K.S. Reddy

Performance of a low cost solar paraboloidal dish steam generating system

This paper presents the design, development and performance characteristics of a low cost solar steam generating system which incorporates recent design and materials innovations of parabolic dish technology. The concentrator is a deep dish of rather imperfect optics, made of silvered polymer reflectors fitted in the aluminum frame of a satellite communication dish. Conventional cavity receivers tend to be inadequate for this concentrator. Semi-cavity and modified cavity receivers, thermally optimised, with the fuzzy focal image have, therefore, been investigated. Preliminary field measurements and cost, as well as performance analyses of the system, indicate a solar to steam conversion efficiency of 70–80% at 450°C and a collector system cost of Rs 8000–9000/m2 (US

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

1=Rs, 40.0).

Numerical Study of Porous Finned 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.

Thermal modeling of PCM-based solar integrated collector storage water heating system

Abstract 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.

Comparative study of transparent insulation materials cover systems for integrated-collector-storage solar water heaters

The thermal modeling and analysis of a transparent insulation materials (TIM) covered solar integrated collector storage (ICS) water heating system with phase-change material (PCM) is carried out in this paper. The system consists of a double rectangular enclosure of cross section I m X 1 m where the top enclosure is filled with paraffin wax and that of the bottom is with water. The transient response of the PCM-water solar ICS system is studied with and without fins on the diurnal basis. The performance of the system is investigated with 4, 9, and 19 fins inside the wax having a pitch of 20 cm, 10 cm, and 5 cm, respectively. The latent heat storage with nine fins is found to be optimum for maximum water temperature and minimum heat losses to the surroundings. The temperature of water in the ICS exceeds 50° C with a temperature drop of only 1.5-2 °C during nighttime. The nine-fin solar ICS configuration attains ∼9°C higher than other configurations.

Studies on photogalvanic effect in systems containing toluidine blue

Abstract The thermal performance of transparently insulated integrated-collector-storage solar water heaters is investigated theoretically as well as experimentally for a comparative study of cover systems having transparent insulation materials devices placed between the top glazing and the absorber. The data on solar transmittance, heat loss reduction characteristics and solar collector-storage efficiencies of various configurations is generated for the system performance comparisons. These hot water systems exhibit average (diurnal basis) solar collection and storage efficiencies in the range of 20–40% at a collection temperature of 40–50°C. The performance of water heaters with cover system having absorber-perpendicular configuration of TIM excel over absorber-parallel TIM covers. The effect of variation in the temperature of heat collected and cost of cover systems on the performance comparisons is also discussed.

Investigation of Convection and Radiation Heat Losses From Modified Cavity Receiver of Solar Parabolic Dish Using Asymptotic Computational Fluid Dynamics

Abstract The photovoltages and photocurrents in photogalvanic cells containing a dye toluidine blue (Tb+) and reducing agents, Fe(II), EDTA, triethanolamine and triethylamine have been determined. The photo-outputs with EDTA or amines as reducing agents are higher than when Fe(II) is the reducing agent. The efficiency of the EDTA-Tb+ photogalvanic cell has been estimated to be ∼ 0.0022%. The electrochemical behaviour of toluidine blue in presence of all the reducing agents has been examined by cyclic voltametry. Plausible mechanisms of photogalvanic action have been discussed.

Estimation of Effective Thermal Conductivity of Two-Phase Materials Using Collocated Parameter Model

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.

Thermodynamic Optimization of Advanced Steam Power Plants Retrofitted for Oxy-Coal Combustion

In this article, the collocated parameter models are used to estimate the effective thermal conductivity of the two-phase materials. The algebraic equations are derived using a unit-cell-based isotherm approach for a two- and three-dimensional spatially periodic medium. The geometry of the medium is considered as matrix of touching and nontouching in-line square and circular cylinders as well as touching and nontouching in-line solid and hollow cubes. The models are used to predict the thermal conductivity of numerous two-phase materials (maximum conductivity ratio of 1000 and concentration ranging between 0 and 1). The estimated thermal conductivity data is in good agreement with experimental data within ± 16.67% deviation for various two-phase systems. The results are compared with the standard models and experimental data for different types of two-phase systems; it is shown that the touching in-line solid cube model predicts better as compared to other geometrical configurations.

Applicability of silicon micro-finned heat sinks for 500× concentrating photovoltaics systems

Thermodynamic optimization of power plants based on supercritical (SupC) and ultrasupercritical (USC) steam parameters is reported in this article. The objective is to compute the maximum attainable power plant efficiency in Indian climatic conditions using high ash (HA) indigenous coal. A unit size of 800 MWe presently under development in India is considered for energy and exergy analysis of power plants. Commercially established steam turbine parameters are used for the optimization of SupC power plant, whereas advanced steam turbine parameters currently under research and development are used for the optimization of USC power plant. The plant energy efficiency of the optimized SupC and USC power plant based on air-coal combustion (ACC) show considerable increases of 2.8 and 5.2% points, respectively compared with the current SupC ACC power plant (reference plant) being commissioned in India. The increases in plant exergy efficiency for the same power plants are 2.6 and 4.8% points and the corresponding CO2 reductions are about 6 and 11%, respectively. The maximum possible plant energy efficiency in Indian climatic conditions using HA Indian coal is about 42.7% (USC power plant). The effect of low ash coal on plant energy and exergy efficiencies compared with HA coal is also presented. Further, the effect of oxy-coal combustion (OCC) on the plant energy and exergy efficiencies compared with the ACC is studied for the double reheat SupC and USC power plants to account for the impact of CO2 capture. A significant reduction of 8.8 and 6.6% points in plant energy efficiency is observed for SupC and USC OCC power plants, respectively compared with the reference SupC ACC power plant.