Wang Xiaojing

Experiment and Simulations on Lubrication Performance of EMP Journal Bearing

In recent years, much attention has been devoted to the design and operation of bearings made of elastic metal plastic (EMP). The surface of the bearing bush is covered by a layer of polymer PTFE(polytetrafluoroethylene). The physical performances of the polymer are quite different from that of metal. It can reduce friction because of its lower surface energy, and it is more difficult for the fluid to be adhered. Consequently, the slip will exist at the oil-bush interface. The journal bearings made of this material are researched in this article. Through test, the existence of slip is proven and the equation of the slip velocity for the EMP journal bearing is established when shear stress up to a certain value. Thus, the classical Reynolds equation is modified. The lubrication mechanism is analyzed by some simulation results.

Heat transfer simulation of nanofluids in micro channel cooler

Since the pioneering work by Tuckerman & Pease, lots of publications about heat sink has been researched in the last decade. Many enhancements are proposed in order to increase the thermal conductivity of micro-channels including nanofluids, special shapes, and two phase flows. The nanofluid is a solid-liquid mixture which is composed of nanoparticles and a basic liquid. In this paper, the nanofluids with suspended multiwalled carbon nanotube and other metallic or nonmetallic particles are compared to enhance the heat transfer performance. The thermal resistance of the heat sink with nanofluids is simulated.

Experimental research of micro-channel cooler

With the continuously decreasing size and constantly increasing integration of IC chips, the heat flux is increasing rapidly. Many enhancements are proposed in order to increase the thermal conductivity of micro-channels including nano-fluids, special shapes, and two phase flows, etc. This paper explores a new test system to measure the heat transfer performance of micro-channel cooler. Considering the accuracy of the test, materials with lower thermal conductivity is selected to package the cooler, and a DAQ system is set up to collect the test data. Its found that in most cases laminar flow occur, and some relationships between temperature, pressure, heat flux and mass flow are obtained. And this research proceeds as foundation for the further research work.

Numerical simulation of the micro-channel heat sink on non-uniform heat source

In this paper, the different heat source distributions are studied in the micro-channel heat sink (MCHS) cooler. The simulation model is established to analyze the heat distributing and temperature rise of the MCHS with different channel width-dimensions. Uniform and non-uniform heat source are used to offer a constant heat flux, and the total heat flux amount is 270 W. Water is chosen as the coolant for its superior hot properties and the velocity range is from 0.01 m/s to 10 m/s. The results show that tradition type MCHS will be under a low efficiency for cooling a non-uniform heat source. And the non-equal displacement of fins can effective decrease the temperature rise about 10% under the same cooling conditions cooling a non-uniform heat source. We also find that it is impossible to enhance the cooling effect through adding the flow rate if it has surpassed itpsilas limitation.

Analytical Model of the Electrostatic Scratch Drive Actuator

In the field of micro-electro-mechanical system actuator, the scratch drive actuator (SDA) is the one, which can realize long distance travel with precise nanometer step sizes. In this paper, a newly revisory analytical model of the scratch drive actuator including the effects of the MEMS surface - micromachining processing parameter and the counterforce of the support arms is proposed. The performance of the SDA is analyzed, such as the critical voltage, the step size and the total displacement. The good agreement between the simulation results and the experimental data is obtained.

Geometric optimization of carbon nanotubes (CNTs) microchannel with liquid flow

Recent advances in micro electromechanical devices, advanced very large-scale integration technologies and the associated micro miniaturization, have led to significant increases in the packing densities and heat fluxes generated within these devices. How to remove so high heat fluxes, it becomes more and more important. In this paper, three models of CNTs micro channel coolers are established, which are rectangular channel model, rectangular array model and diamond array model. The variations of the pressure drop and temperature rise of different models are compared. It is found that the rectangular array model has good heat dissipation performance.

Experimental investigation of gas flow in copper channel carbon nanotubes coated micro coolers

As the integrity of micro electronic devices improves, the heat power of chips is getting higher and higher. How to reduce the temperature of micro electronic devices effectively becomes more and more important. In this paper, a micro-channel cooler test system is set up. By measuring the temperature and pressure at inlet and outlet of the micro cooler and the average temperature of micro cooler bottom, the heat transfer performance of the copper based CNTs coated micro cooler is researched. The thermal resistance of copper and silicon based CNTs coated micro cooler are compared. It is shown that the copper based CNTs coated micro cooler has good thermal dissipation capacity than that of the Silicon based CNTs coated micro cooler.

Analysis of the motion between CNTs and water in CNTs micro channel cooler with molecular simulation

As the integrity of micro electronic devices improves, the heat power of chips is getting higher and higher. Micro-channel heat sink has been got more and more concerns for its better cooling performance. A lot of investigations about micro-channel coolers have been undertaken in the past years. As a result of the impact of micro-pump power, the traditional silicon micro-channel heat sink cooling has shown its weakness. Considering the orders of magnitude of the thermal conductivity of carbon nanotubes (CNTs) are higher than the metal material, therefore, using carbon nanotube fin to replace silicon fin will improve the micro-cooler performance significantly. This paper carried out the molecular dynamics simulation of water besides CNTs in CNTs micro-channel cooler. The motion model of CNTs and water molecule was established. The movements of water molecule at the interface of the CNTs with the different inlet velocities and the density were analysed. The study found that the number of water molecules close to the CNTs was the minimum and that of the second closing layer of water molecules was more because the repulsion force between the CNTs and water molecules and the attraction effect between the CNTs and less water molecules, some water molecules moved into the CNTs. Simulation results showed that the water molecules at the surface of the CNTs had the velocity slip phenomenon.

The Analysis of Performance on Spring Supported Thrust Pads Inclusive of One Dimensional Pressure Build up

In the paper, a solution of one dimensional fore-region pressure build-up is put forward. The performance of spring-supported thrust bearing is carried out with 3-dimensional thermo-elasto hydrodynamic (TEHD) lubrication theory inclusive of inlet pressure build-up, thermal-elastic distortion of pad and thermal effect. The effects of fore-region pressure build-up and the variation of some operating conditions on the performance of the pad are studied.