Thermal Pulse Energy Harvesting Strategy and Device

Technology

This technology takes advantage of transient heat transfer properties to maximize the temperature difference between the hot and cold sides of the engine.  Heat transfer is not instantaneous so heat applied to the hot side of the engine will heat up the hot side before the other side (the cold side) experiences a temperature increase.  Before the heat flux penetrates to the cold side, the temperature difference between the two sides of the engine is maximized.  When a constant heat flux is applied to the engine, the cold side eventually warms up, reducing the temperature difference across the engine and the engine's harvesting effectiveness.  Delivering heat to the engine in pulses maintains the high temperature difference across the engine since the heat flux is cut off before the cold side warms up.  Then, the engine cools down so the next pulse can recreate the high temperature difference.  The heat pulse can either come from a non-steady heat source or be created with a thermal switch.Interrupting the heat flux to prevent the cold side from warming up can improve the heat harvesting efficiency and power.  In certain configurations, pulse heating can simultaneously increase power by 60% and increase efficiency by 15% over that of a constant heat flux at the same temperature.  With other configurations, pulse heating can increase the efficiency by more than 80% at a decreased power level.  

Problem Addressed

Thermal harvesting systems often consist of a heat sink and heat engine connected to a heat source.  In steady state operations, the overall temperature gradient provided by the heat source is split over the engine and heat sink so a portion of the temperature gradient is not available to the heat engine.  This technology uses pulses of heat, instead of a constant heat flux, to concentrate the temperature gradient over the heat engine and increase harvesting performance.  

Advantages      

• Increased heat harvesting efficiencySuitable for remote applications
• Efficient energy harvesting from time-variant and constant heat sources  

Publications

Thermal Pulse Energy Harvesting. Energy 57, (August 2013): 340-345.