Thermal transpiration based micro-scale pumping and power generation devices

Because hydrocarbon fuels have higher energy storage density than commercially available batteries, there is considerable interest in miniaturizing thermochemical systems for electrical power generation for portable electronic devices such as laptop computers, cell phones, PDA's, remote sensors, autonomous air and space vehicles, etc. Even with low conversion efficiencies, fuel-driven generators will still have superior energy density. Most current micro-scale power generation concepts employ scaled-down versions of existing macroscale devices, in particular internal combustion (IC) engines, though such micro-devices experience more difficulties with heat and friction losses due to higher surface to volume ratios than their macroscale counterparts. Moreover sealing, fabrication and assembly are much more difficult at small scales because microfabrication processes have much poorer relative precision than conventional macroscale processes. Consequently, the objective of this work is to develop a meso/micro-scale self-sustaining power generator that is self-contained, has pumping and power generation integrated into one device, has no moving parts and operates only on thermal and electrochemical energy supplied by hydrocarbon fuels, thus it has no parasitic electrical energy losses. It is proposed to develop a microscale or mesoscale propulsion system based on a catalytic combustion-driven thermal transpiration pump. Thermal transpiration (thus pressurization) is accomplished using nanoporous materials whose pore size is comparable to the mean free path of gas molecules at relevant conditions. This system has no moving parts, no supplemental working or pressurization fluids, very low mass and integrates pressurization and thrust generation. Moreover, an integrated power generator is proposed that is self-contained, provides pumping and power-generation in one device, has no moving parts and operates only on thermal and electrochemical energy supplied by hydrocarbon fuels. The system consists of a catalytic combustion-driven thermal transpiration-based pumping device, and integrated with single-chamber Solid Oxide Fuel Cells (SOFCs). This particular type of SOFCs requires no seals (the Achilles heel of conventional SOFCs) and has already demonstrated > 400 mW/cm² power density. A novel cubic configuration is used for optimal thermal management. With this device 2 Watts of electrical power are expected at ∼ 20 % conversion efficiency (chemical to electrical), with energy storage densities exceeding commercially available batteries by a factor of 10.