An experimental investigation of cryogenic chilldown time in a polyurethane-coated helical coil

To optimize the cryogenic chilldown of transfer lines and to improve the efficiency of cryogenic systems, chilldown time should be reduced. Such time saving is associated with reduced consumption of cryogenic fluids. Experiments were performed on helical channels with a polyurethane coating for different inlet pressures, and the performance of an untreated helical surface and one with a coating were compared at corresponding pressures. The results indicated that there are substantial savings in chilldown times with coated surfaces compared to non-coated ones. Liquid nitrogen was used as the cryogen and was passed through helical coils made of copper. The significant reduction in chilldown time is observed only after the onset of a nucleate boiling regime, as indicated by a graph of average surface temperature versus time.