In practise, all heat engines have efficiency less than that of a carnot engine because

Options

A. Carnot engine is irreversible
B. A reversible process can never be attained in a real world
C. Irreversible engine has higher efficiency than reversible engine
D. Efficiency of carnot engine is always one

Answer

To understand why all heat engines have efficiency less than that of a Carnot engine, we can break down the explanation into several steps:

### Step-by-Step Solution:

1. **Understanding Carnot Engine**:
- The Carnot engine is an idealized engine that operates on the Carnot cycle. It is the most efficient engine possible, as it operates between two heat reservoirs at different temperatures (T_H for the hot reservoir and T_C for the cold reservoir).
- The efficiency (η) of a Carnot engine is given by the formula:
\[ η_{Carnot} = 1 - \frac{T_C}{T_H} \]
- This efficiency represents the maximum theoretical efficiency that any heat engine can achieve.

2. **Real-World Constraints**:
- In real-world scenarios, heat engines face various constraints that prevent them from achieving Carnot efficiency. These include:
- **Irreversibilities**: Real processes involve friction, turbulence, and other dissipative effects that lead to energy losses.
- **Heat Losses**: Some heat is always lost to the surroundings, which reduces the amount of useful work that can be extracted from the engine.
- **Material Limitations**: The materials used in constructing engines have thermal and mechanical limits that can affect performance.

3. **Non-Ideal Working Fluids**:
- Real engines often use working fluids that do not behave ideally. The properties of these fluids can lead to inefficiencies in heat transfer and work output.

4. **Operational Conditions**:
- The conditions under which real engines operate (such as varying loads and temperatures) can also lead to deviations from ideal performance.

5. **Conclusion**:
- Due to these factors, all real heat engines have efficiencies that are less than that of a Carnot engine. The Carnot engine serves as a benchmark, but practical limitations ensure that real engines cannot reach this ideal efficiency.

### Summary:
In summary, while the Carnot engine represents the maximum efficiency achievable between two temperatures, real heat engines are subject to irreversibilities, heat losses, material limitations, and non-ideal working conditions, which all contribute to their lower efficiencies.