Tubular Receiver Research Articles

Three-Dimensional Optical and Thermal Numerical Model of Solar Tubular Receivers in Parabolic Trough Concentrators

Monte Carlo ray tracing, coupled to a finite volume solver, is used to model 3D heat transfer in a parabolic trough solar concentrator system. The nonuniform distribution of the incident solar radiation, the radiative exchange between the various receiver surfaces, and the heat gain/loss around the receiver's circumference and along the system's axis are determined for spectral radiative properties of the receiver and concentrator surfaces. The computed heat losses and thermal efficiencies agree well with experimental data. Besides the beneficial information on peak temperatures and heat flux, the 3D model is able to predict glass temperatures more accurately than previous gray models and temperature correlations.

공기식 태양열 흡수기의 설계 및 성능평가

It is important to produce the high-temperature and high-pressure air for the concentrated solar power system using the combined cycle. In this paper, we designed two types of tubular receivers to heat up the compressed air and provided their preliminary experimental results for performance evaluation and further improvements. The developed receivers are in a square cavity shape surrounded by flow conduits for easy scale-up and radiation loss reduction. The two receivers were tested with 5 bar air in the KIER solar furnace and evaluated in terms of the outlet temperature and the efficiency.

Effect of porous disc receiver configurations on performance of solar parabolic trough concentrator

In this article, heat transfer enhancement of line focus solar collector with porous disc receiver is studied with water and therminol oil. A three dimensional (3-D) numerical simulation of porous disc enhanced receiver is carried out using commercial CFD software Fluent 6.3 to evolve the optimum configuration. The 3-D numerical model is solved by renormalization-group based k-e turbulent model associated with standard wall function. The effect of porous disc receiver configurations (solid disc at bottom; porous disc at bottom; porous disc at top; and alternative porous disc) on performance of the trough concentrator is investigated. The effect of porous disc geometric parameters (φ, θ, W, H and t) and fluid parameters (Pr and m) on heat transfer enhancement of the receiver is also studied. The numerical simulation results show that the flow pattern around the solid and porous discs are entirely different and it significantly influences the local heat transfer coefficient. The porous disc receiver experiences low pressure drop as compared to that of solid disc receiver due to less obstruction. The optimum configuration of porous disc receiver enhances the heat transfer rate of 221 W m−1 and 13.5% with pumping penalty of 0.014 W m−1 for water and for therminol oil-55, heat transfer rate enhances of 575 W m−1 and 31.4% with pumping penalty of 0.074 W m−1 as compared to that of tubular receiver at the mass flow rate of 0.5 kg s−1. The Nusselt number and friction factor correlations are proposed for porous disc receiver to calculate heat transfer characteristics. The porous disc receiver can be used to increase the performance of solar parabolic trough concentrator.

A prototype receiver for medium temperature conversion of solar radiation to heat

In this article, a solar receiver prototype (marked as P2CC, parabolic-and-circular collector) is described for medium temperature conversion of solar radiation in heat. The investigated concentrator has a tubular receiver and two identical reflectors, one from each side of the tubular receiver. The tubular receiver is a concentric tube consisting of a metal tube (absorber) inside the glass tube. Each reflector curve is defined using three curves where one curve is parabola and two curves are circular arcs. The demonstrated prototype has the reception angle of 110° at concentration ratio CR = 1.38, with the significant reception of diffuse radiation. The hydraulic measurements reveal the pressure drop up to 200 Pa. Thermal measurements discover the high efficiency of the P2CC of up to 75 per cent. The prototype application would mean significant savings of electric energy which is now used for preparation of warm water, and in central and long-distance heating systems.

Development and experimental investigation of a compound parabolic concentrator

The numerical simulation and experimental validation of a compound parabolic concentrator (CPC) are presented. The solar device had an aperture area of 1.33 m2, a real concentration ratio of 3.5, an acceptance half angle of 15°, and a carbon steel (or aluminum) tubular receiver with an outer diameter of 0.0603 m and coated with a commercial selective surface. Experimental tests were performed using water as working fluid at solar noon; the inlet temperatures used varied from 30 °C to 70 °C and the mass flow rates from 0.05 kg/s to 0.25 kg/s. A comparison of the experimental results with the numerical model developed was carried out. The results of the thermal efficiency, outlet temperature, and pressure drop were compared and found to be in close agreement with the experimental data. Therefore, the model is a reliable tool for the design and optimization of compound parabolic concentrators. Because the numerical model is based on the application of physical laws, it is possible to extrapolate its use with confidence to other fluids, mixtures, and operating conditions. Copyright © 2011 John Wiley & Sons, Ltd.

Performance analysis of a mid- and low-temperature solar receiver/reactor for hydrogen production with methanol steam reforming

Mid- and low-temperature solar thermochemical hydrogen production is considered as a promising field in the utilization of solar thermal applications. In this paper, a novel solar thermochemical receiver/reactor, which combines a tubular reactor and a parabolic trough collector (PTC) with the evacuated tubular receiver, was investigated. A non-isothermal model, based on a model of thermal energy loss from a PTC and a complex kinetic model of methanol steam reforming employing the Cu/ZnO/Al2O3 catalyst, was developed to analyze the performance of the mid- and low-temperature solar receiver/reactor for the new approach to solar hydrogen production. It is found that the catalytic bed temperature increased with the increment of the solar radiation. The factors influencing the hydrogen production, such as the feeding rates of the reactants, the solar radiation, the inlet temperature of the solar receiver/reactor, and the mole ratios of water to methanol, were investigated in detail. In the range of the solar radiation considered in this work, the solar thermochemical efficiency exceeds 50%, which is very competitive when compared with other high-temperature solar reactors. The inlet temperature of the solar receiver/reactor has a small impact on the hydrogen production for the whole solar reactor. At a mole ratio of water to methanol of 1, solar collector area of 600 m2 and a reactant feeding inlet-temperature of 423 K, the maximal hydrogen production capacity of the whole solar receiver/reactor can reach 54 kmol h−1 under the solar radiation intensity of 1000 W m−2. The encouraging results indicate a promising approach for the effective utilization of mid- and low-temperature solar thermal energy via the solar thermochemical process. Copyright © 2010 John Wiley & Sons, Ltd.

Assessment of Solar Power Tower Driven Ultrasupercritical Steam Cycles Applying Tubular Central Receivers With Varied Heat Transfer Media

For clean and efficient electric power generation, the combination of solar power towers (SPTs) with ultrasupercritical steam cycle power plants could be the next development step. The methodology of the European concentrated solar thermal roadmap study was used to predict the annual performance and the cost reduction potential of this option applying tubular receivers with various appropriate high temperature heat transfer media (HTM). For the assessment, an analytical model of the heat transfer in a parametric 360 deg cylindrical and tubular central receiver was developed to examine the receiver’s efficiency characteristics. The receiver’s efficiency characteristics, which are based on different irradiation levels relative to the receiver’s design point, are, then, used to interpolate the receiver’s thermal efficiency in an hourly based annual calculation of one typical year that is defined by hourly based real measurements of the direct normal irradiance and the ambient temperature. Applying appropriate cost assumptions from literature, the levelized electricity costs (LEC) were estimated for each considered SPT concept and compared with the reference case, which is a scale-up of the state of the art molten salt concept. The power level of all compared concepts and the reference case is 50 MWel. The sensitivity of the specific cost assumptions for the LEC was evaluated for each concept variation. No detailed evaluation was done for the thermal storage but comparable costs were assumed for all cases. The results indicate a significant cost reduction potential of up to 15% LEC reduction in the liquid metal HTM processes. Due to annual performance based parametric studies of the number of receiver panels and storage capacity, the results also indicate the optimal values of these parameters concerning minimal LEC.

Experimental and Model Based Performance Analysis of a Linear Parabolic Trough Solar Collector in a High Temperature Solar Cooling and Heating System

An innovative solar cooling and heating system has been designed, installed, tested, and modeled at Carnegie Mellon University to assess the technical and economic feasibility of high temperature solar cooling and heating system. This system primarily consists of parabolic trough solar collectors (PTSC) and a double effect absorption chiller. A comprehensive model for the tubular receiver of the PTSC has been developed to improve the PTSC design and overall system performance. The model has been verified by the experimental data from the tests on the PTSC in this system. The experimental data and theoretical analysis demonstrated that the properties of the glass envelope of PTSC significantly impacted the PTSC’s performance. The model calculations indicated that the vacuum in the annular space between the glass tube and absorber pipe of the PTSC does not markedly improve its efficiency. In addition, the system performance of the high temperature solar cooling and heating system has been presented and evaluated by using experimental data. Based on these model calculations, the performance of the PTSC installed has been projected and measures to improve the PTSC design have been recommended.

Optical simulation of a parabolic solar trough collector

The optical simulation of a linear parabolic solar collector with a tubular receiver is presented. The simulation considers a general model of a trough collector with a pipe receiver, with or without a glass covering, and with a realistic solar irradiation from an arbitrary direction. Optical properties can depend on the wavelength. The simulation is performed using a three-dimensional ray-tracing technique and allows us to follow a ray along all the multiple reflections and refractions that occur at the mirror and at the receiver. Defects of various kinds are simulated. The simulation computes the total optical efficiency, the distribution of the absorbed radiation on the surface of the receiver, and the energy absorbed by the glass covering (if present). The results for a typical trough electric production system are shown and commented upon.

Thermal analysis of solar parabolic trough with porous disc receiver

In this paper, 3-D numerical analysis of the porous disc line receiver for solar parabolic trough collector is presented. The influence of thermic fluid properties, receiver design and solar radiation concentration on overall heat collection is investigated. The analysis is carried out based on renormalization-group (RNG) k– ε turbulent model by using Therminol-VP1 as working fluid. The thermal analysis of the receiver is carried out for various geometrical parameters such as angle ( θ), orientation, height of the disc ( H) and distance between the discs ( w) and for different heat flux conditions. The receiver showed better heat transfer characteristics; the top porous disc configuration having w = d i , H = 0.5 d i and θ = 30°. The heat transfer characteristic enhances about 64.3% in terms of Nusselt number with a pressure drop of 457 Pa against the tubular receiver. The use of porous medium in tubular solar receiver enhances the system performance significantly.

Numerical Investigation of Energy-Efficient Receiver for Solar Parabolic Trough Concentrator

In this paper, a thermal analysis of an energy-efficient receiver for solar parabolic trough concentrator is presented. Various porous receiver geometries are considered for the performance evaluation of a solar parabolic trough concentrator. Numerical models are proposed for a porous energy-efficient receiver for internal heat gain characteristics and heat loss due to natural convection. The internal flow and heat transfer analysis is carried out based on a RNG k-ϵ turbulent model, whereas external heat losses are treated as a laminar natural convection model. The numerical models have been solved using the commercial engineering package, FLUENT. The thermal analysis of the receiver is carried out for various geometrical parameters, such as fin aspect ratio, thickness, and porosity, for different heat flux conditions. The inclusion of porous inserts in tubular receiver of solar trough concentrator enhanced the heat transfer about 17.5% with a pressure penalty of 2 kPa. The Nusselt number correlation is proposed based on the extensive numerical data for internal heat transfer inside the receiver. The proposed model is compared with more well-known natural convection models. A comparative study is carried out with different porous geometries to evolve an optimum configuration of energy-efficient receivers.

Numerical Study of Porous Finned Receiver for Solar Parabolic Trough Concentrator

In this article a new receiver for parabolic trough concentrator is proposed to enhance heat transfer. A 3-D numerical model is developed to evaluate the performance of the receiver with various configurations of porous inserts of square, triangular, trapezoidal and circular shapes. The model is solved by k-ε RNG with standard wall function approach using the CFD package FLUENT. The performance of the receiver is investigated under various solar radiation and heat loss conditions. The effect of porous fin geometry on heat transfer characteristics and pressure drop is studied. The trapezoidal fin receiver with a tip-to-base ratio (λ) = 0.25 showed better performance than other receiver configurations. The trapezoidal porous inserts in the tubular receiver of the solar trough concentrator enhanced the heat transfer for about 13.8% at a fluid mass flow rate of 6.4 kg/s with only 1.7 kPa of pressure penalty.

Solar powered adsorption refrigerator with CPC collection system: Collector design and experimental test

Abstract Solar adsorption cooling systems are usually based on the flat plate collector, whereas little attention has been paid to concentrating collectors. Compound parabolic concentrators (CPC) are a versatile class of solar collectors that can be adapted to a large variety of applications and geometries. This work presents a CPC collector whose tubular receiver contains the sorption bed and where only a portion of the receiver is exposed to sunlight. Geometric characteristics of the proposed CPC, such as the profile, the length and the height of the reflective sheet are given. A prototype of a solar adsorption chiller using this type of collector and the activated carbon–methanol working pair is described, and typical experimental results are reported. In particular, the measured solar COP ranges from 0.078 to 0.096.

G223 太陽光を模擬した平行輻射光によるパイプ列の加熱(ふく射)

We have been developing a tubular solar receiver to be applied in beam-down solar concentration systems for solar thermal power generation. In the tubular receiver, concentrated solar light irradiates the surface of pipes and heats a thermal medium flowing in the pipes. Analysis of radiation heat transfer on pipe array is required to design the tubular receiver. A numerical simulation program which analyzes heat transfer on the pipes and behind wall was developed and verified with the pipe array heating experiments. Heat absorption performance of a pipe array was compared with a flat surface thermal medium channels. A method for approximating complicated heat transfer in pipe arrays by that in simple flat surfaces was developed.

Solar hydrogen production from the thermal splitting of methane in a high temperature solar chemical reactor

This study addresses the single-step thermal decomposition (pyrolysis) of methane without catalysts. The process co-produces hydrogen-rich gas and high-grade carbon black (CB) from concentrated solar energy and methane. It is an unconventional route for potentially cost effective hydrogen production from solar energy without emitting carbon dioxide since solid carbon is sequestered. A high temperature solar chemical reactor has been designed to study the thermal splitting of methane for hydrogen generation. It features a nozzle-type graphite receiver which absorbs the solar power and transfers the heat to the flow of reactant at a temperature that allows dissociation. Theoretical and experimental investigations have been performed to study the performances of the solar reactor. The experimental set-up and effect of operating conditions are described in this paper. In addition, simulation results are presented to interpret the experimental results and to improve the solar reactor concept. The temperature, geometry of the graphite nozzle, gas flow rates, and CH 4 mole fraction have a strong effect on the final chemical conversion of methane. Numerical simulations have shown that a simple tubular receiver is not enough efficient to heat the bulk gas in the central zone, thus limiting the chemical conversion. In that case, the reaction takes place only within a thin region located near the hot graphite wall. The maximum CH 4 conversion (98%) was obtained with an improved nozzle, which allows a more efficient gas heating due to its higher heat exchange area.

Decolouration of textile dyes in wastewaters by photocatalysis with TiO 2

The photocatalytic removal of colour of a synthetic textile effluent, using TiO 2 suspensions under solar radiation, has been studied at pilot plant scale. A synthetic dye solution was prepared by a mix of six commercial textile dyes. A photochemical reactor of parallel CPC reflectors with UV-transparent tubular receivers was used. The study of photodegradation was carried out using the Taguchi’s parameter design method. Following this methodology, the reaction was conducted under different flow conditions, pH and H 2O 2 concentrations. The results show that all dyes used in the experiences can be degraded successfully by photo-oxidation. The process shows a significant enhancement when it is carried out at high flows, alkaline media and high H 2O 2 concentration. Colour removal from the effluent was reached at 55 min operating time.

A Multistage Solar Receiver:: The Route To High Temperature

A high-temperature solar thermal receiver is subject to temperature-dependent emission and convection losses. Minimizing these losses is essential to realization of high temperature, high efficiency systems. Dividing the aperture into separate stages according to the irradiance distribution has been shown theoretically to significantly reduce these losses. In such a partitioned system, the working fluid is gradually heated as it passes through a sequence of receiver elements with increasing irradiance levels. An experiment to demonstrate this principle using two heating stages has been constructed at the Weizmann Institute’s Solar Tower. The high-temperature receiver stage is the Directly Irradiated Annular Pressurized Receiver (DIAPR). The low-temperature stage is implemented as a partial ring of intermediate-temperature cavity tubular receivers (Preheaters) surrounding the central high-temperature stage. Following initial concentration by a part of the Weizmann Institute heliostat field, the light enters the receivers via secondary concentrators constructed as approximate CPCs. We present recent test results with the two-stage system. Air exit temperatures of up to 1000°C were obtained, with the low-temperature stage supplying up to 750°C. The power output was up to 55 kW th. Heat transfer in the high-temperature receiver, losses due to the partitioning, and future plans for partitioned receivers are discussed.

Contactless two-stage line focus collectors

Two new two-mirror solar collectors for tubular receiver, the Snail concentrator and the Helmet concentrator, are presented. The main feature of these concentrators is that they have a sizeable gap between the secondary mirror and the absorber, and they still achieve concentrations close to the thermodynamic limit with high collection efficiencies. This characteristic makes them unique and, on the contrary to the present two-stage designs, avoids the location of the secondary inside the evacuated tube. One of the differences between the Snail and the Helmet concentrators is that the last is symmetric (as the conventional parabolic trough) but the first is not. For an acceptance angle of α = ±0.73 degs and a collection efficiency of 96.8% (i.e. 3.2% of the rays incident on the primary mirror within the acceptance angle are rejected), the Snail concentrator and the Helmet concentrator achieve an average flux concentration of 91.1% and 72.8% of the thermodynamic limit, respectively. Moreover, both concentrators have also high rim angles of the primary mirror: ±86.2 degs (Helmet) and 98.8 degs (Snail). This is of interest for a good mechanical stability of the collector.

Contactless efficient two-stage solar concentrator for tubular absorber

The design of a new type of two-mirror solar concentrator for a tubular receiver, the XX concentrator, is presented. The main feature of the XX is that it has a sizable gap between the secondary mirror and the absorber and it still achieves concentrations close to the thermodynamic limit with high collection efficiencies. This characteristic makes the XX unique and, contrary to current two-stage designs, allows for the location of the secondary outside the evacuated tube. One of the XX concentrators presented achieves an average flux concentration within +/-0.73 deg of 91.1% of the thermodynamic limit with a collection efficiency of 96.8% (i.e., 3.2% of the rays incident on the primary mirror within +/-0.73 deg are rejected). Another XX design is 92.5% efficient and receives 95.1% of the maximum concentration. These values are the highest reported for practical concentrators, to our knowledge. The gap between the absorber and the secondary mirror is 6.8 and 10.5 times the absorber radius for each concentrator. Moreover the rim angle of the primary mirror is 98.8 and 104.4 deg in each case, which is of interest for the collector's good mechanical stability.

Analysis of a Two-Stage Linear Fresnel Reflector Solar Concentrator

The two-stage linear Fresnel reflector solar concentrator is analyzed via an in-depth study of an installed, nominally 220 KWt system. The concentrator includes: (1) a primary linear Fresnel reflector comprised of curved mirrors and (2) a secondary nonimaging CPC-type trough with a tubular receiver. The principal practical design options for the secondary concentrator are evaluated. Via a computer simulation which includes ray-tracing of the primary reflector, we evaluate the sensitivity of energy output to: concentrator optical errors, system geometry, tracking mode, and the option of using flat versus curved primary mirrors. The two-stage Fresnel concentrator can be considerably less expensive than the corresponding parabolic trough collector, but is found to deliver about one-fourth less yearly energy. However, much of this difference could be eliminated through the use of higher-quality CPC reflectors.