Thermodynamic engines have inherent difficulties in achieving high compression ratios and in achieving the near constant temperature compression and expansion processes needed to approximate Carnot equivalent cycles. Solid-state thermoelectric converters that utilize semiconductor materials have only been able to achieve single digit conversion efficiency. Alkali Metal Thermoelectric Converters (AMTEC), which operate on a modified Rankine cycle and the Stirling engine, have inherent limitations and these systems have not achieved performance levels as envisioned.

The Johnson Thermo-Electrochemical Convertor (JTEC) is an all solid-state device that operates on the Ericsson cycle. Equivalent to Carnot, the Ericsson Cycle offers the maximum theoretical efficiency available from a converter operating between two temperatures. The JTEC system utilizes the electro-chemical potential of fluid pressure applied across a proton conductive membrane (PCM). The membrane and a pair of electrodes form a Membrane Electrode Assembly (MEA) similar to those used in fuel cells. However, in the JTEC the hydrogen circulates continually inside the device, which is different from a fuel cell in which hydrogen is consumed and must be continually replenished.



(Click diagrams to enlarge)

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System

On the high-pressure side of the MEA, hydrogen gas is oxidized resulting in the creation of protons and electrons. The pressure differential forces protons through the membrane causing the electrodes to conduct electrons through an external load. On the low-pressure side, the protons are reduced with the electrons to re-form hydrogen gas. This process can also operate in reverse. If current is passed through the MEA a low-pressure gas can be “pumped” to a higher pressure.

The JTEC uses two membrane electrode assembly (MEA) stacks. One stack is coupled to a high temperature heat source and the other to a low temperature heat sink. Hydrogen circulates within the engine between the two MEA stacks via a counter flow regenerative heat exchanger. For some applications the engine does not require oxygen or a continuous fuel supply, only a temperature difference of at least 10% between two areas. Like a gas turbine engine, the low temperature MEA stack is the compressor stage and the high temperature MEA is the power stage. The MEA stacks will be designed for sufficient heat transfer with the heat source and sink to allow near constant temperature expansion and compression processes. This feature coupled with the use of a regenerative counter flow heat exchanger will allow the engine to approximate the Ericsson cycle.

The engine is scalable and has applications ranging from supplying power for Micro Electro Mechanical Systems (MEMS) to power for large-scale applications such as fixed power plants. The technology is applicable to field generators, land vehicles, air vehicles and spacecraft. The JTEC could utilize heat from solar, fuel combustion, low grade industrial waste heat or waste heat from other power generation systems including fuel cells, internal combustion engines combustion turbines and nuclear power plants.

As a heat pump, the JTEC system could be used as a drop-in replacement for existing HVAC equipment in residential, commercial, or industrial settings.

JTEC has an efficiency goal 85% of Carnot