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View Diary: Energy, Water, and You: Something to think about tomorrow morning (49 comments)

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  •  Huh? (0+ / 0-)

    The definition of heat capacity is definitely thermodynamics. I haven't used any heat transfer arguments at all. It's all based on enthalpy content--I haven't said anything about friction losses in the pipe, heat transfer from the water to the pipes carrying the water, or any other fluid mechanics type arguments.

    •  well... (0+ / 0-)

      I covered these concepts in heat transfer class but obviously the content is covered in both.  It's just that the focus of thermodynamics is on concepts like work and entropy and heat engines -- not simplistic little heat capacity calculations which you cover in high school physics.  

      BTW, you are still incorrect in your statement that you have violated the laws of thermodynamics if you use less energy.

      •  Less work, not less energy (0+ / 0-)

        Yes, you can get more energy out than the work put into a heat pump. But you can't get more energy out than the total energy transferred to the hot "sink." (But that's not really relevant in this problem, since most home water heaters aren't heat pumps.)  

        (I'll agree I probably could have been more careful in my analysis--but like you said, I was just doing a "simplistic little heat capacity calculation," not do a detailed study. Sometimes there's value in the quick-and-dirty calculation, too.)

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