Plate-fin heat exchanger suitable for rack-mountable cooling unit

A plate-fin heat exchanger, comprising:

• a series of spaced-apart, substantially parallel plates;
• each plate being spaced from each adjacent plate by a plurality of fins forming sets of substantially parallel, longitudinally extending fluid flow channels between adjacent plates;
• the fins being configured and sealed relative to the plates so that each set of fluid flow channels is substantially transverse to each adjacent set of fluid flow channels whereby there is a first group of fluid flow channel sets and a second group of fluid flow channel sets that is substantially transverse to the first group of fluid flow channel sets;
• the first group of fluid flow channel sets forming a gas coolant flow path through the heat exchanger;
• the second group of fluid flow channel sets forming a liquid coolant flow path through the heat exchanger substantially transverse to the gas coolant flow path;
• the heat exchanger having a thickness substantially transverse to the gas coolant flow path and substantially transverse to the liquid coolant flow path;
• characterized in that:
• the gas coolant flow path has a length that is at least twice the thickness substantially transverse to the gas coolant flow path and substantially transverse to the liquid coolant flow path.