Can Thermodynamic Cycle Have Negative Efficiency

Question

Answer

What happens when efficiency is negative?

If the actual amount of inputs used exceeds the amount theoretically required, there is a negative efficiency variance. On the other hand, if actual inputs are less than the amounts theoretically required, then there would be a positive efficiency variance.

Why can’t we get 100% efficiency in a thermodynamic cycle?

It is impossible for heat engines to achieve 100% thermal efficiency () according to the Second law of thermodynamics. This is impossible because some waste heat is always produced produced in a heat engine, shown in Figure 1 by the term.

What is cycle efficiency in thermodynamics?

The cycle efficiency is defined with the assumption that the initial energy form is electricity or another high-quality energy form, and the value quoted for hydrogen is based on electrolysis of water as the first step in the storage cycle.

Which of the following is not a factor why machines can never be 100% efficient?

A machine cannot be 100 percent efficient because output of a machine is always less than input. A certain amount of work done on a machine is lost to overcome friction and to lift some moving parts of the machine.

How do you calculate the efficiency of a thermodynamic cycle?

The thermal efficiency, ηth, represents the fraction of heat, QH, converted to work. The air-standard Otto cycle thermal efficiency is a function of compression ratio and κ = cp/cv. The thermal efficiency, ηth, represents the fraction of heat, QH, converted to work.

Which law of thermodynamics says that 100% efficiency is not possible?

We know from the second law of thermodynamics that a heat engine cannot be 100 percent efficient, since there must always be some heat transfer Qc to the environment.

Which law of thermodynamics implies that no heat engine can be 100% efficient?

∴ The second law of thermodynamics implies that no heat engine can be 100% efficient.

Why 100 efficiency is impossible?

A heat engine is considered to be 100% efficient if only all the heat is converted into useful work or mechanical energy. Since heat engines cannot convert all the heat energy into mechanical energy, their efficiency can never be 100%.

Why Carnot cycle limits the thermodynamic efficiency of a heat engine?

The Carnot cycle can be thought of as the most efficient heat engine cycle allowed by physical laws. When the second law of thermodynamics states that not all the supplied heat in a heat engine can be used to do work, the Carnot efficiency sets the limiting value on the fraction of the heat which can be so used.

What is the thermodynamic efficiency of the engine?

According to MDPI, gasoline engines have a thermal efficiency of between 30% and 36% while diesel engines can reach a thermal efficiency of almost 50%.