Loop heat pipes (LHPs) with a flat disk-shaped evaporator are regarded as an alternative to similar devices with a cylindrical evaporator equipped with a “cylinder to plane” reducer. The paper presents a qualitative analysis of technical problems and contradictions connected with the creation of LHPs with flat evaporators. It also gives the results of development and tests of four versions of ammonia LHPs equipped with flat disk-shaped evaporators (FDEs), 10 and 13 mm thick with an active-zone diameter of 30 mm. The length of the transportation lines for vapor and liquid (2 mm in diameter) varied from 400 to 1000 mm. The devices were tested at different orientations in 1-g conditions. The maximum capacity achieved was in the range from 80 to 180 W. The minimum value of the total thermal resistance was between 0.2 and 0.3 K/W