Thermosyphon has begun to be used in the midium-high temperature trough type solar energy heat utilization system. The characteristics of the solar radiation makes a great influence on the solar collection efficiency in the start-up performance of thermosyphon

and thus solar collecting performance changes. The novel horizontal loop thermosyphon (HLTS) with the dowtherm has been developed. The platform has been set up to test the influence of filling content

heat flux and ambient temperature to the start-up performance of the HLTS. As the result

the direction flow of steam in the evaporator of HLTS is single and the filling content has influenced the operation of heat pipe. The best filling content of injection is 3.325 kg

and the pulsating flow forms in the evaporator when the ratio is 100%. The start-up time changes short when the heat flux increases in the same filling

while the start-up temperature of HLTS does not change and keeps in the temperature of 150℃ when the filling content is 3.325 kg. The best heat flux is 7.619 kW·m-2 as the NHLT used in the solar collector. Moreover

the low temperature makes the oil frozen in the evaporator at below 9℃ with extending time of the start-up of thermosyphon.