ENERGY ANALYSIS OF CLOSED
SYSTEMS
1. Moving Boundary Work (Polytropic)
Contoh Soal :
1. Suatu fluida pada tekanan 3 bar dengan volume spesifik 0,18 m3/kg,
diisikan dalam suatu silinder yang berpiston (torak), berekspansi secara reversibel mencapai tekanan 0,6 bar yang mengikuti persamaan p = c/v2 , dengan c adalah konstanta. Hitung kerja yang
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 pv2 = konstan sampai volumenya mencapai 2 kali. Fluida
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 m3. Hitung
kerja yang dilakukan bila fluida tersebut mengembang secara reversibel …
a. Pada tekanan konstan sampai volume akhirnya 0,2 m3.
b. Menurut persamaan linier sampai volume akhirnya 0,2 m3 dan
tekanan akhirnya 2 bar.
c. Menurut persamaan p.V = c sampai volume akhirnya 0,1 m3. d. Menurut persamaan p.V3 = c sampai volume akhirnya 0,06 m3. e. Menurut persamaan p = (A/V2) – (B/V) sampai volume akhirnya
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
∆Esystem = E2- E1= 0 Then the energy balance for a cycle simplifies to
Ein – Eout= 0 or Ein= Eout
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.
3. Specific Heats
5. Internal Energy, Enthalpy, and Specific Heats of Solids and Liquids
Internal Energy Changes
5. Internal Energy, Enthalpy, and Specific Heats of Solids and Liquids
MASS AND ENERGY ANALYSIS
OF CONTROL VOLUMES
Flow Work and The Energy of a Flowing Fluid
Unlike closed systems, control volumes involve mass flow across their
Flow Work and The Energy of a Flowing Fluid
Flow Work and The Energy of a Flowing Fluid
Flow Work and The Energy of a Flowing Fluid
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
Flow Work and The Energy of a Flowing Fluid
Energy Transport by Mass
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...
