The research on the flow and heat transfer of alkali metals is an important technical means to strengthen the heat transfer of the core. In this paper, the 15 cooling channels with different structures are established. Under Re = 2.85 × 104–2.17 × 105, several operating parameters, such as core inlet temperature (T = 350 K, 390 K, 450 K, 550 K, 850 K), fuel rod pitch ratio (P = 1.2, 1.4, 1.6, 1.8, 2.0), and channel shape (triangle and square) on the heat transfer performance are numerically simulated. At the same time, this work introduces an evaluation criterion, entransy dissipation, to measure the irreversibility of the heat transfer process. The results show that the triangular channel has a stronger heat transfer capacity than the square. And the increase of the rod diameter ratio is a positive means to enhance the heat transfer. Among the studied channels, Model “I” (triangle channel, P = 2.0) has the best heat transfer performance. The above results have some guiding value to realize core heat transfer enhancement by adjusting fuel rod arrangement.