Simulation of Heat Transfer With LBM and Lagrangian Methods for Microfluidic Applications

This work presents a Lagrangian approach to simulate convective heat transfer in small scales. The fully developed flow field, simulated by a Lattice Boltzmann Method, is combined with Lagrangian tracking of thermal markers to determine the behavior of an instantaneous scalar line source located at the wall of a channel. The resulting probability density functions are used to calculate the behavior of continuous line sources of heat at the wall of the channel, as well as the temperature for the case of constant temperature or constant heat flux from the wall. This method is resourceful in terms of computational efficiency, in that it can be used to simulate various thermal boundary conditions and Prandtl number fluids with a single flow field resulting from a Lattice Boltzmann simulation.

Fluid Flow and Heat Transfer Analysis of Automotive Radiator Using CFD Tools

This paper presents a three-dimensional numerical analysis of flow and heat transfer over plate fins in a compact heat exchanger used as a radiator in the automotive industry. The aim of this study is to predict the heat transfer and pressure drop in the radiator. FLUENT 6.1 is used for simulation. Several cases are simulated in order to investigate the coolant temperature drop, heat transfer coefficient for the coolant and the air side along with the corresponding pressure drop. It is observed that the heat transfer and pressure drop fairly agree with experimental data. It is also found that the fin temperature depends on the frontal air velocity and the coolant side heat transfer coefficient is in good agreement with classical Dittus–Boelter correlation. It is also found that the specific dissipation increases with the coolant and the air flow rates. This work can further be extended to perform optimization study for radiator design.

Heat Transfer Analysis of Human Cell Culture Under RF Exposure

A 2.45 GHz radio frequency (RF) exposure system was designed and used to study the RF effects on the genome-wide gene expression in cultured human cells. In this system, a T-25 culture flask, which contains 10 × 106 cells in a 10ml medium, is placed in a WR 340 waveguide. The waveguide serves as an environmental chamber. The source is a pulsed magnetron for obtaining a high electric field with the specific absorption rate (SAR) at approximately 10 W/kg. In order to ensure the non-thermal effect, the system was designed to maintain a temperature of 37°C. In this research, the heat transfer analysis of the system was conducted using the computational fluid dynamic (CFD) software FLUENT® coupled with the finite element software, High Frequency Structural Simulation (HFSS) by Ansoft. The electric field was first analyzed by using HFSS to calculate the SAR distribution as a heat source input for CFD calculations. The fluid flow and temperature distributions within the flask were then analyzed using FLUENT®. The results were validated experimentally by measuring the temperatures with fluoroptic thermometer probes as well as by examining the level of heat shock gene expression. These results provide useful information for a better understanding and controlling of the operating conditions of the system.

Three-Dimensional Analysis on the Performance of the Thermoelectric Micro-Cooler

Three-dimensional numerical analysis has been carried out using the FEMLAB software package to figure out the performance of the thermoelectric micro-cooler. A small-size and column-type thermoelectric cooler is considered and Bi2Te3 and Sb2Te3 are selected as the n- and p-type thermoelectric materials, respectively. The thickness of the thermoelectric element considered is 5 to 20 μm and the thickness affects the performance of the cooler. The effect of parameters such as the temperature difference, the current, and the thickness of the thermoelectric element on the performance of the cooler has also been investigated. The coefficient of performance (COP) is the primary factor to evaluate the performance of the cooler and the COP varies with the parameters. The COP has the maximum value at a certain current and the value decreases with the temperature difference or the thickness. The predicted results also show that the performance can be improved for thick thermoelectric element at the small temperature difference and small current.

Multiscale Analysis of Silicon LPCVD Reactor

We demonstrate the multiscale analysis of the transport phenomena in a low pressure reactor. In this method, the macroscopic phenomena such as the temperature and the density distribution are related to the microscopic electronic structure of atom/molecule. By connecting the different scales with physical models, the macroscopic properties are obtained starting from the first principle calculation without any empirical parameters. Here, we take the silicon epitaxial growth from a gas mixture of silane and hydrogen as an example. As the first step of this method, we calculated the intermolecular potential energy of SiH4/H2 using the ab initio molecular orbital calculations. Then, an analytical pair potential model was constructed to reproduce the potential energy surface obtained from the ab initio calculation. We have confirmed the validation of the potential model by comparing the experimental data of the transport properties with the molecular dynamics simulation using the potential model. Subsequently, the binary molecular collision models were constructed by the classical trajectory calculation using the potential model as the second step of the multiscale analysis. The trajectory calculations were conducted for the various combinations of the initial translational and the rotational energy. Through the statistical analysis of the trajectory calculations, the elastic/inelastic collision cross section and the scattering angle model were constructed. Finally, the direct simulation Monte Carlo simulation of flow field in a low parssure reactor was executed. The thin film thickness distribution was also investigated and discussed. This method was extended to analyze the surface reaction, which is an ongoing research work and only the current progress is reported here.

A New Computational Method for Free Surface Problems

A new technique, called the surface velocity correction technique (SVC), is developed to track a free surface such as a liquid-vapor interface. SVC is a computationally inexpensive, and accurate method to capture interfacial fluid phenomena. This method uses a finite volume technique to discretize the governing equations, and a semi-Legrangian mesh to locate the interface between two fluids. The effectiveness of this technique is demonstrated through several classical examples and the results are also compared to both analytical and VOF solutions. The examples include: the shape of a meniscus in a capillary tube in mechanical equilibrium, the rise of a meniscus in a capillary tube, and the instability growth of a free flowing cylindrical column of fluid.

Diode Laser Cladding on A5052 Aluminium Alloy for Wear Resistance

In order to improve a wear resistance of aluminium alloy, we proposed a diode laser cladding on the surface of a A5052 aluminium alloy. Firstly, an applicability of diode laser to laser cladding was evaluated. In this result, application of diode laser made it possible to obtain stable beads in low heat input compared with CO2 laser. According to the increase in aluminium content in the obtained clad layer, the microstructure of the clad layer changed as γ (8∼20%) → γ + α (10∼30%) → Fe3Al (30%∼). At the interface between the clad layer and the aluminium alloy substrate, the reaction layer consisting of Fe2Al5 and FeAl3 formed. In the abrasion wear the obtained clad layers exhibited a higher wear resistance compared with the aluminium alloy.

Large Eddy Simulations of Staggered Parallel-Plate Flows

Heat transfer enhancement is a subject of major concern in numerous fields of industry and research. Having received undivided attention over the years, it is still studied worldwide. Given the exponential growth of computing power, large-scale numerical simulations are growing steadily more realistic, and it is now possible to obtain accurate time-dependent solutions with far fewer preliminary assumptions about the problems. As a result, an increasingly wide range of physics is now open for exploration. More specifically, it is time to take full advantage of large eddy simulation technique so as to describe heat transfer in staggered parallel-plate flows. In fact, from simple theory through experimental results, it has been demonstrated that surface interruption enhances heat transfer. Staggered parallel-plate geometries are of great potential interest, and yet many numerical works dedicated to them have been tarnished by excessively simple assumptions. That is to say, numerical simulations have generally hypothesized lengthwise periodicity, even though flows are not periodic; moreover, the LES technique has not been employed with sufficient frequency. Actually, our primary objective is to analyze turbulent influence with regard to heat transfers in staggered parallel-plate fin geometries. In order to do so, we have developed a LES code, and numerical results are compared with regard to several grid mesh resolutions. We have focused mainly upon identification of turbulent structures and their role in heat transfer enhancement. Another key point involves the distinct roles of boundary restart and the vortex shedding mechanism on heat transfer and friction factor.

Direct Numerical Simulation of Liquid Flow in a Horizontal Microchannel

Numerical Simulations of liquid flow in a micro-channel between two horizontal plates are performed. The channel is infinite in streamwise and spanwise directions and its height is taken as 3.1×10−4 m which falls within the dimension ranges of micro-channels. The Navier-Stokes equations with the addition of Brinkman number (Br) to the energy equation are used as the governing equations and a spectral methods based approach is applied to obtain the required accuracy to handle liquid flow in the micro-channel. It is known for micro-channels that Br combines the effects of conduction and viscous dissipation in liquids and is also a way of comparing the importance of later relative to former. A laminar flow of a liquid in a micro-channel shows different characteristics compared to a similar flow in a macro-channel. To observe the differences, three different cases are run over each of a range of Reynolds numbers: one with no axial conduction assumption that correspond to a case similar to macro-channel flow, another case with axial conduction included in the energy equation to simulate one of the main differences and lastly a case with inclusion of Br number in the governing equations. The results are compared with each other to see the effects of axial conduction and Br inclusion. A qualitative comparison is made with the previous results in literature.

Feature Evolution During Sub 100NM Gap-Fill and Etch

Inductively coupled plasma (ICP) reactors are being used at low gas pressure (<100mTorr) and high plasma density ([e] > 1013/cm2) processes in semiconductor fabrication. In these reactors plasma is generated by inductively coupled electric field while positive ions are accelerated anisotropically by applying a negative bias RF to the substrate. Semiconductor manufacturers face many challenges as wafer size increases while device geometries decrease. Two key challenges for both process design and electronics processing equipment design are (a) scale up of process from 200mm to 300mm diameter substrate, and (b) deposition and etching features with high aspect ratios. A unified phenomenological model to explain profile evolution trend as a function of aspect ratio for deposition (gap fill) and trench etch using ICP reactors is presented. Trends for feature evolution as a function of pressure for gap fill and trench etch are reviewed and explained. The article emphasizes importance of low pressure for sub-100nm gap-fill and trench-etch applications in ICP processing reactors.