Numerical investigation on multi-inner-tube co-rotating tube-in-tube spiral heat exchanger in cold energy transfer of cryogenic hydrogen

The cold energy utilization in cryogenic hydrogen is a current hotspot. A hydrogen-helium heat exchanger of better heat transfer property is critical to cold energy release, only after which the chemical energy in cryogenic hydrogen can be utilized. To release the cold energy, using spiral tube-in-tube heat exchanger is a practical method. Unlike conventional single-inner-tube spiral heat exchangers with non-smooth surface structure or turbulators for turbulence generation which may cause thermal stress concentration, this study proposes a tube-in-tube spiral heat exchanger with multiple inner tubes to generate turbulence for hydrogen-helium heat transfer. Numerically, we investigated the heat transfer performances and the mechanisms of the proposed heat exchanger under two temperature differences by comparing with two baselines. The overall heat transfer coefficient of the proposed heat exchanger is at the maximum 32.09% and 80.37% higher than the two baselines in the studied range. Apart from the increase of heat transfer area, interaction between fluid and multiple inner tubes, decomposition of secondary circulations are factors contributing to the enhancement. For the helium channel, PEC reaches maximum 1.43 under large temperature difference at 2.5 m/s helium inlet velocity, compared with double tube spiral heat exchanger; reaches 1.40 at 2.5 m/s helium inlet velocity, compared with straight multi-inner-tube heat exchanger. Subsequently, the effects of inner tube distribution circle and inner tube number are investigated. This investigation provides guidance for heat exchanger selection and optimization in the cold energy release of cryogenic hydrogen.