Surendra Singh Kachhwaha

Exergy analysis of a vapour compression–absorption cascaded refrigeration system using modified Gouy–Stodola equation

In the present study, the performance of vapour compression–absorption cascaded refrigeration system (VCACRS) is studied with modified Gouy–Stodola equation and the results are compared with the classical approach of exergy evaluation. The quantitative difference in two approaches is presented which necessitates the need to employ modified approach. The expressions are formulated for effective temperature and real irreversible loss for different components of VCACRS. The overall performance of system can be improved by increasing the evaporator and generator temperature and by decreasing the absorber, cascade condenser and condenser temperature. Coefficient of structural bonds (CSB) analysis shows evaporator is relatively more sensitive to change in its temperature as compared with the other components.

System modeling and analysis of a combined cycle power plant

The performance of a combined cycle power plant (CCPP) and cost of electricity generation per unit is a function of its basic structure (i.e., layout and design), availability (maintenance aspects), efficiency (trained manpower and technically advanced equipments), cost of equipments and maintenance, pollutants emission and other regulatory aspects. Understanding of its structure will help in the improvement of performance, design, maintenance planning, and selection of new power generation systems. A mathematical model using the graph theory and matrix method is developed to evaluate the performance of a gas based CCPP. In the graph theoretic model, a directed graph or digraph is used to represent abstract information of the system using directed edges, which is useful for visual analysis. The matrix model developed from the digraph is useful for computer processing. Detailed methodology for developing a system structure graph, various system structure matrices, and their permanent functions are described for the combined cycle power plant. A top–down approach for complete analysis of CCPP is given.

Development of reliability index for cogeneration cycle power plant using graph theoretic approach

A logical approach based on graph theory and matrix method (GTMM) is developed for assessment of reliability index for a co-generation cycle power plant (CGCPP). For a humongous and multipart system such as CGCPP, reliability of its components or subsystems is closely intertwined and insuperable without taking the effect of others. For the ease of analysis CGCPP system is divided into four sub-systems. Reliability of CGCPP is modeled in terms of a reliability attributes digraph which is developed from system reliability digraph. Nodes in the digraph represent sub-system reliability and reliability of interrelations is represented by the directed edges. The digraph is represented by one-to-one matrix called as variable system reliability permanent matrix (VSRPM). A step by step procedure is developed for calculating variable permanent function for reliability (VPF-r) from VSRPM. A higher value of index implies that the plant is available with better reliability. The developed methodology is illustrated step-by-step with the help of an example.

ENERGY ANALYSIS OF A VAPOR COMPRESSION SYSTEM CASCADED WITH AMMONIA–WATER ABSORPTION SYSTEM

The first law analysis of a vapor compression–vapor absorption (VC–VA) cascade system is carried out for a wide range of cooling capacity. While ammonia–water is the working pair in VA section, R407C is used in VC section. The influences of change in cooling capacity, superheating and subcooling in the condenser, temperature in the generator, degree of overlap in cascade condenser, size of the heat exchangers etc. on the system performance are investigated. It is concluded that the COP of the VC section of the cascade system could be improved by 146% and the electricity consumption could be reduced by 64% compared to an equivalent VC unit. Separately the results showed the considerable increase in the generator heat when cooling capacity was increased from 83.33 kW. The COP of the cascade system at high cooling capacity is strongly dependent on the performance of condenser.

EXERGY ANALYSIS OF A VAPOR COMPRESSION–VAPOR ABSORPTION CASCADE SYSTEM

In this paper, second law analysis has been done for the vapor compression–vapor absorption (VC–VA) cascade system. Ammonia–water is considered as the working pair in absorption section and R407C is dealt as the working fluid in VC section. Exergy destruction or the irreversibility rate is determined in each components of VC–VA cascade system, for a wide range of cooling capacity by considering a variable speed reciprocating compressor. Further in this, Coefficient of structural bond (CSB) analysis is carried out to quantify the effect of varying the generator temperature, effectiveness of solution heat exchanger, inlet temperature of external fluids in evaporator/condenser and some other variables. Solution heat exchanger and the condenser are reported to have high CSB value, so have a great scope of improvement to reduce the irreversibility rate of the whole system.

Mathematical Modeling and Computer Simulation of a Combined Cycle Power Plant

This paper presents the simulation procedure developed to predict the performance of a combined cycle power plant from given performance characteristics of its main components. Effects of gas turbine and steam turbine cycle parameters on combined cycle power plant (CCPP) output in terms of efficiency, work output and power output, particularly analyzing the influence of ambient conditions on the plant performance. The results of the mathematical model, implemented in “Matlab” software, have been compared with the simulation results presented in literature. Result shows that as the compression ratio increase the increase in efficiency becomes less. Increase in work output is observed upto a pressure ratio of 18 after this it starts decreasing. Increase in TIT increases cycle work output and efficiency. Turbine outlet temperature decreases with increase in compression ratio. Combined cycle efficiency and output first increases with rise in drum pressure and then decreases. Increasing superheater temperature is found to increase the specific work output and efficiency of steam and combined cycle. Increasing superheater temperature is found to increase the specific work output and efficiency of steam and combined cycle. Lowering the pinch point and approach point also results in an improvement in the combined cycle performance, Specific heats are considered to be changing with temperature. The present work will make the base for exergy analysis of combined cycle for varying parameters.

In-situ reactive extraction of castor seeds for biodiesel production using the coordinated ultrasound – microwave irradiation: Process optimization and kinetic modeling

The present study demonstrates innovative and industrially viable in-situ biodiesel production process using coordinated ultrasound-microwave reactor. Reactive extraction process has been carried out by mixing grinded castor seeds with methanol in the presence of base catalyst (KOH). Response surface methodology coupled with central composite design has been applied for process optimization to achieve maximum yield. The result shows that maximum biodiesel yield of 93.5 ± 0.76% was obtained under favorable conditions of: molar ratio (350:1), catalyst (w/w) (1.74%), reaction temperature (43 °C) and reaction time (30 min). Regression equation obtained for the model having (R2), and (R2adj) equal to 0.9737 and 0.9507 respectively shows goodness of fit. First time reaction kinetics as well as oil extraction kinetics studies have been performed on coordinated ultrasound-microwave reactor. Assuming pseudo first order reaction activation energy was found to be 28.27 kJ·mol-1 and activation energy for oil extraction was observed to be 9.11 kJ mol-1. Estimated activation energy for the reaction kinetics and extraction kinetics was reduced by 27%, reaction rate constants were eight to ten times higher and diffusion coefficient was found to be two times higher in case of hybrid system as compared to conventional mechanical stirring technique. Estimated thermo-physical properties of biodiesel were found in agreement with ASTM and DIN standards in comparison to gasoline diesel.

Comparative performance study of vapour compression-absorption cascaded system at optimum condensing temperature

The present study thermodynamically analyse a vapour compression-absorption cascaded refrigeration system (CRS) that uses R407C and H2O-LiBr as refrigerants, to determine the optimal condensing temperature of cascade condenser. The optimum condensing temperature of cascade condenser is found to be 18°C for 83.09 kW refrigeration capacity at an evaporating and condensing temperature of 0.4°C and 46.8°C respectively. The optimum condensing temperature is found, to maximise the rational efficiency of CRS and minimise the total irreversibility of system. Further comparative study of CRS with equivalent vapour compression refrigeration system (VCRS) used for water chilling applications shows that the electric power consumption in CRS is reduced by 70% and COP of compression section is improved by 235% as compared to equivalent VCRS.

Simulation of Gas Turbine Combustion Chamber for CO2 Emission Minimization

In the present analysis combustion products of a 30 MW cogeneration cycle are studied on the basis of their concentration with change in cycle pressure ratio (CR). Mathematical modeling is done on the basis of exergy, energy and mass balance across the components. A computer program is made in EES (engineering equation solver) software and different parameters are studied for the analysis. For the present analysis air is considered to be a combination of N2 (77.48%), O2 (20.59%), CO2 (.03%) and H2O (1.9%). After combustion their concentration is changed. From the results it is observed that with change in cycle pressure ratio the concentration of N2 and O2 decreases and that of CO2 and H2O increases. Mass of CO2 in combustion products is directly proportional to the mass of fuel injected in combustion chamber. With increase in cycle pressure ratio / compression ratio (CR) fuel consumption decreases upto a pressure ratio of 15 and after CR 15 it starts increasing again. As the fuel is the combination of the carbon and hydrogen, after burning with oxygen it generates heat energy, CO2 and H2O. Although upto a CR 15 mass of CO2decreases in combustion products, but due to change in the concentration of other constituents, concentration of CO2is increased. That is why concentration of H2O and CO2 in combustion product increases and that of oxygen decreases. From the results it is also concluded that increase in pressure ratio not only increases the efficiency of GT cycle but generates a concentration of N2, O2, CO2 and H2O in such a manner that specific heat (Cp) of combustion gas is increased.