Thermodynamics I: Energy & Heat Transfer

1. Thermodynamics I: Energy &Heat Transfer

3. Objectives • Comprehend the various forms of energy including potential/kinetic, thermal, and mechanical • Understand the process of energy conversion • Comprehend the heat transfer process of conduction, convection, and radiation

4. Introduction • Naval ships use either fossil fuel or nuclear fuel as energy for operation • Definition of energy? • Types of energy/sources • Important for ALL officers to have basic understanding of engineering behind naval vessels

5. Thermodynamics • Def’n: science concerned with the interrelationship between thermal energy and mechanical energy • Energy conversion of greatest significance on ship is thermal mechanical • Heat transfer: science that deals with methods by which thermal energy is able to translate

6. Classifications of Energy

7. Thermal Energy • Def’n: Energy associated primarily with systems of molecules (vice particles) • Internal Energy (stored): • PE: associated w/ forces of attraction between molecules (bonding) • KE: associated with motion/activity of molecules (vibration, rotation, translation)

8. Thermal Energy - Heat • Heat: thermal energy in transition (parallel of work) - must have DT • Temperature: the measure of an object’s internal kinetic energy • Units for heat: BTU

9. Mechanical Energy • Energy associated with large bodies or objects • Potential: relative position between particles • PE = mgh • Kinetic: relative velocities between particles • KE = 1/2mv2

10. Mechanical Energy - Work • Work: mechanical energy in transition (affect of an object using force over a distance) • Units: same as energy (ft-lbf or J) • Ex: Is a bullet moving through air at high speed producing work?

11. Power • Def’n: measure of the rate at which work is done • Units: Hp or J/s • Ex: Who was done more work? • Man who carries 55 lb box up 10ft of stairs in one minute, or • Woman who carries 55 lb box up 10ft of stairs in 30 seconds?

12. Mechanisms of Heat Transfer • Energy moves from higher temp -> lower temp • Types: conduction, radiation, and convection • Convention: • Higher temp: source • Lower temp: sink or receiver

13. Conduction • Def’n: transfer of thermal energy when source and sink are in physical contact • Energy transfer occurs layer to layer • General Conduction Equation: Q=kA/L*DT

14. Radiation • Def’n: electromagnetic wave phenomenon (like radio or light) • No physical contact • All objects radiate some energy • Transparent substances are poor absorbers of radiant energy -> radiation passes through (i.e. tinted glass)

15. Convection • Not really a transfer, but a transport • Def’n: transportation or movement of some portions of a fluid within a mass of fluid • Due to density differences caused by temperature differences • Natural circulation: due to density only • Forced circulation: mechanical device

16. Effects of Heat Transfer • Sensible vs Latent Heat • Sensible Heat: • Heat absorbed or rejected with a corresponding change of temp, but no change in phase • Latent Heat: • Heat absorbed or lost w/ a change in phase

17. Effects of Heat Transfer

18. Effects of Heat Transfer • Latent Heat of Vaporization/Condensation: • Liquid Vapor (no change in temp) • Latent Heat of Fusion: • Liquid Solid • Saturated liquid/saturated vapor • Subcooled liquid • Superheated vapor

19. Effects of Heat Transfer

20. Questions?