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L6-7_Material_Balance

# L6-7_Material_Balance - Material and Energy Balances Mass...

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Material and Energy Balances 03/21/10 Mass Balances

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Material and Energy Balances 03/21/10 Objectives At the end of this chapter, you should be able to: Apply material balances for simple systems Formulate and solve material balance problems
Material and Energy Balances 03/21/10 Mass Balance Law of Conservation of Mass: Mass can neither be created nor destroyed (except in nuclear reactions) Because of this, we can write equations called "mass balances" or "material balances“ Any process being studied must satisfy balances on the total amount of material, on each chemical component, and on individual atomic species Later in the course, we'll use the Law of Conservation of Energy (1 st Law of Thermodynamics) to write similar balance equations for energy

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Material and Energy Balances 03/21/10 General Balance Equation The system is any process or portion of a process chosen by the engineer for analysis. A system is said to be "open" if material flows across the system boundary during the interval of time being studied; "closed" if there are no flows in or out.
Material and Energy Balances 03/21/10 General Balance Equation Accumulation is usually the rate of change of holdup within the system -- the change of material. It may be positive (material is increasing), negative (material decreasing), or zero (steady state). If the system does not change with time, it is said to be at steady state , and the net accumulation will be zero. The generation and consumption terms are the consequence of chemical reaction. Note that while the total mass of a system and elements (or "atoms") are conserved, individual species are not. If there is no chemical reaction, the production and consumption terms are typically zero.

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03/21/10 Forms of Balance Equations Differential Form All the terms are rates, so the balance describes an instant in time. Usually the best choice for a continuous
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L6-7_Material_Balance - Material and Energy Balances Mass...

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