A very long pure copper bar is initially at a uniform temperature of 20°C. The bar's cross-section is a 20-mm x20-mm square. The copper bar will be heated to a

temperature of 100°C by blowing 250°C air over its surface. The convective heat transfer coefficient for the air is h = 7O W/m K. a) Verify that cooling the copper bar may be treated as a lumped-capacity process. a) Find how long it will take to heat the copper bar to 100 C (answer: 105 s).