Flow and Conjugate Heat Transfer Characteristics of Real-scale IRS (Infrared suppression) Device

Abstract

An infrared suppression (IRS) device has complicated thermo-fluid characteristics because they involve complex flow features. The entrainment of surrounding cold air and subsequent mixing with the hot turbine exhaust gas in cargo/naval ships occurs in the device. The thermo-fluid behavior of three types of IRS systems has been elucidated here. The shapes of the funnels used in the IRS system are conical, louvered cylindrical, and louvered conical. Numerical simulations are performed for the real-scale IRS unit by solving the equations of mass, momentum, energy, and radiation in the computational domain surrounding the IRS system. Three types of funnel shapes are considered for the present study: conical, louvered cylindrical, and louvered conical. The study elucidates the influence of the Reynolds number (6.1 × 105 to 3.18 × 106), nozzle overlapping (zero, negative, and positive), inclination angle, funnel-overlapping (zero, negative, and positive), and guide vanes on the air intake and system outlet temperature. It is found that the maximum air intake and minimum outlet temperature for the conical funnel can be achieved with five funnels. Therefore, the authors choose five funnels for analyzing louvered cylindrical and louvered conical funnel situations. The mass intake and device outlet temperature are also affected by funnel-overlapping and nozzle-overlapping. The maximum air intake and minimum outlet temperature are obtained by zero funnel-overlapping and zero nozzle-overlapping conditions. The mass intake increases when diathermic funnels are used in place of the adiabatic funnels with surface radiation for all situations. The impact of funnel wall inclination and the type of guide vanes are also discussed. Using nonlinear regression analysis of the data, empirical relationships for mass intake and outlet temperature ratio are established. Calculation of the lock-on range of the ship with or without the IRS device is also carried out for louvered cylindrical and louvered conical funnels. The present research also takes into account the entropy generation analysis of an infrared suppression (IRS) system. The effect of different boundary conditions for funnel walls (i.e., adiabatic, diathermic with or without radiation) on entropy generation is discussed. Furthermore, entropy generation due to heat transfer has a prominent contribution to total entropy generation. This entropy production study also helps us suggest a configuration of the IRS device with minimum entropy production and how this configuration relates to mass entrainment and device outlet temperature. The entropy generation is lowest for diathermic funnel walls compared to other boundary conditions for the funnel.