The development of a liquid cooling test system for the analysis of porous surfaces

<p>Closed-loop liquid cooling systems are used in a wide variety of high temperature environments, as liquids tend a higher thermal conductivity than air. Microchannels and porous microstructures have proved to be useful in improving the cooling capabilities of cooling systems, due to their increased surface area in contact with the cooling fluid. This thesis describes the design, development, and evaluation of a closed-loop liquid cooling test system. This system was utilised in analysing the thermal properties of porous microstructures for use in improving cooling capabilities. Flow rate and pressure sensors were fitted onto a standard closed loop liquid cooling system design, and thermocouples were attached to the system to measure the temperature at various points, as well as measure heat flux. Using these measurements, the thermal and hydraulic resistances of the system could be calculated. Various substrates were fabricated using both freeze casting and other techniques, and the thermal and hydraulic resistances of these substrates were characterized using the test system. The test system performed very well, with results matching the trends as expected from theory. However, no improvement in heat transfer was observed from microstructured silver surfaces compared to a solid copper reference surface. This may be due to the formation of oxides and/or sulphides on these silver surfaces, resulting in a reduction in the convective heat transfer from these layers.</p>

The development of a liquid cooling test system for the analysis of porous surfaces

<p>Closed-loop liquid cooling systems are used in a wide variety of high temperature environments, as liquids tend a higher thermal conductivity than air. Microchannels and porous microstructures have proved to be useful in improving the cooling capabilities of cooling systems, due to their increased surface area in contact with the cooling fluid. This thesis describes the design, development, and evaluation of a closed-loop liquid cooling test system. This system was utilised in analysing the thermal properties of porous microstructures for use in improving cooling capabilities. Flow rate and pressure sensors were fitted onto a standard closed loop liquid cooling system design, and thermocouples were attached to the system to measure the temperature at various points, as well as measure heat flux. Using these measurements, the thermal and hydraulic resistances of the system could be calculated. Various substrates were fabricated using both freeze casting and other techniques, and the thermal and hydraulic resistances of these substrates were characterized using the test system. The test system performed very well, with results matching the trends as expected from theory. However, no improvement in heat transfer was observed from microstructured silver surfaces compared to a solid copper reference surface. This may be due to the formation of oxides and/or sulphides on these silver surfaces, resulting in a reduction in the convective heat transfer from these layers.</p>

Ni–citric acid coordination polymer as a practical catalyst for multicomponent reactions

Coordinative polymers (CP) are a subclass of Metal–organic frameworks (MOFs) with porous microstructures which have been widely synthesized in recent years and applied in various fields especially in catalysis science. In this work Coordinative polymers (CP) of nickel and citric acid (CA) was prepared as a new catalyst (Ni-CP) and applied in organic multicomponent reactions. The obtained catalyst was characterized by SEM, WDX, EDS, AAS, FT-IR, XRD and BET analysis. N2 adsorption–desorption isotherms indicate good BET surface area for Ni-CP; therefore can be employed as an efficient catalyst in multicomponent reactions for the synthesis of polyhydroquinoline and 2,3-dihydroquinazolin-4(1H)-one derivatives. Finally, this catalyst was recovered and reused several consecutive times.

Influence and Possibility of Using Limestone Dust Replacement of Sand for Sustainability in Concrete Production

This paper aimed to assess the potential of using limestone dust to replace sand at levels of 0, 20, 40, 60, 80 and 100% by weight. Concrete mix design for cement : fine aggregate : coarse aggregate was 1: 2 : 4 and 0.40, 0.50, 0.60 water-to-cement ratios were used. The study started by testing the basic properties of the material. The compressive strength test was done with curing for 7, 14, 21 and 28 days and modulus of elasticity of concrete at 28 days, after which the microstructural properties of concrete modified with limestone dust were investigated. The study found that the concrete had better workability when increasing the limestone dust content. The incorporation of 40% limestone dust at 0.50 water-to-cement ratios was found to improve the compressive strength of the concrete and resulted in the maximum compressive strength. However, high levels of replacement lead to porous microstructures. Moreover, the use of limestone dust in concrete production tends to be more cost-effective. Therefore, the results of this research seemingly provide confirmation and support for the utilization of these waste materials by reducing the use of natural resources. Further, it is a goal of local governments to help promote the value of limestone dust for future use.

Mechanical Properties of Porous Structures for Dental Implants: Experimental Study and Computational Homogenization

A combined experimental and numerical study on titanium porous microstructures intended to interface the bone tissue and the solid homogeneous part of a modern dental implant is presented. A specific class of trabecular geometries is compared to a gyroid structure. Limitations associated with the application of the adopted selective laser melting technology to small microstructures with a pore size of 500 μm are first examined experimentally. The measured effective elastic properties of trabecular structures made of Ti6Al4V material support the computational framework based on homogenization with the difference between the measured and predicted Young’s moduli of the Dode Thick structure being less than 5%. In this regard, the extended finite element method is promoted, particularly in light of the complex sheet gyroid studied next. While for plastic material-based structures a close match between experiments and simulations was observed, an order of magnitude difference was encountered for titanium specimens. This calls for further study and we expect to reconcile this inconsistency with the help of computational microtomography.

Finite element analysis to determine the role of porosity in dynamic localization and fragmentation: Application to porous microstructures obtained from additively manufactured materials

In this paper, we have performed a microstructurally-informed finite element analysis on the effect of porosity on the formation of multiple necks and fragments in ductile thin rings subjected to dynamic expansion. For that purpose, we have characterized by X-ray tomography the porous microstructure of 4 different additively manufactured materials (aluminium alloy AlSi10Mg, stainless steel 316L, titanium alloy Ti6Al4V and Inconel 718L) with initial void volume fractions ranging from 0.0007 % to 2 %, and pore sizes varying between 6 micrometers 110 micrometers. Three-dimensional analysis of the tomograms has revealed that the voids generally have nearly spherical shape and quite homogeneous spatial distribution in the bulk of the four materials tested. The pore size distributions quantified from the tomograms have been characterized using a Log-normal statistical function, which has been used in conjunction with a Force Biased Algorithm that replicates the experimentally observed random spatial distribution of the voids, to generate ring expansion finite element models in ABAQUS/Explicit which include actual porous microstructures representative of the materials tested. We have modeled the materials behavior using von Mises plasticity, and we have carried out finite element calculations for both elastic perfectly-plastic materials, and materials which show strain hardening, strain rate hardening and temperature softening effects. Moreover, we have assumed that fracture occurs when a critical value of effective plastic strain is reached. The finite element calculations have been performed for expansion velocities ranging from 50 m/s to 500 m/s. A key point of this investigation is that we have established individualized correlations between the main features of the porous microstructure (i.e. initial void volume fraction, average void size and maximum void size) and the number of necks and fragments formed in the calculations. In addition, we have brought out the effect of the porous microstrucure and inertia on the distributions of neck and fragment sizes. To the authors' knowledge, this is the first paper ever considering actual porous microstructures to investigate the role of material defects in multiple localization and dynamic fragmentation of ductile metallic materials.