Find the Mass Flow Rate Through the Nozzle

[Northbysouth]

Homework Statement

Helium gas flows through a well-insulated nozzle at steady state. The temperature and the velocity at the inlet are 550°R and 150 ft/s, respectively. At the exit, the temperature is 400°R and the pressure is 40 lbf/in². The area of the exit is 0.0085 ft². Using the ideal gas model with k = 1.67, and neglecting potential energy effects, determine the mass flow rate in lb/s through the nozzle

Homework Equations

The Attempt at a Solution

My initial response is to use:

m' = ρvA

but I'm not sure if this is how they want me to find the answer. My professor mentioned:

C_p - C_c = R

Is this referring to specific heats?

My notes also say C_p is constant. What is this referring to? Likewise, what is the significance of the k=1.67?

 

[SteamKing]

k is the ratio of specific heats of the gas:

k = Cp/Cv

 

[Northbysouth]

What is the significance of giving me the ratio of the specific heats of the helium?