| Natural cold resource is a special renewable energy,there is abundant natural cold resource in cold region of China.The development of dairy industry in cold region is rapidly,the large demand for cooling in dairy processing leads to the huge energy consumption of refrigeration equipment.Using natural cold resource for cooling is a simple and effective way to save energy.In this paper,a natural cold resource heat exchanger similar to a shell and tube heat exchanger is designed.The heat transfer inside the shell side of natural cold resource heat exchanger is mainly studied.The main research contents and achievements are listed as follows:(1)Structure design of natural cold source heat exchanger.Analyze the climatic characteristics of the cold regions,determine the month and temperature range of available natural cold resources.The main cold places in cold regions in winter are selected to determine the application conditions of natural cold resource heat exchanger.The heat transfer coefficient and heat exchange area of natural cold resource heat exchanger are calculated by theoretical formula,and the preliminary structural parameters of natural cold source heat exchanger are determined according to the structural requirements of national standard heat exchanger.(2)Model establishment of natural cold source heat exchanger.The heat transfer process of natural cold source heat exchanger is studied by numerical simulation method,and the model with different mesh number is verified to determine the best mesh number.A small experimental platform was built to verify the reliability of the numerical simulation results.The results show that the deviation between the experimental results and the numerical simulation results is very small,and the numerical simulation process of the natural cold source heat exchanger is reliable.(3)Comparison between heat transfer characteristics of segmental baffle heat exchanger and improved baffle heat exchanger.The results show that the flow field distribution of the improved baffle heat exchanger is more uniform,the flow dead zone is smaller,and the temperature field distribution of the shell side of the heat exchanger is more uniform.The frozen area of fluid in the shell side is obviously reduced.In the inlet velocity range studied in this paper,compared with the segmental baffle heat exchanger,the pressure drop on the shell side can be reduced by up to 10.61%,and the outlet temperature is stable at 275.08K,which meets the requirement of the application.(4)Study on the influence of improved baffle structure parameters on heat transfer characteristics of the heat exchanger.The structural parameters of the baffle are divided into three aspects:the number of baffle groups,the inclined Angle of oblique baffle and the aperture of vertical baffle holes.By comprehensive analysis of the influence of structural parameters of baffle on the comprehensive performance of heat exchanger,it is finally determined that the total performance of natural cold resource heat exchanger is better when the number of baffle groups is 4 groups,the inclination angle is 45°,and the aperture is 21mm.(5)Operation strategy of natural cold resource heat exchanger.In order to maximize the use of outdoor natural cold resource,four operation modes are developed for natural cold resource heat exchanger,and the stability of the outlet temperature of the heat exchanger is guaranteed by the regulation of variable air volume.Three operating conditions of each operating mode are simulated and verified.The results show that the outlet temperature of the heat exchanger can be stabilized within ±0.5℃ of the target temperature under each operation mode,which can meet the accuracy requirements of application sites.In this paper,the heat transfer process of natural cold resource heat exchanger is studied in depth.The research results can provide a theoretical basis for the structure optimization and practical application of natural cold resource heat exchanger. |
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