Читать книгу Fundamentals of Heat Engines - Jamil Ghojel - Страница 45

A hot object tends to cool to the temperature of colder surroundings, and a cold object is warmed to the temperature of hotter surroundings. The phenomenon is caused by the heat‐transfer process, in which the energy of a system changes while no work is done on or by the system (no work exchange with the surroundings). This process can occur with the volume remaining constant, and the change of energy in the system for an ideal gas is then

(1.49)

ΔU is the internal energy of the system.

If the pressure remains constant during the process, the change of energy in the system is

(1.50)

The source of the heat in both these cases could be external or internal. Examples of processes with internal heat sources are the spark ignition engine (constant‐volume combustion of the fuel) and the gas turbine combustor (constant‐pressure combustion of the fuel).