Reported here are results of an experimental study on the heat-transfer characteristics of liquid evaporation from capillary structures. Thirty-five types of wicks typical for low-temperature heat pipes have been studied. It has been found that at high heat flux densities, there is no liquid boiling in wick structures. Heat is removed by evaporation from a meniscus-free surface and is accompanied by the entrainment of drops of the heat-transfer medium. Critical conditions of capillary structures filled with liquid are studied. It is shown that under the conditions of heat transfer, a complicated deformation of the meniscus profile takes place in capillary structure cells.