Numerical Study Of Heat Transfer Enhancement In The Tubes

Energy-saving and emission reduction has become an important link of the economic and national development in China, even all the countries in the world, and the practical and efficient heat transfer enhancement technology is an important means of energy-efficient, which is widely used in the industrial fields, such as petroleum, chemical industry, energy, metallurgy etc, also has a wide range of applications in the fields of aerospace, electronics cooling and the safety use of nuclear energy. Therefore, the development of new types of heat transfer enhancement technology and highly efficient heat exchanger can bring huge economic and social benefits.First, three types ( triangle,square and pentagon ) of polygonal inserts used in the tube had been designed, and numerical study was undertaken to investigate the heat transfer enhancement. Consequently, the variation of Nusselt numbers, friction factors and overall enhancement ratios (PEC : Performance Evaluation Criteria) for the tube with the inserts were presented. The results obtained from a smooth tube were compared with those from the studies in literature in order to validate the numerical method.Then, louvered strip inserts was analyzed through numerical computation method to find the best structural parameter (inclined angle and distance between each louvered strip).The strips are expected to induce a rapid mixing and a high turbulent and longitudinal vortex flow like a delta wing, of course, resulting in an excellent rate of heat transfer in the tube. The louvered strips have various inclined angles (θ=15°, 25°and 30°), and different distances between each louvered strip (30 mm, 45mm, 60mm). The flow rate of the tube was in a range of Reynolds number between 12000 and 42,000. Numerical calculations were performed with FLUENT 6.3.26 code. The best overall enhancement (200% from Nu , 1.6～2 for PEC )was achieved for which the inclined angle is 30°. At last, a numerical analysis was taken on an improved design based on louvered strip. Compare with louvered strip, new design provides smaller friction loss and better overall enhancement ratios.