| In the nuclear power plant, the bearing is an indispensable component, so effectively extending the service life of bearings is the foundation to ensure sustained, safe and stable operation for nuclear power facilities. For the lubrication of bearing, generally, we use lubrication oil to bring out the heat generated by bearing and re-enter into bearing after acquiring the right temperature with cooler. Therefore, the oil cooler is important to keep safety of nuclear power plant. Furthermore, researching the heat transfer mechanism and enhancement characteristics of oil cooler is very important to increase the localization rate of nuclear system, reliability of facilities and to achieve equipment miniaturization.In the project, plain tubes commonly are used as heat exchanger components in the oil cooler, which have disadvantages of low heat transfer efficiency, bulky and complicated structure. On the basis of a large number of domestic and international references, in this paper, entire pin-fin tube and fluorescent tubes were chose as heat exchanger, and designed mixed bundle using their self-supporting characteristic, moreover, design shell-side oil flow to dual process and tube side of the cooling water to single side according to the actual project. Meanwhile, visible study was conducted by using the transparent plexiglass plate both sides in the oil cooler in order to obersive the real flowing situation of shell-side lubrication oil. To compensate for the lack of experiment, the numerical simulation calculations was also conducted. The main work and results of this paper are given as follows:1. In this paper, to test new oil cooler, lots of experiments were conducted and68#turbine oil was used as working fluid. The result showed that heat transfer coefficient was420W/(m2-K))and heat per unit volume was1190kW/m3when the oil inlet temperature is55℃, cooling water inlet temperature is24℃, oil flow is20.7m3/h and cooling water flow is20m3/h. After the research, the speed of oil flow, as the key factor, was found to affect heat transfer and resistance characteristics of oil cooler. The temperature and flow of cooling water also can affect heat transfer to a certain extent and have little effect on the resistance characteristics. To oil cooler, the way of placement has little effect on heat transfer characteristics. By analysis and regressing experiment data, the experimental correlation formula was obtained, that can be used for project engineers. 2. On this base, the experiment data of dual-process round oil cooler and that of single square oil cooler were compared. And the results showed that heat transfer coefficient and heat per unit volume of new oil cooler are higher, and it also can achieve the goal of enhancing heat transfer and miniaturizing equipment. Under the same shell-side Re, compared dual-process square oil cooler to round one, the former one had1.1～1.3times overall coefficient of heat transfer,1.2-1.4times heat per unit volume and it also had0.73～0.88times overall heat transfer coefficient as well as0.80-0.91times heat per unit volume than single square oil cooler.3. In the visible study, flowing situation of shell-side lubrication oil was observed with different flow. Some situations were found that oil was not pure single phase flow in the first flowing, mixed some small bubbles, in a certain range, in the second flow small bubbles could converge and become gas bombs, however, this situation cannot emerge within any first flow. And on the base of it, the mechanism of bubble influencing on heat transfer was analyzed and the precious video and photos were gained with different flow can be for furthermore study.4. Because of low experimental pressure of oil cooler (<1Mpa) rather than engineering designing request (4.5Mpa), the oil cooler whether can meet the engineering requirements or not still need to be answered. In order to make sure the experiment whether can be used in practical situation or not, to compensate for the lack of experiment, and to provide a basis for designing the new oil cooler, calculation of the stress of new square head and shell and a stress numerical simulation with ansys software were conducted.5. FLUENT software was used to study on simulation of overall pin-fin tube oil cooler data. Using porous media model to study on velocity, temperature and pressure contour of shell-side oil can help acquire the inner distribution of them. The result showed that pin-fin stimulated separation and turbulence of fluid boundary layer and enhanced heat transfer; however fluid was non-uniform flowing in the cross-section of the oil cooler and leaded to non-uniform temperature distribution. But the numerical results and experiment data were in good agreement. |
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