Science  BTUs Please help
posted by Sejul on .
Although I vaguely see DrBob222's concept, I still need some help in the set up. Thank you.
A 10 lb. frozen boneless roast needs to be thawed and baked to a temperature of 200 degrees F.
The storage freezer maintains a temperature of 10 degrees F.
Pork changes from solid to a thawed state at 30 degrees F and has the following properties:
Heat Capacity "c" (frozen) = 0.50 BTU/(lb x F degrees)
"c" thawed = 1.2 BTU/(lb. x F degrees)
Heat of fusion (hf) = 125 BTU/lb.
How many BTUs does it take to bring the roast to a tasty 200 degrees F?
â€¢Science  DrBob222, Sunday, September 2, 2012 at 6:47pm
q1 is heat from 10 to 30
q1 = mass x specific heat of frozen x (TfinalTinitial)
q2 = heat at 30 to thaw at 30.
q2 = mass x heat fusion
q3 = heat from 30 to 200
q3 = mass x specific heat of thawed x (TfinalTinitial)
Total heat = q1 + q2 + q3

All you need to do is to substitute the numbers and solve for q1, q2, and q3. There isn't anything vague about it.
q1 = 10 lbs x 0.5 BTU/lb*F x 40F = ?BTU (note:TfinalTinitial) = 30F(10F) = 40F
q2 = 10 lbs x 125 BTU/lb = ? BTU
etc.