A window receives 800 Btu/h of heat transfer at the inside surface of 70 F and transmits the 800 Btu/h from its outside surface at 36 F continuing to ambient air at 23 F. Find the flux of entropy at all three surfaces and the window’s rate of entropy generation.
Question 6.241E: A window receives 800 Btu/h of heat transfer at the inside s...
Flux of entropy: \dot{ S }=\frac{\dot{ Q }}{ T }
\dot{ S }_{\text {inside }}=\frac{800}{529.7} \frac{ Btu }{ h – R }=1.51 Btu / h – R
\dot{ S }_{ win }=\frac{800}{495.7} \frac{ Btu }{ h – R }=1.614 Btu / h – R
\dot{ S }_{ amb }=\frac{800}{482.7} \frac{ Btu }{ h – R }=1.657 Btu / h – R
Window only: \dot{ S }_{\text {gen win }}=\dot{ S }_{ win }-\dot{ S }_{\text {inside }}=1.614-1.51= 0 . 1 0 4 B t u / h – R
If you want to include the generation in the outside air boundary layer where T changes from 36 F to the ambient 23 F then it is
\dot{ S }_{\text {gen tot }}=\dot{ S }_{ amb }-\dot{ S }_{\text {inside }}=1.657-1.51=0.147 Btu / h – R
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