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ENGR5003 / Week 3
Old spec L5 worked example 1 - boiling water at constant pressureTutorialOld spec ENGR217Third8 min

ENGR217 Lecture 5 steam tables worked example 1 (slides 6-11)

1 kg of water at T1=30 ∘CT_1 = 30\ ^\circ\mathrm{C} and p=1p = 1 bar (100 kPa) is heated at constant pressure until it becomes dry saturated steam. Determine the heat added, the work that the expanding steam does on the atmosphere and therefore the change in internal energy. Use steam tables.

Formulas you may need
  • First law: ΔU=Q−W\Delta U = Q - W (heat in and work out positive) (on the formula sheet)
  • Enthalpy: h=u+pvh = u + pv (on the formula sheet)
  • Constant-pressure boundary work: W=p(V2−V1)W = p(V_2 - V_1) (on the formula sheet as dW=p dVdW = p\,dV)
  • Constant-pressure heat for a closed system: Q=mΔhQ = m\Delta h (learn this: Q=ΔU+pΔV=ΔHQ = \Delta U + p\Delta V = \Delta H)
  1. (a)
    Heat added.
  2. (b)
    Work done by the expanding steam on the atmosphere.
  3. (c)
    Change in internal energy.