Circular Absorber Research Articles

Performance Assessment of Hybrid PV/PVT Collectors Incorporating Natural Water-Cooling Circulation

The present work investigates outdoor recitals and characteristics of hybrid PVT collectors and compares using non-cooled Photo-Voltaic (PV) collectors on a clear day at Khamshet, Pune, India. The hybrid PVT is designed, fabricated, and mounted on the terraces of the institute to ensure maximum radiation will fall on PV and PVT collector. The spiral circular thermal absorber is manufactured and placed at the backside of the photovoltaic to lower the surface temperature by extracting heat through water flowing through the absorber. The experimentation is performed at 0.03 kg/sec of water and natural cooling circulation is adopted for experimental work. The uncertainty analysis is also performed to ensure the accuracy of the results. The investigation observed that the PVT collector is superior to the PV system from electrical and thermal efficiency viewpoints. The cutback in PV module temperature was observed in a variation of 8.7-13.7%, which justifies using the water-cooling technique. The maximum electrical and thermal efficiency of 6.93 % and 52.7% were found for PVT collectors while sole maximum electrical efficiency of 5.62 % was found for PV collectors. This study concludes that the PVT collector has better performance characteristics than the PV collector and can be further enhanced using different fluid and thermal absorber designs.

Strong circular dichroism absorbers using chiral metamaterials with circular polarization

We designed and characterized a chiral metamaterial circularly polarized strong circular dichroism absorber with dynamic tuning capabilities using graphene. The synergistic combination of strong circular dichroism and perfect absorption, coupled with the tunability afforded by graphene, positions this absorber as a promising candidate for advanced electromagnetic applications. Employing a frequency-domain solver in electromagnetic simulation software, the impact of parameters such as the thickness of a metal U-ring, a silica dielectric layer, and the polarization angle of incident light on circular dichroism is systematically analyzed. Strong circular dichroism can be achieved by adjusting the misalignment angle of the metal U-ring, reaching a value as high as 0.91. At an incident angle of 60°, left-circularly polarized (LCP) light demonstrates outstanding wide-angle absorption performance, absorbing over 80% in the x-z plane and more than 70% in the y-z plane. Transitioning from circular to linear polarization and changing the tilt angle of the metal U-ring also achieves a 99.99% absorption peak at 1.33 THz. Moreover, in comparison to conventional absorbers, the structure presented in this study offers enhanced controllability of absorption performance through external voltage manipulation. This research not only refines the existing concepts but also introduces novel ideas for the development of tunable chiral optical devices.

Tunable asymmetric square split ring resonator based triple band metamaterial absorber for wireless communication system

This article presents a triple band square split ring with double circular split ring resonator incident angle-insensitive perfect metamaterial absorber. The MMA unit cell was manufactured using a FR4 substrate that had dimensions of 8 mm by 8 mm. With the flexibility of on-design adjusting of the highest absorption frequencies, the suggested MA displays peak absorption of 99.67 %, 99.85 %, and 99.97 % at 2.52 GHz, 6.99 GHz, and 9.28 GHz, correspondingly. The tuning metallic two circular split rings and square split ring resonator provide the possibility of frequency modification throughout three distinct frequency ranges: the first frequency range extends from 2.45 GHz to 2.53 GHz, the second frequency range extends from 6.91 GHz to 7 GHz, and the third frequency range extends from 8.85 GHz to 10.32 GHz. Furthermore, the suggested MA displays near-zero absorption at an oblique incidence angle of up to 45° for both the TE as well as TM modes. The unit cell demonstrates single negative properties, such as an effective medium ratio (EMR) of 14.88 and a quality factor (Q factor) that is more than 30 for both the TM mode as well as the TE mode. An equivalent circuit successfully demonstrated its performance capability, which indicated that it would create an MMA of good quality when using ADS software. A comparison between the measured results of the suggested MMA and the simulated one reveals that there is a significant amount of a similarity between both of them. Because of its easy design within small dimension, wide angular stability, strong absorption, good EMR, and flexibility to frequency tuning is suitable for a wide range of wireless communication system, especially satellite applications like electromagnetic interference reduction, radar systems, imaging, and stealth technology.

Use of machine learning in predicting heat transfer and entropy generation in a flat plate solar collector with twisted tape turbulator and ferrofluid under the influence of an external uniform magnetic field: A numerical study

The flat-plate solar collector is the most common and widely used model of solar collectors. This model of solar collectors is more popular than other solar collectors due to its easy installation and lower cost. It is possible to further reduce the cost and size of these systems by improving their performance. For this purpose, simultaneous application of external uniform magnetic field (MF), water-Fe3O4 ferrofluid, and twisted tape turbulator along with changing the cross-section of the serpentine absorber tube of a collector is proposed in the present research. The outlet temperature of working fluid, pressure drop of working fluid, the rate of thermal energy transferred to the flowing fluid in the collector along with the entropy production rate in the system due to fluid friction and heat transfer were considered as the performance parameters of the system. The effect of cross-section of absorber tube (circular, square, triangular), Reynolds number (Re = 500, 1000, 1500 and 2000), pitch distance of turbulator (δ = 150 mm, 200 mm and 250 mm), ferrofluid volume fraction (σ = 0, 1 %, 2 % and 4 %) and magnetic field intensity (0, 600, 900 and 1200 Gauss) on these parameters was investigated numerically using the finite volume method. In the investigations conducted in the absence of MF, collectors equipped with circular and triangular absorber tubes showed the best and worst thermal performance, respectively, while the lowest and highest total entropy production rate was associated with collectors equipped with circular and rectangular tubes, respectively. Moreover, the escalation in σ from 0 % to 4 % and under the MF effect showed an increase of 0.14 %, 8.62 %, 0.45 %, and 4.55 % in the outlet temperature, pressure drop, useful heat, and thermal entropy generation rate, respectively. While the frictional entropy generation diminished by 8.73 %. In addition, the intensification of MF intensity from 0 G to 1200 G led to enhance the outlet temperature, useful heat, and pressure drop, by almost 0.0014 %, 3.96 %, and 0.013 %, respectively at three different σ values. While total entropy generation rate reduces by 0.195 % as MF intensity increases from 0 G to 1200G. Meanwhile, the results of neural network modeling were presented as two second-order polynomial functions to predict the total entropy generation rate and useful heat under the MF effects.

Numerical analysis of thermo hydro-dynamics behavior of solar flat plate collector with square and V-cut twisted tape inserts

Numerical analysis has been conducted for a solar collector with two circular pipes having semi-circular contact with absorber plate. The tubes are analyzed with and without the inclusion of twisted tape inserts of twist ratio Y = 3 and Y = 4. The comparison between the heat transfer and pressure drop characteristics of a plain tube to that fitted with the twisted tape inserts is done and validated against experimental results with good agreement. Additionally, helical twisted tape is modeled with square- and V-cut to analyze its influence on flow and heat transfer phenomenon. V-cut twisted tape inserts act as turbulence promoters, increasing fluid flow and inducing vortex-like motion. As a result, boundary layer around the absorber plate is disrupted with decrease in stagnation temperature, resulting in better heat transfer and more effective absorption and conversion of solar energy. The Nusselt number, friction factor, and heat transfer coefficient variation with the Reynolds number have been studied for the given heat fluxes. It is found that the Nusselt number of the fluid flowing in the plain tube is increased by 76.44% when the tube is fitted with twisted tape inserts. The pressure drop in the tube is found to increase with the presence of the twisted tapes. The average temperature along the length of the circular tube and absorber plate has also been reported.

Energy Absorption Analysis of Circular Tube of The Foam for High-Speed Train

This paper discusses the outcomes concerning the crushing properties of aluminum foam–filled tubes with a circular cross-section. The review assessed the impact of placing aluminum foam in single- and double-walled circular. A parametric evaluation was performed concerning the circular with the single- and double-walled variants. Validation results were contrasted against the documented experimental data, and a noteworthy alignment was observed. The foam strain rate is vital in regulating the crushing properties of the foam-loaded circular, and this factor must be considered. The outcomes also indicate the interaction between the circular wall and foam core has a varying deformation category and specific energy absorption. Foam loading had a similar effect concerning double-walled circular loads with foam. Moreover, evaluations were performed to determine the impact of core thickness and impact velocity on the crashworthiness performance. Further, it was discovered that a rise in core thickness for double-walled foam-loaded circular enhances crushing characteristics until the walls still interact. Subsequently, any rise in core thickness leads to the response aligning more with the single-walled circular energy absorber of a high-speed train.

Enhancing the performance of water-based PVT collectors with nano-PCM and twisted absorber tubes

The study investigated the thermal performance of a photovoltaic thermal (PVT) collector with a twisted absorber tube and nanoparticle-enhanced phase change material (nano-PCM). The PVT collector consisted of twisted absorber tubes, a container filled with nano-PCM, and a photovoltaic (PV) panel. To assess its efficiency, five different configurations were tested using an indoor solar simulator. The configurations analyzed were as follows: (a) an unenhanced PV panel, (b) PVT with circular absorber tubes (C-PVT), (c) PVT with twisted absorber tubes (T-PVT), (d) C-PVT with nano-PCM (C-PVT-PCM), and (e) T-PVT with nano-PCM (T-PVT-PCM). The thermal, photovoltaic, and combined photovoltaic-thermal efficiencies were evaluated at varying mass flow rates (0.008-0.04kg/s) and a constant solar irradiance of 800W/m2. Among the configurations tested, the T-PVT-PCM configuration demonstrated the highest performance. Specifically, at a mass flow rate of 0.04kg/s, solar irradiance of 800W/m2, and an ambient temperature of 27°C, it achieved photovoltaic, thermal, and combined photovoltaic-thermal efficiencies of 9.46%, 79.40%, and 88.86%, respectively. The utilization of twisted absorber tubes in the design notably improved thermal efficiency by enhancing heat transmission between the liquid and the tube surface. Furthermore, the implementation of T-PVT-PCM led to a significant reduction in surface temperature. Compared to the unenhanced PV panel, it lowered the surface temperature by approximately 30°C, and when compared to C-PVT-PCM, it reduced it by around 10°C. Notably, T-PVT-PCM outperformed the unenhanced PV panel by exhibiting a 34.5% higher photovoltaic efficiency. Overall, the study highlights the performance of the PVT collector with twisted absorber tubes and nanoparticle-enhanced phase change material. The innovative design achieved remarkable thermal efficiency, reduced surface temperatures, and significantly enhanced photovoltaic efficiency compared to traditional configurations. These findings contribute to the development of more efficient and versatile solar energy systems with the potential for broader applications in renewable energy technology.

Nanofluid-based photovoltaic thermal solar collector with nanoparticle-enhanced phase change material (Nano-PCM) and twisted absorber tubes

Photovoltaic thermal (PVT) collectors convert solar energy into thermal and photovoltaic energy. The thermal performance of a PVT collector with a twisted absorber tube and nanoparticle-enhanced phase change material (Nano-PCM) was evaluated. The experiments were aimed to evaluate the photovoltaic, thermal and combination photovoltaic thermal efficiencies using an indoor solar simulator. Circular and twisted absorber tubes with Nano-PCM were evaluated in two designs. The working fluid was water with 0%, 0.3%, and 0.6% volume fractions of SiC nanofluids. The highest photovoltaic, thermal, and combined photovoltaic thermal efficiencies for the PVT-PCM with twisted tube and 0.6% nanofluids were 9.57, 84.74, and 94.31, respectively. The use of twisted absorber tubes with Nano-PCM increased the efficiency of the PVT collector.

Model construction and performance analysis for asymmetric compound parabolic concentrator with circular absorber

Model construction and performance analysis for asymmetric compound parabolic concentrator with circular absorber

Novel Dual-Mode Polarization Insensitive Wide Angular Stable Circular Ring Based Deca-Band Absorber for RCS and EMI Shielding Applications

A simple concentric circular ring resonator-based nonreciprocal deca-band absorber is demonstrated in this article. The design primarily consists of two frequency selective surfaces (FSSs) among one is a compliment to the other printed on either side of the 2.4 mm thin FR-4 dielectric substrate. It exhibits near-unity absorption effectively at ten different resonant frequencies over X-Ka bands with an average absorption efficiency of 94.6%. Surface plasmonic resonances are the reason behind the multiband absorption and are illustrated with current profiles at resonant frequencies. The performance is angular stable for both transverse electric and transverse magnetic oblique incidences up to 60 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">o</sup> . The design is compact with a structural periodicity of 0.210 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${{\boldsymbol{\lambda }}}_{\boldsymbol{o}}$</tex-math></inline-formula> and thickness 0.07 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${{\boldsymbol{\lambda }}}_{\boldsymbol{o}}$</tex-math></inline-formula> , where <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">${{\boldsymbol{\lambda }}}_{\boldsymbol{o}}$</tex-math></inline-formula> is the lowest resonant peak's free-space wavelength. The 20×20 array of the design prototype is fabricated, and the measured results agree with the full-wave analysis. Bistatic radar cross section (RCS) analysis of the proposed absorber is evaluated along with a conventional microstrip patch antenna at <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">X</i> -band. Since the absorber design is based on complementary FSSs, it can also be utilized as a reflector for the not absorbing frequencies. The novelty lies in the utilization of the dual-side of the substrate made this design compact with a greater number of absorption peaks and good angular stability, making it potential for real-time RCS, and electromagnetic interference and shielding applications.

Study and Analysis of Different Absorber Geometry of Compound Parabolic Solar Collector and its Effect on Thermal Efficiency for Heating Water for Sanitary Use

Abstract: This project is focused on carrying out a study of the absorber geometry of the parabolic solar collector compound for heating water for sanitary use, to evaluate the temperature gradient between the inlet and outlet of the water of this concentraDDDtor collector, and the efficiency achieved according to the absorber configuration to later compare it with collectors with a conventional flat absorber surface. The parabola of the reflector of the composite parabolic solar collector was obtained considering the circular absorber, with a concentration ratio of 4 plus 10% of this, to consider a truncation of the reflector, the circular absorber was configured with a small absorber plate of aluminum which has a thermal conductivity of 401 W /mK The values obtained experimentally in the collector were based on the data collected in the field files. It was considered to experience the heating of water on different days with the climatic conditions, cloudy, partially cloudy and sunny, with a totally clear sky. The water heating tests were carried out with two types of geometric configuration of the absorber of the composite parabolic solar collector; circular absorber and configured circular absorber, with which a water outlet temperature of 61 ° C and 76 ° C and a thermal efficiency of 60% respectively were obtained, these results were presented taking into account a climatic condition (sunny day) approximately the same for the two absorber configurations, and with average values of wind speed, ambient temperature and solar radiation.

Heat transfer enhancement of a parabolic trough solar collector using a semicircular multitube absorber

This experimental work investigates the thermal performance of a parabolic trough solar collector (PTC) with a semicircular absorber tube of 7 mm diameter with a double inlet and outlets. The double inlets are provided to absorb more heat due to the increased length of the absorber tube with minimal heat loss. The tested water mass flow rates are 0.1, 0.15, and 0.2 kg/s. The thermal and exergy efficiencies, the heat transfer coefficient, the Nusselt number, and the friction factor of the modified absorber are compared with that of the conventional single-tube circular absorber of 25 mm diameter. The modified absorber's thermal and exergy efficiencies are 43.9% and 33.6% higher than conventional ones. The heat transfer coefficient of the modified absorber is 541 W/m2K which is 28.5% higher than the conventional absorber. The increased pressure drop results in more pump power, and it increases with an increase in mass flow rate. Thus, the proposed solar absorber improves the heat transfer rate through its semicircular arrangement with reduced hydraulic mean diameter. The outcomes are beneficial to designing line-focus solar absorbers for line-focus solar collectors.

Thermodynamic optimization of parallel and spiral plate heat exchangers for modified solar thermal Brayton cycle models

The receiver and heat exchangers in a Solar Thermal Brayton Cycle (STBC) have been the main sources of exergy loss. Duct profiles used in the heat exchange process have been observed to possess varying degrees of heat transfer effectiveness. To this end, the effects of the elliptical, circular and rectangular absorber tubes are investigated on three variants of the dual serial-regenerative STBC models employing reheater, intercooler, or in a combined arrangement. Also, the impact of the parallel plate heat exchanger (PPHE) and spiral plate heat exchangers (SPHE) on irreversibility is investigated. The particle swarm algorithm (PSA), a stochastic optimization tool is used for the minimization of irreversibilities within the cycle and optimization of the geometric parameters of the STBC components. The largest irreversibility loss on a component-basis is observed on the receiver. The rectangular absorber system for the receiver has the least irreversibility loss compared to other profiles studied, though, a higher internal to external irreversibility ratio was noticed. Improved exergy use via the dual regenerative system was observed on all models with reductions of 22% and 15% in irreversibility obtained from the receiver and recuperator respectively. In addition, the SPHE produced less irreversibilities compared to the PPHE system and this could be attributed to its large surface area available for heat transfer. An optimal second law efficiency of 62% and 74% on the PPHE and SPHE STBC systems, respectively is achieved at around a pressure ratio of 2.2. The dual serial-regenerative system without reheats and intercooling has the advantage of optimal energy available and efficient exergy use followed by the combined system.

Thermo-Economic Performance Evaluation of a Conical Solar Concentrating System Using Coil-Based Absorber

Pollution and the increase in greenhouse gas (GHG) emissions have long been linked to the world’s increasing need for fossil fuels to generate energy. Every day, the energy consumption is increasing; therefore, it is important to improve technologies that use renewable energy sources. With the abundant availability of sustainable energy, solar power is becoming a necessity. However, solar energy has a low energy density and therefore requires a large installation area, which requires heat collection and heat storage technology. Much research is now being done on the conical solar systems to improve efficiency including calculating an optimal cone angle, finding the best flow ratio and the best absorber design, etc. Therefore, in this study, thermal performance of a conical solar collector (CSC) was assessed with a new design of concentric tube absorber (addition of a coil) and compared to the existing circular tube absorber. It was found that 6 L/min flow rate of heating medium (distilled water and CuO nanofluid) gave lower payback period and higher solar fraction of the system in both cases of absorber tube, i.e., without coil and with coil. However, comparatively, thermal efficiency of CSC with coil-based absorber was almost 10–12% higher than conventional system (without coil) regardless of type of heating medium used.

Comparative performance analysis of flat plate solar collector having circular &trapezoidal corrugated absorber plate designs

Flat plate Solar collectors are in use for a long time and have well-established technologies for low-temperature thermal applications. Use of newglazing materials, absorber plate designs, selective coatings, and advanced working fluids, thermal conversion efficiencies of these devices can be further improved. Design modification always comes under top priority because it brings auxiliary changes that further modify the system's overall efficiency. Increasing energy demand puts extra attention on the researchers to develop solar thermal energy-based systems. The presented experimental analysis is based on the design modification of the collector absorber plate to modify the contact area between the absorber plate and collector tubes. We performed a comparative performance of the circular absorber surface and the trapezoidal surface of contact with absorber tubes. The following results indicate that the trapezoidal absorber surface serves better over circular and plate absorber surfaces.Thermal efficiency increases by 8.74% and 12.85% for absorber plate's circular and trapezoidal corrugated surfaces. Exergy efficiency is improved by 16.88, 23.31%, and the overall heat loss coefficient decreases by 7.49 and 8.72% for circular and trapezoidal corrugated surfaces, respectively. The collector's heat removal factor is also significantly higher for trapezoidal corrugated absorber plate than the normal collector absorber surface.

A novel solution method for reflector shape of solar Compound Parabolic Concentrator and verification

In the existing studies, there are many methods to obtain the reflector shape equations of a CPC(Compound Parabolic Concentrator), but these methods are complicated and not unified. This paper aims to propose a novel method that is based on the edge-ray principle, the differential geometry theory, and the geometrical optical reflection law to get the reflector shape equations. Then, the reflector shape equations of an arc absorber CPC (A-CPC) which focuses light on the lower part of a circular absorber are calculated. The optical properties of such an A-CPC experimental model determined by these equations are studied via laser experiments. Afterward, the error between the calculated values obtained by MCRT(Monte Carlo Ray-Trace) method and experimental values are analyzed. The experimental results show that the optical properties of the A-CPC are in accordance with the theoretical expectations. They indicate also that the theoretical method is flexible and suitable for calculating a specific CPC reflector shape.

Construction and analysis of a compound parabolic concentrator to eliminate light escape in the interlayer of solar vacuum tube

The common circular absorber compound parabolic concentrator (CPC) is directly coupled to the solar vacuum tube, through which part of the solar rays will escape from its vacuum interlayer. Based on the principle of non-imaging optical edge light and the law of geometrical optics reflection, the mathematical model of CPC without light escape is constructed in the present research. The limit of allowable gap is analyzed theoretically, and the numerical solution of the reflector with equal length is obtained by program calculation. The correctness of the designed CPC without light escape is verified by experiments. Under the condition of the consistent acceptance half angles, compared with the standard- CPC (S-CPC), it is found that the optical efficiency of the CPC without light escape is increased by 15.7%, the energy flux density distribution on the absorber surface is also improved, and the radiation collected in spring, summer, autumn and winter increased by 4.8%, 4.9%, 5.0% and 7.7%, respectively. It can effectively improve the collection of solar radiation by the CPC in cold winter. The research results show that the circular solar vacuum tube absorber coupled CPC without light escape has a good engineering application prospect.

A novel modified circular ring-based broadband polarization-insensitive angular stable circuit analog absorber (CAA) for RCS applications

AbstractIn this study, a compact modified circular ring-based circuit analog absorber (CAA) is proposed. It comprises a resistor-loaded frequency selective surface (FSS) underneath an FR-4 substrate, and the other end is terminated with a perfect electric conductor (PEC) separated by an air-spacer. The proposed design shows a minimum −10 dB reflectance from 10.55 to 36.03 GHz (25.48 GHz bandwidth and 109.4% fractional bandwidth) with two dips at 13.5 GHz and 35.23 GHz having reflectivity −17.18 dB and −24.9 dB, respectively. The existing four-fold circular symmetry architecture shows insensitivity for different polarization angles under normal incidences and up to 45° stability for Transverse Electric (TE) and Transverse Magnetic (TM) modes under oblique incidences. The proposed cell is compact with a periodicity of 0.193λL, and a thickness of 0.09λL, where λL is the free-space wavelength corresponding to the lowest frequency of the absorption band. The novelty of the design lies in the topology of using an underneath FSS to take advantage of effective permittivity control for both broader bandwidth and better angular stability. To demonstrate the ability of the proposed design, a 28 GHz microstrip patch antenna prototype is fabricated, and its radar cross section (RCS) is measured after loading with the absorber. A 15.15 dBsm RCS reduction is observed in comparison with the PEC. The authors strongly believe that the proposed design has potential applications such as RCS reduction and radio-frequency energy harvesting.

Performance Assessment of a Combined Circular Aquaculture Cage Floater and Point Absorber Wave Energy Converters

Performance Assessment of a Combined Circular Aquaculture Cage Floater and Point Absorber Wave Energy Converters

Performance assessment of a solar water distiller using circular parabolic absorber: An experimental investigation

When distilling water using a solar still, utilization of a circular parabolic absorber increases the absorber surface area over the flat absorber. It enables a solar energy tracking system, which increases the solar heat gained and the evaporation rate inside the distillation cavity with a compact design. The recent research describes an experimental study of a solar-powered water distiller with a circular parabolic absorber (SWD-PA). The experimental model has been designed, built, and trialed in Ras El-Bar City's actual operational weather conditions., Damietta, Egypt (Latitude of 31.49° N, Longitude of 31.30° E). The SWD-PA thermodynamic and economic analyses and water yield were investigated and discussed. The SWD-PA maximum daily water yield was 2.31 L/(m2.day) with first and second law efficiencies of about 41.7% and 3.021%, respectively. The cost of distillate water for SWD-PA at a 20% interest rate was between 0.00213 US$/(L.m2) and 0.00278 US$/(L.m2) at water yield between 2189.8 mL/(m2.day) and 2047.7 mL/(m2.day). The water cost reduces by about 6.5%, with the increment of water yield by about 7%. The proposed system with a circular parabolic absorber is a good design, gives considerable performance and productivity, and is qualified to install a solar tracking system.