\documentclass[border=3mm]{standalone}
\usepackage{luacoolprop}
\pgfplotsset{compat=1.18}
\usetikzlibrary{arrows.meta}
\begin{document}
\begin{tikzpicture}
\begin{axis}[
  width=13cm,height=8cm,
  xlabel={$h/{\rm kJ\,kg^{-1}}$},
  ylabel={$p/{\rm bar}$},
  ymode=log,
  grid=both,
  ymin=0.08,ymax=45,
]
\LCPAddPHPlots[
  fluid=R134a,
  isochore=false,
  isotherm=true,
  isentrope=false,
  labels=false,
  quality step=0.1,
  temperature preset=sparse
]
\LCPAddPHProcess[
  fluid=R134a,
  type=isentropic,
  from={pressure=1bar,quality=1},
  to={pressure=10bar},
  color=black,
  style={very thick,-Latex},
  label={$1\to2$},
  label pos=0.55,
  mark endpoints=true
]
\LCPAddPHProcess[
  fluid=R134a,
  type=quality,
  quality=0.5,
  from={temperature=50C},
  to={temperature=-20C},
  color=purple!80!black,
  style={very thick,-Latex},
  label={$Q=0.5$},
  label pos=0.50
]
\end{axis}
\end{tikzpicture}
\end{document}

.