Heat engine

Definition

A heat engine is a device that converts thermal energy into mechanical work by exploiting the temperature difference between a hot and a cold reservoir. It operates in cycles, absorbing heat from the hot reservoir and expelling some of it to the cold reservoir while performing work.

5 Must Know Facts For Your Next Test

1. The efficiency of a heat engine is defined as the ratio of the work output to the heat input, and it can never be 100% due to unavoidable energy losses.
2. The Carnot cycle represents an idealized heat engine cycle with maximum possible efficiency limited by the temperatures of the hot and cold reservoirs.
3. Real-world heat engines operate on various cycles like the Otto cycle (used in gasoline engines) and Diesel cycle (used in diesel engines).
4. According to the Second Law of Thermodynamics, no heat engine can convert all absorbed heat into work; some energy is always lost as waste heat.
5. The First Law of Thermodynamics, which states that energy cannot be created or destroyed, applies to heat engines by ensuring that all input energy is accounted for as either work done or waste heat.

Review Questions

• What is the primary function of a heat engine?
• Why can't a real-world heat engine achieve 100% efficiency?
• How does the Carnot cycle relate to the concept of an idealized heat engine?

Related terms

Carnot Cycle: An idealized thermodynamic cycle proposed by Sadi Carnot, representing the most efficient possible conversion between thermal and mechanical energy.

First Law of Thermodynamics:

$\text{\Delta U = Q - W}$; states that energy cannot be created or destroyed, only transferred or converted.

Entropy:

A measure of disorder or randomness in a system; dictates that total entropy always increases over time in an isolated system.