Kau Fui V Wong

A Review of Additive Manufacturing

Additive manufacturing processes take the information from a computer-aided design (CAD) file that is later converted to a stereolithography (STL) file. In this process, the drawing made in the CAD software is approximated by triangles and sliced containing the information of each layer that is going to be printed. There is a discussion of the relevant additive manufacturing processes and their applications. The aerospace industry employs them because of the possibility of manufacturing lighter structures to reduce weight. Additive manufacturing is transforming the practice of medicine and making work easier for architects. In 2004, the Society of Manufacturing Engineers did a classification of the various technologies and there are at least four additional significant technologies in 2012. Studies are reviewed which were about the strength of products made in additive manufacturing processes. However, there is still a lot of work and research to be accomplished before additive manufacturing technologies become standard in the manufacturing industry because not every commonly used manufacturing material can be handled. The accuracy needs improvement to eliminate the necessity of a finishing process. The continuous and increasing growth experienced since the early days and the successful results up to the present time allow for optimism that additive manufacturing has a significant place in the future of manufacturing.

Applications of Nanofluids: Current and Future:

Nanofluids are suspensions of nanoparticles in fluids that show significant enhancement of their properties at modest nanoparticle concentrations. Many of the publications on nanofluids are about understanding their behavior so that they can be utilized where straight heat transfer enhancement is paramount as in many industrial applications, nuclear reactors, transportation, electronics as well as biomedicine and food. Nanofluid as a smart fluid, where heat transfer can be reduced or enhanced at will, has also been reported. This paper focuses on presenting the broad range of current and future applications that involve nanofluids, emphasizing their improved heat transfer properties that are controllable and the specific characteristics that these nanofluids possess that make them suitable for such applications.

Comparative analysis of energy security in the Nordic countries: The role of renewable energy resources in diversification

Security of energy supply has been one of the important debates among citizens and governments of the Nordic countries after the first energy crisis. In response, diversification was defined as the heart strategy to reach a certain level of energy supply. This article discusses about the level of energy security in the Nordic countries with comparison to other developed countries and their neighbors. Then, the support schemes and policies to achieve the energy security and diversification are reviewed based on the system thinking approach with especial focus on the renewable energy resources. This approach provides a unique and powerful tool to explain the complexity and the relationships among the elements of the support schemes in the energy security analysis.

Heat Transfer Mechanisms and Clustering in Nanofluids

This paper surveys heat transfer in nanofluids. It summarizes and analyzes the theories regarding heat transfer mechanisms in nanofluids, and it discusses the effects of clustering on thermal conductivity. The heat transfer associated with conduction is presented through various experiments followed by a discussion of the theories developed. Relationships between thermal conductivity and various factors such as temperature, concentration, and particle size are also displayed along with a discussion on clustering. There is a brief discussion on convection where the number of studies is limited. There is research currently being performed on the manipulation of the properties governing the thermal conductivity of nanofluids—the particle size, shape, and surface area. Other factors that affect heat transfer are the material of the nanoparticle, particle volume concentration, and the fluid used. Although the interest in this relatively new class of fluids has generated many experimental studies, there is still disagreement over several aspects of heat transfer in nanofluids, primarily concerning the mechanisms behind the increased thermal conductivity. Although nanoparticles have greatly decreased the risks, there is still evidence of unwanted agglomeration which causes erosion and affect the overall conductivity. Research is currently being conducted to determine how to minimize this unwanted clustering.

Oil spill containment by a flexible boom system

Abstract In this paper, a specific boom arrangement is quantitatively analyzed. The boom arrangement was led by a flexible ramp boom, which used the energy of the incoming flow to attain a desirable angle of inclination. It consisted of a number of flaps to adjust itself to non-uniform flow conditions. Vinyl sheets of varying bending stiffness were used to achieve necessary deflections. The ramp boom was setup with three conventional booms downstream. Open channel experiments were carried out for a large number of dimensionless parameters. Volume analysis was performed to determine the amount of the collected oil. The effects of Reynolds number, Froude number, depth ratio, oil relative viscosity, oil relative density, number of flaps and inclination angle on the collection efficiency of the boom system were investigated. The separation distances of the consecutive booms were also investigated. The variation of the scales of the geometric parameters with respect to the draft of the ramp boom and the variation of the above-mentioned dimensionless parameters aided in determining the optimum interval for the total span of the boom system. The critical limiting ratios of total span of the ramp boom system to the draft of the ramp boom were determined as 9.9 and 14.6. The optimum collection efficiency of 100% was obtained at a maximum flow speed of 0.305 m/s corresponding to a Froude number of 0.51. This value would correspond to a prototype flow speed of 1 m/s (about 2 knots) with Froude number scaling.

Empirical heat transfer and frost thickness correlations during frost deposition on a cylinder in cross-flow in the transient regime

This paper reports on results of an experimental investigation where the emphasis was placed on obtaining empirical correlations for the frost thickness–time history and the heat transfer coefficient–time history for a cylinder in humid air cross-flow. The facility employed for the investigation consisted of a low-velocity wind tunnel comprised of a rectangular test section, a transition section and a honeycomb placed at the tunnel entrance. An external refrigerator was used to cool an antifreeze solution having a mixture of 90% methanol and 10% ethylene glycol. Measured parameters included, among other things, the heat transfer coefficient as well as the frost thickness.

Smart Glass and Its Potential in Energy Savings

Smart glass is such that its properties may be changed by application of a potential across it. The change in properties may be engineered to alter the amount of heat energy that can penetrate the glass which provides heating and cooling design options. Therein lies its potential in energy savings. Smart glass may be classified into three types: electrochromic, suspended particle, and polymer dispersed liquid crystal (PDLC). Each of these types has their own mechanisms, advantages, and disadvantages. Electrochromic smart glass is the most popular, currently it utilizes an electrochromic film with an ion storage layer and ion conductor placed between two transparent plates. The electrochromic film is usually made of tungsten oxide, owing to the electrochromic nature of transition metals. An electric potential initiates a redox reaction of the electrochromic film transitioning the color and the transparency of the smart glass. Suspended particle smart glass has needle shaped particles suspended within an organic gel placed between two electrodes. In its off state, the particles are randomly dispersed and have a low light transmittance. Once a voltage is applied, the needle particles will orient themselves to allow for light to pass through. PDLC smart glass works similarly to the suspended particle variety. However, in PDLC smart glass, the central layer is a liquid crystal placed within a polymer matrix between electrodes. Similar in behavior to the suspended particles, in the off position the liquid crystals are randomly dispersed and have low transmittance. With the application of a voltage, the liquid crystals orient themselves, thereby allowing for the transmittance of light. These different smart glasses have many different applications, but with one hindrance. The requirement of a voltage source is a major disadvantage which greatly complicates the overall installation and manufacturing processes. However, the integration of photovoltaic (PV) devices into smart glass technology has provided one solution. Photovoltaic films attached in the smart glass will provide the necessary voltage source. The photovoltaic film may even be designed to produce more voltage than needed. The use a photovoltaic smart glass system provides significant cost savings in regards to heating, cooling, lighting, and overall energy bills. Smart glass represents a technology with a great deal of potential to reduce energy demand. Action steps have been identified to propagate the popular use of smart glass.

Recommendations for Energy–Water–Food Nexus Problems

The chronic water problems in parts of India are probably due mainly to mismanagement. The rolling blackout and brownout problems in the larger Indian cities are due to lack of generation capacity. Since about ninety percent of the worlds electricity is generated based on the steam Rankine cycle, environmental water is necessary for cooling, and freshwater is used as the working fluid. Furthermore, electricity is tied to water as part of the bigger water energy nexus phenomena occurring worldwide. China has started and continued with many initiatives to correct problems with water management. Projects do exist where the climatically dry north is being fed water from the wet south. China has water energy nexus conditions occurring too. The review of the scientific literature on studies about the sources of the Ganges, the Yangtze, the Yellow river, the Indus and the Mekong (the drinking water source of about forty percent of the Worlds population), the glaciers that feed these sources and how they are shrinking with global warming, has yielded a simple policy decision. Mass balance considerations provide the answer that the logical solution of the recent accelerated water changing from solid to liquid on mountain tops, requires dams and storage areas (lakes) to prevent all that freshwater from escaping to the lowlands, and ultimately being discharged into the oceans. One of the other major contributions in this work is to suggest conversion of (old) Rankine cycle generation of electricity to (new) combined gas cycle generation and/or simple gas cycle generation. The combined gas cycle generation can achieve efficiencies of 55–60%, while that of the Rankine cycle power generation languishes around 30%. Less water is required per MW electric power generated for condenser cooling in the combined cycle. The simple gas cycle generation can achieve 40% thermal efficiency on the average and use no water for cooling. There is also the suggestion to upgrade to supercritical power plants due to the advances in power plant technologies. The improved thermal efficiencies gained from this upgrade generate other benefits as well. Another contribution is the suggestion to use seawater for closed system condenser cooling in power plants that are not near the sea or ocean or any large body of freshwater. The open system seawater condenser cooling has been practiced for years throughout the world. This will definitely reduce the demand for freshwater, which could otherwise be used for human consumption or agriculture. Additionally, the rising seas problem locally may be reduced somewhat if enough of the seawater is used.

Oil Spill Boom Design for Waves

Abstract The objective of this research was to design and test boom arrangements that will be able to function effectively in the presence of waves and turbulent conditions and be modular and free floating. The designs were based on the principle that fluid particles in waves traverse in a circular pattern, so it was imperative to take advantage of that feature. Three models were built and tested in the open channel apparatus introducing the plausible validity of vertical cascading and sinusoidal tapering of an oil boom system. Given several flow velocities, the first two designs averaged efficiencies of 79.2% and 68.2%, respectively. The final model was tested through a series of three conditions: An ideal straight-on condition, a straight-on condition with the first surface was completely out of the water and one condition where the center line of the boom was at an angle to the water current. These three configurations yielded averaged efficiencies of 87%, 80.1%, and 70.9%, respectively.

Study of Nanofluid Natural Convection Phenomena in Rectangular Enclosures

Buoyancy induced flows in rectangular enclosures using nanofluids were investigated. The effects of mass fraction concentration of nanoparticles, enclosure aspect ratio and inclination were observed. The nanofluid under investigation was a water-based alumina nanofluid. Since water exhibits an anomalous density extremum near 4°C the additional effect of buoyancy force reversal will also be observed. The opacity of nanofluid does not permit the use of particle image velocimetry, laser induced fluorescence or any other means of flow visualization or visual temperature measurement of the local fluid temperature. Therefore to investigate the temperature field a non-invasive method, namely ultrasound thermometry, will be used to observe the temperature field. The experimental enclosure was validated using water as the initial fluid; measured values of the local fluid temperature were compared with numerical simulations utilizing COMSOL Multiphysics. Nanofluid mass fractions of 10% and 25% were used for comparative purposes of the effects of concentration on the temperature field. Buoyancy force reversal effects were witnessed in both 10% and 25% concentrations. The nanofluid also prolonged the multicellular effects that occur in buoyancy inversion flows. A Rayleigh number inversion was observed for the 25% mass fraction nanofluid. The multicellular regime transitions to boundary layer regime at about Ra=1E+07 when the aspect ratio is 2.625 and at about Ra=2E+08 when the aspect ratio is 1.000, for different concentrations of nanofluid. For these concentrations of nanofluid and aspect ratio equal to 2.625, instability in the core region occurred at about Ra=1.2E+07.Copyright