Two-phase Heat Transfer Characteristics Study And Structural Optimization Of Small Shell And Tube Heat Exchanger

As one of the important parts of the aviation engine oil system, the rational design of the fuel-oil heat exchanger is the basic conditions to ensure the stable operation of the oil-system.There are two kinds of heat exchangers liquid to liquid and liquid to gas-liquid in the practical work of the fuel-oil heat exchanger. To design the fuel-oil heat exchanger, the heat transfer coefficient of the fuel-oil heat exchanger first should be calculated accurately and the influence of the structural parameters on the flow and heat transfer should be grasped.Therefore, this paper carried out an experimental and numerical research of the flow and heat transfer on the two working conditions of the fuel-oil heat exchanger.Based on the test bed of the aviation engine oil system, this paper carried out an experimentally study on the liquid to liquid and liquid to gas-liquid two-phase heat tranfer of the fuel-oil heat exchanger; it also verified that the applicability of the traditional formula on the fuel-oil heat exchanger when perpetrating the liquid - liquid heat exchange; and the paper determined that the heat flow pattern is the bubbly flow within the experimental range through the flow chart. The changing curve of the heat transfer coefficient complying with the conversion rate of the gas and liquid was given out and the impact mechanism of the conversion rate of the gas and liquid on the heat transfer coefficient was analyzed. The paper carried out an empirical formula of the two-phase flow heat transfer coefficient in the fuel-oil heat exchanger according to the experimental data, and the maximum error is less than 15%.Simultaneously, this paper carried out a numerical simulation of two-phase flow and heat transfer on the fuel-oil heat exchanger of the different baffle space and different baffle gap height. Firstly, it studied the influnce of the baffle gap height and space on the two-phase heat transfer characteristics and flow characteristics of the sides of the fuel-oil heat exchanger; it also given out the changing curve of the heat two-phase flow heat transfer coefficient and the flow pressure drop of the sides of the fuel-oil heat exchanger on the baffle space and baffle gap height. Then it found out that the the pressure drop of the fuel-oil heat exchanger mainly being produced in the cross-flow zone and received the impact mechanism of the baffle space and baffle gap height on the pressure drop through the analysis of the pressure distribution within the flow cell. Ultimately, it given out the performance curve of the heat exchanger on the different baffle parameters according to the simulation data and some suggestions when improving the structure of the heat exchanger.