\documentclass[11pt]{article}
\usepackage[a4paper,margin=18mm]{geometry}
\usepackage{tikzphysics}
\pagestyle{empty}
\begin{document}
\section*{Thermodynamic components and energy flow}
\begin{center}
\begin{tikzpicture}[>=latex,font=\small]
 \node[gas chamber] (G) {$p,V,T$};
 \node[insulated wall] (I) at (3,0) {};
 \node[conducting wall] (C) at (6,0) {};
 \node[below=10pt] at (G.south) {Gas chamber};
 \node[below=10pt] at (I.south) {Insulating wall};
 \node[below=10pt] at (C.south) {Conducting wall};
\end{tikzpicture}
\end{center}
\begin{center}
\begin{tikzpicture}[>=latex,font=\small]
 \pic (E) {heat engine diagram};
 \pic (R) at (7,0) {refrigerator diagram};
 \node[below=12pt] at (E-cold.south) {Heat engine};
 \node[below=12pt] at (R-cold.south) {Refrigerator / heat pump};
\end{tikzpicture}
\end{center}
Heat and work labels denote positive magnitudes. Arrow direction distinguishes
energy entering and leaving the device. The schematic does not calculate efficiency.
\clearpage
\section*{Pressure--volume processes}
\begin{center}
\begin{tikzpicture}[>=latex,font=\small]
 \foreach \name/\style/\xx/\yy in {
 A/isothermal process/0/0,B/isobaric process/7/0,
 C/isochoric process/0/-5,D/adiabatic process/7/-5,
 E/polytropic process/0/-10}{
  \node[\style] (\name) at (\xx,\yy) {};
  \node[above] at (\name.pressure-end) {$P$};
  \node[right] at (\name.volume-end) {$V$};
  \fill (\name.start) circle(1.5pt);
  \fill (\name.end) circle(1.5pt);
  \draw[->] (\name.process-45)--(\name.process-55);
  \node[below=14pt] at (\name.south) {\style};
 }
\end{tikzpicture}
\end{center}
Curves use consistent author-chosen pressure and volume units. Defaults show
expansion, except the isochoric example, which shows decreasing pressure.
\clearpage
\section*{Closed cycles}
\begin{center}
\begin{tikzpicture}[>=latex,font=\small]
 \node[carnot cycle,pv width=6,pv height=4] (C) {};
 \node[above] at (C.pressure-end) {$P$};
 \node[right] at (C.volume-end) {$V$};
 \foreach \state/\position in {A/above,B/above,C/below,D/below}{
  \fill (C.state-\state) circle(1.5pt);
  \node[\position] at (C.state-\state) {\state};
 }
 \foreach \branch in {hot,expansion,cold,compression}{
  \draw[->] (C.\branch-45)--(C.\branch-55);
 }
 \node[below=20pt] at (C.south) {Carnot cycle: two isotherms and two reversible adiabats};
 \node[rectangular cycle,pv width=6,pv height=4] (R) at (0,-7) {};
 \node[above] at (R.pressure-end) {$P$};
 \node[right] at (R.volume-end) {$V$};
 \foreach \branch in {AB,BC,CD,DA}{\draw[->] (R.\branch-45)--(R.\branch-55);}
 \foreach \state in {A,B,C,D}{\fill (R.state-\state) circle(1.5pt);}
 \node[below=20pt] at (R.south) {Clockwise isobaric--isochoric cycle};
\end{tikzpicture}
\end{center}
\end{document}