I've got this diagram visualising the interrelation of various reaction extends Xi on the duties of reactors R101 and R102, consequentially dictating recycle ratio R, purge and makeup flow. After playing around with my first draft for a few hours, I'm still not quite content with the result:
That's my code. Suggestions on improvement are greatly appreciated.
\begin{figure}[!ht]
\centering
\scalebox{1.2}[1.2]{
\begin{tikzpicture}[node distance=2cm,>=stealth',bend angle=45,auto]
\tikzstyle{place}=[circle,thick,draw=blue!75,fill=blue!20,minimum size=6mm]
\tikzstyle{red place}=[place,draw=red!75,fill=red!20]
\tikzstyle{transition}=[rectangle,thick,draw=black!75,
fill=black!10,minimum size=13mm]
\tikzstyle{every label}=[red]
\begin{scope}[xshift=0cm]
\node[]
at (-4, -2) (start) {};
\node[]
at (4, -2) (end) {};
\node [red place,tokens=0]
(w1') {};
\node [place] (c1') [below of=w1'] {};
\node [red place] (s1') [below of=c1',xshift=-15mm,label=left:$\xi_1$] {};
\node [red place,tokens=0]
(s2') [below of=c1',xshift=15mm,label=right:$\xi_2$] {};
\node [transition] (e1') [left of=c1'] {}
edge [post,bend left] (w1')
edge [post] (s1')
edge [pre] (s2')
edge [pre] (c1')
edge [pre,dotted] (start);
\node [transition] (l1') [right of=c1'] {}
edge [post] (c1')
edge [pre] (s1')
edge [post] (s2')
edge [pre,bend right] node[swap] {} (w1')
edge[post,dotted] (end);
\node[]
at (-2, -2) (c) {R101};
\node[]
at (2, -2) (c2) {R102};
\node[red]
at (0, +0.65) (c2) {$\xi_3$};
\node[blue]
at (0, -1.35) (c2) {$R$};
\node[black]
at (-5, -2) (c2) {make-up};
\node[black]
at (4.5, -2) (c2) {purge};
\end{scope}
\end{tikzpicture}
}
\end{figure}