## Equivalent Evaporation

**Introduction:**

The performance of boilers need to be evaluated periodically to ensure that the boiler operates satisfactorily.

**Description:**

- Different boilers are designed to generate steam at different pressures and also during operation the steam generation pressure could be different from that envisaged at the time of designing it.

- Therefore, we need to relate the ability of Steam Generators boiler to raise steam to standard conditions.

- For all boilers the stand conditions considered are :

Temperature of feed water = 100^{o}C,

steam generated is dry saturated at 100^{o}C.

Accordingly for this condition the enthalpy of vaporisation (latent heat) at 100^{o}C is found to be 2257 kJ/kg.

The term ‘Equivalent Evaporation’ is defined as the amount of water evaporated from saturated liquid water at 100^{o}C to dry saturated steam at 100^{o}C.

Let us consider a boiler generating mw kg of steam per hour at a pressure p and temperature T.

For this given p and T the enthalpy of steam generated is h. (The value of h needs to be taken from steam tables by considering T and p and depending up on T and p steam could be wet, saturated or super heated).

Let the specific enthalpy of water entering boiler be h_{f}.

The heat gained by water in boiler per hour = mw (h – h_{f}). The equivalent evaporation (me) from an definition is given as