| Heat exchanger is a very important apparatus in many fields, such as petroleum refining, power generation, chemical engineering, process industry, food industry, etc. Among the all types of heat exchangers, shell-and-tube heat exchanger (STHX) has many advantages such as mature technique, reliable structure and widely applicability, which make it widely utilized in industrials. The baffle element plays very important roles in shell-and-tube heat exchangers, which can not only support the heat transfer tube bundles, but also disturb the fluid flow of shell side. According the direction of fluid flow of shell side, the shell-and-tube heat exchanger can be divided transverse flow, longitudinal flow and helical flow. With different flow states, the performance of the STHX will be different. The heat transfer coefficient of the shell side has a heavy impact on the performance of the heat exchanger.The traditional shell-and-tube heat exchanger with segmental baffles have many disadvantages, such as high pressure drop, low heat transfer efficiency, harmful vibration caused by the shell-side flow normal to tube bundles. When the traditional segmental baffles are used in STHX, higher pumping power is often needed to offset the higher pressure drop under the same heat load. Therefore, it is essential to develop a new type of STHX using different types of baffles to achieve higher heat transfer efficiency and lower pressure drop. Pressure drop and heat transfer are interdependent and both of them essentially influence the capital and operating costs of any heat exchange system. In order to improve the performance for shell-and-tube heat exchanger, heat exchangers with different types of baffles are developed, which have relatively higher heat transfer efficiency and relatively lower pressure drop. Therefore, theoretical and experimental sdudies are conducted to investigate the flow and heat transfer characteristics of longitudinal flow heat exchanger, and combined with the pricinple of heat transfer enhancement in the core flow, the new kinds of heat exchangers can be proposed and investigated.As one of major devices, the rod baffle heat exchangers are wildly used in various industrials, but there has no uniform recongnization for the the mechanism of heat transfer enhancement. Based on the physical and mathematical model for rod baffle heat exchangers, the fluid flow and heat tranfse characteristics are investigated, and the results present that the mechanism of heat transfer enhancement can be interpreted by the pricinple of heat transfer enhancement in the core flow. Besides, studies on defferent section configiuation of rod are carried out, and the results show that the shape of the cross section of rod has a heavy impact for flow and heat transfer characteristics. And the rod with rect shape has high heat transfer coefficient and pressure drop, whereas the rod with circle section has lower heat transdfer coefficient and flow resistance. And with the combination of rect and circle shape of rod, the heat transfer coefficient can be improved.On the basis of pricinple of heat transfer enhancement in the core flow, a new kind of rod baffle heat exchanger with thick and thin rod are proposed and investigated, and CFD technique are used to investigate the performance, and the results present that with the combined structure the heat tranfe present no significant degradation. But the flow resistance can be reduced; as a result, the overall performance can be greatly improved. Besides, a new type of shell-and-tube heat exchanger with a combination of rod and van type spoiler was designed. Corresponding mathematical and physical model on the shell side about the new type heat exchanger are established, and fluid flow and heat transfer characteristics are numerically analyzed. The simulation results showed that heat transfer coefficient of the new type of heat exchanger approximates that of rod baffle heat exchanger, but flow pressure drop is much less than the latter, which indicates that comprehensive performance of the former is superior to that of the latter. Compared with rod baffle heat exchanger, heat transfer coefficient of the heat exchanger under investigation is higher under same pressure drop, especially under the high Reynolds numbers.On the basis of the anasysis of the geometry and flow characteristic, combined with periodical full developed model, an integrated model was made to investigate the performance, and the results are analyzed according to the first low of the thermodymics and the seconde low of thermodymics. And the results show that, there would present some difference for the evaluation results.The mechanism of heat transfer enhancement of flower baffles exchanger need to be deeply investigated. The CFD technique is adopted to study the performance of flower baffle heat exchanger, and a comparision with segmental baffle heat echanger are made. The results show that, under the same Re number, the pressure drop of the flower baffle heat exchanger is 0.45 times of that of segmental baffle heat exchanger, but the heat transfer coefficients are nearly same, as results, the overall evaluation coefficiency is 2.2 times of that of the segmental buffle heat exchanger.On the basis of theoretical studies, a type of shell-and-tube heat exchanger with flowerbaffles is designed, fabricated and tested. The experimental investigation for flower baffles and segmental baffle heat exchanger are conducted, and comparisons of operation performance between the two type heat exchanger are also conducted. The results present that, under same conditions, the comprehensive performance of the new type heat exchanger is 20%~30% higher than that of the segmental baffle heat exchanger. Experimental investigation of heat transfer and pressure drop for the new type of rod baffle heat exchanger are slso conducted, and the experience relation of Nu ,Δp with Re are also obtained based on the experimental data.,The research results can serve as guardline for the design and application of longitudinal flow heat exchangers.
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