Good afternoon all,

I am doing some back of napkin calcs for work and am having trouble finding an answer (or one that I can understand--its been a while since undergrad). We have a valve that has particular flow rate requirements to prevent unseating the valve seal. This is a mass flow rate and our customer has requested a pressure flow rate (so instead of lbm/s, they want psi/s). I can do it for a simple isothermal system using the ideal gas law, but system is adiabatic.

I have found various explanations, but ultimately arrive at PV^Cp/Cv=Constant.

Question

Good afternoon all,

 I am doing some back of napkin calcs for work and am having trouble finding an answer (or one that I can understand--its been a while since undergrad). We have a valve that has particular flow rate requirements to prevent unseating the valve seal. This is a mass flow rate and our customer has requested a pressure flow rate (so instead of lbm/s, they want psi/s). I can do it for a simple isothermal system using the ideal gas law, but system is adiabatic.

 I have found various explanations, but ultimately arrive at PV^Cp/Cv=Constant.

osprey · Answer

Hi kerky I've had a head scratch, and now have lots of splinters in my fingers. The formula you quote $$pV ^{\gamma}=constant$$ where gamma's the ratio of the specifi heats is one I've just checked from a UK A level physics book. It's for adiabatics as you say. 
However ... 
I can’t really understand your question ... Is lbm/s the same as “pounds mass per second” ?
I don’t really know what “pressure flow rate” means – I’m ok, with pressure difference, and with pressure difference causing a mass flow. But I don’t see how pressure can “flow” as such ... 
At the risk of having something thrown at me, you could always just fasten the seal down "tightly", say to a couple of atmospheres ?
Let me know of any developments.
Did you have a good feed with the said napkin ?