What was Lonnie Johnson researching when he accidentally conceived the Super Soaker?

Answer

A heat pump refrigeration system

The invention was not a planned endeavor for a toy but rather an unintended outcome of scientific research regarding a sophisticated new plumbing system. Specifically, the experiments involved creating a heat pump refrigeration system based on water evaporation. During this work, a forceful stream of water generated during a test provided the conceptual breakthrough for a powerful, pressurized water gun, shifting the focus from climate control engineering to consumer toy manufacturing.

What was Lonnie Johnson researching when he accidentally conceived the Super Soaker?
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