Prediction Of Four-quadrant External Characteristics Of Reactor Coolant Pump Under Variable Rotational Speeds

Nuclear power is not only used to generate electricity,but also a vital source of power in the military.Due to its simple structure,compact size and flexible operation,the pressurized water reactor is more suitable for ship power system.In this paper,the fourquadrant characteristics of the model pump(at a scale of 0.5)of RCP were studied,and the main conclusions are as follows:(1)In positive speed conditions,calculate the performance of RCP under designed speed(n = 1750 r/min),half speed(n = 875 r/min),a quarter of the speed(n = 438 r/min)and the minimum limit speed(n = 100 r/min).With the increase of the flow rate,the head curves are decreasing gradually,and there is a formation of the hump at small flow range.The torque curve drops gradually in the negative discharge,slowly rises in the positive discharge,peaks at the design flow rate point and then decreases gradually.There is an anti “N” shape in the small flow range of the impeller head curve.The minimum loss of the RCP at design point and its corresponding similar working condition in positive discharge and the loss of the volute and diffuser gradually increased when the flow rate leave the design point.When the speed is greater than n/2,the loss of the volute higher than the diffuser.However,the loss of the volute less than the diffuser when the speed is less than n/2.The loss mainly comes from the impeller when the RCP working in negative discharge conditions.The minimum radial force of the RCP at design point and its corresponding similar working condition and it gradually increased when the flow rate leave the design point.The mean of radial force decreases with the speed slowing down.(2)In negative speed conditions,calculate the performance of RCP under reverse rated speed(n=-1750 r /min),the reverse half speed(n=-875 r /min)and a quarter of the reverse rated speed(n=-438 r /min).With the increase of the flow rate,the head curves are decreasing gradually,but the trend is reduced in the small flow range of negative flow,and the curves is raised up.The torque curve decreases with the increase of flow,and the three curves are almost parallel.There is an anti “N” shape in the small flow range of the impeller head curve.When the RCP working as turbine,the loss mainly from the impeller.The loss of diffuser and suction gradually increased in the small flow range.The loss mainly comes from the diffuser and the volute under positive discharge.The loss in the volute is gradually increased from zero to the parabola.The impeller head tends to be constant at a flow rate point,which indicates the work ability of the reverse impeller is limited.The minimum value of the radial force curve is near the zero flow point and it gradually increased when the flow rate leave the zero point.The mean of the radial force decreases with the speed slowing down.(3)Under zero speed condition,the head curve decreases with the increase of flow rate,and central symmetry about zero flow point.The torque curve is similar to the pump head curve.In the negative discharge,the torque value is positive,indicating that the liquid has the tendency to push the impeller to reverse;in the positive discharge,the torque value is negative,indicating that the liquid has the tendency to push the impeller forward.When the RCP working as turbine,the loss mainly from the impeller.The loss of diffuser and suction gradually increased in the small flow range.Under the negative discharge conditions,the energy loss of the RCP is mainly derived from the impeller.Under the positive discharge conditions,the loss mainly comes from the diffuser,according to the proportion of loss,the order is the diffuser,volute,impeller,discharge section and suction section.The minimum value of the radial force curve at the point of zero and it is gradually increased when the flow rate leave the zero point.In positive discharge condition,the increase of radial force is not obvious;in negative discharge condition,radial force increases greatly.(4)As can be seen from the dimensionless four-quadrant characteristic curve,as the flow rate and speed increase,the equal head curve will get closer and closer to the zero head line h=0,and the torque will be closer to the zero torque line.According to the dimensionless coordinate axis,zero head line and zero torque boundary,the entire four quadrant can be divided into eight regions,corresponding to eight different working conditions.