Experimental Investigation On Steam Condensation Characteristics Outside An Inclined Single Tube/Tube Bundle Accompanying With Air

In the event of a serious accident at a nuclear power plant,such as Loss of Coolant Accident(LOCA)or Main Steam Line Break(MSLB),there are measures that need to be taken to remove excess heat in order to ensure that there is no serious impact on the operation of the nuclear power plant.However,the presence of non-condensable gases can have an impact on the rate of condensation heat transfer.The deterioration effect of non-condensable gases needs to be taken into account in the design of passive heat exchangers.Most of the published studies are conducted for the vertical single tube and flat plate,where studies for inclined heat transfer tubes are lacking.In addition,the current study was conducted at low pressures below 0.6 MPa,which cannot meet the design pressure of 1.3 MPa for the miniaturized integrated reactor.The location of the heat transfer tubes in the heat exchanger and the selection of the heat transfer tube diameter have a significant impact on the overall heat transfer rate of the heat exchanger.The influence law of the heat transfer tube tilt angle and tube diameter under single tube/tube bundle conditions lacks the support of thermal hydraulic experiments.Based on the above background,the following research work was conducted and completed in this paper:(1)In this paper,a COAST(Condensation and Species Transport)experimental setup was built to study the effect of single heat transfer tube inclination angle and diameter on the steam condensation heat transfer with air.The experimental setup can provide a parameter range of0.2～1.6 MPa pressure,0.15～0.9 air mass fraction,and 30～120 °C subcooling for this experiment.Based on this experimental setup,the 19 mm,15 mm and 12 mm heat transfer tubes were studied and analyzed in this paper at 0° to 90° inclination angles.Combining a large amount of experimental data obtained from this experiment and classical data in published literature for unified generalization and analysis,the correlation with the largest amount of data,the widest range of parameter applicability and the largest number of influencing factors covered was fitted so far.The correlation agrees well with the experimental results and its accuracy is ±15%.(2)In this paper,the condensation heat transfer characteristics of 3×3 heat transfer tube bundles are investigated on the same experimental setup and with the same range of parameters.In which the heat transfer tube tube spacing is 2 d,the tube diameter and inclination angle are the same as the single tube experiment.The heat transfer characteristics of the tube bundle were analyzed by the coupling effect between three key mechanisms(tube bundle pumping effect,air layer superposition effect,and inter-row flushing effect)that affect the condensation heat transfer pattern of the tube bundle.The results show that the tube bundle has a different heat transfer pattern compared with the single tube in terms of inclination angle and tube diameter.(3)In this study,an artificial neural network(ANN)method is applied for the first time to the heat transfer experiment of air-containing steam condensation.In this study,a model was developed based on a large amount of data obtained from this experiment and related experimental data from published domestic and international literature to predict the heat transfer coefficient differently from the traditional multivariate nonlinear fitting method.The results show that the results predicted by the neural network method are more accurate than those predicted by the multivariate nonlinear fitting method in this study.The model can achieve a prediction accuracy of ±10%,which reduces the error by ±5% compared with the experimental correlation fitted in this paper,and can better predict the experimental data.