1.22

The free convection heat transfer coefficient on a thin hot vertical plate suspended in still air can be determined from observations of the change in plate temperature with time as it cools. Assuming the plate is isothermal and radiation exchange with its surroundings is negligible, evaluate the convection coefficient at the instant of time when the plate temperature is 225°C and the change in plate temperature with times (dT/dt) is -0.022 K/s. The ambient air temperature is 25°C and the plate measures 0.3X0.3 m with a mass of 3.75 kg and a specific heat of 2770 J/kg. K

1.27 Consider the conditions of problem 1.22. However, now the plate is in a vacuum with a surrounding temperature of 25°C. What is the emissivity of the plate?What is the rate at which radiation is emitted by the surface?