Heat Transfer Performance of Micro-Porous Copper Foams with Homogeneous and Hybrid Structures Manufactured by Lost Carbonate Sintering

ABSTRACTThe heat transfer coefficients of homogeneous and hybrid micro-porous copper foams, produced by the Lost Carbonate Sintering (LCS) process, were measured under one-dimensional forced convection conditions using water coolant. In general, increasing the water flow rate led to an increase in the heat transfer coefficients. For homogeneous samples, the optimum heat transfer performance was observed for samples with 60% porosity. Different trends in the heat transfer coefficients were found in samples with hybrid structures. Firstly, for horizontal bilayer structures, placing the high porosity layer by the heater gave a higher heat transfer coefficient than the other way round. Secondly, for integrated vertical bilayer structures, having the high porosity layer by the water inlet gave a better heat transfer performance. Lastly, for segmented vertical bilayer samples, having the low porosity layer by the water inlet offered the greatest heat transfer coefficient overall, which is five times higher than its homogeneous counterpart.</jats:p

Specific Surface Areas of Porous Cu Manufactured by Lost Carbonate Sintering: Measurements by Quantitative Stereology and Cyclic Voltammetry

Open-cell porous metals have many applications due to high surface area to volume ratios. Porous metals manufactured by the space holder methods have distinctively different porous structure from commercial open-cell metal foams, but very little research has been conducted to characterise the surface area of this class of materials. This paper measured the geometric, electroactive and real surface areas of porous Cu samples manufactured by the Lost Carbonate Sintering process by quantitative stereology and cyclic voltammetry. A cyclic voltammetry (peak current) procedure has been developed and successfully applied to the measurement of electroactive surface areas of the porous Cu. For porous Cu samples with pore sizes 75-1500 µm and porosities 0.5-0.8, the volumetric and gravimetric specific geometric, electroactive and real surface areas are in the ranges of 15-90 cm-1 and 5-45 cm2/g, 200-400 cm-1 and 40-130 cm2/g, and 1000-2500 cm-1 and 400-800 cm2/g, respectively, varying with pore size and porosity. The geometric, electroactive and real surface areas are found to result from the contributions from primary porosity, primary and secondary porosities, and surfaces of metal particles, respectively. The measurement methods adopted in this study can provide vital information of surface areas at different length scales, which is important for many applications

Specific Surface Areas of Porous Cu Manufactured by Lost Carbonate Sintering: Measurements by Quantitative Stereology and Cyclic Voltammetry

Open-cell porous metals have many applications due to high surface area to volume ratios. Porous metals manufactured by the space holder methods have distinctively different porous structure from commercial open-cell metal foams, but very little research has been conducted to characterise the surface area of this class of materials. This paper measured the geometric, electroactive and real surface areas of porous Cu samples manufactured by the Lost Carbonate Sintering process by quantitative stereology and cyclic voltammetry. A cyclic voltammetry (peak current) procedure has been developed and successfully applied to the measurement of electroactive surface areas of the porous Cu. For porous Cu samples with pore sizes 75-1500 µm and porosities 0.5-0.8, the volumetric and gravimetric specific geometric, electroactive and real surface areas are in the ranges of 15-90 cm-1 and 5-45 cm2/g, 200-400 cm-1 and 40-130 cm2/g, and 1000-2500 cm-1 and 400-800 cm2/g, respectively, varying with pore size and porosity. The geometric, electroactive and real surface areas are found to result from the contributions from primary porosity, primary and secondary porosities, and surfaces of metal particles, respectively. The measurement methods adopted in this study can provide vital information of surface areas at different length scales, which is important for many applications

Fluid flow characterisation in randomly packed microscale porous beds with different sphere sizes using micro-particle image velocimetry

An experimental study using pressure-drop and μ-PIV measurements was undertaken to better understand the fluid flow characteristics in different flow regimes within randomly packed microscale porous beds with different sized spheres. Three sintered glass samples were made with glass spheres having a mean diameter of 170 μm, 430 μm and 710 μm by slightly sintering them between two glass slides, forming a sample with a sandwich structure. Four different regimes, pre-Darcy, Darcy, Forchheimer and turbulent were identified in each sintered glass sample using the pressure-drop measurements. The permeability increases with glass sphere size and so does the Reynolds number corresponding to each flow regime boundary. It was found that for a given Re, the pressure drop in the sample with 170 μm diameter spheres can be ten times higher than the pressure drop in the sample with 710 μm diameter spheres. Four different pore geometries were identified to be the focus of the measurement zones of the μ-PIV, which were taken across a range of Re spanning all the flow regimes identified in the pressure-drop measurements. The non-dimensional time-averaged velocity distribution was found to be similar in each flow regime for the samples with 170 μm and 430 μm diameter spheres, whereas it changed dramatically for the sample with 710 μm diameter spheres. In general the velocity profiles through the channels within the porous media were found to be near-parabolic, especially in the Darcy and Forchheimer regimes, but in the turbulent regime inertial effects such as localised jets were observed. Detailed observational and statistical analysis of the velocity distributions highlights their very strong dependency on the local geometry with highly localised regions of flow apparently in a different flow regime to that of the bulk flow. However, the global average of the fluctuations throughout the measurement zone does align well with the pressure drop measurements

Flow measurements in microporous media using micro-particle image velocimetry

An experimental study focused on the identification of the flow regimes and quantification of the velocity field at pore scale in microporous media is presented and discussed. Transparent porous media are fabricated by removing a pore forming agent in slightly sintered glass beads of size 50 μ m between two glass slides, leaving typical pores with a size of 500 μ m . Pressure-drop measurements and particle image velocimetry measurements are conducted simultaneously in order to evaluate the flow regimes and flow behaviors at pore size based Reynolds numbers from 0.1 to 140. Four different regimes, pre-Darcy, Darcy, Forchheimer, and turbulent, are found and presented. Spatial distribution and characteristics of the time-averaged velocity in all regimes and fluctuation intensity in transitional and turbulent regimes are investigated. Critical Reynolds numbers are identified using both velocity and pressure-drop measurements and the results agree very well, providing direct evidence underpinning the transition. The effects of porosity on these flow properties are also studied, and finally the flow regime boundaries are compared with the literature. These data provide an insight into the flow properties in microporous media with various porosities and an improved understanding that could be further utilized to enhance the flow and heat transfer performance of microporous media. It also demonstrates that velocity and pressure measurements used in combination can be an effective method for studying microporous media