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Abstract The reverse flat-plate collector is a non-concentrating collector. It can collect solar heat at high temperatures which cannot be achieved by conventional non-concentrating collectors. In this paper, the authors have proposed a number of modified versions of the originally proposed reverse flat-plate collector. The new designs are of single, as well as double, absorber type. The thermal performance of these modified reverse flat-plate collectors is compared with that of a single absorber reverse flat-plate collector, as well as with the corresponding normal flat-plate collector. It is found that the new design having two absorbers gives the best thermal performance as compared with other configurations. The analytical models presented in this paper very well describe the experimental results.

Drying experiments have been performed with potato cylinders and slices using a laboratory scale designed natural convection mixed-mode solar dryer. The drying data were fitted to eight different mathematical models to predict the drying kinetics, and the validity of these models were evaluated statistically through coefficient of determination (R(2)), root mean square error (RMSE) and reduced chi-square (χ (2)). The present investigation showed that amongst all the mathematical models studied, the Modified Page model was in good agreement with the experimental drying data for both potato cylinders and slices. A mathematical framework has been proposed to estimate the performance of the food dryer in terms of net CO2 emissions mitigation potential along with unit cost of CO2 mitigation arising because of replacement of different fossil fuels by renewable solar energy. For each fossil fuel replaced, the gross annual amount of CO2 as well as net amount of annual CO2 emissions mitigation potential considering CO2 emissions embodied in the manufacture of mixed-mode solar dryer has been estimated. The CO2 mitigation potential and amount of fossil fuels saved while drying potato samples were found to be the maximum for coal followed by light diesel oil and natural gas. It was inferred from the present study that by the year 2020, 23 % of CO2 emissions can be mitigated by the use of mixed-mode solar dryer for drying of agricultural products.

Energy conservation potential of the evaporative roof cooling technique for a cinema house in a composite climate (characterized by Delhi) has been evaluated. Thermal loads due to heat conduction through the building envelope, the required ventilation and the occupants have been taken into account. Life-cycle-cost analysis has been employed to evaluate the cost effectiveness of this energy conservation technique. It is seen that evaporative cooling on the roof leads to a net saving of 14% in the initial investment and 17% in the annual cost.

Abstract In this work, we investigate the radial flow structure in gas–solids downer using Euler–Euler computational fluid dynamics (CFD) models. Solids are modeled as pseudo-fluid using kinetic theory of granular flow. In addition to the mass and momentum conservation equations, transport equation for fluctuating kinetic energy of the solids (modeled as granular temperature) is solved. The main focus of this work is the systematic investigation of the most suitable closures for the various force interactions in the system of interest. Results are presented for mean solids velocity, volume fraction, granular temperature and slip velocities for various closure forms. Sensitivity of the predicted results to the choice of closure forms is presented. Finally we emphasize the idea of matching slip velocities and the trends thereof with solids fraction as the key to developing a robust CFD model which has predictive capability over a wide variety of flow conditions.

Abstract State space modelling and synthesis of decentralized suboptimal load-frequency control for hydro-thermal power systems are described in this paper. The state space models are derived by the partial fraction technique for reheat steam turbines, hydro turbines and hydro governors having numerator dynamics. Decentralized suboptimal load-frequency controls are synthesized by using the method of minimum error excitation and their performance is analysed as a function of tie-line power level. It is shown that the suboptimal control with feedback of some, but not all, of the remote area state variables is a feasible alternative to the optimal control, whereas local control without feedback of any remote state variable is inadequate for stabilizing the system.

This paper proposes a fuzzy based steam diversion valve to divert the steam to a storage tank during the occurance of a fault in a power system in order to improve stability of the system. The advantages of this technique over fast valving are discussed. The rate of opening and closing of valve are decided by the fuzzy controller. The valve operation is coordinated with fuzzy based braker. The technique is demonstrated for a single machine infinite bus system as well as four generators-ten bus multimachine system.

Abstract This paper describes an experimental study on the effect of tube diameter on the mechanism of flooding in vertical gas–liquid countercurrent annular flow. Flooding experiments were conducted with three different tube inner diameters, namely, 25, 67 and 99 mm with smooth inlet and outlet conditions for air and water. The results indicate that the mechanism of flooding is qualitatively different in the small and the large diameter test sections. While flooding in the 25 mm diameter section occurred essentially by the upward movement of large waves created near the liquid outlet, no such waves could be seen in the 67 and the 99 mm diameter test sections. Here, flooding occurred by droplet carryover or by an unstable, churn-like motion in the liquid film. The results are compared with existing correlations. The effect of test section length on flooding was also investigated.

ABSTRACT This paper presents a second order decoupled load flow method. The salient features are consideration of all terms in the Taylor series expansion, use of constant decoupled Jacobians and extremely simple computations involved in evaluating the active and reactive power mis-match vectors. Load flow solutions for several test systems have been obtained using the proposed and Fast Decoupled Load Flow (FDLF) methods. The test cases include systems with large R/X ratio transmission lines and series compensated lines.Limited investigations reveal that the proposed method has an edge over the FDLF method in terms of reliability of convergence and solution time.

This paper presents an investigation on using an ammonia refrigerant with liquid/solid absorbents in an absorber heat recovery cycle where heat released during the absorption process is used to heat up the strong solution coming out of the absorber, thereby reducing the generator heat input and hence improving the coefficient of performance. A comparative thermodynamic study is made with NH3-H2O and NH3-LiNO3 pairs as working fluids for both conventional absorption and absorber heat recovery systems. It is found that an improvement of about 10 per cent in COP for the absorber heat recovery cycle is achieved over the conventional absorption cycle and the NH3-LiNO3 system yields a higher COP than for NH3-H2O over a wide range of generator temperatures and condenser/absorber temperatures. A detailed parametric study is also presented in this paper.