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Concept to extract heat energy from objects

  1. May 11, 2013 #1
    I was just thinking about absolute zero temprature roughly -250 c degress
    Lets say an object has a room temprature of 20 degrees celcius
    Doesnt it mean i has a lot of thermal emegy
    So i used the equation

    H= Cp x M x ΔT

    H = Heat energy (in Joules)
    m = mass (in kilograms)
    delta T = change in temperature (in degrees Celsius)
    Cp = Specific heat (in J/kg x degrees C)

    If the material is glass with mass of 1 kg it would have 263550 joules of energy??

    Im just a as student im completly wrong just say so
  2. jcsd
  3. May 11, 2013 #2
    Q = M . C . dt (How do you get the triangle symbol) is how I write the equation, but they are the same thing.

    You should work in kelvin really, but a change of 1 in either unit is equal so that's no big deal here.

    Anyway, 0k is ~-273 degrees celsius.

    What your equation says, is that it takes 263550 joules of energy to heat 1 kg of glass from 0k to 293k.

    p.s I haven't actually checked your numbers, but assuming they work out.
    Last edited: May 11, 2013
  4. May 11, 2013 #3
    yes but the object is already heated to room temperature from its surroundings
  5. May 11, 2013 #4


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    Yes, your object at room temperature has 263550 Joules more heat energy per kilogram than the same object at absolute 0. But so what? You titled this "Concept to extract heat energy from objects" and you said nothing about extracting the energy
  6. May 11, 2013 #5
    If what you're looking for is an efficient way to 'extract' that energy from an object, you simply need to place the object in a large temperature differential with good conductance.

    It's basically a fridge.
  7. May 11, 2013 #6


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    Gold Member

    Specific Heat capacity of glass is 840 Joules/kg/k so yes 1kg at room temperature 293K contains about 250,000 Joules.

    It's not too hard to extract some of it. As lntz said you could put it in a fridge or use another type of heat pump.

    Heat pumps for houses work by extracting heat from the outside air or ground and moving it indoors. They can even operate when the outside temperature is below freezing. The problem is that even the best heat pumps need some energy to run. The COP (Coefficient of Performance) for a typical heat pump for houses is typically in the range 2 to 6. In other words they use 1 unit of energy to move between 2 and 6 units of energy from outside to inside.
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