 #1
 13
 3
Homework Statement
Hello. First of all sorry about this question, it has to do a little with heat transfer from engineering. This situation is not real, I was working in a proyect and this doubt came to me.
I have a heat exchanger of parallel tubes. Water flows in a tube and oil flows in another one. The initial conditions are shown in the picture. I will write them here:
Water
To= 18°C
Tf= 26°C
m=0.25 kg/s
cp= 4.18 kJ/kg°C
Oil
To: 0°C
m= 0.1 kg/s
Cp= 1.79 kJ/kg°C
Homework Equations
Q= m.cp (Tfto)
The Attempt at a Solution
I found the heat transfer from the water to the oil
Qw= (0.25)(4.18)(2618)=8.36
This is the same heat that comes in to the oil.
So
8.36=(0.1)(1.79)(Tf0)
Tf= 46.7°C
This result does not make sense to me, because I find impossible that the oil has increased its temperature more than water. I thought that the maximum possible temperature than the oil can reach is the same 26°C of water ( Assuming an infinite length in the heat exchanger)
In the picture I put a axis with the temperatures.
Could anyone explain me why, according with the calculations, I got Tf= 46.7°C for the oil?
Attachments

40 KB Views: 277