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This work investigates the effects of Ar-based shielding gases on the microstructure and phase balance of duplex stainless steel (DSS) depositions. The results are then used for fabrication of DSS walls using wire arc additive manufacturing (WAAM), and the microstructural characteristics and mechanical performance of the products are assessed. WAAM currently poses as one of the most interesting methods of manufacturing by enabling joining of materials to fabricate structures layer by layer. However, the extreme conditions imposed by the process, such as high heat inputs and re-melt and solidification of the deposited layers, could compromise the performance of the products. A detailed microstructural analysis is conducted on single layer and double layer depositions of DSS to assess the effects of different shielding gases on the ferrite/austenite phase balance in the specimens. The results show that the depositions shielded with a small fraction of carbon dioxide (CO2) present better microstructural features in comparison to depositions shielded with the other selected gases. A mixture of 98%Ar + 2%CO2 was employed for fabrication of a 60-layer DSS WAAM-made wall and some mechanical characteristics were studied. The mechanical examinations demonstrate that the properties of the parts fabricated using WAAM are comparable with their wrought counterparts.

In this study, Wire Arc Additive Manufacturing (WAAM) based Directed Energy Deposition (DED) process is used to build two parts, tube and wall from 2209 Duplex Stainless Steel. Duplex stainless steel is extremely effective against stress corrosion cracking due to existence of an equal portion of austenite and ferrite phases. The challenge is monitoring of the process parameters and cooling rate to promote ferrite phase formation. To this end, three-dimensional transient thermal models of the additive manufactured (AM) parts are presented and the simulated thermal cycles are verified with the experimental results. The correlation between the calculated cooling rates and the phases formation in the WAAM parts is studied and revealed. The results highlight that slow cooling rate of the built layers at elevated temperatures promote austenite formation significantly in a ferrite matrix. Furthermore, the experimental mechanical examinations will illustrate the quality of the WAAM-made parts and compare their mechanical properties with their wrought counter-parts.

Wire Arc Additive Manufacturing (WAAM) is a combination of an electric arc and wire feeding system used extensively in building components and repair operations. The heat transfer, fluid flow and mass transport were investigated in a numerical simulation of WAAM process with dissimilar substrate. Experiments were performed to verify the numerical results. The predicted clad layer (1st layer) profile (width and height) is in good agreement with experiment. The cold wire transfer (CWT) impact on the velocity field and mass transport were predicted around the cold wire immersion inlet in the weld pool (WP). The effect of arc travel speed and wire feed rate on the homogenization process were studied. Both the numerical and experimental results show that the increase of wire feed rate leads to homogenous composition in fusion zone (FZ). The predicted composition distribution in the clad layer and measured concentrations in experiments show a well-mixed region in middle of the clad layer.

Dissimilar welding was achieved between martensitic stainless steel type AISI 410 and Inconel 718 using Cold Wire Gas Tungsten Arc Welding (CW-GTAW). Two types of consumables namely 718-410 and 82-410 were selected for this study. In both weldments, the microstructure investigation showed fully austenitic weldments with formation of secondary phases. Secondary phases were present in the heat affected zone (HAZ) of 718, and an unmixed melted zone (UMMZ) was observed on the 410 interface. The hardness of the secondary phases and UMMZ were determined using nano-indentation, and results revealed higher hardness in these regions compared to the weld zone (WZ) matrix. The UMMZ was removed by arc current enhancement. Mechanical examinations indicated that secondary phases and UMMZ did not significantly affect tensile strength and resistance to plastic deformation. However, investigation revealed that secondary phases can have a detrimental effect on ductility. Filler wire 82-410 demonstrated improved mechanical properties compared to filler 718-410 at room temperature and resulted in a stronger weld compared to 410 base metal (BM).

The hydrogen embrittlement susceptibility of near-peak-aged UNS N07718 (Alloy 718) was evaluated by performing slow strain rate tests at room temperature in air and substitute ocean water. Tests in substitute ocean water were accomplished in an environmental cell that enabled in situ cathodic charging under an applied potential of −1.1 V versus SCE. Some specimens were cathodically precharged for 4 or 16 weeks at the same potential in a 3.5 wt.% NaCl-distilled water solution at 50 °C. Unprecharged specimens tested in substitute ocean water exhibited only moderate embrittlement with plastic strain to failure decreasing by about 20% compared to unprecharged specimens tested in air. However, precharged specimens exhibited significant embrittlement with plastic strain to failure decreasing by about 70%. Test environment (air or substitute ocean water with in situ charging) and precharge time (4 or 16 weeks) had little effect on the results of the precharged specimens. Fracture surfaces of precharged specimens were typical of hydrogen embrittlement and consisted of an outer brittle ring related to the region in which hydrogen infused during precharging, a finely dimpled transition zone probably related to the region where hydrogen was drawn in by dislocation transport, and a central highly dimpled ductile region. Fracture surfaces of unprecharged specimens tested in substitute ocean water consisted of a finely dimpled outer ring and heavily dimpled central region typical of ductile fracture.

Optimizing welding parameters to achieve low residual stress (RS) with the aid of stress reduction techniques usually relies on the study of residual strain distribution in weldment. However, investigating transient strains using experimental methods such as strain gauges gives an additional view on how RS is reduced. In this work, the transient strain and stress on the surface of dissimilar plate during gas-tungsten arc (GTA) welding process have been studied using non-destructive strain gauge method. It is demonstrated that strain gauge measurements during dissimilar welding processes can be used to indicate residual elastic strain and stress. Moreover, three- dimensional (3D) finite element (FE) model has been developed and verified with experimental work (neutron diffraction measurement), and was employed to examine the formation of RS upon cooling of a 304-1018 dissimilar weldment. The strain gauge (SG) measurement method shows good agreement with FE model and neutron diffraction measurements. The assumptions and limitations associated with strain measurement and determination of the stress state are explored. Lastly, curvature due to dissimilar weld and its effects on strain measurement, which is in contrast with similar weld, was measured and discussed.

In this investigation the heat, fluid flow, and mass transfer for linear autogenous gas tungsten arc (GTA) welding of austenitic stainless steel to low carbon steel is presented. A numerical model was built in COMSOL Multiphysics which included the electromagnetic field, fluid flow, and heat and mass transfer. The results show that there is a toroidal fluid motion at the center of the weld pool, which circulates the molten base metals and completely mixes them with each other. The numerical predictions of the weld-pool shape and the concentrations of iron (Fe), chromium (Cr) and nickel (Ni) were compared to the experimental determinations of the weld-zone and the concentrations of Fe, Cr and Ni. Both numerical and experimental results show that the alloying elements are uniformly mixed throughout the weld zone. The numerical predictions are quantitatively in reasonable agreement with the experimentally determined results.

The reliability of shell and tube heat exchanger is predicted using a 2-stage physics-based simulation. The first stage uses stochastic porous models of the bundle to estimate operational and environmental uncertainties in flow conditions, such as flow velocity and inlet temperature. The results are used for the second stage, which is the CFD simulation of the sub-model. The most critical part of shell and tube heat exchangers is the tube bundle. The technique integrates stochastic fluid-structure interaction with fatigue and Monte Carlo simulations. Heating loads are transferred between models by mapping of actual temperature distributions. A sensitivity analysis is conducted to determine the significant factors that may lead to failure, as it is impractical to consider all input variables. In the sub-model, which is a tube bank, air flow and heat transfer inter-effects between the three tubes and the fins are measured. Thermal stresses are highest at the bonding regions between the water tubes and the fins, and that is because of the high temperature gradient combined with different material properties. Thermal stress in the model is relatively low, however, it has a high effect on fatigue life, and consequently on reliability result. The presented model can be used as a useful tool for reliability-based design of shell and tube heat exchangers.

Using a finite element analysis (FEA) model, the residual stress (RS) formation in an autogenous GTA dissimilar weld between austenitic stainless steel (304) and low carbon steel (A36) are analyzed. The effect of material properties on RS formation was determined by first considering a similar weld of 304 plates, and then changing only a selected mechanical property of the 304 plate on one side of weld to that corresponding to an A36 plate. Enforcing one set of mechanical property to be different at a time helped to isolate the role of these individual properties on the RS formation in the dissimilar weld. The effect of mechanical tensioning on dissimilar welds is then investigated. Results show that the longitudinal RS in both the similar and dissimilar welds can be reduced in the weld zone (WZ) by an amount equal to the stress corresponding to the applied mechanical tensioning load, as the tensioning load is removed after cooling. The mechanism of RS formation in dissimilar weld, and its mitigation by mechanical tensioning are determined by comparing the longitudinal stress evolution on a cross-section of the dissimilar weld plates under the mechanically tensioned and free conditions.

The transport processes associated with mixing of two dissimilar alloys in a gas-tungsten arc weld pool are investigated numerically and experimentally. The numerical model includes the electromagnetic, velocity, temperature, and concentration fields. The model is solved fully coupled using the finite element software COMSOL Multiphysics®. The simulation shows that at early times surface tension drives a toroidal vortex flow around the circumference of the weld pool. At these times, the distribution of metals in the weld pool is not uniform since the fluid flow within the melt is not fully developed. At later times, the weld pool expands and deepens, and a secondary flow develops that circulates the flow along the bottom of the weld pool and then back along its edges where it is coupled with a toroidal vortex. This flow causes the melt to quickly become homogeneous. The numerical predictions of the concentration distribution were verified by comparison with experimental results obtained from electron dispersive spectroscopy (EDS). The predicted weld-pool geometry was also in reasonable agreement with the experimental result. In examining the surface tension effects, it was found that, except at early times, the temperature driven Marangoni forces dominate the surfactant driven effects (sulfur). However, the surfactant still has an important role because it modifies the temperature sensitivity of the surface tension.

The electrical energy needed in welding processes is a major factor of energy consumption in manufacturing processes that use welds to fabricate structures. In the arc welding process an intense electrical arc is used as the heat source to melt locally metallic materials to join them once they solidify. Although the arc is focused at the joint, a large portion of energy is dissipated as heat through the base metals to the surroundings. In this paper it is shown that selecting the welding parameters appropriately, viz., the power supplied to the arc and the translation speed of the arc, can reduce the energy consumed per unit length of weld. The range of parameters examined was selected such that the vaporization of the molten metal was negligible. It is shown that increasing the arc power in conjunction with increasing the travel speed of the arc leads to reduced energy consumption per unit length of weld; this reduction in energy consumption is for equivalent welds, i.e., welds with identical geometric features.

A 3D transient numerical simulation is developed to study the arc welding of dissimilar metals for three sets of processing parameters. The model is used to investigate the fluid flow impacts on mass transport during the process. The predicted mass distribution agrees well with experimental composition measurements obtained from electron dispersive spectroscopy (EDS) analysis. The temperature distribution and the top surface shapes also match well with the experimental data. The morphology of the weld metal has a crucial impact on the weldment’s mechanical properties, and the prediction of solidification structure is key to improving weld quality. To this end, thermal results are applied to analyze the solidification behavior of the weld pool. The solidification parameters are calculated at the weld pool interface and the results are compared with the observed morphology from the experiments. The experimental observations confirm the presence of asymmetric solidification as demonstrated by the proposed model.

Hybrid systems consisting of a single or multiple primary sources along with a storage component are used in renewable energy production due to the wide disparity between the intermittent power generated and the power demand. Finding the optimal size of a hybrid system with no loss of power supply (LPS) is of utmost concern when considering the levelized cost of energy (LCE) of the project over its lifecycle. In this study, an optimization routine employing a search algorithm is developed to find the minimum LCE that meets zero LPS in the context of data center application. To this end, a system model is developed by integrating basic models of the subsystems. The system model is then used to investigate two different loading cases, 1) a case where the demand cannot be controlled as in the case of power demand in a residential network, and 2) a case where the demand can be controlled up to certain limits, as in the case of power demand in a data center or a data center network. Various types of controllable power demand scenarios are studied. The results demonstrate a significant reduction in the life cycle costs of the system when controllable power demand is considered, especially in regions where wind and solar resources are relatively low.

The fouling effect of seawater samples collected from three New Hampshire beaches on a 90/10 Cu/Ni commercial heat exchanger tube was investigated. A fouling monitoring device, designed on the basis of fouling thermal resistance, was used for this experimental study. The filtered seawater samples were circulated through the closed loop experimental setup for durations of seven and 14 days and the fouling thermal resistance was measured continuously. Analytical microscopy was performed on the tube surface before and after the experiments to see the effect of seawater fouling on the tube surface. The results show different fouling behavior for the seawater samples. This different behavior is confirmed by the different composition of the samples. Fouling monitoring experiments reveal a higher fouling thermal resistance for one of the seawater samples, Hampton seawater, contrary to the results of SEM analysis which show a lower crystallization rate for Hampton sample. Water decomposition analysis shows the lowest sodium content for Hampton seawater compared to the other samples. Accordingly, corrosion of the tube surface occurs with a higher rate for Hampton seawater due to the presence of chlorine ions and a lower concentration of sodium. The high fouling resistance of Hampton seawater can be explained as the result of several simultaneous fouling mechanisms, corrosion and crystallization indicating composite fouling behavior. The results of the current study are critical for the industries which use seawater as the cooling water source.

In this paper, the mechanical properties of crystalline silicon carbide nanowires, synthesized with a catalyst-free chemical vapor deposition method, were characterized with nanoscale tensile testing and mechanical resonance testing methods inside a scanning electron microscope. Tensile testing of individual silicon carbide nanowire was performed to determine the tensile properties of the material including the tensile strength, failure strain and Young's modulus. The silicon carbide nanowires were also excited to mechanical resonance in the scanning electron microscope vacuum chamber using mechanical excitation and electrical excitation methods, and the corresponding resonance frequencies were used to determine the Young's modulus of the material according to the simple beam theory. The Young's modulus values from tensile tests were in good agreement with the ones obtained from the mechanical resonance tests.

A computational model was used to simulate stationary and linear gas-tungsten-arc (GTA) welds and to study the effect of surface-tension as well as arc position. The results show that the surface-tension gradient with respect to temperature is a dominating factor in determining the direction of the convective flow within the molten weld pool. Furthermore, a linear-arc movement leads to a convective pattern, which is different from that of a stationary weld.

The corrosion resistance of a newly developed iron-base, Fe-Mn-Al austenitic, and duplex weld metal has been examined in the NACE solution consisting of 5 wt.% NaCl, 0.5 wt.% acetic acid, and the balance distilled water. The electrochemical techniques such as potentiodynamic polarization, Tafel plots, linear polarization, cyclic polarization, and open-circuit potential versus time were employed. The Fe-Mn-Al weld metals did not passivate and exhibited high corrosion rates. Fe-Cr-Ni (310 and 316) weld and base metals were also examined in the NACE solution at room temperature. The 310 and 316 base metals were more resistant to corrosion than the as-welded 310 and 316 weld metals. Postweld heat treatment (PWHT) improved the corrosion performance of the Fe-Mn-Al weld metals. The corrosion resistance of Fe-Mn-Al weld metals after PWHT was still inferior to that of the 310 and 316 weld and base metals.

Whether welding processes are used on earth or in space, they have the same objective: to obtain defect-free welds. To fully understand the effect of gravity on the weld pool geometry and solidification one should perform experiments within a broad range of gravitational acceleration. High-gravity arc welding experiments were done on Al–Li alloy using the centrifuge called Multi-Gravity Research Welding System (MGRWS). At a high “ g ” level, buoyancy-driven flow is the dominant force in the weld pool over the Marangoni and the electromagnetic forces. Preliminary results show that the average grain size in the fusion zone at 1 g is smaller that at 5 g .

Convective flow during arc welding processes mainly depends on electromagnetic force, Marangoni force, and buoyancy force. The Marangoni flow (caused by surface tension gradient,dγ/dT)and the buoyancy driven flow are the major factors in controlling weld penetration in austenitic stainless steels, such as types 304 and 316. Alloys 304 and 316 were subjected to a 7 s spot gas-tungsten arc (SGTA) welding at 1 g (g = 9.8 m/s2)and 5 g accelerations. The welds at 5 g were performed on Clarkson University’s multigravity research welding system (MGRWS). The cross sections of the fusion zones were polished/etched, and their depth (D)and width (W)were measured to ± 0.025 mm. It was determined that the depth/width ratio (D/W)of the welds decreased as the acceleration increased from 1 to 5 g. This result indicates that increase in buoyancy driven flow will produce wider but shallower welds during SGTA welding.

CdTe crystals were uniaxially compressed along several crystallographic axes at temperatures from 773 to 1353 K. The applied stress ranged from 14 to 74% of the critical resolved shear stress (CRSS) measured in the authors’ laboratory. The deformed specimens were annealed without applying stress at temperatures from 573 to 1073 K. No twins were observed after the above operations. Dense slip bands were observed on most of the compressed specimens. Secondary slip systems were activated in some experiments. CdTe crystals were sheared along {111} at 1073 K with a load of 40% CRSS. Slip bands, but no twins, were observed. Synchrotron x-ray topography was used to study in situ the effect of stress on crystal deformation. CdTe specimens were uniaxially stressed in tension along at 293 to 673 K. When the load reached ~50% of the CRSS, the topograph began to distort, indicating the beginning of plastic deformation. No twins were observed on the stressed specimens.

Convective flow during arc welding depends upon the surface tension gradient (dy/dT, Marangoni flow), buoyancy, arc drag force, electromagnetic force, shielding gas, and the viscosity of the melt. The Marangoni and the buoyancy-driven flow are the major factors in controlling weld penetration in ferrous alloys, especially austenitic stainless steels such as 304 and 316. Small variations in the concentration of surfactants, such as sulfur and oxygen, in stainless steels cause significant changes in the weld penetration and depth/width (D/W) ratio of the fusion zone. Gas-tungsten arc (GTA) welds were done on low- and high-sulfur 304 and 316 heats using pure argon and argon/oxygen shielding gases. Also, laser beam (LB) welds were done on the 304 and 316 heats using pure argon as the shielding gas. Increase in the sulfur content decreased the D/W ratio for the GTA 304 welds using pure argon, but for the case of LB 304 welds the results were the opposite. For the GTA 316 welds and LB 316 welds, increase in sulfur increased the D/W ratio of the fusion zone. Oxygen increased the D/W ratio of both the 304 and 316 GTA welds.

Hybrid systems consisting of a single or multiple renewable energy generators coupled with an environmentally-friendly storage system are used in renewable power production due to wide disparity between the intermittent power generated and the power demand. These systems also have the potential to provide 24/7 power without leaving a carbon footprint in operation. Finding the optimal size of a Hybrid Renewable Energy System (HRES) with no Loss of Power Supply (LPS) is of utmost concern when considering the Levelized Cost of Energy (LCE) of the system over its lifecycle. In this study, an optimization routine employing a search algorithm is developed to find the system configuration with a minimized LCE that meets also meets zero LPS. To this end, a system model is developed by integrating basic models of the subsystems. The system model is then used to investigate two different loading cases, 1) where the demand cannot be controlled as in the case of the power demand of a residential network, and 2) where the demand can be controlled up to certain limits, as in the case of the power demand of a data center or a data center network. Various types of controllable power demands (CoD) are studied. When compared to the power demand of a residential network, results demonstrate a significant reduction in the life cycle costs for CoD conditions.Copyright © 2012 by ASME

A novel stochastic simulation approach is employed to predict the reliability of an air-supply expansion joint. This component is part of a large electric power generating system. In order to perform this task, multiple modeling tools are integrated, including Computational Fluid Dynamics, Finite Element Analysis, Stress-life method, and Latin Hypercube Sampling. As a result of the stochastic nature of the input parameters, the resulted life is in the form of a Probability Density Function, which enables the calculation of the reliability of the component at a given life. The application of this method to the air joint can be used to enhance the design and operation of the component by uncovering under-design or over-design. Furthermore, various alternative designs and operational scenarios can be studies using this stochastic model.

The large difference between maximum and minimum daily temperatures and considerable amount of solar heat gain are characteristics of hot and dry climate. In this situation walls and roof of a building act as thermal storage elements which store heat during the day and remove it at night therefore the direction of heat transfer can change throughout a day. This should be considered in total conduction heat gain calculation. In the present study the effect of wall and insulation material is studied in a simple office building. Outside temperature is considered to change periodically with time. In addition, the outside surface of the wall is considered to be exposed to the sun during day light. A one-dimensional transient heat conduction equation with time dependent boundary conditions is solved numerically using the Crank-Nicolson method. Different wall materials and insulations were investigated in order to find the best insulation and material from total conduction heat gain viewpoint. It is shown that by using proper materials and location of insulation within the wall the heat gain and energy cost can be decreased considerably.Copyright © 2011 by ASME

Small villages in remote locations of developing countries rarely have access to electricity and are highly dependent on burning fossil fuels for energy. In an effort to provide these villages with a quality power supply and to replace their current emissions-producing energy generation, we propose a Hybrid Power System (HPS) that uses small wind turbines and solar panels for power generation. The system manages the intermittency of the renewable power by storing excess energy during periods of low user demand (such as night time) and releasing that energy at demand peaks (times when people are using demanding appliances). The proposed storage method uses electrolysis, which is the separation of water molecules into hydrogen and oxygen by excess DC currents produced by the wind and solar. The hydrogen is then compressed and stored in metal hydride tanks and when demand exceeds wind and solar generation, power is provided using a Proton Exchange Membrane Fuel Cell (PEMFC), which is highly responsive in peak demand periods compared to other types of hydrogen fuel cells. A physics-based model of the HPS is constructed in order to improve its efficiency, and statistics-based reliability models are formed to evaluate its potential for loss of load. Efficiency of a HPS can be viewed as balancing the energy production with user consumption. For this purpose, accurate models of the subsystems (wind turbines, solar panels, an electrolyzer using metal hydride tanks for hydrogen storage, fuel cell stack) are created. Realistic models of the AC loads are also required; this includes models of a performance optimized data center (POD) and the power demanded by a small community. As to optimize the energy management of the entire system, a model of a main controller that utilizes closed-loop control systems to maintain power stability is designed. On the reliability side, analysis is performed to assess the system’s response to various failures over time. This work is aimed at examining the reliability of the power system; not the examination of failure data in order to improve the reliability of various components. Models for testing of performance are created on a MATLAB Simulink and SimPowerSystems platform.

Infrared microscopy and scanning electron microscopy with energy dispersive spectroscopy were employed to characterize etch pits formed on CdTe and (Cd,Zn)Te surfaces with E-solution, EAg, Bagai and Nakagawa etchants. Some of the larger flat-bottomed triangular etch pits on the (111)A or (111)B surfaces originated from precipitates. Thus, the etch pit density may differ from the true dislocation density by the presence of etch pits from precipitates.

Different polishing solutions were tested for exposing precipitates in CdTe and Cd(0.96)Zn(0.04) single crystals grown by vertical Bridgman-Stockbarger technique. A solution of 5-7% Br2 in methanol and E-solution were both effective. High resolution scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS) was employed to characterize those exposed precipitates. Most of the polyhedral-shaped Te precipitates with a size range from 3 to 20 microns had voids inside. Partially dissolved Te precipitates were observed in CdTe samples that had been annealed in Cd vapor at 700 C for 10 min. Isolated areas mis-oriented from the matrix were observed in CdTe and Cd(0.96)Zn(0.04)Te that had been annealed in Cd vapor at 700 C for 20 and 50 h, respectively. Te precipitate images were recorded with EDS. By SEM/EDS, Cd-rich precipitates were observed in some Cd-annealed CdTe. C and Na impurities were detected in some Te precipitates.

The effect of annealing in cadmium or tellurium vapor on CdTe and Cd 0.96 Zn 0.04 Te was investigated using different characterization methods. Tellurium-rich precipitates with a size between 0.5 and 5.0 μm were no longer seen after annealing in tellerium vapor, while precipitates between 5.0 and 15 μm appeared. Annealing in cadmium the concentration of the larger precipitates to diminish. The lattice constant was decreased by annealing in cadmium vapor and increased by annealing in tellurium vapor. The etch pit density was decreased by annelling in tel tellurium vapor and increased by annealing in cadmium vapor.

Calcium carbonate is predominantly present in cooling tower’s water and is usually the principal cause of hard water. This paper applies the modeling technique typically used for aerosol deposition to simulate the deposition process of calcium carbonate nano- and micro-particles suspended in turbulent cooling water flows. The mean turbulent velocity field and the fluctuating velocities are determined by the k-e and RSM turbulence models by simulating the water flow in a typical heat exchanger horizontal tube. Commercial software (ANSYS FLUENT™ 12.1.4) is used for turbulence mean flow modeling and the simulation of turbulence fluctuations is performed by stochastic models. Particle deposition velocities are obtained for the particles with diameters in the range 0.01–50 μm by the k-e and RSM models and compared to the deposition velocities calculated from semi-empirical correlations to investigate the effect of the turbulence model on the deposition velocity. Results show that the proposed numerical model can predict deposition velocity of micro-particles in water accurately and can be useful in determining the range of particle diameters in which the highest deposition velocity occurs. However, for nano-particles, the model’s results do not agree with the correlations due to the higher lateral turbulence fluctuations calculated by ANSYS FLUENT™ code. The proposed model can be useful for predicting fouling in industrial heat exchangers, for planning operations and cleaning schedules, and proposing efficient filtering processes for lowering deposition rate and cleaning costs.Copyright © 2010 by ASME

The effect of surface roughness on the fouling behavior of calcium carbonate is experimentally investigated. The real operating conditions of a tubular heat exchanger are simulated by performing prolonged experiments with duration of 3 to 7 days. The solution used is a mixture of sodium bicarbonate and calcium chloride in de-ionized water with the concentration of 0.4 g/l of each. An on-line fouling evaluation system was developed such that the fouling resistance for a selected solution could be measured in real time. The experiments are repeated with the same procedure for 90/10 Cu/Ni tubes with different internal surface roughness. After the experiment the surface is analyzed by analytical microscopy to investigate the morphology of the deposit layer. Comparison of the experimental results of smooth and rough surfaces shows that a combination of aragonite and calcite polymorphs are formed on rough surface while only dendritic porous aragonite crystals are formed on smooth surface. Accordingly, the deposit layer formed on rough surface is denser and has a higher thermal resistance comparing to that formed on smooth surface. The fouling factor-time curves of smooth and rough surfaces obtained by the current experimental study agree with the results found by the analytical microscopy of the surface and show higher fouling resistances for rough surface. Experimental data is significantly important for the design, and formulating operating, and cleaning schedules of the equipment.Copyright © 2010 by ASME

This paper evaluates the possibility of combining an intercooled gas turbine power cycle with a steam turbine cycle and the application of the intercooler as a feed-water heater for the heat recovery steam generator. In advance gas turbines the intercooler is used to improve the overall efficiency of the simple cycle but a noticeable amount of heat is wasted to the atmosphere. However, this energy can be recovered by using the proposed method in the current study. Accordingly, a thermodynamic study is done to investigate the improvement in efficiency achieved by feed-water heating. First the effect of intercooler parameters on the outlet condition of the water is studied. The bottoming cycle is then studied in details for the effect of feed-water temperature. An estimate of the energy saving by using the proposed method will be reported. The results show that less heat input will be required for the same amount of steam generation. The current study provides a theoretical support for waste heat recovery from the intercooler.Copyright © 2010 by ASME

Silicon carbide (SiC) material has many outstanding physical and mechanical properties such as high strength, high hardness, low density, high thermal conductivity, low thermal expansion coefficient, large band-gap, and excellent oxidation and corrosion resistances [1–3]. It is a leading material for components and devices operating at high temperature, high power and under harsh environments [4–5]. Micro-sized SiC particles and whiskers are commonly used as reinforcement materials for ceramics, metals and alloys in various structural and tribological applications [6–7].Copyright © 2010 by ASME

The effects of heat treatments on the mechanical and fracture properties of continuous fiber Pitch 100 graphite/6061 aluminum (P100 Gr/6061 Al) composite were evaluated by varying solution temperature and aging time. All heat treatments resulted in decreased mechanical properties due to the reaction at the fiber/matrix interface during solution treatments. SEM analysis of the fractured samples showed a large degree of fiber pullout, interface failure, and matrix cracking.

The objective of this paper is to evaluate methods to increase the efficiency of a gas turbine power plant. Advanced intercooled gas turbine power plants are quite efficient, efficiency reaching about 47%. The efficiency could be further increased by recovering wasted heat. The system under consideration includes an intercooled gas turbine. The heat is being wasted in the intercooler and a temperature drop happens at the exhaust. For the current system it will be shown that combining the gas cycle with steam cycle and removing the intercooler will increase the efficiency of the combined cycle power plant up to 60%. In combined cycles the efficiency depends greatly on the exhaust temperature of the gas turbine and the higher gas temperature leads to the higher efficiency of the steam cycle. The analysis shows that the latest gas turbines with the intercooler can be employed more efficiently in a combined cycle power application if the intercooler is removed from the system.Copyright © 2009 by ASME

Many engineering thermal systems involve a high degree of technical risk. Their deterioration could be induced by the flow of high temperature fluids. A high-fidelity assessment tool is presented which enables the simulation of a wide array of thermal systems. It is based on linking multiple computational tools to deal with complex thermal systems. These systems may involve fluid-structure interactions. Computational Fluid Dynamics (CFD), Finite Element Method (FEM), and Fatigue tools are integrated within this approach. The CFD part of the method is first applied to an existing model, where the internal and external heat transfer coefficients are determined, and then compared to the manually-computed coefficients. The results showed good agreement between the two methods. Next, the process is applied to a simple cylindrical ring model, where CFD simulation is first performed to determine the heat transfer parameters that are needed for the transient FEM simulation. The FEM analysis results in the maximum thermal stress whereby the fatigue life of the component is computed. Finally, the effect of varying the turbulence intensity on heat transfer coefficients, thermal stress, and fatigue life is investigated.

This paper discusses an experimental study on how water quality affects the corrosion rate of Cu-Ni Alloys, such as those used within a heat exchanger system. Various types of water suitable for the heat exchanger operation have been tested to predict the duration during which corrosion would become a risk. Since corrosion is governed by electrochemistry, an electrochemical experimental setup was designed, consisting of a three-electrode electrochemical cell designed to simulate the on-site state and conditions of a 90–10 Cu-Ni tube bundle inside the heat exchanger. The working electrode in use is a 90-10 Cu-Ni Rotating Cylinder Electrode (RCE). The electrolyte solution was varied with different pH values, temperature and compositions. The corrosion rate was measured by use of the Tafel method. Experiments were performed with two solutions; De-Ionized water and Tap water. Further experimentation with anti-corrosives was also performed. All measurements were produced using a G300 Gamry® Potentiostat (computer controlled) conjugated with two general purpose electrochemical softwares: Gamry Framework® and Gamry Echem Analyst®. Trends of the corrosion rate as a function of pH and temperature were analyzed. Field Emission Scanning Electron Microscope (FE-SEM) tests have also been performed to determine the products, methods and elemental effects of the corrosion. Results and discussions are provided with pertinent conclusions.Copyright © 2009 by ASME

The objective of this program is to apply theoretical and experimental methods to optimize the equipment and procedures for floating zone melting and Bridgman-Stockbarger growth of cadmium telluride crystals in space. Computer codes were developed for the computation of heat transfer in the furnace and thermal stress in the resulting crystal. The predictions for the temperature field are being compared with experimental measurements. It was found that if the crystal sticks to the ampoule wall, differential thermal expansion between crystal and ampoule contributes much more to the stress than does the temperature field in the crystal. Thus, one goal of solidification of cadmium telluride in space is to reduce or eliminate contact of the crystal with the ampoule wall. Another goal is to find coatings and linings which reduce sticking of the grown crystal onto the ampoule. We developed techniques for measuring the surface tension and contact angle of molten cadmium telluride vs temperature and stoichiometry. The surface tension decreased with increasing temperature and with decreasing cadmium concentration. Wetting increased in the following order: pyrolytic boron nitride, carbon-coated quartz, sandblasted quartz, HF-etched quartz, and plain quartz. Additional coatings and potential ampoule lining materials are being developed and will be tested both for wetting by the melt and for sticking by the solid. Techniques are being developed for measuring sticking. We are also developing techniques for measuring the mechanical properties of cadmium telluride and for the direct observation of defect formation and evolution vs temperature. X-ray topography will be done in real time using the National Synchrotron Light Source at Brookhaven National Laboratory, in collaboration with the National Institute of Standards and Technology. Techniques are being developed for floating zone melting of cadmium telluride in space. We have successfully float zoned 5 mm rods on Earth. Evaporation of cadmium and tellurium from the molten zone is prevented by adding excess cadmium combined with heating of the entire ampoule. Still needed is a suitable automatic method to assure that the proper zone length is achieved in larger diameter rods in space.

A method that links several commercially available tools to estimate the fatigue life of thermal systems is introduced. The procedure provides an engineering tool based on existing computational packages. It is sufficiently general that it can be used for any thermal application involving fluid flow and a solid medium. A cylindrical ring model is presented to clarify the process. Computational Fluid Dynamics (CFD) and Finite Element Modeling (FEM) tools are integrated within the proposed approach. ANSYS/CFX® and Simulation® are used for such purpose. The process starts with CFD simulation to determine the convective terms necessary for the transient FEM thermal analysis. The transient FEM thermal analysis provides maximum thermal stress values. These values are employed in the fatigue life analysis to determine the fatigue life of the component.

The purpose of this research project is to examine the effects of “simulated” enhanced buoyancy convection on gas-metal arc (GMA) weld bead geometry of 304 stainless steel welds at various “simulated” gravity conditions (g -levels). It was evident that gravity did have an effect on shape and geometry of the weld zone. The 4g and 8g welds had wider but shallower weld zones. The competition among the main convective forces such as Buoyancy, Lorentz, and Marangoni can significantly alter the weld zone aspect ratio as well as the shape.Copyright © 2008 by ASME

A general procedure for reliability prediction is introduced. The procedure is applied to a cylindrical ring and can be used for any similar thermal application. The procedure is classified as a physics-based reliability prediction method. It utilizes different computational tools such as Computational Fluid Dynamics (CFD), Finite Element Method (FEM), and Monte Carlo Simulations (MCS). The process starts with CFD simulation to find the convective terms necessary for the transient FEM thermal analysis. The transient FEM thermal analysis provides values for thermal stress. These values are used in the fatigue life analysis. The end result is the fatigue life of the component. As a result of input parameters uncertainty, the resulting life will be in the form of a Probability Density Function (PDF), which enables the calculation of the reliability of the component.Copyright © 2008 by ASME

The aim of this paper is to describe a monitoring system for fouling phenomenon in tubular heat exchangers. This system is based on a physical model of the fouling resistance. A mathematical model of the fouling resistance is also developed based on applied thermal heat, the inside heat transfer coefficient and geometrical characteristics of the heat exchanger. The resulting model is a function of measured quantities such as water and tube wall temperatures, fluid flow velocities, and some physical properties of the fluid flowing inside the tubes such as viscosity, conductivity, and density. An on-line fouling evaluation system has been prepared and heat transfer resistance for selected solutions has been measured in real time by this system. Experimental results provide quantitative information of liquid-side fouling on heat transfer surfaces, and its effects on the thermal efficiency. Output data is significantly important for the design, and for formulating operating and cleaning schedules of the equipment.Copyright © 2008 by ASME

To obtain a high quality weld we need to understand the mechanical and thermal properties of the material and its melt, and the solidification mode and its morphology. Convective flow during welding is dependent upon buoyancy, surface tension and its temperature coefficient (dγ/dT), the arc drag and electromagnetic forces, the shielding gas, and the viscosity of the melt. By controlling fluid flow and heat transfer during welding, one should be able to control the weld solidification mode, morphology and segregation, and by that, prevent defects in the fusion zone. Buoyancy and Marangoni flow are major factors in controlling weld solidification.1,2 There is a lack of knowledge on the effect of gravity, especially macro-gravity (> lg), on weld pool geometry. Thus, the objective of this work is to evaluate the shape and profile of the fusion zone of 304 and 316 gas-tungsten arc welds during centrifugation.

Understanding the physical phenomena involved in the welding process is of substantial value to improving the weldability of materials. The intense heat and the arc inherent in fusion welding make direct experimental observation of the weld pool behavior rather difficult. Thus numerical models that can predict the processes involved have become an invaluable tool for studying welding.

A broad reliability prediction method that can deal with complex thermo-fluidic systems is introduced. The procedure provides an engineering tool by integrating multiple computational packages to enable the simulation of a wide array of systems, especially those involving physics interactions such as fluid flow and solid medium. Computational Fluid Dynamics (CFD), Finite Element Method (FEM), Monte Carlo Simulation (MCS), and Fatigue analysis tools are integrated within this approach. CFD simulation is used to determine the heat convection terms used for the transient FEM analysis. Maximum thermal stress is provided by the FEM analysis whereby the fatigue life of the component is evaluated. Due to uncertainty of input parameters, the fatigue life will be in a Probability Density Function (PDF) form, which provides the relationship between the reliability and the service life of the system. The complete procedure is demonstrated using a cylindrical ring model, and then validated using experimental data gathered for power plant boiler pipes. The results show good agreement between the two methods.

A direct computer simulation technique, discrete element analysis (DEA), was utilized in the development of a transient multidimensional (2-D and 3-D) mathematical model for investi-gating coupled conduction and convection heat transfer problems associated with stationary and moving arc welding processes. The mathematical formulation considers buoyancy, electro-magnetic, and surface tension driving forces in the solution of the overall heat transfer conditions in the specimen. Furthermore, the formulation of the model allows realistic consideration of the geometrical variations in the workpiece. The model treats the -weld pool surface as a truly deformable free surface, allowing for the prediction of the weld surface deformations such as the “weld crown.≓ A marked element formulation was employed to monitor the transient de-velopment of the weld pool as determined by the latent heat considerations and the calculated velocities in the weld pool. The model was utilized to simulate the heat and fluid flows in the weld pool that occur during stationary (spot) and moving (linear) gas tungsten-arc welding. Also, the present analysis considers a simple rectangular specimen and a geometrically complex specimen to demonstrate the capability of the model to simulate realistic 3-D arc welding prob-lems. The results of the present investigation clearly demonstrate the significant influence of the heat and fluid flows and the specimen geometry on the development of the weld. Comparison of the predicted and the experimentally observed fusion zone and heat-affected zone (HAZ) geometries indicate good agreement.