Temperature drop during emptying of pressurized tank
Temperature drop during emptying of pressurized tank
(OP)
Dear Forum,
i have a system with a pressurized air tank connected via a filter regulator (automatically adjusting throttling valve) to an air motor. Air is dry.
The concept is that when I open the valve, air passes from the air tank through the filter regulator which adjusts the outlet pressure to a certain level. The air motor will then be able to operate at constant pressure as long as the pressure in the tank is higher than the set point of the filter regulator.
Now my question is; what will happen to the temperature inside the tank, assuming that the heat capacity of the tank is negligible and the tank is isolated.
I know that over the filter regulator no external work is done , so w=o, and assuming adiabatic conditions -> h_in = h_out, and there will be a small temperature drop due to the Joules Thompson effect. Over the air motor, assuming an completely isentropic process the temperature will drop acc. to laws of isentropic expansion:
T2/T1 = (p2/p1)^(1-1/gamma),
gamma = cp/cv = 1.4 for air
However I am unsure how this affects the temperature of the remaining air in the tank. During the open valve period the tank pressure drops from p1 to p2, but what thermodynamic conditions govern?
Thanks
i have a system with a pressurized air tank connected via a filter regulator (automatically adjusting throttling valve) to an air motor. Air is dry.
The concept is that when I open the valve, air passes from the air tank through the filter regulator which adjusts the outlet pressure to a certain level. The air motor will then be able to operate at constant pressure as long as the pressure in the tank is higher than the set point of the filter regulator.
Now my question is; what will happen to the temperature inside the tank, assuming that the heat capacity of the tank is negligible and the tank is isolated.
I know that over the filter regulator no external work is done , so w=o, and assuming adiabatic conditions -> h_in = h_out, and there will be a small temperature drop due to the Joules Thompson effect. Over the air motor, assuming an completely isentropic process the temperature will drop acc. to laws of isentropic expansion:
T2/T1 = (p2/p1)^(1-1/gamma),
gamma = cp/cv = 1.4 for air
However I am unsure how this affects the temperature of the remaining air in the tank. During the open valve period the tank pressure drops from p1 to p2, but what thermodynamic conditions govern?
Thanks





RE: Temperature drop during emptying of pressurized tank
RE: Temperature drop during emptying of pressurized tank
David Simpson, PE
MuleShoe Engineering
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"
RE: Temperature drop during emptying of pressurized tank
TTFN

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RE: Temperature drop during emptying of pressurized tank
David Simpson, PE
MuleShoe Engineering
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"
RE: Temperature drop during emptying of pressurized tank
TTFN

FAQ731-376: Eng-Tips.com Forum Policies
Need help writing a question or understanding a reply? forum1529: Translation Assistance for Engineers
RE: Temperature drop during emptying of pressurized tank
David Simpson, PE
MuleShoe Engineering
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"
RE: Temperature drop during emptying of pressurized tank
RE: Temperature drop during emptying of pressurized tank
Thank you all for the input, but I am looking for a thermodynamical answer rather than practical.
Please notice that the case I am talking about the tank is:
- isolated, so adiabatic
- the tank itself has no heat capacity
There tank does not receive air from a high pressure source during the operation.The starting pressure in the tank is 7 barg
The pressure after the filter regulator is 3 barg
The pressure after the air motor is 0 barg (1 atmosphere absolute)
RE: Temperature drop during emptying of pressurized tank
That is an interesting picture. My explanation for it is that the pressure on the inlet side does note change significantly fast (if at all) compared to the heat transfer with its surroundings.
In my case the tank size is sized in such a way that the pressure would drop from 7 barg to 3.53 barg during 10 minutes of operation (open valve).
Also I consider my system as adiabatic and the piping and tank material has no heat capacity --- so purely a speculative setup.
RE: Temperature drop during emptying of pressurized tank
David Simpson, PE
MuleShoe Engineering
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"
RE: Temperature drop during emptying of pressurized tank
I don't know which kind of engineer you are, but if you are like me I want to know about the physics involved when designing a system, and not only rely on practical experience.
For the record, this is not a study related question, so I will qoute your signature:
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"
RE: Temperature drop during emptying of pressurized tank
RE: Temperature drop during emptying of pressurized tank
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