Renewable Energy Global Innovations features: Experimental study of the functionality of a semisubmersible wind turbine combined with flap-type Wave Energy Converters

Significance Statement

Offshore renewable energy systems, namely Floating Wind Turbines (FWTs) and Wave Energy Converters (WECs), are expected to contribute significantly to reach the sustainable energy targets in the world in an efficient manner.

It might be beneficial to combine offshore renewable energy systems of different technologies into one facility. This in turn implies new design, research and technological challenges. Novel and reliable combined energy systems should be developed, satisfying functionality (high energy effectiveness), survivability and endurance requirements, but at the same time at low costs. High fidelity computational tools for the integrated dynamic analysis of these solutions should be developed to assess the concepts, while appropriate laboratory experiments for demonstrating the potential and validating the developed numerical models should be conducted.

In the EU project MARINA Platform three combined concepts have been selected and studied both numerically and experimentally under operational and survival conditions. One of the selected concepts is the Semisubmersible wind energy and Flap-type wave energy Converter (SFC) developed at the Centre for Ships and Offshore Structures (CeSOS). The SFC concept  consists of a FWT of a braceless semisubmersible platform type, a 5 MW wind turbine placed on the central column of the platform, three fully submerged rotating flap-type WECs hinged at the pontoons of the semisubmersible and three catenary mooring lines for station keeping.

The functionality and survivability of the SFC concept has been examined experimentally in operational and extreme environmental conditions and the measured responses are compared with predictions obtained by a numerical analysis model. The tests were performed in the Hydrodynamic and Ocean Engineering Tank in Ecole Centrale de Nantes, France.

The laboratory model of the SFC was built in an 1:50 scale. The Power Take-Off system of each of the WECs was modelled using a linear mechanical rotary damper that provides a constant damping force. The wind turbine rotor is modelled with a redesigned small-scale rotor that was driven by a motor to rotate during the experiments and produces an equivalent thrust force in model scale.

Different test conditions have been considered in order to study the responses of the SFC in operational and extreme conditions. Quasi-static, motion decay, regular and irregular waves without and with aligned wind excitation tests have been conducted.

The responses measured during the experiments were compared with numerical predictions obtained by a fully coupled multibody numerical analysis model (Simo-Riflex-Aerodyn). The responses considered are the motions of the semisubmersible platform, produced power by one flap-type WEC, tension of mooring lines, internal loads of the arms that connect the rotating flap with the pontoon of the semisubmersible platform, acceleration of the nacelle and bending moment in wind turbines tower base. A very good agreement between experimental and numerical results is observed for the motions of the semisubmersible platform, rotation of WECs and internal loads of different parts of SFC (e.g. mooring lines, arms of WEC, tower of wind turbine) highlighting the accuracy of the numerical methods that were used. The combined operation of the WECs does not affect the acceleration of nacelle, the tower base bending moment and the tension of the mooring lines, while insignificantly affects the motions of the platform.

The validated results that are obtained confirm the good performance of the SFC concept in extreme environmental conditions and its survivability without the observation of strong nonlinear hydrodynamic phenomena. An indication about the relative contribution of the power from flap-type WECs for selected wind and wave environmental conditions is concluded. It is both experimentally and numerically justified that combining the flap-type WECs with the FWT has an insignificant effect on the wind power production but increases the total power production by 3~5% for the selected facility layout and environmental conditions. The functionality and survivability of the combined SFC concept was demonstrated. However, a further study to maximize the produced power by means of geometrical optimization of the flap-type WECs and an appropriate control scheme for the operation of the PTO configuration is required in the years to come.

The present studies serve towards demonstrating the feasibility of combined wind/wave energy systems and their future potential.

Journal References

Michailides C, Gao Z and Moan T. Experimental Study of the Functionality of a Semisubmersible Wind Turbine Combined with Flap-Type Wave Energy Converters, Renewable Energy, Volume 93, 2016, Pages 675-690.

Michailides C, Gao Z and Moan T. Experimental and numerical study of the response of the offshore combined wind/wave energy concept SFC in extreme environmental conditions, Marine Structures, Volume 50, 2016 Pages 35-54.

Centre for Ships and Ocean Structures (CeSOS), Centre for Autonomous Marine Operations and Systems (AMOS), Department of Marine Technology, Norwegian University of Science and Technology (NTNU), Otto Nielsens vei 10, NO-7491, Trondheim, Norway.

Figure Legend: Different views of the physical model of SFC during experiments.

About The Author

Constantine Michailides, senior lecturer, holds a BSc, MSc and PhD in Civil Engineering from Aristotle University of Thessaloniki, Greece. In the period of May 2013 – Dec. 2015, he was postdoctoral fellow in CeSOS and AMOS at NTNU mainly working on experimental and numerical investigation of the SFC concept as well as numerical analysis of floating submerged road tunnels. In January 2016 he joined Liverpool John Moores University, UK as a Senior Lecturer.

Constantine is performing research on numerical analysis, experimental testing and structural-field monitoring of offshore and coastal structures and systems. Constantine is a member of research/professional bodies in marine and offshore engineering technology (e.g. ISOPE, ISSC) and member of the Physical Sciences Research Council (EPSRC) Peer Review Associate College.

 

About The Author

Dr. Zhen Gao is a professor of marine structures at the Department of Marine Technology, NTNU since 2015. His main research areas cover coupled dynamic analysis of offshore renewable energy devices (including offshore wind turbines, both bottom-fixed and floating, wave energy converters, floating tidal turbines and combined concepts); marine operations related to installation and maintenance for offshore renewable energy devices.

He is a member of the Specialist Committee V.4 Offshore Renewable Energy in the International Ship and Offshore Structures Congress (ISSC) for 2009-2012 (committee member) and 2012-2015, 2015-2018 (committee chair). He has participated and is now participating in several research projects and education programs on offshore renewable energy, including EU FP7 MARINA Platform Project (2010-2014) and EWEM (European Wind Energy Master) Program (2012- ).

 

About The Author

Dr. Torgeir Moan has been Professor of Marine Technology at NTNU since 1977, has e.g. been Director of CeSOS in the period 2002-2013 and is currently senior adviser of AMOS. Professor Moan’s main disciplines are structural analysis and design and he has carried out research as well as engineering design and analyses of innovative concepts of high speed vessels, LNG and FPSO ships, oil and gas platforms, floating bridges as well as offshore wind turbines and wave energy converters.

He has delivered several keynote lectures at major conferences and received several international awards. He has been elected Fellow of several Scientific Academies and professional societies.

 

Journal Reference

Constantine Michailides^, , Zhen Gao , Torgeir Moan. Experimental study of the functionality of a semisubmersible wind turbine combined with flap-type Wave Energy Converters. Renewable Energy, Volume 93, 2016, Pages 675–690.

Centre for Ships and Ocean Structures (CeSOS), Centre for Autonomous Marine Operations and Systems (AMOS), Department of Marine Technology, Norwegian University of Science and Technology (NTNU), Otto Nielsens vei 10, NO-7491, Trondheim, Norway.

 

 

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Renewable Energy Global Innovations features: Experimental verification of a floating ocean-current turbine with a single rotor for use in Kuroshio currents

Significance Statement

Most promising source of sustainable energy is ocean currents as the flow of water provides frequent and predictable energy. Ocean currents have excellent potential towards future renewable energy resources. There are various oceanic energy forms such as wave, marine currents, tidal currents, and thermal energy. In contrast the research and development are technically challenging and potentially expensive.

The Kuroshio current is a stout ocean current in the western North Pacific Ocean which tide steadily closer the Japanese seaside. This current was forenamed as an energy resource with only small fluctuations in flow, regardless of the time of day or the season and flow is almost 500 meter deep and 100 kilometer wide with a flow speed of 1 to 1.5 m/s. This materializes to be a fain slow flow, merely sufficient for generating electricity because the density of water is 800 times higher than that of air. Also Kuroshio current is said to has  power density equivalent to that of a wind flow at 9 to 14 m/s.

Dr. Katsutoshi Shirasawa and colleagues from Okinawa Institute of Science and Technology Graduate University and Hiroshima University in Japan proposed a new ocean-current turbine which was designed with a float at its top and a counterweight at its bottom. Payable to buoyancy and gravity, the turbine maintains a stable position. Ocean-current turbine has many advantages for power production which includes stability, availability of large water flow, predictability of flow speeds and paths and no visual impact.

The research team experimented by attaching the turbine with a strut to a small fishing boat and towed to simulate an ocean current. Before towing, part of the float was slightly above the sea surface. The depth of the towing point was two metre below the surface. The tow rope was connected to the float and nacelle. In order for the turbine to operate in water, the rope connected to the float had a forward-bent posture. The output cable from the electric generator was connected to a resistive load on the boat. The electrical output was rectified from three-phase alternating current  to direct current. The voltage and current of the load were then measured to determine output power

The authors study depicted the owing experiments bring to vindicate the float and counterweight configuration off and also to show that the results bear hydrostatic stability and electric power generation for the proposed turbine out. The ocean current turbine was operated within the flow to convert the kinetic energy of an ocean current into electricity.

After several experiments, they proposed a new marine current turbine with high hydrostatic stability. The rotor torque developed when the turbine was operated in the middle layer of machine current should be cancelled. Hence, they employed a turbine with a float at its top and a weight at its bottom. Thereby the kinetic energy of currents at sea is harnessed by the proposed marine current turbine to achieve stable power generation. Lately, optimization of the entire turbine system will be analysed using computational fluid dynamics.  

About The Author

Dr. Katsutoshi Shirasawa is a staff scientist of the Okinawa Institute of Science and Technology Graduate University (OIST).

He received his PhD from the Hiroshima University in 2004. His thesis focused on the polarization control using insertion device in soft X-ray region. After graduation, he joined the Japanese X-ray Free Electron Laser project.

In 2012, he joined the OIST and started R&D work of an ocean-current turbine.

His research is focused on harnessing the power of the ocean currents as a sustainable energy resource.  

Journal Reference

Renewable Energy, Volume 91, June 2016, Pages 189–195.

Katsutoshi Shirasawa ¹, Kohei Tokunaga², Hidetsugu Iwashita², Tsumoru Shintake¹, Experimental verification of a floating ocean-current turbine with a single rotor for use in Kuroshio currents, Renewable Energy, Volume 91, 2016, Pages 189–195.

Show Affiliations

1. Okinawa Institute of Science and Technology Graduate University, Onna, Okinawa 904-0495, Japan.
2. Graduate School of Engineering, Hiroshima University, 1-4-1 Kagamiyama, Higashi-Hiroshima, Hiroshima 739-8527, Japan.

 

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Renewable Energy Global Innovations features: Plasma-Induced Polyaniline Grafted on Carbon Nanotube-embedded Carbon Nanofibers for High-Performance Supercapacitors

Significance Statement

Supercapacitor is a high-capacity electrochemical capacitor with capacitance values much higher than other capacitors that bridge the gap between electrolytic capacitors and rechargeable batteries.

Professor Chuh-Yung Chen and his student Wei-Min Chang from National Cheng Kung University, Taiwan with Professor Cheng-Chien Wang from Southern Taiwan University of Science and Technology proposed a method for grafting polyaniline PANi onto carbon nanofiber (CNF) which contented carbon nanotube grafted maleic acid (CNT-MA) by plasma to generate a high-performance supercapacitor. The work appeared in the peer-reviewed Journal, Electrochimica Acta.

Conducting polymers are commonly used materials for supercapacitor applications due to it good intrinsic conductivity, light weight and low cost compared to transition metal oxides, explained the primary author, Wei-Min Chang. Conducting polymers can be classified as pseudocapacitors, which store energy by reversible faradic reaction, the pseudocapacitor has higher capacitance than an electric double layer capacitor with the same electrode surface. According to the authors, pseudocapacitor make use of the whole electrode on the molecular level to absorbed and desorbed ions during oxidation and reduction process. The pseudocapacitor has been developed through extensive and intensive research, and conducting polymers have been used as active materials for high energy density applications.

 Polyaniline is a representative conducting polymer for supercapacitance research because the entire volume of PANi can conduct the redox reaction and energy storage to obtain high capacitance. The capacitance performance of PANi/carbon materials depends on the interfacial interaction between PANi and the carbon material. Literature shows that, fabricated PANi-grafted CNF by three-step chemical modification of the CNF produces a strong interfacial forces, make charge transfer faster and successfully reduced the interfacial resistance, thereby enhancing the capacitance and improved cyclability. This method was found to be too complex to commercialize. The researchers came up with a one-step, modified plasma technique to graft PANi onto the surface of the CNT-MA/CNF with chemical bonding.

The fabrication of CNF from electrospun polyacrylonitrile nanofiber at low carbonization temperature is suspected to increase the capacitance because more nitrogen groups are retained on the large surface area, explained the research team. The high retain nitrogen groups also can increase the wettability and electrochemical properties in aqueous solution. At this study, the contact angle of the CNF was 33.20 and PANi-P-1.0 was increasing to 62.50 due to the surface of CNT-MA/CNF grafted by PANi which was investigated by the Wilhelmy plate method. Both electrodes are suitable for supercapacitor with aqueous electrolyte.

At low carbonization, the low conductivity limited the performance of CNF as the electrode of the supercapacitor at low carbonization temperature. Therefore, the CNT-MA was added into CNF to improve the conductivity. This high conductivity CNT-MA/CNF was used to graft PANi by plasma modification to fabricate high-performance electrodes.

A one-step method for grafting PANi onto CNT-MA/CNF by plasma was successfully developed and generated a high-performance supercapacitor(606 F/g) with excellent cyclability(100%, 1000 cycles) as proposed by the researchers.

The research team confirmed that the unique structure of the PANiP-1.0 can be employed in equipment with high energy and power applications and that the PANiP-1.0 had good long-term stability.   

About The Author

Prof.  Chuh-Yung Chen is Distinguished Professor in the Department of Chemical Engineering at National Cheng Kung University, Taiwan. His researches are focused on (1) Polymer Science and Engineering:   Living Free-Radical Polymerization; Nano-Composite Polymer Materials (LDH-PMMA, LDH-Epoxy, DH-Polyimide, Clay-Nylon, Clay-PET, Clay-TPU); Impact Polymer Materials. (2) Liquid Crystal Display (LCD): Back-Light Module-Design of Diffusion Particles. (3) Nano-Technology: Design of Molecule Template; Design of Nano-particles; Design of Dispersion Agents for Nano-Particles;  Nano-composite materials. (4) Plasma Technology: Plasma Treatment of CNT; Plasma Treatment of Polymer Surface. (5) Membrane Separation: Prevaporization of Alcohol/Water; Bipolar Membrane for Hydrogen Generation. (6) Design of Polymer Catalyst: Synthesis of Peroxides. (7) Design of Electrolyte Materials for Dye-Sensitive Solar Cell, Li-Battery and Fuel Cell. (8) Bio-Plastics: Synthesis and Application of Polyoxalate and PLA. (9) Flexible Conductive Transparent Film and photovoltaic film of CIGS. He has published more than 200 articles in international journals.  

About The Author

Prof.  Cheng-Chien Wang is Professor in the Department of Chemical and Materials Engineering at Southern Taiwan University of Science and Technology, Taiwan. His researches are focused on Polymer Chemistry, Chelating Polymer, Organic/Inorganic Nanocomposite, Emulsion polymerization,  Pickering Emulsion polymerization, Polymer Reinforcement/Toughness, Carbon dioxide captures. 

Journal Reference

Wei-Min Chang¹, Cheng-Chien Wang², Chuh-Yung Chen¹, Plasma-Induced Polyaniline Grafted on Carbon Nanotube-embedded Carbon Nanofibers for High-Performance Supercapacitors, Electrochimica Acta 212 (2016) 130–140

Show Affiliations

1.  Department of Chemical Engineering, National Cheng Kung University, Taiwan.
2.  Department of Chemical and Materials Engineering, Southern Taiwan University of Science and Technology, Taiwan.

 

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Renewable Energy Global Innovations features: Tightness and suitability evaluation of abandoned salt caverns served as hydrocarbon energies storage under adverse geological conditions

Significance Statement

The existence of a large number of abandoned underground salt caverns poses seriously potential threats to safety and geological environments. Some of these caverns, defined as abandoned caverns under adverse geological conditions (AGC), are expected to store hydrocarbon energies (mainly natural gas or oil) to reduce the risk of potential disasters and simultaneously to support the national strategic energy reserve of China.

To achieve this target, a series of investigations primarily related with tightness and suitability of the caverns under AGC are initiated in this paper. Laboratory measurements to determine physical and mechanical properties as well as porosity and permeability of bedded salt cores from near target caverns are implemented to determine the petro-mechanical properties and basic parameters for further study.

The results show that the mechanical properties of the bedded rock salts are satisfactory for the cavern’s stability. The mechanical properties of interface between salt and interlayers behave in between those of rock salt and interlayers, and in particular, the interface is not a weak zone. The silty mudstone interlayers have relatively high porosity and permeability, probably due to their low content of clay minerals and the presence of halite-filled cracks. Conditions for evaluating the tightness and suitability of the cavern for storing hydrocarbons are proposed, including “No tensile stress”, “Factor of Safety” and “Threshold of leakage amount”. 3D numerical geomechanical models are developed to indicate how gas seepage evolves around the caverns.

Results show that the permeability of the interlayers is a key factor to influence the gas seepage in the vicinity of the caverns, and interlayers form primary channels for gas migration. By evaluating the fluid seepage around the cavern by the above Conditions, the upper threshold permeability of the interlayers is suggested to be no more than 10^-16 ~ 10^-17 m² to guarantee the tightness when storing natural gas, and no more than 10^-16 m² when storing oil.

This study provides references for alternate uses of abandoned caverns for hydrocarbons storage under adverse geological conditions. 

About The Author

Wei Liu, postdoctoral and assistant researcher at Chongqing University, Chongqing, China. In 2015, he received his Ph.D degree in University of Chinese Academy of Sciences, Wuhan, China.

He is now taking charge of several funds supported by the National Science Foundation (NSF) and China Postdoctoral Science Foundation.

His research areas include rock mechanics, permeability/damage of low permeable rock materials and energy storage technologies. He has published more than 40 papers and served as a reviewer for many journals, such as Energy, Appl Thermal Eng, Environ Earth Science.  

About The Author

Jie Chen, associate professor at Chongqing University, Chongqing, China. In 2012, he received his Ph.D. degree in College of Resource and Environmental Science from Chongqing University, Chongqing, China. In 2013, he stated Postdoctoral researsh at State Key Laboratory of Rock and Soil Mechanics and Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan, China.（jiechen023@cqu.edu.cn）

He has accomplished several projects from National Science Foundation (NSF) and China Postdoctoral Science Foundation.

His research areas include rock mechanics, damage and self-healing of rock materials, and energy storage. He has published more than 60 papers and served as a reviewer for many prestigious journals.  

About The Author

Deyi Jiang, was born on June 13, 1962, in Sichuan, China. He finished his studies at Chongqing University in 1985 and obtained his Ph.D. degree in 2001, in China

He is the Dean of College of Resources and Environmental Science, Chongqing University. Also, He is the Executive Deputy Director of State Key Laboratory of Coal Mine Disaster and Control from 2011 to present.

His research areas include rock mechanics, solution mining disasters control and salt cavern comprehensive utilization. He has published more than 100 articles in international periodicals, many of which in high-ranking journals, and held more than 30 lectures worldwide. Under his guidance, more than 60 master theses and the same number of Ph.D. dissertations have been done.  

Journal Reference

Applied Energy, Volume 178,  2016, Pages 703–720. 

Liu Wei ^1,2,3, Chen Jie^1,2,3 , Jiang Deyi^1,2, Shi Xilin ³, Li Yinping^1,3, J.J.K. Daemen⁴, Yang Chunhe^1,3.

Show Affiliations

1. State Key Laboratory of Coal Mine Disaster and Control, Chongqing University, Chongqing 400044, China.
2. College of Resources and Environmental Sciences, Chongqing University, Chongqing 400044, China.
3. State Key Laboratory of Rock and Soil Mechanics and Engineering, Institute of Rock and Soil Mechanics, Chinese Academy of Sciences, Wuhan 430071, China.
4. Mackay School of Earth Sciences and Engineering, University of Nevada, Reno, NV, USA.

 

 

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Renewable Energy Global Innovations features: Effect of microbial inoculant or molasses on fermentative quality and aerobic stability of sawdust-based spent mushroom substrate

Significance Statement

Rise in feed costs will lead to rise in the production costs of animal based food in future. Hence in future, there will be a new demand for inexpensive feed from underutilized resources. Mushroom growing is a gradually developing eco-friendly activity which generates tonnes of Spent Mushroom Substrate (SMS), a year. SMS are the remains of Mushroom harvest.

In some parts of the world, this residual material is underutilized. This leads to environmental problems such as landfill accumulation and can be a greater nuisance. Hence it is necessary to effectively recycle the residual material. SMS decays rapidly as it has high moisture content and hence it needs to be processed quickly.

Professor Kwak and colleagues from South Korea came up with an effective technique which uses lactic acid in fermentation process. This lactic acid fermentation technique is simple and the process is done under anaerobic condition. In this technique, clostridia growth and other microbial population are suppressed. Lactic acid is efficiently produced by eco-friendly lactic acid bacterial inoculants. These inoculants are safe and non-corrosive to machinery equipment. The ensiling characteristics are determined greatly by the compatibility of the inoculants between its strain and plant biomass.

Many lactic acid bacterial strains are isolated from the ensiled SMS of which Lactobacillus plantarum is identified as the most efficient acidifiers at lactate production. The quality of fermentation of cotton waste-based SMS silage is improved by combining Lactobacillus plantarum with molasses and yeast but there were no reports on saw dust-based SMS. Hence two experiments were performed; one with an objective of selecting the strain with silage quality parameters and other with an objective to study silage conservation characteristics and how it is affected.

The research team took samples of fresh SMS from the biomass and the inoculants suspended in deionized water are sprayed on the material. The inoculants are uniformly applied with constant mixing. A hydraulic press is used to pack the treated SMS into polyvinylchloride silos. The silos are a kept at room temperature for about ten days. After ten days the silos are opened and the contents in it were mixed thoroughly and the samples were taken for chemical and biological analysis.

Compared with those before ensiling, 100% SMS (control) after ensiling showed unstable fermentative properties with high pH (5.2) and little lactic acid production. Compared with the ensiled control, treatments (T1, T2 and T3) resulted in decreased pH, 18–20 times higher concentrations of lactic acid, and greater populations of total bacteria, LAB and yeast . The addition of 5% molasses, 0.5% LAB and 0.5% yeast (T3) to the SMS resulted in the lowest pH (4.25) and the greatest microbial populations. Treatment T3 was selected for a large scale silo study which was ensiled for 10, 20 and 30 d. As in the small-silo study, the T3 treatment showed favorable fermentative and microbial parameters, compared with the control, by decreasing pH and increasing lactic acid concentrations, LAB and yeast populations. The minimum ensiling period was 20 d, when pH was reasonably low and LAB and yeast populations were greatest.

In order to determine the aerobic deterioration, the samples are subjected to aerobic stability test. The extent of aerobic stability varied depending on the ensiling environment. The aerobic stability of the Lactobacillus treated SMS after 28 days of ensiling lasted for 84 hours. They also found that the packing density and the exclusion of oxygen will have an impact on the extent of aerobic stability. Thus, this study identified Lactobacillus plantarum as the best strain for SMS fermentation. In conclusion, molasses and microbial inoculation improved silage quality of SMS.  

 

About The Author

Wan Sup Kwak

Full Professor at Division of Food Bio-science, Konkuk University in Korea.

Received Master and PhD degrees at Virginia Tech, USA in 1990.

Won 2004 yr research award from Journal of Animal Science & Technology, Korea.

Served as a chief-in-editor of Journal of Korean Livestock Facility & Environment.

Presently serve as an editorial board of an international Journal of Research of Animal & Veterinary Science in Pakistan.

Specialize in not only co-product recycling as animal feed of poultry litter, garlic stalk, spent mushroom substrate and other organic waste but also effective use of co-products as ingredient of total mixed ration (TMR) for functional, high quality of beef production.

and start from 2017 a 3 yr-governmental research project in use of fruit and vegetable by-product as feed.  

Journal Reference 

Kim JS¹, Lee YH¹, Kim YI², Ahmadi F¹, Oh YK³, Park JM², Kwak WS⁴. Effect of microbial inoculant ormolasses on fermentative quality and aerobic stability of sawdust-basedspent mushroom substrate, Bioresource Technology, Volume 216, 2016, Pages 188-195.

Show Affiliations

1. Division of Food Bio-science, College of Medical Life Sciences, Konkuk University, Chungju, Chung-Buk, Republic of Korea.
2. Egreen Co. LTD, Icheon, Gyeong-Gi, Republic of Korea.
3. National Institute of Animal Science, RDA, Jeonju, Jeon-Buk, Republic of Korea.
4. Division of Food Bio-science, College of Medical Life Sciences, Konkuk University, Chungju, Chung-Buk, Republic of Korea. Electronic address: wsk@kku.ac.kr.

 

 

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Renewable Energy Global Innovations features: Molecular insights into water vapor absorption by aqueous lithium bromide and lithium bromide/sodium formate solutions

Significance Statement

A commonly used liquid desiccant, lithium bromide faces some shortcomings such as corrosion, crystallization at high concentrations and their need for high energy inputs to regenerate the absorbent.

Molecular dynamic simulations have recently been applied in understanding of molecular driving forces such as vapor pressure and absorption rate that influence performance of liquid desiccants. Despite knowledge provided by molecular dynamic simulations on solution behavior, little efforts have been made on microscale kinetics of liquid desiccants including current ternary working fluids.

Researchers led by Professor Gloria D. Elliott from University of North Carolina at Charlotte, published an article in Applied Thermal Engineering conducted a series of molecular dynamic simulations of the absorption of water vapor into aqueous lithium bromide and lithium bromide /sodium formate mixtures at various temperatures.

The molecular dynamic simulation was able to provide a quasi-static absorption process as lithium bromide solution absorbs water vapor at a nearly constant rate. Large number of water molecules was absorbed by 60wt% lithium bromide solution at a temperature of 443K after a simulation time of 20ns which yielded an approximate absorption rate of 38Kg·m²/s but decreased as temperature decreases. It was also seen that absorption of water molecules increases as concentration of lithium bromide increases at a minimum temperature of 373K.

Analysis on mass density profiles of lithium and bromide ions with water molecules showed a decrease in interfacial thickness layer of lithium bromide solution as its concentration increases when observed at 383K and 408K, but no effect was found with respect to temperature. It was also observed that the interfacial dipoles were most likely to lie in a plane parallel to the interface.

Effects of addition of sodium formate into the LiBr + H₂O system when simulated at a temperature of 373K showed good correlation of density profile of lithium ions Li⁺ to that of formate anion COOH^– in all the mass ratios which maintains local proximity throughout the solution.

“What we found the most interesting was that the strong interaction between Li⁺ and COOH^– created cavities of various sizes that can accommodate water molecules,” said Dr. Lindong Weng, a former postdoctoral researcher in Elliott’s lab and the first author of the study. “Such fascinating morphology of ion placement provides a geometrical explanation for the increase in absorption capacity with added formate.”

The study also found that when the molar ratios of LiBr to NaCOOH are about 1.5:1 and 0.8:1, respectively, Li+-COOH^– clusters size mainly 5< (cluster size: defined as number of lithium ions that can be linked together with each other via COOH^–). This result showed that more addition of sodium formate led to more extended and interwoven lithium and formate ion clusters. The effect of addition of sodium formate also led to a decrease in water vapor absorption rate despite increase in absorption capacity.

The authors successfully optimized the advantages of lithium bromide and lowered crystallization temperature (minimal thermal energy needed via including formate salt). The molecular design and simulation methods presented in this study can aid in improved defined compositions to undergo more detailed experimental studies.  

About The Author

Dr. Gloria D. Elliott

Professor and Associate Chair, Research.
Department of Mechanical Engineering & Engineering Science- University of North Carolina at Charlotte

Dr. Gloria Elliott is the founding Director of the Charlotte Banks Research Initiative, an academic think tank integrating economics, technology, and policy to address logistical challenges in organ and tissue transport, with the aim of accelerating growth in regenerative medicine, transplantation, and the tissue engineering sector.

Dr. Elliott completed post-doctoral training at Harvard Medical School and Massachusetts General Hospital.  She received her BS degree in Applied Chemistry at the University of Waterloo in Canada, and her MS and PhD in Mechanical Engineering from Michigan State University.

Dr. Elliott currently directs the Biostability Lab at the University of North Carolina at Charlotte (UNCC). Her research area is experimental thermodynamics with applications to living systems.  Dr. Elliott’s group has been developing technology and investigating the underlying science of biopreservation, and she holds several patents in this area.  Her research program has included the development of stabilization technologies for biomolecules, viruses, cells, gametes, and tissues, for diagnostic and therapeutic use.

Dr. Elliott has over a decade of experience as a pioneer in engineering education at UNCC, with a focus on training in thermodynamics and energy transport phenomena. She has created numerous new courses with biomedical engineering and energy production themes, and has also been an architect of several new programs, including a Research Experience for Undergraduates program and two separate degree concentrations in Energy Engineering and Biomedical Engineering.  She currently provides academic integrity oversight as a member of the Chancellor’s Advisory Council on Inter-collegiate Athletics, and she has also previously served on the UNCC Academic Integrity Board.

Dr. Elliott currently serves as a scientific advisor to the Organ Preservation Alliance and is a co-organizer of the upcoming Organ Banking Summit.  She is a member of the Bioengineering Technology Advisory Panel for the American Society of Mechanical Engineers. Dr. Elliott’s strategic planning experience also includes service on the executive committee of the Society of Cryobiology.

She currently serves on several research advisory committees at the university, most notably the Standing Committee on Conflicts of Interest and Commitment, the university’s highest research integrity oversight and advisory committee.  

Journal Reference

Lindong Weng ¹, Wei Song^2, ,  Donald J. Jacobs², Gloria D. Elliott¹. Molecular insights into water vapor absorption by aqueous lithium bromide and lithium bromide/sodium formate solutions, Applied Thermal Engineering 102 (2016) 125-133.

Show Affiliations

1. Department of Mechanical Engineering and Engineering Sciences, University of North Carolina at Charlotte, Charlotte, NC 28223, United States.
2. Department of Physics and Optical Science, University of North Carolina at Charlotte, Charlotte, NC 28223, United States.

 

 

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