# Calculating Heat Energy and Work

Please see the attached file for the fully formatted problem(s).

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.

Rankine Cycle Problem

Rankine Cycle Problem. See attached file for full problem description.

A supply of geothermal hot water is to be used as the energy source in an ideal Rankine cycle, with R-134a as the cycle working fluid. (See the diagrams below) Saturated vapor R-134a leaves the boiler at a temperature of 85°C, and the condenser temperature is 40°C. Calculate the heat transfers in kJ/kg at the boiler and condenser.

Calculate the work in kJ/kg at the pump and turbine thermal efficiency of this cycle