A radiation flux of 1000W/m' is incident upon a surface that absorbs 80 percent of the incident radiation. Calculate the amount of radiation energy absorbed by a 4-m? area of the surface over a period of 2h.

When two objects at different temperatures are brought into contact with one another (such as a hot steel bar dropped into cold water), the cold object will O increase in temperature to the same temperature as the hot object before being placed in the water. O lose as much heat as the hot object loses the cold object will remain unchanged O gain as much heat as the hot object loses

radiation

A piece of beef steak 7 cm thick will be frozen in the freezer room -30 ° C. This product has a moisture content of 73%, a density of 970 kg / m³, and a thermal conductivity (frozen) of 1.1 W / (m K). Estimate the freezing time. using the Plank equation. This product has an initial freezing temperature of -1.75 ° C, and the movement of air in the freezing room gives a convective heat transfer coefficient of 15 W / (m² K). t f = ... hour.