12.6   Natural gas at 238C, 1 bar enters a furnace with the

(a)   the molar flow rate of the entering air at 2, in kmol/min.

(b)   the mass flow rate of oxygen in the exiting stream, in kg/min.

 

 

 

 

20% C H , 80%  Air

 

3   8

 

following molar analysis: 40% propane (C3H8), 40% ethane

(C2H6), 20% methane (CH4).  Determine

(a)   the analysis in terms of mass fractions.

(b)  the partial pressure of each component, in bar.

(c)   the mass flow rate, in kg/s, for a volumetric flow rate of 20 m3/s.

m·                                               1 = 5 kg/min

 

 

Air (21% O2, 79% N2)

Fig. P12.10

 

3% C3H8,

97% Air

 

 

a.  A gas mixture in a piston–cylinder assembly consists of 2 lb of N2 and 3 lb of He. Determine

(a)   the composition in terms of mass fractions.

(b)   the composition in terms of mole fractions.

(c)   the heat transfer, in Btu, required to increase the mixture temperature from 70 to 1508F, while keeping the pressure constant.

(d)   the change in entropy of the mixture for the process of part (c), in Btu/ 8R.

For parts (c) and (d), use the ideal gas model with constant specific heats.

b.  Two kg of a mixture having an analysis on a mass basis of 30% N2, 40% CO2, 30% O2 is compressed adiabatically from 1 bar, 300 K to 4 bar, 500 K. Determine

(a)   the work, in kJ.

(b)   the amount of entropy produced, in kJ/K.

c.  As illustrated in Fig. P12.13, an ideal gas mixture in a piston–cylinder assembly has a molar analysis of 30% carbon dioxide (CO2) and 70% nitrogen (N2). The mixture is cooled at constant pressure from 425 to 325 K. Assuming constant specific heats evaluated at 375 K, determine the heat transfer and the work, each in kJ per kg of mixture.

 

 

 

p = constant

xCO2 = 0.3                            T1 = 425K

(a)   Neglecting potential energy effects, determine the power input to the compressor, in kW.

(b)   If the compression is polytropic, evaluate the polytropic exponent n and the exit pressure, in bar.

 

 

 

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1-----------2.6----------- Â----------- Â -----------Nat-----------ura-----------l g-----------as -----------at -----------238-----------C, -----------1 b-----------ar -----------ent-----------ers----------- a -----------fur-----------nac-----------e w-----------ith----------- th-----------e -----------(a)----------- Â-----------  t-----------he -----------mol-----------ar -----------flo-----------w r-----------ate----------- of----------- th-----------e e-----------nte-----------rin-----------g a-----------ir -----------at -----------2, -----------in -----------kmo-----------l/m-----------in.----------- (-----------b)Â----------- Â ----------- th-----------e m-----------ass----------- fl-----------ow -----------rat-----------e o-----------f o-----------xyg-----------en -----------in -----------the----------- ex-----------iti-----------ng -----------str-----------eam-----------, i-----------n k-----------g/m-----------in.----------- Â-----------  -----------  -----------  ----------- Â-----------  -----------20%----------- C -----------H ,----------- 80-----------% Â----------- Ai-----------r ----------- 3-----------  ----------- 8----------- ----------- fo-----------llo-----------win-----------g m-----------ola-----------r a-----------nal-----------ysi-----------s: -----------40%----------- pr-----------opa-----------ne -----------(C3-----------H8)-----------, 4-----------0% -----------eth-----------ane----------- (-----------C2H-----------6),----------- 20-----------% m-----------eth-----------ane----------- (C-----------H4)-----------. Â----------- De-----------ter-----------min-----------e -----------(a)----------- Â-----------  t-----------he -----------ana-----------lys-----------is -----------in -----------ter-----------ms -----------of -----------mas-----------s f-----------rac-----------tio-----------ns.----------- (-----------b)Â-----------  t-----------he -----------par-----------tia-----------l p-----------res-----------sur-----------e o-----------f

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