A novel micropump is proposed for delivering liquid with constant flow rates of 0∼250 nl/s continuously. The liquid is pumped by the surface transpiration in a micro evaporator, which consists of a gradient capillary surface by microfabricating micropost arrays. The micropost arrays are patterned such that the gaps between microposts reduce gradually away from the center microwell to surface edge, by which a capillary force formed to pull the liquid spreading on the evaporator surface. The simple analytical model is proposed to obtain the primary characteristics of the micropump, by which the influences of geometric parameters and the contact angle of fluid on the flow rate, and also the corresponding parameters during the operation of micropump are analyzed in detail. The most striking feature of the micropump is that it can be precisely and simply controlled only by varying the surface wall temperature. A much linear relationship between the flow rate and solid wall temperature can be achieved by the present design. Other features of this novel micropump include its simplicity, no-moving-parts, and ease of controlling the temperature of biological samples. The present micropump concept may be potentially used in delivering a precisely-controlled, continuous flow rate for many new applications in the fields of biotechnology, environmental testing, and instrumentation for analytical chemistry.

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