Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Work Done / Thermal Efficiency

  1. Jun 6, 2005 #1
    A steam plant burns 6000 kg/hr coal, heat value 34 MJ/kg
    18kg of air at 15 C is used/kg coal burned. Flue gas tem is 250 C.
    46000 L/min cooling water used for condenser - inlet at 8 C and outlet 20 C

    Find max work done kW/h and thermal efficiency.

    I tried the following formula : Thermal Eff = heat energy converted to work / heat energy supplied or Themal Eff = heat energy equivalent (MJ/Kwh) / spec fuel cons. x calorific value.

    but I must be missing something here ??

    Any direction would be appreciated.
  2. jcsd
  3. Jun 6, 2005 #2

    Andrew Mason

    User Avatar
    Science Advisor
    Homework Helper

    Your approach is correct. The work done per unit of heat supplied is not given. Instead they give you information from which you can determine the heat supplied and the heat not converted to work (ie Q_C - the heat delivered to the cold reservoir or surroundings):

    [tex]\eta = \frac{W}{Q_H} = \frac{Q_H - Q_C}{Q_H} = 1-\frac{Q_C}{Q_H}[/tex]

    Last edited: Jun 6, 2005
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook