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Direct simulation of a volumetric solar receiver with different cell sizes at high outlet temperatures (1,000–1,500 °C)

Nakakura, Mitsuho, Matsubara, Koji, Bellan, Selvan, Kodama, Tatsuya
Renewable energy 2020 v.146 pp. 1143-1152
air, convection, irradiation, mass transfer, mathematical models, renewable energy sources, solar collectors, temperature
This paper describes and presents the direct numerical simulation of a volumetric solar receiver under concentrated irradiation. The simulations systematically analyze the receiver performance and thermal loss mechanisms for operating conditions when outlet temperatures are in the 1000–1500 °C range. The implemented numerical method fully considers interactions between radiation, convection, and conduction using a discrete ordinates approach as a radiation model. The power over air mass (POM) and air mass flux were modified for six receiver channels with different cell sizes. The receiver efficiency decreased when the air mass flux increased beyond a certain criterion for constant POM. For a 3.8 mm cell, the receiver efficiency decreased to <0.4 when the air mass flux was greater than a critical value. However, the efficiency was improved to 0.7 by reducing the cell size from 3.8 mm to 0.475 mm. The outlet temperature of the smallest cell exceeded 1500 °C. The improvement in the efficiency is discussed considering the temperature distribution and loss analysis. It is found that a smaller cell size led to reduced wall temperature at the channel inlet and attenuated the re-radiation loss.