Study On Condensation Heat Transfer Characteristics Of Tube Bundle In Vacuum Boiler

Since the vacuum boiler was first launched in Japan, due to its operation such as safe and reliable, no oxygen corrosion, long life, compact structure, less land occupation, high efficiency, flexible HTM temperature and so on, it has received more and more attention and research at home and abroad in the field of thermal equipment.The vacuum boiler is also called vacuum phase-change boiler, it has two characteristics, one is the "vacuum", the other is "phase-change ". This thesis mainly discusses the steam-water heat transfer characteristics outside heat exchanger of the gas vacuum boiler. The steam-water heat process in vacuum boiler is very complex. There are a lot of factors, such as vacuum degree, cooling water flow rate, inlet temperature and outlet temperature, steam flow, heat flux, tube arrangement etc. The impact of these factors on the bundle condensation heat exchange efficiency performance called "bundle effect". In order to get the mechanism of the influence of these factors on tube bundle heat transfer efficiency, this paper carried out experimental research and numerical simulation, and put forward the measures to enhance heat transfer according to the research results.In the experiment, in cooperation with the Ningbo Fulton thermal equipment limited company to build an experimental platform of the vacuum boiler. The boiler type is WNS0.47-1.0-60/50-YQ, and its rated thermal power is 0.47MW. Install the measuring points in the experimental stage, and set different conditions, at last get the result what is the effects of tube row position, pipe flow velocity, heat flux, the vacuum degree on bundle effect. The experimental result shows that heat exchanger is not uniform in vacuum boiler. The heat flux is larger, heat transfer is more uneven.Then we used the ANSYS software to simulate the steam flow with the non condensable gas. The model selects a typical experimental condition. It included mass conservation equation, momentum conservation equation, energy conservation equation. The results of the model can well explain the experimental bundle condensation heat transfer in uneven phenomenon.According to the experimental results and numerical simulation results, this paper presents the heat transfer enhancement measures. To solve evaporation-condensation coexistence problem, it put forward some measures such as split type boiler which introduces the steam from the top of the boiler, or installing oblique baffle plate outside the tube bundles. In order to weaken the bundle effect, it added a guide groove under the bundles. This subject has a certain reference value for the study of vacuum boiler, and provides a direction of development of energy equipment.