From what I read about the Carnot Cycle, there are 4 major steps involved, viz. Isothermal Expansion, Adiabatic expansion, Isothermal compression and Adiabatic compression. During the Isothermal expansion phase, the piston-cylinder setup is at a temperature T₁ and a heat reservoir is at the same temperature T₁. When they are brought in contact, heat flows from the hot reservoir to the cylinder and since the temperature of the cylinder remains the same, the cylinder does work (Expands) isothermally. If heat always flows from a hotter body to a colder body, why did heat flow from the hot reservoir to the cylinder given that they are the same temperature?
Carnot Engine – How Does Heat Flow From the Reservoir to the Engine at Same Temperature?
carnot-cycleheat-enginethermodynamics
Best Answer
Allowing the gas to expand a tiny amount (and do a small amount of work on the surroundings) causes the gas temperature to drop a tiny amount relative to the hot reservoir. This then provides the driving force for a small amount of heat to flow from the reservoir to the gas, and restores its original temperature. This is repeated over and over again. The net result is that the gas does work with its temperature essentially equal to the reservoir temperature.