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A feature of reverse circulation pneumatic down-the-hole (DTH) hammer drilling system is its ability to reduce the emission of respirable dust which is known to be harmful to drilling workers and equipment. The enhanced dust control performance of the drilling system requires better understanding and insight into the airflow behavior at the bottom of the borehole. To investigate the transportation and distribution of cuttings under various drilling parameters, and to evaluate the dust control performance, we conducted a series of simulations using computational fluid dynamics (CFD) multiphase modeling. Finite volume analysis was performed on a reverse circulation drill bit with an optimized structure reported in a previous study. The results show that increasing the input airflow rate can directly improve the dust control efficiency. The rising value in terms of cuttings feed concentration, rate of penetration (ROP), particle diameter, and specularity coefficient would decrease the dust control performance. Furthermore, the characteristics of the cutting distribution vary with the operating parameters and demonstrate the multiphase flow pattern in the RC-bit. This work may provide instructive insights into cutting transportation under various drilling parameters commonly considered in the drilling process and promote the development of dust suppression with efficient drilling operations.

Microscale resonators are widely used in modern technology and achieving large tunability of their resonant frequency is highly desirable. Here, a design for electro-superlubric springs, based on a restoring force between sliding solid surfaces, is predicted to have continuously tunable resonant frequencies from zero to several GHz.

It is difficult to achieve high current density and long lifetime for micro generators owing to the common friction and wear. Here the authors invent a microscale Schottky superlubric generator to tackle this issue, reporting not only high current and power densities but also long lifetime of at least 5,000 cycles.

Structural superlubricity (SSL) is a state of nearly zero friction and zero wear between two directly contacted solid surfaces. Recently, SSL was achieved in mesoscale and thus opened the SSL technology which promises great applications in Micro-electromechanical Systems (MEMS), sensors, storage technologies, etc. However, load issues in current mesoscale SSL studies are still not clear. The great challenge is to simultaneously measure both the ultralow shear forces and the much larger normal forces, although the widely used frictional force microscopes (FFM) and micro tribometers can satisfy the shear forces and normal forces requirements, respectively. Here we propose a hybrid two-axis force sensor that can well fill the blank between the capabilities of FFM and micro tribometers for the mesoscopic SSL studies. The proposed sensor can afford 1mN normal load with 10 nN lateral resolution. Moreover, the probe of the sensor is designed at the edge of the structure for the convenience of real-time optical observation. Calibrations and preliminary experiments are conducted to validate the performance of the design.