Thermodynamics Eng 103 Lecture 11 Chapter 6 Introduction Pre

Thermodynamicsengr 103 Lecture 11chapter 6introductionpressuretempera

Identify the main concepts introduced in the lecture, including pressure, temperature, and energy in thermodynamics. Understand the definitions and units of pressure (including atmospheric, gauge, absolute, and vacuum pressures) and their relationships. Know how to convert between different pressure types and units such as psi, Pa, bar, and mm Hg. Grasp the concept of temperature as a measure of atomic and molecular kinetic energy, with knowledge of the various scales (Celsius, Fahrenheit, Kelvin, Rankine), their conversion formulas, and what specific points like boiling and freezing points of water represent. Understand different forms of energy—potential (elastic and gravitational), kinetic, and internal energy—in terms of formulas and physical interpretations. Recognize how energy is transferred via work and heat, and the principles behind the first and second laws of thermodynamics. Application examples include checking which object exerts more pressure on the ground, converting pressures between absolute and gauge, and calculating energy transfer during heating of water.

Paper For Above instruction

Thermodynamics is a fundamental branch of physics and engineering that deals with the relationship between heat, work, and energy within a system. It encompasses various core concepts such as pressure, temperature, and different energy forms, which are essential for understanding how energy interacts and transforms in natural and engineered systems. A clear comprehension of these concepts enables engineers to analyze and optimize processes in numerous applications, from engines and turbines to cooling and heating systems.

Pressure in Thermodynamics

Pressure fundamentally refers to the normal force exerted by a fluid per unit area, mathematically expressed as P = F/A, and measured in units such as Pascal (Pa), pounds per square inch (psi), bar, or mm Hg. Atmospheric pressure, often taken as the standard pressure at sea level (1 atm = 101,325 Pa), influences many thermodynamic processes. Variations in pressure are categorized as gauge, absolute, or vacuum pressures. Gauge pressure measures the difference relative to atmospheric pressure, while absolute pressure references a perfect vacuum. For example, in tire inflation, the gauge pressure is the pressure above atmospheric, whereas the absolute pressure combines the gauge reading with atmospheric pressure, crucial for scientific calculations.

Pressure examples demonstrate the significance of understanding these relationships. For example, an elephant exerts less pressure on the ground than a woman wearing high heels due to the difference in force and contact surface area. Similarly, atmospheric pressure varies with altitude; Denver's atmospheric pressure (approximately 83.4 kPa) affects tire pressures computed with gauge and absolute readings, highlighting the importance of precise pressure measurement in engineering applications.

Temperature in Thermodynamics

Temperature quantifies the average kinetic energy of atoms and molecules, making it a key parameter in thermodynamic analysis. It can be measured on various scales: Celsius (ºC), Fahrenheit (ºF), Kelvin (K), and Rankine (ºR). Conversions between these scales are vital for consistent calculations. For example, boiling point and freezing point of water are 100°C and 0°C, respectively, with their corresponding Fahrenheit equivalents being 212°F and 32°F. Absolute temperature scales like Kelvin and Rankine are required for thermodynamic equations, as they begin at absolute zero — the theoretical point where atomic motion ceases.

Converting temperatures involves straightforward formulas, such as T(ºF) = 1.8 T(ºC) + 32, and T(K) = T(ºC) + 273. Recognizing the differences and applications of each scale ensures accurate analysis of temperature-dependent processes. Temperature change calculations use these conversion factors to compare effects across systems or different measurement standards.

Energy in Thermodynamics

Energy embodies the capacity to perform work and manifests in various forms, including potential, kinetic, and internal energy. Potential energy stored due to position (e.g., gravitational PE = mgz or elastic PE = ½ kx²) is significant in mechanical systems like springs and objects elevated against gravity. Kinetic energy, given by KE = ½ mv², depends on the mass and velocity of moving systems, exemplified by running athletes or moving machinery.

Internal energy encompasses all microscopic forms of energy within a system, including translational, rotational, and vibrational energies of molecules, as well as electronic and nuclear energies. Changes in internal energy are described by the first law of thermodynamics, often expressed as ΔU = Q – W, relating heat transfer (Q) and work done (W) in energy exchange. Sensible energy relates to temperature changes; latent energy involves phase changes, such as fusion or vaporization, requiring energy input without temperature change.

Applications and Implications

Practical examples highlight the importance of these concepts. Calculating the potential energy stored in a spring or the gravitational potential energy of an object illustrates fundamental energy principles. Energy transfer during water heating (Q = m cp ΔT) demonstrates the application of internal energy concepts. Similarly, understanding pressure variations, units, and conversions informs the design of systems like tires, pressure vessels, and atmospheric modeling.

Conclusion

In conclusion, the foundational ideas of pressure, temperature, and energy in thermodynamics provide necessary tools for analyzing energy systems. Recognizing units, conversion methods, and the physical significance of different energy forms equips engineers and scientists to optimize processes, improve system efficiency, and understand natural phenomena. Mastery of these principles forms the basis for advanced thermodynamic analysis, ensuring safe, effective, and innovative technological solutions that impact every facet of modern life.

References

• Cengel, Y. A., & Boles, M. A. (2015). Thermodynamics: An Engineering Approach. McGraw-Hill Education.
• Hoyt, J. E. (2008). Basic Thermodynamics. John Wiley & Sons.
• Çengel, Y. A., & Boles, M. A. (2015). Thermodynamics: An Engineering Approach. McGraw-Hill Education.
• Bejan, A. (2016). Advanced Engineering Thermodynamics. John Wiley & Sons.
• Sinnot, R. K. (2010). Mechanical and Electrical Equipment for Buildings. John Wiley & Sons.
• Rugh, J. P. (2004). Fundamentals of Thermodynamics. Springer.
• Turner, J. A. (2010). Introduction to Thermodynamics. Oxford University Press.
• Baumeister, B. (2010). Heat Transfer. ADIS International.
• Kakac, S., & Yener, Y. (1995). Heat Conduction. CRC Press.
• Moran, M. J., & Shapiro, H. N. (2010). Fundamentals of Engineering Thermodynamics. John Wiley & Sons.