Numerical Analysis And Optimal Design Of Single-phase Heat Transfer And Fouling Performance In Helically Ribbed Tubes

Recently, internal helically ribbed tube becomes one of the most widely used passive heat transfer enhancement technique, because of its effective heat transfer effect, low pressure drop loss and low cost of mass production. And fouling in enhanced heat transfer exchangers is an inenvitable and complex problem, which has many influential factors, so more and more investigations are needed in the detail researches of heat transfer and fouling performance. From mass balance in the investigation, this paper uses Von-Karman analogy to predict the fouling performance and numerically study the effect on heat transfer enhancement and fouling of each main parameter in helically ribbed tubes, which can be used to optimize the design of helically ribbed tube generally and broaden its further applications. Results are as follows:(1) The numerical analysis of heat transfer and pressure drop for turbulent flow in eight helically ribbed tubes with15.54mm inside diameter has been performed. The turbulent model is selected carefully and the effect of grid independence is extensively examined. The computational results match well with the experimental data to validate the accuracy of the numerical model.(2) The fouling model is established based on Kern-Seaton mass balance model and Von-Karman analogy. Combined with numerical model, heat transfer effect and fouling performance on the helical surface can be obtained. By comparing the results with experimental fouling data, the investigation method the paper used is right.(3) The effect of each main parameter:rib shape, rib starts, helix angle, and rib height, on heat transfer and pressure drop is investigated. Every parameter has been analyzed and compared by enhancement factor carefully, so that we can select the optimum geometry: rib shape of rectangle, trapezoid and triangle with small inclueded angle are better than other shapes; rib starts is better aroud50and helix angle is best at25°-35°; rib height looks like the higher the better.(4) Considering fouling in practical situation, the ratio of pitch over rib height is an important parameter to select the tubes. It is advisable to select the tubes with pitch over rib height ratio greater than3.5, which have better heat transfer and lower fouling potential. Therefore, when rib starts is50and helix angle is25°, the maximum of the ratio of rib height over diameter is0.0385. And if the diameter of tube is15.54mm, the maximum of rib height is0.6mm.