i would like to solve the exercice chapter 5-exercice 195 from Thermodynamics an
ID: 2994518 • Letter: I
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i would like to solve the exercice chapter 5-exercice 195 from Thermodynamics an engineering approach the 7th edition
The turbocharger of an internal combustion engine consists of a turbine and a compressor. Hot exhaust gases flow through the turbine to produce work and the work output from the turbine is used as die work input to the compressor. The pressure of ambient air is increased as it flows through the compressor before it enters the engine cylinders. Thus, the purpose of a turbocharger is to increase the pressure of air so that more air gets into the cylinder. Consequently more fuel can be burned and more power can be produced by the engine. In a turbocharger exhaust gases enter the turbine at 4 degree C and 12 kPa at a rate of .2 kg/s and leave at 35T. Air enters the compressor at 5 degree C and 1 kPa and leaves at 13 kPa at a rate of .18 kg/s. The compressor increases the air pressure with a side effect: It also increases the air temperature, which increases the possibility of a gasoline engine to experience an engine knock. To avoid this, an after cooler is placed after the compressor to cool the warm air by cold ambient air before it enters the engine cylinders. It is estimated that the after cooler must decrease the air temperature below 8 degree C if knock is to be avoided. The cold ambient air enters the after-cooler at 3 degree C and leaves at 4 degree C. Disregarding any frictional losses in the turbine and the compressor and treating the exhaust gases as air, determine (a) the temperature of the air at the compressor outlet and (b) the minimum volume flow rate of ambient air required to avoid knock.Explanation / Answer
For compressor:
T2 / T1 = (P2 / P1)^((n-1)/n)
T2 / (50+273) = (130/100)^((1.4-1)/1.4)
T2 = 348 K (= 75 deg C)
m_comp*Cp*(T2 - T_aftercooler) = m_amb*Cp*(Temp. change of ambient air)
0.018*(75 - 80) = m_amb*(40 - 30)
m_amb = -0.0087 kg/hr (Since m_amb turns to be negative, there is something wrong with input values.)
V_amb = m_amb / rho....where rho = ambient density = P/RT = 100*10^3 / (287*(40+273)) = 1.11 kg/m^3
V_amb = -0.0087 / 1.11 = -0.0078 m^3/s
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