让箭头在单个节点的不同点进入和离开

Question

我希望从本质上使用 TikZ 重新制作下面的图像，但使用更多颜色并在框内使用不同的语言。

我尝试了以下方法：

\documentclass[tikz]{standalone}

  \usepackage{mathtools}
    \usetikzlibrary{shapes,arrows}
    % Define block styles
      \tikzstyle{HOTRES} = [rectangle, draw, fill=red!20, 
      text width=20em, text centered, rounded corners, minimum height=1.5em]
      \tikzstyle{COLDRES} = [rectangle, draw, fill=blue!20, 
      text width=20em, text centered, rounded corners, minimum height=1.5em]
      \tikzstyle{line} = [draw, -latex']
      \tikzstyle{cloud} = [draw, ellipse,fill=yellow!20, node distance=3cm,
      minimum height=4em]

\begin{document}
    \begin{tikzpicture}

    % Reservoirs
    \node [HOTRES] (HOT)  at (0,2) {Kuuma};
    \node [COLDRES] (COLD) at (0,-2) {Kylmä};

    % Heat transfer
    \node [cloud] (HOT->COLD) at (-2,0) {\(Q\)};
    \node [cloud] (COLD->HOT) at (2,0) {\(Q\)};

    % Lines
    \draw [line] (HOT) -- (HOT->COLD) -- (COLD);
    \draw [line] (COLD) -- (COLD->HOT) -- (HOT);

  \end{tikzpicture}
\end{document}

生成了如下图片：

我只是不知道如何实现箭头（可以是简单的 TikZ 箭头）在不同点离开和进入同一节点的效果，以便最后一张图片中的所有箭头都是垂直的。我如何才能相对轻松地实现这种效果？

Answer 1

这很简单，如果您使用坐标，(nodea -| nodeb)您就会得到nodea的y坐标和nodeb的x坐标。

离题：另请参阅应该使用 \tikzset 还是 \tikzstyle 来定义 TikZ 样式？。

\documentclass[tikz]{standalone}

  \usepackage{mathtools}
    \usetikzlibrary{shapes,arrows.meta}
    % Define block styles
    \tikzset{
        HOTRES/.style={
            rectangle, draw,     fill=red!20, 
            text width=20em, text centered, rounded corners, minimum height=1.5em
            },
        COLDRES/.style ={
            rectangle, draw, fill=blue!20, text width=20em, text centered, rounded corners, minimum height=1.5em
            },
        line/.style = {draw, -Latex},
        cloud/.style = {
            draw, ellipse,fill=yellow!20, node distance=3cm,
            minimum height=4em
            }
      }

\begin{document}
    \begin{tikzpicture}

    % Reservoirs
    \node [HOTRES] (HOT)  at (0,2) {Kuuma};
    \node [COLDRES] (COLD) at (0,-2) {Kylmä};

    % Heat transfer
    \node [cloud] (HOT->COLD) at (-2,0) {\(Q\)};
    \node [cloud] (COLD->HOT) at (2,0) {\(Q\)};

    % Lines
    \draw (HOT.south -| HOT->COLD) -- (HOT->COLD.north);
    \draw [line] (HOT->COLD) -- (COLD.north -| HOT->COLD);
    \draw (COLD.north -| COLD->HOT) -- (COLD->HOT);
    \draw [line] (COLD->HOT) -- (HOT.south -| COLD->HOT);
  \end{tikzpicture}
\end{document}

Answer 2

\documentclass[border = 5pt]{standalone}

\usepackage{tikz}
\usetikzlibrary{calc}
\usetikzlibrary{positioning}
\usetikzlibrary{shadows.blur}

\begin{document}
\begin{tikzpicture}[
  reserv/.style = {
    draw = #1, fill = #1!50, text = white,
    rounded corners = 5pt,
    minimum width = 6cm,
    minimum height = 1cm, inner sep = 1pt,
    drop shadow
    },
  proc/.style = {
    draw = #1, fill = #1!50, text = black,
    circle,
    minimum size = 1.5cm,
    drop shadow, inner sep = 1pt,
    },
  arrow/.style = {
    line width = 1mm, draw = gray!30, >=latex
  }
  ]

  \node[reserv=red] (HOT) at (0, 0){$T_\textrm{\tiny HOT}$};
  \node[proc=yellow] (M) at (-2, -3) {$\textrm{eff.} = \eta_M$};
  \node[proc=yellow] (L) at ( 2, -3) {$\textrm{eff.} = \eta_L$};
  \node[reserv=blue] (COLD) at (0, -6){$T_\textrm{\tiny COLD}$};

  \draw[arrow, ->] (HOT.south -| M) -- (M) node[left, midway, black]{$Q$};
  \draw[arrow, <-] (HOT.south -| L) -- (L) node[right, midway, black]{$\displaystyle{\frac{\eta_M}{\eta_L}}Q$};
  \draw[arrow, <-] (COLD.north -| M) -- (M) node[left, midway, black]{$(1 - \eta_M)Q$};
  \draw[arrow, ->] (COLD.north -| L) -- (L) node[right, midway, black]{$\eta_M Q\displaystyle{\left(\frac{1}{\eta_L} - 1\right)}$};
  \draw[arrow, ->] (M) -- (L) node[below, midway]{$\eta_M Q$};

  \node[left = 0.1cm of M, black, align = center] {More\\efficient};
  \node[right = 0.1cm of L, black, align = center] {Less\\efficient};
  \node[above = 1cm] at ($(M)!0.5!(L)$){$\eta_M \geq \eta_L$};

\end{tikzpicture}
\end{document}