Flat Collector Research Articles

High Throughput Centrifugal Electrospinning of Polyacrylonitrile Nanofibers for Carbon Fiber Nonwovens.

Carbon nanofiber nonwovens are promising materials for electrode or filtration applications; however, their utilization is obviated by a lack of high throughput production methods. In this study, we utilize a highly effective high-throughput method for the fabrication of polyacrylonitrile (PAN) nanofibers as a nonwoven on a dedicated substrate. The method employs rotational-, air pressure- and electrostatic forces to produce fibers from the inner edge of a rotating bell towards a flat collector. We investigate the impact of all above-mentioned forces on the fiber diameter, morphology, and bundling of the carbon-precursor PAN fibers. The interplay of radial forces with collector-facing forces has an influence on the uniformity of fiber deposition. Finally, the obtained PAN nanofibers are converted to carbon nonwovens by thermal treatment.

Energy analysis and economic feasibility of wood dryers integrated with heat recovery unit and solar air heaters in cold and hot climates

In this paper, the energy performance and economic feasibility of conventional wood dryer systems integrated with a heat recovery unit and solar air heaters are numerically investigated. Four different designs of wood dryers, composed of an insulated drying chamber, a heat recovery unit (HRU), a flat plate air collector (FPC), a photovoltaic/thermal air collector (PVT) and an auxiliary heater, are presented and compared. Annual dynamic simulations were carried out using a heat and mass transfer model with realistic meteorological data from two different climatic zones as boundary conditions. The effect of recovering waste heat and integrating each type of solar air heaters on the wood dryer energy consumption are presented and analyzed. Results show that recovering waste heat from conventional wood dryers in cold climate is more beneficial than in hot climate with an annual energy consumption reduction up to 41%. It is also shown that using a combined heat recovery unit and PVT collector improved significantly the energy efficiency of conventional dryers and reduced by about 67.5% and 49.5% the yearly energy consumption in hot and cold climates, respectively. Based on the economic analysis, the use of the HRU is beneficial in both climatic zones with a maximum payback period of 2 years. However, the use of the PVT collector is recommended only for wood dryers in hot climates where the payback period is about 3.5 years.

Improvement of the Solar-Thermal Characteristics of the Flat-Plate Collector Using a Composite Coating

A commercially available matt black paint is used as the primary component of a composite coating for low-temperature flat collector systems. The composite coating is composed of the paint, carbon black powder (CBP) and lithium metal oxide (LMO) powder. The CBP and LMO powders are added on the top of the primary paint to improve the solar-thermal conversion characteristics of the collector. The optical and solar-thermal conversion characteristics of these coatings are investigated by means of optical microscopy, optical spectrophotometry, total reflectance measurement, and the measurement of the maximum collector temperature. Results show that the solar-thermal conversion response (maximum temperature) of the collector plate can be improved with the addition of the CBP and LMO powder at low concentrations. This is been demonstrated and discussed in this report. The coatings prepared in the present work can easily be applied on the collector surface and exhibit competing characteristics to other coatings.

A Selective Solar Absorber for Unconcentrated Solar Thermal Panels

A new Selective Solar Absorber, designed to improve the Sun-to-thermal conversion efficiency at mid temperatures in high vacuum flat thermal collectors, is presented. Efficiency has been evaluated by using analytical formulas and a numerical thermal model. Both results have been experimentally validated using a commercial absorber in a custom experimental set-up. The optimization procedure aimed at obtaining Selective Solar Absorber is presented and discussed in the case of a metal dielectric multilayer based on Cr2O3 and Ti. The importance of adopting a real spectral emissivity curve to estimate high thermal efficiency at high temperatures in a selective solar absorber is outlined. Optimized absorber multilayers can be 10% more efficient than the commercial alternative at 250 °C operating temperatures, reaching 400 °C stagnation temperature without Sun concentration confirming that high vacuum flat thermal collectors can give important contribution to the energy transition from fossil fuels to renewable energy for efficient heat production.

Modeling the Performance of a Flat Solar Collector Based on Cellular Polymeric Materials

Currently, in the field of energy supply of agro-industrial facilities, there is an increasing interest in the development of new structures and engineering systems using solar energy, including flat solar collectors based on cellular polymer materials. Modern solar collectors based on metal absorbers, despite their high efficiency, have a large specific weight, high metal consumption and cost. The use of cellular polymer materials for the manufacture of solar collector absorbers reduces the cost and reduces the weight of the installation. (Research purpose) The research purpose is in conducting a numerical simulation of the performance of a flat solar collector based on cellular polymer materials. (Materials and methods) Authors used analytical methods for mathematical modeling of a flat salt collector based on cellular polymer materials. The article presents a mathematical model of a flat solar collector in the computer program ANSYS Fluent. The distribution contours of temperature and pressure of the coolant in the channels of a flat solar collector were obtained at different values of the coolant flow rate at the inlet. (Results and discussion) The article presents comparison the temperature of the coolant at the output of the solar collector on the flow rate of the coolant obtained analytically and using the developed CFD model. The results of verification of the calculated model of the solar collector showed its adequacy and high convergence of the data obtained using the computer model. (Conclusions) The article presents a design of a flat solar collector based on cellular polymer materials. The developed design of a flat solar collector allows us to reduce the specific weight more than three times and reduce the cost while maintaining high thermal performance.

Research of flat plate solar air collector in drying

Solar drying technology has been widely used in engineering fields such us chemical drying because of its low cost and low pollution advantages. In this review, the structural forms, materials and coatings of the heat-absorbing panels of flat plate solar air collector are classified, and the experimental and theoretical results of the performance level of the solar air flat panel collector are summarized. In indoor tests, the energy efficiency of flat plate solar air collector is 30% to 79%, and the energy efficiency of flat plate solar air collector in drying applications is 28% to 62%.

Comparative study of acrylic flat plate and dome shaped collector for summer and winter solstice conditions

In the presented study, an acrylic flat plate passive daylight collector is compared with the acrylic dome shaped daylight collector for 21st June (summer solstice) and 21st December (winter solstice) day. Daylighting system with both acrylic dome shaped and flat plate collector was designed and simulated using TracePro, an optical designing and simulation tool. A highly reflective light pipe with reflectivity of 95% was utilized as a light transportation device. Collectors are made up of Polymethyl methacrylate (PMMA), boasting higher transmission efficiency, weather resistant and shock resistant properties than glass, easy to manufacture, light weight and cost-effective alternative to glass. Simulations performed for the Chandigarh location showed that the dome shaped collector delivered better results than the flat plate collector.

Experimental study about utilization of MWCNTs and graphene nanoplatelets water-based nanofluids in flat non-concentrating PVT systems

Although the increment the performance of photovoltaic thermal (PVT) systems by using the nanofluids as working fluids have gained the attention of researchers during the last two decades, there is still, a lack in the literature study associated to this application. This study contributes to the investigations and researches of applying the nanofluids to increase the performance of PVT collectors. A flat non-concentrating PVT collector has been designed, constructed and, outdoor tested in Karabuk University, Turkey. The considered working fluids in this study are multiwall carbon nanotubes (MWCNT), and graphene nanoplatelets dispersed in water as a base fluid with a concentration of 0.5 wt.%. The experiments were run with a volume flow rate of 0.5 L per minute for the aforementioned nanofluids and distilled water (as a reference fluid). The study results have shown and revealed that the MWCNT-water nanofluid presented a better performance in terms of eletrical energetic efficiency compared to graphene nanoplatelets-water nanofluid and distilled water, while graphene nanoplatelets-water nanofluid revealed the highest thermal energetic efficiency. Moreover adding thermal unit to photovoltaic module enhanced the total energetic efficiency by 53.4% for distilled water, 57.2% for MWCNT-water, and 63.1% for graphene-water.

Simulation studies on a new innovative design of a hybrid solar distiller MSDH alimented with a thermal and photovoltaic energy

In this paper, we present the structure, the simulation the operation of a multi-stage, hybrid solar desalination system (MSDH), powered by thermal and photovoltaic (PV) (MSDH) energy. The MSDH system consists of a lower basin, eight horizontal stages, a field of four flat thermal collectors with a total area of 8.4 m2, 3 Kw PV panels and solar batteries. During the day the system is heated by thermal energy, and at night by heating resistors, powered by solar batteries. These batteries are charged by the photovoltaic panels during the day. More specifically, during the day and at night, we analyse the temperature of the stages and the production of distilled water according to the solar irradiation intensity and the electric heating power, supplied by the solar batteries. The simulations were carried out in the meteorological conditions of the winter month (February 2020), presenting intensities of irradiance and ambient temperature reaching 824 W/m2 and 23 °C respectively. The results obtained show that during the day the system is heated by the thermal collectors, the temperature of the stages and the quantity of water produced reach 80 °C and 30 Kg respectively. At night, from 6p.m. the system is heated by the electric energy stored in the batteries, the temperature of the stages and the quantity of water produced reach respectively 90 °C and 104 Kg for an electric heating power of 2 Kw. Moreover, when the electric power varies from 1 Kw to 3 Kw the quantity of water produced varies from 92 Kg to 134 Kg. The analysis of these results and their comparison with conventional solar thermal desalination systems shows a clear improvement both in the heating of the stages, by 10%, and in the quantity of water produced by a factor of 3.

Güneş Fırınlarında Yapı Malzemesi Seçimi ve Tasarım Stilinin Fırın Isıl Özelliklerine Etkisinin İncelenmesi

The negative effects of intensive energy consumption in timber drying on costs and environmental pollution have strengthened the tendency to utilize solar energy in recent years. Although drying of timber in flat collector solar furnaces takes more time than conventional drying, energy costs are low and there are no negative environmental effects. In this study, the selection of building materials and design type to be used in the design of solar furnaces was evaluated in terms of thermal properties. Materials with different thermal capacities create different thermal properties in different designs. Therefore, it is possible to control the course of the temperature distribution in the solar timber drying oven throughout the day with the choice of different building materials and design forms.

Performance Analysis of Flat-Plate and V-groove Solar Air Heater Through CFD Simulation

The simplicity of solar flat plate air collector and free availability of solar energy sources attract attention to the optimization of the collector. This study aims to assess the effect of double pass air flow on the performance of flat plate air collectors. The analysis of the performance characteristics of the indirect solar dryer was carried out by CFD simulation with three different smooth, rough and V-grooved surfaces, keeping the lower and lateral collector well insulated and the drying chamber acting as a vertical chimney. The average thermal efficiency of the V-grooved surface, smooth surface, and rough surface is 90%, 78%, and 62% respectively. The total area of the collector is 1.20 × 2.0 = 2.40 m2 with the dimension of drying cabinet width, depth, and height 1200 × 650 × 1000 mm respectively. The pressure drop observed at the entrance to the drying chamber is high in the case of a smooth surface, medium in a rough surface and low in a V-grooved plate which will allow sufficient gas pressure to pass through completely.The air mass flow rate is the most important and effective factor during drying. The humidity of the air, as well as air velocity, is also an important factor in improving the drying rate.

Evaluation studies of a mixed mode solar kiln with phase change material and distributed-type solar kiln

The passive thermal performance of a distributed and mixed-mode model solar kiln was compared in the present study. The two kilns were made of double glazed flat plate thermal collector in which paraffin was used as the thermal storage medium. The range of ambient temperatures and daily radiation during the period when the study was carried out were 18.3–33.2 °C and 11.8–20.9 MJ m-2 respectively. The study revealed a peak cumulative efficiency of 44.3% and 40.7% for distributed kiln and 40.7% for mixed mode type. An average efficiency of 38.8% was obtained in the mixed-mode and 43.0% in the distributed type. The results show that low temperature operations such as drying of agricultural produce can conveniently be carried out with these solar kilns. The use of paraffin in the study ensured that the temperatures of the system were all time higher than the ambient temperature. Hence, when mixed-mode type is intended to be used at sun-sets, it is suggested that the top glazing of the working section should be covered with opaque materials to reduce the thermal loss as a result of the glazing to enhance efficient heat utilization.

Productivity enhancement of solar still with phase change materials and water-absorbing material

Due to the lower productivity of solar still, researchers from all around the world are continually ensuing to improve distillate output. Hence, there are lots of opportunities and scope of research work on the solar still. Solar desalination is the process of purification saline water to get fresh potable water using direct solar energy. Seawater is available in abundance but the process of desalinating the seawater is very expensive due to enormous energy requirements. Over the years direct solar energy is used as one of the cheapest desalination methods to drive the desalination systems which has no environmental impact also. The solar-based desalination system is referred to as solar still. The basin water depth is inversely proportional to the productivity of potable water. The difference between saline water temperature and glass temperature controls the evaporation rate. The water surface area is directly proportional to the distillation rate. The water surface area has been increased by submerging the wicks in the water, the use of porous materials, fins, sponge, etc. Instead of a single flat horizontal collector, the cascade style still gives more useful results in terms of desalination. The use of phase change materials helped further in the overall increase in the distillation rate. In the present short review paper research works done in this decade have been considered and four primary methods like the effect of the finned absorber plate, cotton wick, and phase change material and nanoparticles have been discussed. It will help future research in the area of solar still to provide an economically viable solution for sustainable potable water.

Submicron interlayer for stabilizing thin Li metal powder electrode

The surface area of the lithium metal electrode must be considered when attempting to suppress dendritic growth of lithium metal, as surface area can lower the effective current density. For this reason, lithium metal powder (LiMP) has attracted much attention for use in electrodes because of its higher surface area. However, repeated cycling, even in aging time, leads to delamination of lithium particles from flat metal current collectors and results excess dead lithium particles, even in LiMP electrodes. Herein, this problem is addressed by coating submicron-thickness carbon interlayers on copper current collectors for LiMP electrodes. This thin carbon layer plays important roles in both maintaining the interfacial contact between Cu foil and LiMP particles and lowering overpotential in Li/Li symmetric cells, which leads to improve electrochemical performance in thin LiMP (40 μm) based cell. These enhancements are related to the enlarged surface area, as confirmed by higher adhesion of the electrode after precycling. Furthermore, the carbon materials are also believed to contribute to seeding for efficient lithium nucleation. Thus, thin carbon layers on current collectors can provide simple but powerful enhancements to the electrochemical performance of high-energy-density LMSBs.

Energy metrics assessment of a photovoltaic thermal air collector (PVTAC): a comparison between flat and wavy collector

ABSTRACT In this paper, the performances of two different configurations of the PVT air collector (PVTAC) were studied and compared with respect to three energy matrices: energy payback time, electricity production factor, and life-cycle conversion efficiency. Geometrically, both configurations are similar except one equipped with a flat plate collector (PVTACF) and other with a wavy plate collector (PVTACW). An experimental investigation was performed for both the models, located at Silchar (Latitude: 24.8333° N and Longitude: 92.7789° E) over a period of 1 year (May 2017 to April 2018). Initially, airflow velocity was varied between 1–3 m/s and ideal airflow velocity (2.5 m/s) was identified. The yearly energetic and exergetic performance was studied and presented. The overall annual energy and exergy of the PVTACW were achieved by 8.2% and 2.3% higher than the PVTACF. The energy payback time, electricity production factor, and life-cycle conversion efficiency of the PVTACW were also achieved better than the PVTACF. The study provides useful information on the energetic performance and environmental impact of the PVTAC system under North-East Indian climatic conditions.

The mechanism of the controlled deposition of electrospun fibers

AbstractThe controlled deposition of electrospun fibers means that the electrospun fibers can be collected in a limited and specified area and can present better applications in the fields of medical treatment, garment making, and 3D printing. In order to study the mechanism of the controlled deposition of electrospun fibers, simulation and experimental methods were used. Specifically, in the electrospinning experiment, circular copper sheets of different diameters were used as collectors. The effect of different collector areas on the morphology of fiber deposition was discussed. The electric field distribution of electrospinning with different specifications of collectors was simulated correspondingly. The experimental results show that, as compared to the traditional large flat collector, the area where the electrospun fibers are deposited is significantly reduced when a smaller circular copper plate was used as a collector. The smaller the area of the collector, the more the fibers tend to deposit at the center area of the collector, and the more likely the morphology of the product formed by the fiber deposition to exhibit a center protrusion shape. The controlled deposition of the electrospun fiber technology can provide more opportunities for the application of the electrospinning technology.

Effect of secondary reflector on solar flux intensity and uniformity of a Fresnel concentrator

Nowadays, consumption of renewable energies such as solar energies is increasing. Electricity in solar systems is produced using either photovoltaics or concentrated solar power (CSP) systems. Therefore, concentrating technologies are key parts of CSP systems. The lower cost of linear Fresnel collectors makes them attractive for electricity production and thermal energy applications. However, due to partly losing the reflected rays, their optical efficiency is low. By installing a secondary reflector above the absorber tube of Fresnel collectors, lost rays are mostly redirected toward the absorber tube and a higher optical efficiency is achieved. The geometry and configuration of secondary reflectors have an intense influence on the optical efficiency. Therefore, there is a need to determine the most appropriate shape and configuration of secondary reflectors. In this study, four different types and orientations of secondary reflectors including circular, flat, few segmented, and parabolic were investigated and compared optically. All the geometric parameters were optimized for each case individually. To calculate the solar flux intensity and uniformity on the absorber tube, a ray-tracing method was implemented using a mathematical code that was developed based on MATLAB software. All the secondary reflectors were simulated in the code, with variable geometrical parameters. A wide range of geometrical parameters were investigated to obtain the most efficient geometry of every secondary reflector design in flux intensity and flux uniformity in comparison with the other cases. The results showed that few flat segmented collectors increase the flux to 87.9%. In addition, the highest uniformity of solar flux was obtained by using the circular and parabolic secondary reflectors. Considering the manufacturing cost as an important parameter, the flat reflector was the favorable one from the flux quantity point of view. Finally, if all the three criteria, i.e., flux quantity, its distribution, and manufacturing cost, were essential to be considered, the flat reflector might be chosen as the most appropriate secondary reflector.

Design tools for patient specific and highly controlled melt electrowritten scaffolds

Melt electrowriting (MEW) has grown in popularity in biofabrication research due to its ability to fabricate complex, high-precision networks of fibres. These fibres can mimic the morphology of a natural extracellular matrix, enabling tissue analogues for transplantation or personalised drug screening. To date, MEW has employed two different collector-plate modalities for the fabrication of constructs. Flat collector plates, typical of traditional 3D printing methods, allow for the layer-by-layer fabrication of 2D structures into complex 3D structures. Alternatively, rotating mandrels can be used for the creation of tubular scaffolds. However, unlike other additive manufacturing techniques that can immediately start and stop the extrusion of material during printing, MEW instead requires a continuous flow of polymer. Consequently, conventional g-code control software packages are unsuitable. To overcome this challenge, a suite of customised pattern generation software tools have been developed to enable the design of MEW scaffolds with highly-controlled geometry, including crosshatch, gradient porosity, tubular, and patient-specific configurations. The high level of design control using this approach enables the production of scaffolds with highly adaptable mechanical properties, as well as the potential to influence biological properties for cell attachment and proliferation.

EXPERIMENTAL STUDY OF SOLAR AIR HEATER USING OF PHOTOVOLTAIC CELLS

In this paper, we are studying about solar air heater. The solar air heater are consisting the several component such as flat glass, collector, D.C. fan, photovoltaic cells and electrical storage system. In this study we are achieving the various type of outlet temperature with the help of D.C. fan and various Mass air flow rate using of simple absorber trays forced convection.

Experimental study on the performance of flat air collector with reticulated endothermic body

Because the flat air collector is simple in structure, reliable in operation, and resistant to cold and frost, it is more suitable for applications such as building heating. This paper presents a flat air collector with a mesh heat sink, and analyzes the effects of air flow, temperature difference between inlet and outlet, and wire mesh density on the heat collection efficiency of the collector. The results show that when the pore density is fixed, the heat collection efficiency increases with the increase of air flow rate, which is 10% higher than that of natural convection when the air flow rate is maximum; when the air flow rate is fixed, the heat collection efficiency increases with the increase of the pore density and the temperature difference between the inlet and outlet, which can be increased by 10% -20%.