In which direction does heat energy always flow?

Heat energy always flows from a higher temperature to a lower temperature due to the second law of thermodynamics. This law states that energy spontaneously tends to disperse or spread out. When two objects at different temperatures come into contact, the heat transfers from the hotter object, which has more thermal energy, to the cooler object, which has less thermal energy. This process continues until thermal equilibrium is achieved, meaning both objects reach the same temperature.

In practical terms, this principle can be observed in everyday scenarios, such as warming your hands by holding them near a hot surface. Understanding this concept is crucial in refrigeration and HVAC applications, as controlling the direction of heat flow is fundamental to efficient operation. It governs how refrigeration systems are designed to remove heat from spaces or substances in order to lower their temperature.