Low grade heat (waste heat at low temperature) from solar thermal energy, geothermal energy, and industrial waste heat is of enormous importance for energy sustainability. Lots of countries including America and China have been engaged in the research of how to efficiently capture and utilize the resource. However, compared to conventional energy, low grade heat has the limitations of low density, high investment and sophisticated recycling technology, which hampers its large-scale utilization and results in energy waste.
In order to blaze a new trail in the respect, the Technical Institute of Physics and Chemistry, Chinese Academy of Sciences (TIPC) proposed a novel technical strategy of harvesting low grade heat to generate electricity based on thermosyphon effect of room temperature liquid metal (LM). LM has much higher thermal conductivity than that of water and can serve as an excellent heat transfer medium. It can remain at liquid state until more than 2000 °C while having high chemical stability.
Heat is transferred from heat source to the generator through LM driven by thermosyphon effect and then converted to electricity. Thermosyphon refers to a phenomenon of passive heat exchange based on natural convection which circulates liquid without a pump. Driving force of liquid is buoyancy evolving from density gradients produced by temperature differences of fluid. Therefore, no moving parts and energy are needed.
A conceptual system was constructed and an open circuit voltage of 2.62 V with an electrical output power of 110 mW was yielded when the heating power was 45.6 W. This method resolves the difficulty of installing an electric generator in confined space and significantly enlarges the area for converting heat to electricity. Due to its simplicity, avoidance of moving parts, wide working temperature range, and self powering feature, this electricity generation system is extremely reliable, completely silent, and flexible. The work has been published in Applied Physics Letters.
Figure 1 Conceptual experiment of harvesting heat to generate electricity with thermosyphon effect based on room temperature liquid metal. ( Image by TIPC )
Figure 2 Liquid metal based thermoelectric generation system for waste heat recovery. ( Image by TIPC )
