A computational study on air-entrainment and pressure distribution for natural convection cooling of a hybrid IRS device

The infrared suppression (IRS) device is an essential component of a naval warship, which passively cools the hot flue gas issuing out of the engine exhaust so as to suppress the infrared emissions. In this work, the natural convection cooling of the hot funnels of a hybrid-type IRS device has been numerically investigated in a finite volume framework by varying the diameter ratio (DR) and the Rayleigh number (Ra) in the range of 1.025 <= DR <= 1.5, and 1010 <= Ra <= 1012, respectively. It is observed that the Nusselt number as well the air entrainment ratio augments with the Rayleigh number. However, we noticed an initial increment in the Nusselt number with DR, and thereafter decreases marginally with a further increase in diameter ratio after attaining a peak. An optimum diameter ratio (DR = 1.1) has been obtained for the maximum heat transfer from the funnel walls. At the entry of the base and third funnel, intense suction pressure is induced, whereas the pressure recovers throughout the remaining portions of the IRS device. The influence of air entrainment on the flow and heat transfer phenomenon has been explained by delineating temperature contours, velocity vectors, and streamlines for different repre-sentative cases of the computational study. In addition, we nonlinearly regressed the computational data to propose an empirical correlation for the average Nusselt number. Furthermore, the estimation of cooling time has been done through lumped capacitance model.