We were discussing various basic concepts of thermodynamics such as thermodynamic system, boundary and surrounding and also we have seen thermodynamic equilibrium, intensive and extensive properties in our previous post.

Today we will see here the very important and basic term used in thermodynamics i.e. thermal reservoir in our thermal engineering category with the help of this post.

### Let us see thermal reservoir

Thermal reservoir or thermal energy reservoir is also termed as thermal bath and it is basically defined as a system with infinite capacity and with constant temperature. Temperature of thermal reservoir will never be affected due to transfer of quantity of heat energy from it or to it.

Thermal reservoir will either provide the heat energy or receive the heat energy but its temperature will be remaining constant.

Thermal reservoir which will be at higher temperature will be termed as heat source and it will give the heat energy to the system. Whereas thermal reservoir which will be at lower temperature will be termed as heat sink and it will receive the heat energy to the system but we must note it here that temperature of heat source or heat sink will be remaining constant.
Thermal energy reservoir: Heat source and heat sink
Let us see one example, ocean could be considered as thermal reservoir. Let us assume that   we are pouring 5 or 10 liter worm water in to the ocean and after that we are measuring the temperature of ocean water.

Is temperature of ocean water will be increased? Your answer will be surely no because ocean will be the infinite capacity system and its temperature will never be affected due to the addition of heat energy in terms of 5 or 10 liter worm water.

In simple words, we can say that thermal reservoir is basically defined as the constant temperature and infinite capacity system which will receive the heat energy from the system or will provide the heat energy to the system but its temperature will be remaining constant.

Atmospheric air, boiler furnace, river and combustion chamber another example of thermal reservoir could be seen.

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we will see another topic in our next post i.e.

#### Reference:

Engineering thermodynamics by P.K. Nag