This paper presents a method to optimize wick shape in the capillary evaporator of loop heat pipes and capillary pumped loops. The evaporator heat-transfer coefficient is maximized using only the length of a three-phase contact line (TPCL) within the case, wick, and grooves as a variable wick dimension. The heat-transfer coefficient is formulated taking the following two particular aspects into account. The heat-transfer coefficient initially increases with TPCL length. However, when TPCL becomes too long, the heat-transfer coefficient decreases because of a large pressure loss in the grooves. The proposed model is validated experimentally. Both the model and experiment show the heat-transfer coefficient reached a local maximum in terms of the TPCL length. It is concluded that wick shape can be optimized by just using the TPCL length. The effects of the material of an evaporator's case, wick, and working fluid are also discussed. (C) 2016 The Authors. Published by Elsevier Ltd.