BE2103 Thermodynamics in Biosystem_Module 3 Segment 1

Summary

This module of Thermodynamics in Biosystems explores the various forms of energy and their roles in biological and engineering systems. It distinguishes between macroscopic energies, like kinetic and potential energy, and microscopic energies, such as internal, chemical, latent, and nuclear energy. The session also explains energy transfer, mechanical work, and the concept of flow work in fluids. Key principles, including the first law of thermodynamics, energy conversion, and efficiency, are discussed, along with stationary and control volume systems. By examining energy at molecular and system levels, the module highlights how energy is stored, transferred, and transformed in practical and natural processes.

Takeaways

• 🔥 Energy exists in various forms including thermal, mechanical, kinetic, potential, electric, magnetic, chemical, and nuclear, all contributing to the total energy of a system.
• ⚡ Thermodynamics focuses on changes in energy rather than its absolute value, allowing engineers to set a reference point for total energy.
• 🔍 Energy in a system can be classified as macroscopic (kinetic and potential) and microscopic (internal energy related to molecular activity).
• ⚙️ Kinetic energy is due to the motion of the system relative to a reference frame, while potential energy is due to its position in a gravitational field.
• 🌡️ Internal energy includes molecular kinetic energies (translational, rotational, vibrational, electron spin) and energies from atomic bonds (chemical energy).
• 💧 Latent energy is the internal energy associated with phase changes, occurring without altering chemical composition, like melting or vaporization.
• ☢️ Nuclear energy is the tremendous energy stored in the nucleus of atoms due to strong nuclear forces.
• 🛠️ Mechanical energy can be fully converted to work via ideal mechanical devices, while thermal energy cannot be directly and completely converted to mechanical work.
• -
• 💨 Flow work or flow energy arises when pressure forces act on a fluid through a distance, contributing to the mechanical energy of flowing fluids.
• 🌐 Energy interactions at a system boundary occur as either heat transfer (driven by temperature difference) or work, the only two forms for closed systems.
• 📏 Stationary systems, where kinetic and potential energies remain constant, simplify analysis as changes in total energy equal changes in internal energy.
• 💡 Understanding energy transfer and conversion efficiencies is crucial in analyzing engineering and biosystem thermodynamics processes.

Q & A

What are the main forms of energy discussed in this thermodynamics module?

The main forms of energy discussed are thermal, mechanical, kinetic, potential, electric, magnetic, chemical, and nuclear energy.

How does thermodynamics treat the total energy of a system?

Thermodynamics does not provide the absolute value of total energy; it only deals with changes in total energy. The total energy can be assigned a convenient reference value of zero.

What is the difference between macroscopic and microscopic forms of energy?

Macroscopic energy is the energy a system possesses as a whole with respect to an external reference frame, such as kinetic and potential energy. Microscopic energy relates to molecular structure and activity, independent of outside reference frames, and their sum is called internal energy.

What constitutes the internal energy of a system?

Internal energy is the sum of all microscopic forms of energy, including translational, rotational, vibrational, spin energy of electrons, nuclear spin energy, sensible energy (kinetic energy of molecules), latent energy (associated with phase changes), and chemical energy (associated with atomic bonds).

How is kinetic energy of a system defined?

Kinetic energy is the energy a system possesses due to its motion relative to a reference frame. If all parts of the system move with the same velocity, kinetic energy can be calculated using equation 3.2 (not provided in the transcript).

What is potential energy in thermodynamics?

Potential energy is the energy a system possesses as a result of its position in a gravitational field, calculated relative to a reference elevation (equation 3.3).

What are stationary systems in thermodynamics?

Stationary systems are closed systems whose velocity and elevation of the center of gravity remain constant during a process. For these systems, changes in total energy are equal to changes in internal energy.

How is energy associated with flowing fluids expressed?

For control volumes with fluid flow, energy flow is expressed in rate form using mass flow rate (ṁ) and volume flow rate (V̇). Flow work, or energy required to move the fluid through the system boundary, is included as part of mechanical energy.

What is the difference between static and dynamic forms of energy?

Static energy refers to energy stored within a system, such as internal, kinetic, and potential energy. Dynamic energy refers to energy in transit across a system boundary, which appears as heat transfer or work.

Why is thermal energy not considered mechanical energy?

Thermal energy cannot be completely and directly converted into mechanical work by an ideal mechanical device, unlike kinetic or potential energy. It requires an intermediate process for conversion.

What is flow work and how is it related to mechanical energy?

Flow work is the work done by pressure forces to move a fluid through a control volume boundary. It is not a form of energy itself, but when combined with kinetic and potential energy, it constitutes the mechanical energy of a flowing fluid.

How does temperature affect the internal energy of a gas?

The kinetic energy of molecules is proportional to temperature, so higher temperatures increase molecular activity, resulting in higher internal energy.