Numerical Simulationof Flow And Heat Transfer Characteristics Of A Water-cooled Radiator With Cylindrical Fins

With the continuous development of electric system and transportation industry, the electronic componentsdevelop rapidly towards high performance, high power and miniaturization. Massive amounts of heat will be generated in operation. If the heat cannot be dissipated effectively, the temperature of the electronic components would rise. When the junction temperature of the electronic device reaches a certain value, each 1? increase will lead to reliability decrease by 5%. And the failure rate will increase sharply with the increasing temperature. Thus it will affect the operating stability and reliability,and then affect the normal operation of electric system or electric locomotive. The water-cooled radiator with cylindrical fins applied in the high power thyristor was used as model in thisthesis. Heat transfer and flow characteristics of the radiator have been obtained by numerical simulation. The present thesis analyses the existing problems of the prototype radiator, and the structure of the radiator is improved based on the principles of heat transfer enhancement.The main results are shown as follows:Firstly,the credibility of the numerical simulation method is checked bycontrasting the experimental data and the simulations in different flow rate,andanalyze the error margin and its causes.Three-dimensional flow and heat transfer processes inside the prototype water-cooled radiator were simulated using FLUENT software. Temperature distribution of the heated surfaces,velocity and pressure distribution in the flow passage have been obtained.The results showed that the temperature distribution is related to the velocity distribution and both are non-uniform. The velocity distribution is high in the middle and low on the edge, while the temperature distribution is low in the middle and high on the edge. With the increase of inlet flow rate, the thermal resistance decreases and flow resistance increases. With the increase of heating power, the thermal resistance and flow resistance change negligibly.Secondly, relative standard deviation, uniformity index and Christiansen uniformity coefficient have been introduced. And the temperature and flowuniformity of the prototype radiator have been analyzed,which have verified that the three uniformity coefficient can be all used to characterize the temperature and flow uniformity of the radiator.Finally,the design improvement is made for the radiator. By means of adding baffles and increasing cylinder diameter can reduce the thermal resistant and increase the flow resistant. Moreover, the comprehensive performance and uniformity of the radiator all have improved in different degree. By the means of increasing the included angle between the inlet and outlet flow paths, the thermal resistant reduces less while the flow resistant increases more, so its comprehensive performance evaluation is worse than the prototype radiator. Hence, it cannot improve the comprehensive performance of radiator purely by increasing the included angle, but can be optimized by combined with other methods.