Choose the situation that is an example of heat transfer by radiation. a. an ice cube melts while you hold it in your hand. b. hot soup rises to the top of the bowl, while cooler soup sinks to the bottom. c. coastal temperature are cooler than temperatures in inland areas. d. the sun's energy is transferred through the vacuum of space to earth.

Air enters a gas turbine with two stages of compression and two stages of expansion at 100 kpa and 17°c. this system uses a regenerator as well as reheating and intercooling – the intercooler returns the air to the inlet temperature. the pressure ratio across each compressor is 4 ; 300 kj/kg of heat are added to the air in each combustion chamber; and the regenerator operates perfectly while increasing the temperature of the cold air by 20°c. determine the system’s thermal efficiency. assume isentropic operations for all compressor and the turbine stages and use constant specific heats at room temperature. (0.378)