ADVANCED THERMODYNAMICS ENGINEERING phần 8

Pin được đặt trên piston để ngăn chặn chuyển động của nó. Nitơ khí là isothermally tiêm vào khối lượng cho đến khi áp suất đạt đến 2 bar. Phân mol nitơ trong giai đoạn khí là gì? Giả sử rằng N2 không hòa tan trong chất lỏng. Điều gì sẽ xảy ra nếu có là chân không trong thời gian tiêm N2. | dnk dt V N S . 35 1. Steady State System Under steady state conditions dNk dt 0 dN dt 0 dmk dt 0 dm dt 0 and from Eq. 28 m i m e. Likewise from Eq. 33 N i N gen N e. n. Example 13 A combustor is fired with 2 kmole of CO and 3 k mole of O2. When the combustor is just started very little CO burns. As it warms up more and more CO are burnt. Assume that mass does not accumulate within the reactor. At the point when the combustor achieves 40 efficiency write the mass conservation mole balance and energy conservation equations. If the combustor reaches a steady state with combustion efficiency of 90 write the mass conservation and mole balance equations. Solution The reaction equation is written as follows 2 CO 3 O2 NCO e CO NCO2 e CO2 NO2 e O2. A Since mass does not accumulate within the reactor the atom balance for C and O atoms yields 2 NCO e NCO2 e and B 2 6 NCO e 2 NCO2 e 2 NO2 e . C 2 - NCO e 2. D With the three equations Eqs. B through D we can solve for the three unknowns NCO e NCO2 e and NO2 e . NCO e NCO2 e and NO2 e . The mass conservation implies dmCO dt 2x28 m CO gen - m CO gen. Similarly dNCO dt 2 N CO gen - N CO gen Normally NCO gen is a negative quantity since CO is consumed. The term dNCO dt represents the accumulation destruction since negative rate of CO in the reactor. Similarly for CO2 dNCO2 dt 0 NCO2 gen - where NCO2 gen 0 since CO2 is a product that is generated. In the initial periods when the combustor is being fired the CO2 concentration gradually increases due to the term dNCO2 dt. Similarly for 90 efficiency NCO e NCO2 e and NO2 e dmcO dt 2x28 m CO gen - m CO gen. The combustor is operating steadily so that dmcO dt 0 m CO gen - kg s Similarly dNCO dt 2 - N CO gen NCO gen. Since dNCO dt 0 N CO gen - k mole s-1 and dNcO2 dt 0 N CO 2 gen - If the combustor is operating steadily then dNCO2 dt 0 and N CO 2 gen k mole s-1 N O 2 gen kmole s-1. .