Experimental Investigation Of Heat Transfer Enhancement And Flow Resistance Characteristics Of Air In Three-dimensional Internally Finned Tubes

The heat transfer enhancement technology is known as the second generation heat transfer technology,which can significantly improve the heat transfer performance of the heat exchanger.In practical engineering applications,heat transfer enhancement technology is one of the main ways to achieve heat transfer and energy saving.The main purpose of heat transfer enhancement is to reduce equipment size and improve thermal efficiency.The three-dimensional internally finned tube is one of the most widely used heat transfer tubes.3-D IFT have three fin arrangements: staggered arrangement fins,in-line arrangement fins and spiral arrangement fins,which all have good heat transfer enhancement effect and excellent thermal performance.But the fin structure is very complex,different fins size will produce different experimental results.This paper mainly uses the method of orthogonal experiment,use the fin height h,fin width b,fin pitch Pt,and density z of 3-D TFT as the influence factors,the thermodynamic performance coefficient as the evaluation index.The orthogonal test is mainly research the three-dimensional innernally finned tube with diameter of 57 mm and 127 mm.The three-dimensional internally finned tube of 57 mm is widely used,while the 127 mm three-dimensional internally finned tube has not been studied.In this paper,the heat transfer and flow resistance characteristics of the three-dimensional internally finned tubes are systematically studied.Using air as working medium,the orthogonal experiment was used to study heat and flow characteristics of turbulent flow in 57 mm and 127 mm,two kinds of big diameter three-dimensional internally finned tube while the Reynolds number within the range of 15000 ~ 150000.Using the thermal performance coefficient defined by Webb as reinforcement index.The influence factors of the thermal performance coefficient of three-dimensional finned tube are analyzed by range method.It is found that the fin height h is the main influencing factor.Thus to get the direction to optimize and to select the best type tube.Least square method will be used to obtain the experimental correlations of Nusselt number and the fanning friction factor with Reynolds number and parameters of three-dimensional internally finned tube.The results of analysis show that the 3-D IFT characteristics are better than the same diameter light pipe,57 mm 3-D IFT average thermal performance coefficient is 1.359,127 mm of 3-D IFT average thermal performance coefficient is 1.098;57mm 3-D IFT average resistance is higher than light pipe 8.79 times,127 mm 3-D IFT average resistance is higher than light pipe 4.98 times.The experimental results show that the enhancement of heat transfer performance of the three-dimensional internally finned tube is at the expense of increasing resistance.In actual design,we should consider not only the heat transfer effect,but also the consumption of pump power when the resistance increases.The fitting criterion equations and important results which are obtained by the experimental data can be used in the design field of heat exchanger.