Experimental and Numerical Thermal Transient Behavior of Chips in a Liquid Channel During Loss of Pumping Power

2004 ◽  
Vol 126 (4) ◽  
pp. 546-553 ◽  
Author(s):  
C. P. Tso ◽  
K. W. Tou ◽  
H. Bhowmik
Keyword(s):  
Single Phase ◽  
Rectangular Channel ◽  
Three Dimensional ◽  
Transient Behavior ◽  
Heat Fluxes ◽  
Coolant Flow ◽  
Pumping Power ◽  
Channel Water ◽  
Wide Range ◽  
Transient And Steady State

Both transient and steady-state experiments are performed to study the single-phase heat transfer characteristics on an array of four in-line, flush-mounted simulated chips in a vertical rectangular channel. Water is the coolant media, and the flow covers the wide range of laminar regimes with the Reynolds number, based on heat source length, from 800 to 2625. The effect of heat fluxes, coolant flow rates, and geometric parameters (such as chip configuration number) are investigated. The operation is extended to study the transient natural convection during an accidental stoppage of coolant flow due to loss of pumping power. Results compare favorably with those obtained from three-dimensional numerical calculations. The transient correlation recommended is Nul=0.3Fo−0.2Ral*1/4.

Heat Transfer Investigation of an Additively Manufactured Minichannel Heat Exchanger

2019 ◽  
Author(s):  
Hamidreza Rastan ◽  
Amir Abdi ◽  
Monika Ignatowicz ◽  
Bejan Hamawandi ◽  
Poh Seng Lee ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Single Phase ◽  
Three Dimensional ◽  
Heat Fluxes ◽  
Experimental Results ◽  
Working Fluid ◽  
Minichannel Heat Exchanger ◽  
Simulation Results ◽  
Good Agreement

Abstract This study investigates the thermal performance of laminar single-phase flow in an additively manufactured minichannel heat exchanger both experimentally and numerically. Distilled water was employed as the working fluid, and the minichannel heat exchanger was made from aluminum alloy (AlSi10Mg) through direct metal laser sintering (DMLS). The minichannel was designed with a hydraulic diameter of 2.86 mm. The Reynolds number ranged from 175 to 1360, and the heat exchanger was tested under two different heat fluxes of 1.5 kWm−2 and 3 kWm−2. A detailed experiment was conducted to obtain the thermal properties of AlSi10Mg. Furthermore, the heat transfer characteristics of the minichannel heat exchanger was analyzed numerically by solving a three-dimensional conjugate heat transfer using the COMSOL Multiphysics® to verify the experimental results. The experimental results were also compared to widely accepted correlations in literature. It is found that 95% and 79% of the experimental data are within ±10% range of both the simulation results and the values from the existing correlations, respectively. Hence, the good agreement found between the experimental and simulation results highlights the possibility of the DMLS technique as a promising method for manufacturing future multiport minichannel heat exchangers.

A Study of the Accuracy, Global Performance, and Computational Expenses of k–ε, k–ω, and RSM Turbulent Models for Flow in an Industrial Static Mixer

2004 ◽  
Author(s):  
Ramin K. Rahmani ◽  
Theo G. Keith ◽  
Anahita Ayasoufi
Keyword(s):  
Single Phase ◽  
Critical Role ◽  
Three Dimensional ◽  
Static Mixer ◽  
Mixing Processes ◽  
Viscous Liquids ◽  
Pressure Drops ◽  
Wide Range ◽  
Global Performance ◽  
Turbulent Models

Viscous liquids have to be homogenized in continuous operations in many branches of processing industries; and therefore, fluid mixing plays a critical role in the success or failure of many industrial processes. The use of static mixers has been utilized over a wide range of applications such as continuous mixing, blending, heat and mass transfer processes, chemical reactions, etc. Consequences of improper mixing include non-reproducible processing conditions and lowered product quality, resulting in the need for more elaborate downstream purification processes and increased waste disposal costs. This paper extends previous studies by the authors on an industrial helical static mixer and illustrates how static mixing processes of single-phase viscous liquids can be simulated numerically. It also intends to present an improved understanding of the turbulent flow pattern for single-phase liquids through the mixer. Three-dimensional finite volume simulations are used to study the performance of the mixer for a range of practical Reynolds numbers, using three different turbulent models: k–ε model, k–ω model, and RSM model. The accuracy, global performance and costs of the different turbulent models have been examined. The flow velocities, pressure drops, etc. are calculated for each model. The calculated pressure drop of each case is compared with experimental results. Using different tools, the mixing results obtained from the different models are studied and compared.

Three-Dimensional Numerical Simulation and Performance Study of an Industrial Static Mixer Using Pseudo-Plastic Fluids

2004 ◽  
Author(s):  
Ramin K. Rahmani ◽  
Theo G. Keith ◽  
Anahita Ayasoufi
Keyword(s):  
Numerical Simulation ◽  
Single Phase ◽  
Three Dimensional ◽  
Phase Reaction ◽  
Static Mixer ◽  
Performance Study ◽  
Mixing Processes ◽  
Numerical Predictions ◽  
Wide Range ◽  
Plastic Fluids

Mixing is an essential component of nearly all industrial chemical processes, ranging from simple blending to complex multi-phase reaction systems for which the reaction rate, the yield and the selectivity are highly dependent upon the mixing performance. Consequences of improper mixing include nonreproducible processing conditions and lowered product quality, resulting in the need for more elaborate downstream purification processes and increased waste disposal costs. A wide range of working fluids in industrial mixers are non-Newtonian. The non-Newtonian fluid studied here is a member of the pseudo-plastic fluids group, characterized by a progressively decreasing slope or shear stress versus shear rate. These fluids are termed shear thinning; the viscosity decreases with increasing velocity gradient. In this paper, a previous study by the authors on an industrial helical static mixer is extended to illustrate how static mixing processes of single-phase pseudo-plastic liquids can be simulated numerically. A further aim is to provide an improved understanding of the flow pattern of pseudo-plastic single-phase liquids through the mixer. A three-dimensional finite volume simulation is used to study the performance of the mixer. A commercial software, FLUENT, is used in a part of the numerical simulation. The flow velocities, pressure drops, etc. are calculated for various flow rates, using the Carreau and the power law models for non-Newtonian fluids. The numerical predictions by these two models are compared to existing experimental data. Also, a comparison of the mixer performance for both Newtonian and pseudo-plastic fluids is presented.

Predictions of Flow Boiling in Fractal-Like Branching Microchannels

2005 ◽  
Author(s):  
Brian J. Daniels ◽  
Deborah V. Pence ◽  
James A. Liburdy
Keyword(s):  
Pressure Drop ◽  
Single Phase ◽  
Heat Fluxes ◽  
Phase Flow ◽  
Parallel Channel ◽  
Pumping Power ◽  
Flow Networks ◽  
Two Phase ◽  
Flow Rates ◽  
Flow Through

Single-phase and two-phase flows in microscale fractal-like branching flow networks are studied using a one-dimensional model that includes variable property and developing flow effects. Pressure drop, pumping power, changes in the bulk fluid temperature and a performance parameter are reported for mass flow rates ranging from 25 to 500 g/min and wall heat fluxes from 5 to 40 W/cm2. Two-phase flow through fractal-like flow networks is also compared to flow through a series of parallel channels for identical wall heat fluxes and for flow rates between 25 and 100 g/min. Channel length, height, convective surface area, heat flux and flow rate were the same between the fractal-like and parallel channel array. It was found that single-phase flows through fractal-like flow networks exhibit lower pressure drop and pumping power than do two-phase flows at the same wall heat flux and mass flow rate. The inlet temperature for the single-phase cases is 20°C, whereas the two-phase flow enters as a saturated liquid. The pressure drop and pumping power were always lowest for the fractal-like flow networks compared with the parallel channel arrays for identical heat transfer and flow rates.

scholarly journals Distributed observations of wind direction using microstructures attached to actively heated fiber-optic cables

2020 ◽  
Vol 13 (3) ◽  
pp. 1563-1573 ◽  
Author(s):  
Karl Lapo ◽  
Anita Freundorfer ◽  
Lena Pfister ◽  
Johann Schneider ◽  
John Selker ◽  
...  
Keyword(s):  
Wind Speed ◽  
Wind Direction ◽  
Fiber Optic ◽  
Deterministic Model ◽  
Three Dimensional ◽  
Heat Fluxes ◽  
Fiber System ◽  
Wide Range ◽  
Spatially Distributed ◽  
Dynamics Simulations

Abstract. The weak-wind boundary layer is characterized by turbulent and submesoscale motions that break the assumptions necessary for using traditional eddy covariance observations such as horizontal homogeneity and stationarity, motivating the need for an observational system that allows spatially resolving measurements of atmospheric flows near the surface. Fiber-optic distributed sensing (FODS) potentially opens the door to observing a wide range of atmospheric processes on a spatially distributed basis and to date has been used to resolve the turbulent fields of air temperature and wind speed on scales of seconds and decimeters. Here we report on progress developing a FODS technique for observing spatially distributed wind direction. We affixed microstructures shaped as cones to actively heated fiber-optic cables with opposing orientations to impose directionally sensitive convective heat fluxes from the fiber-optic cable to the air, leading to a difference in sensed temperature that depends on the wind direction. We demonstrate the behavior of a range of microstructure parameters including aspect ratio, spacing, and size and develop a simple deterministic model to explain the temperature differences as a function of wind speed. The mechanism behind the directionally sensitive heat loss is explored using computational fluid dynamics simulations and infrared images of the cone-fiber system. While the results presented here are only relevant for observing wind direction along one dimension, it is an important step towards the ultimate goal of a full three-dimensional, distributed flow sensor.

scholarly journals Investigation of the mobile granular layer in bedload transport by laminar shearing flows

2013 ◽  
Vol 736 ◽  
pp. 594-615 ◽  
Author(s):  
Pascale Aussillous ◽  
Julien Chauchat ◽  
Mickael Pailha ◽  
Marc Médale ◽  
Élisabeth Guazzelli
Keyword(s):  
Granular Layer ◽  
Fluid Velocity ◽  
Rectangular Channel ◽  
Three Dimensional ◽  
Bedload Transport ◽  
Spherical Particles ◽  
Particle Interactions ◽  
Two Phase ◽  
Image Velocimetry ◽  
Wide Range

AbstractThe mobile layer of a granular bed composed of spherical particles is experimentally investigated in a laminar rectangular channel flow. Both particle and fluid velocity profiles are obtained using particle image velocimetry for different index-matched combinations of particles and fluid and for a wide range of fluid flow rates above incipient motion. A full three-dimensional investigation of the flow field inside the mobile layer is also provided. These experimental observations are compared to the predictions of a two-phase continuum model having a frictional rheology to describe particle–particle interactions. Different rheological constitutive laws having increasing degrees of sophistication are tested and discussed.

scholarly journals Three-Dimensional Numerical Simulation and Performance Study of an Industrial Helical Static Mixer

2003 ◽  
Author(s):  
Ramin K. Rahmani ◽  
Theo G. Keith ◽  
Anahita Ayasoufi
Keyword(s):  
Turbulent Flow ◽  
Single Phase ◽  
Stokes Equations ◽  
Critical Role ◽  
Three Dimensional ◽  
Static Mixer ◽  
Performance Study ◽  
Mixing Processes ◽  
Viscous Liquids ◽  
Wide Range

Viscous liquids have to be homogenized in continuous operations in many branches of processing industries. Consequently, fluid mixing plays a critical role in the success or failure of many industrial processes. The use of static mixers has been utilized over a wide range of applications such as continuous mixing, blending, heat and mass transfer processes, chemical reactions, etc. This paper illustrates how static mixing processes of single-phase viscous liquids can be simulated numerically, and presents the flow pattern of both Newtonian and non-Newtonian single-phase liquids through a helical static mixer, and provides useful information that can be extracted from the simulation results. Three-dimensional finite volume simulations are used to study the performance of the mixer. The CFD code used here solves the Navier-Stokes equations for both laminar and turbulent flow cases. The turbulent flow cases were solved using k–ω and Reynolds Stress models. The flow properties are calculated for both Newtonian and non-Newtonian fluids. The calculated pressure drop is in good agreement with existing experimental data.

scholarly journals Distributed observations of wind direction using microstructures attached to actively heated fiber-optic cables

2019 ◽  
Author(s):  
Karl Lapo ◽  
Anita Freundorfer ◽  
Lena Pfister ◽  
Johann Schneider ◽  
John Selker ◽  
...  
Keyword(s):  
Wind Speed ◽  
Wind Direction ◽  
Fiber Optic ◽  
Deterministic Model ◽  
Three Dimensional ◽  
Heat Fluxes ◽  
Fiber System ◽  
Wide Range ◽  
Spatially Distributed ◽  
Dynamics Simulations

Abstract. The weak-wind boundary layer is characterized by turbulent and submeso-scale motions that break the assumptions necessary for using traditional eddy covariance observations such as horizontal homogeneity and stationarity, motivating the need for an observational system that allows spatially resolving measurements of atmospheric flows near the surface. Fiber-Optic Distributed Sensing (FODS) potentially opens the door to observing a wide-range of atmospheric processes on a spatially distributed basis and to date has been used to resolve the turbulent fields of air temperature and wind speed on scales of second and decimeters. Here we report on progress developing a FODS technique for observing spatially distributed wind direction. We affixed microstructures shaped as cones to actively-heated fiber-optic cables with opposing orientations to impose directionally-sensitive convective heat fluxes from the fiber-optic cable to the air, leading to a difference in sensed temperature that depends on the wind direction. We demonstrate the behavior of a range of microstructure parameters including aspect ratio, spacing, and size and develop a simple deterministic model to explain the temperature differences as a function of wind speed. The mechanism behind the directionally-sensitive heat loss is explored using Computational Fluid Dynamics simulations and infrared images of the cone-fiber system. While the results presented here are only relevant for observing wind direction along one dimension it is an important step towards the ultimate goal of a full three-dimensional, distributed flow sensor.

Comparing Single Phase Heat Transfer to Arrays of Impinging Jets and Sprays

2002 ◽  
Author(s):  
Ricardo H. Pereira ◽  
Sergio L. Braga ◽  
Jose´ A. R. Parise
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Single Phase ◽  
Impinging Jets ◽  
Average Heat Transfer Coefficient ◽  
Pumping Power ◽  
Flow Rates ◽  
Average Heat ◽  
Wide Range

The single phase heat transfer characteristics of square arrays of impinging water sprays were investigated experimentally. A total of 230 experimental points, covering a wide range of flow rates and different spray array geometries were obtained with three different models of commercially available full cone spray nozzles. Results were compared to an available correlation for the area average heat transfer coefficient of impinging arrays of submerged jets. It is shown that spray impingement techniques may provide the same heat transfer coefficient obtained with impinging jets under much smaller coolant flow rates per unit heated area. Coolant pumping power required by both techniques was also compared. It is shown that spray arrays require, for the establishment of a given area average heat transfer coefficient, more pumping power than submerged jet arrays.

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