3D Numerical Simulation Of Thermal-hydraulic Performance On Convective Heat Transfer Through A Trapezoid Passage

The heat transfer in a trapezoidal cross-section channel is widespread in engineering applications, such as water cooling systems. In recent years, extensive numerical simulations and experimental studies have been performed on the flow and heat transfer characteristics in trapezoidal cross-section channel. The thermal-dynamic performance of trapezoidal cross-section channel has been researched by some scholars; however, it is found that most of the previous studies are restricted to the laminar and turbulent convection heat transfer characteristics of a trapezoidal cross-section channel with four walls heated. None literature has not been reported on the convection heat transfer characteristics in a trapezoidal cross-section channel with asymmetry heating conditions. Therefore, this investigation has both important theoretical significance and potential applications.Based on previous research results of the flow and heat transfer characteristics in a non-circular channel, the physical and mathematical models have been established. A three-dimensional numerical simulation by the use of sophisticated business software Fluent6.2, has been carried out to investigate the laminar and turbulent convection heat transfer characteristics of a trapezoidal cross-section channel with water as the working liquid and asymmetry walls heated by constant heat flux. This paper covers a Reynolds number Re range of 150-1500 for laminar flow, and 2×104-3×104 for turbulent flow; the effects of geometric parameters, including the bottom side angleθ(60°-85°) and the dimensionless structure parameter b/a (1/4-4/3), where a is the upper wall width and b is the height of trapezoidal cross-section channel. Detailed discussions are conducted on the temperature and velocity distributions on varying cross-sections in a trapezoidal cross-section channel with three different asymmetric heating modes, which are one-wall heating, two-wall heating and three-wall heating. The influences of structural parameters b/a, angleθand Reynolds number Re on the convection heat transfer coefficient are also presented. The results show that:①For the laminar flow in a trapezoidal cross-section channel with asymmetric heating modes, the variations of the axial cross section-average Nusselt number Num with the structural parameters b/a are totally different from those of four-wall heating mode. In the non-entrance region, Num is minimum when b/a = 3/4 for the three-wall heating mode; Num increases with the increase of b/a in the case of two walls heated; while Num decreases with the increase of b/a when single wall is heated.②From the temperature distribution of laminar flow in a trapezoidal cross-section channel with asymmetric heating modes, it is shown that the temperature firstly rises at the wall region, and then heat concentration occurs in the corner, and the temperature around the corner region increases quickly, finally the temperature distribution appears symmetry; the velocity distribution in the entrance region is nonuniform, however, no significant changes can be found when the flowing distance reaches over 1/3 of channel length.③Comparison of the laminar convection heat transfer characteristics in a trapezoidal cross-section channel with asymmetric heating modes and four-wall heating mode, it is seen that Num shows the largest difference between the two-wall heating mode and four-wall heating mode, especially whenθ= 85°, b/a = 1/4, the difference of Num is up to 46.98%, the minimum difference of 0.92% occurs whenθ= 75°, b/a = 4/3.④For the turbulent convection heat transfer in a trapezoidal cross-section channel with three-wall heated, the velocity distribution is the same as that of four-wall heating mode. The isothermal curves near the wall areas are dense and symmetrical. The distinction is that, the temperature firstly increases in the corner region for the four-wall heating mode, while the temperature initially increases at the wall region for the three-wall heating mode. The Num of the three-wall heating mode is slightly smaller than that of the four-wall heating mode.