Muammer Koç

Critical Review on Nanofluids

Heat transfer fluids are a crucial parameter that affects the size and costs of heat exchangers. However, the available coolants like water and oils have low thermal conductivities, which put many limitations to the development of heat transfer to achieve high performance cooling. The need for development of new classes of fluids which enhance the heat transfer capabilities attracted the attention of many researchers. In the last few decades, modern nanotechnology developed nanoparticles, which have unique thermal and electrical properties that could help improve heat transfer using nanofluids. A “nanofluid” is a fluid with suspended fine nanoparticles which increases the heat transfer properties compared with the original fluid. Nanofluids are considered a new generation of heat transfer fluids and are considered two-phase fluids of liquid solid mixtures. The efficiency of the fluid could be improved by enhancing its thermal properties, especially the thermal conductivity, and it is expected that the nanofluids will have a greater thermal conductivity than the base fluids. This paper reviews the preparation of metallic and nonmetallic nanofluids along with the stability of the produced nanofluids. Physical and thermal properties as well as a range of applications are also discussed in detail.

Design, Fabrication, and Experimental Validation of a Warm Hydroforming Test System

In this study, a hydroforming system was designed, built, and experimentally validated to perform lab-scale warm hydromechanical deep drawing (WHDD) tests and small-scale industrial production with all necessary heating, cooling, control and sealing systems. This manuscript describes the detailed design and fabrication stages of a warm hydroforming test and production system for the first time. In addition, performance of each subsystem is validated through repeated production and/or test runs as well as through part quality measurements. The sealing at high temperatures, the proper insulation and isolation of the press frame from the tooling and synchronized control had to be overcome. Furthermore, in the designed system, the flange area can be heated up to 400 °C using induction heaters in the die and blank holders (BH), whereas the punch can be cooled down to temperatures of around 10 °C. Validation and performance tests were performed to characterize the capacity and limits of the system. As a result of these tests, the fluid pressure, the blank holder force (BHF), the punch position and speed were fine-tuned independent of each other and the desired temperature distribution on the sheet metal was obtained by the heating and cooling systems. Thus, an expanded optimal process window was obtained to enable all or either of increased production/test speed, reduced energy usage and time. Consequently, this study is expected to provide other researchers and manufacturers with a set of design and process guidelines to develop similar systems.

Demand side management for peak reduction and PV integration in Qatar

The electricity demand in Qatar has grown more than twofold within merely a decade. Highly subsidized electricity tariffs combined with decreased government revenues has urged local authorities to reduce the energy consumption, improve the energy efficiency, and deploy environmentally friendly renewable energy alternatives. In this study, we present the role of demand-side management (DSM) techniques for energy savings and photovoltaic (PV) renewable energy integration. DSM techniques are classified into technological, economical, and social layers. The technology layer has been supported by the government while incentive/pricing based economic layer options are yet to be deployed. To pave the way for such studies, we present evidence from Bahrains, a neighboring country with similar climate, government and social structures, new pricing policy to show the customer responsiveness on electricity prices. Moreover, we present a case study on how to use direct load control framework during summer months in Qatar. In the last section, we present the output of Qatars first large-scale PV deployment in Education City. The results show that due to local weather conditions, large-scale PV adoption can easily affect the grid operations and a more responsive load is required to mitigate the potential impacts.

The Effect of Temperature and Strain-Rate Sensitivity on Formability of AA 5754

Aluminum alloys have limited usage because of their limited formability at room temperatures. In order to design and develop more parts made of aluminum, new forming techniques such as hydroforming, warm forming and warm hydroforming have been researched to overcome the low formability issues. This, in turn, necessitates understanding and modeling the behavior of aluminum alloys at different temperatures and strain rates. This paper deals with the investigation of the effect of temperature and strain rate sensitivity on the formability of AA 5754 aluminum alloy. Tensile tests were carried out at temperatures of 20,100,180 and 260°C and forming rates of 25, 100 and 250 mm/min. The mechanical properties and flow curves were obtained and the strain rate sensitivities were calculated at different strains and temperatures. The effects of temperature and strain rate sensitivity on the formability were introduced.

On the Formability of Ultrasonic Additive Manufactured Al-Ti Laminated Composites

Ultrasonic additive manufacturing (UAM), different from most of additive manufacturing technologies, enables manufacturing of composite parts consisting of two or more materials. The current study focuses on mechanical characterization of Al-Ti laminated composites. For this purpose, first, Al-Ti laminates were built onto a 1.527-mm-thick aluminum substrate by means of UAM with different number of layer configurations (e.g., 1,3,5 bi-layers). Then, fabricated samples were subjected to uniaxial tensile and biaxial hydraulic bulge tests at the different temperatures, deformation rates, and sample orientations. Results yielded different failure mechanisms and distinct mechanical properties depending on the test type, condition, and number of bi-layer configurations. For example, delamination was observed for 3 bi-layer sample configuration while curling was experienced at elevated temperature tests due to different thermal conductivity properties of Al and Ti. The highest strain value of 0.46 was obtained at 573xa0K (300xa0°C) temperature for 5 bi-layered tensile test samples.

A review on the direct effect of particulate atmospheric pollution on materials and its mitigation for sustainable cities and societies

Particulate matter (PM) has gained significant attention due to the increasing concerns related to their effects on human health. Although several reviews have shed light on the effect of PM on human health, their critical adverse effect on material’s structure and sustainability was almost neglected. The current study is an attempt to fill this gap related to PM impact on structural materials under the overall consideration of sustainability. More specifically, this review highlights the existing knowledge by providing an overview on PM classification, composition, and sources in different locations around the world. Then, it focuses on PM soiling of surfaces such as solar panels due to an increasing need to mitigate the impact of soiling on reducing photovoltaic (PV) power output and financial competitiveness in dusty regions. This topic is of critical importance for sustainable deployment of solar energy in arid and desert areas around the world to help in reducing their impact on overall climate change and life quality. In addition, this review summarizes climate change phenomena driven by the increase of PM concentration in air such as radiative forcing and acid rain deposition due to their impact on human health, visibility and biodiversity. To this end, this work highlights the role of process management, choice of fuel, the implementation of clean technologies and urban vegetation as some possible sustainable mitigation policies to control PM pollution in cities and urban regions. This research is designed to conduct a comprehensive narrative literature review which targets broad spectrum of readers and new researchers in the field. Moreover, it provides a critical analysis highlighting the need to fill main research gaps in this domain. The findings of this review paper show that PM pollution imposes severe adverse impacts on materials, structures and climate which directly affect the sustainability of urban cities. The advantages of this review include the value of the extensive works that elaborate on the negative impacts of PM atmospheric pollution towards high level of public awareness, management flexibility, stakeholder’s involvements, and collaboration between academy, research, and industry to mitigate PM impact on materials and human welfare.

Material Characterization of Ultrasonically Consolidated Laminated Ti-Al Composites (UC-LMC)

Ultrasonic consolidation (UC) is an additive manufacturing process where thin and dissimilar metallic layers are bonded through the action of ultrasonic oscillation energy with low energy consumption. The surface oxide layer and the other contaminations between two surfaces are broken up with ultrasonic oscillation improving the bonding strength. This study aimed for investigating the mechanical behavior of laminated metal composite (LMC) blanks that consist of several layers of commercially pure titanium (CP-1) and pure aluminum (AA 1100) foils with different number of layers. The LMC blanks were ultrasonically consolidated on a thick aluminum substrate with three different numbers (1, 3, 5) of bi-layers. Each bi-layer consists of UC bonded one AA 1100 and one Ti foils. Both uniaxial (tensile) and biaxial (hydraulic bulge) tests were carried out under two strain rates and four different temperature levels to reveal the mechanical response of LMCs with different conditions. Increase in number of bi-layers resulted in higher overall strength of LMC’s as titanium content in LMC is increased. Delamination of layers was observed for 1-bilayer LMC’s at room temperature while curling was noted at higher temperature tests. The results obtained from tensile and hydraulic bulge tests were compared to observe significant differences in UTS values and elongation. The effect of temperature, loading condition, and strain rate on the material responses were discussed on the basis of test results. At low temperature, the strain and strength values of bulge samples were higher than the values of tensile samples. However, at high temperatures, lower strain and lower strength were obtained from bulge test. The maximum strain of 0.46 was obtained at 300°C test temperature for 5 bi-layer both parallel rolling direction sample in the all LMCs from tensile test.Copyright

Determination of Proper Loading Profiles for Hydro-Mechanical Deep Drawing Process Using FEA

Hydro-mechanical Deep Drawing (HMD) is an advanced manufacturing process developed to form sheet metal blanks into complex shapes with smooth surfaces using hydraulic pressure as an additional source of deformation force. There are many factors affecting the successful production of desired parts using this manufacturing process. The most important factors are the fluid pressure and blank holder force. Having proper values of these parameters during forming has a direct impact on part properties such as drawing ratio and thinning. In order to determine desired the fluid pressure and blank holder force profiles, which are different for every geometry, material and other process conditions, finite element simulations are conducted to save time and cost. Abaqus FEA software is used in this study. In order to define the continuously changing fluid pressure application area on the sheet material, which is not an available module or standard interface of software, sub-programs (sub-routines) are developed to properly and dynamically define the fluid pressure area. Proper, if not optimal, fluid pressure and blank holder force profiles, which allow the formability (LDR) of sheet material to be maximum, were obtained using trial and error method. Maximum thinning values on metal blank were used as a control parameter to determine if selected loading profiles result in the highest LDR with lowest thinning.

Surface Topography Evolution During Long-Run Micro-Stamping of Bipolar Plates (BPPs) and Effects on Corrosion and Contact Resistance Characteristics

Micro-stamping, as a promising sheet metal forming process for mass production of small parts, can meet the expectations such as durability, strength, surface finish, and low cost for miniaturized metal products and features. The purpose of this research was set to investigate surface interactions during mass manufacturing of micro-stamped sheets, and its consequences; then establish correlations (if any) between surface interactions vs. corrosion and contact resistance of bipolar plates (BPPs) to be used in proton exchange membrane fuel cells (PEMFC).In experimental part of this study, 10,000 SS316L sheet blanks were micro-stamped using a stamping die set with 750 μm-deep micro-channels under 200 kN stamping force, and with a constant stamping speed of 1mm/s. Surface inspections (surface roughness and micro-channel height measurements), corrosion and contact resistance tests were carried out on BPPs. Analysis of variance (ANOVA) technique was utilized to investigate the significance of surface roughness, channel heights, corrosion and contact resistance variations for BPPs. Moreover, three-dimensional (3D) finite element models of micro-stamping process were established to approximate the stress and strain levels as well as coefficient of friction value experienced at contact interface.The results revealed that the roughness values for micro-stamping dies and BPPs followed similar trends during 10,000 micro-stampings. Since surface defects trigger corrosion, the correlation between surface roughness and corrosion resistance of BPPs was found to be direct. Increasing number of surface irregularities (asperities) lowered contact surface area that resulted in increased contact resistance. Finally, comparison of experimental and numerical channel height values showed that the coefficient of friction did not change considerably during the mass production of BPPs, at least within the 10,000 stamping cycle.Copyright