# Methane Gas Density in Adiabatic Compressible Flow Hi.. The question above is one of the tutorial question from fluid mechanics textbook. In the textbook solution for this question, the density of the methane gas stream at downstream was computed with the ideal gas law equation. What I don't understand is it possible for us to compute the density of the methane stream at downstream with the equation on below provided we know the density of methane gas and mach number at downstream. From datasheet, the density of methane gas = 0.678 kg/m^3 and Mach number at downstream, Ma= 0.4537

The answer from the textbook solution was 2.858 kg/m^3 The text book answer is correct. I think you missed to calculate the density of the downstream of the shock. the equation you entered is valid only in the region 1 or in region 2. means the isentropic relations are not valid across the shock. Across the shock you have to use normal shock relations. Then you would get the right answer
• Hi Mike, probably the ratio of specific heats is different from my calculation. I have taken $k = 1.304$. apologies for not mentioning it. Nov 28 '17 at 9:43