An important consideration while designing the shape of a capillary evaporator is the phase distribution in the wick. However, the distribution depends on the working fluids and porous materials. This study investigates the heat-transfer characteristics of a loop heat pipe (LHP) evaporator by using a threedimensional pore network model with a dispersed pore size wick. The simulation considers saturated and unsaturated wicks. A stainless steel (SS)-ammonia, polytetrafluoroethylene (PTFE)-ammonia, and copper-water LHP are simulated. The copper-water LHP has the highest transition heat flux to the unsaturated wick. When the optimum evaporator shape of the copper-water LHP is designed, it is reasonable to assume that the phase state is saturated. On the other hand, for the ammonia LHP design, the state is assumed to be unsaturated. Simulation results show the heat-transfer structure in the evaporator and indicate that the applied heat flux concentrates on the three-phase contact line (TPCL) within the case, wick, and grooves. An evaporator configuration with circumferential and axial grooves is simulated to investigate the effect of the TPCL length. Results indicate that the optimum shape can be realized by varying the TPCL length. The proposed method is expected to serve as a simple approach to design an evaporator.