The Experimental Study On Enhancing The Heat Transfer Of Passive Residual Heat Removal Exchanger

The heat exchanger of passive residual heat removal system of a nuclear power plant is a main energy output device with strong heat transfer capacity, applying which can not only improve the safety of nuclear reactor, but also increase the economy of nuclear facilities.In this paper, the experimental studies on the heat transfer performance of heat exchanger with 5 different kinds of enhanced tubes were executed under different operation conditions. In the experiments, the purified water was selected as working fluid. Meanwhile, the condensation heat transfer characteristics of B30 tube were also primarily studied. Finally, the simulation of heat transfer with the loss of cooling water was performed experimentally. The main content of the research and the main conclusions are as following:1. The experimental studies on the extended surface tube (integral pin-fin tube, porous surface tube) and smooth tube were performed. Through the analysis and calculation for experimental date, the empirical formula about boiling transfer's characteristics of three kinds of vertical tube was given out.2. The heat transfer characteristics of two kinds of composite enhancing tubes were also studied. The first tube was winded pin-fin tube which was improved and self-designed. The experimental results showed that the heat transfer coefficient on the external surface of this kind pin-fin tube was 1.6～2 times compared with the sooth surface tube ; the surface temperature reduced 2～5℃compared with sooth surface tube under the condition of the same vapor pressure. The other kind of enhancing tube is annular gap tube , whose heat transfer capacity increased 1.2～1.8 times compared with the sooth surface tube. However, this kind of annular gap tube's enhancing effect was very good in low heat -flow density; the enhancing effect was not obvious in high heat-flow density.3. The study on the characteristics of condensation heat transfer in B30 tube was performed experimentally. In the initial service stage of B30 tube, the inside of the tube took drop wise condensation as the main heat transfer mode, and this kind of mode exhibited strong heat transfer capacity. With the increasing of service time or deposit time, the mode changed to film condensation heat transfer. Heat transfer capacity decreased sharply and continuously until the mode become steady film boiling. The reason was analyzed in the thesis.4. The case of the loss of the water in In-containment Refueling Water Storage Tank (IRWST), which means the tube of the passive residual heat exchanger partially submerged in the water, was also simulated. The research indicated that when the residual heat transfer capacity of three kinds strengthening heat exchanger tubes equaled with whole length of smooth tube's, the allowable falling-height of water level were as follows respectively: 20% for pin-fin tube and 39% for both winded pin-fin tube and porous surface tube. The experiment results also indicated that the boiling water level was not linear to the heat transfer capacity of all kinds of heat tube which used in experiment, the heat transfer of vertical heat tube at condition of incompletely submerged was analyzed , and the formula about residual heat capacity of heat exchanger was given out at last.