The average convection heat transfer coefficient during this cooling process is ____ W/m2·°C
A stainless steel ball (ρ = 8055 kg/m3, cp = 480 J/kg·K) of diameter D = 0.15 m is removed from the oven at a uniform temperature of 350°C. The ball is then subjected to the flow of air at 1 atm pressure and 30°C with a velocity of 6 m/s. The surface temperature of the ball eventually drops to 250°C. Determine the average convection heat transfer coefficient during this cooling process and estimate how long this process has taken.
The average surface temperature is 300°C, and the properties of air at 1 atm pressure and the free stream temperature of 30°C are Pr = 0.7282, μs at 300°C = 2.934 × 10–5 kg/m·s, μ∞ = 1.872 × 10–5 kg/m·s, v = 1.608 × 10–5 m2/s, and k = 0.02588 W/m·°C.
The average convection heat transfer coefficient during this cooling process is ____ W/m2·°C and time taken is ____ minutes.
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