Recent advances in electronics technology have led to growing demand for highly efficient heat transfer devices with operating temperature controllability. Although capillary pumped loops are excellent candidates for this requirement and have been successful in various applications, their typical cylindrical evaporator shape has been a major drawback for applications to flat heat sources. Moreover, operating characteristics and the corresponding physical understanding of the capillary pumped loops are still uncertain, and lack of data for their operation makes their application unreliable. Thus, in this work, a capillary pumped loop with a flat evaporator was devised, and its operating characteristics were investigated. (C) 2009 Elsevier Ltd. All rights reserved.