Version with flux lines converted with stroke-to-path. Remove this file once wikimedia's servers start rendering mid-marks and dashed strokes correctly. Schematic of a spiral heat exchanger cross-section. The hot medium 1 warms the cold medium 2 flowing in the opposite direction (and, respectively, medium 2 cools medium 1 down)
<ul><li>derivative work: <a href="//commons.wikimedia.org/wiki/User:Anasofiapaixao" title="User:Anasofiapaixao">Anasofiapaixao</a></li>
<li><a href="//commons.wikimedia.org/wiki/File:Spiral_heat_exchanger.png" title="File:Spiral heat exchanger.png">Spiral_heat_exchanger.png</a>: <a href="//commons.wikimedia.org/wiki/User:Schmid" title="User:Schmid">Michael Schmid</a></li></ul>
CC BY 2.5
<ul><li><a href="//commons.wikimedia.org/wiki/File:Spiral_heat_exchanger.png" title="File:Spiral heat exchanger.png">Spiral_heat_exchanger.png</a></li></ul>