• Question: How many AA batteries does it take to cook a chicken?

    Asked by 446xmasen22 to Tom C, Thomas, Saiful, Piers, Laurence, Karl, Javier, Chris on 9 Jan 2017. This question was also asked by 426xmasen24.
    • Photo: Piers Barnes

      Piers Barnes answered on 9 Jan 2017:


      Recipe: Joule’s chicken

      Here is an estimate of the absolute minimum energy required to cook a chicken assuming negligible energy losses. The procedure is as follows:

      Take one chicken (2 kg) at room temperature (21 deg C). Place an electrical heating element inside the chicken cavity, stich up the cavity, so only the wires to the heating element come out. Place the chicken in a silvered vacuum flask with electrical connections to allow the wires to come out. The silvered vacuum flask will minimise heat loss to the surroundings during cooking. The minimum safe cooking temperature for a chicken is 74 deg C, so we must ensure that the whole chicken has reached this temperature before it can be eaten. The heat capacity of a chicken is about 3500 J/deg C/kg, and this is relatively constant all the way up to 74 deg C. So the energy required to heat the chicken up from 21 to 74 deg C (a change of 53 deg C) is:

      Heat energy required = 53 deg C x 3500 J/deg C/kg x 2 kg = 371 kJ

      About 9 kJ of electrical energy that can be extracted from a long life alkaline AA battery. We want to convert all the electrical energy to heat, which can be done reasonably efficiently, so the number of batteries required to ‘cook’ the chicken is: 371 kJ / 9 kJ = 41. Unfortunately we cannot completely neglect the heat capacity of the glass in the vacuum flask, so about another 6 AA batteries to heat this to the same temperature as the chicken are needed.

      Take the batteries and discharge them through the heating element, the heat released per second by heating element will be given by the square of the current multiplied by the resistance of the element. Allow additional time for the heat to diffuse through the chicken so that it is warmed evenly.

      Remove the chicken from the vacuum flask and remove the heating element from it’s cavity. Season with iron filings before serving.

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