Renewable Energy Global Innovations features: Solar collector integrated with a pulsating heat pipe and a compound parabolic concentrator

Significance 

Solar energy is the most abundant renewable energy that has the capability to meet the world’s growing demand. However, it requires good solar concentrators to increase the trap efficiency. The efficient mean to utilize solar energy is to convert solar energy into heat stored in water by solar thermal collectors. Techniques such as high efficiency heat transfer absorber and solar radiation concentration are the main methods to improve the performance of solar thermal collector.

Pulsating heat pipe is one of the highly efficient absorber with simple stricture and low cost. The pulsating heat pipe has three working states namely: start-up, steady state and dry-out as the heat input increases.  Altogether, the pulsating heat pipe exhibits an excellent potential for application as heat collector credit due to its high heat transfer capacity. However, the heat flux of the of the evaporation section of pulsating heat pipe should be sufficiently high to meet the demand of its steady and high-efficiency work, which has a significant effect on the thermal performance of pulsating heat pipe. Therefore, a solar concentrator is necessary in order to increase the heat flux of the pulsating heat pipe absorber to ensure that efficient heat transfer capacity of pulsating heat pipe can be fully utilized.

Researchers led by Professor Rong Ji Xu from Beijing University of Civil Engineering and Architecture and in collaboration with Dr. Hua Sheng Wang at Queen Mary University of London proposed a study on a novel solar collector that integrates a closed-end pulsating heat pipe and a compound parabolic concentrator. Their main objective was to test the operating characteristics and thermal performance of the detailed designed collector, under different weather conditions. Their work is now published in the research journal, Energy Conversion and Management.

Briefly, the research team initiated their empirical procedure by developing a prototype of the solar collector. Secondly, they analyzed the operating characteristics of the pulsating heat pipe absorber. The team then assessed the thermal efficiency of the solar collector under different weather conditions.

The authors observed that the collector showed start-up, operational and shutdown stages at the starting and ending temperatures of 75 ⁰C. More so, they noted that the solar collector operated stably even in cloudy days. Additionally, the thermal resistance of the pulsating heat pipe absorber was seen to decrease with the increase in ambient temperature, solar intensity, and evaporation temperature which was found to be the main factor that affects the thermal efficiency of the collector.

Rong Ji Xu and colleagues successfully presented a novel solar collector that integrates a closed-end pulsating heat pipe and a compound parabolic concentrator. In their study, they have assessed the effects of operating parameters on the operating characteristics of the pulsating heat pipe and the performance of the solar collector under varying weather conditions. The experimental results suggest that the heat flux of the pulsating heat pipe absorber’s evaporation section concentrated by compound parabolic concentrator with a concentration ratio of 3.4 is appropriate and the use of compound parabolic concentrator is reasonable. Their proposed design offers a promising efficiency of 50% when compared with conventional solar collectors and pulsating heat pipe solar collectors.

According to Rong Ji Xu, the mathematical model of the solar collector has been built. The effects of the solar density, ambient temperature, weed speed, glass thickness and collecting temperature on the thermal performance were simulated. A theoretical efficiency of 70% can be realized which is more promising than experimental results.

About the author

Rongji Xu，PhD，Associate Professor
School of Environment and Energy Engineering, Beijing University of Civil Engineering and Architecture
1 Zhanlanguan Road, Beijing 100044, China
Email: xurongji@bucea.edu.cn

Research interests:

• Heat and mass transfer
• Development and utilization of solar energy
• Design and optimization of refrigeration & air-conditioning system
• Organic Rankine cycle (ORC)

Research grant applications:

• Failure mechanism study on pulsating heat pipe used in solar energy collector, Project principal, NSFC (No. 51506004)
• Mechanism study on pulsating heat pipe with mixture working fluid, Project principal, BNSF (No. 3162009)
• Development of PV air conditioner, researcher co-investigator, Project principal, University-Industrial Collaboration Project
• Design and optimization on fin-and-tube heat exchanger of air conditioner, Project principal, University- Industrial Collaboration Project

Reference

Rong Ji Xu, Xiao Hui Zhang, Rui Xiang Wang, Shu Hui Xu, Hua Sheng Wang. Experimental investigation of a solar collector integrated with a pulsating heat pipe and a compound parabolic concentrator. Energy Conversion and Management 148 (2017) 68–77

 

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Renewable Energy Global Innovations features: Dynamic filtration control performance of N2/liquid CO2 foam in porous media

Significance 

In the extraction of oil and gas, fracturing fluids are used to create and widen a fracture for easier production. The fluid should be compatible with the rocks. Liquid CO₂ has been used as a fracturing fluid because it is highly soluble in most oil extracts therefore less damaging to the oil extracted as compared to water-based fluids. The high solubility in oil helps in lowering the viscosity of oil and improves the extraction of oil from the ground.

Liquid CO₂ is, however, difficult to control in porous media due to its low viscosity and lack of filter cake formation properties for controlled filtration. This may affect the shape of the desired fracture. Researchers have tried to improve on the viscosity of liquid CO₂ by adding thickening agents, however, improvement of viscosity of liquid CO₂ by enhancement does not guarantee a change in its filtration performance and liquid CO₂ dissolves poorly with thickening agents making the insoluble residues potential pollutants.

Filtration control performance of liquid CO₂ was improved without pollution by mixing it with Nitrogen (N₂). Gupta et al. stabilized the N₂ and CO₂ mixture by introducing fluorochemical stabilizers into the liquid CO₂ and then bubbling N₂ into the liquid to form the N₂/liquid CO₂ foam. The liquid CO₂ was the external phase while the N₂ was the inner face and the fluorochemical stabilizers separated the two phases.

Qichao Lv, under the guidance of Professor Zhaomin Li, at China University of Petroleum investigated the dynamic filtration control performance of N₂/liquid CO₂ foam with a fluorochemical (HFE) as a stabilizer.

The filtration behavior of N₂/liquid CO₂ foam is uncertain as the external phase of the foam is unstable. Temperature and pressure can affect its density, viscosity and phase and changing the flow properties of the foam. Moreover, the behavior of waterless foam with the unique fluorochemical interface is uncertain. The interface may also be a potential pollutant. The experiment seeks to study the factors that may affect the dynamic filtration performance of N₂/liquid CO₂ foam including viscosity, foam quality, temperature, pressure, permeability and the damaging effects of the foam on porous media after filtration.

The setup for the experiment was done as shown in their paper where the preparation for the foaming solution was done and the viscosity measurement and dynamic filtration tests were done. The viscosity measurement results showed that the use of foam enhanced the viscosity of liquid CO₂. The apparent viscosity is related to temperature, pressure and foam quality. The viscosity increased as the foam quality was increased from 31 % to 71 %. The viscosity of high quality foams were 1 order of magnitude larger than that of liquid CO₂ at the same conditions. The apparent viscosity is at a maximum at a foam quality of about 80 % before it starts decreasing as it becomes fragile and sensitive to disturbances such as interactions and pressure fluctuations.

The filtration control performance of the N₂/liquid CO₂ foam was compared to that of liquid CO₂ and a N₂/liquid CO₂ mixture. The results showed that the filtration control properties of the N₂/liquid CO₂ foam was better than the others. The leak off coefficient lowered with an increase in foam quality up to 80 % where it increased. Foams of 50 – 80 % quality had a high filtration performance with permeability change. Low initial foam quality foams had better filtration performance at high pressure difference. As the foam enters the porous media, the liquid part would evaporate hence increasing the foam quality with depth. Damage by the foam on the porous media depends upon the pressure difference between the two sides of the porous media.  Damage is small under low pressure difference as the CO₂ turns to gas under a high pressure media damaging the porous media.

In their study the research team were able to prove that by mixing N₂, liquid CO₂ and HFE, properties such as viscosity and filtration control performance of the resultant N₂/liquid CO₂ foam, increased substantially without damage to porous media.

About the author

Qichao Lv is currently a doctoral candidate at China University of Petroleum, East China and a research scholar of Foam Fluid Enhanced Oil & Gas Production Engineering Research Center in Shandong province. He is also a member of Nano-Technology for Energy and Environment Group in University of Calgary. His primary areas of interest include foam technology for EOR and fracturing. In particular, he has done an excellent work in green and clean foam fracturing for unconventional oil and gas reservoirs such as shale gas, tight sand oil and gas, and CBM formations. He has published more than 20 articles in peer-reviewed scientific journals and applied for 15 patents of China and US. Because of his contribution to the development of unconventional reservoirs, he has won a first prize of provincial science and technology award as first investigator.

Contact: qichaolv@s.upc.edu.cn

About the author

Prof. Zhaomin Li is vice president of the China University of Petroleum, East China and director of Foam Fluid Enhanced Oil & Gas Production Engineering Research Center in Shandong province. His research emphasis is on the flow laws and equipment for foam fluid, new technologies of heavy oil recovery, CCUS theories and their application. In recent years, he has participated in more than 10 national programs as main contributor, and published more than 100 articles, of which 34 articles are indexed by SCI and 36 articles are indexed by EI.

He also holds more than 30 invention patents, and has established 3 standards for oil and gas industry as manager. In addition, he has won three first prizes of provincial science and technology award as first investigator. In particular, one of his invention as participant, HDCS enhanced oil recovery technology for ultra-heavy oil reservoirs, has increased crude oil production by several millions of tons, which was also selected as one of ten chemical technology highlights by China Chemical Industry News in 2010. A serials of foam stimulation techniques he invented are serving B&R countries, which has been reported by the Journal of International Innovation.

Contact: lizhm@upc.edu.cn

Reference

Lv Q, Li Z, Li B, Zhang C, Shi D, Zheng C, Zhou T. Experimental study on the dynamic filtration control performance of N2/liquid CO2 foam in porous media. Fuel. 2017 Aug 15; 202:435-45.

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Renewable Energy Global Innovations features: Titanium oxide nanofibers decorated nickel-rich cathodes as high performance electrodes in lithium ion batteries

Significance

Layered cathode active materials partially-substituted cobalt with transition metals and spinel active materials have been received more attention due to their cost effectiveness as compared to lithium cobaltate. Scholars have realized with time that the spinel cathode active materials are safe with limited specific capacities while layered cathode active materials possess high specific capacity with safety issues. Presently, layered cathode active materials are more preferred as cathode materials for lithium ion batteries, where nickel-rich layered cathode active materials are front runners except for safety issues, due to their high capacity. To overcome the safety issue challenge, measures, such as the substitution of the transition metal ions with other metal counter ions and the modification of the surface by means of coating with metal oxides, have been put in place.

Nanoparticle coatings on layered cathode active materials have been known to suppress the thermal reaction between the electrode and electrolyte. It has thus been seen necessary to coat or decorate the surface of the cathode since probable exothermic reaction starts from the cathode surface when the electrolyte is decomposed. Extensive studies have been performed on coating materials that inhibit this reaction but little exists about nanofibers-based metal oxides decorated on lithium nickel cobalt aluminum oxide cathode active materials.

Professor Chang Woo Lee and colleagues from the Department of Chemical Engineering, College of Engineering, Kyung Hee University in South Korea proposed a study to modify the surface of lithium nickel cobalt aluminum oxide particles by decorating them with titania nanofibers. They aimed at comparatively studying, with the novel lithium nickel cobalt aluminum oxide, the various quantities of titania nanofibers decorated over lithium nickel cobalt aluminum oxide (LNCA). Their research work is now published in the peer-reviewed journal, Journal of Industrial and Engineering Chemistry.

The researchers commenced their empirical procedure by obtaining titania nanofibers precursor through electrospinning a sol-gel polymeric solution. They then obtained the LNCA precursor. The titania nanofibers precursors were split at 0.5 wt%, 1 wt% and 1.5 wt% before addition of the LNCA precursor powders. The precursor powder mixture was then sintered at 465^oC for three hours and then calcined at 850^oC for five hours in air. The team then conducted an X-ray photoelectron spectroscopic analysis to investigate the chemical composition of the cycled electrode surface. The team eventually obtained cathode samples and used them to conduct differential scanning calorimetry scans.

The authors also observed that the increase of titania nanofibers decoration over 1wt% ratio showed negative effect during the electrochemical process, as observed using electrochemical impedance spectra for the 1.5wt% titania nanofibers-decorated LNCA. Hence usage of titania nanofibers more than 1wt% was excluded from detailed investigation. The surface modification of LNCA electrodes by 1wt% titania nanofibers decoration greatly increased the cycleability, capacity, and thermal stability of lithium ion batteries at room temperature as well as at elevated temperature. Among titania nanofibers decorated LNCAs, the 1wt% titania nanofibers -decorated LNCA cathode had shown better capacity retention of 89.2% and 81.9% at room and elevated temperature, respectively.

The results of their study second the suggestion of the applicability of titania nanofibers as surface modifiers in order to enhance the electrochemical and thermal properties of lithium ion batteries. Moreover, it has been seen that the capability of the titania nanofibers-decorated LNCA was enhanced compared to that of the pristine LNCA. The onset temperature of thermal decomposition is also shifted towards higher temperature for titania nanofibers-decorated LNCA electrodes than pristine LNCA electrodes.     

About the author

Mr. Kijae Kim is currently a Ph.D. candidate at the Department of Chemical System Engineering in The University of Tokyo, Japan. He received his B.S. and M.S. degrees in the Department of Chemical Engineering at Kyung Hee University, S. Korea. He has studied synthesis and analysis of electrode materials for energy storage devices for the M.S. under the supervision of Prof. Chang Woo Lee. He has published several scientific papers and received the Best Poster Award from Korean Battery Society and bachelor graduation with honors.

About the author

Dr. K. Prasanna obtained his B.S. and M.S. degrees from Bharathidasan University and Anna University in India, respectively. He then joined as assistant professor in the Department of Biotechnology at Vinayaka Missions University, Salem. He joined as a Ph.D. student under Professor Chang Woo Lee in the Department of Chemical Engineering at Kyung Hee University, S. Korea in September, 2011 and received his Ph.D. degree in Aug, 2015. He then continued his career as a postdoctoral fellow at Electrochemical Energy Storage and Conversion Laboratory, Kyung Hee University for two years. Currently he is working as a postdoctoral fellow in Technical University of Denmark, under the H.C. Ørsted Postdoc programme, co-funded by Marie Skłodowska-Curie Actions. His recent research interests include supercapacitors, Li-ion batteries, Mg-ion batteries, and Metal-air batteries.

About the author

Dr. T. Subburaj received his Ph.D. at Kyung Hee University, South Korea in 2015 under the supervision of Prof. Chang Woo Lee in the Department of Chemical Engineering and he received his M.S. degree from the Department of Chemical Engineering, Anna University, Chennai, India in 2010. Currently, he works with Prof. Chung-Hsin Lu as a MoST Postdoctoral Scholar at National Taiwan University, Taiwan. His research interests focus on synthesis and applications of nanostructured and hybrid materials for electrochemical energy storage and conversion, including rechargeable batteries, electrochemical capacitors, and solar cells.

About the author

Dr. Yong Nam Jo received his M.S. and Ph.D. degrees in Department of Chemical Engineering from Kyung Hee University, S. Korea in 2013 and 2017, respectively, under the supervision of Prof. Chang Woo Lee. He received Best Thesis Award for the Ph.D. from the President of Kyung Hee University and also several Best Poster and Outstanding Paper Awards from domestic and international conferences. He is currently working as a postdoctoral fellow at the Center for SMART Energy Platform at Kyung Hee University. His current research is focused on enhancement of materials for energy storage and conversion with Li-ion batteries and metal-air batteries.

About the author

Professor Chang Woo Lee is currently serving in the Department of Chemical Engineering and also Director of Center for the SMART Energy Platform at Kyung Hee University, S. Korea. He joined Kyung Hee University in 2006, having received B.S. and M.S. degrees in 1994 and 1996, respectively, at Kyung Hee University, S. Korea and a Ph.D. at the Illinois Institute of Technology, USA in 2003, both in the field of Chemical Engineering. Prof. Lee has also worked as a Senior Researcher at Korea Electrotechnology Research Institute (KERI) since he obtained Ph.D. degree. He was appointed as a Visiting Scholar in the Materials Department, College of Engineering and Applied Science, at the University of Wisconsin-Milwaukee, for the 2012-2015 academic year.

Prof. Lee’s research is focused on electrochemical energy storage & conversion and seek to synthesize energy materials in metallic micro- and/or nanostructures for the purpose of improving electrochemical properties in the area of batteries, supercapacitors, and fuel cells.

 

Reference

Subburaj, Yong Nam Jo, K. Prasanna, Ki Jae Kim, Chang Woo Lee. Titanium oxide nanofibers decorated nickel-rich cathodes as high performance electrodes in lithium ion batteries. Journal of Industrial and Engineering Chemistry, volume 51 (2017) pages 223–228.

 

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Renewable Energy Global Innovations features: A non-fullerene acceptor with a diagnostic morphological handle for streamlined screening of donor materials in organic solar cells

Significance 

Solution-processable organic solar cells are an emerging technology that is capable of providing a cheap route for solar energy conversion. Researchers continue to set new records in power conversion efficiencies every year, yet the organic solar cell technology has remained more of an academic interest. In order to extend the existing lab-scale methodologies to large-scale commercialization, there are a number of inadequacies that will have to be addressed.

Transitioning to high-performance practical materials from currentmaterials with complex and multi-step preparations remains a major issue. This has made the materials expensive and more or less limited to academic settings. To address this issue, low cost and scalable N-annulated perylene diimide building blocks have been incorporated into a wide range of final materials with overall power conversion efficiencies between 2-8% when implemented as a non-fullerene acceptor. While these materials are simple to access and scale-up, their high efficiencies have relied on the use of polymeric donor materials, which are often quite expensive.

In view of the above limitations, solar energy scientists have now shifted their focus to finding simple and scalable donor materials that can sufficiently complement these acceptor materials. Researchers led by Professor Gregory Welch at the University of Calgary streamlined the screening of low cost and scalable donor materials using an N-annulated perylene diimide derivative. The authors established a simple air-processed and air-tested organic photovoltaic device preparation method in order to realize their objective. Their research work is published in Journal of Materials Chemistry A.

The authors took advantage of the diagnostic morphological handle inherent in N-annulated perylene diimide derivative and devised an approach for screening compatible donor materials. Implementing this efficient approach, the authors were able to screen a series of simple donor polymers constructed from low-cost building blocks and settled on PDTT-BOBT as good competitor to the now standard, high performance, yet expensive polymer, PTB7-Th.

The authors observed that optimizing the active layer blend of PDTT-BOBT:PDI-DPP-PDI led to an increase in the performance upon post-deposition chloroform vapor annealing. The best cell power conversion efficiency improved from 1.9 to 4.5% compared to 1.7 to 4.6% for the PTB7-Th. These high efficiencies made the authors recognize PDTT-BOBT as an alternative to PTB7-Th and supported its credibility for screening new acceptor materials.

While performance was impressive, negligible light absorption of PDTT-BOBT beyond 700nm as well as poor photochemical stability in air appear to be the major drawbacks to the polymer design. This polymer has high ionization potential and a high open circuit voltage. It would be therefore prudent to red-shift the onset of absorption with less alteration on the ionization potential. For this reason, any future modifications to the polymer design must be centrally focused on modifying the acceptor component.

Enhancing light stability of this polymer would definitely necessitate substituting the alkoxy side chains on the benzothiadiazole moiety with stable solubilizing substituents, without necessarily minimizing polymer solubility or affecting its self-assembly tendencies.

Addressing these challenges will call for the preparation of a number of new polymeric materials. Seth McAfee and colleagues in this study therefore proposed a simple approach for easy screening of these derivatives to come up with superior polymer designs.

About the author

Seth McAfee is a PhD candidate in Chemistry at the University of Calgary (Canada) working under the supervision of Dr. Gregory Welch.

Seth’s research in the Welch Research Group is focused on practical organic materials development for use in electronic devices, specifically organic solar cells. Motivated to access more sustainable and cost-effective active layer materials, Seth has been designing his organic pi-conjugated compounds to make use of organic dyes, known for their ease of commercial accessibility and excellent light harvesting capabilities.

Current efforts are focused on exploiting a material composed of perylene diimide (structural derivative of Pigment Red 190) and diketopyrrolopyrrole (structural derivative of Pigment Red 254). This compound is easily synthesized in high yields on multi-gram scale and has been able to achieve impressive device efficiencies acting as the electron-accepting material within the bulk heterojunction of solution-processable organic solar cells. A key feature of this material is the solvent vapour annealing induced solid-state re-organization of the compound. This was found to dramatically improve organic solar cell device efficiencies with an array of different electron-donating materials and highlights the versatile compatibility of the compound.

Contact: seth.mcafee@ucalgary.ca

Reference

Seth M. McAfee, Abby-Jo Payne, Sergey V. Dayneko, Gururaj P. Kini, Chang Eun Song, Jong-Cheol Lee and Gregory C. Welch. A non-fullerene acceptor with a diagnostic morphological handle for streamlined screening of donor materials in organic solar cells. Journal of Materials Chemistry A, 2017, 5, 16907.

 

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Renewable Energy Global Innovations features: Facile Fabrication of Porous Ti2Nb10O29 Microspheres for High-Rate Lithium Storage Applications

Significance 

Most microelectronic devices use lithium-ion batteries as their main power source. This is due to their high power density and long life. However, current trends in microelectronic evolution demand higher energy output and therefore there is need to develop new electrode materials with improved cycling stability, high power density and higher safety. For a long time, graphite has been the main anode material despite the fact that it poses safety issues related to lithium dendrites formation. Dendrite formation is attributed to the relatively low lithium ion intercalation potential, overcharge and high current. Recently, titanium based oxides have drawn much attention. Specifically, Titanium-Niobium-Oxide (TNO) has received a higher concern due to its high theoretical capacity and a higher discharge platform. Unfortunately, fabricating TNO is quite challenging as it requires high temperatures for processing and a long reaction time. More so, the particle size and morphology, which display a significant influence on the electrochemical performance, cannot be effectively controlled.

A team of researchers led by Professor Bo Jin from the Key Laboratory of Automobile Materials, at Jilin University in China developed a facile preparation technique for fabricating TNO materials with a meticulous morphology that would ensure improved electrochemical performance. They aimed at fabricating the TNO microspheres by combining a solvothermal method with a subsequent heat-treatment. Their work is now published in International Journal of Hydrogen Energy.

The researchers commenced the proposed investigation by preparing TNO microspheres. They then characterized the structural and morphological properties of the prepared samples by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and nitrogen adsorption/desorption. Eventually, they evaluated the electrochemical performance by performing cyclic voltammograms and galvanostatic discharge/charge tests.

From the electrochemical tests undertaken, the authors of this paper were able to demonstrate that the as-prepared TNO microspheres exhibited high yet stable electrochemical properties. To be precise, they noted that TNO microspheres exhibited a discharge capacity of 185 mAh g^-1 after 200 cycles at 10 C. The team therefore argued that the good electrochemical properties of TNO microspheres were ascribed to its convenient structure with porosity and small particle size, which favors the infiltration of the electrolyte, accelerates Li-ion diffusion, and improves the cycling lifetime by an efficient accommodation of the volume change upon charging/discharging.

In their study, Bo Jin and colleagues have presented a new facile technique for fabricating TNO materials of improved electrochemical performance. From the electrochemical characterization undertaken, it has been demonstrated that the as-prepared TNO microspheres exhibit a good electrochemical performance with an excellent discharge capacity and an outstanding capacity retention. This is a clear indication that the proposed TNO microspheres are prospective high power anode materials application which may react with lithium at voltages above 1.0 V vs. Li⁺/Li.

Ti₂Nb₁₀O₂₉ – Titanium-Niobium-Oxide (TNO)

About the author

Associate Professor Bo Jin is currently serving in College of Materials Science and Engineering at Jilin University, China. He joined Jilin University in 2003, having received M.S. and Ph.D. degrees in 2003 and 2008, respectively, at Chonnam National University, Korea, both in Department of Electrical Engineering. He then continued his career as a postdoctoral fellow at Key Laboratory of Automobile Materials, Ministry of Education, Jilin University for two years.

Asso. Prof. Jin’s research is focused on energy storage & conversion, and seeks to prepare electrode materials in micro- and/or nanostructures for the purpose of improving electrochemical performance of lithium batteries.

Reference

Guangyin Liu, Bo Jin*, Keyan Bao, Ying Liu, Haiquan Xie, Min Hu, Ruixue Zhang, Qing Jiang. Facile fabrication of porous Ti₂Nb₁₀O₂₉ microspheres for high-rate lithium storage applications. International Journal of Hydrogen Energy volume 42 (2017) pages 22965-22972.

 

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Renewable Energy Global Innovations features: Boiling heat transfer performance enhancement using micro and nano structured surfaces for high heat flux electronics cooling systems

Significance 

Chemical and petro-chemical engineering, cooling of power electronic devices, air conditioning and refrigeration are among the many phenomena in our daily activities that utilize boiling. In the past fifty years, the boiling phenomenon has been studied far and wide. Most of the studies undertaken have, however, concentrated on parameters such as dimension, configuration, heat flux, type of working fluid and the topography of the surface. More so, majority of the researchers have focused on the use of enhanced surfaces in boiling by preparing mechanically deformed structures, sintered wires porous, materials and complex geometries. The importance of surface condition on nucleate boiling cannot be ignored. Fortunately, recent advances in nanotechnology have led to the conceptualization of efforts aimed at enhancing boiling heat transfer by using nanostructured surfaces such as deposited nanoparticles, nanowires, carbon nanotubes and metal oxide structures. Flow boiling enhancement using structured surfaces in micro-channels is a promising method to achieve high heat removal rates. Regardless, there are few studies focusing on boiling heat transfer in high aspect ratio micro-channels.

Researchers (Abdolali K Sadaghiani, Sorour Semsari Parapari, and Professor Mehmet Keskinoz from Sabanci University, Nawzat S. Saadi and Professor Tansel Karabacak from University of Arkansas at Little Rock) led by professor Ali Kosar from the Center of Excellence for Functional Surfaces and Interfaces for Nano diagnostics (EFSUN) and Sabanci University Nanotechnology and Applications Center (SUNUM) at Sabanci University in Turkey, investigated the effect of surface structure size (size scale: micro and nano) on boiling heat transfer characteristics of samples with different surface morphology. The researchers aimed at conducting flow experiments on samples of different surface morphologies: micro and nano structured, in a high aspect ratio micro channel. A new flow map have developed demonstrating the differences in flow morphologies due to structure size. Their work is now published in the research journal, Applied Thermal Engineering.

The research team undertook the experimental procedure where they investigated heat removal capacity of nano-structured, micro structured and micro-nano structured surfaces. They then employed thermal and high speed camera systems to clarify the differences in heat transfer mechanisms. The team then obtained heat transfer coefficients along with associated boiling images. Eventually, based on the visualization study results, two flow maps were constructed for a rectangular microchannel with micro and nano scale structures on copper surfaces.

From the experiment undertaken, the authors of the paper observed that the surface morphology remarkably changed boiling heat transfer mechanisms. According to the obtained thermal images, bubble departure frequency increased with surface structures, and the surface temperature distribution was more uniform for surfaces with nano scale structures (nano-structured and micro-nano-structured) compared to other surfaces (untreated, micro-structured).

In their study, copper surfaces have been used as the test samples. From the results obtained, it has been found that structured surfaces have a better heat removal capacity in comparison to the bare surface. This is good evidence that micro-structured, nano-structured and micro-nano-structured plates can be implemented in innumerable cooling applications to achieve higher energy efficiency. More so, according to the observations higher heat transfer coefficients are obtained from nano scale structured surfaces in comparison to the micro scale structured sample. Therefore, these promising results obtained in Ali Koşar lab reveal the potential of micro and nano scale structured surfaces application that will help achieve improved energy efficiency for electronics cooling systems.

About the author

Abdolali K Sadaghiani received his M.Sc. degree in Mechatronics Engineering from Sabanci University, Istanbul, in 2015. Currently, he is pursuing his Ph.D. under the supervision of Prof. Ali Koşar at Sabanci University. His research focuses on numerical and experimental studies of multiphase flows in microchannels. His research interests lie in microscale heat and mass transfer, phase change, microfabrication, and microfluidics. He received several awards including Sedat Simavi Foundation Natural Sciences Award (2016), and Best Paper Award in ASME IMECE 2014 – MEMS Track (2014).

About the author

Nawzat Saadi received his BS degree in 2003 from physics department at Duhok University, Iraq. In 2008, Nawzat get his MSc in the field of computational physics from Physics department at Duhok University. Currently, he is a PhD student at University of Arkansas at Little Rock (UALR) Department of Applied Science and works in Dr.Tansel Karabacak group. He is primarily interested in metal oxide nanostructures fabrication and material with special wettability for oil-water separation applications. He is the author and co-author of several peer-reviewed journal papers and conference proceedings, several pending patents.

About the author

Sorour Semsari Parapari received her B.Sc. degree in Materials Engineering from University of Tabriz, Iran in 2009. She continued her graduate studies at Sabanci University, Turkey and obtained her M.Sc. degree in 2015 in Materials Science and Engineering. Sorour is pursuing her Ph.D. under the supervision of Prof. Mehmet Ali Gülgün at Sabanci University. She is currently working at the National Institute of Chemistry, Slovenia as a visiting student. Her primary interests are lithium ion battery materials, structure-property relationships, electron microscopy and materials characterization.

About the author

Dr. Tansel Karabacak received his BS degree in 1996 from Physics at Middle East Technical University in Turkey. He conducted his PhD studies at Rensselaer Polytechnic Institute (RPI) Department of Applied Physics in the field of growth dynamics of thin film coatings and glancing angle deposited (GLAD) nanostructures. After he received his doctoral degree in 2003 and a period of postdoctoral research at RPI, in 2006 he joined University of Arkansas at Little Rock (UALR) Department of Applied Science as a faculty member. He also became the graduate coordinator of the Applied Science PhD program at UALR. In recent years, Dr. Karabacak has been working on various projects on the properties and applications of GLAD nanostructures and physical vapor deposited thin films. He is primarily interested in alternative energy technologies including solar cells, fuel cells, and batteries. His research led to numerous awards including American Vacuum Society Graduate Research Award and University of Arkansas Excellence in Research Award, and also to several grants from NSF, NASA, and DOE. He is the author and co-author of about 130 peer-reviewed journal papers and conference proceedings, two book chapters, one patent, and several pending patents.

About the author

Dr. Mehmet Keskinoz got his M.S. and Ph.D. degrees from Electrical and Computer Engineering, Carnegie Mellon University, Pittsburgh (USA), in 1997 and 2001, respectively. In 2001, he joined to Electronics Engineering Program of Sabanci University Istanbul, Turkey where he is now an Associate Professor. His research interests include signal processing for wired and wireless communications, UWB communications, Multi-band OFDM UWB systems, Wireless Mesh Networks, magnetic and optical data storage systems, distributed detection and data fusion for wireless sensor networks, Turbo and LDPC coding, synchronization, digital watermarking. He is a recipient of Turkish NSF Research grant on distributed detection in wireless sensor networks and Career Award on wireless mesh networks in August 2005. He is a co-guest editor of IEEE Communications Magazine January 2009 Special Issue on Advances in Signal Processing for Wireless and Wired Communications. He is a member of IEEE Communication Society, IEEE Signal Processing Society and Optical Society of America.

About the author

Ali Koşar received his B.S. degree in Mechanical Engineering from Bogazici (Bosphorus) University, Istanbul, in 2001. He pursued his graduate study in the Department of Mechanical Engineering at Rensselaer Polytechnic Institute between 2001 and 2006. He joined Mechatronics Engineering Program at Sabanci University in Fall 2007. He is one of the pioneers in the design and development of new generation micro heat sinks and microfluidic devices.

His research interests lie in heat and fluid flow in micro/nano scale, boiling heat transfer, and cavitation. The results of his research have already generated more than 100 journal research articles in prestigious journals. He received  many awards such as METU (Middle East Technical University) Prof. Mustafa N. Parlar Foundation Technology Award (2017), Sedat Simavi Foundation Natural Sciences Award (2016), Ten Outstanding Young Persons Turkey Award in Scientific Leadership (TOYP 2015), ASME (American Society of Mechanical Engineers) ICNMM (International Conference on Nanochannels, Microchannels and Minichannels) Outstanding Early Career Award, Japan, Sapporo (2013), Kadir Has Outstanding Young Investigator Award (March 2013), TUBITAK (The Scientific and Technological Research Council of Turkey) Incentive Award (July 2012), and Outstanding Young Researcher Award, Turkish Academy of Sciences (2011). He is currently a Professor at Sabanci University and the Co-director of Center of Excellence for Functional Surfaces and Interfaces for Nano diagnostics (EFSUN).

Reference

Abdolali Khalili Sadaghiani, Nawzat S. Saadi, Sorour Semsari Parapari, Tansel Karabacak, Mehmet Keskinoz, Ali Kosar. Boiling heat transfer performance enhancement using micro and nano structured surfaces for high heat flux electronics cooling systems. Applied Thermal Engineering volume 127 (2017) page 484–498.

 

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Renewable Energy Global Innovations features: Molten salt-enhanced production of hydrogen by using skimmed hot dross from aluminum re-melting

Significance 

The unprecedented global rise in temperature and climatic change has triggered the need for a clean and regenerative energy. This in return has created an urgent need for hydrogen and alternative means of producing it. Presently, 95% of hydrogen is produced by steam/partial oxidation reforming of natural gas and coal gasification. Recent technological advances have seen the development of a variety of alternative techniques and materials that can be used for hydrogen generation. Amongst them, aluminum and its alloys is the most promising material. Unfortunately, its application has been limited due to the absence of a technique that can minimize the formation of a passive oxide layer. As a partial remedy, several pretreatments have been established so as to accelerate hydrogen generation by activating metallic aluminum. Previous studies have already shown that production of hydrogen by use of secondary aluminum, aluminum scrap and waste or aluminum dross is economical and environmentally friendly. Surprisingly, little has been done on hydrogen production using water steam at high temperature from skimmed hot dross as an alternative technique.

Peng Li and colleagues developed an innovative process for hydrogen generation using skimmed hot dross from aluminum remelting industry. The team hoped to put into use the skimmed hot dross generated during the secondary production of aluminum which contains both high amount of metallic aluminum and potential heat. They aimed at carrying out studies on the reaction behavior between the skimmed dross and water steam in terms of hydrogen evolution variation at high temperature. Their research work is currently published in the research journal, International journal of hydrogen energy.

The procedure used involved, first, the preparation of the samples to be used in the experiments which was achieved by air drying crushed salt cake at 150 ^°C and splitting them into various concentrations. The team then proceeded to hydrogen production where isothermal studies were carried out at the temperature range of between 600 – 900 ^°C for a specified duration. Eventually, the team employed various techniques to analyze and characterize the contents of specific elements of the prepared skimmed dross.

The authors observed that the inherent salts in the dross accelerated hydrogen generation at temperature region of between 600 – 850 ^°C by dissolving the amorphous and γ-alumina product layer in water steam atmosphere. They also noted that the maximum aluminum conversion degree was more than 60%, and the hydrogen evolution rate was over 60 cubic centimeter/gram/minute when skimmed dross with 30 wt% aluminum was used in non-isothermal mode. More so, the presence of the salt flux was seen to alter the water/aluminum interaction mechanism by altering the polymorphic alumina transitions.

Here-in, a study on the reaction behavior between skimmed dross and water steam in terms of hydrogen evolution variation at high temperature and the influences of impurities existing in the skimmed dross on the aluminum/water reaction has been presented. The results obtained have confirmed that the inherent salt flux in the dross could be used as catalyst to enhance the hydrogen production in a relatively lower temperature region of 600 – 850 ^°C, by dissolving the product layer containing amorphous and γ-alumina. The advanced technique here enables economical hydrogen production by skimmed hot dross. Also, the inherent salt flux impurities in the dross enhances hydrogen production from aluminum/water high-temperature reaction without any pre-activation process.

About the author

Dr. Peng Li is currently a lecturer at School of Iron and Steel, Soochow University, Suzhou, PR. China. He received his Ph.D degree in Department of Materials Science and Engineering, the Royal Institute of Technology, Sweden in 2012. His research interest mainly focuses on thermodynamics and kinetics behavior of high temperature reactions, which are involved in the extraction of valuable elements, recovery of waste heat, and energy production from metallurgical wastes.

About the author

Dr. Hong Wei Guo works in School of Iron and Steel, Soochow University since 2014, after 7 years’ work experience in University of Science and Technology Beijing from 2007 to 2014, owning Metallurgical Engineering master degree, and Management Science and Engineering Ph. D degree. He has done many work with the cross of the two subjects, such as development of Blast Furnace Expert System and Hot Blast Stove Combustion Optimization System.

Besides, as the director of the Department of Resource Recycling Science and Engineering, resources recycling of metallurgical slag is also his main research direction, especially on the efficient utilization of metallurgical slag.

About the author

Dr. Bing Ji Yan works in School of Iron and Steel, Soochow University since 2015, and got doctorate from University of Science and Technology Beijing majored in Metallurgical Engineering in the same year. The main research directions focus on reuse of metallurgical solid wastes to prepare building material or reuse the energy, and the efficient utilization of ferrous materials in the process of ironmaking.

Reference

Peng Li, Jun Wang, Xiuxia Zhang, Xinmei Hou, Bingji Yan, Hongwei Guo, Seshadri Seetharaman. Molten salt-enhanced production of hydrogen by using skimmed hot dross from aluminum re-melting at high temperature. International journal of hydrogen energy volume 42(2017) pages 12956-12966.

 

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Renewable Energy Global Innovations features: Continuous Ozonolysis Process to Produce Non-CO Off-Gassing Wood Pellets

Significance 

Exposure to carbon monoxide off-gassed from stored wood pellets can be a major health problem leading to critical occupational and residential exposures. Hazardous incidents and fatalities have been reported from carbon monoxide exposure related to transportation and storage of wood pellets (Gauthier, 2012). The use of wood pellets is on the rise across the world in view of the high demand for high-density, concerns about climate change, renewable energy, and the long-term decline of fossil fuel resources.

Wood pellets are easy to handle, have a homogeneous quality, and high energy density, which make them competitive with fossil fuels for heating applications. In view of the fact that wood pellet consumption as well as production has risen considerably in the last few years, concerns relating to health issues and safety due to CO exposure resulting from  off-gassing from wood pellets  are on the rise.

Researchers have mounted studies to analyze the processes that result in formation of carbon monoxide from stored wood pellets. A previous study has shown that autoxidation of unsaturated compounds, such as terpenes and fatty acids is responsible for the production of carbon monoxide from wood pellets. It was also shown that ozonation of wood fiber passivated the reactive hydrocarbons under static conditions.

Unfortunately, the kinetics of continuous ozonolysis reactions has not been determined.  Elucidating the kinetics would be required for analyzing the feasibility of a continuous process as demanded in a commercial pellet mill. Researchers led by Professor Philip Hopke at Clarkson University in New York studied the kinetics of continuous ozonolysis of wood fiber and implemented those details to adopt ozonolysis at industrial scales. They showed  that a considerable reduction of carbon monoxide emissions achieved at low cost in the pellet production process would eliminate one barrier limiting the expanded use of wood pellets. Their research is published in journal, Energy & Fuels. This work was supported by the New York State Energy Research and Development Authority intend to provide technical assistance to all pellet mills in New York to eliminate CO off-gassing from pellets with the intention of  removing the hazard to consumers

The authors observed that the reaction followed a pseudo-first-order reaction implying that the reduction in carbon monoxide emissions was linearly proportional to the ozone exposure. They also observed that the exposure required to minimize or eliminate completely carbon monoxide formation from the exposed fiber was approximately 42000 ppm min at about 0.57kg/min of fiber or about 0.032g of O3/kg of fiber to be passivated.

The research team investigated the volatile organic compounds generated during the ozonolysis of the fiber implementing gas chromatography. They identified aldehydes such as decanal, and nonanal. This indicated that linoleic, oleic, and linolenic acids were ozonized. The authors also performed thermogravimetric analysis in a bid to analyze changes in wood characteristics following exposure to ozone. However, no major changes in the wood characteristics were observed.

In order to establish an industrial viability of the proposed process, the researchers performed trials at scale in a commercial pellet mill (in collaboration with scientists at Queenaire Technologies and Curran Renewable Energy). The pellets produced through this process had no measurable carbon monoxide off-gassing when given sufficient ozone exposure, therefore this provided the viability of the process.

Fuel attributes of the produced pellets were established and indicated that the wood pellets produced from the treated fiber had a similar calorific value content but had different moisture and ash contents from non-treated pellets.

About the author

Dr. Philip K. Hopke is the Bayard D. Clarkson Distinguished Professor Emeritus at Clarkson University, and former Director of the Center for Air Resources Engineering and Science (CARES), and former Director of the Institute for a Sustainable Environment (ISE).  He holds an adjunct professorship in the Department of Public Health Sciences at the University of Rochester School of Medicine and Dentistry.

Dr. Hopke is a past Chair of EPA’s Clean Air Scientific Advisory Committee (CASAC), and has served on the EPA Science Advisory Board (SAB). Professor Hopke is a Past President of the American Association for Aerosol Research (AAAR), and was a member of the more than a dozen National Research Council committees. He is a member of the NRC’s Board of Environmental Studies and Toxicology.  He is a fellow of the International Aerosol Research Assembly, the American Association for the Advancement of Science and the American Association for Aerosol Research.  He is an elected member of the International Statistics Institute and was the recipient of the Eastern Analytical Symposium Award in Chemometrics and the Chemometrics in Analytical Chemistry Conference Lifetime Achievement Award. He is also a recipient of the David Sinclair Award of the AAAR. He served as a Jefferson Science Fellow at the U.S. Department of State during the 2008-09 academic year. Professor Hopke received his B.S. in Chemistry from Trinity College (Hartford) and his M.A. and Ph.D. degrees in chemistry from Princeton University. After a post-doctoral appointment at M.I.T. and four years as an assistant professor at the State University College at Fredonia, NY, Dr. Hopke joined the University of Illinois at Urbana-Champaign, rising to the rank of professor of environmental chemistry, and subsequently came to Clarkson in 1989 as the first Robert A. Plane Professor with a principal appointment in the Department of Chemistry. He moved his principal appointment to the Department of Chemical and Biomolecular Engineering in 2000.

In 2002, he became the Clarkson Professor and Director of CARES.  On July 1, 2010, he became Director of ISE that houses Clarkson’s undergraduate and graduate environmental science degree programs as well as managing its sustainability initiatives. In May 2016 he moved to emeritus status.  In 2017, he moved to Rochester, NY to work at the University of Rochester.

Reference

Mohammad Arifur Rahman, Stefania Squizzato, Richard Luscombe-Mills, Patrick Curran, and Philip K. Hopke. Continuous Ozonolysis Process to Produce Non-CO Off-Gassing Wood Pellets. Energy Fuels, volume 31 (2017), pages 8228−8234.

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