Heat Transfer And Persure Drop Performances Of Twisted Oval Tube Heat Exchanger

Material and Equipment cost will be seriously saved when smooth tubes are replaced by enhanced tubes in the heat exchangers. Also the utilization rate of heat will be obviously promoted, more energy will be saved. Comparing with the traditional shell-tube heat exchangers, advantages just like higher heat transfer coefficient, lower pressure drop, higher clean ability and smaller volume will be found in twisted tube heat exchangers. This new type of heat exchanger is gradually showing their superiority in petroleum chemical industry.Aiming at obtaining the heat transfer and pressure drop correlations of both the shell side and tube side of the twisted oval tube heat exchanger, the present work analyzes the heat transfer and fluid flow characteristics of the twisted oval tube theoretically. Heat transfer and pressure drop performances of twisted oval tubes with different geometrical parameters were studied experimentally and numerically. Fluid flow and heat transfer characteristics in both the tube side and shell side of the twisted oval tube heat exchanger are studied numerically. Main component and major findings of the present work are as follow:1. In terms of tensor technique, perturbation method and Galerkin method, analytic solutions of each order perturbation components of velocity and temperature are obtained. Comparatively analyzed the heat transfer and pressure drop performances of smooth round tube, smooth oval tube and twisted oval tubes with different geometrical parameters. Each order components of velocity and temperature of smooth round tube and twisted oval tube are analyzed and also their influences on each other are also studied. Their influence on the distribution of local Nusselt number and wall shear stress are also studied. Influences of geometrical parameters on the distribution of secondary flow and the magnitude of secondary flow are analyzed. Heat transfer enhancement mechanism of the twisted oval tubes in laminar state is obtained.2. Heat transfer and pressure drop performance testing system of the twisted oval tube is established. Performances of the twisted oval tubes with major axis2b=24mm, minor axis2a=9.5mm, twisted pitch length equals200mm and230mm are experimentally studied. Correlations for calculating their heat transfer and pressure drop performances are also fitted. The reliability of the correlations from former researchers is analyzed. And also the heat transfer and pressure drop performance of smooth round tube and twisted oval tubes are comparatively analyzed.3. Shell side heat transfer and pressure drop performance testing system of the twisted oval tube heat exchanger is established. Shell performances of twisted oval tube heat exchanger with FrM=79is experimentally studied. The reliability of the correlations from former researchers is analyzed. And also shell side heat transfer and pressure drop performances of twisted oval tube heat exchanger and rod baffle heat exchanger are compared with each other. The overall performance evaluation factor η is optimized in the present work. With the optimized overall performance evaluation factor ηM, the overall performance of the twisted oval tube heat exchanger is evaluated.4. With Realizable k-ε turbulence model and relevant model parameters, shell side and tube side heat transfer and pressure drop performances of twisted oval tube heat exchanger are simulated. Influences of twisted oval tube geometrical parameters on the performance of the twisted oval tube heat exchanger are analyzed. Based on the numerical result, Influence of temperature, velocity, secondary flow distributions on the performances of the twisted oval tube heat exchanger are analyzed. In terms of field synergy principle, both the shell side and tube side heat transfer enhancement mechanism of the twisted oval tube heat exchanger are summarized. And also the general correlations for calculating the heat transfer and pressure drop performance of the twisted oval tube heat exchanger are fitted.