小孔混流折流板换热器壳程传热性能研究

Study of the shell-side heat transfer performance of the heat exchangers with small-hole mixed-flow baffles

传统弓形折流板换热器在折流板背流侧存在“流动死区”,会减小壳程传热效率。为降低“流动死区”的影响,提出小孔混流折流板结构,并建立小孔型混流折流板换热器有限元模型,研究小孔位置和数量对换热器壳程传热性能的影响。结果发现,壳程流体在折流板小孔处会形成射流,增强了附近流体的湍流程度,减小了“流动死区”的范围,提高了壳程传热效率。在研究范围内,随着折流板小孔位置向缺口处移动,壳程强化传热能力先增强、后减少。壳程强化传热能力最强的小孔位置靠近折流板缺口,相比没有小孔的传统折流板换热器,此时的努塞尔数提高了17.02%,压力降减少了3.58%。同时还发现,折流板小孔数目越多,虽然壳程流体的流动阻力越小,但换热效率变化不是单调的,意味着折流板的小孔布孔方案存在优化设计空间。

There exists a“flow dead zone”on the leeward side of traditional heat exchanger with segmental baffles,which will reduce the shell-side heat transfer efficiency.In order to alleviate the effects of the“flow dead zone”,a so-called small-hole mixed-flow baffle structure was proposed,and finite element models for the heat exchangers with small-hole mixed-flow baffles were established to find out the effects of position and number of the small holes on the shell-side heat transfer performances of the heat exchangers.Results show that the shell-side fluid will form the jet-flow at the position of the small holes,thus enhancing the degree of turbulence of adjacent fluid,reducing the range of“flow dead zone”and improving shell-side heat transfer efficiency.Within the research scope,as the position of the small holes moves towards the window of the baffles,the shell-side heat transfer enhancement capability generally increases first then decreases.The position of the small holes with strongest shell-side heat transfer enhancement capability is close to the window of the segmental baffles,compared to the conventional baffle heat exchanger without small holes,the Nusselt number is increased by 17.02%,whereas the pressure drop is decreased by 3.58%.In addition,it is found that with the increase of the number of the small holes,the shell-side flow resistance also deceases,but the heat transfer efficiency does not change monotonously.Therefore,there is still a room for optimization design of the heat exchangers with small-hole mixed-flow baffles.