Now showing 1 - 10 of 26
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Sensitivity study of thermal performance characteristics based on optical parameters for direct steam generation in parabolic trough collectors

15-07-2018, Reddy, K. S., Ajay, C. S., Nitin Kumar, Bohra

Solar parabolic trough collector is one of the most potential Concentrated Solar Power (CSP) technologies with high dispatchability. The performance of the Parabolic Trough Collector (PTC) is significantly influenced by the distribution of radiant flux around the line focus receiver. In this paper, an accurate estimation of radiant flux around the line focus receivers of different parabolic trough collectors of varying aperture widths from 5 to 7.5 m has been studied. Effects of total internal reflection in the glass tube, glass tube absorptivity, receiver reflectivity, limb-darkening effect, surface errors and anti-reflective coating have been considered. A direct steam generation model (recirculation mode) has been developed and the effect of geometric errors in the collector on its optical and thermal performance characteristics has been discussed. The thermal efficiency of the direct steam generation collector is influenced by the optical characteristics of the collector and hence the thermal efficiency at different optical errors has been evaluated for the fore-mentioned commercial collectors under the influence of declination. The thermal efficiency is more sensitive to optical errors at low insolation levels and vice versa. For a change in tracking from 0 to 10 mrad, for PTC7.3 configuration, thermal efficiency drops by 0.58% at 1000 W/m2, and 2.02% at 300 W/m2. The thermal efficiency is also more sensitive to optical errors at higher values of declination. The collector of low geometric concentration ratio has a low sensitivity and low thermal efficiency and vice versa. Hence, the overall efficiency of different collectors at different optical errors has to be studied so as to obtain the appropriate collector configuration for specified optical errors and location of installation. Based on the analysis, graphical results which could aid in the selection of best collectors based on the latitude location, DNI and optical errors has been developed. The evaluation of collectors has also been extended towards power plant characteristics. The nominal power has been set to 50 MW. The location of Jodhpur in India has been selected and the total power generated per unit area has been studied for different collectors, for different optical errors. Based on the graphical results developed, appropriate collectors may be chosen for those locations based on their associated optical errors.

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Experimental performance investigation of tilted solar still with basin and wick for distillate quality and enviro-economic aspects

01-01-2017, Sharon, H., Srinivasa K Reddy, Krithika, D., Ligy Philip

Tilted wick type and stepped solar stills are well known for their increased distillate yield compared to basin type stills. In this study experiments were conducted on tilted solar still with basin and tilted solar still with wick to assess their performance, distillate quality, environmental benefits and economic feasibility. Distillate quality of both the tested units was superior. Annual average distillate yield of tilted solar still with basin was nearly 19.76% higher than that of the unit with wick. Maximum distillate yield of 4.99 L/d and 4.54 L/d was noticed for tilted solar still with basin and wick, respectively during April. Yearly average thermal and exergy efficiency was around 41.06% and 3.06% for the unit with basin and 33.83% and 2.88% for the unit with wick. Energy payback time of the unit with basin was around 2.80 yrs and it can prevent 17.65 tons of CO2emission during 20 yrs of life time. Distillate production cost was around 0.026 USD/L (Rs. 1.74/L) and 0.046 USD/L (Rs. 3.08/L) for an interest rate of 5% and 12%, respectively. Tilted solar still with basin has superior performance compared to that of unit with wick and can produce 21.76 L of distillate/USD invested on it.

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Numerical investigation of micro-channel based active module cooling for solar CPV system

01-01-2014, Srinivasa K Reddy, Lokeswaran, S., Agarwal, Pulkit, Mallick, Tapas K.

Concentrating photovoltaic (CPV) technology is one of the fastest growing solar energy technologies achieving higher electrical conversion efficiencies. The increase in temperature of solar CPV cell significantly reduces the performance; the efficiency of a CPV system can be improved by introducing effective thermal management or cooling system. This paper presents the design and numerical analysis of a heat sink based on micro-channels for efficient cooling of a commercial high concentration photovoltaic (HCPV) cell. A combinatory model of an array of micro-channels enclosed in a wide parallel flow channel design is developed. The optimized geometry of the micro-channel heat sink was found by using commercial CFD software ANSYS 13. Based on numerical simulations, it is found that the optimum configuration of micro-channel with 0.5mm width and aspect ratio of 8. The micro-channels provided high heat transfer over heat generations spots and parallel flow channels resulted in lower pressure drop. The temperature rise across the micro-channel is estimated as10K in CPV module of 120 × 120 mm2 and with a pressure drop of 8.5 kPa along a single channel with six such channels in each modules at a flow rate of 0.105 liter/s. © 2014 The Authors.

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Performance analysis of concave cavity surface receiver for a non - Imaging solar concentrator

01-01-2015, Srinivasa K Reddy, Srihari Vikram, T.

In the present study, a numerical investigation of concave surface cavity receiver of non-imaging solar concentrator is carried out considering various operating and geometrical parameters such as mass flow rate of the fluid, solar radiation and receiver configuration. The fluid outlet temperature, pressure drop across the coil for different receiver configurations are studied along with the heat loss estimation of concave cavity surface receiver for non-imaging concentrating collector. The convective and radiative heat loss from the receiver surface is calculated based on 3-D numerical simulations. For helical receiver, the temperature rise is found to be 30°C (0.5kg/min) and 17°C (1kg/min) respectively; whereas for helical-spiral receiver, the temperature rise is found to be 27°C (0.5 kg/min) and 15°C (1 kg/min). The pressure drop across the coil ranges between 1kPa to 14kPa for different mass flow rate and solar radiation for two configurations of the receiver. The present model can be used for estimating the heat transfer and fluid flow characteristics of helical receiver for EHC.

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Experimental performance investigations of an elliptical hyperbolic non-imaging solar concentrator with trapezoidal surface receiver for process heat applications

10-08-2018, Reddy, K. S., Vikram, T. Srihari, Mallick, Tapas K.

The use of non-imaging collectors has a wide scope in process heat applications based on its performance and economics. An experimental investigation of trapezoidal/concave cavity surface receiver (TSR) for non-imaging solar concentrating collector is carried out in this paper. The implementation of surface/coil receiver instead of tubular receiver for non-imaging collector is presented in this paper. A TSR with helical coil is developed for non – imaging concentrating collector, Elliptical Hyperbolic Collector (EHC). Experiments are carried to estimate the thermal performance of the system under various operating conditions such as two operating modes: series and parallel modes of operation of the collector, two circulation modes: passive and active modes. The stagnation temperature of the trapezoidal/concave cavity surface receiver is measured to be 118 °C on a clear sunny day in October and 102 °C on a cloudy day in February. The daily performance tests are performed under different operating conditions. Based on the experimental study, for the flow rate of 0.03 kg/min and 0.5 kg/min, the fluid outlet temperature is estimated to be 87 °C at 768 W/m2 and 49 °C at 908 W/m2 respectively. The corresponding instantaneous efficiency was calculated to be 9% and 40% respectively. The numerical model is developed to predict the temperature of the fluid along the receiver. The pressure drop across a receiver is estimated to be 9.3 kPa for a flow rate of 0.5 kg/min. Exergy analysis of the system is carried out and it ranges between 10 and 20%. The costs involved in fabricating the EHC system are compared to that of a non-imaging concentrating collector (CPC) of same aperture area. An economic analysis of the system is also carried out to study the feasibility of the system based on the life cycle savings method by estimating the annual solar savings from the EHC system. The present system can be a suitable option for low and medium temperature process heat applications.

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A review of solar energy driven desalination technologies

01-01-2015, Sharon, H., Srinivasa K Reddy

Water plays an important role in all our day to day activities and its consumption is increasing day by day because of increased living standards of mankind. Some regions of the globe are under severe stress due to water scarcity and pollution. The fresh water needs of mankind can be only satisfied if saline water which is available in plenty is converted to potable water by desalination. Desalination industry has shown increased threats of CO2 emissions and severe environmental impacts. Desalination industry can be made sustainable if they are integrated with renewable energy and if proper brine disposal methods are followed. In this review different desalination units integrated with renewable energy with special emphasis given to solar energy is discussed. The problems associated with desalination units and their remedies have been presented. Apart from this some novel methods of desalination process has also been explained. This review will allow the researchers to choose appropriate desalination technology for further development.

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Experimental investigation of porous disc enhanced receiver for solar parabolic trough collector

01-05-2015, Srinivasa K Reddy, Ravi Kumar, K., Ajay, C. S.

In this article, experimental investigation of 15m2 solar parabolic trough collector with porous disc enhanced receiver is carried out according to ASHRAE 93-1986 test procedure. Six different receiver configurations are developed and investigated to compare their performance. The performance of solar parabolic trough collector with two conventional and four porous disc receivers is characterized in terms of time constant, collector acceptance angle, peak performance, daily performance and heat loss tests. The tests are carried out for wide range of flow rates (100L/h-1000L/h) and weather conditions. Based on experimental investigation, the time constant of the parabolic trough collector is varied from 70s to 260s for different receiver configurations. The collector acceptance angle is determined for both un-shielded tubular receiver (USTR) and shielded tubular receiver (STR) as 0.58° and 0.68° respectively. The collector efficiencies are obtained as in the range of 63.9%-66.66% under ASHRAE standard test condition. Off-Sunset heat loss test is conducted to determine the steady state heat losses from the parabolic trough collector receiver. The heat losses from the parabolic trough collector are in the range of 455W/m2-1732W/m2 for average fluid temperature of Tamb+30°C. Stagnation temperature of the collector is obtained as 258°C and 312°C respectively for USTR and STR corresponding to direct normal insolation (DNI) of 786W/m2 and 761W/m2. Based on the above analysis, the porous disc enhanced receiver improves the performance of the parabolic trough collector significantly and it can be used effectively for process heat applications.

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Energy-environment-economic investigations on evacuated active multiple stage series flow solar distillation unit for potable water production

01-11-2017, Reddy, K. S., Sharon, H.

Multi stage solar distillation units are well known for their higher distillate productivity and are capable of fulfilling the potable water requirements of families in remote, rural, and coastal regions. In this article, active multiple stage series flow solar distillation unit has been proposed for desalting saline water and its performance, environmental benefits and economic feasibility were assessed by carrying out 3E (Energy-Environment-Economic) analyses using the developed mathematical model. Better performance was observed for the distillation unit with five distillation stages, two solar collectors connected in parallel configuration and saline water mass flow rate of 135.0 kg/d and 75.0 kg/d, during summer and winter seasons. Low-pressure operation in combination with evaporative cooling of condenser of last stage has enhanced the annual average daily distillate productivity from 12.60 kg/d to 48.80 kg/d. Distillate production was found to drop from 48.80 kg/d to 38.90 kg/d with the increase in salt concentration of saline water from 0 wt% to 10 wt%. Energy payback time of the unit desalting saline water with 5 wt% salt concentration was within 1.0 yr and the unit can mitigate nearly 221.80 tons of CO2 emission, 1594.73 kg of SO2 emission and 651.37 kg of NO emission from Indian coal based power plants during its 20 yrs lifespan under 250 clear day operation. Increased salt concentration in saline water reduces the emission mitigation potential and increases the energy payback time of the proposed distillation unit. Distillate production cost was increased by 16.0% for every 5 wt% increase in salt concentration. Amount invested in the unit can be regained with in 3.56 yr irrespective of interest rate for distilled water selling price of 0.06 USD/L (Rs. 3.91/L).

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Review of latent heat thermal energy storage for improved material stability and effective load management

01-02-2018, Reddy, K. S., Mudgal, Vijay, Mallick, T. K.

Thermal energy storage is important to counter balance demand and supply of energy and maintain balance in the system and boost the use of intermittent renewable energy source. Phase change material-based thermal energy storage has massive potential to substitute large-scale energy demand and assist both economic and environmental benefits. This paper reviews functional principle, thermophysical properties and other material characteristics of different phase change materials for thermal energy storage system. Long-term stability of phase change material and its interaction with storage container have been discussed. Various heat transfer and thermal conductivity enhancement technique to enhance latent thermal energy storage system have been discussed. The paper also examines the schematics of some of the proposed & tested systems and describes the results of prototype setup for thermal load management and application in water heating system and buildings. The paper also summarizes energy and exergy analysis of some thermal energy storage systems.

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Optical modelling and performance analysis of a solar LFR receiver system with parabolic and involute secondary reflectors

01-10-2016, Balaji, Shanmugapriya, Srinivasa K Reddy, Sundararajan, T.

In this paper, a pilot scale solar Linear Fresnel Reflector of 154 m2 is designed and optically analyzed with two different profiles for the secondary concentrator. Compounded profiles of parabolic (PB) and involute (IN) shapes are compared for the secondary reflector geometry. Non-uniform intensity distribution of the solar disc with the flux transmission by the Monte Carlo Ray tracing method is used. Analyses are carried out with a 3D optical model and the combined optical performance of the Linear Fresnel Reflector (LFR) system with the parabolic secondary reflector is compared with that of the involute secondary reflector. The effects of truncating the secondary reflectors, optimizing the focusing distance of the absorber and the gap between the absorber and the secondary reflector, are investigated. Also the effects of errors caused by sun-tracking and contour of the mirror surface are studied. The efficiency of the Linear Fresnel Reflector system with the two models of secondary concentrators at different incidence angles of the solar beam are evaluated with Incidence Angle Modifier. Optical performance at different Direct Normal Irradiance (DNI) conditions is also performed. It is found that the Linear Fresnel Reflector system with Parabolic secondary reflector provides a higher optical efficiency of 62.3% with secondary efficiency of 83.3%. The Involute secondary on the other hand, provides an optical efficiency of 59.5% and secondary efficiency of 78.33%.