Heat reservoir

From ArticleWorld

A heat reservoir is a region of constant temperature that allows either the addition or removal of heat. Also termed as 'heat bath', a heat reservoir is normally vast enough to absorb heat from or donate heat to the surroundings without a significant change to its own temperature.

The concept of heat reservoir is in accordance with the Second Law of Thermodynamics, which states that the total entropy of an isolated thermodynamic system tends to increase over time and approaches a maximum value. The entropy of a heat reservoir changes though its temperature does not change. This is because of the large heat capacity. Since the temperature of a heat reservoir is uniform, the heat exchange that takes place across the reservoir and another substance is reversible.

Types of heat reservoirs

There are two types of heat reservoirs:

• Heat source: a heat reservoir is considered a 'heat source' if it is at high temperature and is capable of transferring heat to the surroundings or to another object.
• Heat sink: a heat reservoir is considered a 'heat sink' if it is at low temperature and is capable of absorbing heat.

Common examples of heat reservoir

There are several examples of heat reservoirs found in systems in nature. The atmosphere acts as a heat reservoir when hot air emerges as exhaust from the internal combustion of a vehicle. The exhaust air may be at a temperature of several hundred degrees Celsius, but there is a negligible rise in the temperature of the surrounding air in the atmosphere.

The sea acts as a heat reservoir with the result that coastal tides are set up. Heat that is absorbed during the day is stored for a long time well into the night. In addition, as the day progresses, heat is absorbed very slowly by the sea. This results in an equable climate near coastlines.