ENERGY ANALYSIS OF CLOSED SYSTEMS Omil C.Chatib, M.Si

Transkripsi

1 ENERGY ANALYSIS OF CLOSED SYSTEMS Omil C.Chatib, M.Si

2 1. Moving Boundary Work

3 1. Moving Boundary Work

4 1. Moving Boundary Work (Isokhoric)

5 1. Moving Boundary Work (Isobaric)

6 1. Moving Boundary Work (Isobaric)

7 1. Moving Boundary Work (Isothermal)

8 1. Moving Boundary Work (Polytropic)

9 1. Moving Boundary Work (Polytropic)

10 1. Moving Boundary Work (Polytropic)

11 1. Moving Boundary Work (Polytropic)

12 1. Moving Boundary Work (Polytropic) Contoh Soal : 1. Suatu fluida pada tekanan 3 bar dengan volume spesifik 0,18 m 3 /kg, diisikan dalam suatu silinder yang berpiston (torak), berekspansi secara reversibel mencapai tekanan 0,6 bar yang mengikuti persamaan p = c/v 2, dengan c adalah konstanta. Hitung kerja yang dilakukan oleh fluida pada piston!

13 1. Moving Boundary Work (Polytropic) Contoh Soal : 2. Sebanyak 1 kg fluida diisikan dalam sebuah silinder pada tekanan awal 20 bar. Dilanjutkan ekspansi secara reversibel dibelakang suatu piston dengan mengikuti hukum pv 2 = konstan sampai volumenya mencapai 2 kali. Fluida kemudian didinginkan secara reversibel pada tekanan konstan sampai piston kembali ke posisi awalnya. Panas kemudian diberikan secara reversibel dengan piston dikunci tertutup dalam suatu posisi sampai tekanannya naik mencapai nilai awal 20 bar. Hitung kerja bersih yang dilakukan oleh fluida! Untuk volume awal 0,05 m 3.

14 1. Moving Boundary Work (Polytropic) Contoh Soal : 3. Fluida tertentu pada 10 bar diisikan pada silinder yang berdampingan dengan suatu piston, volume awalnya 0,05 m 3. Hitung kerja yang dilakukan bila fluida tersebut mengembang secara reversibel a. Pada tekanan konstan sampai volume akhirnya 0,2 m 3. b. Menurut persamaan linier sampai volume akhirnya 0,2 m 3 dan tekanan akhirnya 2 bar. c. Menurut persamaan p.v = c sampai volume akhirnya 0,1 m 3. d. Menurut persamaan p.v 3 = c sampai volume akhirnya 0,06 m 3. e. Menurut persamaan p = (A/V 2 ) (B/V) sampai volume akhirnya 0,1 m 3 dan tekanan akhirnya 1 bar.

15 2. Energy Balance for Closed Systems For constant rates, the total quantities during a time interval t are related to the quantities per unit time as... For a closed system undergoing a cycle, the initial and final states are identical, and thus E system = E 2 - E 1 = 0 Then the energy balance for a cycle simplifies to E in E out = 0 or E in = E out Noting that a closed system does not involve any mass flow across its boundaries, the energy balance for a cycle can be expressed in terms of heat and work interactions as

16 2. Energy Balance for Closed Systems

17 2. Energy Balance for Closed Systems

18 2. Energy Balance for Closed Systems

19 2. Energy Balance for Closed Systems

20 2. Energy Balance for Closed Systems

21 2. Energy Balance for Closed Systems

22 2. Energy Balance for Closed Systems

23 3. Specific Heats The specific heat is defined as... the energy required to raise the temperature of a unit mass of a substance by one degree In general, this energy depends on how the process is executed. In thermodynamics, we are interested in two kinds of specific heats: specific heat at constant volume c v and specific heat at constant pressure c p.

24 3. Specific Heats The specific heat at constant pressure cp is always greater than cv because at constant pressure the system is allowed to expand and the energy for this expansion work must also be supplied to the system.

25 4. Internal Energy, Enthalpy, and Specific Heats of Ideal Gases

26 4. Internal Energy, Enthalpy, and Specific Heats of Ideal Gases

27 4. Internal Energy, Enthalpy, and Specific Heats of Ideal Gases

28 4. Internal Energy, Enthalpy, and Specific Heats of Ideal Gases

29 4. Internal Energy, Enthalpy, and Specific Heats of Ideal Gases

30 4. Internal Energy, Enthalpy, and Specific Heats of Ideal Gases

31 4. Internal Energy, Enthalpy, and Specific Heats of Ideal Gases

32 4. Internal Energy, Enthalpy, and Specific Heats of Ideal Gases

33 5. Internal Energy, Enthalpy, and Specific Heats of Solids and Liquids Internal Energy Changes Enthalpy Changes

34 5. Internal Energy, Enthalpy, and Specific Heats of Solids and Liquids Enthalpy Changes

35 5. Internal Energy, Enthalpy, and Specific Heats of Solids and Liquids

36 5. Internal Energy, Enthalpy, and Specific Heats of Solids and Liquids

37 5. Internal Energy, Enthalpy, and Specific Heats of Solids and Liquids

38 MASS AND ENERGY ANALYSIS OF CONTROL VOLUMES Omil C.Chatib, M.Si

39 Flow Work and The Energy of a Flowing Fluid Unlike closed systems, control volumes involve mass flow across their boundaries, and some work is required to push the mass into or out of the control volume. This work is known as the flow work, or flow energy, and is necessary for maintaining a continuous flow through a control volume.

40 Flow Work and The Energy of a Flowing Fluid To push the entire fluid element into the control volume, this force must act through a distance L. Thus, the work done in pushing the fluid element across the boundary (i.e., the flow work) is...

41 Flow Work and The Energy of a Flowing Fluid Total Energy of a Flowing Fluid

42 Flow Work and The Energy of a Flowing Fluid Energy Transport by Mass

43 Flow Work and The Energy of a Flowing Fluid Energy Transport by Mass Steam is leaving a 4-L pressure cooker whose operating pressure is 150 kpa. It is observed that the amount of liquid in the cooker has decreased by 0.6 L in 40 min after the steady operating conditions are established, and the cross-sectional area of the exit opening is 8 mm2. Determine... (a) the mass flow rate of the steam and the exit velocity, (b) the total and flow energies of the steam per unit mass, and (c) the rate at which energy leaves the cooker by steam.

44 Flow Work and The Energy of a Flowing Fluid Energy Transport by Mass (a) Saturation conditions exist in a pressure cooker at all times after the steady operating conditions are established. Therefore, the liquid has the properties of saturated liquid and the exiting steam has the properties of saturated vapor at the operating pressure. The amount of liquid that has evaporated, the mass flow rate of the exiting steam, and the exit velocity are...

45 Flow Work and The Energy of a Flowing Fluid Energy Transport by Mass (b) Noting that h = u + Pv and that the kinetic and potential energies are disregarded, the flow and total energies of the exiting steam are... (c) The rate at which energy is leaving the cooker by mass is simply the product of the mass flow rate and the total energy of the exiting steam per unit mass,

46 Energy Analysis of Steady-Flow Systems

47 Energy Analysis of Steady-Flow Systems

48 Energy Analysis of Steady-Flow Systems

49 Some Stedy-Flow Engineering Devices 1. Nozzels and Diffusers

50 Some Stedy-Flow Engineering Devices 1. Nozzels and Diffusers

51 Some Stedy-Flow Engineering Devices 1. Nozzels and Diffusers

52 Some Stedy-Flow Engineering Devices 2. Turbines and Compressors

53 Some Stedy-Flow Engineering Devices 2. Turbines and Compressors

54 Some Stedy-Flow Engineering Devices 2. Turbines and Compressors

55 Some Stedy-Flow Engineering Devices 2. Turbines and Compressors

56 Some Stedy-Flow Engineering Devices 3. Throttling Valves

57 Some Stedy-Flow Engineering Devices 3. Throttling Valves

58 Some Stedy-Flow Engineering Devices 4. Mixing Chambers and Heat Exchangers

59 Some Stedy-Flow Engineering Devices 4. Mixing Chambers and Heat Exchangers

60 Some Stedy-Flow Engineering Devices 4. Mixing Chambers and Heat Exchangers

61 Some Stedy-Flow Engineering Devices 4. Mixing Chambers and Heat Exchangers

62 Some Stedy-Flow Engineering Devices 4. Mixing Chambers and Heat Exchangers

63 Some Stedy-Flow Engineering Devices 4. Mixing Chambers and Heat Exchangers

64 Some Stedy-Flow Engineering Devices 5. Pipe and Duct Flow

65 Some Stedy-Flow Engineering Devices 5. Pipe and Duct Flow

66 Energy Analysis of Unstedy-Flow Processes

67 Energy Analysis of Unstedy-Flow Processes

68 Energy Analysis of Unstedy-Flow Processes

69 Energy Analysis of Unstedy-Flow Processes

70 Energy Analysis of Unstedy-Flow Processes

71 Energy Analysis of Unstedy-Flow Processes