Design and Output Performance Model of Turbodrill Blade Used in a Slim Borehole
Small-diameter turbodrills have great potential for use in slim boreholes because of their lower cost and higher efficiency when used in geothermal energy and other underground resource applications. Multistage hydraulic components consisting of stators and rotors are key aspects of turbodrills. This study aimed to develop a suitable blade that can be used under high temperature in granite formations. First, prediction models for single- and multi-stage blades were established based on Bernoulli’s Equation. The design requirement of the blade for high-temperature geothermal drilling in granite was proposed. A Φ89 blade was developed based on the dimensionless parameter method and Bezier curve; the parameters of the blade, including its radial size, symotric parameters, and blade profiles, were input into ANASYS and CFX to establish a calculation model of the single-stage blade. The optimization of the blade structure of the small-diameter turbodrill enabled a multistage turbodrill model to be established and the turbodrill’s overall output performance to be predicted. The results demonstrate that the design can meet the turbodrill’s performance requirements and that the multistage model can effectively improve the accuracy of the prediction.
Performance Prediction of a Turbodrill Based on the Properties of the Drilling Fluid
High-temperature geothermal well resource exploration faces high-temperature and high-pressure environments at the bottom of the hole. The all-metal turbodrill has the advantages of high-temperature resistance and corrosion resistance and has good application prospects. Multistage hydraulic components, consisting of stators and rotors, are the key to the turbodrill. The purpose of this paper is to provide a basis for designing turbodrill blades with high-density drilling fluid under high-temperature conditions. Based on the basic equation of pseudo-fluid two-phase flow and the modified Bernoulli equation, a mathematical model for the coupling of two-phase viscous fluid flow with the turbodrill blade is established. A single-stage blade performance prediction model is proposed and extended to multi-stage blades. A Computational Fluid Dynamics (CFD) model of a 100-stage turbodrill blade channel is established, and the multi-stage blade simulation results for different fluid properties are given. The analysis confirms the influence of fluid viscosity and fluid density on the output performance of the turbodrill. The research results show that compared with the condition of clear water, the high-viscosity and high-density conditions (viscosity 16 mPa∙s, density 1.4 g/cm3) will increase the braking torque of the turbodrill by 24.2%, the peak power by 19.8%, and the pressure drop by 52.1%. The results will be beneficial to the modification of the geometry model of the blade and guide the on-site application of the turbodrill to improve drilling efficiency.
Phase formation during mechanical alloying in the Ti–Si system
Abstract Mechanical alloying of Ti–Si powder mixture or TiH 1.924 –Si powder mixture was performed by high-energy ball milling, in which the Ti to Si mole ratio was 1:2. The phase formations in both mixtures during milling were investigated by X-ray diffraction. Mechanical alloying a mixture of elemental powders led to the formation of TiSi 2 equilibrium compound, while when starting from Si + TiH 1.924 , a metastable phase was formed. The metastable phase completely transforms to TiSi 2 when the mechanically alloyed powder is annealed at temperatures above 800 °C. Two different pathways of phase transitions during mechanical alloying are attributed to the existence of hydrogen atoms, i.e., when starting from Si + TiH 1.924 compared to Si + Ti, the kinetics for the formation of the TiSi 2 intermetallic compound slows down. The kinetics related to the different phase transitions depending on the starting powder mixture are discussed.