射流管插入深度对螺旋通道传热性能的影响

Influence of the jet tube insertion depth on the heat transfer performance of a spiral channel

为了揭示射流管插入深度对螺旋通道传热性能的影响规律,采用数值模拟方法对不同相对插入深度(δ=0~0.625)下通道内流场特性和强化换热特性进行了分析。结果表明:随着δ的增大,射流核心区到达外壁面的距离变短,在射流入射位置处射流管两侧的二次涡范围扩大,流体对上下壁面的冲击作用增强;上、下传热壁面的局部努赛尔数Nu_(c)随着δ的变化规律基本相同,最佳传热位置(Nu_(c)最大的位置)随着δ的增大向外壁面靠拢;内壁面的Nu_(c)在射流管壁内侧范围随着δ的增大而减小,在外侧范围随着δ的增大而增大;射流管插入深度增加对螺旋通道外壁面传热性能提高的效果最为明显;截面努赛尔数Nu_(θ)随着螺旋角度γ的增大呈现3个变化区域,即入口区域、射流影响区域和出口区域,其中入口区域和出口区域的Nu_(θ)随着γ的变化保持稳定,但出口区域的Nu_(θ)比入口区域高19%左右,Nu_(θ)最大值位于射流入射点下游5°左右的位置;在螺旋角度γ=-15°~45°的范围内射流对传热的影响最大,传热的影响范围基本与射流管的插入深度无关;综合换热评价指标(PEC)随着δ的增加呈现先增大后减小的变化规律,δ=0.250是螺旋通道最佳的综合传热性能结构参数。

The flow field characteristics and heat transfer characteristics of a spiral channel with different relative jet tube insertion depths(δ=0-0.625)have been analyzed by numerical simulation.The results show that with an increase inδ,the distance from the jet core region to the outer wall becomes shorter,and the range of secondary vortexes on both sides of the jet tube at the jet incident position also increases,thus enhancing the impact of the fluid on the top and bottom walls.The local Nusselt numbers Nu_(c) on the top and bottom heat transfer walls show the same variation asδ,and the optimal heat transfer position(the location of the largest Nu_(c))becomes closer to the outside wall with increasingδ.The Nu_(c) of the inner wall surface decreases with increasingδin the inner range of the jet pipe wall,whilst Nu_(c) increases with increasingδin the outer range.Increasing the insertion depth of the jet tube results in the most significant improvement in the heat transfer performance of the outer wall of the spiral channel.The cross-section Nusselt number Nu_(θ) shows three distinct regions with increasing spiral angleγ,namely the inlet region,the jet influence region and the outlet region.The Nu_(θ) of the inlet and outlet regions remains stable with the variation inγ,but the Nu_(θ)of the outlet region is about 19%higher than that of the inlet region.The maximum value of Nu_(θ)is located at about 5°downstream of the jet incident point.In the range of spiral angle from-15°to 45°,the jet has the greatest influence on heat transfer.The influence range of heat transfer is essentially independent of the insertion depth of the jet tube.The comprehensive heat transfer evaluation index(PEC)initially increases and then decreases with increasing δ,and a spiral channel with δ=0.250 shows the best comprehensive heat transfer performance.