (PID). Their distribution represented the impact range of irradiation, and was found to be essentially coaxial with the irradiation beam. The mean evaporation rate (ER) and absorptivity were introduced to measure the speed and efficiency of evaporation respectively. The ER was the ratio of total evaporated mass to initial mass of PID. The absorptivity was the ratio of latent heat in generated vapor to the total irradiation energy. Both could be significantly improved by increasing initial volume fraction from 0.01 to 0.10. Based on whether the optical thickness was less or greater than 1, the evaporation could be classified as absorption control (AC) or size control (SC). Both ER and absorptivity could be improved only by increasing absorption coefficient in AC or reducing droplet size in SC. Due to higher performance, SC was the ideal working state to evaporate water droplet array with reasonable irradiation waveband of 1430–1466, 1877–2099 or 2324–2500 nm. According to above results, the empirical formulae for absorptivity and ER were proposed. They could be used to quickly estimate the evaporation performance of droplet array, and also provide a reference for future research on moving droplet array with multi-component.