BE2001 Mass and Energy Balance for Biosystem Module 4 Segment 3

Summary

This segment explores how mass and energy balances are applied through accounting and conservation equations in biosystems. It explains how accurately defining a system as open, closed, or isolated determines which governing equations and assumptions are appropriate. The lecture clarifies input, output, generation, consumption, and accumulation terms, distinguishing between conserved and non-conserved extensive properties. It also examines reacting versus non-reacting systems, energy interconversion, and the difference between steady-state and dynamic conditions. By understanding these classifications, engineers can correctly formulate equations, avoid flawed assumptions, and solve complex system problems with greater precision and confidence.

Takeaways

• 😀 Open systems exchange extensive properties (mass, energy, charge, or momentum) with their surroundings through bulk material transfer.
• 😀 Closed systems do not transfer mass or charge but can exchange energy or momentum, for example, through heat or gravitational force.
• 😀 Isolated systems do not exchange any extensive properties (mass, energy, charge, or momentum) with their surroundings.
• 😀 The generation and consumption terms in accounting equations describe the creation and destruction of extensive properties within a system.
• 😀 A chemical reaction in a system requires accounting equations to track non-conserved extensive properties created or destroyed in the process.
• 😀 Energy interconversion occurs when one form of energy is converted into another, leading to a depletion of the initial energy form in the system.
• 😀 Conserved properties like total mass, energy, charge, linear momentum, and angular momentum cannot be created or destroyed, and thus use conservation equations.
• 😀 Accounting equations are used for non-conserved properties, especially when energy or mass is generated or consumed within a system.
• 😀 Accumulation terms represent the net gain or loss of an extensive property within a system over time.
• 😀 Steady-state systems have no change in property values over time, while dynamic systems exhibit changes in property values, leading to positive or negative accumulation.

Q & A

What are the three main types of systems described in the transcript?

The three main types of systems described are open, closed, and isolated systems. An open system exchanges mass, energy, charge, or momentum with its surroundings. A closed system exchanges energy and momentum but not mass. An isolated system does not exchange any extensive properties with its surroundings.

What is the key difference between an open and a closed system?

The key difference is that an open system exchanges mass, energy, charge, or momentum with its surroundings, while a closed system only exchanges energy and momentum, but not mass.

How are generation and consumption terms used in accounting equations?

Generation and consumption terms describe the creation or destruction of an extensive property within a system. These terms are important in accounting equations when dealing with non-conserved properties, such as during chemical reactions or energy interconversion.

What is the role of a chemical reaction in a system's generation and consumption terms?

In a system with a chemical reaction, generation and consumption terms are required to account for the non-conserved properties. These reactions result in the creation or destruction of substances, which need to be considered in the system's accounting equations.

What does the term 'accumulation' refer to in the context of system analysis?

Accumulation refers to the net gain or loss of an extensive property within a system over a given time period. It describes how the amount of a property changes within the system.

What is the difference between a steady state and a dynamic state?

In a steady state, the system's variables do not change over time, and the accumulation term is zero. In a dynamic state, at least one variable changes over time, leading to either a positive or negative accumulation of properties within the system.

Why is it important to correctly label a system as open, closed, or isolated?

Labeling a system correctly helps in identifying the correct governing equations and making appropriate assumptions. It ensures that the system's behavior is modeled accurately, leading to proper application of accounting and conservation equations.

How does energy interconversion affect the system's accounting equations?

In systems with energy interconversion, one form of energy is converted to another. This conversion results in the depletion of the original energy form, and accounting equations must be used to track this change, especially when analyzing specific types of energy within the system.

What types of properties are governed by conservation equations?

Conserved properties, such as total mass, elemental mass, energy, net charge, and momentum, are governed by conservation equations. These properties cannot be created or destroyed within the system or the universe.

How do assumptions about a system affect the application of equations?

The assumptions made about a system, such as whether it is open, closed, isolated, steady, or dynamic, directly impact the application of accounting and conservation equations. Incorrect assumptions can lead to errors in solving for the system's behavior.