Chemical and Thermal AnalysesofReactingSystemAnalyses of Reacting System

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Chapter 6

Chemical and Thermal

Analyses of Reacting System Analyses of Reacting System

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Chonnam Nat. Univ.

School of Mechanical Systems Engineering

Prof. Byung-Chul Choi

Chemical Reacting Systems

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Constant-Pressure, Fixed-Mass Reactor

Conservation of Energy

(1) h = u + Pv, u = h -Pv

Only work (P-dv work) at the piston (2)

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(3) Substituting (2), (3) into (1)

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(5)

(6)

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Substituting (7)-(9) into (6)

Energy conservation

미분

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Energy conservation Chemical production

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For mass conservation

Ni = V [Xi], dNi/dt = V ω’_i

i id l l li i dV/d

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using ideal-gas law to eliminate dV/dt

P=const. PV = ΣNi RuT, PdV/dt= ………..??

(14b) Substituting (14b) into (13b)

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V/N_j_j= 1/[X[ _j_j],],

The rate of change of the species molar concentration

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Constant-Volume, Fixed-Mass Reactor

Q’ – W’ = m du/dt, W’=0

for ideal-gases From (5)-(7)

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for ideal gases

To calculate dP/dt

Conservation Laws

Applying [X_i], ω’_i, N_i= V [X_i], dNi/dt = V ω’_i

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Project 2

Solve example 6.1)

Change fuel and properties, CH₄, C₃H₆ , C₃H₈,

C₄H₁₀, C₈H₁₈, CH₃OH

D d t O t 29 2008

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Due date : Oct. 29, 2008.

Well-Stirred Reactor

Mass conservation eq.

-Flame stabilization -NOx formation

called Longwell reactor

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The continuity eq.

The mass generation rate

Production rate Ignoring diffusional flux species mass flow rate

Longwell reactor inch

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Ignoring diffusional flux, species mass flow rate m’_i= m’ Y_i

Steady-state, dm/dt=0

완전혼합반응기, 완전혼합반응기, 출구 질량분율=내부 ” Conservation of Energy Eq.

N개 방정식과, N+1개 미지수 나머지 하나 방정식(T)

Steady-state, steady-flow, well-stirred Ignoring PE KE Ignoring PE, KE

Temperature ?

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A mean residence time :

Where,

ρ = P MW_mix/(R_uT)

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Plug-Flow Reactor

Assumptions

1 St d t t t d fl 1. Steady-state, steady-flow

2. No mixing in the axial direction.

3. Uniform properties, one-D flow.

4. Ideal friction flow.

5. Ideal-gas behavior.

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Conservation laws

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Mass conservation

x-momentum conservation

Energy conservation Species conservation

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Rearrange of the mass and energy conservations

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Species conservation

Rearrange of the mass and energy conservations h=h(T, Yi), dh/dx, dT/dx

Rearrange of the momentum conservations Rearrange of the momentum conservations, differentiate the ideal-gas eq. of state

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이상의 식들로부터

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Initial conditions

A residence time t_R dt_R/dx = 1/v_x

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Homework Chapter 6 Project Ex6 1)

Project Ex6.1) Problems 6.1, 6.7

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