Koon Chun Lai

4.20 Thermoelectric Energy Conversion

This article is focused on thermoelectric cooling (TEC) and thermoelectric power generation (TEG). Detailed theoretical modeling and characterization were presented with the key performance highlighted. Heat transfers from heat sinks on both hot and cold surfaces of the thermoelectric models were discussed and measures to enhance and increase heat transfer rates were proposed. Waste heat from the steel industry, vehicle exhaust gas and solar energy for TEG power generation were discussed. Two advanced technologies, i.e., two-stage TEG and heat pipe assisted TEG, were listed to increase the overall efficiencies of power generation.

Effect of Preparation Methods on the Tensile, Morphology and Solar Energy Conversion Efficiency of RGO/PMMA Nanocomposites

In this study, reduced graphene oxide (RGO)/polymethyl methacrylate (PMMA) nanocomposites were prepared by employing in situ polymerization and solution blending methods. In terms of mechanical properties, RGO loading increased the Young’s modulus but decreased the elongation at break for RGO/PMMA nanocomposites. Tensile strength for solution blended RGO/PMMA nanocomposites increased after adding 0.5 wt % RGO, which was attributed to the good dispersion of RGO in the nanocomposites as evidenced from SEM and TEM. Solar energy conversion efficiency measurement results showed that the optimum concentration of RGO in the RGO/PMMA nanocomposites was found to be 1.0 wt % in order to achieve the maximum solar energy conversion efficiency of 25%. In the present study, the solution blended nanocomposites exhibited better overall properties than in situ polymerized nanocomposites owing to the better dispersion of RGO in solution blending. These findings would contribute to future work in search of higher conversion efficiency using nanocomposites.

Segmentation Approach Towards Phase-Contrast Microscopic Images of Activated Sludge to Monitor the Wastewater Treatment

Image processing and analysis is an effective tool for monitoring and fault diagnosis of activated sludge (AS) wastewater treatment plants. The AS image comprise of flocs (microbial aggregates) and filamentous bacteria. In this paper, nine different approaches are proposed for image segmentation of phase-contrast microscopic (PCM) images of AS samples. The proposed strategies are assessed for their effectiveness from the perspective of microscopic artifacts associated with PCM. The first approach uses an algorithm that is based on the idea that different color space representation of images other than red-green-blue may have better contrast. The second uses an edge detection approach. The third strategy, employs a clustering algorithm for the segmentation and the fourth applies local adaptive thresholding. The fifth technique is based on texture-based segmentation and the sixth uses watershed algorithm. The seventh adopts a split-and-merge approach. The eighth employs Kittlers thresholding. Finally, the ninth uses a top-hat and bottom-hat filtering-based technique. The approaches are assessed, and analyzed critically with reference to the artifacts of PCM. Gold approximations of ground truth images are prepared to assess the segmentations. Overall, the edge detection-based approach exhibits the best results in terms of accuracy, and the texture-based algorithm in terms of false negative ratio. The respective scenarios are explained for suitability of edge detection and texture-based algorithms.

Thermal Performance Study of Composite Phase Change Material with Polyacrylicand Conformal Coating

The composite PCM was prepared by blending polymethyl methacrylate (PMMA) and myristic acid (MA) in different weight percentages. The MA and PMMA were selected as PCM and supporting material, respectively. As liquid MA may leak out during the phase transition, this study proposes the use of two coatings, namely a polyacrylic coating and a conformal coating to overcome the leakage problem. Both coatings were studied in terms of the leakage test, chemical compatibility, thermal stability, morphology, and reliability. No leakage was found in the PCMs with coatings compared to those without under the same proportions of MA/PMMA, thus justifying the use of coatings in the present study. The chemically compatibility was confirmed by FTIR spectra: the functional groups of PCMs were in accordance with those of coatings. DSC showed that the coatings did not significantly change the melting and freezing temperatures, however, they improved the thermal stability of composite PCMs as seen in TGA analysis. Furthermore, the composite PCMs demonstrated good thermal reliability after 1000 times thermal cycling. The latent heat of melting reduced by only 0.16% and 1.02% for the PCMs coated with conformal coating and polyacrylic coating, respectively. Therefore, the proposed coatings can be considered in preparing fatty acid/PMMA blends attributed to the good stability, compatibility and leakage prevention.

Water contaminants detection by a supercontinuum laser system

Heavy metal contaminant in the water aquifers is an environmental threat. In present study, by utilizing a broadband supercontinuum (SC) laser source, detection of the contaminants is achieved through emission of broad spectrum of lights. By measuring the amount of light transmitted through the water sample, the presence of heavy metal contaminants is thus determined. A statistical analysis is conducted to analyze the performance of water contaminants detection. Interactive effects between three independent factors namely wavelength of the SC source, concentration of the heavy metal contaminants and input power are examined. Optimal operational conditions are obtained along with longer wavelength, lesser concentration of contaminants and lower power source. Under these conditions, high detection rate could be achieved with a transmittance value at 0.751.

Attenuation in Circular and Rectangular Waveguides

ABSTRACT A closed-form approach to compute the attenuation of electromagnetic waves propagating in lossy circular and rectangular waveguides is presented. A set of characteristic equations, which describes the behavior of the waves, is first derived by matching the tangential fields at the boundary with the electrical properties of the wall material. Perturbation terms are then introduced into the equations to represent fields’ penetration into the lossy wall. The closed-form expressions of the perturbation terms are derived using the finite difference method. The propagation constant is subsequently obtained by incorporating the perturbation terms into the dispersion relation. Good agreement was found between the results of the authors and those from the rigorous equations. Unlike the rigorous transcendental approaches, which may require laborious effort in solving them, the solutions of our closed-form equations can be easily found; while, at the same time, they give reasonably accurate results.

Setup Time Reduction in a CNC Production Facility Through Redesign of Jigs and Fixtures

In CNC manufacturing, jigs and fixtures function to arrange workpiece in a definite position or prevent misalignment during machining operations. The case study of this research is conducted in company ‘X’, where a high demand product ‘Y’ ‘consists of three machining steps, with the first step as the bottleneck. The setup time for first step of product ‘Y’ was studied carefully and analyzed to identify underlying problems. Few suggestions were proposed in order to simplify or eliminate the bottleneck setup procedure, involving the redesigning of jigs and fixtures to eliminate multiple leveling and alignment procedure. Three recommendations for future research are proposed in the last section.

Thermal management of LED with vapor chamber and thermoelectric cooling

A fin heat sink (FHS) is a thermal heat transfer device employed to dissipate heat from a high temperature heat source to a lower temperature surrounding. A typical FHS consists of a flat metal base with an array of cooling fins on top. A problem normally encountered in thermal management of electronic packages is thermal heat spreading resistance which occurs as heat flows by conduction from a high temperature heat source to a low temperature heat sink with different cross-sectional areas. As high powered semiconductor chips are made more compact and requiring greater heat dissipation, more effective cooling systems have to be devised. There are various methods employed to minimize this heat spreading resistance. These include increasing the thickness of the base of the FHS or height of the fins. Another method is to use more expensive highly conductive materials like aluminum, copper and diamond which would increase cost. A more economical alternative would be to combine a flat heat pipe (HP) sometimes termed a vapor chamber (VC) with a conventional FHS to increase effective thermal conductivity at the base. Thermoelectric (TE) is the direct conversion of temperature difference between the junctions of two dissimilar materials (thermocouple) to electricity. The converse is true. A voltage applied between the junctions of the thermocouple creates a temperature difference between them. This effect could be utilized as a heat pump to transfer heat from the cold junction to the hot junction. A dc voltage imposed across a thermoelectric (TE) module causes a temperature difference to be imposed across the surfaces of the resulting in one face to be at a temperature higher than the other face. Heat is absorbed from a heat source in contact with the cold surface and dissipated to a heat sink in contact with the hot surface. This paper presents the results of an investigation conducted to evaluate the performance of VCs and TEs for the thermal management of LEDs.

Novel Detection of Heavy Metals in Water using Supercontinuum Broadband Laser Source

We report a novel detection technique for two types of common heavy metal contaminants in water, copper sulphate and ferric chloride, by analyzing the transmittance measurement of a supercontinuum laser source onto the samples.