The first use of a thermoelectric material in the bidirectional operation of a gas pump using thermal transpiration has been demonstrated. The thermoelectric material maintains a higher temperature difference which favors thermal transpiration and thus increases the efficiency of gas pumping. Since the hot and cold sides of the thermoelectric material are reversible, the direction of the pump may be changed by reversing the electrical current direction. Two different pump designs are presented that illustrate some of the design tradeoffs. The pumps are characterized by measuring the pressure difference that may be generated and by measuring the flow rate in the forward and reverse directions. For a pump composed of a porous material with a pore size of 100 nm, a maximum flow rate of 0.74 cm 3 min −1 and a maximum pressure of 1.69 kPa are achieved.

Pressure and mass flow rate due to thermal transpiration in the transitional flow regime is experimentally investigated for a wide range of Knudsen numbers, from 0.06 to 2.9, using a nanoporous membrane. A temperature gradient is created by heating one side of the membrane, and cooling the other side with a heat sink. The largest pressure difference and mass flow rates are found for the smallest pore size, 25 nm. It is found that a pressure difference and mass flow rate can still be observed for the largest pore size studied, 1.2 μm. This demonstrates that pressures due to thermal transpiration may be significant for certain MEMS devices with temperature gradients and sub-micron gaps. Using a fit for the temperature difference across the membrane, the experimental and theoretical results are in agreement.

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