Question

what is the dryness fraction of the steam if wet saturated steam at 8 bar (hig = 2048 kj/kg) requires 82 kj of heat per kg of steam to completely dry it

Answer 1

The dryness fraction of wet saturated steam at 8 bar that requires 82 kJ/kg to completely dry it is calculated using the formula x =
`Q_(required)` /
`h_(fg)`. Substituting the given values, the dryness fraction is found to be about 0.040, indicating that 4.0% of the wet steam needs additional heat for complete vaporization.

Step-by-step explanation:

The dryness fraction of steam is a measure of the proportion of steam that is in the vapor phase compared to the total weight of the steam mixture, which includes both the vapor and any entrained liquid water (wet steam). To calculate the dryness fraction (x), you need to know the amount of heat required to fully vaporize the wet steam (
`Q_(required)`) and the enthalpy of vaporization (
`h_(fg)`), which is the heat needed to convert water at its boiling point into steam at the same temperature at a constant pressure.

Given that the wet saturated steam at 8 bar requires 82 kJ/kg of heat to become completely dry and the enthalpy of vaporization (
`h_(fg)`) is 2048 kJ/kg, we can use the formula:

x =
`Q_(required)` /
`h_{fg`}

Substituting the values in the formula, we get:

x = 82 kJ/kg / 2048 kJ/kg

x = 0.0400390625, which can be rounded off to 0.040 (or 4.0% when expressed as a percentage).

The dryness fraction indicates that 4.0% of the wet steam needs additional heat to become completely vaporized into dry saturated steam.