Hysteresis phenomena in a boiling helium flow

Hysteresis phenomena in charnels with boiling helium are investigated. The upflow of liquid helium occurs in a vertical heated stainless steel tube. During tests the thermal load was increased in succession up to the nucleate boliling and then gradually reduced. The data are presented for the atmospheric pressure and mass flow rates of 84-140 kg/(m2 x s). As the tests have shown, the heat transfer at helium boiling depends not only on the thermal load but on the direction of its chang, which leads to hysteresis of the nucleate boiling curve. Stability of the developed nucleate boiling regime is also investigated. The intermediate level of heat transfer has been obtained at a heat flux reduced down to 12 W/m2 and at its further increase. The hydraulic resistance is noticed to increase with the heat flux reduction