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Calculating Heat Energy and Work

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Problem 1:

> A piece of wood is 2ft x 2ft x 0.25 ft ----- the hot plate is also 2ft x 2ft square
> A wet piece of wood is placed on a steam heated hot plate ---- the dry weight of the wood is 10 lbs ----- the weight of the water in the wood is 6.5 lbs
> 450 psi saturated steam is used to heat the hot plate ---- the steam is approx. 456 degrees F and has an enthalpy of approx. 1202 btus/lb
> Given are Cp values for wood at .57 btus/lb/oF; water vapor at .46 btus/lb/oF; and water liquid at 1.00 btu's/lb/oF
> Assume no air flow over the wood
> If the steam flow to the hot plate is 25 lbs steam per minute and it is assumed that heat transfer from the hot plate to the wood is 100% efficient:

a) Determine the total energy need to heat the wood to completely bone dry?
b) Determine the time needed to completely dry the wood?
c) Determine how much condensate would be produced on the discharge end of the hot plate (assuming no other radiative or convective losses)
d) From a Physics stand point, would the total energy needed in this case be the amount of work performed?? If not, how would I calculate the work?

Steam inlet condensate out

Hot Plate

Problem 2:

> Exactly the same as above but:

- in this case the heat transfer from the hot plate to the wood is only 70% efficient

But all of the same questions apply as above.

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Solution Summary

The energy and time required to dry a piece of wood are calculated. The amount of condensate and work required are also examined.

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