A correlation is developed to predict mixed convection heat transfer of water flow in rod bundles. The rod bundles are 5 × 5 and the Re number ranges from 1 × 10³ to 3 × 10⁴ in the experiment. In the forced convection region, the Dittus-Boelter correlation predicts well with the experimental data. However, in the mixed convection region, the correlations reported in the literature are all deviated from the measured data. Moreover, based on the classical form of buoyancy parameter, Gr*/Re^3.425/Pr^0.8, the experimental data of circular channels extracted from literature are compared with the measured data. The comparison shows that the buoyancy parameters of the onset point of heat transfer impairment (HTI), turning point of HTI and onset point of heat transfer enhancement (HTE) in rod bundles are very close to that in circular channels, but the maximum degree of HTI in bundles is significantly weaker than that in circular channels. The experimental data indicate that the circumferential heat transfer is significantly uneven in HTI region, which result in the differences of buoyancy parameter of turning point in different circumferential directions and eventually lead to the weaker overall degree of HTI in bundles. Considering the derivation method of the classical form of buoyancy parameter proposed by Rouai, a new buoyancy parameter form for rod bundle channels is derived based on the Dittus-Boelter correlation for forced convection heat transfer and the Cheng and Todreas’s correlation for friction factors in rod bundles. Based on the new buoyancy parameter form, a new correlation to predict mixed convection heat transfer in rod bundles is proposed and provides good prediction accuracy.

建立了相关性以预测棒束中水流的混合对流传热。棒束为5×5，在实验中Re数范围为1×10 ³至3×10 ⁴。在强制对流区域，Dittus-Boelter相关性通过实验数据可以很好地预测。但是，在混合对流区域，文献中报道的相关性均与实测数据有偏差。此外，基于浮力参数的经典形式，Gr * / Re ^3.425 / Pr ^0.8，将从文献中提取的圆形通道的实验数据与实测数据进行比较。比较表明，棒束中的传热障碍起始点（HTI），HTI转折点和传热增强起始点（HTE）的浮力参数与圆形通道的浮力参数非常接近，但最大程度束中的HTI显着弱于循环通道中的HTI。实验数据表明，HTI区域的周向传热明显不均匀，导致转折点的浮力参数在不同的周向方向上存在差异，最终导致束中HTI的整体程度较弱。考虑到Rouai提出的经典浮力参数形式的推导方法，基于对流换热的Dittus-Boelter相关性和棒束摩擦系数的Cheng和Todreas相关性，得出了棒束通道的浮力参数形式。基于新的浮力参数形式，提出了一种新的相关性来预测杆束中的对流混合传热，并提供了良好的预测精度。