Heat transfer characteristics of shrouded longitudinal ribs in turbulent forced convection

Augmenting the heat transfer rates in the internal flow passages of several components of a gas turbine, such as the turbine blades, vanes and combust or walls is an important pre-requisite for maintaining their structural int egrity. This is particularly paramount when higher turbine inlet temperatur es and pressure ratios are utilised for enhancing the thermal efficiencies of the gas turbine plant. In this study, the heat transfer enhancement, whi ch can be achieved by longitudinal ribs in a variable geometry duct, has be en examined. With the base of the ribs maintained at a constant temperature , it was observed that the optimal rib spacing, which corresponded to the m aximum heat transfer from the ribs, was a strong function of the rib height to length ratio and the Reynolds number but relatively insensitive to the amount of clearance above the ribs, A design correlation is proposed which shows the distribution of this optimal rib spacing for a wide range of rib geometrical and operational conditions. Comparisons of the longitudinal rib s with pin fin arrays indicated that at rib height to length ratios of grea ter than or equal to 0.24, higher heat transfers can be achieved with the l ongitudinal ribs. The frictional characteristics of the longitudinal ribs i s comparable to those of circular pin fins. Measurements of the local heat transfer coefficient for the rib surfaces indicate that it is highly non-un iform along the rib height and length and also significantly influenced by the amount of clearance above the ribs. For all the cases examined, it was observed that developing flow conditions (thermally and hydrodynamically) w ere prevalent within the longitudinal rib channels. (C) 1999 Elsevier Scien ce Inc. All rights reserved.