Question

Water at 50°F and 20 psia is heated in a chamber by mixing it with saturated water vapor at 20 psia. If both streams enter the mixing chamber at the same mass flow rate, determine the quality of the exiting stream to 3 significant digits (don't forget a leading o if needed). Mixing section

Answer 1

Consider the following diagram. water 3 vapor Write the expression for the mass balance as follows: торu — т out т, %3D т, + т, Since, the mass flow rate is same. So, т 3 т, т — 2т Apply energy balance to the mixing chamber as follows: Ė, = È in out m,h + m,h, = m,h, m,h + m,h, = 2m,h, 4 +h, = 2h, .... ...

Obtain the following properties from saturated water tables at temperature 50°F. Enthalpy of saturated water, h =h, =18.07Btu/lbm. Obtain the following properties from saturated water tables at pressure 20 psi. Enthalpy of saturated vapor, h, =h, =1156.2Btu/lbm. Form equation (1), h +h, = 2h, 18.07 +1156.2=2h, h, =587.13 Btu/lbm Assume the mixture pressure P, = 20 psi. Obtain the following properties from saturated water tables at pressure 20 psi. Enthalpy of saturated water, h, =196.27Btu/lbm. = 959.93 Btu/lbm. Enthalpy of evaporation, h, Write the expression for the enthalpy at state 3 as follows: h = h; + x,hg h; -h; 587.13 –196.27 X3 959.93 x; = 0.407 %3D Thus, the quality of stream at exit is 0.407