Search results for: inter-seasonal heat storage

Authors: Selma Bouasria, Mahi Abdelkader, Abbès Azzi, Herouz Keltoum

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This paper reports concept was used into the computational fluid dynamics (CFD) code cfx through user-defined functions to assess ventilation efficiency inside (forced-ventilation local). CFX is a simulation tool which uses powerful computer and applied mathematics, to model fluid flow situations for the prediction of heat, mass and momentum transfer and optimal design in various heat transfer and fluid flow processes to evaluate thermal comfort in a room ventilated (highly-glazed). The quality of the solutions obtained from CFD simulations is an effective tool for predicting the behavior and performance indoor thermo-aéraulique comfort.

Keywords: ventilation, thermal comfort, CFD, indoor environment, solar air heater

Procedia PDF Downloads 634

Authors: Zhdanova A. O., Volkov R. S., Kuznetsov G. V., Strizhak P. A.

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Fires in different types of facilities are a serious problem worldwide.It is still an unaccomplished science and technology objective to establish the minimum number and type of sensors in automatic systems of compartment fire suppression which would turn the fire-extinguishing agent spraying on and off in real time depending on the state of the fire, minimize the amount of agent applied, delay time in fire suppression and system response, as well as the time of combustion suppression. Based on the results of experimental studies, the conclusion was made that it is reasonable to use a gas analysis system and heat sensors (in the event of their prior activation) to determine the effectiveness of fire suppression (fire-extinguishing composition interacts with the fire). Thus, the concentration of CO in the interaction of the firefighting liquid with the fire increases to 0.7–1.2%, which indicates a slowdown in the flame combustion, and heat sensors stop responding at a gas medium temperature below 80 ºC, which shows a gradual decrease in the heat release from the fire. The evidence from this study suggests that the information received from the video recording equipment (video camera) should be used in real time as an additional parameter confirming fire suppression. Research was supported by Russian Science Foundation (project No 21-19-00009, https://rscf.ru/en/project/21-19-00009/).

Keywords: compartment fires, fire suppression, continuous control of fire behavior, feedback systems

Procedia PDF Downloads 129

Authors: Youssef Wardeh, Elias Kinab, Pierre Rahme, Gilles Escadeillas, Stephane Ginestet

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Urban heat islands designate a local phenomenon that appears in high density cities. This results in a rise ofambient temperature in the urban area compared to the neighboring rural area. Solar radiation plays an important role in this phenomenon since it is partially absorbed by the materials, especially roads and parking lots. Cool pavements constitute an innovative and promising technique to mitigate urban heat islands. The cool pavements studied in this work allow to limit the increase of the surface temperature, thanks to evaporation of the water conducted through capillary pores, from the humidified base to the surface exposed to solar radiation. However, the performance or the cooling capacity of a pavement sometimes remained difficult to characterize. In this work, a new definition of the cooling capacity of a pavement is presented, and a correlation between the latter and the hydrothermal properties of cool pavements is revealed. Firstly, several porous concrete pavements were characterized through their hydrothermal properties, which can be related to the cooling effect, such as albedo, thermal conductivity, water absorption, etc. Secondly, these pavements initially saturated and continuously supplied with water through their bases, were exposed to external solar radiation during three sunny summer days, and their surface temperatures were measured. For draining pavements, a strong second-degreepolynomial correlation(R² = 0.945) was found between the cooling capacity and the term, which reflects the interconnection of capillary water to the surface. Moreover, it was noticed that the cooling capacity reaches its maximum for an optimal range of capillary pores for which the capillary rise is stronger than gravity. For non-draining pavements, a good negative linear correlation (R² = 0.828) was obtained between the cooling capacity and the term, which expresses the ability to heat the capillary water by the energystored far from the surface, and, therefore, the dominance of the evaporation process by diffusion. The latest tests showed that this process is, however, likely to be disturbed by the material resistance to the water vapor diffusion.

Keywords: urban heat islands, cool pavement, cooling capacity, hydrothermal properties, evaporation

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Authors: Nassima Sotehi

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This article presents experimental and numerical results concerning the thermal properties of the porous materials used as heat insulator in the buildings sector. Initially, the thermal conductivity of three types of studied walls (classic concrete, concrete with cork aggregate and polystyrene concrete) was measured in experiments by the method of the boxes. Then a numerical modeling of the heat and mass transfers which occur within porous materials was applied to these walls. This work shows the influence of the presence of water in building materials on their thermophysical properties, as well as influence of the nature of materials and dosage of fibers introduced within these materials on the thermal and mass transfers.

Keywords: modeling, porous media, thermal materials, thermal properties

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Authors: Majid Javanmard

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In this study, the effects of coating with whey protein concentrate (7.5% w/v) alone and/or in combination with rice bran oil (0.2, 0.4, 0.6 g in 100 ml coating solution) and Zataria multiflora extract (1 and 2 μL in 100 ml coating solution) on the quality attributes and egg shelf life were carefully observed and analyzed. Weight loss, Haugh index, yolk index, pH, air cell depth, shell strength and the impact of this coating on the microbial load of the eggs surface were studied at the end of each week (during the 4 weeks of storage in a room environment temperature and humidity). After 4 weeks of storage, it was observed that the weight loss in all of the treated eggs with whey protein concentrate and 0.2 gr of rice bran oil (experimental group) was significantly lower than that of the control group(P < 0/05). With regard to Haugh index and yolk index, egg shelf life increased about 4 weeks compared with the control samples. Haugh Index changes revealed that the coated samples remained at grade A after 3 weeks of storage, while the control samples were relegated from grade AA to B after one week. Haugh and yolk Indices in all coated eggs were more than those of the control group. In the coated groups, Haugh and yolk indices of the coated samples with whey protein concentrate and 0.2 g rice bran oil and with whey protein concentrate and 0.2g of rice bran oil and 1 micro liter of Zataria multiflora extract were more than those of the other coated eggs and the control group eggs. PH values of the control group were higher than those of the coated groups during the storage of the eggs. The shell strength of the coated group was more than that of the control group (uncoated) and in coated samples, whey protein concentrate and 0.2 gr of rice bran oil coated samples had high shell strength. In the other treatments, no significant differences were observed. The depth of the air cell of the coated groups was determined to be less than that of the control group during the storage period. The minimum inhibitory concentration was 1 μL of Zataria multiflora extract. The results showed that 1 μL concentration of Zataria multiflora extract reduces the microbial load of the egg shell surface to 87% and 2 μL reduced total bacterial load to zero. In sensory evaluation, from evaluator point of view, the coated eggs had more overall acceptance than the uncoated group (control), and in the treatment group coated eggs, those containing a low percentage of rice bran oil had higher overall acceptability. In conclusion, coating as a practical and cost effective method can maintain the quality parameters of eggs and lead to durability of supply conditions in addition to the product marketability.

Keywords: edible coating, chicken egg, whey protein concentrate, rice bran oil, Zataria multiflora extract, shelf life

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Authors: Jaehyug Lee, Tae-Ho Song

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Vacuum insulation panel (VIP) can achieve very low thermal conductivity by evacuating its inner space. Heat transfer in the core materials of highly-evacuated VIP occurs by conduction through the solid structure and radiation through the pore. The effect of various scattering modes in combined conduction-radiation in VIP is investigated through numerical analysis. The discrete ordinates interpolation method (DOIM) incorporated with the commercial code FLUENT® is employed. It is found that backward scattering is more effective in reducing the total heat transfer while isotropic scattering is almost identical with pure absorbing/emitting case of the same optical thickness. For a purely scattering medium, the results agree well with additive solution with diffusion approximation, while a modified term is added in the effect of optical thickness to backward scattering is employed. For other scattering phase functions, it is also confirmed that backwardly scattering phase function gives a lower effective thermal conductivity. Thus, the materials with backward scattering properties, with radiation shields are desirable to lower the thermal conductivity of VIPs.

Keywords: combined conduction and radiation, discrete ordinates interpolation method, scattering phase function, vacuum insulation panel

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Authors: Hyuk Sung Yoon, In-Lee Choi, Mohammad Zahirul Islam, Jun Pill Baek, Ho-Min Kang

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The strawberry ‘Maehyang’ cultivated in South Korea has been increased to export to Southeast Asia. The degradation of quality often occurs in strawberries during short export period. Botrytis cinerea has been known to cause major damage to the export strawberries and the disease was caused during shipping and distribution. This study was conducted to find out the sterilized effect of chlorine dioxide(ClO2) gas and high concentration of CO2 gas injection for ‘Maehyang’ strawberry and it was packaged with oxygen transmission rate (OTR) films. The strawberry was harvested at 80% color changed stage and packaged with OTR film and perforated film (control). The treatments were a MAP used by with 20,000 cc·m-2·day·atm OTR film and gas injection in packages. The gas type of ClO2 and CO2 were injected into OTR film packages, and treatments were 6 mg/L ClO2, 15% CO2, and they were combined. The treated strawberries were stored at 3℃ for 30 days. Fresh weight loss rate was less than 1% in all OTR film packages but it was more than 15% in a perforated film treatment that showed severe deterioration of visual quality during storage. Carbon dioxide concentration within a package showed approximately 15% of the maximum CO2 concentration in all treatments except control until the 21st day, it was the tolerated range of maximum CO2 concentration of strawberry in recommended CA or MA conditions. But, it increased to almost 50% on the 30th day. Oxygen concentration showed a decrease down to approximately 0% in all treatments except control for 25 days. Ethylene concentration was shown to be steady until the 17th day, but it quickly increased on the 17th day and dropped down on the final storage day (30th day). All treatments did not show any significant differences in gas treatments. Firmness increased in CO2 (15%) and ClO2 (6mg/L) + CO2 (15%) treatments during storage. It might be the effect of high concentration CO2 known by reducing decay and cell wall degradation. The soluble solid decreased in all treatments during storage. These results were caused to use up the sugar by the increase of respiration during storage. The titratable acidity showed a similarity in all treatments. Incidence of fungi was 0% in CO2 (15%) and ClO2 (6mg/L)+ CO2 (15%), but was more than 20% in a perforated film treatment. Consequently, The result indicates that Chloride Dioxide(ClO2) and high concentration of CO2 inhibited fungi growth. Due to the fact that fresh weight loss rate and incidence of fungi were lower, the ClO2(6mg/L)+ CO2(15%) prove to be most efficient in sterilization. These results suggest that Chloride Dioxide (ClO2) and high concentration of CO2 gas injection treatments were an effective decontamination technique for improving the safety of strawberries.

Keywords: chloride dioxide, high concentration of CO2, modified atmosphere condition, oxygen transmission rate films

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Authors: Dilin Chen, Kang Luo, Jian Wu, Chun Yang, Hongliang Yi

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Electrically driven flows (EDF) systems play an important role in fuel cells, electrochemistry, bioseparation technology, fluid pumping, and microswimmers. The core scientific problem is multifield coupling, the further development of which depends on the exploration of nonlinear instabilities, force competing mechanisms, and energy budgets. In our study, two categories of electrostatic force-dominated phenomena, induced charge electrosmosis (ICEO) and ion conduction pumping are investigated while considering polymer rheological characteristics and heat gradients. With finite volume methods, the thermal modulation strategy of ICEO under the thermal buoyancy force is numerically analyzed, and the electroelastic instability turn associated with polymer addition is extended. The results reveal that the thermal buoyancy forces are sufficient to create typical thermogravitational convection in competition with electroconvective modes. Electroelastic instability tends to be promoted by weak electrical forces, and polymers effectively alter the unstable transition routes. Our letter paves the way for improved mixing and heat transmission in microdevices, as well as insights into the non-Newtonian nature of electrohydrodynamic dynamics.

Keywords: non-Newtonian fluid, electroosmotic flow, electrohydrodynamic, viscoelastic liquids, heat transfer

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Authors: Yayan Harry Yadi, L. Meily Kurniawidjaja

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Work activities for MMH (Manual Material Handling) in the storage of liquid catalyst raw material workstations in chemical industries identify high-risk MSDs (Musculoskeletal Disorders). Their work is often performed frequently requires an awkward body posture, twisting, bending because of physical space limited, cold, slippery, and limited tools for transfer container and weighing the liquid chemistry of the catalyst into the container. This study aims to develop an ergonomic work system design on the transfer and weighing process of liquid catalyst raw materials at the storage warehouse. A triangulation method through an interview, observation, and detail study team with assessing the level of risk work posture and complaints. Work postures were analyzed using the RULA method, through the support of CATIA software. The study concludes that ergonomic design can make reduce 3 levels of risk scores awkward posture. CATIA Software simulation provided a comprehensive solution for a better posture of manual material handling at task weigh. An addition of manual material handling tools such as adjustable conveyors, trolley and modification tools semi-mechanical weighing with techniques based on rule ergonomic design can reduce the hazard of chemical fluid spills.

Keywords: ergonomic design, MSDs, CATIA software, RULA, chemical industry

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Authors: Kay Thi Yar, Khin Mar Lar Tun

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Nowadays, social networks are so popular and widely used in all over the world. In addition, searching personal information of each person and searching connection between them (peoples’ relation in real world) becomes interesting issue in our society. In this paper, we propose a framework with three portions for exploring peoples’ relations from their connected information. The first portion focuses on the Graph database structure to store the connected data of peoples’ information. The second one proposes the graph database searching algorithm, the Modified-SoS-ACO (Sense of Smell-Ant Colony Optimization). The last portion proposes the Deductive Reasoning Algorithm to define two persons’ relationship. This study reveals the proper storage structure for connected information, graph searching algorithm and deductive reasoning algorithm to predict and analyze the personnel relationship from peoples’ relation in their connected information.

Keywords: personnel information, graph storage structure, graph searching algorithm, deductive reasoning algorithm

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Authors: Utsav Swarnkar, Rabi Pathak, Rina Maiti

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This study aims to investigate the thermoregulatory role of sweating by comprehensively analyzing the evaporation process and its thermal cooling impact on local skin temperature at various time intervals. Traditional experimental methods struggle to fully capture these intricate phenomena. Therefore, numerical simulations play a crucial role in assessing sweat production rates and associated thermal cooling. This research utilizes transient computational fluid dynamics (CFD) to enhance our understanding of the evaporative cooling process on human skin. We conducted a simulation employing the k-w SST turbulence model. This simulation includes a scenario where sweat evaporation occurs over the skin surface, and at particular time intervals, temperatures at different locations have been observed and its effect explained. During this study, sweat evaporation was monitored on the skin surface following the commencement of the simulation. Subsequent to the simulation, various observations were made regarding temperature fluctuations at specific points over time intervals. It was noted that points situated closer to the periphery of the droplets exhibited higher levels of heat transfer and lower temperatures, whereas points within the droplets displayed contrasting trends.

Keywords: CFD, sweat, evaporation, multiphase flow, local heat loss

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Authors: Satish Kolli, Adriana Ferancova, David Porter, Jukka Kömi

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Electrochemical impedance spectroscopy (EIS) has been used to detect sensitization in austenitic stainless steels that are heat treated in the temperature regime 600-820 °C to produce different degrees of sensitization in the material. The tests were conducted at five different DC potentials in the transpassive region. The quantitative determination of degree of sensitization has been done using double loop electrochemical potentiokinetic reactivation tests (DL-EPR). The correlation between EIS Nyquist diagrams and DL-EPR degree of sensitization values has been studied. The EIS technique can be used as a qualitative tool in determining the intergranular corrosion in austenitic stainless steels that are heat treated at a given temperature.

Keywords: electrochemical technique, intergranular corrosion, sensitization, stainless steels

Procedia PDF Downloads 182

Authors: Staņislavs Gendelis, Andris Jakovičs, Jānis Ratnieks, Aigars Laizāns, Dāvids Vardanjans

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Dehumidification of biogas at the biomass plants is very important to provide the energy efficient burning of biomethane at the outlet. A few methods are widely used to reduce the water content in biogas, e.g. chiller/heat exchanger based cooling, usage of different adsorbents like PSA, or the combination of such approaches. A quite different method of biogas dehumidification is offered and analyzed in this paper. The main idea is to direct the flow of biogas from the plant around it downwards; thus, creating additional insulation layer. As the temperature in gas shell layer around the plant will decrease from ~ 38°C to 20°C in the summer or even to 0°C in the winter, condensation of water vapor occurs. The water from the bottom of the gas shell can be collected and drain away. In addition, another upward shell layer is created after the condensate drainage place on the outer side to further reducing heat losses. Thus, counterflow biogas heat exchanger is created around the biogas plant. This research work deals with the numerical modelling of biogas flow, taking into account heat exchange and condensation on cold surfaces. Different kinds of boundary conditions (air and ground temperatures in summer/winter) and various physical properties of constructions (insulation between layers, wall thickness) are included in the model to make it more general and useful for different biogas flow conditions. The complexity of this problem is fact, that the temperatures in both channels are conjugated in case of low thermal resistance between layers. MATLAB programming language is used for multiphysical model development, numerical calculations and result visualization. Experimental installation of a biogas plant’s vertical wall with an additional 2 layers of polycarbonate sheets with the controlled gas flow was set up to verify the modelling results. Gas flow at inlet/outlet, temperatures between the layers and humidity were controlled and measured during a number of experiments. Good correlation with modelling results for vertical wall section allows using of developed numerical model for an estimation of parameters for the whole biogas dehumidification system. Numerical modelling of biogas counterflow heat exchanger system placed on the plant’s wall for various cases allows optimizing of thickness for gas layers and insulation layer to ensure necessary dehumidification of the gas under different climatic conditions. Modelling of system’s defined configuration with known conditions helps to predict the temperature and humidity content of the biogas at the outlet.

Keywords: biogas dehumidification, numerical modelling, condensation, biogas plant experimental model

Procedia PDF Downloads 549

Authors: Nikolaos Katsoulas, Sofia Faliagka, Athanasios Sapounas

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Greenhouse ventilation is an effective way to remove the extra heat from the greenhouse through air exchange between inside and outside when outside air temperature is lower. However, in the Mediterranean areas during summer, most of the day, the outside air temperature reaches values above 25 C; and natural ventilation can not remove the excess heat outside the greenhouse. Shade screens and whitewash are major existing measures used to reduce the greenhouse air temperature during summer by reducing the solar radiation entering the greenhouse. However, the greenhouse air temperature is reduced with a cost in radiation reduction. In addition, due to high air temperature values outside the greenhouse, generally, these systems are not sufficient for extracting the excess energy during sunny summer days and therefore, other cooling methods, such as forced ventilation combined with evaporative cooling, are needed. Evaporative cooling by means of pad and fan or fog systems is a common technique to reduce sensible heat load by increasing the latent heat fraction of dissipated energy. In most of the cases, the greenhouse growers, when all the above systems are available, apply both shading and evaporative cooling. If a movable screen is available, then the screen is usually activated when a certain radiation level is reached. It is not clear whether the shading screens should be used over the growth cycle or only during the most sensitive stages when the crops had a low leaf area and the canopy transpiration rate cannot significantly contribute to the greenhouse cooling. Furthermore, it is not clear which is the optimum radiation level that screen must be activated. This work aims to present the microclimate and cucumber crop physiological response and yield observed in two greenhouse compartments equipped with a pad and fan evaporative cooling system and a thermal/shading screen that is activated at different radiation levels: when the outside solar radiation reaches 700 or 900 W/m2. The greenhouse is located in Velestino, in Central Greece and the measurements are performed during the spring -summer period with the outside air temperature during summer reaching values up to 42C.

Keywords: microclimate, shading, screen, pad and fan, cooling

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Authors: Ibrahim S. Seddiek, Nader R. Ammar

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One of the most important equipment that affects the performance of passenger ships is the air conditioning system, which in turn consumes considerable electric loads. In this paper, the waste heat energies of exhaust gases and jacket cooling water of marine diesel engines for these ships are analyzed to be used as heat sources for absorption refrigeration unit (ARU). Economic and environmental analysis of the absorption refrigeration cycle operated with the two heat sources that use lithium bromide as absorbent is carried out. In addition, environmental and economic analysis for the absorption cycle is performed. As a case study, high-speed passenger vessel operating in the Red Sea area has been investigated. The results show that a considerable specific economic benefit could be achieved in case of applying absorption air condition that operates by water cooling system over that operates by main engine exhaust gases. Environmentally, applying ARU machine during cruise will reduce total ship’s fuel consumption by about 104 ton per year. This will result in reducing NOₓ, SOₓ, and CO₂ emissions with cost-effectiveness of 6.99 $/kg, 18.44 $/kg, and 0.117 $/kg, respectively.

Keywords: ship emissions, IMO, lithium bromide-water ARU, analysis, thermodynamic, economic and environmental analysis

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Authors: Mateusz Kudasik, Katarzyna Kozieł

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The work included detailed studies of CO₂/CH₄ exchange on a shale core from the Lewino-1G2 well (Poland) from a depth of 3408 m. The sample permeability coefficients were determined under conditions of confining pressure from 5 MPa to 35 MPa. These studies showed that at a confining pressure of 35 MPa – corresponding to a depth of about 1000 m, the shale core was impermeable in the direction perpendicular to the bedding, and in the direction parallel to the bedding, the sample had very low permeability (k∞=0.001 mD). The sorption tests performed showed low sorption capacities, which amounted to a maximum of 1.28 cm³/g in relation to CO₂ and 0.87 cm³/g to CH₄ at a pressure of 1.4 MPa. The most important study used to assess the possibilities of CO₂ storage and gas recovery from shale rocks were the CO₂/CH₄ exchange experiments, which were carried out under confining pressure conditions of 5 MPa and 30 MPa. These experiments were carried out on a unique apparatus, which makes it possible to apply a confining pressure corresponding to in situ conditions. The obtained results made it possible to carry out a comprehensive balance of gas exchange during the injection of CO₂ into the shale sample, with simultaneous recovery of CH₄. Based on the conducted sorption and gas exchange studies on the core sample under confining pressure conditions, it was found that in situ conditions, at the depths of shale gas occurrence in Poland of 3000-4000 m, where the confining pressure can be about 100 MPa: (i) poorly developed pore structure, (ii) very low permeability, and (iii) low sorption properties, make shale rocks poorly predisposed to the application of CO₂ storage technology with simultaneous recovery of CH₄. Without the stimulation of CO₂/CH₄ exchange rates through fracturing processes, the effectiveness of CO₂-ESGR technology on shale rock is very low. The research presented in this work is extremely important from the point of view of precise assessment of the potential of CO₂-ESGR technology.

Keywords: shale gas, shale rocks, CO₂/CH₄ exchange, permeability, sorption, CO₂, CH₄

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Authors: Emmanuel Ophel Gilbert, Williams Speret

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The control for fluid flow behaviours of viscous fluids and heat transfer occurrences within heated mini-channel is considered. Heat transfer and flow characteristics of different viscous liquids, such as engine oil, automatic transmission fluid, one-half ethylene glycol, and deionized water were numerically analyzed. Some mathematical applications such as Fourier series and Laplace Z-Transforms were employed to ascertain the behaviour-wave like structure of these each viscous fluids. The steady, laminar flow and heat transfer equations are reckoned by the aid of numerical simulation technique. Further, this numerical simulation technique is endorsed by using the accessible practical values in comparison with the anticipated local thermal resistances. However, the roughness of this mini-channel that is one of the physical limitations was also predicted in this study. This affects the frictional factor. When an additive such as tetracycline was introduced in the fluid, the heat input was lowered, and this caused pro rata effect on the minor and major frictional losses, mostly at a very minute Reynolds number circa 60-80. At this ascertained lower value of Reynolds numbers, there exists decrease in the viscosity and minute frictional losses as a result of the temperature of these viscous liquids been increased. It is inferred that the three equations and models are identified which supported the numerical simulation via interpolation and integration of the variables extended to the walls of the mini-channel, yields the utmost reliance for engineering and technology calculations for turbulence impacting jets in the near imminent age. Out of reasoning with a true equation that could support this control for the fluid flow, Navier-stokes equations were found to tangential to this finding. Though, other physical factors with respect to these Navier-stokes equations are required to be checkmated to avoid uncertain turbulence of the fluid flow. This paradox is resolved within the framework of continuum mechanics using the classical slip condition and an iteration scheme via numerical simulation method that takes into account certain terms in the full Navier-Stokes equations. However, this resulted in dropping out in the approximation of certain assumptions. Concrete questions raised in the main body of the work are sightseen further in the appendices.

Keywords: frictional losses, heat transfer, laminar flow, mini-channel, number simulation, Reynolds number, turbulence, viscous fluids

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Authors: Paramita Banerjee, K. R. S. Chandrakumar, G. P. Das

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Bulk MgH2 has drawn much attention for the purpose of hydrogen storage because of its high hydrogen storage capacity (~7.7 wt %) as well as low cost and abundant availability. However, its practical usage has been hindered because of its high hydrogen desorption enthalpy (~0.8 eV/H2 molecule), which results in an undesirable desorption temperature of 3000C at 1 bar H2 pressure. To surmount the limitations of bulk MgH2 for the purpose of hydrogen storage, a detailed first-principles density functional theory (DFT) based study on the structure and stability of neutral (Mgm) and positively charged (Mgm+) Mg nanoclusters of different sizes (m = 2, 4, 8 and 12), as well as their interaction with molecular hydrogen (H2), is reported here. It has been found that due to the absence of d-electrons within the Mg atoms, hydrogen remained in molecular form even after its interaction with neutral and charged Mg nanoclusters. Interestingly, the H2 molecules do not enter into the interstitial positions of the nanoclusters. Rather, they remain on the surface by ornamenting these nanoclusters and forming new structures with a gravimetric density higher than 15 wt %. Our observation is that the inclusion of Grimme’s DFT-D3 dispersion correction in this weakly interacting system has a significant effect on binding of the H2 molecules with these nanoclusters. The dispersion corrected interaction energy (IE) values (0.1-0.14 eV/H2 molecule) fall in the right energy window, that is ideal for hydrogen storage. These IE values are further verified by using high-level coupled-cluster calculations with non-iterative triples corrections i.e. CCSD(T), (which has been considered to be a highly accurate quantum chemical method) and thereby confirming the accuracy of our ‘dispersion correction’ incorporated DFT calculations. The significance of the polarization and dispersion energy in binding of the H2 molecules are confirmed by performing energy decomposition analysis (EDA). A total of 16, 24, 32 and 36 H2 molecules can be attached to the neutral and charged nanoclusters of size m = 2, 4, 8 and 12 respectively. Ab-initio molecular dynamics (AIMD) simulation shows that the outermost H2 molecules are desorbed at a rather low temperature viz. 150 K (-1230C) which is expected. However, complete dehydrogenation of these nanoclusters occur at around 1000C. Most importantly, the host nanoclusters remain stable up to ~500 K (2270C). All these results on the adsorption and desorption of molecular hydrogen with neutral and charged Mg nanocluster systems indicate towards the possibility of reducing the dehydrogenation temperature of bulk MgH2 by designing new Mg-based nano materials which will be able to adsorb molecular hydrogen via this weak Mg-H2 interaction, rather than the strong Mg-H bonding. Notwithstanding the fact that in practical applications, these interactions will be further complicated by the effect of substrates as well as interactions with other clusters, the present study has implications on our fundamental understanding to this problem.

Keywords: density functional theory, DFT, hydrogen storage, molecular dynamics, molecular hydrogen adsorption, nanoclusters, physisorption

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Authors: María Canal-Rodríguez, María Arnaiz, Natalia Rey-Raap, Ana Arenillas, Jon Ajuria

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The constant demand of electrical energy, as well as the increase in environmental concern, lead to the necessity of investing in clean and eco-friendly energy sources that implies the development of enhanced energy storage devices. Li-ion batteries (LIBs) and Electrical double layer capacitors (EDLCs) are the most widespread energy systems. Batteries are able to storage high energy densities contrary to capacitors, which main strength is the high-power density supply and the long cycle life. The combination of both technologies gave rise to Li-ion capacitors (LICs), which offers all these advantages in a single device. This is achieved combining a capacitive, supercapacitor-like positive electrode with a faradaic, battery-like negative electrode. Due to the abundance and affordability, dual carbon-based LICs are nowadays the common technology. Normally, an Active Carbon (AC) is used as the EDLC like electrode, while graphite is the material commonly employed as anode. LICs are potential systems to be used in applications in which high energy and power densities are required, such us kinetic energy recovery systems. Although these devices are already in the market, some drawbacks like the limited power delivered by graphite or the energy limiting nature of AC must be solved to trigger their used. Focusing on the anode, one possibility could be to replace graphite with Hard Carbon (HC). The better rate capability of the latter increases the power performance of the device. Moreover, the disordered carbonaceous structure of HCs enables storage twice the theoretical capacity of graphite. With respect to the cathode, the ACs are characterized for their high volume of micropores, in which the charge is storage. Nevertheless, they normally do not show mesoporous, which are really important mainly at high C-rates as they act as transport channels for the ions to reach the micropores. Usually, the porosity of ACs cannot be tailored, as it strongly depends on the precursor employed to get the final carbon. Moreover, they are not characterized for having a high electrical conductivity, which is an important characteristic to get a good performance in energy storage applications. A possible candidate to substitute ACs are carbon aerogels (CAs). CAs are materials that combine a high porosity with great electrical conductivity, opposite characteristics in carbon materials. Furthermore, its porous properties can be tailored quite accurately according to with the requirements of the application. In the present study, CAs with controlled porosity were obtained from polymerization of resorcinol and formaldehyde by microwave heating. Varying the synthesis conditions, mainly the amount of precursors and pH of the precursor solution, carbons with different textural properties were obtained. The way the porous characteristics affect the performance of the cathode was studied by means of a half-cell configuration. The material with the best performance was evaluated as cathode in a LIC versus a hard carbon as anode. An analogous full LIC made by a high microporous commercial cathode was also assembled for comparison purposes.

Keywords: li-ion capacitors, energy storage, tailored porosity, carbon aerogels

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Authors: Rose-Juliet Anyanwu

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The principal objective of this paper is to investigate whether some sort of phonological processes, such as elision, aspiration, glottalisation, and hardening can be used to account for the behaviour of the glottal fricative (or approximant, as the case may be) ‘h’ in both French and Yoruba. French and Yoruba speakers generally tend to say, for instance ‘ockey’ and ‘amburger’, instead of ‘hockey’ and ‘hamburger’, respectively. Whereas the Yoruba conversely say, for instance ‘hadd’ for ‘add’, ‘heat’ for ‘eat’ on the one hand and ‘ard’ for ‘hard’, ‘eat’ for ‘heat’ on the other hand, on a similar note, it is not quite clear whether the French, however, if not at least in rare instances, would tend to force themselves to pronounce (in any form whatsoever) the h-sound. Recorded sentences containing h-initial as well as vowel-initial words will be used for the investigation. The present paper is meant to contribute to work on aspiration, compensation, elision, and glottalisation, as well as hardening.

Keywords: aspiration, compensation, glottalisation, hardening

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Authors: S. Alemayehu, F. A. Abera, K. M. Ayimut, R. Mahroof, J. Harvey, B. Subramanyam

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The occurrence of mycotoxins in sesame seeds poses a significant threat to food safety and the economy in Ethiopia. This study aimed to determine the levels and occurrence of mycotoxins in on-farm stored sesame seeds in major-growing districts of Ethiopia. A total of 470 sesame seed samples were collected from randomly selected farmers' storage structures in five major-growing districts using purposive sampling techniques. An enzyme-linked immunosorbent assay (ELISA) was used to analyze the collected samples for the presence of four mycotoxins: total aflatoxins (AFT), ochratoxin A (OTA), total fumonisins (FUM), and deoxynivalenol (DON). The study found that all samples contained varying levels of mycotoxins, with AFT and DON being the most prevalent. AFT concentrations in detected samples ranged from 2.5 to 27.8 parts per billion (ppb), with a mean concentration of 13.8 ppb. OTA levels ranged from 5.0 ppb to 9.7 ppb, with a mean level of 7.1 ppb. Total fumonisin concentrations ranged from 300 to 1300 ppb in all samples, with a mean of 800 ppb. DON concentrations ranged from 560 to 700 ppb in the analyzed samples. The majority (96.8%) of the samples were safe from AFT, FUM, and DON mean levels when compared to the Federal Drug Administration maximum limit. AFT-OTA, DON-OTA, AFT-FUM, FUM-DON, and FUM-OTA, respectively, had co-occurrence rates of 44.0, 38.3, 33.8, 30.2, 29.8 and 26.0% for mycotoxins. On average, 37.2% of the sesame samples had fungal infection, and seed germination rates ranged from 66.8% to 91.1%. The Limmu district had higher levels of total aflatoxins, kernel infection, and lower germination rates than other districts. The Wollega variety of sesame had higher kernel infection, total aflatoxins concentration, and lower germination rates than other varieties. Grain age had a statistically significant (p<0.05) effect on both kernel infection and germination. The storage methods used for sesame in major-growing districts of Ethiopia favor mycotoxin-producing fungi. As the levels of mycotoxins in sesame are of public health significance, stakeholders should come together to identify secure and suitable storage technologies to maintain the quantity and quality of sesame at the level of smallholder farmers. This study suggests the need for suitable storage technologies to maintain the quality of sesame and reduce the risk of mycotoxin contamination.

Keywords: districts, seed germination, kernel infection, moisture content, relative humidity, temperature

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Authors: Charmaine Lamiel, Van Hoa Nguyen, Marjorie Baynosa, Jae-Jin Shim

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The depletion of non-renewable sources had led to the continuous development of various energy storage systems in order to cope with the world’s demand in energy. Supercapacitors have attracted considerable attention because they can store more energy than conventional capacitors and have higher power density than batteries. The combination of carbon-based material and metal chalcogenides are now being considered in response to the search for active electrode materials exhibiting high electrochemical performance. In this study, a hierarchical mesoporous carbon sphere@nickel cobalt sulfide (CS@Ni-Co-S) core-shell was synthesized using a simple hydrothermal method. The CS@Ni-Co-S core-shell microstructures exhibited a high capacitance of 724.4 F g−1 at 2 A g−1 in a 6 M KOH electrolyte. Good specific retention of 86.1% and high Coulombic efficiency of 97.9% was obtained after 2000 charge-discharge cycles. The electrode exhibited a high energy density of 58.0 Wh kg−1 (1440 W kg−1) and high power density of 7200 W kg−1 (34.2 Wh kg−1). The reaction involved green synthesis without further sulfurization or post-heat treatment. Through this study, a cost-effective and facile synthesis of CS@Ni-Co-S as an active electrode showed favorable electrochemical performance.

Keywords: carbon sphere, electrochemical, hydrothermal, nickel cobalt sulfide, supercapacitor

Procedia PDF Downloads 236

Authors: Robel Habtemariam

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Globally, wind energy and photovoltaics (PV) solar energy are among the leading renewable energy sources (RES) in terms of installed capacity. In order to increase the contribution of RES to the power supply system, large scale energy integration is required, mainly due to wind energy and PV. In this paper, an investigation has been made on the electrical power supply systems of Taiwan and Greece in order to integrate high level of wind and photovoltaic (PV) to increase the penetration of renewable energy resources. Currently, both countries heavily depend on fossil fuels to meet the demand and to generate adequate electricity. Therefore, this study is carried out to look into the two cases power supply system by developing a methodology that includes major power units. To address the analysis, an approach for simulation of power systems is formulated and applied. The simulation is based on the non-dynamic analysis of the electrical system. This simulation results in calculating the energy contribution of different types of power units; namely the wind, PV, non-flexible and flexible power units. The calculation is done for three different scenarios (2020, 2030, & 2050), where the first two scenarios are based on national targets and scenario 2050 is a reflection of ambitious global targets. By 2030 in Taiwan, the input of the power units is evaluated as 4.3% (wind), 3.7% (PV), 65.2 (non-flexible), 25.3% (flexible), and 1.5% belongs to hydropower plants. In Greece, much higher renewable energy contribution is observed for the same scenario with 21.7% (wind), 14.3% (PV), 38.7% (non-flexible), 14.9% (flexible), and 10.3% (hydro). Moreover, it examines the ability of the power systems to deal with the variable nature of the wind and PV generation. For this reason, an investigation has also been done on the use of the combined wind power with pumped storage systems (WPS) to enable the system to exploit the curtailed wind energy & surplus PV and thus increase the wind and PV installed capacity and replace the peak supply by conventional power units. Results show that the feasibility of pumped storage can be justified in the high scenario (that is the scenario of 2050) of RES integration especially in the case of Greece.

Keywords: large scale energy integration, photovoltaics solar energy, pumped storage systems, renewable energy sources

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Authors: Mulue Girmay Gebreslasie

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Entomopathogenic fungi are naturally safe and eco-friendly biological agents. Their potential of host specificity and ease handling made them appealing options to substitute synthetic pesticides in pest control programs. However, they are highly delicate and unstable under field conditions. Therefore, the current experiment was held to search out persistent fungal strains by defining the relationship between invitro heat tolerance and field persistence. Current results on leaf and soil persistence assay revealed that strains of Metarhizium species, M. pingshaense (F2685), M. pingshaense (MS2) and M. brunneum (F709) exhibit maximum cumulative CFUs count, relative survival rate and least percent of CFUs reductions showed significant difference at 7 days and 28 days post inoculations (dpi) in hot seasons from sampled soils and leaves and in cold season from soil samples. Whereas relative survival of B. brongniartii (TNO6) found significantly higher in cold weather leaf treatment application as compared to hot season and found as persistent as other fungal strains, while higher deterioration of fungal conidia seen with M. pingshaense (MS2). In the current study, strains of Beauveria brongniartii (TNO6) and Cordyceps javanica (Czy-LP) were relatively vulnerable in field condition with utmost colony forming units (CFUs) reduction and least survival rates. Further, the relationship of the two parameters (heat tolerance and field persistence) was seen with strong linear positive correlations elucidated that heat test could be used in selection of field persistent fungal strains for hot season applications.

Keywords: integrated pest management, biopesticides, Insect pathology and microbial control, entomology

Procedia PDF Downloads 99

Authors: Ekaterina Artiukhina, Panagiotis Grammelis

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Torrefaction of biomass pellets is considered as a useful pretreatment technology in order to convert them into a high quality solid biofuel that is more suitable for pyrolysis, gasification, combustion and co-firing applications. In the course of torrefaction the temperature varies across the pellet, and therefore chemical reactions proceed unevenly within the pellet. However, the uniformity of the thermal distribution along the pellet is generally assumed. The torrefaction process of a single cylindrical pellet is modeled here, accounting for heat transfer coupled with chemical kinetics. The drying sub-model was also introduced. The non-stationary process of wood pellet decomposition is described by the system of non-linear partial differential equations over the temperature and mass. The model captures well the main features of the experimental data.

Keywords: torrefaction, biomass pellets, model, heat, mass transfer

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Authors: Hedaya Ali Al Ameri, Alya A. Arabi

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Measuring the level of carbon storage in mangroves’ biomass has a potential impact in the climate change of UAE. Carbon dioxide is one of greenhouse gases. It is considered to be a main reason for global warming. Deforestation is a key source of the increase in carbon dioxide whereas forests such as mangroves assist in removing carbon dioxide from atmosphere by storing them in its biomass and soil. By using Kauffman and Donato methodology, above- and below-ground biomass and carbon stored in UAE’s natural mangroves were quantified. Carbon dioxide equivalent (CO2eq) released to the atmosphere was then estimated in case of mangroves deforestation in the UAE. The results show that the mean total biomass of mangroves in the UAE ranged from 15.75 Mg/ha to 3098.69 Mg/ha. The estimated CO2eq released upon deforestation in the UAE was found to have a minimal effect on the temperature increase and thus global warming.

Keywords: carbon stored in biomass, mangrove deforestation, temperature change, United Arab Emirate

Procedia PDF Downloads 396

Authors: Azhar Ulhaq, Zubair Yameen, Almas Anjum

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Frequency behaviour of self-excited induction generator (SEIG) wind turbines during control mode transition from grid connected to islanded mode is studied in detail. A robust control scheme for frequency regulation based on combined action of STATCOM, energy storage system (ESS) and pitch angle control for wind powered microgrid (MG) is proposed. Suggested STATCOM controller comprises a 3-phase voltage source converter (VSC) that contains insulated gate bipolar transistors (IGBTs) based pulse width modulation (PWM) inverters along with a capacitor bank. Energy storage system control consists of current controlled voltage source converter and battery bank. Both of them acting simultaneously after detection of island compensates for reactive and active power demands, thus regulating frequency at point of common coupling (PCC) and also improves load stability. STATCOM integrates at point of common coupling and ESS is connected to microgrids main bus. Results reveal that proposed control not only stabilizes frequency during transition duration but also minimizes sudden frequency imbalance caused by load variation or wind intermittencies in islanded operation. System is investigated with and without suggested control scheme. The efficacy of proposed strategy has been verified by simulation in MATLAB/Simulink.

Keywords: energy storage system, island, wind, STATCOM, self-excited induction generator, SEIG, transient

Procedia PDF Downloads 154

Authors: Adine Gericke, Jiri Militky, Mohanapriya Venkataraman

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Mohair, obtained from the Angora goat, is a luxury fiber and recognized as one of the best quality natural fibers. Expansion of the use of mohair into technical and functional textile products necessitates the need for a better understanding of how the use of mohair in fabrics will impact on its thermo-physiological comfort related properties. Despite its popularity, very little information is available on the quantification of the thermal and moisture management properties of mohair fabrics. This study investigated the effect of fibrous matter composition and fabric structural parameters on conductive and convective heat transfers to attain more information on the thermal comfort properties of mohair fabrics. Dry heat transfer through textiles may involve conduction through the fibrous phase, radiation through fabric interstices and convection of air within the structure. Factors that play a major role in heat transfer by conduction are fabric areal density (g/m2) and derived quantities such as cover factor and porosity. Convective heat transfer through fabrics is found in environmental conditions where there is wind-flow or the object is moving (e.g. running or walking). The thermal comfort properties of mohair fibers were objectively evaluated firstly in comparison with other textile fibers and secondly in a variety of fabric structures. Two sample sets were developed for this purpose, with fibre content, yarn structure and fabric design as main variables. SEM and microscopic images were obtained to closely examine the physical structures of the fibers and fabrics. Thermal comfort properties such as thermal resistance and thermal conductivity, as well as fabric thickness, were measured on the well-known Alambeta test instrument. Clothing insulation (clo) was calculated from the above. The thermal properties of fabrics under heat convection was evaluated using a laboratory model device developed at the Technical University of Liberec (referred to as the TP2-instrument). The effects of the different variables on fabric thermal comfort properties were analyzed statistically using TIBCO Statistica Software. The results showed that fabric structural properties, specifically sample thickness, played a significant role in determining the thermal comfort properties of the fabrics tested. It was found that regarding thermal resistance related to conductive heat flow, the effect of fiber type was not always statistically significant, probably as a result of the amount of trapped air within the fabric structure. The very low thermal conductivity of air, compared to that of the fibers, had a significant influence on the total conductivity and thermal resistance of the samples. This was confirmed by the high correlation of these factors with sample thickness. Regarding convective heat flow, the most important factor influencing the ability of the fabric to allow dry heat to move through the structure, was again fabric thickness. However, it would be wrong to totally disregard the effect of fiber composition on the thermal resistance of textile fabrics. In this study, the samples containing mohair or mohair/wool were consistently thicker than the others even though weaving parameters were kept constant. This can be ascribed to the physical properties of the mohair fibers that renders it exceptionally well towards trapping air among fibers (in a yarn) as well as among yarns (inside a fabric structure). The thicker structures trap more air to provide higher thermal insulation, but also prevent the free flow of air that allow thermal convection.

Keywords: mohair fabrics, convective heat transfer, thermal comfort properties, thermal resistance

Procedia PDF Downloads 144

Authors: Muhammad Rafi Ullah Khan, Yaodong Guo, Vanee Chonhenchob, Jinjin Pei, Chongxing Huang

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The effect of sodium alginate (1%) based edible coating incorporated natural essential oils; thymol, carvone and carvacrol as antimicrobial agents at different concentrations (0.1, 0.5 and 1.0 %) on the quality changes of fresh-cut pineapple were investigated. Pineapple dipped in distilled water was served as control. After coating, fruit were sealed in a modified atmosphere package (MAP) using high permeable film; and stored at 5 °C. Gas composition in package headspace, color values (L*, a*, b*, C*), TSS, pH, ethanol, browning, and microbial decay were monitored during storage. Oxygen concentration continuously decreased while carbon dioxide concentration inside all packages continuously increased over time. Color parameters (L*, b*, c*) decreased and a* values increased during storage. All essential oils significantly (p ≤ 0.05) prevented microbial growth than control. A significantly higher (p ≤ 0.05) ethanol content was found in the control than in all other treatments. Visible microbial growth, high ethanol, and low color values limited the shelf life to 6 days in control as compared to 9 days in all other treatments. Among all essential oils, thymol at all concentrations maintained the overall quality of the pineapple and could potentially be used commercially in fresh fruit industries for longer storage.

Keywords: essential oils, antibrowning agents, antimicrobial agents, modified atmosphere packaging, microbial decay, pineapple

Procedia PDF Downloads 59

Authors: Mamta Bulla, Vinay Kumar

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The transition to renewable energy sources is essential due to the finite limitations of conventional fossil fuels, which contribute significantly to environmental pollution and greenhouse gas emissions. Traditional energy storage solutions, such as batteries and capacitors, are also hindered by limitations, particularly in capacity, cycle life, and energy density. Conventional supercapacitors, while able to deliver high power, often suffer from low energy density, limiting their efficiency in storing and providing renewable energy consistently. Renewable energy sources, such as solar and wind, produce power intermittently, so efficient energy storage solutions are required to manage this variability. Advanced materials, particularly those with high capacity and long cycle life, are critical to developing supercapacitors capable of effectively storing renewable energy. Among various electrode materials, vanadium pentoxide (V₂O₅) offers high theoretical capacitance, but its poor conductivity and cycling stability limit practical applications. This study explores the hydrothermal synthesis of a V₂O₅-carbon nanotube (CNT) composite to overcome these drawbacks, combining the high capacitance of V₂O₅ with the exceptional conductivity and mechanical stability of CNTs. The resulting V₂O₅-CNT composite demonstrates enhanced electrochemical performance, showing high specific capacitance of 890 F g⁻¹ at 0.1 A g⁻¹ current density, excellent rate capability, and improved cycling stability, making it a promising candidate for next-generation supercapacitors, with significant improvements in energy storage efficiency and durability.

Keywords: cyclability, energy density, nanocomposite, renewable energy, supercapacitor

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