Twisted symmetry in multiple impingement jets at low Reynolds number

In this study, the cooling effect of nine confined jets arranged in square in-line array is investigated experimentally. The individual jet diameter is 3 mm, the jet-to-jet spacing ratio is two times as much as the jet diameter and the jet-to-plate spacing varies from 1 to 4 times as much as the jet diameter. The jet Reynolds number varies up to 880. An infrared camera is used for quantitative temperature measurement on the rear face of the impingement plate and a PIV system is installed to obtain the velocity field on different planes. The results show a twisted symmetry pattern of the flow field and heat transfer on the impingement plate when the confined ratio equals to jet-to-jet spacing ratio. This condition is produced only for the square in line array configuration and is due to the different interactions of central jet with lateral and corner jets.