Question

Write short notes on the following, illustrating your answers with neat sketches wherever necessary:

1- Effect of supersaturated flow in steam nozzles, and

2- Steam injector.

Answer 1

1. Effect of super saturated flow in steam nozzle:

The vital function of steam nozzle is to produce steam jet with high velocity in order to  drive a turbine. The phenomenon of super saturation is inherent in steam flow through nozzle and the following are the effects:

a.Super saturated flow causes the specific volume and entropy of the steam to increase.

b.Super saturated flow increases the dryness fraction of the steam.

c.Super saturated flow  reduces the heat drop and ultimately the exit velocity of the steam is reduced.

d.The temperature at which the steam becomes supersaturated will be less than the saturation temperature corresponding to that pressure. Therefore, supersaturated steam will have the density more than that of equilibrium condition which results in the increase in the mass of steam discharged.

The super saturated region is shown in the figure by considering temperature-entropy diagram.

2. Effect of super saturated flow in steam injector:

Steam injector is used to deliver cold water to a boiler against its own pressure using its own live or exhaust steam, replacing any mechanical pump and it works on the principal of thermodynamics and pressure. Effect of super saturated flow in it is givean as follows:

a.super saturated flow reduces exit velocity in steam injector.

b.It enhances the dryness fraction and decreses enthalpy variation.

c.It increases the randomness and swirling action of steam.

d. The super saturated temperature corresponding to the pressure is decreased as compared to saturation temperature at tha particular pressure value.