Lentamentalisk wrote:However, if PVC has a lower specific heat (or is it heat capacity, I get them mixed up,) than the steel, which I'm pretty damn sure it does, it will absorb less energy before it reaches that temperature, even if it reaches that temperature in about the same time it takes steel to heat up.
Am I right about that?
Specific heat is the heat capacity per unit mass of material. Heat capacity is for an object. The relationship between the two is that the heat capacity = specific heat X mass of object.
So, when you compare say PVC with steel and you want to calculate the final temperatures you need to know the specific heats and the two masses.
<table border="1"><tr><td>Material</td><td>Specific Heat
(g/cc)</td></tr> <tr><td>PVC</td><td>0.25</td><td>1.4</td></tr> <tr><td>steel</td><td>0.4-0.5</td><td>7.8</td></tr> <tr><td> aluminum </td><td>0.96</td><td>2.7</td></tr> <tr><td>air (C<sub>v</sub>) </td><td>~0.3</td><td>~0.0013</td></tr></table>
Air and PVC have very similar specific heats. But the large difference in density means that in a typical gun there is a large swing in the temperature of the gases as they cool but only a minor change in the temperature of the PVC.
Of course, this is all steady state (equilibrium) stuff. The problem is that this isn't steady state, it is a dynamic process and that makes things much more comlex.