Thermal Buoyancy Engine

Nitinol Thermal Buoyancy Engine for Underwater Gliders: Fall 2013-Spring 2014 (as an undergraduate researcher and a member of the MIT Marine Robotics Team, advised by Franz Hover and Chris Welch)

Goal: design a thermal buoyancy engine actuated with nitinol wire that is powered using the energy stored in the ocean's thermocline

Role: iteratively designed, fabricated, and testing a miniature nitinol buoyancy engine

 When the glider is in warm surface water, the nitinol contracts, making the vehicle negatively buoyant and causing it to dive.  When the glider reaches ~150m, the cold ocean water causes the nitinol to elongate, making the vehicle positively buoyant and initiating an ascent.  

Subimage on nitinol transformation from: https://commons.wikimedia.org/wiki/File:Nitinol_Transformation.jpg

 

 

Before testing the engine in water, benchtop tests using electric current to heat the wire showed the mechanism working correctly

 

 

 

 

 

Preliminary (left) and final design iterations (right) of miniature thermal buoyancy engine.  In the final design, the pressure in the syringe is enough to cause the piston to retract without a spring.  Metal plates replaced plastic plates to prevent temperature-induced distortion.  Reduced friction pulleys with no gap between roller and support plates (to prevent slipping and catching).  Changes in the length of the nitinol wire induced by temperature differences successfully altered the buoyancy of the device.