(Solved): A 5cm in dimeter cylindrical (nickel 80% - steel) alloy is left outdoors to cool from 200C to ...

A $$5\mathrm{cm}$$ in dimeter cylindrical (nickel $$80\%$$ - steel) alloy is left outdoors to cool from $$200^{?}\mathrm{C}$$ to $$90^{?}\mathrm{C}$$ in a horizontal position. It is a warm day in which air is stagnant at $$20^{?}\mathrm{C}$$. Calculate the time (in seconds) it takes the alloy to cool down considering the following assumptions: 1. Use the Lumped heat capacity method 2. The alloy wall temperature could be taken at an average temperature when calculating the convective heat transfer coefficient.