Simulations of Flow and Temperature Fields in a Two Heater PCR Device

Volume 4 ◽  
2004 ◽  
Author(s):  
Tom Mautner
Keyword(s):  
Thermal Diffusion ◽  
Wall Temperature ◽  
Lattice Boltzmann ◽  
Three Dimensional ◽  
Temperature Fields ◽  
Thermal Coupling ◽  
Uniform Temperature ◽  
Temperature Distributions ◽  
Flow Through ◽  
Heater Design

One module in a bioagent detector currently under development involves a new two-heater, flow-through polymerase chain reaction (PCR) module which is being designed to save space and power and to reduce the amplification time. As in all PCR devices, thermal cycling requires three temperatures and residence times. These are 90–95°C for DNA denaturation, 50–65°C for hybridization and 72–77°C for replication with a time ratio of 4:9:4. The current design uses two heaters with heat conduction in the substrate providing the hybridization temperature. Typically, the flow and temperature fields in microfluidic devices have three-dimensional complexity, thus numerical simulations were performed to provide design guidelines in the development of the two-heater PCR device. The lattice Boltzmann (LB) method was used to perform low Reynolds number (typically Re = 0.10) simulations for two and three dimensional channel geometries having various wall temperature distributions. The momentum and thermal lattice Boltzmann equations were coupled via a body force term in the momentum equation. Initial computations using two- and three-heater configurations in two dimensions demonstrated excellent comparisons with published data provided that both the top and bottom walls were heated. If only one wall was heated, large vertical thermal gradients occurred resulting in non-uniform temperature fields. However, when the same conditions were applied to three dimensional channels, lower temperatures were observed in the center of the channel regardless of the wall temperatures or channel aspect ratio. Parametric studies were performed to evaluate the effects of thermal coupling, thermal diffusion coefficients, entrance temperatures, wall temperature configurations and channel geometry. If was found that moderate variation of the thermal diffusion coefficient produced only minor differences in the temperature field, and large changes in the thermal coupling magnitude demonstrated transition from natural to forced convection flows. The simulations also indicate that the largest effect on flow and temperature uniformity arises from the applied wall temperature distribution (various thickness channel walls). It was found, in 2D, that if the channel wall starts from ambient temperature, the applied heating, on the outer surfaces only, may not result in the desired wall or fluid temperatures. However, once the channel walls are heated to a uniform temperature, excellent temperature distributions are obtained for both thick and thin channel walls. These results indicate that the two-heater design has potential in providing a new flow-through PCR device. However, careful attention must be paid to the wall heater design to provide the required sample temperatures.

Manipulation of Microfluidic Flows Using Time Dependent Wall Temperatures

2004 ◽  
Author(s):  
Tom Mautner
Keyword(s):  
Thermal Diffusion ◽  
Wall Temperature ◽  
Lattice Boltzmann ◽  
Channel Wall ◽  
Three Dimensional ◽  
Temperature Profiles ◽  
Thermal Coupling ◽  
Uniform Temperature ◽  
Temperature Distributions ◽  
Flow Through

One module in a bioagent detector currently under development involves a flow-through PCR module [1] [3] [4]. Conventional, flow-through PCR devices utilize three heaters to obtain the required temperatures in each zone, the length of which is specified by the required sample residence times. An alternate design uses two wall heaters with substrate conduction supplying the center zone temperature. The concept of using a conduction based PCR device led to an extensive computational study of various channel wall temperature profiles that would produce enhanced mixing in a variety of microfluidic devices. The results are applicable to micro channel designs in general even tough motivated by the conduction based PCR configuration. The lattice Boltzmann (LB) method was used to perform low Reynolds number (typically Re=0.10) simulations for two and three dimensional channel geometries having various wall temperature distributions. The momentum and thermal lattice Boltzmann equations were coupled via a body force term in the momentum equation. Initial computations using two- and three-heater configurations in two dimensions demonstrated excellent comparisons with published data provided that both the top and bottom walls were heated. If only one wall was heated, large vertical thermal gradients occurred resulting in non-uniform temperature fields. However, when the same conditions were applied to three dimensional channels, lower temperatures were observed in the center of the channel regardless of the wall temperatures or channel aspect ratio. Parametric studies were performed to evaluate the effects of thermal coupling, thermal diffusion coefficients, entrance temperatures, wall temperature configurations and channel geometry. If was found that moderate variation of the thermal diffusion coefficient produced only minor differences in the temperature field, and large changes in the thermal coupling magnitude demonstrated transition from natural to forced convection flows. The simulations also indicate that the largest effect on flow and temperature uniformity arises from the applied wall temperature distribution (various thickness channel walls). It was found, in 2D, that if the channel wall starts from ambient temperature, the applied heating, on the outer surfaces only, may not result in the desired wall or fluid temperatures. However, once the channel walls are heated to a uniform temperature, excellent temperature distributions are obtained for both thick and thin channel walls. Additionally, a checkerboard pattern of wall heaters was used to test its application to promoting mixing. Results were favorable in creating enhanced mixing; however, the temperature pattern did not produce uniform temperature profiles in the channel.

Visualization and Prediction of Natural Convection of Water Near Its Density Maximum in a Tall Rectangular Enclosure at High Rayleigh Numbers

2000 ◽  
Vol 123 (1) ◽  
pp. 84-95 ◽  
Author(s):  
C. J. Ho ◽  
F. J. Tu
Keyword(s):  
Natural Convection ◽  
Vertical Wall ◽  
Three Dimensional ◽  
Temperature Fields ◽  
Convection Flow ◽  
Oscillatory Convection ◽  
Uniform Temperature ◽  
Density Maximum ◽  
Rectangular Enclosure ◽  
Rayleigh Numbers

An experimental and numerical investigation is presented concerning the natural convection of water near its maximum-density in a differentially heated rectangular enclosure at high Rayleigh numbers, in which an oscillatory convection regime may arise. The water in a tall enclosure of Ay=8 is initially at rest and at a uniform temperature below 4°C and then the temperature of the hot vertical wall is suddenly raised and kept at a uniform temperature above 4°C. The cold vertical wall is maintained at a constant uniform temperature equal to that of the initial temperature of the water. The top and bottom walls are insulated. Using thermally sensitive liquid crystal particles as tracers, flow and temperature fields of a temporally oscillatory convection was documented experimentally for RaW=3.454×105 with the density inversion parameter θm=0.5. The oscillatory convection features a cyclic sequence of onset at the lower quarter-height region, growth, and decay of the upward-drifting secondary vortices within counter-rotating bicellular flows in the enclosure. Two and three-dimensional numerical simulations corresponding to the visualization experiments are undertaken. Comparison of experimental with numerical results reveals that two-dimensional numerical simulation captures the main features of the observed convection flow.

LATTICE-BOLTZMANN SIMULATIONS OF FLOW THROUGH NAFION POLYMER MEMBRANES

2003 ◽  
Vol 17 (01n02) ◽  
pp. 135-138 ◽  
Author(s):  
HIDEMITSU HAYASHI ◽  
SATORU YAMAMOTO ◽  
SHI-AKI HYODO
Keyword(s):  
Lattice Boltzmann ◽  
Dissipative Particle Dynamics ◽  
Three Dimensional ◽  
Polymer Membranes ◽  
Dynamics Simulation ◽  
Fluid Viscosity ◽  
Lattice Boltzmann Simulations ◽  
Flow Through ◽  
Boltzmann Method ◽  
Dissipative Particle Dynamics Simulation

Simulations of flow through three-dimensional porous structures of NAFION polymer membranes are performed with a Lattice-Boltzmann method (LBM) for incompressible fluid. Geometry data of NAFION are constructed from a result of a dissipative particle dynamics simulation for three values of the water content, 10%, 20%, and 30%, and are used as the geometry input for the LBM. Permeability of the porous structure is extracted from results of the LBM simulation using Darcy's low. The permeability K is shown to be expressed as K = L2 × Ktpl with a characteristic length L and the dimensionless permeability Ktpl depending only on the topological structure of the porous media. Dependence of Ktpl is examined on the pressure gradient, the fluid viscosity, and the resolution of the computational grid.

Thermal Characteristics of Microscale Fractal-Like Branching Channels

2004 ◽  
Vol 126 (5) ◽  
pp. 744-752 ◽  
Author(s):  
Ali Y. Alharbi ◽  
Deborah V. Pence ◽  
Rebecca N. Cullion
Keyword(s):  
Surface Temperature ◽  
Wall Temperature ◽  
Heat Sink ◽  
Three Dimensional ◽  
Dimensional Model ◽  
Channel Network ◽  
Flow Network ◽  
One Dimensional ◽  
Temperature Distributions ◽  
Branching Flow

Heat transfer through a fractal-like branching flow network is investigated using a three-dimensional computational fluid dynamics approach. Results are used for the purpose of assessing the validity of, and providing insight for improving, assumptions imposed in a previously developed one-dimensional model for predicting wall temperature distributions through fractal-like flow networks. As currently modeled, the one-dimensional code fairly well predicts the general wall temperature trend simulated by the three-dimensional model; hence, demonstrating its suitability as a tool for design of fractal-like flow networks. Due to the asymmetry in the branching flow network, wall temperature distributions for the proposed branching flow network are found to vary with flow path and between the various walls forming the channel network. Three-dimensional temperature distributions along the various walls in the branching channel network are compared to those along a straight channel. Surface temperature distributions on a heat sink with a branching flow network and a heat sink with a series of straight, parallel channels are also analyzed and compared. For the same observed maximum surface temperature on these two heat sinks, a lower temperature variation is noted for the fractal-like heat sink.

The development of temperature fields and powder flow during laser direct metal deposition wall growth

2004 ◽  
Vol 218 (5) ◽  
pp. 531-541 ◽  
Author(s):  
A J Pinkerton ◽  
L Li
Keyword(s):  
Flow Model ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Metal Deposition ◽  
Direct Metal Deposition ◽  
Temperature Fields ◽  
Powder Flow ◽  
Powder Concentration ◽  
Melt Pool ◽  
Temperature Distributions

The additive manufacturing technique of laser direct metal deposition (DMD) has had an impact in rapid prototyping, tooling and small-volume manufacturing applications. Components are built from metallic materials that are deposited by the continuous injection of powder into a moving melt pool, created by a defocused laser beam. The size of the melt pool, the temperature distributions around it and the powder flux are critical in determining process characteristics such as deposition rate. In this paper, the effects that changes in the distance between the laser deposition head and the melt pool have on these factors as a part is built using a coaxial powder feeding system are considered via a two-part analytical model. A heat flow model considers three-dimensional temperature distributions due to a moving Gaussian heat source in a finite volume and a simple mass-flow model considers changes in powder concentration with distance from the deposition head. The model demonstrates the effect of adjusting the melt pool standoff in different ways on melt pool and powder flow characteristics as a DMD structure is built, and hence allows the effect on build rate to be predicted. Its validity is verified by comparison with a series of 316L stainless steel walls, built using different standoff adjustment methods. The model is found to be able to explain the dimensional characteristics found.

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