scholarly journals Experimental Investigation of Numerically Optimized Wavy Microchannels Created Through Additive Manufacturing

2017 ◽  
Vol 140 (2) ◽  
Author(s):  
Kathryn L. Kirsch ◽  
Karen A. Thole
Keyword(s):  
Heat Transfer ◽  
Additive Manufacturing ◽  
Pressure Drop ◽  
Numerical Optimization ◽  
High Surface ◽  
Direct Metal Laser Sintering ◽  
Flow Solver ◽  
Skin Cooling ◽  
End Use ◽  
Optimization Schemes

The increased design space offered by additive manufacturing (AM) can inspire unique ideas and different modeling approaches. One tool for generating complex yet effective designs is found in numerical optimization schemes, but until relatively recently, the capability to physically produce such a design had been limited by manufacturing constraints. In this study, a commercial adjoint optimization solver was used in conjunction with a conventional flow solver to optimize the design of wavy microchannels, the end use of which can be found in gas turbine airfoil skin cooling schemes. Three objective functions were chosen for two baseline wavy channel designs: minimize the pressure drop between channel inlet and outlet, maximize the heat transfer on the channel walls, and maximize the ratio between heat transfer and pressure drop. The optimizer was successful in achieving each objective and generated significant geometric variations from the baseline study. The optimized channels were additively manufactured using direct metal laser sintering (DMLS) and printed reasonably true to the design intent. Experimental results showed that the high surface roughness in the channels prevented the objective to minimize pressure loss from being fulfilled. However, where heat transfer was to be maximized, the optimized channels showed a corresponding increase in Nusselt number.

Experimental Investigation of Numerically Optimized Wavy Microchannels Created Through Additive Manufacturing

2017 ◽  
Author(s):  
Kathryn L. Kirsch ◽  
Karen A. Thole
Keyword(s):  
Heat Transfer ◽  
Additive Manufacturing ◽  
Pressure Drop ◽  
Numerical Optimization ◽  
High Surface ◽  
Direct Metal Laser Sintering ◽  
Flow Solver ◽  
Skin Cooling ◽  
End Use ◽  
Optimization Schemes

The increased design space offered by additive manufacturing can inspire unique ideas and different modeling approaches. One tool for generating complex yet effective designs is found in numerical optimization schemes, but until relatively recently, the capability to physically produce such a design had been limited by manufacturing constraints. In this study, a commercial adjoint optimization solver was used in conjunction with a conventional flow solver to optimize the design of wavy microchannels, the end use of which can be found in gas turbine airfoil skin cooling schemes. Three objective functions were chosen for two baseline wavy channel designs: minimize the pressure drop between channel inlet and outlet, maximize the heat transfer on the channel walls and maximize the ratio between heat transfer and pressure drop. The optimizer was successful in achieving each objective and generated significant geometric variations from the baseline study. The optimized channels were additively manufactured using Direct Metal Laser Sintering and printed reasonably true to the design intent. Experimental results showed that the high surface roughness in the channels prevented the objective to minimize pressure loss from being fulfilled. However, where heat transfer was to be maximized, the optimized channels showed a corresponding increase in Nusselt number.

A Comparative Numerical Study on Two-Phase Boiling Fluid Flow and Heat Transfer in the Microchannel Heat Sink With Different Manifold Arrangements

2020 ◽  
Author(s):  
Yang Luo ◽  
Jingzhi Zhang ◽  
Wei Li
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Heat Sink ◽  
Numerical Study ◽  
Flow Boiling ◽  
High Surface ◽  
Volume Ratio ◽  
High Heat Flux ◽  
Two Phase ◽  
Flow Maldistribution

Abstract The manifold microchannel (MMC) heat sink system has been widely used in high-heat-flux chip thermal management due to its high surface-to-volume ratio. Two-phase, three-dimensional numerical methods for subcooled flow boiling have been developed using a self-programming solver based on OpenFOAM. Four different types of manifold arrangements (Z-type, C-type, H-type and U-type) have been investigated at a fixed operational condition. The numerical results evaluate the effects of flow maldistribution caused by different manifold configurations. Before simulating the two-phase boiling flow in MIMC metamodels, single-phase liquid flow fields are performed at first to compare the flow maldistribution in microchannels. It can be concluded from the flow patterns that H-type and U-type manifolds provide a more even and a lower microchannel void fraction, which is conducive to improving the temperature uniformity and decreasing the effective thermal resistance. The simulation results also show that the wall temperature difference of H-type (0.471 K) is only about 10% of the Z-type (4.683 K). In addition, the U-type manifold configuration show the lowest average pressure drop at the inlet and outlet of the MIMC metamodel domain. However, H-type manifold also shows an impressive 59.9% decrease in pressure loss. Results indicate that both the H-type and the U-type manifolds for flow boiling in microchannels are recommended due to their better heat transfer performance and lower pressure drop when compared with Z-type and C-type.

Topology Optimization of Serpentine Channels for Minimization of Pressure Loss and Maximization of Heat Transfer Performance As Applied for Additive Manufacturing

2019 ◽  
Author(s):  
Shinjan Ghosh ◽  
Jayanta S. Kapat
Keyword(s):  
Heat Transfer ◽  
Topology Optimization ◽  
Additive Manufacturing ◽  
Pressure Drop ◽  
Gas Turbine ◽  
Turbine Blades ◽  
Inlet Temperature ◽  
Internal Cooling ◽  
Cooling Channels ◽  
Blade Cooling

Abstract Gas Turbine blade cooling is an important topic of research, as a high turbine inlet temperature (TIT) essentially means an increase in efficiency of gas turbine cycles. Internal cooling channels in gas turbine blades are key to the cooling and prevention of thermal failure of the material. Serpentine channels are a common feature in internal blade cooling. Optimization methods are often employed in the design of blade internal cooling channels to improve heat-transfer and reduce pressure drop. Topology optimization uses a variable porosity approach to manipulate flow geometries by adding or removing material. Such a method has been employed in the current work to modify the geometric configuration of a serpentine channel to improve total heat transferred and reduce the pressure drop. An in-house OpenFOAM solver has been used to create non-traditional geometries from two generic designs. Geometry-1 is a 2-D serpentine passage with an inlet and 4 bleeding holes as outlets for ejection into the trailing edge. Geometry-2 is a 3-D serpentine passage with an aspect ratio of 3:1 and consists of two 180-degree bends. The inlet velocity for both the geometries was used as 20 m/s. The governing equations employ a “Brinkman porosity parameter” to account for the porous cells in the flow domain. Results have shown a change in shape of the channel walls to enhance heat-transfer in the passage. Additive manufacturing can be employed to make such unconventional shapes.

Microtomography-Based Analysis of Pressure Drop and Heat Transfer Through Open Cell Metal Foams

2013 ◽  
Author(s):  
M. Oliviero ◽  
S. Cunsolo ◽  
W. M. Harris ◽  
M. Iasiello ◽  
W. K. S. Chiu ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Pressure Drop ◽  
Metal Foam ◽  
High Surface ◽  
Thermal Characteristics ◽  
Industrial Applications ◽  
Metal Foams ◽  
Surface Evolver ◽  
Periodic Cell ◽  
Numerical Predictions

Their light weight, open porosity, high surface area per unit volume and thermal characteristics make metal foams a promising material for many industrial applications involving fluid flow and heat transfer. Pressure drop and heat transfer of porous media have inspired a number of experimental and numerical studies. Many models have been proposed in the literature that correlate the pressure gradient and the heat transfer coefficient with the mean cell size and porosity. However, large differences exist among results predicted by different models. Most studies are based on idealized periodic cell structures. In this study, the true 3-D micro-structure of the metal foam is obtained by employing x-ray computed microtomography (XCT). For comparison, ideal Kelvin foam structures are developed in the free-to-use software “Surface Evolver” surface energy minimization program. Pressure drop and heat transfer are then investigated using the CFD Module of COMSOL® Multiphysics code. A comparison between the numerical predictions from the real and ideal geometries is carried out.

Effect of Build Direction in Direct Metal Laser Sintering (DMLS) of Inconel 718 on Microstructure and Mechanical Behavior

2019 ◽  
Author(s):  
Sachin Alya ◽  
Chaitanya Vundru ◽  
Ramesh Singh ◽  
Khushahal Thool ◽  
Indradev Samajdar ◽  
...  
Keyword(s):  
Additive Manufacturing ◽  
Mechanical Behavior ◽  
Inconel 718 ◽  
Laser Sintering ◽  
Thermal Gradients ◽  
Layer By Layer ◽  
Direct Metal Laser Sintering ◽  
Powder Bed ◽  
Grain Orientations ◽  
End Use

Abstract Additive manufacturing (AM) technology is gaining enormous popularity in the manufacturing industries. The continuous improvements made in the AM processes features development of 3D metallic prototypes as well as fully functional end-use components. Direct Metal Laser Sintering (DMLS) is a pre-placed powder bed based technique, in which a thin layer of powder is place over the build tray and the areas need to be sintered are exposed to the laser. In the current work the microstructural and mechanical behavior of Inconel 718 parts produced by DMLS are investigated. As the DMLS produces parts in a layer by layer fashion, the orientation of parts with respect to the build direction is an important criterion. Microstructure and mechanical properties of the produce differs depending upon the orientation. This paper emphasize on the variation of grain sizes and grain orientations developed in the components built with different orientations. Another common issue with the additive manufacturing is the development of the residual stresses in the components arising due to the differential thermal gradients experienced during processing. The variation of the residual stress generated in the produced parts has also been characterized and modeled.

Numerical Analysis of Heat Transfer and Pressure Drop in Metal Foams for Different Morphological Models

2014 ◽  
Vol 136 (11) ◽  
Author(s):  
Marcello Iasiello ◽  
Salvatore Cunsolo ◽  
Maria Oliviero ◽  
William M. Harris ◽  
Nicola Bianco ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Pressure Drop ◽  
Metal Foam ◽  
High Surface ◽  
Industrial Applications ◽  
Metal Foams ◽  
The Real ◽  
Numerical Predictions ◽  
The Ideal

Because of their light weight, open porosity, high surface area per unit volume, and thermal characteristics, metal foams are a promising material for many industrial applications involving fluid flow and heat transfer. The pressure drop and heat transfer in porous media have inspired a number of experimental and numerical studies, and many models have been proposed in the literature that correlate the pressure gradient and the heat transfer coefficient with the mean cell size and porosity. However, large differences exist among results predicted by different models, and most studies are based on idealized periodic cell structures. In this study, the true three-dimensional microstructure of the metal foam is obtained by employing x-ray computed microtomography (XCT). This is the “real” structure. For comparison, ideal Kelvin foam structures are developed in the free-to-use software “surface evolver” surface energy minimization program. These are “ideal” structures. Pressure drop and heat transfer are then investigated in each structure using the CFD module of COMSOL® Multiphysics code. A comparison between the numerical predictions from the real and ideal geometries is carried out. The predictions showed that heat transfer characteristics are very close for low values of Reynolds number, but larger Reynolds numbers create larger differences between the results of the ideal and real structures. Conversely, the differences in pressure drop at any Reynolds number are nearly 100%. Results from the models are then validated by comparing them with experimental results taken from the literature. The validation suggests that the ideal structure poorly predicts the heat transfer and pressure drops.

Evaluation of Pressure Drop Performance During Enhanced Flow Boiling in Open Microchannels With Tapered Manifolds

2014 ◽  
Vol 136 (5) ◽  
Author(s):  
Ankit Kalani ◽  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Flow Boiling ◽  
High Surface ◽  
Heat Removal ◽  
Electronics Cooling ◽  
Successful Implementation ◽  
Efficient Operation

Boiling can provide several orders of magnitude higher performance than a traditional air cooled system in electronics cooling applications. It can dissipate large quantities of heat while maintaining a low surface temperature difference. Flow boiling with microchannels has shown a great potential with its high surface area to volume ratio and latent heat removal. However, flow instabilities and low critical heat flux (CHF) have prevented its successful implementation. A novel flow boiling design is experimentally investigated to overcome the above-mentioned disadvantages while presenting a very low pressure drop. The design uses open microchannels with a tapered manifold (OMM) to provide stable and efficient operation. The effect of tapered manifold block with varied dimension is investigated with distilled, degassed water at atmospheric pressure. Heat transfer coefficient and pressure drop results for uniform and tapered manifolds with plain and microchannel chips are presented. The OMM configuration yielded a CHF of over 500 W/cm2 in our earlier work. In the current work, a heat transfer coefficient of 277.8 kW/m2 °C was obtained using an OMM design with an inlet gap of 127 μm and an exit gap of 727 μm over a 10 mm flow length. The OMM geometry also resulted in a dramatic reduction in pressure drop from 158.4 kPa for a plain chip and 62.1 kPa for a microchannel chip with a uniform manifold, to less than 10 kPa with the tapered OMM design. A tapered manifold (inlet and exit manifold heights of 127 and 727 μm, respectively) with microchannel provided the lowest pressure drop of 3.3 kPa.

Performance Characterization of an Additively Manufactured Titanium (Ti64) Heat Exchanger for an Air-Water Cooling Application

2016 ◽  
Author(s):  
M. A. Arie ◽  
A. H. Shooshtari ◽  
S. V. Dessiatoun ◽  
M. M. Ohadi
Keyword(s):  
Heat Transfer ◽  
Heat Transfer Coefficient ◽  
Additive Manufacturing ◽  
Heat Exchanger ◽  
Pressure Drop ◽  
Transfer Coefficient ◽  
Heat Exchanger Design ◽  
Performance Reduction ◽  
Manifold Microchannel ◽  
Microchannel Design

Over the last decade, rapid development of additive manufacturing techniques has allowed the fabrication of innovative designs which could not have been manufactured using conventional fabrication technologies. One field that can benefit from such technology is heat exchanger fabrication, as heat exchanger design has become more and more complex due to the demand for higher performance systems. One specific heat exchanger design that has shown significant performance enhancement potential over conventional designs and can greatly benefit from additive manufacturing technology is a manifold-microchannel heat exchanger. It is a design that combines careful fluid distribution through appropriate manifolds with an enhanced heat transfer surface design to achieve specific thermohydraulics performance expectations. Additive manufacturing allows fins as thin as 150 μm to be fabricated, which is an important enabler feature for the heat exchanger thermal performance. In addition, additive manufacturing allows the manifold and the microchannel sections to be fabricated as a single piece, which eliminates the need to fuse those sections together through a subsequent bonding process. As part of this work, we fabricated and experimentally tested a high-performance titanium alloy (Ti64) air-water heat exchanger that utilizes manifold-microchannel design. The heat exchanger was fabricated using direct metal laser sintering (DMLS) fabrication technique. The air-side implemented a manifold-microchannel design, while the water side used multiple rectangular channels in parallel. This was because the major thermal resistance occurs on the air side. The pressure drop and heat transfer performance of this heat exchanger were evaluated. The experimental results showed a noticeable performance reduction compared to the ones projected by numerical simulation due to an inaccuracy and low fidelity in printing of thin fin profile. However, despite this manufacturing inaccuracy, compared to a conventional wavy-fin surface, 15%–50% increase in heat transfer coefficient was possible for the same pressure drop value. Compared to a plain plate-fin surface, 95%–110% increase in heat transfer coefficient was possible for the same pressure drop value. The air-side heat transfer coefficient in the range of 100–450 W/m2K was achievable using manifold-microchannel technology for air-side pressure drop of 90–1800Pa. Since metal based additive manufacturing is still in the developmental stage, it is anticipated that with further refinement of the manufacturing process in future designs, the fabrication accuracy can be improved.

scholarly journals Thermomechanical Topology Optimization of Lattice Heat Transfer Structure Including Natural Convection and Design Dependent Heat Source

2019 ◽  
Author(s):  
Tong Wu ◽  
Joel C. Najmon ◽  
Andres Tovar
Keyword(s):  
Heat Transfer ◽  
Topology Optimization ◽  
Additive Manufacturing ◽  
Heat Source ◽  
Thermal Performance ◽  
Mass Fraction ◽  
Mechanical Performance ◽  
High Surface ◽  
Design Stage ◽  
Lattice Heat

Abstract Lattice Heat Transfer (LHT) structures provide superior structural support while improving the heat transfer coefficient through their high surface-to-volume ratios. By using current Additive Manufacturing (AM) technologies, LHT with highly complex structures is possible. In this study, the design concept of LHT is further improved by implementing a thermomechanical topology optimization method. With utilization of design-dependent heat source, the method can be applied to generate stiffer LHT structures under mechanical and thermomechanical loads, without decreasing their thermal performance; relative to a design made of a uniform LHT having the same mass fraction. Two numerical examples are presented to illustrate how to use the proposed approach to design LHT sections. The results show that the mechanical performance can be improved more than 50% compared to a uniform LHT with the same mass fraction, without decreasing the thermal performance. The method does not require a fluid mechanics model, thus it is computational effective and particularly suitable for the conceptual design stage. The resulting optimized lattice is made possible by utilizing additive manufacturing technologies.

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