Investigation on natural circulation boiling heat transfer characteristics in tube bundle channels under marine conditions

In the marine environment, the inclination and rolling motion caused by waves complicate the boiling heat transfer in the tube bundle channels of marine nuclear power plants. In addition, the effect of lateral non-uniform heating (NUH) in the special U-tube bundle in steam generators or heat exchangers further exacerbates the uneven boiling heat transfer, which is closely related to the safe operation of the entire device under marine conditions. Therefore, the paper conducted a series of experimental studies considering inclined, rolling, NUH, and coupling conditions, analyzed the influence of the above factors on boiling heat transfer characteristics, and evaluated the heat transfer calculation under the above conditions. The results show that inclined conditions keep the upper tube bundle in a high-temperature zone with multiple bubbles and high heat transfer coefficient compared to the lower tube bundle under uniform heating (UH). The influence of NUH on local heat transfer is closely related to the inclined direction. Rolling motion can cause high-temperature zone with more bubbles to periodically appear at the same local location. However, NUH can cause the high heat flux side to be in a high-temperature zone with multiple bubbles for a long time. Classic heat transfer calculation correlation of Rohsenow only demonstrates good predictive ability for rolling UH conditions with a mean relative error of 10.58 %, and 94 % of data have the predicted relative error of less than 20 %. Finally, considering the inclined and NUH correction terms, the applicable ability and scope of the Rohsenow correlation were improved. The predicted relative errors after correction under inclined UH, inclined NUH, and rolling NUH conditions are approximately 7.18 %, 5.22 %, and 7.60 %, respectively.