Balances in Practice Check

Knowledge check

1. In a Sankey diagram, the width of each arrow represents:
The temperature of that flowThe magnitude of that flow, so wider arrows are bigger flowsHow recently that flow was measuredThe cost per kWh of that flow
2. Exergy (or 'quality of energy') describes:
The total quantity of energy in a stream, exactly as an energy balance measures itHow much of a stream's energy could theoretically be converted into useful work, given its temperature relative to its surroundingsThe price of energy in pounds per kWhA stream's mass flow rate
3. Compared with a heat source close to ambient temperature, a heat source much hotter than ambient has:
Less exergy (less potential to do useful work)More exergy (more potential to do useful work)Exactly the same exergy, since exergy doesn't depend on temperatureNo exergy at all, regardless of temperature
4. Which sequence best describes the general method taught throughout this course?
Guess the losses, then adjust the input to matchDraw a boundary, list every stream crossing it, measure what you can, and use conservation to solve for the restOnly ever measure every single stream directly; never calculate oneSkip the boundary step and go straight to the arithmetic
5. If a generic industry rule of thumb disagrees with a balance you've built from your own measured, plant-specific numbers, you should generally:
Always trust the rule of thumb, since it's based on wide industry experienceTrust your own balance, since rules of thumb are generic approximations meant for quick screening, not site-specific decisionsAverage the two figures togetherDiscard both and use neither

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