Numerical prediction of the operating point for the cryogenic twin-screw hydrogen extruder system

An extruder-type cryogenic pellet injector system for plasma fuelling is under research at Institute for Plasma Research (IPR), India. A twin-screw extruder is a most stable device in the form of closed volumes of hydrogen between screw threads and promising process due to continuous production of hydrogen pellet for plasma reactor. In the present investigation, a non-Newtonian, non-isothermal CFD model was developed which modeled the shear rate and temperature-dependent viscosity in the Herschel Bulkley model. Brinkman number (Br) varies from 0.15 to 0.46 at 5 and 15 rpm respectively. Due to increasing the screw rotation speed for a given throughput, the shear rate increases (therefore, also the Br) and results in larger viscous dissipation. Solid hydrogen temperature is predicted at the location of the flight gap and intermeshing zone for the different barrel temperatures under varying screw rotation speeds (5–15 rpm). Prediction of hydrogen temperature at the intermeshing zone of the extruder system plays a vital role to decide the barrel temperature. Due to more number of moving surfaces at the intermeshing zone of the extruder system, the temperature of solid hydrogen is higher and increases above the melting point temperature. The effect of barrel wall temperature and screw rotation speeds (5–15 rpm) on the viscous dissipation rate and pressure development at required throughput was also examined for an extruder system. It is important to estimate the barrel wall temperature to get an operating point and corresponding viscous dissipation rate, which determines the cooling load required for extruder-die set-up. The results show that as the die wall temperature increases, the viscous dissipation, as well as the pressure drop decreases in the die. The investigation showed that the die’s wall temperature and screw rotation speed affect the operating point of the extruder-die system.