Thermo 3-4

Chapter 3: Energy Transfer by Heat and Work

1. Q: What is work in thermodynamics?
   A: Work is any transfer of energy (except heat) into or out of a system.

2. Q: What is the general formula for work done by a force?
   A: W=∫Fdx, where F is the force and dx is the displacement.

3. Q: How is work expressed for a gas in a piston-cylinder system?
   A: W=∫PdV, where P is pressure and dV is the change in volume.

4. Q: What does the area under a P−V curve represent?
   A: The area under a P−V curve represents the work done during the process.

5. Q: What is a path-dependent process?
   A: A path-dependent process is one where the work done depends on the path taken between the initial and final states.

6. Q: What is a path-independent process?
   A: A path-independent process depends only on the initial and final states, not the path taken (e.g., gravitational potential energy).

7. Q: What is the work done in a constant volume process?
   A: W=0, because dV=0.

8. Q: What is the work done in a constant pressure process?
   A: W=P(Vf​−Vi​), where Vf​ and Vi​ are the final and initial volumes.

9. Q: What is the work done in an isothermal process for an ideal gas?
   A: W=nRTln(Vi​Vf​​), where n is the number of moles, R is the gas constant, and T is the temperature.

10. Q: What is a polytropic process?
    A: A polytropic process is one where PVn=constant, and n is the polytropic index.

11. Q: What is electrical work?
    A: Electrical work is the work done when electrons cross the boundary of a system, calculated as W=∫VIdt, where V is voltage and I is current.

12. Q: What is shaft work?
    A: Shaft work is the work done by a rotating shaft, calculated as W=2πNT, where N is the number of revolutions per unit time and T is torque.

13. Q: What is spring work?
    A: Spring work is the work done by a linear elastic spring, calculated as W=21​k(x22​−x12​), where kk is the spring constant and x1​,x2​ are displacements.

14. Q: What is heat in thermodynamics?
    A: Heat is the transfer of energy across a system boundary due to a temperature difference.

15. Q: What are the three modes of heat transfer?
    A: Conduction, convection, and radiation.

16. Q: What is an adiabatic process?
    A: An adiabatic process is one where no heat is transferred into or out of the system (Q=0).

17. Q: What is the mechanical equivalent of heat?
    A: The mechanical equivalent of heat is the relationship between mechanical work and heat energy, established by Joule’s experiment.

18. Q: What is Joule’s experiment?
    A: Joule’s experiment demonstrated that mechanical work could be converted into heat, leading to the first law of thermodynamics.

19. Q: What is the relationship between work and heat in Joule’s experiment?
    A: The work done by falling weights is converted into heat, raising the temperature of water in a thermally insulated vessel.

Chapter 4: First Law of Thermodynamics

20. Q: What is the first law of thermodynamics for a closed system?
    A: ΔE=Q−W, where ΔE is the change in energy, Q is heat added, and W is work done by the system.

21. Q: What does the first law of thermodynamics state?
    A: Energy cannot be created or destroyed, only transferred or converted from one form to another.

22. Q: What are the components of energy E in the first law?
    A: Internal energy (U), kinetic energy (KE), and potential energy (PE).

23. Q: What is internal energy (U)?
    A: Internal energy is the energy associated with the microscopic motion and interactions of molecules within a system.

24. Q: What is kinetic energy (KE)?
    A: Kinetic energy is the energy due to the motion of the system, calculated as KE=21​mV2.

25. Q: What is potential energy (PE)?
    A: Potential energy is the energy due to the elevation of the system in a gravitational field, calculated as PE=mgz.

26. Q: What is the time rate form of the first law?
    A: dE​/dt​=Q˙​−W˙, where Q˙​ is the rate of heat transfer and W˙ is the rate of work done.

27. Q: What is the first law for a control volume?
    A: dtdECV​​=Q˙​−W˙+∑m˙i​hi​−∑m˙e​he​, where m˙ is mass flow rate and h is enthalpy.

28. Q: What is enthalpy (h)?
    A: Enthalpy is defined as h=u+Pv, where u is internal energy, P is pressure, and v is specific volume.

29. Q: What is the mass flow rate (m˙)?
    A: The mass flow rate is the rate at which mass crosses a boundary, calculated as m˙=ρVn​A, where ρ is density, Vn​ is velocity, and A is area.

30. Q: What is a steady-flow process?
    A: A steady-flow process is one where the properties of the system do not change with time.

31. Q: What is the energy balance for a steady-flow process?
    A: Q˙​+∑m˙i​hi​=W˙+∑m˙e​he​.

32. Q: What is a nozzle?
    A: A nozzle is a device that increases the velocity of a fluid by decreasing its pressure.

33. Q: What is a diffuser?
    A: A diffuser is a device that decreases the velocity of a fluid by increasing its pressure.

34. Q: What is a turbine?
    A: A turbine is a device that extracts work from a fluid by expanding it through a set of blades.

35. Q: What is a compressor?
    A: A compressor is a device that increases the pressure of a gas by doing work on it.

36. Q: What is a pump?
    A: A pump is a device that increases the pressure of a liquid by doing work on it.

37. Q: What is a heat exchanger?
    A: A heat exchanger is a device that transfers heat between two fluids at different temperatures.

38. Q: What is the Rankine cycle?
    A: The Rankine cycle is the ideal cycle for steam power plants, consisting of four processes: isentropic compression, constant pressure heat addition, isentropic expansion, and constant pressure heat rejection.

39. Q: What is the Brayton cycle?
    A: The Brayton cycle is the ideal cycle for gas turbine power plants, consisting of four processes: isentropic compression, constant pressure heat addition, isentropic expansion, and constant pressure heat rejection.

40. Q: What is the Otto cycle?
    A: The Otto cycle is the ideal cycle for spark-ignition engines, consisting of four processes: isentropic compression, constant volume heat addition, isentropic expansion, and constant volume heat rejection.

41. Q: What is the compression ratio in the Otto cycle?
    A: The compression ratio is the ratio of the maximum volume to the minimum volume in the cycle, r=VTDC​VBDC​​.

42. Q: What is the mean effective pressure (MEP)?
    A: The mean effective pressure is the average pressure that would produce the same amount of work as the actual cycle.

43. Q: What is the thermal efficiency of a heat engine?
    A: The thermal efficiency is the ratio of the net work output to the heat input, η=Qin​Wnet​​.

44. Q: What is the coefficient of performance (COP) of a refrigerator?
    A: The COP is the ratio of the heat removed from the cold reservoir to the work input, COP=Win​QL​​.

45. Q: What is the coefficient of performance (COP) of a heat pump?
    A: The COP is the ratio of the heat delivered to the hot reservoir to the work input, COP=Win​QH​​.

Additional Flashcards for Problem-Solving:

46. Q: How do you calculate the work done in a polytropic process?
    A: W=1−nP2​V2​−P1​V1​​, where n is the polytropic index.

47. Q: How do you calculate the heat transfer in a constant pressure process?
    A: Q=mcp​ΔT, where cp​ is the specific heat at constant pressure.

48. Q: How do you calculate the heat transfer in a constant volume process?
    A: Q=mcv​ΔT, where cv​ is the specific heat at constant volume.

49. Q: How do you calculate the power output of a turbine?
    A: W˙=m˙(hin​−hout​), where m˙ is the mass flow rate and h is enthalpy.

50. Q: How do you calculate the power input to a compressor?
    A: W˙=m˙(hout​−hin​), where m˙ is the mass flow rate and h is enthalpy.