## 1 Introduction  
The equal cross-section flow channel heat exchange surface is widely used in plate-fin heat exchangers due to its advantages of a simple structure and low cost [1; 2; 3]. However, the structure of this conventional equal-section flow channel has many defects: (1) The temperature difference at the inlet is large, and the temperature difference at the outlet becomes small during the flow of the cooling medium, which limits the convective heat transfer capacity at the outlet region. (2) The increase in the flow rate of the cooling medium increases the pressure drop (\(\Delta P\)), which increases in the form of a parabola as the flow rate increases. In order to improve these defects, a curved flow channel structure was proposed in this paper. The cross-sectional area that was perpendicular to the flow direction of the cooling medium changed, and the flow channel from the inlet to the outlet was a divergent structure, which is shown in Figure 0(a). In previous research [4; 5], the heat transfer performance of the trapezoidal flow channel was mainly studied. The trapezoidal flow channel is a curved flow channel with a very representative special shape. The results showed that when the slope angle (\(\beta\)) in the trapezoidal flow channel was between \(0^{\circ}\) and \(40^{\circ}\), the overall heat transfer performance of the trapezoidal flow channel was better than that of the equal cross-section flow channel. When the core volume goodness factor (\(\eta_{J}h_{std}a\)) was introduced for evaluation, its overall heat transfer performance was 5-20% higher. At the same time, the temperature difference in the trapezoidal flow channel was linearly distributed, which improved the heat transfer effect at the exit region. The temperature difference distribution is shown in Figure 0(b). In the study of trapezoidal flow channels, research results from theory, simulations and experiments have been obtained. [PERSON] et al. [6] firstly solved the flow characteristics of the wedge plate structure by using the similarity solution method and obtained the velocity discrete equation of the structure. Subsequently, [PERSON] [7] and [PERSON] [8] et al. further derived and improved [PERSON] et al. 's discrete equation. They found that boundary layer separation occurs when the wedge angle exceeds \(-0.199\pi\). A few years later, [PERSON] et al. [9] analyzed different wedge structures and studied the effects of different structures on the boundary layer. [PERSON] et al. [10] used numerical calculation methods to solve the heat transfer and flow properties of the laminar flow in the trapezoidal flow channel for different trapezoidal flow channel structures and sizes. [PERSON] et al. [11] took diffusers of different shapes as research objects and optimized their design with a symmetric structure by using a genetic algorithm. They concluded that the optimum pressure recovery coefficient for different methods did not vary greatly. [PERSON] et al. [12] simulated and analyzed the heat transfer and flow performance of ejectors with different structural parameters and concluded that the maximum entrainment ratio could be obtained by optimizing the geometric parameters. Their research results show that the optimal inclination angle of the mixing chamber is 14, and the optimal ratio of the diameter of the mixing chamber to the diameter of the main nozzle is 1.7. However, in fact, few studies on heat transfer of this kind of extruded structure are available. In application, [PERSON] and [PERSON] [13] first proposed an accelerated flow evaporator, which was a trapezoidal flow channel structure with a large inlet and a small outlet. During the flow in the evaporator, the downstream air flow rate increased, thereby improving the local convective heat transfer performance of the downstream region. However, the accelerated flow evaporator increased the pressure drop. Figure 1: Curved flow channel and temperature difference distribution in a trapezoidal flow channel.