This article aims to examine a novel combined power and refrigeration system, using renewable and waste heat sources suitable for low-temperature applications. The present system is an integrated Kalina cycle and ejector refrigeration system to generate power and refrigeration simultaneously. To improve the vapour generation, the separator vapour fraction is used as a decision variable. Relative irreversibility and efficiency defect as two important parameters considered in this system for an investigation to identify the weaker components. The combined system generates power and refrigeration with two different mediums by the incorporation of the heat exchanger at the turbine exhaust. The novel system's energy and conventional exergy evaluation are carried out through Python Software. The optimum values of decision variables: turbine concentration, separator vapour fraction, entrainment ratio, expander ratio, split ratio and turbine concentration are identified using Python software from an opted range of variables. The maximum value of net power output, first law efficiency for power generation system, combined system, second law efficiency for power generation system, combined system, refrigeration effect and coefficient of performance are obtained as 113 kW, 8.85%, 11.83%, 93.44%, 81.29%, 38.07% and 0.118, respectively, at higher separator vapour fraction. Among the components considered in the combined power generation system, the condenser and LTRGN account for the higher exergy destruction rate of 30.41% and 25.53%. The coefficient of performance is maximized at a higher value of the refrigeration effect. The turbine pressure at the inlet is increased with increments in turbine work on choosing the higher value of the expander ratio. The higher exergetic value components are not emphasized to focus on improvement.

First law analysis assesses the performance of the system considered for investigation in the energy aspect. Low-temperature power generation system suitable to recover waste heat from a renewable source is investigated in the present work. The system is adopted to work at hot sink conditions and investigation on performance assessment is carried out in exergy aspect. Exergy analysis in both conventional and advanced methods proposes the system components which need improvements in themselves and associated with other components more properly. Exergoenvironmental analysis using the Life cycle assessment (LCA) method is examined in the system under the same sink conditions. Exergy analysis reveals that the component with a high source will yield more losses resulting in higher irreversibility. Hence turbine and evaporator need investigation in improving the system’s performance. Exergoenvironmental investigation suggests that the highest impact results in the low-temperature regenerator (LTRGN). The improvement in these components' designs and limitations in the characteristics of the material chosen and the manufacturing methods involved will favor a higher performance of the system. LTRGN has resulted in with high relative cost difference value of 23.85 % and seeks improvement. The exergy destruction is in a larger amount in the components evaporator and turbine with 70.66 kW and 30.99 kW respectively. Avoidable exergy destruction value of evaporator, condenser results 51.11 $/hr and 16.64 $/hr respectively. The LTRGN has an environmental effect rate of 54.83 mPts/hr and device-related environmental effects of 45.16 mPts/hr. The (ĖD/ĖP), (Ẏ/ĖP) and (Ż/ĖP), values at 85% pump efficiency results 2.16, 0.00946 and 0.30871.

ABSTRACT The flow separation occurred at an early angle of attack (AOA) in airfoil directs the researchers to focus on the methods of flow controlling. The present study incorporated a spherical dimple on the NACA (National Advisory Committee for Aeronautics) 4415 leading edge as a passive flow control device and compared the aerodynamic performances with the plain NACA 4415 airfoil. The dimple diameter (d) was varied from 1% to 6% of the chord length (0.01C-0.06C) to generate four numbers of the modified airfoil. A chord-based Reynolds number (Re) of 2 × 105 was selected for the present study. Shear-Stress Transport (SST) k-ω turbulence model with SIMPLE (semi-implicit method for pressure linked equations) scheme was chosen to solve the present problem computationally in ANSYS FLUENT 14.0. The results showed that the modification helped in delaying stall by 6° at the expense of 0.8% maximum lift coefficient with a dimple diameter of 0.01C. The modified airfoils experienced a primary low-velocity circular zone near the trailing edge and a secondary circulation zone at the dimple edges. In contrast, only one larger circulation zone was present near the plain airfoil trailing edge. The smallest dimple (d = 0.01C) showed a maximum lift enhancement ratio and lift to drag enhancement ratio of 14.8% and 7.86%, respectively.

A novel power generation system suitable to recover waste heat from a renewable source at medium temperature level is investigated in the present work. In a regenerative system, saturated vapour is supplied to one of the heat exchangers by a secondary solar collector, which raises the temperature of the boiler as a whole. The main advantage of this method is the reduction in irreversibility in the mixing chamber M3, which encourages a higher flow rate to the turbine. Preheating the circulating solution and completely evaporating the basic stream are used to achieve this. The performance of the system is investigated in energy aspects along with detailed exergy analysis. Environmental impact as a result of the working conditions is essential to propose the optimum decision variables. Exergy analysis in both conventional and advanced methods proposes the system components which need improvements in themselves and associated with other components more properly. Exergoenvironmental analysis using the Life cycle assessment method is examined in the system under the hot sink conditions. Exergy analysis reveals that the component with a high source will yield more losses resulting in higher irreversibility. Hence, turbine and heat exchanger 4 (HE4) need investigation in improving the system's performance. Exergoenvironmental investigation suggests that the highest impact results same components identified by the advanced exergy analysis. Exergoenvironmental analysis on the proposed Kalina power generation system is carried out under hot sink conditions. The exergy destruction and destruction cost rate of 29.23 kW and 0.478 h-1 at turbine inlet conditions of 185 °C and 45 bar. The exergoenvironmental factor fb and the relative difference rb reveal that the components with high environmental impact have to be minimized. Turbine and HE4 are the components resulting in higher total exergy and devise related impact on the environment.

Abstract The current study presents research investigations and developments related to the homogeneous charge compression ignition (HCCI) engine. Research investigations and recent advances, including the role of various operating conditions on HCCI engine combustion phenomena, emissions, and performance, are discussed. There is growing research interest in investigating HCCI engines with diesel fuel to study combustion, emissions, and performance characteristics due to their association with low NOx emissions. In the published literature, research investigations are also conducted with different fuels ranging from biomass to diesel to gasoline in the HCCI engine showing its capability for utilizing various fuels in coming years. The challenges associated with HCCI combustion are reviewed, and the details of excessive carbon monoxide and unburnt hydrocarbon emissions are discussed. The major parameters affecting the hydrogen addition in HCCI diesel engines are also discussed. Overall, adding hydrogen to a diesel‐fueled HCCI engine improves combustion phasing and can potentially increase thermal efficiency while lowering emissions. In addition, the strength, weaknesses, opportunities, and threat analysis is provided and discussed thoroughly.

ABSTRACT The basic needs of man are food, clothing, and shelter besides air and water. In providing these needs, power generation systems play a crucial role. Day by day, for various reasons such as explosion of population, the demand for power is increasing tremendously. Power generation systems need to generate more power. A novel power generation system suitable for recovering waste heat at a medium temperature range is examined in the present work. To assess the performance of a power generation system, energy and exergy measures are necessary. Energy measures provide enough details about the performance of the system. To know the systematic performance analysis, detailed exergy analysis alternatively profound as advanced exergy analysis and environmental impact are to be investigated. Exergoenvironmental analysis on the proposed Kalina power generation system has been carried out under hot sink conditions. Considering the proposed decision variables relative exergy destruction (ĖD/ĖP), relative environmental impact (Ẏ/ĖP), and relative investment cost (Ż/ĖP), the performance of the system has been assessed. The exergy destruction and the destruction cost rate of 29.23 kW and 0.478 $/hr at turbine inlet conditions of 185°C and 45 bar have been achieved. The exergoenvironmental factor fb and the relative difference rb have revealed that the components with high environmental impact have to be minimized. Turbine and HE4 are the components that contribute to higher total exergy and devise related impact on the environment.

A sustainable solar based PVT tea drying system has been developed to minimize the dependency on the nonrenewable commercial tea drying system. In this work, the effect of operating conditions on the performance of a photovoltaic-thermal (PVT) collector-based solar dryer is investigated under sunny and cloudy weather conditions for three different cases- Case-I (natural convection), Case-II (forced convection with an air velocity of 0.096 m/s), and Case-III (forced convection with an air velocity of 0.014 m/s). Firstly, energy performance of the PVT system has been evaluated for all the three cases under sunny and cloudy days, which show that the energy performance has been enhanced to a maximum value of 58.71% and 53.95% for sunny days and cloudy days, respectively, and these are obtained in case of case-III. Then the drying of green tea under mixed-mode drying (MMD) and indirect mode drying (IMD) are presented under sunny days for each of the three cases and compared with open sun drying (OSD) and shade drying (SD). The moisture content has been reduced from 2.95 (d.b.) to 0.14 (d.b.) in all the cases of drying modes. Further, the drying kinetics of green tea leaves is compared using existing models, and a new drying model is proposed, which is found to predict the moisture ratio better. The maximum PVT dryer efficiency, moisture effective diffusivity, and specific moisture extraction rate (SMER) are 26.37%, 4.97 x 10-9 m2/s, and 0.6125 kg/kWh, respectively, for MMD process.

This paper introduces a novel power generation system using solar energy as a heat source. The proposed cycle incorporates heat sources from two solar collectors for the effective utilisation of heat energy. To aid the performance of the proposed system, the turbine flow rate is increased with the specific heater arrangements. Energy and exergy balances of the novel system were generated using Python software. The investigation of the present system was evaluated with high sink temperature. Turbine inlet concentration, turbine inlet pressure, HE4 outlet temperature from the turbine, condenser concentration of ammonia, isentropic efficiency of the turbine and pressure ratio are the design variables considered for the exergy and thermoeconomic investigation. The energy and exergy analyses resulted in suitable design variables to optimise the performance. The optimum Kalina cycle efficiency, solar plant efficiency, exergy efficiency and network output were determined to be 18.51%, 8.28%, 34.51% and 295.24 kW, respectively. Among the components involved in the system, the mixers account for the highest exergy destruction followed by the turbine. The cycle performance can be improved by reducing the exergy destruction rate. The thermal efficiency is maximised by the turbine inlet pressure and temperature. Moreover, a higher relative cost difference has resulted in heat exchanger 5 and pump 2.

Accepted: 28 Dec. 2020 In the present work, economic and environment analyses of multi-generational micro gas turbine systems are reported for a grid-independent dairy farm in Ontario, Canada. Onsite anaerobic digesters utilize farm waste to produce carbon neutral biogas for combustion in the micro gas turbine modules. A range of micro gas turbines coupled with absorption refrigeration units and an organic Rankine cycle are driven by the recovered waste heat to meet the cooling and electrical needs of farm sizes between 250 and 6000 cows. Farms of these sizes are observed to be capable of having their cooling and electricity needs met with micro gas turbines ranging in capacity from 100 to 1000 kW output. Environmental performance is maximized when the net output of the system just matches the energy requirement of the farm, and produces no excess electricity. Thus to minimize the environmental impact, but remain financially viable, various configurations are suggested for farm sizes under 2000 cows.

A parametric investigation of a novel ammonia water mixture power generation system is performed in this study. The overall performance and feasibility of the system of the proposed system are assessed from thermoeconomic, conventional exergy and advanced exergy perspectives. For better heat recovery in the existing medium-temperature heat recovery Kalina system, auxiliary solar heater is considered in the proposed design to improve the overall performance in terms of energy and exergy. The system performance parameters investigated include cycle efficiency, net output, total product cost rate, exergoeconomic factor and total exergy destruction rate. The simulation of the energy and exergy analysis was performed using Python coding. In this respect, the parametric investigation revealed that the cycle efficiency, net output, total product cost rate, exergoeconomic factor and total exergy destruction rate of the system at optimized conditions are 15.5%, 280 kW, 136 $/GJ, 66% and 120 kW, respectively. The irreversibilities of each component and overall system were evaluated and it was found that the turbine accounts for the highest exergy destruction among all components, contributing nearly 13% of the total exergy destruction of the system. Advanced exergy analysis was also performed that involved characterizing the exergy destruction as endogenous, exogenous, avoidable, and unavoidable, leading to specific recommendations for improving the performance of the system. Conventional exergy analysis suggests that the turbine, HE4, and separator are the components typically identified for improvement. The advanced exergy analysis in this study, however, indicated that the separator should be the primary focused for performance improvement, followed by the HE(4)and turbine.

This paper puts forward the simulations of different configurations of combined solar evacuated tubular collector with a ground source heat pump system to meet the heating, cooling and hot water demands of a house in Tabriz. The configurations include: indirect expansion (parallel), indirect expansion (series) and direct expansion. The simulation was done in TRNSYS with 9 m(2) evacuated tubular solar collector and three boreholes with depths of 75 m. Power consumption and COP of all configurations were compared, and the optimum configuration had the highest value of overall COP which is the indirect expansion in parallel mode with the overall COP of 3.96. Furthermore, the economic analysis was done to compare the proposed optimum system with the conventional ones, where a payback period of about 13 years was obtained. On the other hand, by considering the environmental effects of fossil fuels produced by conventional systems and natural gas exporting income, the amount of 433.8 US$ and 2629 US$ will be saved, annually. By adding the environmental and natural gas exporting costs to the operating costs of the conventional system, the payback period was reduced down to 6 years, showing that the system can be feasible in the northern parts of Iran with a cold climate.

In the present work, natural gas combined cycle power generation configurations are investigated with oxyfuel combustion. Steam is also injected in main combustion chamber and reheat combustion chamber to understand the performance of combined cycle work output and greenhouse gas emission. It is observed that the steam injection increases gas cycle efficiency and decreases the steam cycle efficiency. CO2 emission reduction of 3.2% when steam injection in both combustion chambers for oxyfuel cycle. In oxyfuel combustion, higher ratio of recycle flue gas brings higher thermal efficiency and highest thermal efficiency is achieved when steam is injected in gas turbine main combustion chamber only.

The performance of steam power plants, utilizing recovered waste heat from air-fuel and oxy-fuel combustion, are compared. Temperature profiles in the heat recovery steam generator (HRSG), steam production rate, net-work output and energy efficiency are simulated for different conditions. Investigations are made into the effect of varying pinch point on HRSG performance, net-work and energy efficiency for power generation utilizing oxy-fuel combustion. It is found that with increased pinch point there is an associated decrease in HRSG and steam plant efficiencies. Exhaust gas composition influences the energy efficiency of the power plant. When air-fuel and oxy-fuel combustion are compared there is a reduced amount of nitrogen in the oxidant stream in the latter case. When comparing air-fuel and oxy-fuel combustion, a considerable deviation in HRSG and steam power plant performance is exhibited, with oxy-fuel combustion offering benefits in system efficiency and plant output. The exhaust gas composition at the HRSG inlet contributes significantly the performance characteristics of the system. Raising the HRSG inlet temperature also increases power generation and system efficiency. The results provide insights into the use of oxy-fuel combustion for systems utilizing HRSG for power generation while demonstrating the influence of gas composition, pinch point, and exhaust gas temperature on system performance, and suggest that oxy-fuel combustion can help enhance the contribution to sustainable development of some energy systems.

Mining is the typical method of extracting coal, but it can only recover 20%–25% of global coal resources. Mining has many challenges and requires much time, resources, and personnel. A new method of coal extraction, underground coal gasification (UCG), could address some of these problems while greatly expanding recoverable coal resources. Underground coal gasification is a gasification process applied to in situ coal seams. When combined with carbon capture and storage, UCG has significant potential for providing a relatively clean energy source. This chapter reviews key concepts and technologies of UCG, providing insights into this developing coal extraction method. A case study is also presented that illustrates the modeling and analysis of UCG and assesses the feasibility of using an auxiliary power plant and utilizing waste heat rejected syngas processing, to supply the required energy associated with amine-based carbon dioxide capture and compression processes.

A multi-output energy-generation system for providing electricity and cooling for a grid-independent Ontario dairy farm is investigated. A range of biogas-fed micro turbines coupled with absorption refrigeration units and an organic Rankine cycle for heat recovery are considered to meet the electrical and cooling needs of farm sizes between 250 and 6000 cows. An energy analysis is conducted for the entire system and each subsystem. It is found that absorption refrigerators make best use of the energy in the exhaust stream, and increasing the amount of energy input to this subsystem increases overall system energy efficiency. Overall system energy efficiencies vary from 9 to 40%, increasing with farm size, while the energy efficiency of the bottoming cycle is 32-40% depending on farm size. For the range of configurations considered, electricity generation exceeds the farm's internal energy requirements, presenting opportunities for the sale of electricity.

In the present work, combined cycle power generation configuration studies with natural gas as a primary fuel. Steam is injected in main combustion chamber and reheat combustion chamber individually and simultaneously to understand the performance of combined cycle work output and greenhouse gas emissions. The effect of pressure ratio, gas turbine inlet temperature on combined cycle work output, thermal efficiency and exergy efficiency carried out with and without steam injection. It is observed that the steam injection increases gas cycle efficiency and decreases the steam cycle efficiency. Ideal pressure ratio found to be 25 in all different combined cycle power generation system configurations. Maximum CO2 emission reduction (7.2%) occurs when steam injected in reheater combustion chamber.

Background:District Energy (DE) is a technology capable of using renewable energy (e.g., solar thermal systems) and waste heat as energy sources efficiently. DE technology nonetheless has potential for improvement. Thermal Energy Storage (TES) can enhance DE performance significantly.Objective:An exergy analysis of a DE system which includes a solar thermal energy system and TES is performed, so as to improve understanding of its performance.Method:A case study based on the Friedrichshafen DE system in Germany is used to assess thermodynamically the role of solar energy and TES in a DE system. The system performance is separated into three modes: (1) fossil fuel is the only source of energy, (2) a discharging TES and fossil fuel provide heat for the DE system, and (3) solar energy and fossil fuels are the energy supplies. Exergy analyses are conducted for each performance mode and the overall DE system.Results:The results quantify the benefits of incorporating solar energy and TES on the performance of the Friedrichshafen DE system, and demonstrate that the overall exergy efficiency of the DE system increases from 23% to 27% with assistance of solar thermal collectors and TES, while the total energy efficiency increases from 83% to 87%.Conclusion:An increase of exergy efficiency is observed when TES is added to a DE system, due to a reduction in solar thermal energy loss by the TES, which allows more solar energy to be converted to useful energy to satisfy the DE system thermal energy demand.

The deficiency in the energy for the space cooling is overcome by solar energy. Still the input energy is minimized by integrating both power and cooling cycle in common platform, such as working fluid, component and working parameters. The aqua-ammonia is used in both power cycle and vapor cooling cycle. The generator is common for cycles for the production of ammonia vapor. The analyses are made to find out the operational parameters for the cooling cogeneration cycle with solar as source. The analyses are done for the proposed cycle with various atmosphere temperatures. At absorber concentration of 0.42 and turbine inlet concentration of 0.90, with solar collector exit temperature of 155°C and atmosphere temperature of 30°C the generated power and cooling are 21.88 and 215.79 kW, respectively. The power and cooling output range can alter by varying turbine inlet concentration and temperature.

Exergy analyses of multi-generational micro gas turbine systems are reported for a grid-independent dairy farm in Ontario, Canada, with an aim of being environmentally benign. Onsite anaerobic digesters utilize farm waste to produce carbon neutral biogas for combustion in the micro gas turbine modules. A range of micro gas turbines coupled with absorption refrigeration units and an organic Rankine cycle are driven by the recovered waste heat to meet the cooling and electrical needs of farm sizes between 250 and 6000 cows. Exergy balances are applied to each component as well the overall system configuration, and exergy efficiencies are obtained. Small farm sizes with one absorption cooling unit are found to be more exergy efficient than large farm sizes with more than one absorption cooling unit, but the difference is less than 0.5%. Most of exergy destruction within the micro gas turbine module occurs in the combustion chamber, which contributes 79% of the exergy destruction of the system. Farm sizes between 250 and 6000 cows are observed to be capable of having their cooling and electricity needs met with micro gas turbines ranging in capacity from 100 to 1000 kW output, while exhibiting similar exergy efficiencies.