Determine the following parameters for the water having quality x=0.7 at 200 kPa: a) the phase
compressed liquid
superheated vapor
saturated liquid
saturated vapor
saturated mixture
b) temperature (in °C)
c) specific volume, in m3/kg
d) specific energy, in kJ/kg
e) specific enthalpy, in kJ/kg
f) What is the enthalpy of 500 g of water (in kJ)?

Solution :

Given :

Water have quality x = 0.7 (dryness fraction) at around pressure of 200 kPa

The phase diagram is provided below.

a). The phase is a standard mixture.

b). At pressure, p = 200 kPa, T =

   Temperature = 120.21°C

c). Specific volume

d). Specific energy ()

e). Specific enthalpy

   At

f). Enthalpy at m = 0.5 kg

       = 1022.91 kJ

Given Information:

Pressure = 1 atm

Mass of water = 1 kg

time = 10 minutes

Required Information:

Power rating = ?

The correct option is (c)

P = 1.9 kW

Explanation:

We want to find out the power rating of the heating element of the coffeemaker.

The power rating is given by

Where m is the mass of the water, h is the latent heat of vaporization of water, and t is the time in seconds.

From the standard table, the latent heat of vaporization of water at 1 atm and 100 °C is given by

h = 2257 kJ/kg

Time in seconds = 10×60 = 600 seconds

Rounding off yields

Therefore, the correct option is (c) 1.9 kW