Conical Cavity Research Articles

Development and thermal performance evaluation of solar parabolic dish based on fiber‐reinforced plastic

AbstractThis paper illustrates the design and fabrication of a 76° rim angle solar parabolic dish concentrator with low cost based on fiberglass‐reinforced for heating of heat transfer fluid using the hand layup process. Numerous advantages of fiberglass material include corrosion resistance, lightweight, design flexibility, quick installation time, and low cost makes it suitable for fabrication. The concave surface on which the reflective sheets are mounted is made to a high degree of perfection. The design process, as well as the complete fabrication process, are elaborately discussed in this article. The thermal efficiency of the newly constructed fiberglass‐reinforced solar parabolic dish concentrator was assessed by heating the heat transfer fluid in the conical cavity receiver, which was cycled from the sump via a gear pump and flexible stainless steel connecting pipes. The maximum value of heat transfer fluid temperature achieved was 194°C at the sump. The average thermal efficiency achieved for indoor heating at the sump was 17.42%, 17.16%, and 17.21%, respectively, during Experiments 1, 2, and 3. The results indicate that this system is acceptable for indoor cooking in the kitchen, as the system achieves temperatures between 150°C and 194°C.

Steam and electrical power generation by a hybrid photovoltaic/parabolic dish concentrator using beam splitter technology

The parabolic dish is considered the most performant concentrating solar power (CSP) technology since it fits a wide range of domestic and industrial processes and offers better modular deployment than other CSP technologies such as thermal power receivers. The parabolic dish has been widely employed to produce steam and electricity especially when it works in conjunction with Stirling engines; however, the extreme complexity of the latter makes the power generation cost of this technology unfavorable against other competing solutions. In this paper, a comprehensive and detailed optical and thermal performance analysis and optimization study of a hybrid photovoltaic/parabolic dish concentrator with a conical thermal receiver using a beam splitter filter (PV/PDC-CTR-BSF) are carried out. A complete modeling module is developed to assess and optimize the overall yields of the PV/PDC-CTR-BSF. The present work is unique since it encompasses a sophisticated simulation tool enabling performance potential assessment of a novel PV/PDC-CTR-BSF system coupled with a novel conical-shaped helical coiled-tube heat exchanger for steam production and paves the avenue for higher electrical yield using single-junction PV cells mounted over the tip surface area of the paraboloid mirrors. The concentrated solar density (CSD) distribution, optical efficiency, temperature distribution, and steam fraction have particular interest in the performance assessment of the innovative PV/PDC-CTR-BSF package system. As a result, the maximum value of the CSD at the conical cavity receiver and the PV cells is 40 and 8 kW/m2, respectively. The optical efficiency of the proposed design has a breakthrough in the record of the typical hybrid designs reaching the value of 67%. Moreover, the maximum surface solar cells temperature was 80°C, while the temperature reached 170°C at the conical cavity receiver. The optical new hybrid design has maximized the steam productivity up to a steam volume fraction of 98%.

Optical modeling of corrugation cavity receiver for large-aperture solar parabolic dish collector

ABSTRACT This article presents an optical investigation of a corrugation cavity receiver for a 100 m2 parabolic dish collector (PDC). The performance of PDC depends on the selection of the receiver and its mounting distance from the collector base (H) to receive a high amount of reflected radiation. This work performs optical modeling for PDC with a designed corrugation cavity receiver using commercial software, ASAP® 2013. The motivation for this study is derived from the fact that the entrapped internal reflection within the receiver optimizes the system’s optical efficiency. The receiver geometry is such that it attributes to increasing internal reflection and average heat flux intensification. The present optical model is validated with the available literature. The influential geometrical and optical parameters of the receiver have been optimized by simulation by varying the aperture diameter (da,r) from 0.504 to 0.604 m, surface absorptivity (α) from 75 to 95%, receiver coil’s outer and inner pitch (Po and Pi) from 0.00667 to 0.00909 m, and angle of taper (θi) from 50° to 56° for H = 5.35–5.65 m. The performance of the optimized receiver is compared with the conical cavity receiver and is found to be excellent among all values of H. This optical modeling can be expected to be helpful for engineers and researchers in designing the optimized optical receiver for solar parabolic dish collector systems.

СОВРЕМЕННЫЕ КОНСТРУКЦИИ АЛМАЗНЫХ КОРОНОК ДЛЯ БУРЕНИЯ СКВАЖИН

The article presents the results of research on the creation of drill bits with high durability and sufficient productivity when drilling hard rocks. Four areas of research have been identified to solve this problem: the crown must be multilayer, the profile of the diamond-bearing layers must represent annular conical protrusions and cavities; diamond layers should be separated by diamond-free layers of lower hardness and experience uniform specific pressure during operation; the design of the bit should take into account the peculiarities of the rock destruction mechanism under the action of diamond grains; the manufacturing technology of the crown matrix must be perfect. Only defect-free diamonds obtained by sorting with special methods are involved in the creation of the matrix; Adding CrB2 or VN nanopowders to the composition of the charge makes it possible to improve the quality of the matrix structure, all tribiological and operational properties, and due to the preliminary metallization of high-strength synthetic diamonds, a transition zone “diamond-coating-matrix material” is created, which will significantly increase the wear resistance of diamond rock cutting tools. The mentioned problems have been partially solved: a multilayer impregnated bit with a ridged profile of diamond-bearing layers and a uniform specific pressure on the latter during drilling has been created and put into production, laboratory studies have been carried out to improve the quality of composite materials with positive results, further research is being carried out in all other areas.

An experimental examination of a helically coiled conical cavity receiver with Scheffler dish concentrator in terms of energy and exergy performance

In this paper, the thermal performance of a helically coiled conical cavity receiver is investigated under actuation radiation conditions with a 16 m2 parabolic Scheffler dish concentrator. Under three different radiation scenarios, the receiver thermal energy efficiency, exergy efficiency, and overall heat transfer coefficient are investigated. Water is employed as a heat transfer fluid, and the receiver is tested at a flow rate of 2.5 L per minute in a temperature range of 30–100 °C. During the stagnation test, the receiver's maximum stagnation temperature was recorded as 395 °C for an incoming beam radiation of 654 W/m2, which demonstrates the receiver's ability to generate pressurised steam. The overall heat loss coefficient calculated from the stagnation test is 116 W/m2-K. The heat transfer fluid input and output temperature differences, as well as incoming beam radiation, are found to have a significant impact on the receiver's energy and energy efficiency. Under maximum beam radiation conditions during the second experiment (672 W/m2), the average thermal energy efficiency and exergy efficiency were determined to be 70.20% and 8.69%, respectively. Based on the findings, this receiver has the potential to be employed in temperature applications up to 100 °C and above for steam generation under pressurised conditions.

Development of scaling laws for prototyping and heat loss correlations for upward facing cylindrical helical coil and conical spiral coil receivers

A solar receiver is an integral part of any concentrated solar power based plant for energy conversion. An experimental or numerical analysis of a large-scale solar receiver is expensive due to the high infrastructure and computational costs involved. Hence, it becomes necessary to study the effects of scaling on the performance of a solar receiver so that the results of the analysis of small-scale receivers can be extended to large-scale models. Therefore, a scale analysis is carried out in this study to develop constitutional relationships amongst physical and geometrical parameters for upward-facing cylindrical helical coil and conical spiral coil cavity receivers. Similarity parameters are derived from the non-dimensional Navier Stokes equations in the curvilinear coordinate system (s,r,θ). A scaling law is derived based on the identified parameters. A validated numerical model for the cylindrical helical coil receiver and conical spiral coil receiver is used to verify the scaling analysis. Further, Nusselt number correlations for the convective heat losses from the upward-facing cylindrical and conical cavity receivers are proposed. The newly proposed correlations predict the convective losses from the upward-facing cylindrical and conical cavity receivers within the error band of ±20%.

Direct and semi-direct resin composite restoration in large cavity preparations: analysis of dentin bond strength stability and bottom/top microhardness ratio in a cavity model.

To evaluate the influence of the restorative approach and aging time on dentin bond strength (BS), failure mode (FM), and bottom/top microhardness ratio (B/T) in a large dentin cavity model. A total of 102 bovine incisors were used to produce models of conical dentin cavities (4.0mm thickness × 4.8mm top diameter × 2.8mm bottom diameter), which were restored using semi-direct filling (SDF) (Filtek™ Z250 XT + Scotchbond™ Universal/RelyX™ Ultimate luting system), direct bulk filling (DBF) (Filtek™ One Bulk Fill), and direct incremental filling (DIF) (Filtek™ Z250 XT) techniques. B/T, BS, and FM (n = 17) were analyzed in a microhardness tester, a universal testing machine, and a stereomicroscope, respectively, after 24h and 6months of water storage. BS and B/T data were analyzed using two-way ANOVA/Tukey post-hoc test (p < 0.05), while FM data were analyzed descriptively. There was a statistically significant difference in BS between the restorative techniques, and BS was influenced by aging time in the DBF and SDF groups. Mixed failure was predominant for the SDF technique in both aging times. There was no statistically significant difference in B/T among the restorative approaches regardless of the aging time (p > 0.05). Although all restorative approaches provided similar B/T, the semi-direct technique showed better performance on the material bond strength to dentine in large cavities.

Non-uniform magnetic field effects on the phase transition dynamics for PCM-installed 3D conic cavity having ventilation ports under hybrid nanofluid convection

Effects of using non-uniform magnetic field in a PCM installed 3D vented cavity having triangular-cross section on the phase transition dynamics are numerically assessed. Alumina-copper nanoparticles are used in water as the heat transfer fluid. Numerical study is conducted for different Reynolds number (Re-between 100 and 500), Hartmann number (Ha-between 0 and 80), solid volume fraction of particles (svf-between 0.001 and 0.02), amplitude of non-uniform magnetic field (Amp-between 0.2 and 1) and aspect ratio of the cavity (AR-between 0.4 and 2). Phase transition becomes accelerated with higher Re, Ha, Amp, svf and AR. The reduction in phase transition time (tf) becomes 73% when lowest and highest Re cases are compared while by using nanoparticles at the highest amount, up to 42.9% reduction in complete transition time is obtained. For the highest amplitude of non-uniform magnetic field, 6.9% and 15% reduction amounts are obtained at Ha = 20 and Ha = 80. Faster transition times are observed with higher aspect ratio. Artificial neural networks are used for the dynamic characteristics estimations of phase change process while with 10 neuron in the hidden layer, successful estimations are obtained with network modeling approach.

Heat Loss Reduction Approach in Cavity Receiver Design Based on Performance Investigation of a Novel Positive Conical Scheme

The cavity receiver’s thermal conversion performance is critical for parabolic dish and tower Concentrated Solar Power (CSP) systems. Distinct from precedent research aiming to increase the receiver’s absorption through cavity geometry optimization, the objective of this work was to investigate the thermal conversion performance of a novel, positive conical cavity receiver design, following the heat loss reduction approach with simplified pipe forming, to stress the effectiveness of this approach in cavity receiver design, and to provide data for future optimization of the proposed design. To accomplish these goals, the novel receiver and existing designs’ heat flux absorption and heat loss are compared numerically. The resulting conversion power is also experimentally validated. The concept is inspired by analysis of formulas, suggesting the novel design may realize a thermal conversion improvement of 8.6%, at 650 K, and increases with the rise in temperature. The comprehensive numerical investigation combines ray tracing of identical incoming radiation to investigate the receiver absorption and CFD methods to investigate the cavities’ heat loss at identical temperatures. The absorption acquired is unoptimized. The novel design can reduce the heat loss by as much as 91.8% when compared with a negative conical design at 650 K, resulting in a 12.3% improvement in conversion power. The experimental investigation measures the energy conversion to the working fluid in different cavities under identical incoming radiation. The novel receiver outperforms by over 5.6% in the setup. After correcting boundary conditions using experiment measurements, the experimental and numerical results are comparable. This research proves that the novel positive conical receiver has a better thermal conversion performance over 650 K; thus, the heat loss reduction approach is effective and feasible in receiver designs within this temperature range.

Simulating the acoustic response of cavities to improve microphone array measurements in closed test section wind tunnels.

Cavities placed along wind tunnel walls can attenuate the turbulent boundary layer (TBL) fluctuations as they propagate into the cavity. Placing microphones within the cavities can thus improve the signal-to-noise ratio of acoustic data. However, standing waves form within these cavities distorting the acoustic measurements. This work uses a finite element (FE) solver to evaluate how cavity geometry (depth, diameter, and wall angle) and wall material (hard-walled and melamine foam) affect the amplitude and eigenfrequency of standing waves when excited by an incident acoustic plane wave. Good agreement between predicted and measured acoustic transfer functions is shown. Compared to cylindrical cavities, countersunk and conical cavities improve the overall response, i.e., reducing the quality factor quantifying the resonance and damping characteristics. Stainless steel coverings also reduce the quality factor. A finding is that the shape of the external foam holder rather than the cavity shape drives the standing wave characteristics for the melamine foam cavities. The optimization problem of minimizing the acoustic response while also attenuating the TBL is thus decoupled by using the melamine foam. Consequently, these considerations can be addressed independently by optimizing the outer cavity shape for acoustics and the melamine foam insert for TBL attenuation.

Numerical Investigation of Modified Conical Cavity Receiver with Different Heat Transfer Fluids

Numerical Investigation of Modified Conical Cavity Receiver with Different Heat Transfer Fluids

Thermal analysis of modified conical cavity receiver for a paraboloidal dish collector system

ABSTRACT In a solar paraboloidal dish collector system, the receiver is critical for transforming converged solar flux to heat energy. A cavity receiver is the most common type of receiver, as it lowers heat loss. An experimental investigation is carried out in this article to evaluate the thermal performance of a novel cavity receiver for dish system under real direct solar environments. The performance of the modified conical cavity receiver under stagnation condition and with heat transfer fluid was studied experimentally. A solar parabolic dish concentrator of 1.83 m rim diameter and rim angle of 66° was used for the experimentation. For both cases, the experiments were carried out for two days. The highest stagnation temperature of 167.2°C was recorded with a direct irradiance of 803 W/m2, according to the data. For day average direct irradiance of 555 W/m2 and 663 W/m2, the receiver’s average thermal efficiency was found to be 53% and 69%, respectively. For 694 W/m2 direct irradiance, a maximum thermal efficiency of 75% was achieved. The thermal efficiency was shown to be significantly dependent on direct irradiation. According to the results of the experiments, the proposed modified conical cavity receiver is a viable solution for solar parabolic dish collector systems.

Effects of geometric and operating parameters on thermal performance of conical cavity receivers using supercritical CO2 as heat transfer fluid

In this paper, a comprehensive optical-thermal numerical model of the conical cavity receiver using supercritical CO2 (S–CO2) as the heat transfer fluid (HTF) is established by combining ray tracing with computational fluid dynamics method, which is verified with published data in the literature. Based on the model, the effects of critical geometric parameters (tube inner diameter, aspect ratio and cone angle ratio) and operating parameters (solar direct normal irradiance (DNI), HTF inlet mass flow rate and inlet temperature) on the thermal performance of the receiver are discussed thoroughly. The results indicate that a decrease in the tube inner diameter is beneficial to improve the optical-thermal performance of the receiver. When the aspect ratio and cone angle ratio are 1.5 and 0.25, respectively, the optical-thermal conversion efficiencies reach their optima, which are 75.13% and 75.30%, respectively. Moreover, for the S–CO2 receiver with optimal geometric parameters, the HTF outlet temperature increases linearly with increasing DNI and inlet temperature. Increasing mass flow rate can improve the optical-thermal conversion efficiency, but once the flow rate exceeds 0.04 kg/s, it has little effect on the efficiency improvement. These results can provide a reference for the design and operation of the S–CO2 conical cavity receiver.

Design and performance of a new type of boiler using concentrated solar flux

In order to reduce the amount of CO2 emissions associated with industrial boiling, the design of a new solar boiler operating with concentrated solar energy has been proposed and studied in the present work. A lab-scale solar boiler was built to show the feasibility of the concept through experiments, and a thermal model was then developed to study the efficiency of the solar boiler under different boiling conditions. Several peculiarities distinguish this new design from conventional boilers: (i) the use of vertical heating downwards from a receiver placed on top of the boiler, (ii) the conical shape of the receiver oriented upside down and submerged in the liquid, (iii) the solar receiver has a conical cavity on top where vertical solar flux is received, and its lower surface is submerged in boiling fluid, (iv) the direct use of solar energy with optical concentrating facilities for boiling without intermediate heat transfer fluids, and (v) the study of the unconventional film-boiling regime at elevated receiver temperatures which spaces the boiling fluid from the surface of the receiver. The model was validated by the data collected and showed good consistency between predictions and experimental results, with an average error of 3.79% for temperatures and 2.08% for vapor mass flow rate. For the chosen operating conditions studied, the thermal efficiency of the solar boiler varied from 80% to 90%. Such a thermal model can play an important role for the study and design of new thermal processes involving concentrated solar heating for boiling such as desalination.

Integration of a Solar Parabolic Dish Collector with a Small-Scale Multi-Stage Flash Desalination Unit: Experimental Evaluation, Exergy and Economic Analyses

In this study, a small-scale two-stage multi-stage flash (MSF) desalination unit equipped with a vacuum pump and a solar parabolic collector (PDC) with a conical cavity receiver were integrated. To eliminate the need for heat exchangers, a water circulation circuit was designed in a way that the saline feedwater could directly flow through the receiver of the PDC. The system’s performance was examined during six days in July 2020, from 10:00 a.m. to 3:00 p.m., under two distinct scenarios of the MSF desalination operation under the vacuum (−10 kPa) and atmospheric pressure by considering three saline feedwater water flow rates of 0.7, 1 and 1.3 L/min. Furthermore, the performance of the solar PDC-MSF desalination plant was evaluated by conducting energy and exergy analyses. The results indicated that the intensity of solar radiation, which directly affects the top brine temperature (TBT), and the values of the saline feedwater flow rate have the most impact on productivity. The maximum productivity of 3.22 L per 5 h in a day was obtained when the temperature and saline feedwater flow rate were 94.25 °C (at the maximum solar radiation of 1015.3 W/m2) and 0.7 L/min, respectively, and the MSF was under vacuum pressure. Additionally, it was found that increasing the feedwater flow rate from 0.7 to 1.3 L/min reduces distillate production by 76.4% while applying the vacuum improves the productivity by about 34% at feedwater flow rate of 0.7 L/min. The exergy efficiency of the MSF unit was obtained as 0.07% with the highest share of exergy destruction in stages. The quality parameters of the produced distillate including pH, TDS, EC and DO were measured, ensuring they lie within the standard range for drinking water. Moreover, the cost of freshwater produced by the MSF plant varied from 37 US$/m3 to 1.5 US$/m3 when the treatment capacity increased to 8000 L/day.

Effect of Covering Aperture of Conical Cavity Receiver on Thermal Performance of Parabolic Dish Collector: Experimental and Numerical Investigations

In this study, the effect of covering the aperture area of a conical cavity receiver with an ultra-white glass on operational parameters of a Parabolic Dish Collector (PDC) was numerically and experimentally investigated under climate conditions of Tehran (35.44° N latitude and 51.10° longitude). The main components of the experimental setup include a dish reflector, a conical cavity receiver, Heat Transfer Fluid (HTF), hydraulic and cooling cycle, and a sun tracker. For this purpose, a conical cavity receiver with an ultra-white glass cover on its aperture was numerically modeled in Fortran software. During the evaluation, environmental parameters including ambient temperature, solar radiation, and wind speed were considered as inputs of the model. The results revealed fair agreement between the numerical and experimental data with the maximum error of approximately 4.63 % and 7.89 % for receivers with and without the glass cover on the aperture, respectively. For a steady-state analysis, the mean values of useful energy ( ) absorbed by the receiver were calculated as 1,253.25 W and 987.68 W, while thermal efficiency ( ) of the receiver was calculated as 52.61 % and 40.69 % for receivers with and without glass cover, respectively. The results revealed that both and followed a similar trend of the variations in the HTF’s temperature between the inlet and outlet of the receiver. Also, the overall heat loss coefficient ( ) and the collector heat removal factor ( ) were calculated as 420.76 W/m2°C and 0.62 for the conical cavity receiver with the glass cover.

Comparative study of modified conical cavity receiver with other receivers for solar paraboloidal dish collector system.

Solar parabolic dish concentrators are one of the most efficient solar power conversion technologies. The cavity receivers are the most common type, used for reducing the heat losses from the receiver. In this paper, a novel cavity receiver is proposed, and the objective is to compare the novel modified conical cavity receiver with the existing cavity receivers such as cylindrical, conical and modified cavity receivers. The cavity receivers are designed for the parabolic dish of 4-m diameter which is installed at the National Institute of Technology Puducherry, India. Ray-tracing analysis was carried out to determine the size of the receiver. The analysis was carried out for various orientations of the receivers from 0 to 90° with a step size of 15° and also for the cavity temperatures: 300°C, 400°C, 500°C, 600°C and 700°C. Based on the results obtained, the modified conical cavity receiver is found to be the best design in terms of minimum heat losses compared to other receivers. The next best choices are found to be modified cavity, conical cavity and cylindrical cavity receiver. The whole analysis is conducted with a developed model in COMSOL Multiphysics.

Electrotechnology of animal colostrum defrosting in two-resonator microwave installations

The article is devoted to the development of the plants for defrosting and heating animal colostrum. The idea is that the plant should contain two cavities that provide different levels of an ultra-high frequency electromagnetic field exposure on colostrum, which differs in the aggregate state. A laboratory sample of the plant with conical cavities having a common perfo-rated base was constructed. With the help of the plant the technological parameters of cow colostrum defrosting and heating were processed. Analyzing the developed installations with two resonators, from the point of view of the implementation of the main technological criteria, a design with quasi-stationary toroidal resonators connected by a common perforated base is proposed as the most effective. In the condense parts of both cavities, a high-voltage electric field is fed, which is sufficient for a low-temperature bacterial contamination reduction of the fodder product. The use of an installation for defrosting and heating colostrum of animals on farms in rural area will reduce the heating time, preserve the useful properties of colostrum.

Push-Out Bond Strength of Composite Polymerization Methods with Universal Adhesive to Coronal Dentin

Abstract Objective This in vitro study was aimed to determine the effect of composite polymerization methods with universal adhesive on push-out bond strength in coronal dentin. Materials and Methods Using 48 healthy premolar teeth, the almost conical access cavities were excised to the canal entry. Cavity preparations were treated with a universal adhesive in the self-etch mode. Teeth were randomly divided into four groups (n = 12). It was used to restore the cavities with a bulk-fill composite; Tetric N-Ceram, a conventional composite; Filtek Z250, a dual-cure composite; Rebilda DC VOCO, and chemical cure composite; Master-Dent. After applying 10,000 thermal cycles, 1-mm incisions were made in coronal dentin, and slices were placed in a UTM machine in a special jig and tested for push-out bond strength at a crosshead speed of 0.5 mm/min. Data were analyzed using one-way analysis of variance and Games–Howell tests (p &lt; 0.05). Results The highest mean bond strength was of the conventional composite (18.36 ± 5.63) and the lowest mean of bond strength was for the dual-cure composite (5.10 ± 2.74). There was a significant difference among the means of bond strength for various composite resins curing (p &lt; 0.001). Conclusion The bulk-fill and conventional light-cured composites had higher bond strength than self- and dual-cured composite resins.

An experimental investigation on thermal and optical analysis of cylindrical and conical cavity copper tube receivers design for solar dish concentrator

The receiver is crucial in converting concentrated solar radiation to thermal energy in a solar parabolic dish collector. The most popular type of receiver is a cavity receiver, which reduces heat loss from the body. In this paper, an experimental investigation of the energy, exergy, and optical performance of two cavity-type receivers for a solar parabolic dish concentrator was carried out. The cylindrical and conical cavity tube receivers were designed and tested in the temperature range of 35 °C–190 °C, with water as the working fluid and a flow rate of 0.83 L per minute. The results showed that the conical cavity tube receiver is the optimum design, while the cylindrical shape is the second choice. The conical cavity tube design achieved 62% average thermal efficiency, 11% exergy efficiency, while the maximum optical efficiency was 82% under average solar irradiation of 865 W/m2. The overall heat loss coefficients of cylindrical and conical cavity receivers from the stagnation measure were 137 W/m2 and 125 W/m2, respectively. The maximum and average surface temperatures for both cylindrical and conical cavity tube receivers were reached at 140 °C, 115 °C and 155 °C, 125 °C, respectively. The simulation study was conducted using COMSOL Multiphysics software to investigate the temperature distribution of the receivers. The proposed lightweight conical cavity tube receiver was found to have a high capacity to be used with a solar parabolic dish-style concentrating device to operate heating water applications.