| As an effective configuration for heat transfer enhancement, the internally helical finned tube is widely employed. This paper provides heat transfer and friction characteristics of the internally helical finned tube in numerical and experimental investigation, the internally helical finned tubes were measured during fin geometry ranges of non-dimensional rib height(0.02 to 0.05), number of rib starts(35 to 50),helix angle(35 to 45deg).Analysing the impact of fin number,fin height and helix angle on the Nusselt number and the friction factor,then experiments verify the numerical results . Analysing the impact of non-dimensional radius(0.2~0.5) on the Nusselt number and the friction factor of the internally helical finned tube with center blocked in numerical investigation.The major findings are as follows:1. The Nusselt number and the friction factor increase first,then decrease with the increase in helix angle. whenγ=41°,Nu is peak, whenγ=41°,f is peak.The ratio of the internally helical finned tube Nu number to the plain tube Nup is written Nu/Nu p, Nu/Nu p=1.51~1.71,the values of evaluation indexη=(j/jP)/(f/fP)1/3isη1.15~1.28.2. The number of rib starts variation causes a little increase the Nusselt number and the friction factor. The values of Nu/Nu paugment with the increase in the number of rib starts (35~50), Nu/Nup = 1.71～1.73,andη=1.279～1.281.3. The fin height variation causes a dramatic increase of the Nusselt number and the friction factor.When the range of fin height is 0.02~0.05, Nu/Nu p=1.59～1.83,andη= 1.24～1.30.4. Analyzing the numerical results,0.50/40/41 is the best rib combination of all.5. With regard to the internally helical finned tube with center blocked ,when d/D=0.35～0.4, the grades of Nu increase greatly ,however, the grades of f increase smaller.6. With regard to the internally helical finned tube with center blocked ,ηaugment with the increase in d/D when d/D=0.2~0.5,the range ofηvalue isη=1.57～2.05.
|
PDF Full Text Request