This paper reports on conceptual design and thermo-fluid characteristics of two-phase flow devices enabled by dual-mode wicks. In dual-mode wicking structures, liquid and vapor flow paths are integrated on the same plane and segregated flow of the two-phases is achieved by having networks of pores of multiple length-scales. When a mixture of a gas and a liquid flow through this media and the wick material wets the liquid, then the liquid will preferentially segregate to and flow through the mode with the smaller effective pore size. The gas will flow through the paths with the larger effective pore size. These wicks, further, have advantages in phase change heat exchange where the liquid can fill the entire channel. The interwoven liquid and vapor paths facilitate phase segregation and suppress or delay dry out of heated surfaces. Experimental results are presented showing heat transfer coefficients exceeding 25,000 W/m~2K. Other characteristics demonstrated include reduced pressure drop and pressure fluctuations, and lower superheat requirements when compared to empty channels. A theoretical basis for enhanced heat transfer is presented, and merits of employing the technology in energy conversion applications are discussed.
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