Finding Heat Flow in a Brayton Cycle for Helium

[sportsrules]

The question gives a picture of a brayton cycle with temperature on the x-axis and pressure on the y-axis. It is for the monatomic gas, helium, and we are told that there are two moles. The diagram consists of two adiabatic processes and two isobaris processes. You are given two temparatures and the asked to find the other two. I did that just fine. However, then it asks you to find the heat flow (delta Q) per kilogram of helium for the entire cycle. I know that delta Q of adiabatic processes are 0, so I would only have to worry about the isobaric processes. I know that for the isobaric parts, the delta Q will be equal to n*Cp*change in temperature. So, to find the heat flow per kilogram, would I simply just say that since there are 250 moles in 1 kg of helium, I could use 250 moles/kg for n in the equation? I would appreciate any help!

 

[Andrew Mason]

I know that for the isobaric parts, the delta Q will be equal to n*Cp*change in temperature. So, to find the heat flow per kilogram, would I simply just say that since there are 250 moles in 1 kg of helium, I could use 250 moles/kg for n in the equation?

Yes.

AM

 

[thepatientmental]

Yes, you are correct. To find the heat flow per kilogram of helium for the entire cycle, you would use the equation delta Q = n*Cp*change in temperature, where n is the number of moles and Cp is the specific heat capacity. Since there are 250 moles in 1 kg of helium, you would use 250 moles/kg for n in the equation. This will give you the total heat flow for the entire cycle, and then you can divide it by the mass of helium (1 kg) to get the heat flow per kilogram.