Energy Conversion Characteristics Of Stainless Steel Stamping And Welding Centrifugal Pumps And Design Method

With the development of plate stamping and welding techniques for stainless steel, the casting process for centrifugal pump, which is high energy consumption and heavy pollution, has been gradually replaced by the stamping and welding technique. The centrifugal pump made by this technique has developed into a new type which conforms to the low-carbon mode of economic development and has become the successor of casting pump in many fields with the advantages of lower cost and better performance.The reform and development of producing techniques put challenges on the hydraulic design methods of centrifugal pumps, such as (1) The existing design data are not fit for the new producing techniques. (2) The present design theories cannot bring the advantages of the new techniques into full play. (3) The market has new requirements to present diverse and personalized products. In view of the above problems, the present thesis has carried out researches on the energy conversion characteristics of stainless steel stamping and welding centrifugal pump, and has put forward a new hydraulic design method with multiple design objectives.The present research tries to seek the regularity from the internal flow structure and mechanism, and analyes the characteristics of energy conversion by reference to the flowing rules, which aimed at a new design method. The present research includes into the following three parts:1. Analysis of the internal flowFirst, the motion features of internal flows in stainless steel stamping and welding centrifugal pump were explored by using normalized helicity method to find out the structure of longitudinal vortice in the flow field. The results reveal that at the inlet there exist induced vortices in which the vortex core deviates from the central axis. In the passage of impeller under the operating condition of (0.6～1.4)Qd, The longitudinal vortices are mainly composed of slowing rotating curved vortices which distribute in a scattered way and have a weak influence on the performance of centrifugal pump. The volute is occupied by a couple of revelry rotating symmetrical vortices. At the larger flow rates, there are eminent secondary vortices in the divergent section which are companied by vortex breakdown which causes the energy loss increasing.Secondly, the internal steady flow distribution in the passage of impeller was analyzed based on the three-dimensional flow separation vorticity dynamics theory. The key physical parameter---BVF(Boudary Vorticity Flux) in the rotating coordinate system is derived to analyse the relative velocity in impeller. And the conclusions were drawn that the centrifugal force is another important source of BVF besides pressure gradient, and in most area of impeller passage made by stainless steel stamping and welding centrifugal pump, the happening probability of large-scale flow separation is very low, and the flow is uniform mostly.2. Characteristics of energy conversionSeveral energy conversion characteristics such as the process of flow energy transfer and conversion within the impeller and the elements and the distribution law of hydraulic loss were studid based on CFD technology, by analyzing the energy features, including the distribution of the shaft power for different impeller parts, the power change in different radial directions and the radial distribution of profile power density, the dissipation rate, and the hydraulic loss at the near-wall and core-flow regions. The results show that the actual flow channel before the throat at the impeller outlet is a key area of energy conversion, where most energy of the flow is gained; the hydraulic loss in the impeller is mainly caused by wall friction, which is concentrated on suction side of the impeller blade and near the outlet. The study also found that the total energy input and output are transiently inconsistent in unsteady state in a single impeller channel. Based on the theory of fluid mechanics, formulas to figure out the kinetic energy rate and its density rate can be derived from the existing CFD data, which show the characteristics of the temporal and spatial energy distribution and also explain the unsteady characteristic of energy conversion.In steady and unsteady states, the characteristic of spatial distribution of dynamic pressure and static pressure energy which transform into each other, and strength characteristic and the law of energy variation along the flow were studied. The principle of the conservation of moment is applied to reveal the reasons of the unregular circumferential distribution of the static pressure in the volute, which explain that the unregular distribution is a result of inherent attribute for a volute with specific cross-section areas and is also a principle of the waving characeristics for the energy conversion of stainless steel welding and stamping centrifugal pump.3. The hydraulic design method for stainless steel stamping and welding centrifugal pumpFirstly, the calculation of pump head is divided into dynamic pressure head and static pressure head respectively. Based on the relations of energy conversion, a theoretical calculating method of pump head is proposed, which is different from the estimation formulas of hydraulic losses. By comparing with the experimental results of 7 centrifugal pumps, whose specific speed ranging from 32 to 163, the results show that the computational results are with good consistent with the experimental ones, which certified the computational method is reliable and reasonable.Secondly, in light of the current situation during impeller design, the axial and circumferential flow channel is not sole after the define of the inlet and outlet parameters. The effects of impeller blade wrap angle and the shape of axial projection of the impeller on performance of centrifugal pump were analyzed respectively, referring to the research results on characteristics of energy conversion and stainless steel stamping and welding technology. It puts forward the concepts of the average vane angle in the throat at the impeller outletβt2, and the equivalent impeller outlet width be2, and the computing methods ofβt2,be2 and the parameter the slip factor a, in order to obtain the impeller outlet velocity triangle. By combining this method and the theoretical pump head mentioned above, a corrected prediction is made about the effects of impeller blade wrap angle and shape of axial projection of the impeller on the performance of centrifugal pump.Thirdly, according to the independence principle, five parameters are chosen as the main parameters of this design method, including the impeller diameter D2, the average vane angle in the throat at the impeller outletβt2 and the equivalent impeller outlet width be2, the slip factor a and area of the volute throat At. Then the functional relations are established among these parameters and the performance of stainless steel stamping and wielding centrifugal pump. The multiple design objectives are divided into and qualified as constraint conditions while the optimization algorithm is involved in the calculation of the main parameters. On the basis of quintic Hermite interpolation function, an impeller blade drawing method is presented in this paper which realize the multi-objectives hydraulic design of stainless steel stamping and welding centrifugal pump.Finally, three models made by stainless steel stamping and welding technique with the multiple design objectives are designed according to the design methods proposed in this paper. The corresponding tests prove the realization of expectation to the design method.