Experimental study on flow boiling and circumferential non-uniform heat transfer characteristics in helically-coiled tube under coupled heat transfer conditions

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Helically-coiled tube steam generator has been widely used in nuclear reactor, energy power, petrochemical and other systems. In the liquid metal reactor, the liquid metal on the primary side of the helically-coiled tube steam generator exchanges heat with the water on the secondary side. Due to the coupled heat transfer between liquid metal and water, the distribution of the wall temperature or heat transfer coefficient of helically-coiled tube are significant different in the circumferential direction of the tube cross-section. An experimental system of helically-coiled tube steam generator was set up in this paper. The non-uniform heat transfer characteristics of secondary side fluid of helically-coiled tube steam generator were studied under the coupled heat transfer conditions between the heat transfer of primary side and secondary sides fluid. It was found that the wall temperature or heat transfer coefficient in the circumferential direction of tube cross-section were significantly different, the maximum and minimum wall temperature appeared on the inside and bottom of the tube cross-section, respectively, the maximum and minimum heat transfer coefficient appeared on the outside and top of the tube cross-section, respectively. The effect of secondary side refrigerant pressure, secondary side refrigerant supercooling degree, mass flux of secondary side refrigerant, primary side heating water temperature and mass flux of primary side heating water on the maximum wall temperature, minimum wall temperature, maximum heat transfer coefficient, minimum heat transfer coefficient were obtained. Beside, The local and overall non-uniformity of the wall temperature and heat transfer coefficient in the circumferential direction of tube cross-section were obtained and the influence of each parameter on the local and overall non-uniformity were revealed, respectively. Finally, it was concluded that the non-uniformity of heat transfer coefficient in the circumferential direction of tube cross-section under coupled heat transfer conditions was more obvious than that under constant heat flux conditions. And the the overall non-uniformity of heat transfer coefficient (δh) obtained in our experimental were larger than the δh of Chang et al. [33], Zheng et al. [38], Kong et al. [34], Yao et al. [36] and Niu et al. [37] by 130.67%, 48.10%, 289.48%, 151.28% and 271.67%, respectively.