Thermodynamics (Mass flow rate & Volume flow rate)

[jaredogden]

Homework Statement

Steam at 400oC enters a nozzle with an average velocity of 20 m/s. If the specific volume and the flow area at the inlet are measured as 0.1 m^3/kg and 0.01 m^2 respectively, determine (a) the volume flow rate in m^3/s, and (b) the mass flow rate in kg/s

Homework Equations

voldot = AV
mdot = (rho)(voldot)

The Attempt at a Solution

voldot = (0.01m^2)*(20m/s)
= 0.2 m^3/s

mdot = ?*(0.2m^3/s)

I am unsure what to do here. I am given specific volume 0.1 m^3/kg but I need density (kg/m^3) so if specific volume is V/m and density is m/v.. gosh I can't even think straight this late I feel like I'm going to pull some illegal math move and just do the reciprocal of specific volume to get density..

 

[Q_Goest]

Hi jaredogden,

I am unsure what to do here. I am given specific volume 0.1 m^3/kg but I need density (kg/m^3) so if specific volume is V/m and density is m/v.. gosh I can't even think straight this late I feel like I'm going to pull some illegal math move and just do the reciprocal of specific volume to get density..

Sounds like you're feeling a bit uncomfortable about how specific volume and density are related. Try this:
http://en.wikipedia.org/wiki/Volume_(thermodynamics)#Specific_volume

 

[jaredogden]

Well I know that specific volume is the inverse of density but I remember seen on a website that specific volume is the inverse of density but you can't get density by doing the inverse of specific volume so I was confused.

 

[Q_Goest]

Well I know that specific volume is the inverse of density but I remember seen on a website that specific volume is the inverse of density but you can't get density by doing the inverse of specific volume so I was confused.

If specific volume is the inverse of density then why can't you get density by taking the inverse of specific volume? It's just a straightforward equation that relates one to the other, isn't it?

 

[jaredogden]

Well that was my thinking and when I read that I got really confused and didn't understand what the guy running that website was saying. Thanks for the help though.