The Four Questions

Definition

The structured prompts of a mass balance: what enters, what leaves, what accumulates, and what changes form.

Answering all four questions for a defined boundary is the test of whether you understand a system. Inputs include water, heat, dissolved species, gases, treatment chemistry, and biological load. Outputs include water at changed conditions, blowdown, steam, leaks, corrosion products, biomass, and solids. Accumulation covers deposits, sludge, biofilm, and concentrated species, while form changes cover reactions and phase changes.

Related concepts

Free Body Diagram · Transformations · Mass Balance

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Part of The Blueprint of Water · 🛠️ operations