conversion of heat into work

Conversion of heat into work

 

Heat and work are forms of energy. Work can be completely converted to heat but heat cannot be converted fully into work. Limitations are there in converting heat into work imposed by Second Law of Thermodynamics. The Second Law of Thermodynamics states that “heat transfer occurs spontaneously from higher-to-lower temperature bodies but never spontaneously in the reverse direction”. Heat can be converted into work with the use of heat engines. It is the device that uses heat as an input and produces work as an output. All heat cannot be converted fully into work, some heat are lost into the environment. The heat engine converts heat into mechanical energy which is used to do mechanical work. It converts heat into work by working substance from higher temperature to lower temperature. A heat engine have a source and a sink. A source can be a hot body (high temperature) which gives heat and sink is a cold body (low temperature) where the heat that is not converted into work is discarded. The PV diagrams and energy reservoir model are used to explain the working of heat engines.

 

Energy reservoir model

It is used to illustrate the working of heat engines. The hot reservoir produces heat which is converted into work but some of the heat is lost to the cold reservoir due to the limitations imposed by the second law of thermodynamics.

 

 

PV diagram

The Pressure-Volume (PV) diagram is used to study the heat engines. It shows the relationship between pressure and volume. When volume changes work is done. The amount of work is shown by the area inside the loop. It operates in cyclic way, it adds energy in form of heat forming one half of cycle and uses the heat to do work forming other half of cycle.