# New Member RanCam

1. Feb 21, 2016

### rancam

Hi,I'm a new member,both to this site and to physics.My interest is gases (specifically CO2) under pressure,and how how pressure affects their properties.At 65 years I don,t have the time to build up the requisite knowledge and math to thoroughly study this subject,so I appreciate any help.

2. Feb 21, 2016

### mgkii

Hi @rancam which properties in particular are you interested in regarding CO2 (and why)? If you're interested in purely how pressure affects this gas have a look at this diagram; find your temperature, move across to your pressure and it will give you it's phase.

It probably goes without saying that there's a load of great info in Wiki for CO2 as well :-)
https://en.wikipedia.org/wiki/Carbon_dioxide

Best regards
Matt

3. Feb 22, 2016

### rancam

The properties I would like to calculate are temperature,enthalpy and entropy,but especially entropy. Here's some more background info.The one third of a stroke takes one third of a second.I have a book on CO2 properties over a wide range of pressures and temperatures.According to it the properties of CO2 at 670 psi (which is 47.2 bar in IS units) is -42 j/kg/k.At the end of one third of the stroke the pressure is still 670 psi because some of the gas has expanded into the far cylinder while the remainder is being being compressed by the piston.I want to know whether the remaining gas will have (although I would prefer to calculate it) lower,higher, or the same entropy.I thought maybe I could look up these properties for the gas as if there was expansion and no compression,(which would bring the pressure down to 34.85 bar) and then the properties as if there was compression and no expansion (which would bring the pressure up to 56.6 bar) and then take an average of the two sets of properties,but I thought I should ask an expert first.