Thermal Energy Reservoirs

Reservoirs can supply or absorb finite amounts of heat without undergoing any change in temperature

Source - Reservoir that supplies heat

Sink - Reservoir that absorbs heat

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Exergy and Reservoirs

 - Exergy is the maximum useful work that can be extracted from a reservoir -

1) Energy is rejected by a process when it can't

 perform any more useful work

     - Rejecting high quality energy to a heat sink is wasteful

     - Energy of a heat sink has low quality relative to the process

2)  A well-designed process should reject low quality energy

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Reservoir examples

1) In practice, large bodies of water such as oceans and lakes as well ass atmospheric air can be modelled as energy reservoirs, because of their large thermal mass.

- For example the atmosphere does not warm up as a result of heat loss from housing in winter.

2)  A two-phase system can also be modelled as a reservoir since it can absorb and release large quantities of heat while remaining at constant temperature.