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K S Reddy - One of the best experts on this subject based on the ideXlab platform.

  • Estimation of convective heat losses from conical Cavity Receiver of solar parabolic dish collector under wind conditions and Receiver orientations
    'EDP Sciences', 2021
    Co-Authors: Abhinav Rajan, K S Reddy
    Abstract:

    The parabolic dish collector is one of the recognized concentrated solar power systems based on point focusing, which provides high-temperature heat, high concentration ratio, and low heat loss. This system consists of a parabolic reflector and a Cavity Receiver situated in the focus line. In this work, the conical Cavity Receiver with an aperture diameter of 0.5 m is considered for a 100 m2 parabolic reflector having a focal to diameter ratio of 0.48. Due to the complexity of flow and temperature profile, the estimation of convective heat loss is a difficult task in a Cavity Receiver. More heat losses are associated with high temperature obtained in the Cavity Receiver of the parabolic dish collector. Due to diverse wind effect, the convective heat losses ramp up, which significantly influences the thermal performance of the concentrating power system. The present work aims to investigate the heat losses due to convection from the conical Cavity Receiver. The numerical investigation was performed using ANSYS Fluent 20R1 to calculate the convective heat losses from the conical Cavity Receiver of varying diameter to height ratio for varying wind speed, Receiver orientation in head-on, and back-on wind flow directions. The considered influential parameters are varying from 0.5 to 1.5 for diameter to height ratio (d/h), 0° to 90° for Receiver orientation (γ), 0 to 10 m/s for wind speed (V). The heat losses are highest at 60° and 75° Receiver orientation for d/h = 0.5 and d/h = 1-1.5, respectively, at high wind speed in head-on condition, whereas in back-on wind condition, 30° Receiver orientation has more heat losses among all the d/h values at high wind speed. The heat loss at 90° Receiver orientation is low for 4-10 m/s. The trends of heat loss curve at Receiver orientations for given wind conditions are similar for velocity more than 2 m/s. The result reveals that the considered influential parameters have a remarkable effect on convective heat losses from the Cavity Receiver

  • effect of wind speed and direction on convective heat losses from solar parabolic dish modified Cavity Receiver
    Solar Energy, 2016
    Co-Authors: K S Reddy, G Veershetty, Srihari T Vikram
    Abstract:

    Abstract The performance of solar parabolic dish collector is significantly influenced by heat losses due to wind speed and direction. In this article, investigation of convective heat losses from the modified Cavity Receiver of solar parabolic dish collector is carried out numerically by considering the wind direction, wind speed, Receiver configuration and Receiver orientation. The effect of wind on the Receiver in various directions ( φ  = −90° to 90°), wide range of operating wind speeds ( V  = 0–10 m/s), Receiver inclinations ( β  = 0–90°) and varying surface temperature on convective heat loss from the Receiver are studied. Velocity vectors, velocity contours, temperature contours are presented to show the effect of wind on the heat loss from the modified Cavity Receiver. The forced convection is found to have similar trend of free convection heat loss at lower wind speed. However at higher wind speed, such a pattern is not observed. At lower wind speeds say less than critical wind speed ( φ and β values. For side-on winds, at higher wind speeds above 5 m/s, irrespective of Receiver inclination, the variation of forced convection heat loss is marginal (less than 5%). The maximum forced convection heat loss occurs for partly open Receivers (Receiver aperture diameter ratio, R AD  = 0.4 and 0.6) at φ  = 0 (side-on wind) for all Receiver inclinations and at φ  = 30° for R AD  = 0.8 and 1. The Receiver inclination has less effect on heat loss from the Receiver for V  > 2.5 m/s due to side-on wind. The highest convection heat loss occurs for fully open ( R AD  = 1) Receiver as compared to partly open ( R AD

  • combined heat loss analysis of solar parabolic dish modified Cavity Receiver for superheated steam generation
    Solar Energy, 2015
    Co-Authors: K S Reddy, Srihari T Vikram, G Veershetty
    Abstract:

    Abstract In this article, a 3-D numerical modeling is carried out to determine combined convection and surface radiation heat losses from a modified Cavity Receiver of parabolic dish collector used as mono-tube boiler for sub-cooled, saturated and superheated steam generation conditions. The forced convection heat loss from the modified Cavity Receiver is estimated using Nusselt number correlation developed for the modified Cavity Receiver. The effect of Receiver inclination ( β ) , operating temperature ( T w ) , emissivity of the Cavity cover ( ∊ ) , thickness of insulation ( t ins ) on the combined heat losses from the modified Cavity Receiver is investigated. The boundary conditions for wall temperature and insulation thicknesses are chosen to match the three steam generation conditions. It is found that the natural convection heat losses are higher at β = 0 ° (Receiver facing sideward) and lower at β = 90 ° (Receiver facing down) whereas the forced convection heat loss is higher at β = 90 ° and lower at β = 0 ° . The variation of radiation heat losses is marginal for all values of β and vary with T w . The effect of various parameters such as Receiver inclination, wind direction ( φ ) , wind speed and diameter ratios on forced convection heat loss from the Receiver has also been studied. The forced convection heat loss at lower wind speeds ( ( φ = 0 ) followed by head-on wind directions ( φ  = 30–90°) and back-on wind directions ( φ = - 90 ° to - 30 ° ) . The heat losses vary with diameter ratios for different configurations of the Receiver. The forced convection heat loss is 1.2–9 times higher than natural convection heat loss for diameter ratio (ratio of Cavity diameter to aperture diameter, d/D) = 0.4 at 5 m/s and Receiver inclinations varying from 0° to 90 ° . Nusselt number correlations have been proposed based on the numerical analysis to estimate the combined convective and radiative heat loss. The present study attempts to estimate natural convection, forced convection and surface radiation heat losses from the modified Cavity Receiver under various conditions.

  • experimental performance investigation of modified Cavity Receiver with fuzzy focal solar dish concentrator
    Renewable Energy, 2015
    Co-Authors: K S Reddy, Sendhil Kumar Natarajan, G Veershetty
    Abstract:

    Abstract In this paper, thermal performance analysis of 20 m 2 prototype fuzzy focal solar dish collector is presented. The focal image characteristics of the solar dish are determined to propose the suitable design of absorber/Receiver. First, theoretical thermal performance analysis of the fuzzy focal solar parabolic dish concentrator with modified Cavity Receiver is carried out for different operating conditions. Based on the theoretical performance analysis, the total heat loss (conduction, convection and radiation heat losses) from the modified Cavity Receiver is estimated. It is observed that the maximum theoretical efficiencies of solar dish collector are found to be as 79.2% for no wind conditions and 78.2% and 77.8% for side-on and head-on winds speed of 5 m/s respectively. Latter, real time analysis of parabolic dish collector with modified Cavity Receiver is carried out in terms of stagnation test, time constant test and daily performance test. From stagnation test, the overall heat loss coefficient is found to be 356 W/m 2  K. The time constant test is carried out to determine the influence of sudden change in solar radiation at steady state conditions. The daily performance tests are conducted for different flow rates. It is found that the efficiency of the collector increases with the increase of volume flow rates. The average thermal efficiencies of the parabolic dish collector for the volume flow rate of 100 L/h and 250 L/h are found to be 69% and 74% for the average beam radiation (I bn ) of 532 W/m 2 and 641 W/m 2 respectively.

  • estimation of convective and radiative heat losses from an inverted trapezoidal Cavity Receiver of solar linear fresnel reflector system
    International Journal of Thermal Sciences, 2014
    Co-Authors: K S Reddy, Ravi K Kumar
    Abstract:

    Abstract Solar linear Fresnel reflector (LFR) system is simple in design and cost effective technology for medium temperature (400 °C) applications. In this article, convective and radiative heat losses from the inverted trapezoidal Cavity Receiver for solar linear Fresnel reflector are estimated using a two dimensional (2-D) numerical model. The 2-D numerical simulation of trapezoidal Cavity Receiver is carried out by considering the Receiver surface as isothermal conditions. The heat loss analysis is carried out for various Receiver geometric and operating parameters viz. thickness of the insulation ( t ins ), aspect ratio ( A s ), Cavity depth ( D c ), Cavity width ( w ), operating temperature ( T r ), Cavity cover emissivities ( e cc ), and wind speed ( V w ). Based on the numerical simulation of the Receiver, an optimum configuration of trapezoidal Cavity Receiver is obtained with t ins  = 300 mm, D c  = 300 mm and A s  = 2. The total heat losses varies from 663.47 W/m to 1046.3 W/m for w of 300 mm–800 mm at T r  = 500 °C, e cc  = 0.5, V w  = 2.5 m/s. The effect of Cavity cover emissivity on total heat losses is found to be less significant when compared to that of other Cavity parameters. The optimum Receiver configuration of the inverted trapezoidal Cavity Receiver can be used in solar LFR system with minimum heat losses.

Zhifeng Wang - One of the best experts on this subject based on the ideXlab platform.

  • analysis and improvement of solar flux distribution inside a Cavity Receiver based on multi focal points of heliostat field
    Applied Energy, 2014
    Co-Authors: Zhifeng Wang
    Abstract:

    Abstract The strong flux variations distributed on the surfaces of Receiver during its service life can intensify material aging and thus deteriorate the thermal performance of material. Generally, the single focal point heliostat field, i.e., focusing at the centre of the aperture of a Cavity Receiver, could possibly result in an irregular flux distribution, which would have a very high peak value of flux density on the inner sides of the Cavity Receiver at a certain time of sun tracking. In order to give a maximum protection to the central Receiver, in this paper, by taking the 1 MWe “DAHAN” solar tower power plant as the investigating subject, a multi-focal point model for finding the optimum configuration of focal points using an arbitrary heliostat has been developed. Based on the model, the pattern of solar flux distribution for different zones of the heliostat field is investigated to study how the pattern changes with date and time. From the simulation results, a new grouping method for the layout of the focal points of a heliostat field inside the Cavity Receiver is proposed. Then a popular optimization algorithm based on the TABU meta-heuristic method is developed to find the optimal flux distribution on the Receiver surface. The objective is to flatten the flux distribution as much as possible by changing the aiming points of different groups. Simulation results show that the new multi-focal points system can provide a more secure way to safeguard the operation of the Receiver system comparing to the traditional single focal point system.

  • numerical simulation on the thermal performance of a solar molten salt Cavity Receiver
    Renewable Energy, 2014
    Co-Authors: Zheshao Chang, Chun Chang, Zhifeng Wang
    Abstract:

    Abstract The Receiver thermal performance directly affects the efficiency, reliability and safety of the entire solar tower power system. A model combining radiation, convection and conduction heat transfer modes was developed to model a 1 MW molten salt Cavity Receiver with determined basic design parameters. The coupled heat transfer model was used to predict the Receiver's steady-state efficiency, temperature distribution and heat losses for various flow layouts and Receiver aperture lip sizes. The results show that the fraction of reflective loss (18.78%) is the largest in all heat losses, followed by radiative and convective heat losses, with conduction heat losses as the smallest part which is usually negligible. The heat loss distribution is closely related to the external tube temperature field in the Cavity Receiver and the specific structure of the Receiver. 10 cm lips on both the top and bottom of the Receiver aperture reduced the reflective heat loss by 1%. The results for different flow layouts show that center-side flow layout has the best temperature homogeneity, with less possibility of overheating in the central area. This, however, comes at the expense of increased irreversibilities and decreased efficiency. The sides-center flow layout has the worst temperature homogeneity, but the Receiver efficiency is 2.06% higher. These results provide a useful reference for designing and optimizing Cavity Receivers.

  • experimental and theoretical analysis of a dynamic test method for molten salt Cavity Receiver
    Renewable Energy, 2013
    Co-Authors: Qiangqiang Zhang, Zhifeng Wang, Chun Chang, Hong Liu
    Abstract:

    Abstract Test methods for estimating the thermal performance of the molten salt Receiver are a matter of ongoing concern. To date, test methods in the literature require Receiver to be operated in steady state or quasi-steady state. However, the Receiver is always operating in the unsteady state with ongoing changes in power absorption and flow rate. Therefore, research into dynamic test method for the molten salt Cavity Receiver is required. The Transfer Function Method (TFM) is a successful dynamic test method for solar collectors. In this paper, a theoretical analysis of the TFM was applied to the molten salt Cavity Receiver and then verified by indoor transient experiments. The TFM predicted outlet temperature of the Receiver was compared with experimental data. The results showed that the TFM accurately predicted the outlet temperature trends despite some errors between predicted and measured outlet temperature. The errors may have originated from the changing flow rate. The TFM is a good candidate as a dynamic test method for the concentrated solar Receiver.

  • modeling and simulation of 1 mwe solar tower plant s solar flux distribution on the central Cavity Receiver
    Simulation Modelling Practice and Theory, 2012
    Co-Authors: Zhifeng Wang, Hongli Zhang, Xiudong Wei
    Abstract:

    Abstract The solar flux distribution rule inside a central Cavity Receiver is of great significance to the safe operation of solar tower power plants. In this paper, a heliostat field model was fully developed to simulate the solar flux distribution on the inner surfaces of a Cavity Receiver of a solar tower power plant by means of the Monte-Carlo ray-tracing method. In addition, the mathematical modeling process that starts from the incident solar rays to the absorbed energy by the inner surfaces of the Cavity Receiver was presented in detail. According to the final layout of the heliostat field, a dynamic simulation of the solar flux inside the Cavity Receiver during the vernal equinox was performed. The results indicated that the incident energy reflected by the heliostat field was mainly distributed on the rear and lateral surfaces throughout the day. Moreover, at different time points, the solar flux distribution rule inside the Cavity Receiver was also analyzed in detail. In order to verify the validity of this model, the simulation results were taken to compare with the experimental data of a random heliostat. Furthermore, to further testify the accuracy of our model, the simulation results obtained by inputting the coordinates of the CESA-I’s heliostat field into our model were also taken to compare with the published experiment data. Ultimately, both of the comparative results show that they can be good references for the safe design of the whole system.

  • simulation and analysis of the central Cavity Receiver s performance of solar thermal power tower plant
    Solar Energy, 2012
    Co-Authors: Zhifeng Wang
    Abstract:

    Abstract Solar central Receiver, which plays a dominant role in the radiation–heat conversion, is one of the most important components in the solar tower plants. Its performance can directly affect the efficiency of the entire solar power generation system. In this study, an integrated Receiver model for full range operation conditions was proposed in order to simulate and evaluate the dynamic characteristics of a solar Cavity Receiver. It mainly couples the radiation–heat conversion process, the determination of convective heat transfer coefficient, the temperature computation of Receiver walls and the calculation and analysis of the thermal losses. Based on this model, the dynamic characteristics of the solar Cavity Receiver were tested by encountering a sudden solar radiation disturbance. In addition, the thermal loss was also calculated and analyzed with different wind conditions. The results indicated that the parameters of the Receiver had a significant variation under the sharp disturbance of DNI if no control rules were imposed. The wind conditions can obviously affect the thermal losses and the value reaches its maximum when the wind blows from the side of the Receiver ( α  = 90°). In order to verify the validity of this model, the simulation results were used to compare the design points under the same input conditions, and the results showed that simulation data had a good agreement with design data.

Sendhil Kumar Natarajan - One of the best experts on this subject based on the ideXlab platform.

  • experimental performance investigation of modified Cavity Receiver with fuzzy focal solar dish concentrator
    Renewable Energy, 2015
    Co-Authors: K S Reddy, Sendhil Kumar Natarajan, G Veershetty
    Abstract:

    Abstract In this paper, thermal performance analysis of 20 m 2 prototype fuzzy focal solar dish collector is presented. The focal image characteristics of the solar dish are determined to propose the suitable design of absorber/Receiver. First, theoretical thermal performance analysis of the fuzzy focal solar parabolic dish concentrator with modified Cavity Receiver is carried out for different operating conditions. Based on the theoretical performance analysis, the total heat loss (conduction, convection and radiation heat losses) from the modified Cavity Receiver is estimated. It is observed that the maximum theoretical efficiencies of solar dish collector are found to be as 79.2% for no wind conditions and 78.2% and 77.8% for side-on and head-on winds speed of 5 m/s respectively. Latter, real time analysis of parabolic dish collector with modified Cavity Receiver is carried out in terms of stagnation test, time constant test and daily performance test. From stagnation test, the overall heat loss coefficient is found to be 356 W/m 2  K. The time constant test is carried out to determine the influence of sudden change in solar radiation at steady state conditions. The daily performance tests are conducted for different flow rates. It is found that the efficiency of the collector increases with the increase of volume flow rates. The average thermal efficiencies of the parabolic dish collector for the volume flow rate of 100 L/h and 250 L/h are found to be 69% and 74% for the average beam radiation (I bn ) of 532 W/m 2 and 641 W/m 2 respectively.

  • investigation of convection and radiation heat losses from modified Cavity Receiver of solar parabolic dish using asymptotic computational fluid dynamics
    Heat Transfer Engineering, 2010
    Co-Authors: Sendhil Kumar Natarajan, K S Reddy
    Abstract:

    In this article, numerical study of combined natural convection and radiation heat loss from a modified Cavity Receiver of a solar dish collector using asymptotic computational fluid dynamics approach is presented. The natural convection and radiation heat losses are estimated for different angle of inclinations ranging from 0° (aperture facing sideways) to 90° (aperture facing downward). The numerical results are presented to show the effect of parameters such as Grashof number, angle of inclination, emissivity, temperature ratio, and diameter ratio on convection and radiation heat losses. Separate Nusselt number correlations for natural convection heat loss and combined convective and radiative heat loss are given using the method of asymptotic expansions. The heat loss model is comparable with well-known models. It is observed that the present heat loss model follows the same trend as that of the other heat loss models.

  • an improved model for natural convection heat loss from modified Cavity Receiver of solar dish concentrator
    Solar Energy, 2009
    Co-Authors: K S Reddy, Sendhil Kumar Natarajan
    Abstract:

    A 2-D model has been proposed to investigate the approximate estimation of the natural convection heat loss from modified Cavity Receiver of without insulation (WOI) and with insulation (WI) at the bottom of the aperture plane in our previous article. In this paper, a 3-D numerical model is presented to investigate the accurate estimation of natural convection heat loss from modified Cavity Receiver (WOI) of fuzzy focal solar dish concentrator. A comparison of 2-D and 3-D natural convection heat loss from a modified Cavity Receiver is carried out. A parametric study is carried out to develop separate Nusselt number correlations for 2-D and 3-D geometries of modified Cavity Receiver for estimation of convective heat loss from the Receiver. The results show that the 2-D and 3-D are comparable only at higher angle of inclinations (60 {<=} {beta} {<=} 90 ) of the Receiver. The present 3-D numerical model is compared with other well known Cavity Receiver models. The 3-D model can be used for accurate estimation of heat losses from solar dish collector, when compared with other well known models. (author)

  • comparison of Receivers for solar dish collector system
    Energy Conversion and Management, 2008
    Co-Authors: Sendhil Kumar Natarajan, K S Reddy
    Abstract:

    Abstract In this paper, a numerical investigation is performed to study the natural convective heat loss from three types of Receivers for a fuzzy focal solar dish concentrator, namely Cavity Receiver, semi-Cavity Receiver and modified Cavity Receiver. The natural convection heat loss from the Receivers is estimated by varying the inclination from 0° (Cavity aperture facing sideways) to 90° (Cavity aperture facing down). The orientation and geometry of the Receiver strongly affect the natural convection heat loss. A comparative study is performed to predict the natural convection heat loss from the Cavity, semi-Cavity and modified Cavity Receivers. The convection heat loss is high at 0° and decreases monotonically with increase in angle up to 90° in all three cases. The convection heat losses at 0° and 90° inclination of the modified Cavity Receiver are 26.03% and 25.42% of the convection heat loss of the Cavity Receiver, respectively. The influence of area ratio (Aw/A1) on the convective heat loss is investigated for the modified Cavity Receiver, and an optimum Aw/A1 of 8 is found for minimum natural convection heat loss. Among the three Receivers, the modified Cavity Receiver is the preferred Receiver for a fuzzy focal solar dish collector system.

  • numerical investigation of natural convection heat loss in modified Cavity Receiver for fuzzy focal solar dish concentrator
    Solar Energy, 2007
    Co-Authors: Sendhil Kumar Natarajan, K S Reddy
    Abstract:

    Abstract In the present work, a 2-D-model is used to investigate the approximate estimation of the natural convection heat loss from an actual geometry of the modified Cavity Receiver (hemisphere with aperture plate) of fuzzy focal solar dish concentrator. The analysis of the Receiver has been carried out based on the assumption of the uniform and maximum solar flux distribution in the central plane of the Receiver. The total heat loss from the Receiver has been estimated for both the configurations “with insulation” (WI) and “without insulation” (WOI) at the protecting aperture plane of the Receiver. The convection heat loss of the modified Cavity Receiver was estimated by varying the inclinations of the Receiver from 0° (Cavity aperture facing sideways) to 90° (Cavity aperture facing down). The convection heat loss is maximum at 0° and decreases monotonically with increase in angle upto 90°. The effect of operating temperature on convection heat loss for different orientations of the Receiver was studied. The results of the numerical analysis are presented for a modified Cavity Receiver “with insulation” (WI) and “without insulation” (WOI) in the form of Nusselt number correlation: Nu D ( WI ) = 0.0303 Gr D 0.315 ( 1 + cos θ ) 3.551 ( T w / T ∞ ) - 0.086 ( d / D ) 0.878 , 10 6 ⩽ Gr D ⩽ 10 7 and Nu D ( WOI ) = 0.503 Gr D 0.222 ( 1 + cos θ ) 1.231 ( T w / T ∞ ) - 0.165 ( d / D ) 0.304 , 10 6 ⩽ Gr D ⩽ 10 7 . The maximum convection heat loss occurs at 0° inclination for both cases of the Receiver, which is 63.0% (WI) and 42.8% (WOI) of the total heat loss, though the heat loss in WI configuration is lower than that of WOI configuration. Upon increasing the inclination of the Receiver, the convection heat loss reduces to a minimum of 12.5% (WI) and 24.9% (WOI) of the total heat loss at 90°. The result of the present numerical model of standard Receiver configuration (modified Cavity Receiver with insulation at bottom) is comparable with other well-known models.

G Veershetty - One of the best experts on this subject based on the ideXlab platform.

  • effect of wind speed and direction on convective heat losses from solar parabolic dish modified Cavity Receiver
    Solar Energy, 2016
    Co-Authors: K S Reddy, G Veershetty, Srihari T Vikram
    Abstract:

    Abstract The performance of solar parabolic dish collector is significantly influenced by heat losses due to wind speed and direction. In this article, investigation of convective heat losses from the modified Cavity Receiver of solar parabolic dish collector is carried out numerically by considering the wind direction, wind speed, Receiver configuration and Receiver orientation. The effect of wind on the Receiver in various directions ( φ  = −90° to 90°), wide range of operating wind speeds ( V  = 0–10 m/s), Receiver inclinations ( β  = 0–90°) and varying surface temperature on convective heat loss from the Receiver are studied. Velocity vectors, velocity contours, temperature contours are presented to show the effect of wind on the heat loss from the modified Cavity Receiver. The forced convection is found to have similar trend of free convection heat loss at lower wind speed. However at higher wind speed, such a pattern is not observed. At lower wind speeds say less than critical wind speed ( φ and β values. For side-on winds, at higher wind speeds above 5 m/s, irrespective of Receiver inclination, the variation of forced convection heat loss is marginal (less than 5%). The maximum forced convection heat loss occurs for partly open Receivers (Receiver aperture diameter ratio, R AD  = 0.4 and 0.6) at φ  = 0 (side-on wind) for all Receiver inclinations and at φ  = 30° for R AD  = 0.8 and 1. The Receiver inclination has less effect on heat loss from the Receiver for V  > 2.5 m/s due to side-on wind. The highest convection heat loss occurs for fully open ( R AD  = 1) Receiver as compared to partly open ( R AD

  • combined heat loss analysis of solar parabolic dish modified Cavity Receiver for superheated steam generation
    Solar Energy, 2015
    Co-Authors: K S Reddy, Srihari T Vikram, G Veershetty
    Abstract:

    Abstract In this article, a 3-D numerical modeling is carried out to determine combined convection and surface radiation heat losses from a modified Cavity Receiver of parabolic dish collector used as mono-tube boiler for sub-cooled, saturated and superheated steam generation conditions. The forced convection heat loss from the modified Cavity Receiver is estimated using Nusselt number correlation developed for the modified Cavity Receiver. The effect of Receiver inclination ( β ) , operating temperature ( T w ) , emissivity of the Cavity cover ( ∊ ) , thickness of insulation ( t ins ) on the combined heat losses from the modified Cavity Receiver is investigated. The boundary conditions for wall temperature and insulation thicknesses are chosen to match the three steam generation conditions. It is found that the natural convection heat losses are higher at β = 0 ° (Receiver facing sideward) and lower at β = 90 ° (Receiver facing down) whereas the forced convection heat loss is higher at β = 90 ° and lower at β = 0 ° . The variation of radiation heat losses is marginal for all values of β and vary with T w . The effect of various parameters such as Receiver inclination, wind direction ( φ ) , wind speed and diameter ratios on forced convection heat loss from the Receiver has also been studied. The forced convection heat loss at lower wind speeds ( ( φ = 0 ) followed by head-on wind directions ( φ  = 30–90°) and back-on wind directions ( φ = - 90 ° to - 30 ° ) . The heat losses vary with diameter ratios for different configurations of the Receiver. The forced convection heat loss is 1.2–9 times higher than natural convection heat loss for diameter ratio (ratio of Cavity diameter to aperture diameter, d/D) = 0.4 at 5 m/s and Receiver inclinations varying from 0° to 90 ° . Nusselt number correlations have been proposed based on the numerical analysis to estimate the combined convective and radiative heat loss. The present study attempts to estimate natural convection, forced convection and surface radiation heat losses from the modified Cavity Receiver under various conditions.

  • experimental performance investigation of modified Cavity Receiver with fuzzy focal solar dish concentrator
    Renewable Energy, 2015
    Co-Authors: K S Reddy, Sendhil Kumar Natarajan, G Veershetty
    Abstract:

    Abstract In this paper, thermal performance analysis of 20 m 2 prototype fuzzy focal solar dish collector is presented. The focal image characteristics of the solar dish are determined to propose the suitable design of absorber/Receiver. First, theoretical thermal performance analysis of the fuzzy focal solar parabolic dish concentrator with modified Cavity Receiver is carried out for different operating conditions. Based on the theoretical performance analysis, the total heat loss (conduction, convection and radiation heat losses) from the modified Cavity Receiver is estimated. It is observed that the maximum theoretical efficiencies of solar dish collector are found to be as 79.2% for no wind conditions and 78.2% and 77.8% for side-on and head-on winds speed of 5 m/s respectively. Latter, real time analysis of parabolic dish collector with modified Cavity Receiver is carried out in terms of stagnation test, time constant test and daily performance test. From stagnation test, the overall heat loss coefficient is found to be 356 W/m 2  K. The time constant test is carried out to determine the influence of sudden change in solar radiation at steady state conditions. The daily performance tests are conducted for different flow rates. It is found that the efficiency of the collector increases with the increase of volume flow rates. The average thermal efficiencies of the parabolic dish collector for the volume flow rate of 100 L/h and 250 L/h are found to be 69% and 74% for the average beam radiation (I bn ) of 532 W/m 2 and 641 W/m 2 respectively.

Josua P Meyer - One of the best experts on this subject based on the ideXlab platform.

  • a computational approach to simulate the optical and thermal performance of a novel complex geometry solar tower molten salt Cavity Receiver
    Solar Energy, 2019
    Co-Authors: M Slootweg, K J Craig, Josua P Meyer
    Abstract:

    Abstract A novel complex geometry solar tower molten salt Cavity Receiver is presented and investigated with regard to its optical and thermal performance. The Receiver’s design consists of a collector with the goal of limiting the concentrated rays from escaping, which is further enhanced by an absorber design that consists of an array of hexagonal pyramid elements inspired by Garbrecht et al. (2013) that limits re-radiative and convective losses. The performance analysis considers the solar position, DNI and sun shape with an existing heliostat field (PS-10 field) to analyse the Receiver, rather than assuming a flux. The optical analysis is conducted with the Monte Carlo ray-tracing approach, while the thermal analysis is conducted using computational fluid dynamics (CFD). The initial design showed impractical Receiver efficiencies of 32.8%, while preliminary sensitivity studies on selected parameters increased efficiencies up to 69.9%. In the process a design with improved optics was developed and proposed, with initial results increasing efficiencies up to 82.4%. The study indicates that the design is promising from a heat transfer point of view, although many improvements are still to be made to the design to make it competitive.

  • three dimensional analysis and numerical optimization of combined natural convection and radiation heat loss in solar Cavity Receiver with plate fins insert
    Energy Conversion and Management, 2015
    Co-Authors: Tunde Belloochende, Josua P Meyer
    Abstract:

    The numerical study and optimization of combined laminar natural convection and surface radiation heat transfer in solar Cavity Receiver with plate fins is presented in this paper. Minimizing heat loss in Cavity Receivers is seen as an effective way to enhance the thermal performance and the use of plate fins has been proposed as a low cost means to minimize heat loss. Firstly, the influence of operating temperature, emissivity of the surface, orientation and the geometric parameters on the total heat loss from the Receiver was investigated. It was observed that convective heat loss is largely affected by the angle of inclination of the Receiver, the presence of fins and the number of fins in the Receiver. As for the radiation heat loss it was observed that it is mainly influenced by the properties of the Cavity Receiver surface. The radiation heat loss was found to be constant at all the angles of the Receiver. Significant reduction in natural convection heat loss from the Cavity Receiver was accomplished by using the plate fins whereas radiation heat loss was marginally reduced by about 5%. Secondly, the optimization was conducted to obtain the optimal fin geometry and lastly, the overall thermal efficiency of the Receiver was presented at different operating temperatures. The overall Cavity efficiency marginally increased by approximately 2% with the insertion of fin plates although the convective heat loss was suppressed by about 20%. This is due to the fact that radiation heat loss dominates at high operating temperatures compared to convective heat loss.

  • numerical modelling and optimisation of natural convection heat loss suppression in a solar Cavity Receiver with plate fins
    Renewable Energy, 2015
    Co-Authors: L C Ngo, Tunde Belloochende, Josua P Meyer
    Abstract:

    This study details the numerical modelling and optimization of natural convection heat suppression in a solar Cavity Receiver with plate fins. The use of plate fins attached to the inner aperture surface is presented as a possible low cost means of suppressing natural convection heat loss in a Cavity Receiver. In the first part of the study a three-dimensional numerical model that captures the heat transfer and flow processes in the Cavity Receiver is analyzed, and the possibilities of optimization were then established. The model is laminar in the range of Rayleigh number, inclination angle, plate height and thickness considered. In the second part of the study, the geometric parameters considered were optimized using optimization programme with search algorithm. The results indicate that significant reduction on the natural convection heat loss can be achieved from Cavity Receivers by using plate fins, and an optimal plate fins configuration exit for minimal natural convection heat loss for a given range of Rayleigh number. Reduction of up to a maximum of 20% at 0° Receiver inclination was observed. The results obtained provide a novel approach for improving design of Cavity Receiver for optimal performance.

  • computational fluid dynamics analysis of parabolic dish tubular Cavity Receiver
    2015
    Co-Authors: K J Craig, Josua P Meyer, Willem Gabriel Le Roux
    Abstract:

    The paper describes the Computational Fluid Dynamics (CFD) analysis of a parabolic dish tubular Cavity Receiver. The analysis uses the geometry of an experimental setup and considers experimental conditions as well as ideal conditions linked to a Brayton cycle microturbine implementation. The CFD analysis comprises of two parts. First, the Radiative Transfer Equation (RTE) is solved with a Finite Volume (FV) method using the Discrete Ordinates (DO) method for the optical performance of the dish and Receiver to obtain the absorbed radiation on the Receiver tube. In this method both an axi-symmetric model with a ring-like Receiver is considered utilizing a 2-D mesh as well as a 3-D model with the spiraling tubular Receiver. The former is much less computationally intensive because of the extra dimension but simplifies the Receiver shape. The result of this FV simulation is an absorbed radiation distribution that is patched as volumetric heat source in the second CFD simulation. This simulation is a conjugate heat transfer model that evaluates the heat transfer to the heat transfer fluid as well as the losses from the Cavity insulation and due to thermal re-radiation. The method is evaluated for an ambient lower pressure experimental test at the University of Pretoria as well as a theoretical implementation at Brayton cycle conditions.

  • thermodynamic optimisation of the integrated design of a small scale solar thermal brayton cycle
    International Journal of Energy Research, 2012
    Co-Authors: Willem Gabriel Le Roux, Tunde Belloochende, Josua P Meyer
    Abstract:

    SUMMARY The Brayton cycle's heat source does not need to be from combustion but can be extracted from solar energy. When a black Cavity Receiver is mounted at the focus of a parabolic dish concentrator, the reflected light is absorbed and converted into a heat source. The second law of thermodynamics and entropy generation minimisation are applied to optimise the geometries of the recuperator and Receiver. The irreversibilities in the recuperative solar thermal Brayton cycle are mainly due to heat transfer across a finite temperature difference and fluid friction. In a small-scale open and direct solar thermal Brayton cycle with a micro-turbine operating at its highest compressor efficiency, the geometries of a Cavity Receiver and counterflow-plated recuperator can be optimised in such a way that the system produces maximum net power output. A modified Cavity Receiver is used in the analysis, and parabolic dish concentrator diameters of 6 to 18 m are considered. Two Cavity construction methods are compared. Results show that the maximum thermal efficiency of the system is a function of the solar concentrator diameter and choice of micro-turbine. The optimum Receiver tube diameter is relatively large when compared with the Receiver size. The optimum recuperator channel aspect ratio for the highest maximum net power output of a micro-turbine is a linear function of the system mass flow rate for a constant recuperator height. For a system operating at a relatively small mass flow rate, with a specific concentrator size, the optimum recuperator length is small. For the systems with the highest maximum net power output, the irreversibilities are spread throughout the system in such a way that the internal irreversibility rate is almost three times the external irreversibility rate. Copyright © 2011 John Wiley & Sons, Ltd.