Impingement/effusion cooling wall heat transfer: Conjugate heat transfer computational fluid dynamic predictions

Impingement/effusion internal wall heat transfer was investigated using conjugate heat transfer (CHT) computational fluid dynamics (CFD). ANSYS Fluent was used with the k-? turbulence model. Impingement/effusion configurations were modelled with the impingement hole on the centre of the effusion hole square array. Impingement/effusion geometries with equal number of holes were modelled with hole density n (m2) of 4306/4306, 9687/9687 and 26910/26910 m-2 for an impingement hole pitch to diameter ratio X/D of ∼ 11 at an effusion hole X/D of 4.7 for all configurations. The experimental test wall size was 152mm square this was square hole arrays of 102, 152 and 252. The main reason for investigating the number of holes was that effusion cooling has been shown to improve the greater the number of holes used for the same wall porosity or X/D. The coolant mass flux G was varied from 0.1-0.94 kg/sm2bar for all n. A constant impingement gap Z of 8 mm was used with both walls 6.35 mm thick. The range of gap to diameter ratio Z/D was from 2.4-12.5, with the smallest n having the lowest Z/D. Locally surface average heat transfer coefficient (HTC) h values showed reasonable agreement with previously published experimental results. Comparison of the h predictions on the effusion (target) approach wall with those for the effusion and impingement walls alone, were made and this showed that impingement/effusion wall heat transfer was less than the sum of the two components. The reason was shown to be due to the reduced internal gap flow recirculation with reduced heat transfer to the impingement wall for impingement/effusion cooling.