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Wenquan Tao - One of the best experts on this subject based on the ideXlab platform.
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numerical investigations on fully developed mixed turbulent convection in dimpled parabolic trough Receiver Tubes
Applied Thermal Engineering, 2017Co-Authors: Zhen Huang, Wenquan TaoAbstract:Abstract The fully-developed mixed turbulent convective heat transfer characteristics in dimpled Tubes of parabolic trough Receiver are numerically studied at a certain Reynolds number of 2 × 104 and different Grashof numbers ranged from 0 to 3.2 × 1010 to produce substantial surface heat transfer augmentations with relatively small pressure drop penalties. The Boussinesq approximation is applied, in which variations in fluid properties other than density are ignored. The Realizable k-e two-equation turbulence model with enhancement wall treatment is adopted. The influences of outer wall heat flux distributions and dimple depth on flow resistance and heat transfer rate are illustrated and analyzed. The results indicate that the average friction factor and Nusselt number in dimpled Receiver Tubes under non-uniform heat flux (NUHF) are larger than those under uniform heat flux (UHF). In most cases, the comprehensive performance of dimpled Receiver Tube under NUHF is also better than that under UHF. The deep dimples (d/Di = 0.875) are far superior to the shallow dimples (d/Di = 0.125) at a same Grashof number.
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numerical study on combined natural and forced convection in the fully developed turbulent region for a horizontal circular Tube heated by non uniform heat flux
Applied Energy, 2017Co-Authors: Zhen Huang, Wenquan TaoAbstract:Abstract The present work focuses on the fully developed mixed turbulent flow and heat transfer in Receiver Tube heated by non-uniform heat flux, especially the effect of local buoyancy force induced by the non-uniform heat flux at Reynolds number of 2 × 104–105, Prandtl number of 1.5 and Grashof number of 0–1012. The friction factor and Nusselt number between forced convection and mixed convection under uniform heat flux and non-uniform heat flux are analyzed quantitatively. The effect of solar elevation angle on the fluid flow and heat transfer is also investigated. It is concluded that the mixed fluid flow and heat transfer under non-uniform heat flux is different from that under uniform heat flux. The solar elevation angle has strong influence on the mixed fluid flow and heat transfer characteristics. A criterion for the buoyancy free is proposed. It is not feasible to perform the heat transfer design and prediction for parabolic trough solar collector based on the experimental correlations for forced convection or conventional mixed convention.
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three dimensional numerical study on fully developed mixed laminar convection in parabolic trough solar Receiver Tube
Energy, 2016Co-Authors: Zhen Huang, Wenquan TaoAbstract:Abstract In this paper, a numerical investigation is presented, aiming at the effect of the buoyancy force induced by the non-uniform heat flux on the laminar flow and heat transfer characteristics in the solar Receiver Tube of parabolic trough collector. The flow and heat transfer performances are analyzed for forced and mixed laminar convection in Receiver Tube heated by uniform and non-uniform heat fluxes with different Grashof numbers, Reynolds numbers and solar elevation angles. The results show that the natural convection can increase heat transfer rate of laminar forced convection by more than 10% when the Grashof number is greater than a threshold value. The mixed fluid flow and heat transfer characteristics vary with solar elevation angle. Heat transfer deterioration occurs when the Richardson number is greater than 12.8.
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three dimensional numerical study on turbulent mixed convection in parabolic trough solar Receiver Tube
Energy Procedia, 2015Co-Authors: Zhen Huang, Wenquan TaoAbstract:Abstract The present work focuses on the fully developed mixed turbulent flow and heat transfer in Receiver Tube heated by non-uniform heat flux, especially the effect of local buoyancy force induced by the non-uniform heat flux at Reynolds number of 2×104-105, Prandtl number of 1.5 and Grashof number of 0-1012. The friction factor and Nusselt number between forced convection and mixed convection under uniform heat flux and non-uniform heat flux are analyzed quantitatively. The effect of solar elevation angel on the fluid flow and heat transfer is also investigated. We found that it is not feasible to perform the heat transfer design and prediction for parabolic trough solar collector based on the experimental correlations for forced convection or traditional mixed convention.
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numerical study on heat transfer enhancement in a Receiver Tube of parabolic trough solar collector with dimples protrusions and helical fins
Energy Procedia, 2015Co-Authors: Zhen Huang, Wenquan TaoAbstract:Abstract Vacuum tubular Receiver is the core component of parabolic trough solar collectors (PTCs). To enhance the heat transfer rate from solar radiation to heat transfer fluid (HTF), one of the effective techniques is to improve the convective heat transfer inside the inner Tube. In this study, we focus the heat transfer of the HTF side. A numerical simulation on the fully developed turbulent flow and heat transfer in the inner Tube with and without helical fins, protrusions and dimples has been investigated. The results show that the Receiver Tubes with dimples have superior performance of heat transfer augmentation compared with that with protrusions or helical fins. Then, the effects of the geometry sizes and arrangements of dimples on the convective heat transfer performance are further studied. The performance evaluation plot of heat transfer enhancement techniques show that dimples with deeper depth, narrower pitch and more numbers in the circumference direction is benefit for improving the performance of heat transfer enhancement while the varied arrangements have no obvious influence.
Zhangjing Zheng - One of the best experts on this subject based on the ideXlab platform.
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thermal analysis of solar central Receiver Tube with porous inserts and non uniform heat flux
Applied Energy, 2017Co-Authors: Zhangjing ZhengAbstract:Abstract In this paper, enhancement for convection heat transfer of turbulent flow in a solar central Receiver Tube with porous medium and non-uniform circumferential heat flux was numerically investigated. A new method was introduced to build different porous medium configurations in a unified grid system. Four kinds of enhanced Receiver Tubes (ERTs) with different porous insert configurations were modeled to optimize the performance of ERT. Furthermore, parameters including filling ratio of porous medium, thermal conductivity ratio (thermal conductivity of porous medium versus that of working fluid), porosity and Reynolds number were analyzed. The results showed that ERT partially filled with porous medium has better heat transfer performance than that fully filled with porous medium. The configuration of porous insert for optimal thermal or thermo-hydraulic performance is interactively affected by all the parameters discussed in this paper. The thermal conductivity ratio is the most crucial parameter to the thermal or thermo-hydraulic performance of ERT. The value of thermal conductivity ratio should be greater than 100 to obtain a good thermo-hydraulic performance. The ERTs with horizontal cylindrical segment shaped porous inserts and hollow cylinder shaped porous inserts are proposed because they can obtain optimal thermal or thermo-hydraulic performance.
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thermal analysis of a solar parabolic trough Receiver Tube with porous insert optimized by coupling genetic algorithm and cfd
Science China-technological Sciences, 2016Co-Authors: Zhangjing ZhengAbstract:In this paper, the heat transfer enhancement in a solar parabolic trough Receiver Tube with porous insert and non-uniform heat flux condition was investigated. A new optimization method, which couples genetic algorithm (GA) and computational fluid dynamics (CFD) based on Socket communication, was proposed to optimize the configuration of porous insert. After the acquisition of the optimal porous inserts, some performance evaluation criterions such as synergy angle, entransy dissipation and exergy loss were introduced to discuss the heat transfer performance of the enhanced Receiver Tubes (ERTs) with optimal and referenced porous inserts. The results showed that, for a large range of properties of porous insert (including porosity and thermal conductivity) and Reynolds number, the heat-transfer performance of ERT with porous insert optimized by GA is always higher than that of the referenced ERTs. Better heat-transfer performance can further improve the solar-to-thermal energy conversion efficiency and mechanical property of the solar parabolic trough Receiver. When some porous materials with high thermal conductivity are adopted, ERT can simultaneously obtain perfect thermal and thermo-hydraulic performance by using the same optimized porous insert, which cannot be achieved by using the referenced porous insert. In the view of those introduced evaluation criterions, using the optimized porous insert can obtain better synergy performance and lesser irreversibility of heat transfer than using the referenced porous insert. Entransy dissipation per unit energy transferred and exergy loss rate have equivalent effects on the evaluation of irreversibility of heat transfer process. These evaluation criterions can be used as optimization goals for enhancing the comprehensive performance of the solar parabolic trough Receiver.
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analysis of thermal stress and fatigue fracture for the solar tower molten salt Receiver
Applied Thermal Engineering, 2016Co-Authors: Zhangjing Zheng, Zedong ChengAbstract:Abstract In this paper, the thermal stress and fatigue fracture of a single Tube for the solar tower molten salt Receiver are presented. First, the temperature distribution of the Tube is simulated. Second, the thermal stress is calculated by solving stress equations. Then the minimum heat flux formula is derived when damage occurs on wall based on the yield criterion and heat conduction equation. Finally, the critical crack length on outer wall is investigated by using the Crack Tip Opening Displacement (CTOD) method. The results show that the distribution of stress is similar to that of inner/outer wall temperature difference. The maximum stress, which causes plastic deformation, occurs on outer wall. According to the minimum heat flux formula q ≥ [ σ s ] / ( K A 2 + B 2 + C 2 − A B − A C − B C ) derived in this paper, the heat flux is only 0.19 MW⋅m−2 when damage appears on the Receiver Tube if the inlet temperature and safety factor are 560 K and 1.5 respectively. Furthermore, the critical crack length is 17 mm when the heat flux is 0.7 MW⋅m−2.
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numerical optimization of catalyst configurations in a solar parabolic trough Receiver reactor with non uniform heat flux
Solar Energy, 2015Co-Authors: Zhangjing Zheng, Kun WangAbstract:Abstract A three-dimensional numerical model of a solar parabolic trough Receiver–reactor (SPTRR) with methanol steam reforming reaction was developed. Based on this model, the characteristics of hydrodynamics, heat transfer and chemical reaction of SPTRR were studied. Also, the effects of non-uniform heat flux boundary condition, catalyst layout and mass flow rate on the performances of SPTRR were analyzed. The results showed that SPTRRs partially filled with catalyst have better comprehensive performance than those fully filled with catalyst, and the SPTRR with horizontal cylindrical segment shaped catalyst in the lower part of Receiver Tube is recommended to substitute the fully catalyst-filled SPTRR. The chemical energy conversion per unit pump power of the proposed partially catalyst-filled SPTRR is one order of magnitude larger than that of the fully catalyst-filled SPTRR, and the mean outer surface temperature and maximum outer surface temperature difference of the proposed partially catalyst-filled SPTRR can be as low as that of the fully catalyst-filled SPTRR, when the mass of the catalyst in the partially catalyst-filled SPTRR is 0.4 times as much as that in the fully catalyst-filled SPTRR.
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optimization of porous insert configuration in a central Receiver Tube for heat transfer enhancement
Energy Procedia, 2015Co-Authors: Zhangjing ZhengAbstract:Abstract In this paper, the heat transfer enhancement for convection heat transfer of turbulent flow in a central Receiver Tube filled with porous medium under non-uniform circumferential heat flux was numerically investigated. The effects of some parameters of porous medium (layout, thermal conductivity and porosity) and the Reynolds number (Re) on the thermal and thermo-hydraulic performance were discussed. The results showed that the enhanced Receiver Tube (ERT) with down-filling porous inserts and in-filling porous inserts have good thermal performance when the ratio of thermal conductivity of porous medium to working fluid (λs/λf) is less than 1,000. The ERT with out-filling porous inserts and up-filling porous inserts have good thermo-hydraulic performance when λs/λf >100. The porosity (ɛ) and Re also affect the thermal and thermo-hydraulic performance, the Nusselt number (Nu) and performance evaluation criteria (PEC) of heat transfer enhancement under constant pumping power of most kinds of ERTs decrease with the increase of ɛ, but the PEC of the ERT with in-filling porous inserts increases with the increase of ɛ. The Nu of all kinds of ERTs increases with the increase of Re, but the PEC decreases with the increase of Re.
Harish C. Barshilia - One of the best experts on this subject based on the ideXlab platform.
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Selective properties of high-temperature stable spinel absorber coatings for concentrated solar thermal application
Solar Energy, 2020Co-Authors: S R Atchuta, S Sakthivel, Harish C. BarshiliaAbstract:Abstract In concentrated solar thermal (CST) system, Receiver Tube is one of the key important elements in the photothermal conversion process. The high photothermal efficiency of the Receiver Tube greatly depends upon the coating type, angular selectiveness of the coating, and radiative, conductive and convective losses. Apart from the efficiency, cost-effectiveness of the components is the major hurdle for the CST system to make it a viable technology. In this regard, we have implemented wet-chemical based spinel absorber coatings in a tandem layer approach to make the coating more selective in terms of high absorptance (95%), low emissivity (13%) and wide angular selectiveness (0 to 60°). The coatings are tested for thermal stability and corrosion resistance to check their stability in open-air atmosphere condition. Further, the photothermal conversion efficiencies of the developed coatings are calculated at different temperatures ranging from 300 to 500 °C by considering the actual thermal emissivity values of the absorber coating at that particular temperature.
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nickel doped cobaltite spinel as a solar selective absorber coating for efficient photothermal conversion with a low thermal radiative loss at high operating temperatures
Solar Energy Materials and Solar Cells, 2019Co-Authors: S R Atchuta, S Sakthivel, Harish C. BarshiliaAbstract:Abstract Concentrated Solar Thermal (CST) system efficiency depends mainly on the operating temperature. One of the key components in the CST system is the Receiver Tube to attain higher temperatures, where the challenge remains on developing a solar absorber coating with high photothermal conversion and thermal stability at high temperatures. Nickel doped cobaltite (NixCo3-xO4; 0 ≤ x ≥ 1) thin film has been developed with spinel oxide phase on top of stainless steel substrates using a simple wet-chemical dip coating method as a base absorber layer (absorptance, α = 0.92; emittance, e = 0.14). On top of the base absorber layer, coating integrated with silica (SiO2) as an optical enhancement layer (OPEL) has been deposited to make the coating more selective (α = 0.94 and e = 0.13). A thorough investigation has been done to characterize the samples through UV–Vis–NIR spectrophotometer, Fourier transform infra-red spectroscopy, X-ray diffraction, transmission electron microscopy and thermogravimetric analyzer for the optical and physiochemical properties. Besides, the optimized spinel coating exhibits a low radiative loss with a minimum thermal emissivity of 0.07 at 100 °C and 0.18 at 500 °C, which indicates that the nickel cobaltite spinels are a very good candidate for high temperature solar selective applications.
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high temperature stable spinel nanocomposite solar selective absorber coating for concentrated solar thermal application
Proceedings of the ISES Solar World Congress 2019, 2019Co-Authors: S R Atchuta, Harish C. Barshilia, Sakthivel ShanmugasundaramAbstract:A new Cu-Ni-Co ternary spinel/SiO2 nanocomposite oxide absorber with tandem layer approach is designed and developed for medium and high temperature solar selective Receiver Tube in concentrated solar thermal applications. The base absorber layer, developed by combining of nanostructured, transition metal spinel and composite oxides with a series of transition metal based salts (Co, Ni, and Cu) in wet chemical method. By optimizing the sol concentration, withdrawal speed and annealing temperature, uniform absorber layer with solar absorptance (α) of 0.91 and emittance (e) of 0.14 were achieved in a single layer coating with a composite oxide formation. On top of the base absorber layer, coating integrated with silica (SiO2) nanoparticles added as an optical enhancement layer to make the coating more selective (α: 0.95 & e: 0.13). A thorough characterization has been done for the optical and physiochemical properties of the samples. Besides, the optimized spinel coating exhibits a low radiative loss of about 0.18 thermal emissivity at 500 °C and 89.3 % photothermal conversion efficiency at 500 °C, which identifies that the spinels are a very good candidate for medium and high temperature solar selective absorbers.
Zhirong Liao - One of the best experts on this subject based on the ideXlab platform.
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thermal analysis of a heat pipe solar central Receiver for concentrated solar power tower
Applied Thermal Engineering, 2016Co-Authors: Zhirong Liao, Amir FaghriAbstract:Abstract A novel heat pipe solar central Receiver for a molten salt solar power tower is presented. The basic element consists of a reflector, heat pipe, and Receiver Tube. The reflector redirects concentrated sunlight from the heliostats field onto the evaporator section of the heat pipe. After absorbing the radiative heat energy, the working fluid inside the heat pipe is vaporized at the evaporator section, and flows to the condenser section of the heat pipe where it condenses. The condenser section is inserted into the Receiver Tube, and is cooled by a cross flow of the heat transfer fluid inside the Receiver Tube. In the proposed concept, the Receiver Tube is free from direct irradiation by the sunlight and therefore can be kept warm by electrical heating. This will extend the daily operating time of the Receiver and greatly reduce possible freezing of the molten salt. In this study, a cavity Receiver with the same geometry and boundary conditions as the Molten Salt Electrical Experiment (MSEE) cavity Receiver was developed. Numerical simulation for the basic element of the cavity Receiver was conducted. An 88.5% efficiency was obtained, which is slightly higher than the MSEE. Moreover, the Receiver efficiency under a different number of flow passes and various heat flux density on the absorbing surface was also studied. Results show that the Receiver efficiency can be as high as 91.5%.
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numerical model and validation for simulating the cold filling of the molten salt Receiver Tube
Energy Procedia, 2015Co-Authors: Zhirong Liao, Z Wang, Chaoyi ChangAbstract:Abstract Anti-protecting against freezing and preheating the components are the most critical problems of molten salt Receiver. Cold filling is a potential solution to these problems. This paper presents a numerical model for simulating the cold filling of a Receiver Tube. The model uses the volume of fractionmethod to track the interface betweenthe molten salt and the air and the enthalpy method to describe the liquid-solid phase change of the molten salt. This model was used to simulate the cold filling tests of the Molten Salt Electric Experiment (MSEE) Receiver. This model was then use to simulate the dynamic process of cold filling a vertical Receiver Tube. Three modes of cold filling, including successful filling, partial frozen filling and fully frozen filling, were demonstrated. The results show that high initial temperature of the Receiver Tubes is benefit for successful filling.
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phase change of molten salt during the cold filling of a Receiver Tube
Solar Energy, 2014Co-Authors: Zhirong Liao, Zhifeng Wang, Chun ChangAbstract:Abstract The most critical problems for the molten salt solar power plant are protecting against freezing and preheating of the flow pipes and equipments. A candidate way to solve these problems is cold filling. In this study, the dynamic process of molten salt cold filling into a Receiver Tube was simulated by combining the volume of fluid method and the enthalpy method. The detailed mechanism of melting-solidification and the evolution of the pressure drop along the Tube were demonstrated. The influence of cold filling on the temperature across the Tube wall was analysed as well. The results indicate that a lower pressure drop can be obtained by increasing the salt temperature and the initial Tube temperature, and that an optimal velocity is required to get minimum pressure drop. The temperature difference between the external and internal surfaces of the Tube wall increases with the filling velocity and the filling temperature whereas decreases with the initial Tube temperature and the heat flux on the external surface. A large filling velocity and a high filling temperature that results in large temperature difference across the wall of the Tube should be avoided. This study gives practical reference to the application of cold filling in molten salt Receiver.
Zhen Huang - One of the best experts on this subject based on the ideXlab platform.
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numerical investigations on fully developed mixed turbulent convection in dimpled parabolic trough Receiver Tubes
Applied Thermal Engineering, 2017Co-Authors: Zhen Huang, Wenquan TaoAbstract:Abstract The fully-developed mixed turbulent convective heat transfer characteristics in dimpled Tubes of parabolic trough Receiver are numerically studied at a certain Reynolds number of 2 × 104 and different Grashof numbers ranged from 0 to 3.2 × 1010 to produce substantial surface heat transfer augmentations with relatively small pressure drop penalties. The Boussinesq approximation is applied, in which variations in fluid properties other than density are ignored. The Realizable k-e two-equation turbulence model with enhancement wall treatment is adopted. The influences of outer wall heat flux distributions and dimple depth on flow resistance and heat transfer rate are illustrated and analyzed. The results indicate that the average friction factor and Nusselt number in dimpled Receiver Tubes under non-uniform heat flux (NUHF) are larger than those under uniform heat flux (UHF). In most cases, the comprehensive performance of dimpled Receiver Tube under NUHF is also better than that under UHF. The deep dimples (d/Di = 0.875) are far superior to the shallow dimples (d/Di = 0.125) at a same Grashof number.
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numerical study on combined natural and forced convection in the fully developed turbulent region for a horizontal circular Tube heated by non uniform heat flux
Applied Energy, 2017Co-Authors: Zhen Huang, Wenquan TaoAbstract:Abstract The present work focuses on the fully developed mixed turbulent flow and heat transfer in Receiver Tube heated by non-uniform heat flux, especially the effect of local buoyancy force induced by the non-uniform heat flux at Reynolds number of 2 × 104–105, Prandtl number of 1.5 and Grashof number of 0–1012. The friction factor and Nusselt number between forced convection and mixed convection under uniform heat flux and non-uniform heat flux are analyzed quantitatively. The effect of solar elevation angle on the fluid flow and heat transfer is also investigated. It is concluded that the mixed fluid flow and heat transfer under non-uniform heat flux is different from that under uniform heat flux. The solar elevation angle has strong influence on the mixed fluid flow and heat transfer characteristics. A criterion for the buoyancy free is proposed. It is not feasible to perform the heat transfer design and prediction for parabolic trough solar collector based on the experimental correlations for forced convection or conventional mixed convention.
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three dimensional numerical study on fully developed mixed laminar convection in parabolic trough solar Receiver Tube
Energy, 2016Co-Authors: Zhen Huang, Wenquan TaoAbstract:Abstract In this paper, a numerical investigation is presented, aiming at the effect of the buoyancy force induced by the non-uniform heat flux on the laminar flow and heat transfer characteristics in the solar Receiver Tube of parabolic trough collector. The flow and heat transfer performances are analyzed for forced and mixed laminar convection in Receiver Tube heated by uniform and non-uniform heat fluxes with different Grashof numbers, Reynolds numbers and solar elevation angles. The results show that the natural convection can increase heat transfer rate of laminar forced convection by more than 10% when the Grashof number is greater than a threshold value. The mixed fluid flow and heat transfer characteristics vary with solar elevation angle. Heat transfer deterioration occurs when the Richardson number is greater than 12.8.
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three dimensional numerical study on turbulent mixed convection in parabolic trough solar Receiver Tube
Energy Procedia, 2015Co-Authors: Zhen Huang, Wenquan TaoAbstract:Abstract The present work focuses on the fully developed mixed turbulent flow and heat transfer in Receiver Tube heated by non-uniform heat flux, especially the effect of local buoyancy force induced by the non-uniform heat flux at Reynolds number of 2×104-105, Prandtl number of 1.5 and Grashof number of 0-1012. The friction factor and Nusselt number between forced convection and mixed convection under uniform heat flux and non-uniform heat flux are analyzed quantitatively. The effect of solar elevation angel on the fluid flow and heat transfer is also investigated. We found that it is not feasible to perform the heat transfer design and prediction for parabolic trough solar collector based on the experimental correlations for forced convection or traditional mixed convention.
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numerical study on heat transfer enhancement in a Receiver Tube of parabolic trough solar collector with dimples protrusions and helical fins
Energy Procedia, 2015Co-Authors: Zhen Huang, Wenquan TaoAbstract:Abstract Vacuum tubular Receiver is the core component of parabolic trough solar collectors (PTCs). To enhance the heat transfer rate from solar radiation to heat transfer fluid (HTF), one of the effective techniques is to improve the convective heat transfer inside the inner Tube. In this study, we focus the heat transfer of the HTF side. A numerical simulation on the fully developed turbulent flow and heat transfer in the inner Tube with and without helical fins, protrusions and dimples has been investigated. The results show that the Receiver Tubes with dimples have superior performance of heat transfer augmentation compared with that with protrusions or helical fins. Then, the effects of the geometry sizes and arrangements of dimples on the convective heat transfer performance are further studied. The performance evaluation plot of heat transfer enhancement techniques show that dimples with deeper depth, narrower pitch and more numbers in the circumference direction is benefit for improving the performance of heat transfer enhancement while the varied arrangements have no obvious influence.
