Thermodynamics (Mass flow rate & Volume flow rate)

In summary, the problem involves determining the volume and mass flow rates of steam entering a nozzle at 400oC with given values for specific volume and flow area. The volume flow rate is calculated by multiplying the flow area by the average velocity, and the mass flow rate can be found using the equation mdot = (rho)(voldot), where mdot is the mass flow rate, rho is the density, and voldot is the volume flow rate. The confusion comes from the relationship between specific volume and density, but it can be solved by using the equation specific volume = volume/mass.
  • #1
jaredogden
79
0

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..
 
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  • #2
Hi jaredogden,
jaredogden said:
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
 
  • #3
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.
 
  • #4
jaredogden said:
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?
 
  • #5
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.
 

1. What is mass flow rate in thermodynamics?

Mass flow rate in thermodynamics refers to the amount of mass that passes through a specific point in a system per unit time. It is measured in kilograms per second and is an important parameter in understanding the dynamics of fluid flow.

2. How is mass flow rate calculated?

Mass flow rate can be calculated by dividing the mass of the substance passing through a specific point by the time it takes to pass through that point. This can be represented by the formula: mass flow rate = mass / time.

3. What is volume flow rate in thermodynamics?

Volume flow rate in thermodynamics refers to the amount of volume that passes through a specific point in a system per unit time. It is measured in cubic meters per second and is used to understand the flow dynamics of gases and liquids.

4. How is volume flow rate related to mass flow rate?

Volume flow rate and mass flow rate are related by the density of the substance flowing through the system. The relationship can be represented by the formula: volume flow rate = mass flow rate / density. This means that if the density of the substance is known, the volume flow rate can be calculated from the mass flow rate, and vice versa.

5. How is mass flow rate affected by changes in temperature and pressure?

Changes in temperature and pressure can affect the mass flow rate in a system. In general, an increase in temperature and a decrease in pressure will result in an increase in mass flow rate, while a decrease in temperature and an increase in pressure will result in a decrease in mass flow rate. This is because changes in temperature and pressure can alter the density of the substance, which in turn affects the mass flow rate.

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