| Currently,the number of skyscrapers is increasing in most cities.It is nearly impossible for the existing fire pumps to reach the height of fire disaster due to the low head.Therefore,the fire would be hardly controlled instantly.The application of high-speed centrifugal pumps has become an important field of fighting fire in high-rise buildings in order to enable fire pumps reach effective height and avoid disadvantages,such as huge size,complicated structure,inconvenient maintenance,which are caused by multi-stage pumps.The full name of pump system that is mounted on fire vehicle is called fire pump system for vehicle.Generally,it consists of PTO device(power take-off),pump,inlet and outlet pipes and manipulation mechanism.The fire pumps are equipped with different fire equipment according to different situations.Fire pump is the basic and core part,which maximum discharge is 288m3/h and maximum head is 150 m.However,it cannot meet the requirement of fire.It is necessary to increase stage of pump on the premise of maintaining discharge,but the increased stages will cause the slow increase of head and largely increase volume of pump and decrease the discharge,whichcannot still meet the requirements in the limited room of fire vehicle.Consequently,the developing of a small volume high-speed centrifugal pump can meet the requirements of fire-fighting in high rise buildings.In most cases,high-speed rotation of high-speed centrifugal pumps and flow will lead to low-efficiency,serious cavitation and loud noise.Design methods for improvements should be taken into account to handle with disadvantages above and meet standards of fire pumps.Firstly,equal-pitch inducers and front-set orifice plates could be added to improve cavitation performance of pumps.The equal-pitch inducers with simple design methods are practical for mass production with low cost and solid hydraulic performance.In addition,the front-set orifice plates restrict back flow at inlet and strengthen anti-cavitation performance of inducers.Secondly,flow enlargement method and non-overload design have been employed on impeller parameter.Moreover,5+5 splitter blades are used on impellers.These methods can not only increase the efficiency of pumps and avoid the overload results,but also lower pressure fluctuation amplitude and play the role in reducing fluctuation and noise.Finally,the channel can be extended by adding vaned diffusers to increase head of centrifugal pumps and lower pressure fluctuation amplitude.Head can be designed as 500 meters,rotation speed 10000 rounds per minute,flow 170 cubic meters per hour of pumps and modeled through the UG based on the methods above.Steady and unsteady characteristics can be analyzed through Ansys after finishing the hydraulic model.Steady results show that the distribution effects of cloud pictures for velocity,pressure and turbulent kinetic energy are desirable.External characteristic curve results show that head curves of pumps are smooth,high efficiency areas are wide,the shaft power curves are stable and the overload result is not obvious.Data above are in line with relative standards of pumps.Unsteady results show that head,efficiency and shaft power output of pumps are stable,fluctuation amplitude is little and hydraulic performance is desirable.Through setting pressure fluctuation monitoring points at key positions of centrifugal pumps and selecting eight points to analyze,which are three points at impellors,two points at inducers and three points at spiral-shaped volutes respectively,the result shows that pressure fluctuation at different positions is featured by periodic law,that is,the pressure fluctuation amplitude is small.In general,pumps operate stably at different conditions and can meet requirements of fighting fire in high-rise buildings. |
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