Problem 148P

Reviewing Concepts

Answer the following true or false. Explain

(a) The change in specific volume from saturated liquid to saturated vapor, (vg − vf), at a specified saturation pressure increases as the pressure decreases.

(b) A two-phase liquid-vapor mixture with equal volumes of saturated liquid and saturated vapor has a quality of 50%.

(c) The following assumptions apply for a liquid modeled as incompressible: The specific volume (density) is constant and the specific internal energy is a function only of temperature.

(d) Carbon dioxide (CO2) at 320 K and 55 bar can be modeled as an ideal gas.

(e) When an ideal gas undergoes a polytropic process with n = 1, the gas temperature remains constant.

Solution 148P:

a)

This is true.

As the pressure decreases, the change in saturated liquid and saturated vapour volume decreases.

b)

This is false.

The formula to calculate the quality is:

c)

This is true.

Because we know that,

if

.

d)

This is true.

Carbon dioxide can be treated as an ideal gas at this temperature and pressure.

The behaviour is very similar with the ideal gas.

e)

This is true.

As we know the condition of polytropic process,

When

.

So, the gas temperature will not change during the process.