高低双螺旋片强化套管换热器壳侧换热

采用实验和数值模拟相结合的方法,研究了高低双螺旋片对套管换热器壳侧的强化换热效果.以仅带有高螺旋片的换热器结构为基础,研究了曲率ε分别为0.44、0.321和0.131时,Reynolds数在4000~20000范围内,低、高螺旋片高度之比l/W对壳侧换热平均Nusselt数Nu_m和流动阻力系数f的影响,考察了等泵功条件下换热器的综合传热性能.对ε=0.44的换热器研究结果表明:当l/W>1/2时双螺旋片强化传热效果显著,且研究工况中l/W=3/4时最优,此时与单一高螺旋片相比,Nu_m值平均提高了10.8%;研究范围内,综合强化传热因子PEC数在1.044~1.204.对不同曲率换热器的研究结果表明,同一l/W值下,PEC数随着曲率ε值的增大而增大,说明双螺旋片结构更适合强化曲率较大的套管换热器壳侧换热.

Heat transfer enhancement on shells of double-pipe exchanger with double helix fins

Experimental and numerical methods were adopted to study the heat transfer enhancement effect for double-pipe exchangers by installing high and low double strand helix fins on the outer wall of inner tube. The double-pipe heat exchanger with single high helical fin was treated as referenced structure. The curvature ratios were set to 0.44, 0.321 and 0.131 and the Reynolds number was in the range of 4000 to 20000. The impact of the ratio of low to high helical fin heights on the average Nusselt number of shell wall Nu_m and flow resistance coefficient f were studied. The comprehensive heat transfer performances of heat exchanger were examined at the same pump power condition. The study on heat exchanger with ε=0.44 showed that enhanced heat transfer effect was distinct when l/W value is greater than 1/2. The condition of l/W=3/4 is an optimal plan. For this case, the Nu_m of heat exchanger with double helical fins was improved by 10.8 percent on average compared to that of single high fins. PEC values are in the range of 1.044 to 1.204 within the researched scope. The study on heat exchangers with different ε values showed that PEC values are raised with the increases of curvature ratio ε at the same l/W values, which indicates that low and high double helical fins are more suitable to double-pipe exchangers with larger curvature ratio.