A turbine blade with a characteristic length of 1 m is cooled in an atmospheric pressure wind tunnel by air
A turbine blade with a characteristic length of 1 m is cooled in an atmospheric pressure wind tunnel by air at 40?C and a velocity of 100 m/s. At a surface temperature of 500 K, the cooling rate is found to be 10,000 watts. Apply these results to estimate the cooling rate from another turbine blade of similar shape, but with a characteristic length of 0.5 m operating with a surface temperature of 600 K in air at 40?C and a velocity of 200 m/s.GIVENA turbine blade in a wind tunnelLength of blade (L1) = 1 mAir temperature (Tai) = 40?C = 313 KAir velocity (U??1) = 100 m/sAir pressure = 1 atmBlade surface temperature (Ts) = 500 KCooling rate (q) = 10,000 WASSUMPTIONSSteady state for both casesUniform blade surface temperatureAir temperature is constant and the same in both cases
From Appendix 2, Table 27, for dry air at the film temperatures Case 1 Case 2T = 406.5 K T = 456.5 KKinematic viscosity, v × 106 (m2/s) 27.6 33.2Thermal conductivity, k (W/(mK)) 0.0328 0.0360
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