间断螺旋片强化套管换热器传热性能分析

Study on the heat transfer enhancement performance of a double-pipe heat exchanger by the discontinuous helical fins

为改善套管换热器环侧流体流动状态,进一步强化环侧换热性能,提出一种新型间断螺旋翅片套管换热器。通过三维数值模拟研究不同螺旋片布置形式(顺排、叉排和螺旋排)下肋片螺旋升角(α=30°,40°,50°和55°)对环侧流动和传热性能的影响,应用火积耗散理论对其强化传热机理进行分析。结果表明:相比光滑套管换热器,顺排、叉排、螺旋排布置肋片的环侧Nu分别增加了28%~80.83%,31.11%~81.73%,33.64%~86.3%;随着螺旋升角的增大,Nu和摩擦因数f不断减小;螺旋排布肋片环侧综合强化换热因子PEC最高,螺旋升角为30°,40°,50°,55°时环侧PEC分别为0.96~1.15,0.95~1.13,0.93~1.1,0.92~1.07;间断螺旋片强化双管换热器的火积耗散大于光滑圆管;传热温差引起的火积耗散热阻小于光滑圆管,传热过程的不可逆损失减小,且在大螺旋升角下流动阻力引起的传热过程不可逆损失减小。

In order to improve the fluid flow and further enhance the heat transfer performance on the ring side of the doublepipe heat exchanger,a new type of double-pipe heat exchanger with discontinuous helical fins was proposed.Three-dimensional numerical simulation was conducted to study the impacts of the different helix angles(α =30 °,40 °,50 ° and 55 °) on flow and heat transfer performance on annulus side of the double-pipe heat exchanger under the different arrangement forms(in-line,cross-row and helical-row).The mechanism of the heat transfer enhancement was analyzed by the entransy dissipation theory.The results show that,compared with the smooth circular tube,the Nu on the annulus side of the double-pipe heat exchanger corresponding to the in-line,cross-row and helical-row arrangement is increased by 63.4%,65.2%,and 74.6%,respectively.The Nu number and friction factor f decrease continuously with the increase of helix angle.Compared with the smooth circular pipe,the comprehensive heat exchange enhancement factor PEC on the annulus side is the highest under the helical-row arrangement,and the PEC of the annulus side is 0.96~1.15,0.95~1.13,0.93~1.1,0.92~1.07 respectively when the helix angle is 30°,40°,50°,55°,respectively.In addition,compared with the smooth tube,the entransy dissipation of the double-pipe heat exchanger with the discontinuous helical fins is greater.The heat transfer thermal resistance of entransy dissipation caused by the heat transfer temperature difference is less than that of smooth circular pipe.The irreversible loss of the heat transfer process is reduced.And the irreversible loss of the heat transfer process caused by flow resistance under large helix angle is reduced.