Papers by Author: Min Li Bai

Abstract: Nanofluids is an innovative study of nanotechnology applied to the traditional field of thermal engineering. It refers to the metal or non-metallic nanopowder was dispersed into water, alcohol, oil and other traditional heat transfer medium, to prepared as a new heat transfer medium with high thermal conductivity. The role of nanofluids in strengthening heat transfer has been confirmed by a large number of experimental studies. Its heat transfer mechanism is mainly divided into two aspects. On the one hand, the addition of nanoparticles enhances the thermal conductivity. On the other hand, due to the interaction between the nanoparticles and base fluid causing the changes in the flow characteristics, which is also the main factor affecting the heat transfer of nanofluids. Therefore, a intensive study on the flow characteristics of nanofluids will make the study of heat transfer more meaningful. In this experiment, the flow characteristics of SiO₂-water nanofluids in two-dimensional backward step flow are quantitatively studied by PIV. The results show that under the same Reynolds number, the turbulence of nanofluids is larger than that of pure water. With the increase of nanofluids volume fraction, the flow characteristics are constantly changing. The quantitative analysis proved that the nanofluids disturbance was enhanced compared with the base liquid, which resulting in the heat transfer enhancement.

Abstract: Simulation of nanoscale thermo-fluidic transport has attracted considerable attention in recent years owing to rapid advances in nanoscience and nanotechnology. The three- dimensional molecular dynamics simulations are performed for the system of a liquid layer between two parallel solid walls at different wall temperatures. The solid-solid interaction is modeled by the embedded atom method. The heat flux through the solid-liquid interface is calculated by Green-Kubo method. The effects of interface wettability and wall temperature on the interfacial thermal resistance are also analyzed. It is found that there exist the relatively immobile quasi-crystalline interfacial layers close to each solid wall surface with higher number density and thus higher local thermal conductivity than the corresponding liquid phase. The interfacial thermal resistance length is overestimated by 8.72% to 19.05% for the solid-solid interaction modeled by the Lennard-Jones potential, and underestimated based on heat fluxes calculated by Fourier equation.

Abstract: A novel flat heat pipe is put forward. The novel flat heat pipe is characteristic of its integral wick structure of microgrooves, which is made of a series of thin aluminum foils folded side by side. The thermal performance of the novel flat heat pipe under the different heat loads and incline angles has been investigated experimentally. It is found that the equivalent thermal conductivity of the novel flat heat pipe can be 12.3 times higher than that of the heat pipe material. Moreover, the novel flat heat pipe with integral micro-grooved wick has good temperature uniformity. The novel flat heat pipe can play a pronounced role in heat transfer enhancement, and be expected to be good candidates for thermal management of electronic devices.

Abstract: Evaporation at thin liquid film can significantly enhance heat transfer process. A detailed mathematical model predicting the heat and mass characteristics of the evaporating thin film is developed. The model considers effects of inertial force, evaporation coefficient, interface thermal resistance, and disjoining pressure. It is found that the interface thermal resistance is in inverse proportion to the evaporation coefficient. The heat and mass transport characteristics decreases sharply as the evaporation coefficient decreases. The inertial force tends to enhance the heat and mass transport characteristics of the evaporating thin film. However the Reynolds number of the liquid flow in the evaporating thin film is far lower than unity, and thus the effect of the inertial force can be neglected.

Abstract: Simulation of microscale thermo-fluidic transport has attracted considerable attention in recent years owing to rapid advances in nanoscience and nanotechnology. The three-dimensional molecular dynamics simulations are performed for coupling between flow and heat transfer in a nanochannel. Effects of interface wettability, shear rate and wall temperature are discussed. It is found that there exist the relatively immobile solid-like layers adjacent to each solid wall with higher number density. Both slip length and Kapitza length at the solid-liquid interface increase linearly with the increasing wall temperature. The Kapitza length decreases monotonously with the increasing shear rates. The slip length is found to be overestimated by 5.10% to 10.27%, while Kapitza length is overestimated by 8.92% to 19.09% for the solid-solid interaction modeled by the Lennard-Jones potential.

Abstract: The composition and principles of the digital measuring system was investigated on the basis of digital oil measuring method. Fly attitude-oil quality - measuring height data tables were generated by using UG software calculation of oil quantity characteristics. Then the oil surface angle under different fly attitude and overload was calculated through coordinate transformation method. Finally the amount of oil was calculated by three-dimensional liner interpolation method. Meanwhile, the free surface movement of lubricating oil tank under different overload was simulated through VOF numerical model. The results showed that using UG software to build model and generate fly attitude-oil quantity-measuring height data tables is accurate and useful. The VOF model method is a complement to digital measurement, which can track the phase interface of continuum, analyze the movement of oil qualitatively and calculate the dead volume of digital method.

Abstract: This research applied molecular dynamics method to micro Couette flow of nanofluids, in order to examine the absorption layer near solid surfaces, and propose mechanisms of heat transfer enhancement due to flow. The model of nanofluids consisted of 4 nm Cu nanoparticles and liquid argon as base liquid, Lennard-Jones potential function was adopted to deal with the interactions between atoms. Through visual observation and analysis, it was found that the even-distributed liquid argon atoms near solid surfaces could be seemed as a reform to base liquid and had contributed to heat transfer enhancement. In the process of Couette flow, nanoparticles were rotating and vibrating besides moving translationally. The micro-motions of nanoparticles could disturb the continuity of fluid and strengthen partial flow nearby nanoparticles, and enhance heat transfer in nanofluids.

Abstract: A method for synthesizing carbon-encapsulated metal nanoparticles(CEMNPs) is reported. In the proposed method, a composite precursors containing various nitrate dissolved in absolute ethanol is ignited by a nonelectric detonator in nitrogen gas in an explosion vessel. Upon the completion of detonation reaction, CEMNPs (Fe@C, Ni@C, Co@C) with diameters ranging from a few nanometers to about 20 nm are produced in the explosion vessel.The material characteristics of these nanoparticles are then examined with the XRD, TEM, EDX and VSM, which characterize the feature of morphology, components, phases and magnetism of nano-composite particles. The composite particles whose coating shell were graphite carbon could be dispersed finely. The core of nanoparticles were composed of iron,cobalt and nickel crystal to that of the above explosive precursors.The magnetic analysis indicated that the different composite nanoparticles have good ferromagnetism and superparamagetism in room temperature.