Research On Heat Transfer Enhancement Of Heat Transfer Tubes In The Gas-fired Vacuum Boiler

This topic is the project of Zhengzhou University Research Center of Energy Saving Technology and Hennan Liwei heat energy equipment manufacturing Co Ltd. Based on the practical application of products and the feedback information of users, a series of research about vacuum boiler is carried out. At first, the background and significance of the research is introducted, and the problem of low heat efficiency in vacuum boiler is put forward and analysed. Next, the article researches the diffirent methods of heat transfer enhancement about two type tubes. At last. it improve steam circulation in order to optimize heat transfer.The main works and productions in this paper are as follows:(1) According to the direction of study, the topic points out the disadvantages about vacuum boiler. It summarizes two disadvantages. One is that the common heat transfer tube has the larger thermal resistance. Because the fluid near the tube wall velocity is almost zero, forming a greatly thermal resistance. Another is that the condensation water between tubes can not be timely eliminated, weakening the condensation heat transfer.(2) The research sets up a model of equal chord waveform tube. It analysis the tube’s heat transfer mechanism based on the principle of field synergy. The tube can make the fluid flow, which mainstream fluid come to boundary or boundary fluid come to mainstream. This flow improves the collaborative feature of temperature field and velocity field and reduce the synergy angle, achieving the effect of heat transfer enhancement. Then, by means of orthogonal test and Fluent, we simulation16models one by one. And we get the best structure by the methods of range analysis. Next, we get the synergy angle of temperature field and velocity field by calculation. Based on the calculation of overall thermal performance, the convective heat transfer coefficient of equal chord waveform tube increased by47.6%than commen tube. At last, we put forward the processing method of qual chord waveform tube.(3) Be directed against large diameter heat transfer tube, we also develop the reearch. Becanse it is difficulty to change the structure of large diameter tube, the article put forward the method of inserting the spiral ligament to enhance heat transfer. In virtue of the commen spiral ligament having a greater resisrance for water, we invent the grid spiral ligament. First, the article analysis3kinds principle of heat transfer using the grid spiral ligament. Second, we set up the models of commen spiral ligament and grid spiral ligament by the same structure, getting the grid spiral ligament having the better effect of heat transfer. Finally, we set up25working conditions, getting the different feature of heat transfer and pressure drop. And we point out the orderliness of heat transfer and pressure drop with the changes of Reynold number and twist ratio.(4) Based on the practical application of products and the feedback information of users and the principles include of field synergy, the article analysis systemly the condensation heat transfer mechanism of the part of beat transferr in the boiler. In order to promote the groom of condensed water and change the flow direction of steam, we set up some baffles, achieving an effective combination of structural modification and enhancement of heat transfer. At the same time, we set forth the mechanism of enhancement of heat transfer. Although this part is not the research focus of the article, it has the certain instruction significance for the condensation heat transfer of this kind of boilers.