Heat transfer reduction between two finite concentric cylinders using radiation shields; Experimental and numerical studies

Energy consumption and its efficient utilization are two important factors of thermal systems. This work concerns with numerical and experimental studies about the surface radiation and natural convection effects on the heat transfer and flow field between two finite concentric cylinders, using one radiation shield between them. This study reveals material and geometric effects of the radiation shield on heat losses from two concentric cylinders enclosure at different temperatures and enclosure pressures. The enclosure consists of two concentric cylinders with hotter inner cylinder and colder outer one. The radiation shield with three different materials (aluminum, copper and steel) is inserted between the cylinders at two different radial positions. Validations are carried out for the temperature of the radiation shield with experimental data and numerical ones. After validation, forty eight different experiments and numerical simulations are carried out by varying the inner cylinder temperature between 373 K and 673 K at two enclosure pressures of 0.2 and 1.0 atm, corresponding to three different materials as radiation shields. The outer cylinder temperature from experiments is used in numerical simulations. The results show that the enclosure pressure and radiation shield emissivity together are responsible for reduction in the total heat loss from the inner cylinder. It was also found that among the three considered materials as radiation shields, copper is the most effective one to reduce the heat loss. In a specific case, the total heat loss with copper radiation shield was 14.99% and 57.7% lower than steel and aluminum shields, respectively.