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This study investigates the synergistic performance of hybrid micro-nano porous surfaces (HMNP) for Nucleate pool boiling (NBHT) and its application to thermal management of concentrated photovoltaics (CPV). A new set of HMNP surfaces was prepared by two-step method of hot powder compaction of micro-particles followed by nanoparticles coating. Three different surfaces, i.e., plain (P), microporous (MP), and hybrid micro-nano porous (HMNP) were examined for NBHT performance with de-ionized (DI) water as working fluid. In HMNP surfaces three different concentration of nanoparticles 0.0001%, 0.001%, and 0.01% were used for coating. MP showed enhanced HTC and CHF performance, which was further improved by HMNP coating with the highest performance at 0.01% concentration. Compared to P surface, the maximum increase for CHF of MP and HMNP was 1.79 and 2.5 times while the maximum increase in HTC was 1.8 and 2.33 for MP and HMNP surfaces, respectively. For the lowest applied heat flux of 110 kW/m2, the maximum decrease in wall superheat for MP, and HMNP coating was 2.5 °C and 3.7 °C, respectively as compared to the P surface. The increase in CHF and HTC was observed to increase with an increase in the concentration of coated nanoparticles in HMNP surface. Bubble dynamics were observed by the high-speed camera and Scanning Electron Microscope (SEM) analysis, and contact angle analysis were performed for P, MP and HMNP surfaces. In the end, an analytical study is performed to analyze the effect of P, MP and HMNP surface as a resulted enhancement of CPV cell performance.

Recently, carbon-based colloid materials gained popularity in boiling heat transfer (BHT) research. Among them, carbon nanotubes (CNT), functionalized CNT, graphene, graphene oxide, reduced graphene oxide, and nanodiamonds have been investigated in the literature. Most of the studies reported enhanced BHT performance. This study aimed to investigate the BHT performance of the colloidal dispersions of carbon black (CB), which has favorable intrinsic properties but it has not yet been studied in BHT research. Experimentally, stable dispersions of CB colloids were prepared in deionized water at three different weight concentrations: 0.001%, 0.005% and 0.01%. A custom-built experimental pool boiling setup with a flat copper heating surface was used to investigate the BHT performance of the CB colloids. The heat transfer coefficient (HTC) and critical heat flux (CHF) enhancements of the nanofluids increased with the increasing CB concentration and reached 190.5% and 67.8%, respectively at 0.01 wt% CB. The CHF enhancement was attributed to the decent lateral heat conduction of the CB microlayer. It prevented localized heating by spreading the surface heat in lateral directions and delayed the formation of hot/dry spots to higher heat fluxes. The HTC enhancement was due to the densely distributed small cavities on the coating layer, which increased the surface roughness by ∼9-fold. This provided a larger effective surface area for heat transfer, and a greater active bubble nucleation site density. The more hydrophobic surface rendered higher bubble departure frequency that effectively transferred the heat from the heating surface to the bulk fluid.

Future technological products are increasingly becoming compact, integrated and multi-functional with higher heat loads in confined spaces. This has impelled the quest for improved heat management solutions to ensure the devices maintain their full performance as designed. Due to the associated latent heat, nucleate pool-boiling heat transfer (NBHT) systems are proven to dissipate the high heat flux at low-temperature gradients. NBHT systems with nano-scale and micro-scale porous structured surfaces are reported to possess enhanced heat transfer coefficient (HTC) and critical heat flux (CHF). The potential synergistic benefits of combining these two unique structures into an integrated surface coating fabrication technology have been a key question of interest. This study aimed to investigate the effect of uniformly coated nanoparticles on 2-D modulated micro-porous surfaces in NBHT. The NBHT performance of four different surface types; (1) flat untreated copper surface (UnCu surface), (2) nanocoated copper surface (NPC surface), (3) 2-D modulated micro-porous surface (MMPC surface), and (4) hybrid micro/nano-scale 2-D modulated porous coated surface (HMPC surface) are investigated. The UnCu surface and MMPC surface are employed for uniform nanoparticle coating to fabricate NPC surface and HMPC surface, respectively. Morphological characteristics of the surfaces were observed using the scanning electron microscopy (SEM). According to the results, the NPC surface and MMPC surface showed an enhanced NBHT performance by 81.6% and 50.6% improvement in CHF and 130.3% and 45% enhancement in HTC, respectively. However, as compared to the MMPC surface, the NBHT performance of the HMPC surface decreased. The average reduction in CHF and HTC of the HMPC surface was 16.8% and 24%, respectively. The reduction in the NBHT performance of HMPC is explained by the deterioration of the capillary wicking characteristics of the MMPC surface.

This study analyzes a new renewable energy-based multigeneration system, in which the energy sources are efficiently utilized to generate several useful commodities such as hydrogen, oxygen, desalted water, and refrigeration along with electricity. Osmotic power from desalination brine solution is harvested to contribute to the electricity generation and to reduce the environmental impact of brine. The system units are concentrated photovoltaics/thermal (CPVT), wind turbines, thermal energy storage (TES), hydrogen electrolyzer, hydrogen fuel cell, multistage flash (MSF) distillation, vapor compression refrigeration (VCR) cycle, and pressure retarded osmosis (PRO). The energetic and exergetic performance of the overall system, as well as the system units, are calculated based on the first and second law of thermodynamics. Further, a comprehensive parametric study is conducted to investigate the effect of varying environmental and operational conditions, and the input parameters on the production rate, exergy destruction rate and efficiencies. For maintaining the high efficiency of CPV operation, the heat generated on photovoltaic (PV) cells is dissipated by an effective cooling system. This heat is then stored in the TES to be further utilized in desalination. The TES is used for eliminating energy fluctuations in the system and for a continuous operation by storing the energy for the time, when energy from the sun is not available. The electricity from CPV and wind power is used in the VCR cycle and hydrogen electrolysis. The fuel cell can be operated during the time of peak electricity demand. After performing thermodynamic analysis over the system, the overall energy and exergy efficiencies are determined as 73.3% and 30.6%, respectively. The exergy destruction rates of the components are specified. In brief, generation of multiple commodities is assured based on a clean operation by a novel integration of multiple clean energy sources in one system.

This study investigated the oxidative acid treatment of multi-walled carbon nanotubes (MWCNT). Experiments were conducted by refluxing MWCNT with HNO3 and H2SO4/HNO3 (3:1 v/v) at two different molar concentrations. Treated MWCNT were characterized for their weight loss, surface chemistry, surface morphology, structural integrity, thermal stability and dispersion stability using a precision scale, X-ray Photoelectron Spectroscopy (XPS), Transmission Electron Microscopy (TEM), Thermogravimetric Analysis (TGA), and visual observation. The results showed that treatment with 15 M HNO3 introduced the highest atomic % of oxygen-containing chemical moieties to MWCNT surface with less sample weight loss. The TEM micrographs showed that during treatment with 15 M HNO3, MWCNT fragmented into smaller nanotubes of an average length of 900 nm. MWCNT experienced the most severe structural degradation after treatment with 15 M H2SO4/HNO3, where the nanotubes were completely dissolved during the refluxing process. Carboxyl and carbonyl groups were identified as the predominant functional groups present on treated MWCNT surfaces. TGA study revealed the preservation of graphitic MWCNT structure, increased water sorption capacity, and newly formed functional groups after the treatments. Dispersion of MWCNT was improved after all treatments. However, 10 M HNO3-treated sample showed the weakest stability. According to the experimental results, MWCNT treatment with 15 M HNO3, yielded a formation of 5.2 at% surface oxygen with only 6.8% sample weight loss. The extent of surface oxidation in the case of 10 M H2SO4/HNO3 treatment was 3.2 at% and the weight loss was about 17%.

Nanofluids are a new generation of heat transfer fluids that have attracted researchers' attention from diverse fields due to their anomalous thermal behavior and potential applications. In the past few decades, numerous studies have been carried out to investigate the thermal properties of nanofluids. A long-term stability is the first basic requirement in nanofluids research for maintaining their enhanced thermophysical properties. Thus, a holistic approach including stability and thermophysical properties is needed to achieve the synthesis of nanofluids with outstanding thermal properties. In this paper, a comprehensive literature on the synthesis, stability, thermophysical properties, and the characterization of nanofluids has been reviewed. Moreover, the factors that influence the thermophysical properties have been discussed. Finally, the applications and challenges of nanofluids have been mentioned. This paper provides an extensive review on nanofluids that critically summarizes and analyzes the recent research studies on nanofluids and sheds light on gaps, opportunities and further enhancement towards performance improvement of nanofluids.

This paper presents experimental investigations on aqueous dispersion of multi-walled carbon nanotubes (MWCNTs). Three experimental approaches are considered to improve MWCNTs dispersion; through functionalization of MWCNTs (1) with surfactants, (2) with oxidative acid treatment and (3) with metal decoration. The first approach investigated the dispersion stability of MWCNTs using different surfactants. In the second approach, surface of MWCNTs is functionalized through nitric acid treatment to facilitate the dispersion of MWCNTs. In the third approach, MWCNTs are decorated with silver nanoparticles and their dispersion behavior is investigated. In the experiments with surfactant addition, the ideal surfactant type and concentration are found as acacia gum at 1 surfactant:MWCNTs weight ratio, which yielded the highest zeta potential value of 26.7 mV. The second approach yielded an improved dispersion stability by visual observation of the fluid over a period of three months with no trace of sedimentation. Visual observation of the fluids prepared using silver-decorated MWCNTs showed a weak dispersion behavior. Thermal conductivity enhancement of the nanofluids at 0.1 wt% nanoparticle loading are calculated as 5.84% for silver-decorated MWCNT nanofluids, 8.14% for acid-functionalized MWCNT nanofluids and 8.85% for surfactant-functionalized MWCNT nanofluids. Functionalization with surfactant and oxidative acid treatment are found as the two useful methods for the stability and enhanced thermal conductivity of MWCNT dispersions.

In biomedical applications, the conventionally used metallic materials, including stainless steel, Co-based alloys and Ti alloys, often times exhibit unsatisfactory results such as stress shielding and metal ion releases. Secondary surgical operation(s) usually become inevitable to prevent long term exposure of body with the toxic implant contents. The metallic biomaterials are being revolutionized with the development of biodegradable materials including several metals, alloys, and metallic glasses. As such, the nature of metallic biomaterials are transformed from the bioinert to bioactive and multi-biofunctional (anti-bacterial, anti-proliferation, anti-cancer, etc.). Magnesium-based biomaterials are candidates to be used as new generation biodegradable metals. Magnesium (Mg) can dissolve in body fluid that means the implanted Mg can degrade during healing process, and if the degradation is controlled it would leave no debris after the completion of healing. Hence, the need for secondary surgical operation(s) for the implant removal could be eliminated. Besides its biocompatibility, the inherent mechanical properties of Mg are very similar to those of human bone. Researchers have been working on synthesis and characterization of Mg-based biomaterials with a variety of composition in order to control the degradation rate of Mg since uncontrolled degradation could result in loss of mechanical integrity, metal contamination in the body and intolerable hydrogen evolution by tissue. It was observed that the applied methods of synthesis and the choice of components affect the characteristics and performance of the Mg-based biomaterials. Researchers have synthesized many Mg-based materials through several synthesis routes and investigated their mechanical properties, biocompatibility and degradation behavior through in vitro, in vivo and in silico studies. This paper is a comprehensive review that compiles, analyses and critically discusses the recent literature on the important aspects of Mg-based biomaterials. Keywords: Mg-based biomaterials, Mechanical properties, Implant, Biomedical applications, Biodegradation

This study investigates the synthesis and characterization of graphene/zinc oxide nanocomposites. Wet impregnation method was employed for the synthesis. Firstly, graphene nanoplatelets and zinc nitrate hexahydrate were concurrently dispersed in ethanol and subjected to sonication for 1 h. Then, the dispersion was put in a furnace at 70 °C overnight. The paste was then collected and heated further up to 400 °C in air for a duration of 4 h. The process was proceeded to yield insoluble nanocomposites. The synthesis was followed by characterization of the nanocomposite samples by Field Emission Scanning Electron Microscopy (FESEM), X-Ray Diffraction (XRD) and Thermal Gravimetric Analysis (TGA). The XRD pattern revealed the presence of ZnO crystals and graphene. The FESEM images showed that ZnO crystals with average particle size of 30 nm are uniformly distributed on graphene surfaces. According to the TGA result, the content of nanocomposites is in good agreement with the materials used during synthesis.

Recently, the use of flapping plates or ‘flags’ as vortex generators has gained attention for its potential application in heat transfer enhancement in channels. The motion of the flag generates additional turbulence which leads to enhanced heat transfer. However, very few reports deal with the turbulence characteristics inside a channel with flag vortex generators. This paper presents some flow turbulence properties experimentally measured behind a flapping flag. Using multi-hole pressure (cobra) probes, the flow properties behind a flag (M* = 0.42) were measured in a rectangular channel (aspect ratio, α = 1/3) at four levels of flow Reynolds number (Redh = 11.5k–19.7k). Results show that the spectral properties of the flow parameters are closely dependent on the flag oscillation properties. Depending on streamwise location and Redh, measurements reveal that the flag can generate as high as 20% turbulence intensity in the channel centerline, almost six times that of a bare channel at the same Redh. In addition, a streamwise location has been identified where the flag’s oscillation no longer influences the spectral characteristics of the flow. The insights gained from this study may serve as a basis for the design and analysis of systems using flags as turbulence enhancers.

This study investigates the boiling heat transfer enhancement of 3D porous graphene/carbon nanotube hybrid surface formed via self-assembling. Experimentally, colloidal suspensions of functionalized carbon nanotubes and graphene oxide (at 1:10 wt ratio) and only graphene oxide in water are prepared via sonication using three weight concentrations; 0.00005%, 0.0005%, and 0.005%. Boiling tests are conducted for each prepared fluid using a custom-made boiling apparatus. After boiling tests, Scanning Electron Microscopy analysis is carried out over the heating surfaces in order to observe the deposition behavior of the suspended nanoparticles. For wettability analysis, the contact angle of sessile water droplets on the heating surfaces are measured using the goniometry method. The boiling performance of the heating surface formed by self-assembling of graphene oxide/functionalized carbon nanotube outperforms the self-assembled graphene oxide-only surface with greater critical heat flux and heat transfer coefficient values at all the tested concentrations. A decent interfacial contact of graphene sheets and carbon nanotubes improves surface capillarity and thermal activity. The highly porous surface improves the nucleation site density, bubble departure diameter, and frequency of departure. All these factors contribute enhancement of heat transfer coefficient and critical heat flux.

Broadly speaking, one of the most important aspects of Sustainable Development Goals (SDGs) of United Nations is to increase awareness of people for sustainability related issues namely economic, environmental and social problems. In this direction, it can be concluded that there is a lack of awareness for individuals regarding their habits and their related impacts on sustainability. Especially in developed countries, it is well-known that people are linked to over consumption, overweight, over waste, over pollution and so on. However, most of them are not aware of the results which are caused from their daily activities in terms of pollution, waste, energy footprints and their related effects on global sustainability. Mobility is one such area resulting in that kind of problems especially in urban areas. Our current road-based transportation system which is mainly dependent on automobile use causes a wide range of formidable problems. These include traffic congestion, air pollution, noise, accidents and related fatalities, depletion of non-renewable resources and inaccessibility of amenities and services. To illustrate this, more than one-quarter of total U.S. greenhouse gas emissions come from the transportation sector and light vehicles are responsible for 59% of transportation energy use (see Fig. 1). Due to the accidents on roads, approximately one million people dies except the millions of injuries (WHO, 2010). In addition to that, there are many cities suffering from traffic congestion which slows down daily businesses, causes unreliability in terms of time, results in unpleasant life in urban life and costs billions of dollars to the economies (Everyday Money, 2014; TomTom, 2013). These are just few figures to illustrate detrimental effects of transportation especially due to automobile use in urban areas. Transport demand, however, increases as economic growth increases (EU Energy, 2012) which will make the situation even worse in the upcoming years. Therefore, there are various dimensions of transport system which can be group into three categories: economic, environmental, and social (see Table 1). Given these problems, and their associated economic, environmental, and social impacts, the current transportation system especially in urban areas may be considered as unsustainable from various respects. To counter this challenge of moving towards sustainable transportation, much more effort is needed.According to World Business Council on Sustainable Development (2004), sustainable mobility is defined as ‘the ability to meet the needs of society to move freely, gain access, communicate, trade, and establish relationships without sacrificing other essential human or ecological values today or in the future’. To this end, there are certain areas to focus on to mitigate transport related problems and make a transition towards sustainable transport (C2ES, 2012). Firstly, on the fuels side, transitioning to low-carbon energy sources such as biofuels or electricity from renewable resources to directly reduce emissions from fuel consumption is required. Secondly, more efficient transportation equipment is needed to run on these low-carbon fuel sources. Thirdly, increasing the efficiency of existing transportation system is needed such as applying advanced traffic monitoring and signaling. Lastly, switching from unsustainable modes (mostly personal car usage) to alternative (or sustainable) travel modes such as public transportation, walking and cycling is needed to reduce the demand for the use of more energy intensive by changing land use patterns, increasing and promoting sustainable travel options while dis-incentivizing the use of unsustainable modes. After all, it can be said that a “new mobility” is needed which is a vision of the cities in which resident no longer excessively rely on their cars but on public transportation, shared cars, bikes or walking. Therefore, there will be less pollution, less noise, less stress at the end; cities will be more livable environments.In this direction, we are working on a mobile application project which will be capable of tracking individuals’ daily mobility activities; walking, bicycling, and driving. According to these mobility activities, the application will present the sustainability level of each individual in a sustainability scale and its related impacts on his\her health and the environment. By doing that, we aim to increase awareness of individuals for their current actions and encourage them to change their related behaviors into more sustainable ways by using different incentive and awareness tools. The application will prepare individualized packages to show people their mobility footprint with its effects on their life and on the environment and suggest other sustainable mobility ways.Our main target group will be mostly educated people from younger and middle age groups, rich-enough to having a smart-phone, and most importantly having unsustainable mobility activities. After successfully completion of the application, as a pilot area, Education City would be a perfect place to conduct pilot experiments where members of the community are suitable to our potential customer portfolio then it can spread all over the world through Qatar and Gulf Cooperation Council (GCC) countries. By doing that, we need to tailor incentive and awareness tools towards culture and expectations of the community. In this sense, we are going to present our findings from initial phases we have conducted so far in this developing process which includes; (1) literature review, (2) market assessments via various interviews with different stakeholders and survey questionnaire with people from potential target groups to figure out their perceptions and needs regarding this behavioral change for mobility, (3) analysis of requirements based on the results from previous phase and (4) concept design which includes flow diagrams, database schema and sketching user interfaces etc. In addition to these, we will utilize Quality Function Deployment (QFD) in our concept design to transform business requirements and specs of GMAP into it. Comparison of the competitive mobile applications will be able to seen in QFD as well. GMAP intends to raise public awareness on the impacts of their behaviors, to make them healthier, to reduce carbon emissions a little by walking much more and to build a green social network who shares the same thoughts on sustainability. In short, we believe our application (when being turned into reality) will contribute orienting people into the new sustainable lifestyles or it will pave the way at least.ReferencesC2ES. (2012). Transportation Overview | Center for Climate and Energy Solutions. Retrieved November 9, 2015, from http://www.c2es.org/energy/use/transportation EU Energy. (2012). Transport in Figures, Statistical Pocketbook 2012, European Commission.Everyday Money. (2014). No Title. Retrieved November 10, 2015, from http://time.com/money/3511481/traffic-jams-cost-americans-124-billion-time-money/Rahman, A., & Grol, R. van. (2005). SUMMA final publishable report v. 2.0; July 2005. Available Online on Http://www. Summa-Eu.Org/control/TomTom. (2013). TomTom Congestion Index -. Retrieved from http://www.tomtom.com/en_gb/congestionindex/WHO. (2010). Number of road traffic deaths. Retrieved November 9, 2015, from http://www.who.int/gho/road_safety/mortality/traffic_deaths_number/en/World Business Council on Sustainable Development. (2004). Mobility 2030: Meeting the Challenges to Sustainability.