The startup company Thermo311, Inc. has developed a unique device to split a str
ID: 2998209 • Letter: T
Question
The startup company Thermo311, Inc. has developed a unique device to split a stream of gas into two streams at different temperatures. It seems pretty amazing that Thermo311, Inc. can pull that off. This mysterious black box devices can take an inlet stream of ideal gas at 2 kg/s and 4 bar and cool part of it (0.5 kg/s) from 50
The startup company Thermo311, Inc. has developed a unique device to split a stream of gas into two streams at different temperatures. It seems pretty amazing that Thermo311, Inc. can pull that off. This mysterious black box devices can take an inlet stream of ideal gas at 2 kg/s and 4 bar and cool part of it (0.5 kg/s) from 50 hat A degree C to -10 hat A degree Cwith no external parts, as shown below. They are trying to convince you to invest in their company with a substantial promise on the return over your investment. You are feeling adventurous and tempted by this offer but before writing a check, you must answer the fundamental question: hat a Can it work? hat a??. Do all the necessary calculations to answer this question and explain your results and conclusions.Explanation / Answer
STATE1
m1 = 2 kg/s
P1= 4 bar
T1 = 50 C
At T1 = 50 C the saturation pressure is Psat = 0.13 bar
P1 > Psat The state is compressed liquid (properties can be approx at T1 = 50 C (saturated liquid properties))
h1 = 209.6 kJ/kg
s1 = 0.7035 kJ/kg
STATE 2
m2 = 0.5 kg/s
P2 = 1 bar
T2 = -10 C
h2 = -354.1 kJ/kg
s2 = -1.299 kJ/kg/K
STATE 3
m3 = 1.5 kg/s
P3 = 1 bar
T3 = 70 C
h3 = 293 kJ/kg
s3 = 0.9548 kJ/kg/K
Mass balance
m1 = m2 + m3 (satisfied)
Energy balance
Qin = Qused + Qlost
Qin > Qused (or equal if there is no energy lost in the process, general for ideal cases)
m1*h1 > m2*h2 + m3*h3
2*209.6 > 0.5*-354.1 + 1.5*293
419.2 > 262.45
It is also satisfied
ENTROPY BAALNCE
For any process to occur entropy must be greater than zero
S2 + S3 -S1 > 0
m2*s2 + m3*s3 - m1*s1 > 0
0.5*-1.299 + 1.5*0.9548 - 2*0.7035 >0
-0.624 > 0
Which is not true
So it can't work
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