ME300Lecture23

ME300Lecture23 - Lecture 23: Energy Balance for Reacting...

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23.1 Lecture 23: Energy Balance for Reacting Systems From previous lecture: 1 st Law, energy balance: i i i i fuel react prod oo i f,i T 298 i i f,i T 298 i fuel prod react ii hh Q 0 n h n h n Q =q= n h (h h ) n h h ) n Assumptions: - SSSF - ∆KE = ∆PE = 0 - No work Combustion (Reaction) Chamber . Q CV Exhaust gases Products Reactants fuel air
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23.2 Question: » What is the condition of the products for maximum heat transfer? Answer: » T prod T surr : home furnace, for example (useful to know for maximum heating value) Energy Balance for Reacting Systems
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23.3 Example 23.1 Given: Ethane, C 2 H 6 , is burned completely with 30% excess air. The reactants are initially @ 298 K and 1 atm. Find: What is the maximum heat release from the reaction chamber? 30% excess air Products Ethane, C 2 H 6 at 298 K, 1 atm at T prod =T react 1 atm Q max
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23.4 Continue Example 23.1 Assumptions: » SSSF » ΔKE = ΔPE = 0 » No work, W = 0 » Constant pressure » Products and reactants are ideal gases Solution: » Stoichiometric combustion reaction: C 2 H 6 + a (O 2 + 3.76 N 2 ) → b CO 2 + c H 2 O + d N 2
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23.5 Continue Example 23.1 Continue Solution: » Stoichiometric atom balances: C: 2 = b → b = 2 H: 6 = 2 c → c = 3 O: 2 a = 2 b + c = 7 → a = 3.5 N: 2 a · 3.76 = 2 d → d = 13.16
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ME300Lecture23 - Lecture 23: Energy Balance for Reacting...

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