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Inducer has significant effect on improving the cavitation characteristic of centrifugal pump. Several inducers were designed and modeled by Pro/E software. The mesh of flow field was done by ICEM and then was imported to ANSYS CFX to analyze the inducer's cavitation characteristic. Effects of the blade number on the performance of an inducer are investigated in the present paper. The inducers were designed on the basis of identical design flow rate and identical pressure elevation at nominal flow rate. The study focuses on the steady behavior of the inducers in cavitating conditions. Evolutions of performance, torque, mass flow rate, and amplitude of radial forces on the shaft according to the inlet pressure are considered. Furthermore, cavitation instabilities are analyzed in the study. The purpose of the present study is to investigate the pressure distribution and vapour volume fraction distribution through numerical simulations using the Navier-stokes solver with computational fluid dynamics (CFD) code. IntroductionThe phenomenon of cavitation in centrifugal pump is an important feature of the process of its operation and one of the concern issues of the design, manufacture, use and management of a centrifugal pump.In the process of pump operation, for some reason, when the absolute pressure of conveying liquid medium dropped to vaporization pressure at that temperature in the flow section of the local area, liquid in this area begin to boil, produce steam, form bubbles. These bubbles flow forward along with the liquid until a certain place of high pressure, high pressure liquid around the bubbles result in the bubbles shrink sharply that broken, and at the same time, the liquid particle filling holes at high speed, hit each other and form water hammer. This phenomenon will make the flow components suffer from corrosion damage when occurred in the solid wall. The process which bubbles was formed and then ruptured and cause damage to flow components is the process of water pump cavitation.Inducer is actually a kind of axial flow impeller with small blade load, the effect of the centrifugal force is small. It is not easy to produce the two phase separation of liquid and bubbles. It has high performance of resistance to cavitation. It also can work normally and not blocked even under the condition of local cavitation. For centrifugal pump, the model of installing inducer in front of the centrifugal impeller, the essence of which is greatly reduces the required NPSH of pump unit, was used more in order to improve its performance of resistance to cavitation. In order to improve both the cavitation resistance of the inducer itself and the head of the inducer to meet the requirement of high cavitation performance of the main impeller, the model of varying pitch inducer is often used. Under the condition of same impeller import outer diameter, the variable pitch inducer can more effectively reduce the necessary NPSH of pump unit than uniform pitch inducer.

A one-dimensional unsteady heat conduction simulation for downhole heat exchanger (DHE) is established in this paper, and the Lattice Boltzmann Method is used for the numerical simulation. In the model proposed, the influence factors of the temperature gradient with well depth, well pipe diameter, thermal properties of pipe, circulating water flow rate and inlet temperature on the outlet water temperature or heat output have been taken into account. According to the DHE experimental data, a comparison was made between the results of simulation and experiment. The result shows that the model can be used to predict the outlet water temperature of DHE at given conditions, but the deviation from the experiment increases with time, which is probably resulted from the natural convection occurred in the aquifer, and its intensity is gradually strengthened.

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