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[en] This communication presents thermodynamic methodology for the performance evaluation of combustion gas turbine cogeneration system with reheat. The energetic and exergetic efficiencies have been defined. The effects of process steam pressure and pinch point temperature used in the design of heat recovery steam generator, and reheat on energetic and exergetic efficiencies have been investigated. From the results obtained in graphs it is observed that the power to heat ratio increases with an increase in pinch point, but the first-law efficiency and second-law efficiency decreases with an increase in pinch point. The power to heat ratio and second-law efficiency increases significantly with increase in process steam pressure, but the first-law efficiency decreases with the same. Results also show that inclusion of reheat, provide significant improvement in electrical power output, process heat production, fuel-utilization (energetic) efficiency and second-law (exergetic) efficiency. This methodology may be quite useful in the selection and comparison of combined energy production systems from thermodynamic performance point of view
[en] An investigation of the generation of plasma waves at twice the pump wave frequency in a hot collisionless plasma by Gaussian laser beams is presented. On account of Gaussian intensity distribution of the laser beam a time independent component of ponderomotive force becomes finite in a direction transverse to the beam propagation. This causes redistribution of the carriers and the beam gets self-focused. Intensity of the generated plasma waves is found to be further enhanced due to self-focusing of the pump wave. Stimulated Raman scattering from these excited plasma waves is also enhanced. (author)
[en] An investigation is presented of the effect of self-focusing on the absolute growth rates of parametric back-scattering (e.g. stimulated Raman and Brillouin scatterings) and absorptive instabilities (e.g. two-plasmon decay and ion-plasmon decay) in a homogeneous and collisionless plasma. Gaussian intensity distribution of the pump laser beam causes the redistribution of carriers in the plane transverse to the beam propagation on account of the ponderomotive force, and leads the beam to propagate in an oscillatory wave guide mode. The modifications in plasma frequency and intensity of the beam cause the growth rates of the above parametric instabilities to show an oscillatory behaviour with the distance of propagation. (author)
[en] Highlights: • A novel thermodynamic modelling of photovoltaic energy system has been proposed. • The entropy, optical, thermal, spectral and fill factor losses are assessed. • The expression of energetic and exergetic efficiencies have been derived. • Reversible, endoreversible, exoreversible and irreversible systems are presented. - Abstract: The photovoltaic energy conversion is a thermodynamic system which converts the solar energy to the electrical and thermal energy. In this paper, a novel thermodynamic model of photovoltaic energy conversion system has been proposed on the basis of the first and second law of thermodynamics including entropy generation, optical, thermal, spectral and fill factor losses. Based on the irreversibilities, the proposed model has been classified into four cases i.e. reversible, endoreversible, exoreversible and irreversible systems, for which, the expressions of energetic and exergetic efficiencies have been derived. The upper limit efficiency of an ideal photovoltaic module placed in an irreversible environment, i.e. endoreversible system, is determined to be 82.8%. The effect of wind speed and module temperature on the energetic and exergetic efficiencies, thermodynamic losses and irreversibilities has also been presented.
[en] Highlights: • Exergy analysis in the annular thermoelectric cooler (ATEC) system is proposed. • Analytical expressions for the cooling power, exergy efficiency of an ATEC is derived. • The effects of S_r and θ in Q_c and exergy efficiency of an ATEC is studied. - Abstract: In this paper the concept of annular thermoelectric cooler (ATEC) has been introduced. An exoreversible thermodynamic model of the annular thermoelectric cooler considering Thomson effect in conjunction with Peltier, Joule and Fourier heat conduction has been investigated using exergy analysis. New expressions for optimum current at the maximum energy/exergy efficiency, maximum cooling power conditions and dimensionless irreversibilities in the ATEC are derived. The modified expression for figure of merit of a thermoelectric cooler considering the Thomson effect has also been obtained. The results show that the cooling power, energy and exergy efficiency of the ATEC is lower than the flat plate thermoelectric cooler. The effects of annular shape parameter (S_r = r_2/r_1), dimensionless temperature ratio (θ = T_h/T_c) and the electrical contact resistances on cooling power, energy/exergy efficiency of an ATEC have been studied. It has also been proved that because of the influence of Thomson effect, the cooling power and energy/exergy efficiency of the ATEC is increased. This study will help in the designing of the actual annular thermoelectric cooling systems.
[en] In this paper, the exoreversible and irreversible thermodynamic models of a TTEG (two stage thermoelectric Generator) considering Thomson effect combined with Peltier, Joule and Fourier heat conduction have been investigated using exergy analysis. The expressions for interstage temperature, optimum current for the maximum power output condition and energy/exergy efficiency of a TTEG are derived. The number of thermocouples in the first and second stages of a TTEG for the maximum power output and energy/exergy efficiency conditions are optimized as well. The results show that the exergy efficiency of TTEG is greater than the energy efficiency. In an irreversible TTEG with 30 thermocouples, and with heat source temperature (T_H) of 450 K and heat sink temperature (T_C) of 300 K, the obtained maximum power output, maximum energy and exergy efficiency are 0.2996 W, 4.35% and 13.05% respectively. It has also been proved that the optimum number of thermocouples obtained in the first and second stages of a TTEG are different from the previous studies because of the influence of Thomson effect. This study will help in the designing of the actual multistage thermoelectric generator systems. - Highlights: • This paper proposes the exergy analysis in a two stage thermoelectric generator. • Analytical expressions for the energy and exergy efficiency in TTEG is derived. • The influence of Thomson effect in the performance parameters of TTEG is studied. • The influence of Thomson effect in optimizing the number of thermocouples is studied.
[en] Highlights: • Thermodynamic model of concentrated photovoltaic–thermoelectric system is analysed. • Thomson effect reduces the power output of PV, TE and hybrid PV–TEG system. • Effect of thermocouple number, irradiance, PV and TE current have been studied. • The optimum concentration ratio for maximum power output has been found out. • The overall efficiency and power output of hybrid PV–TEG system has been improved. - Abstract: In this study, a thermodynamic model for analysing the performance of a concentrated photovoltaic–thermoelectric generator (CPV–TEG) hybrid system including Thomson effect in conjunction with Seebeck, Joule and Fourier heat conduction effects has been developed and simulated in MATALB environment. The expressions for calculating the temperature of photovoltaic (PV) module, hot and cold sides of thermoelectric (TE) module are derived analytically as well. The effect of concentration ratio, number of thermocouples in TE module, solar irradiance, PV module current and TE module current on power output and efficiency of the PV, TEG and hybrid PV–TEG system have been studied. The optimum concentration ratio corresponding to maximum power output of the hybrid system has been found out. It has been observed that by considering Thomson effect in TEG module, the power output of the PV, TE and hybrid PV–TEG systems decreases and at C = 1 and 5, it reduces the power output of hybrid system by 0.7% and 4.78% respectively. The results of this study may provide basis for performance optimization of a practical irreversible CPV–TEG hybrid system.
[en] Highlights: • Exergy analysis in the annular thermoelectric generator (ATEG) system is proposed. • Analytical expressions for the power output, exergy efficiency of an ATEG is derived. • The effects of S_r, R_L, and θ in P_o_u_t and exergy efficiency of an ATEG is studied. • The influence of Thomson effect in P_o_u_t and exergy efficiency of an ATEG is studied. - Abstract: The exoreversible thermodynamic model of an annular thermoelectric generator (ATEG) considering Thomson effect in conjunction with Peltier, Joule and Fourier heat conduction has been investigated using exergy analysis. New expressions for optimum current at the maximum power output and maximum energy, exergy efficiency conditions, and dimensionless irreversibilities in the ATEG are derived. The modified expression for figure of merit of a thermoelectric generator considering the Thomson effect has also been obtained. The results show that the power output, energy and exergy efficiency of the ATEG is lower than the flat plate thermoelectric generator. The effects of annular shape parameter (S_r = r_2/r_1), load resistance (R_L), dimensionless temperature ratio (θ = T_h/T_c) and the thermal and electrical contact resistances in power output, energy/exergy efficiency of the ATEG have been studied. It has also been proved that because of the influence of Thomson effect, the power output and energy/exergy efficiency of the ATEG is reduced. This study will help in the designing of the actual annular thermoelectric generation systems
[en] This paper analyzes the likely impacts of the major policy reforms unveiled by the Government of India for revamping the country's power sector. The provisions of the new enactment have recently come into force and seek a paradigm policy shift in the form of the Electricity Act 2003. The paper details out the key features of the Act and the likely power industry changes being brought about in the new regime. These changes comprise the structural changes in the power industry as well as the policy issues related to generation, transmission and distribution of power. Also discussed are the other major areas where transformation is sought and impacts are expected: power trading, role of regulator in the new regime, issue of open access, empowerment of the consumers and the environmental issues
[en] The propagation of a gaussian electromagnetic pulse in a growing/decaying (time-dependent) plasma has been studied when the duration of the pulse is comparable with the decay/growing time of the plasma. Because of the different group velocities of the front and tail portions of the pulse, the pulse is compressed/broadened in a time-dependent plasma. The effect of absorption on the compression/broadening is found to be negligible. However, the peak value of the pulse is suppressed by attenuation. (author)