*Explain the following in brief*

**Clausius inequality**

The following equation is known as the inequality of Clausius. It provides the criterion of the reversibility of a cycle.

∮(dQ/T) ≤ 0

- If ∮(dQ/T) = 0 then the cycle is reversible
- If ∮(dQ/T) < 0 then the cycle is irreversible and possible
- If ∮(dQ/T) > 0 the cycle is irreversible and possible

**Nucleate boiling**

In nucleate boiling, steam bubbles form at the heat transfer surface and then break away and are carried into the mainstream of the fluid. It is a type of boiling that takes place when the surface temperature is hotter than the saturated fluid temperature by a certain amount but where the heat flux is below the critical heat flux.

**Entropy principle**

All heat is not equally valuable for converting into work. The heat that is supplied to a substance at a high temperature has a greater possibility of conversion into work than heat supplied to a substance at a lower temperature.

*“Entropy is a function of a quantity of heat which shows the possibility of conversion of that heat into work. The increase in entropy is small when heat is added at a high temperature and is great when heat addition is made at a lower temperature. Thus for maximum entropy, there is minimum availability for conversion into work and for minimum entropy there is maximum availability for conversion into work”*

**Kelvin-Planck law**

*“It is impossible to construct an engine, which while operating in a cycle produces no other effect except to extract heat from a single reservoir and do the equivalent amount of work”.*

It says that in order to get net work from a device operating in the cycle (i.e. heat engine) it must have heat interaction at two different temperatures or with body/reservoirs at different temperatures (i.e. source and sink).

**View factor**

A radiation shape factor F

_{12}(or view factor) is defined as the fraction of energy leaving surface 1 and reaching surface 2.---

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