Saturated liquid water at 200 kPa enters an insulated mixing chamber at a rate of 15 kg/s. The water is mixed with superheated steam at 200 kPa and 125°C. The combined flow will exit as a saturated mixture at 200 kPa. Using your mixing chamber model to calculate the data, plot the quality of the combined exit flow for superheated steam entrance flow rates ranging from 5 kg/s to 200 kg/s.

Question

State 1: Liquid inlet; State 2: Steam inlet; State 3: Outlet
Given: P1 = P2 = P3 = 200 kPa; x1 = 0.0; T2 = 125°C; x3 = 1.0; m?1= 15 kg/s
Assume: Q?=0 (insulated). Given no other information regarding the mixing chamber, make the following common assumptions: W?=?KE=?PE=0
Also, assume the mixing chamber is a multiple-inlet, single-outlet, steady-state, steady-flow device.

What will be an ideal response?

Answer 1

The First Law for Open Systems reduces to

m?1h1+m?2h2=m?3h3

The conservation of mass yields: m?1 + m?2 = m?3

For the water:

h1 = 504.68 kJ/kg

h2 = 2716.58 kJ/kg

The enthalpy at state 3 will depend on the superheated steam flow rate.

h3 =m?1h1 + m?2h2/m?1 + m?2

Then x3 = (h3 – hf)/(hfg)



For the range of possible steam flow rates: