Propane Tank problem

by nineeyes
Tags: propane, tank
 P: 21 I've been having some trouble with the following Question. { A rigid tank contains 90% by volume propane at -40 F. The tank is then heated to 80 F. A pressure relief valve in the tank is set at 125 psi. Will any propane be vented. If yes, how much? Tables for propane at http://www.elyenergy.com/pdf/CO37.pdf } Please let me know if I'm doing this completely wrong. I was told that 90% by volume meant that 90% of the propane was liquid. I got v1 by using $$v_1=.9(.02763)+.1(3.13)$$ I was thinking that there were 3 states. The first process would be const. volume, up to 125 psi State 1 -- isochoric (v = const.) --> State 2 state 1 T1 =-40 F v1=.337 ft^3/lbm P1 = 16.2 psi state 2 T2 = 70.54 F v2 = .337 ft^3/lbm P2 = 125 psi then once it reaches 125 psi, I thought that it would be an isobaric, const. pressure, process until it reached 80 F. State 2 -- isobaric --> State 3 State 3 T3 = 80 F v3 = ?? P3 = 125 psi I was thinking if I could find v3, I could use it to find the amount (lb_mass) of propane that was vented. But I'm having some trouble with finding v3, not really sure how to solve for it. I'm pretty sure its in the super heated region though. Any help would be great, thanks.