Viscous dissipation and the convection heat transfer coefficient are two key flow parameters that control the operation of twin‐screw solidifying extruders. This type of extruder is used to produce hydrogenic pellets that fuel fusion energy machines like the ITER device. This paper discusses a Cryogenic Couette Viscometer (CCV) that is used to measure the viscous dissipation and convective heat transfer coefficient associated with the solidification of cryogenic fluids. Preliminary viscous dissipation measurements of solidifying nitrogen are presented and examined. Modifications to the apparatus are proposed that will allow the measurement of the wall‐to‐fluid convective heat transfer coefficient and improve the measurement of viscous dissipation.

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