Shisong Li

Shear force induced monodisperse droplet formation in a microfluidic device by controlling wetting properties

Perpendicular flow is used to induce oil droplet breakup by using a capillary as water phase flow channel. It is a new route to produce monodisperse emulsions. The wetting properties of the fluids on the walls are exceedingly important parameters. Depending on the oil and water flow rates, different spatial distributions of the two phases as laminar, plugs, cobbles and drops, are obtained. The effects of two-phase flow rates on plugs and drop size are studied, and the different droplet formation mechanisms of plug flow and drop flow are discussed. Two quantitative equations utilized to predict the droplet size are developed.

Controllable gas-liquid phase flow patterns and monodisperse microbubbles in a microfluidic T-junction device

This letter describes the gas-liquid phase flow patterns and the mechanism of generation of monodisperse microbubbles in a T-junction microfluidic device using the crossflowing shear-rupturing technique. The bubble size is ranged from 100 to 500μm. The air phase states as isolate air slugs, “pearl necklaces,” periodic isolate bubbles, zig-zag bubble patterns, and multiple-bubble layer can be observed in the wider measured channel. The bubble size relates with the continuous phase flow velocity and viscosity as Vb∝1∕(μcuc), while being almost independent of surface tension γ and air phase flow rate Qg, for the conditions used in this work. The bubble formation mechanism by using the crossflowing shear-rupturing technique is different from the hydrodynamic flow focusing and both geometry-dominated breakup techniques. Our system provides independent control of both the size and volume fraction of dispersed bubbles.

A determination of the Planck constant by the generalized joule balance method with a permanent-magnet system at NIM

The joule balance experiment has been carried out at the National Institute of Metrology, China (NIM) since 2007. By the end of 2013 the first generation of the joule balance (NIM-1) achieved a measurement uncertainty of 7.2 × 10−6 (k = 1). To reduce the measurement uncertainty further, the next generation of the joule balance apparatus (NIM-2) system is under construction. A new coil system using ferromagnetic material is being adopted in NIM-2 to reduce self-heating in the coils. However, the effects on the measurement of the mutual inductance from the nonlinearity and hysteresis of the ferromagnetic material will bring a considerable measurement uncertainty. Inspired by the watt balance, the measurement of the mutual inductance is replaced by an equivalent measurement of the magnetic flux linkage difference. The nonlinearity and hysteresis will not be a problem in the measurement of the magnetic flux linkage difference. This technique comes from the watt balance method. It is called the generalized joule balance method, which is actually a modification of the watt balance method. However, it still represents a valid change that can reduce the difficulty of dynamic measurement experienced using the watt balance. Permanent magnets can also be adopted in the generalized joule balance. To check the feasibility of the generalized joule balance method, some preliminary experiments have been performed on NIM-1. A yokeless permanent magnet system has been designed and used to replace the exciting coils in NIM-1. In this paper, the structure of the yokeless permanent magnet system is introduced. Furthermore, a determination of the Planck constant with the permanent magnet system is presented. The value of the Planck constant h we obtained is 6.626 069(17) × 10−34 J s with a relative standard uncertainty of 2.6 × 10−6.

Field representation of a watt balance magnet by partial profile measurements

Permanent magnets with high-permeability yokes have been widely used in watt balances for supplying a robust and strong magnetic field at the coil position. Subjected to the mechanical realization, only several

Designing Model and Optimization of the Permanent Magnet for Joule Balance NIM-2

B_r(z)

A magnetic damping device for watt and joule balances

(radial magnetic field along the vertical direction) profiles can be measured by coils for field characterization. In this article, we present an algorithm that can construct the global magnetic field of the air gap based on

A Five-Freedom Active Damping and Alignment Device Used in the Joule Balance

N(Ngeq1)

The Design and Construction of the Joule Balance NIM-2

additional measurements of

Improvements of a kilogram level inertial mass measurement experiment

B_r(z)

An analytical algorithm for 3D magnetic field mapping of a watt balance magnet

profiles. The proposed algorithm is realized by polynomially estimating the