10/3/2011
Chemical Engineering Thermodynamics Prepared by: by: Dr. NINIEK Fajar Puspita Puspita,, M.Eng August, 20 2011 11 2011Gs_V_The 2011Gs_V_ The First Law of Thermodynamics_Open Systems
1
Lesson 5 Lesson
Topics
Descriptions
Lesson 5A
Konservasi massa
Mempresentasikan diskusi NM untuk sistem terbuka. Mempertimbangkan hubungan antara kecepatan alir massa, kecepatan alir volumetrik dan sifat-sifat fluida lokal.
Lesson 5B
Konservasi panas
Menerapkan hukum I termodinamika (FLT) pada sistem terbuka. Mempertimbangan interaksi kerja yang disebut dengan kerja aliran (flow work).
Lesson 5C
Proses-proses
Mempelajari penyederhanaan proses proses-proses proses keadaan tunak (steady) dan pengurangan dari persamaan ODE (Ordinary Differential Equation) ke persamaan aljabar. Menyederhanakan FLT untuk alat-alat nozzle, difuser, turbine, kompresor, throtting, mixing dan aliran didalam pipa dan didalam saluran pembuluh (duct flow).
steady state
2
1
10/3/2011
Lesson 5 Lesson
Topics
Descriptions
Lesson 5D
Neraca massa transien
Mempelajari bagaimana menerapkan prinsip konservasi massa pada d proses-proses transien t i dan d tidak tid k tunak t k (unsteady)
Lesson 5E
Neraca energi transien
Mempelajari bagaimana menerapkan FLT pada prosesproses transien dan tidak tunak.
3
Open and Closed Systems In Chapter 4 we studied closed systems in which nomass crossed the system boundaries. In this chapter we will be considering open systems. For closed systems we considered a control mass. The mass remains constant throughout the process. process Thus
`
` `
For open systems we consider a control volume. Th mass does The d nott necessarily il remain i constant. Thus, we must keep track of the mass flow rate min, and the mass flow rate mout, of the control volume .
4
2
10/3/2011
Mass Balance for Open Systems
5
Mass Balances: Systems with Multiple Inlets and Outlets
3
10/3/2011
Mass Flow Rate and Fluid Velocity
Equations for Determing the Mass Flow Rate
4
10/3/2011
Summary Chapter 5, Lesson A - The First Law of Thermodynamics - Open Systems `
CHAPTER 5, LESSON A - THE FIRST LAW OF THERMODYNAMICS - OPEN SYSTEMS
`
Memperkenalkan konservasi masa untuk open sistem Æ persamaan NM
Energy Balance on a Closed System
5
10/3/2011
Energy Balance on an Open System
Enthalpy Form of the 1st Law for Open Systems
6
10/3/2011
1st Law: Multiple Inlets & Outlets
Summary Chapter 5, Lesson B - Conservation of Mass `
CHAPTER 5, LESSON B - CONSERVATION OF MASS
7
10/3/2011
General Form of the 1st Law for Open Systems 1st Law: Enthalpy Form, Muliple Inlets & Outlets
Steady-State Energy Balances
8
10/3/2011
1st Law, Open Systems, Steady-State
Steady-State Mass Balances
9
10/3/2011
Single-Input, Single-Output Systems at SteadyState
Steady-State Processes: Building Blocks for Cycles Nama Proses
Tipe Proses
Diskripsi Proses
Efek atau Hasil
Nozzle
SISO
Decrease the crosssectional area for flow in a pipe
Increases velocity and decreases pressure
Diffuser
SISO
Increase cross-sectional area for flow
Decreases velocity & increases pressure
Turbine
SISO
Rotating machine that Decreases pressure, produces shaft work by density and usually reducing the pressure temperature as well. well
Compressor
SISO
Machine that uses shaft work to increase the pressure
Increases pressure, density and usually temperature as well
10
10/3/2011
Steady-State Processes: Building Blocks for Cycles
Nama Proses Process P Heat Exchanger
Tipe Proses
Diskripsi Proses
Efek atau Hasil
Heat transfer between H stream is Hot i cooled l d and d two flowing fluids. Two MIMO the cold stream is inlets and two outlets, warmed without mixing. SISO
Heat exchange with an Temperature increases or unspecified utility decreases stream
Stream Mixer
MISO
A "tee" tee in a pipe pipe. Two streams enter and mix and leave as a single stream
Most properties of the effluent are the massaverage of the properties of the two feed streams
Pipe or Duct
SISO
Fluid flow through a pipeor duct
No terms in the 1st Law cancel
Utility Heat Exchanger
1st Law for Nozzles and Diffusers
11
10/3/2011
Nozzle and Diffuser Example #1
12
10/3/2011
13
10/3/2011
1st Law for Turbines and Compressors
14
10/3/2011
Turbine and Compressor Example #2
15
10/3/2011
16
10/3/2011
17
10/3/2011
18
10/3/2011
19
10/3/2011
1st Law for Throttling Devices
Throttling Valve Example #3
20
10/3/2011
21
10/3/2011
22
10/3/2011
Heat Exchangers: Symbols & Strategy
1st Law for HEXs: SISO Applied Twice
23
10/3/2011
24
10/3/2011
25
10/3/2011
1st Law for Mixing Chambers
26
10/3/2011
Example Problem with Complete Solution
27
10/3/2011
28
10/3/2011
29
10/3/2011
30
10/3/2011
31
10/3/2011
1st Law for Pipe & Duct Flow
Summary Chapter 5, Lesson C - Conservation of Energy CHAPTER 5, LESSON C - CONSERVATION OF ENERGY ` Menerapkan Hukum I Termodinamika pada proses-proses steadystate dimana variabel-variabel state, variabel variabel proses roses tidak berubah dengan waktu. waktu ` ` `
`
Sifat-sifat fisis berbeda dari titik ke titik didalam sistem. Interaksi panas dan kerja diantara sistem dan lingkungannya juga tetap konstan. Pada keadaan steady-state berlaku persamaan aljabar, bukan persamaan diferensial.
Menganalisa alat proses dan menyederhanakan Hukum I Termodinamika berdasarkan pada karakteristik setiap alat.
32
10/3/2011
Summary Chapter 5, Lesson C - Conservation of Energy
Device
Objective
Nozzle
Menurunkan kecepatan fluida dengan menurunkan tekanan.
Diffuser
Menaikkan tekanan fluida dengan menurunkan kecepatannya.
Turbine
Kerja dihasilkan dengan menurunkan entalpi.
Compressor
Kerja merupakan input untuk menaikkan entalpi dan tekanan fluida.
Throttling Devices
Menurunkan tekanan tanpa kerja apapun dan sedikit perpindahan panas.
Heat Exchangers
Dua aliran bertukar panas tanpa pencampuran.
Mixing Chambers
Dua atau lebih aliran umpan bercampur dan membentuk aliran keluar tunggal.
Pipes & Ducts
Fluida mengalir melalui pipa atau saluran: persamaan Bernoulli.
33
