Impingement/Effusion Cooling: Overall Wall Heat Transfer

Abstract

Experimental results are presented for the overall heat transfer coefficient within an impingement/effusion wall, using a transient cooling technique. This was previously used for determining the effusion hole heat transfer alone. Two impingement/effusion geometries were used with an 8 mm gap and the same impingement wall with an X/D of 11. The separate impingement and effusion short hole heat transfer coefficients were also determined. The impingement/effusion overall heat transfer was 45% and 30% higher than the impingement heat transfer alone for the two test geometries. The greater increase was for the higher pressure loss effusion wall. It was shown that the combined heat transfer was predominantly the addition of the impingement and effusion heat transfer coefficients but the interaction effects were significant and resulted in an approximately 15% deterioration in the combined heat transfer coefficient. Overall film cooling effectiveness was obtained that showed a significant improvement with the addition of the impingement cooling, but still had a major effusion film cooling contribution.

Full Coverage Impingement Heat Transfer at High Temperatures

“…To optimise the impingement/effusion designs the impingement and effusion hole configurations were optimised separately (Andrews et al, 1985b(Andrews et al, , 1985c. The combined impingement/effusion cooling has been shown to be very effective at low coolant flow rates (Andrews et al 1988). These designs were aimed at achieving a high cooling effectiveness at a low coolant mass flow so as to leave the maximum proportion of air for combustion purposes.…”

“…This test facility was also used with a transient cooling technique for the determination of the heat transfer coefficients. A similar technique was used for the determination of the heat transfer coefficient as that previously used by Andrews et al (1987bAndrews et al ( , 1988 for effusion and impingement/effusion cooling. The application of the technique to impingement cooling will be described later.…”

“…To overcome this problem two alternative techniques were investigated, both developed from the existing procedures for effusion (Andrews at al 1987b) and impingement/effusion (Andrews et al 1988) heat transfer studies. The test wall was electrically heated in the absence of any impingement coolant flow to a temperature of approximately 80 C. In the first technique the electrical power was switched off and the coolant flow initiated at a preset flowrate and the plate temperature monitored as a function of time, this technique was only applicable to impingement cooling and could not be used with effusion cooling.…”

Full Coverage Impingement Heat Transfer: Cooling Effectiveness

“…The associated research programme of Andrews et al (4,5,13,16,17) has investigated full coverage discrete hole (effusion) film cooling and impingement/effusion cooling using the present test plate geometries. The 2.33 mm hole diameter geometry has been tested as an effusion film cooling system and in combination with the 1.38 mm hole diameter geometry as an impingement wall combined with the 3.27 mm effusion wall with a 6.4 mm gap.…”

“…The approach taken was to separately optimise the impingement and effusion geometries (9)(10)(11)(12)(13)(14)(15). The combined impingement/effusion systems have been shown (4,5,13,16,17) to give a very high cooling effectiveness at low coolant flow rates, well below 50% of current gas turbine combustor film cooling air utilisation rates. Turbine blades also benefit if the internal cooling is maximized, hence minimizing any film cooling requirements.…”