It is desired to describe the performance of the simple double-pipe heat exchang
ID: 1071695 • Letter: I
Question
It is desired to describe the performance of the simple double-pipe heat exchanger with 1m length. Hot oil enters into the exchanger with 420K and discharges from the exchanger with 370K. Cooling water supplies into the exchanger with 200K. To decrease the temperature of the discharged oil to 350K, calculate water flows with count-current flow and with co-current flow against the hot oil, respectively.
Assumption) No heat loss from the exchanger to the outside;
Heat capacity and heat transfer coefficient are constant;
Kinetic and potential energy are neglectable;
The molar and mass flow rates are constant
Explanation / Answer
Q max= mCp (Th1-Tc1)
mCp=Cmin
Q max/Cmin=(420-200)=120 K
Heat gained by water =heat lost by water
Q=C (oil)*(420-370)=50K
Q=C water*(T-200)
Use Q max here,
120 K=T-200K
T =320 K
here,water exit temperature is 320 K.
Q=mcp(320-200)
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