Two types of evaporators, specially developed for pumped two-phase fluid loop use, are illustratively described with drawings from which inner structures can clearly be seen. A significant difference between the two is such that evaporator exit vapors are usually wet in the first while always dry in the second. An outline of microgravity experiments, practiced for functional verifications of the two, is given along with observed inside views and measured temperatures. As a result of the experiments, necessity of suitable control in liquid supply is emphasized from an angle of normal operations. The void fraction, the temperature difference, and the pressure difference are proposed as an input signal for the flow rate control. The whole of microgravity experiments held again is explained with drawings of evaporator test loops, permitting any kind of control based on the above three, and also with figures displaying the temperature/pressure variations. It is then concluded that a recommended control means is the pressure difference method coupled with evaporators of the second mentioned. Reported in the next place are laboratory works done to establish that means on ground; that is, improvement in capillary structures of that evaporator, development of a controller for accumulator pressure regulation and pump speed modulation, and a series of testing. Corroborative demonstrations have actually been made through automatic control tests of a vapor/liquid separated two-phase fluid loop model. The model specifications and the test conditions are listed in the tables. Test results are shown in the figures; displaying the evaporator/vapor temperatures and the vapor to liquid pressure difference, measured in loop start-up, temperature setpoint change, heat load change, uneven heat load, and heat load sharing for warmth.