Flow distribution and heat transfer coefficients inside gas holes discharging

Abstract

Fluid flow and heat transfer coefficient associated with flow inside short holes (L/D=1) discharging orthogonally into a crossflow was investigated experimentally and numerically for (Re) ̅ ranging from 0.5×105 to 2×105, and blowing ratio ranging from 1.3 to 3.2. The basic configuration studied consists of a feed tube with five orthogonally located gas holes. Four different hole configurations were studied. The transient heat transfer study employs an IR-camera to determine the local heat transfer coefficient inside each hole. Velocity measurements and numerical flow simulation were used to better understand the measured heat transfer distribution inside the hole. The Nusselt number distribution along the hole surface exhibits significant circumferential non-uniformity associated with impingement and separation, with localized high heat transfer regions caused by flow impingement. The heat transfer coefficient was observed to be a strong function of the Reynolds number, but a weak function of the blowing ratio. Moreover, Fluid flow and heat transfer coefficient inside gas holes was improved by changing the plenum geometry for (Re) ̅=1.7×105, and blowing ratio of 2.65. To improve the flow structure understanding inside plenum and gas holes, numerical simulation using FLUENT code was employed and verified by experimental measurements. Heat Transfer coefficient contour maps inside gas holes was measured experimentally using IR-camera thermography to investigate the effect of plenum geometry modifications on thermal stresses generated inside gas holes. Results indicate that placing straight baffles at the upstream of cooling holes inlet inside the plenum eliminates vortex generation in the gas holes for H/S=1. The recirculation bubble at the back of each baffle guides air to flow smoothly into cooling holes. Also, by varying baffle height, plenum mass flow rate can be distributed evenly among all gas holes.