Consider the process of heating water on top of an electric range. a) The water

Question

Consider the process of heating water on top of an electric range.

a) The water is heated to 150F. Define a system that could be used and measurements that could be made to determine the energy transfer to the water. Is the system open or closed?

b) The water is heated to 150F. Define a system that could be used and measurements that could be made to determine the energy transfer to the surroundings. Is the system open or closed?

c) The water is heated until it is boiling vigorously. Are the systems defined in (a) and (b) open or closed? How would the determination of energy transfers be more difficult for this case?

Explanation / Answer

(a) If no extra water is added or removed then it's closed system and only energy transfer can take place. Now to determine the energy transfer one has to measure the initial temperature of water as well as final temperature which is given. Also volume of water in the system should be measured to get mass of water. Finally Q = mc(Tf - Ti) will give the energy transfer.

(b) This can be open system as energy transfer to surroundings we are talking about. Thermometer can measure the temperature of water and knowing the temperature of surroundings, along with thermal conductivity of container holding water, outside convective heat transfer coefficient all determines how much energy will actually flow to surroundings.

(c)The vigorous boiling will affect the steady state conditions and thus it becomes difficult to measure the properties at a particular point. There will be certain loss in energy which cannot be measured.

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