The concept of Adiabatic is basically the isolation of a system in a realm where energy doesn't flow either way. Adiabatic compression and expansion is a common phenomenon harnessed in equipments and machines to heat or otherwise cool. The practical application of adiabatic can vary in design and technique, hence my question. If I have a tank of nitrogen gas at 300°C and 4500 psi and I want to cool the gas to 25°C and fill the nitrogen into a large balloon to a pressure of 20 psi, how can I harness adiabatics (especially adiabatic expansion) to cool the gas to my desired temperature between the tank and balloon.
$\begingroup$
$\endgroup$
4
-
1$\begingroup$ If energy does not flow, how will the temperature change? $\endgroup$– Solar MikeCommented Feb 21, 2019 at 11:19
-
1$\begingroup$ Read a textbook or take a class, your lacking fundamentals. Maybe someone else is patient enough to walk you through basic thermodynamics here, I'm not. Good luck. $\endgroup$– martCommented Feb 21, 2019 at 13:40
-
$\begingroup$ @Solar Mike During adiabatic expansion, the internal energy of the gas is used to do work on the surrounding(can be seen by applying 1st law to the expansion process).For an ideal gas temperature decreases with decrease in internal energy.I can't understand your question(i.e. the actual reason for asking this question). $\endgroup$– user17332Commented Feb 21, 2019 at 13:54
-
3$\begingroup$ @Mohan I asked as I was hoping or expecting the OP to think about their own question.... If you look at the questions the OP has asked about this topic - round and round the mulberry bush comes to mind. You are, however, welcome to craft an answer yourself... $\endgroup$– Solar MikeCommented Feb 21, 2019 at 13:56
Add a comment
|
1 Answer
$\begingroup$
$\endgroup$
2
Adiabatic expansion of nitrogen at room temperature will produce Joule-Thomson cooling. If your tank were only slightly above room temperature, the resulting balloon would be quite cold. The bad news is all real gases have an inversion temperature where the J-T coefficient becomes negative and throttling the gas to a lower pressure makes the temperature go UP. Looking at the chart on Wikipedia, I have to wonder if you (or your professor) chose that temperature because it is close to the inversion temperature of nitrogen (348 °C). Adiabatically, taking 300 °C nitrogen from 310 bar (no mixed units, please) to 1 bar, you will get a little cooling, exactly how much requires an Mollier (Pressure-Enthalpy) diagram for nitrogen. Above 350 °C, you are not going to cool it by any adiabatic process.
-
$\begingroup$ I've looked up the mollier diagram for nitrogen but I'm having a hard time making sense of it. And it also reads ideal gas at 0 K, I guess these diagrams are temperature specific. Can you please help with maybe the diagram or the eventually result for the amount of cooling I'll get? $\endgroup$ Commented Feb 22, 2019 at 3:46
-
$\begingroup$ Throttling is isenthalpic. Since you have a pressure-enthalpy diagram, isenthalpic processes are straight lines. With the chart I found, if you find the point for 300°C, which would be just below 600°K, and 300 atm and follow it to 1 atm, the temperature is ...it looks like 620°K. If you start with cooler gas, you will had 300°K nitrogen at 600 atm and reduced the pressure to 1 atm, it looks like it would be cooled to about 260°K. Going from a warm room temperature to below the freezing point of water. $\endgroup$ Commented Feb 22, 2019 at 20:46