Total Exergy Destruction Research Articles

Evaluation of the energy and exergy of a trans‐critical CO2 cycle driven by a double flash geothermal power plant

AbstractFacing the dual challenges of environmental impact and the finite nature of fossil fuels, the shift toward sustainable energy sources is imperative. Geothermal energy, a renewable and underutilized resource, offers a promising alternative. This study ventures into a novel domain, exploring the integration of trans‐critical CO2 (tCO2) cycle with a double‐flash geothermal (DFG) cycle, an area not extensively covered in existing research. This study aims to develop a recovery system that utilizes a tCO2 cycle powered by a DFG cycle. A crucial part of this study involves conducting a sensitivity analysis to evaluate the system's energy and exergy performance. This analysis focuses on understanding the impact of changes in key system design parameters, such as energy efficiency, exergy efficiency, net power output, and total exergy destruction rate, to determine the optimal values for these parameters. The results indicate that the recovery system shows a significant improvement of 22% in energy efficiency over the basic cycle. However, there is a decrease in exergy efficiency in the recovery system, which represents a 5.26% decline. As a result, this study paves the way for innovative approaches in geothermal energy use, suggesting potential breakthroughs in renewable technologies.

Simulation and comprehensive 4E study of a high-efficient CCHP arrangement utilizing geothermal energy and eco-friendly heat recovery

In recent years, geothermal energy has received significant attention as it provides a sustainable and renewable energy resource for various applications. The primary objective of this study is to manage the relative irreversibility and enhance productivity through efficient utilization of geothermal energy. The present paper establishes a high-efficiency and environmentally sustainable heat integration model in a novel configuration to be a geothermal energy source having the ability to produce power, heat, and cooling. The proposed framework consists of a Kalina cycle, two organic Rankine cycles, an ammonia Rankine cycle, a single-flash power unit, and a combined cooling and power unit. The simulation of the proposed system is implemented within the Aspen HYSYS software, with an examination of its feasibility across energy, exergy, economic, and environmental considerations. The research findings indicate that the system can generate 23250.8 kW of power, 582.1 kg/s of hot water, and 2.812 kg/s of chilled water. Therefore, the total exergy destruction rate is 14104 kW, with the Kalina cycle accounting for the majority share at 40.47 % Moreover, the energy and energy efficiencies of the suggested structure are 61.81 % and 72.52 %, respectively. The environmental analysis indicates that the entire process lacks carbon dioxide emissions. Furthermore, the economic analysis reveals that the total unit exergy cost and levelized cost of energy are determined to be 5.13 $/GJ and 0.511 $/kWh, respectively. Also, the proposed system exhibits a favorable net present value of approximately 32.16 M$. Hence, the project demonstrates profitability.

An Ocean Thermal Energy Conversion power plant: Advanced exergy analysis and experimental validation

An ocean thermal energy conversion power plant was simulated from the point of view of the first, the second law of thermodynamics, and advanced exergy analysis with the aim of increasing the efficiency of the cycle, quantifying and knowing the nature of the exergy destruction. First, the net power output and efficiency of the cycle were successfully calculated as a function of the surface temperature and a certain depth of the ocean, given a pinch temperature differential and the mass flow of seawater in the evaporator and condenser. The numerical simulation are compared with experimental evidence, obtaining better results than thermodynamic models previously reported. Then, the second law of thermodynamics analysis was made using appropriate correlations for the estimation of thermo-physical properties of seawater, revealing the imprecision of assuming properties of pure water in the calculation of the total exergy destruction of the system. Finally, advanced exergy analysis is developed, it provides the nature of the exergy destruction and the best strategy to increase the efficiency of the cycle. The evaporator and turbine are presented as the most promising pieces of equipment to be developed in new future research due to their avoidable endogenous nature of exergy destruction.

Multivariate multi-objective collaborative optimization of pumped thermal-liquid air energy storage

Pumped thermal-liquid air energy storage (PTLAES) is a novel energy storage system with high efficiency and energy density that eliminates large volumes of cold storage. In this study, three different configurations of PTLAES systems with direct and indirect thermal energy storage were proposed. The “adaptive segmentation-based temperature transfer matrix” method was developed to capture the heat transfer characteristics of multi-stream plate-fin heat exchangers (MPFHEs), which is the key component of the system. To determine the upper limit of the techno-economic performance of the system, single/multi-objective optimization was performed with up to 35 decision variables. Additionally, the “Pareto efficiency” concept was defined to quantify the goodness of a point compared to the Pareto front. The results showed that the irreversible heat transfer and pressure drop in MPFHEs contribute 20.6 %–44.3 % of the total exergy destruction. Therefore, the design of MPFHEs significantly impacts the system performance. Multivariate multi-objective collaborative optimization can significantly improve the optimization results. PTLAES with closed loop indirect thermal energy storage was determined to have the best overall performance, achieving round-trip efficiency of 63.3–70.1 %, levelized cost of storage (LCOS) of 0.162–0.181 $/kWh, and energy density of 122–161 kWh/m3. The optimized PTLAES system can achieve lower LCOS than lithium-ion batteries when the discharge duration exceeds 3.5 h. Furthermore, it was shown that key criteria including round-trip efficiency, LCOS, and energy density can be traded off over a broad design space of different system configurations, parameter combinations, and material choices. This research demonstrated that PTLAES is a promising choice for long-duration energy storage and provided guidance for the design and techno-economic optimization of PTLAES systems.

Exergy analysis of packed and fluidized bed thermal energy storage systems

This work presents a detailed exergy analysis that compares two different thermal energy storage (TES) systems that use particles as energy storage media and air as the heat transfer fluid: packed and fluidized beds. The study permits the optimization of both TES systems in terms of exergy storage capacity and quantifies the irreversibilities that appear in both cases. In addition, the influence of air flow rate and particle size has been quantified.The results indicate that when focusing solely on the storage process, there is an optimal charging time that minimizes the exergy destruction in both cases: topt∼mscp,s/ṁacp,a. Although the exergy destruction of the fluidized bed during the beginning of the charging process is higher than that in the packed bed, at the end of the process, the total exergy destruction in both beds is similar. However, in the full storage–recovery process the total exergy destruction is doubled in the fluidized case, with an entropy generation number of approximately 0.6 in comparison with a value of 0.3 for the packed bed. Besides, a sensitivity analysis varying the particle size and the air flow rate indicates that the particle size has a much higher influence on the fluidized bed case due to the change in the minimum fluidization velocity and its influence on the heat transfer rate. Finally, a case study is presented using the storage bed for building heating, and an exergy analysis concludes that the fluidized bed generates 534W/K of entropy, more than three times the entropy generated in the packed bed (161W/K), due to the higher pressure drop needed to fluidize the particles.

Energy, exergy, and exergoeconomic analyses of an air source transcritical CO2 heat pump for simultaneous domestic hot water and space heating

The transcritical CO2 heat pump system experiences significant throttling losses in space heating operation due to the higher temperature of returning water. This paper presents an energy, exergy, and exergoeconomic analyses of an air source transcritical CO2 heat pump integrating a tri-partite gas cooler, which is an effective method to match CO2 temperature glide with water for simultaneous domestic hot water and space heating (DHW+SH) production. A pinch point-based numerical model is developed to find the optimal discharge pressure. This validated model is then utilized to investigate the impacts of water inlet temperature and ambient temperature. Two configurations are examined: one with only DHW supply and the other with DHW+SH supply. The results indicate that combining SH with DHW enhances COP by 7.5% with a 7.9% reduction in discharge pressure at 10 °C ambient temperature and 10 °C water inlet temperature. At a water temperature of 10 °C, exergy efficiency improves by 4%. The compressor accounts for 54%–60% of the total exergy loss. The DHW+SH system exhibits an average exergy destruction reduction of 7.6%. With each 5 °C rise in ambient temperature, the DHW+SH system’s total exergy destruction cost rate decreases on average 7.7% compared to the DHW system. Furthermore, the combined exergy destruction cost rate of GC2 and GC3 in DHW+SH is significantly lower (by 48.2%) than only GC3 in DHW. The exergoeconomic factors of the compressor, gas cooler 2, and gas cooler 3 emphasize the need to decrease their costs to enhance cost-effectiveness.

Energy and Exergy Analyses of Supercritical Coal‐Fired Power Plant With Single Reheat and Regenerative

This paper investigates energy and exergy analyses of 660 MW capacity supercritical coal power plant with single reheat and regenerative. The fuel utilized in the plant is a combination of sub‐bituminous and lignite coal. It is found that the turbine section of the system exhibits the highest energy efficiency (around 94.17%) and exergy efficiency (around 90.73%). Also, 82.07% of the total exergy destruction is found for the boiler, and the remaining 17.93% of the irreversibility is determined for the turbine, condenser, and other components. The overall cycle energy efficiency at maximum load is computed as 40.77%, while the overall cycle exergy efficiency at maximum load is found to be 39.69%. These findings provide valuable insights into the performance of the power plant and suggest the improvements needed in performance enhancement of the boiler.

Thermodynamic evaluation of shell and tube heat exchanger through advanced exergy analysis

Shell and tube heat exchanger is a pivotal equipment used in industries for heat transfer. Any effort to minimize the irreversibility in the heat exchanger will enhance the performance and leads to energy optimization and cost savings. In the current study, a water to water, segmental baffled shell and tube heat exchanger was considered for an investigation and designed using the Kern method. Exergy analysis and advanced exergy analysis was carried out to understand the performance of the heat exchanger and to determine the possibility of reducing irreversibilities. The results of the exergy analysis showed that the system has 684.6 kW of exergy destruction. Advanced exergy analysis was carried out through endogenous and exogenous modes and subsequently performed for avoidable and unavoidable components. Majority of the exergy destruction in the heat exchanger is avoidable. The results showed that 97.5 % of the total exergy destruction is of endogenous avoidable type. The system can be improved by changing the system configuration, design variables, mass flow rates, materials, and many other parameters. Subsequently, the exergy destruction in the pumps is unavoidable and no further design improvements are required.

Exergy analysis of a steam power station in a sulfuric acid plant

This study presents energy and exergy analyses of a Steam Power station of a sulfuric acid plant. A heat recovery system is implemented in the plant to recover waste heat from an exothermic chemical reaction of the sulfuric acid production process. This research aims to analyze system components to determine where energy losses are. A mathematical model was developed using the EES software to perform the calculations. Exergy analysis is computed for real ranges of the main operating parameters. It was found that the key sources of exergy destruction are the waste heat boiler 41 %, followed by the heaters 24.7 % then the steam turbine 18.6 %, and the condenser 13.8 % of the total exergy destruction. The 2nd law efficiency obtained for the waste heat boiler, the steam turbine, and the condenser is 80 %, 82 %, and 37.4 % respectively, while the overall plant exergy efficiency is 68.7 %. The effect of varying different parameters such as reference environmental temperature on main plant components is investigated. The effect of increasing steam inlet temperature, pressure, and mass flow rate on plant exergetic efficiency and exergy destruction is also presented. Results showed that lowering condenser vacuum pressure leads to a 7 % improvement in overall system exergetic efficiency.

Exploring an innovative approach to hydrogen generation for fuel cell energy production by integrating a dual organic Rankine system with an absorption chiller powered by geothermal energy

This study delved into the thermodynamic optimization of a geothermal system integrated with a fuel cell unit for energy storage during peak consumption. An innovative system was devised to simultaneously produce cooling, electricity, hydrogen, and freshwater by combining an absorption chiller, reverse osmosis, PEM Electrolyzer, and two double Organic Rankine Cycles. To assess the impact of local weather conditions, case studies were conducted in the cities of Hong Kong (China), Bandar Abbas (Iran), Tepic (Mexico), and Melbourne (Australia). Computational modeling employed EES software, and optimization using Response Surface Methodology aimed to enhance system performance and minimize costs. The geothermal system was engineered to meet the electricity demands of residential households during peak consumption. The optimal results demonstrated that the proposed geothermal system, in its most efficient configuration, could achieve an exergy efficiency of 73.17 % and an energy efficiency of 25.25 % while operating at a cost rate of 74.36 $/h. An economic analysis revealed that among the system components, ORC1 unit and PEME incurred the highest costs. Additionally, the PEME, evaporator, and absorption chiller were identified as the main contributors to exergy destruction. The total exergy destruction rate of the proposed geothermal system is 1840.7 kWh and the total cost rate of the system is 51.73 $/h. Lastly, the assessment of the suggested geothermal system across the studied cities indicated that it performed most effectively in Melbourne, Australia. The results of the study of the production capacity in the four study cities showed that Melbourne has the highest production rate with a rate of 14,573 MWh, Tepic with a rate of 13,425 MWh, and Hong Kong with a rate of 13,174 MWh. The lowest annual rate with the amount of 12,784 MWh belongs to the city of Bandar Abbas. The environmental results showed that by producing 14,573 megawatts of electricity in the city of Melbourne, it is possible to expand 14 hectares of green space per year. Also, prevented the reduction of carbon dioxide emissions by 2972.8 tonsCO2/MWh at 71,349.4 $/tonsCO2. The analysis of the production power of the system showed that the electricity needs of 1533 people can be provided for one year by starting the geothermal system in Melbourne City.

Performance analysis of a dual-ejector enhanced two-stage auto-cascade refrigeration cycle for ultra-low temperature refrigeration

Auto-cascade refrigeration cycle (ARC) is a cost-effective solution for ultra-low temperature refrigeration. This paper proposes a dual-ejector enhanced two-stage auto-cascade refrigeration cycle (ETARC). In ETARC, two ejectors replace the throttle valves at the liquid phase outlet of the two gas–liquid separators in the conventional two-stage auto-cascade refrigeration cycle (CTARC). They are connected in series to recover partial expansion work in the throttling process, aiming to lift the suction pressure of the compressor. The ternary mixture component is selected and R600a/R41/R1150 is supposed to be the working fluid due to the best performance. The mass fraction ratio of the refrigerant mixture components, the quality at the inlet of two separators and the expansion ratio of the throttle valve (EPR) of the two cycles are optimized using particle swarm optimization (PSO) with respect to the maximum COP. The performances of the two cycles at optimum operating conditions are compared using energetic and exergetic methods, and the effect of the evaporation temperature and the condensation temperature on cycle performances and operating characteristics are discussed in detail. The results show that applying the two ejectors effectively improves the performance of ETARC. Compared with the CTARC at the evaporation temperature of −85℃, and the condensation temperature of 45℃, the ETARC cycle exhibits 16.07% improvement in COP, 29.43% increase in the volumetric refrigeration capacity qv, 17.17% reduction in the total exergy destruction rate. ETARC shows significant performance improvement and has a remarkable energy-saving potential.

Application of response surface methodology and desirability approach to optimize the performance of an ultra-low temperature cascade refrigeration system

In this paper, multi-objective optimization of an ultra-low temperature cascade refrigeration system is presented using response surface methodology and desirability approach. Evaporation temperature, high-temperature circuit and low-temperature circuit condensation temperature, cascade temperature difference, and superheat degrees of the compressor suction are chosen as the variables, whereas COP, total exergy destruction and exergy efficiency are adopted as the responses that simultaneously maximizing COP and exergy efficiency while minimizing the exergy destruction. The quadratic models for three responses are obtained after the analysis of variance. The interactive influences of the variables on the responses are indicated. The results present that the maximum deviations between the predicted and actual values for the COP and exergy efficiency are 0.84% and 0.96%, whereas the deviations for the exergy destruction are within ± 2% accounting for 96% of the samples. Evaporator temperature, condenser temperature, cascade temperature difference, ect. are found to be important parameters which cause great conflicts among the objective functions. A group of optimum values for the input variables are selected and validated. The derivations between predicted modeling and simulation values for the COP, total exergy destruction, and exergy efficiency are −0.604%, 2.886%, and 0.0452%, respectively, indicating that the method is efficient to optimize the performance.

Pinch and exergy assessment of an innovative hydrogen and methane purification process configuration based on solar renewable energy

Energy recovery from waste sources and developing new high-performance systems are essential to minimize energy consumption. A novel purification structure is developed to produce hydrogen and liquid natural gas (LNG) using exhaust gases from various industries, mixed refrigeration system, organic Rankine cycle (ORC), and solar energy sources. Solar parabolic trough collectors are used to supply energy in the low-temperature ORC. The proposed system produces 1.922 kg/s hydrogen with purity of 94.25 mol% and 1.777 kg/s LNG as the main product by consuming 10.56 kg/s crude hydrogen feed gas. The LNG and pure hydrogen specific power consumption (SPC) are 0.4111 and 0.3803 kWh/kg, respectively. The SPC of the sum of both products is obtained at 0.1975 kWh/kg. The methane and hydrogen recovery factors are 94.80% and 98%, respectively, indicating maximum methane and hydrogen absorption of the crude hydrogen feed gas. The exergy analysis indicates that the total exergy destruction of the integrated system is calculated at 5561 kW, and its exergy efficiency is obtained as 28.56%. The heat exchanger networks for the HE1, HE2, HE3, HE4, and HE6 multi-stream heat exchangers are extracted through the pinch strategy. The multi-stream heat exchangers have 8, 13, 6, 8, and 2 simple heat exchangers. The outcome results obtained from the parametric study is a 25.88% increase in the production rate of the main products (LNG and pure hydrogen). In addition, when the ratio of LNG to fuel gas increases by 48.08%, the ratio of main product to by-product increases from 54 to 62 mol%. By performing parametric analysis, it can be concluded that increasing the hydrogen content of the crude feed improves the performance of the system.

Performance improvement potential of ejector-based dual-evaporator refrigeration system using photovoltaic modules and nano-refrigerant

This paper presents a novel system for resolving the high energy consumption of conventional vapor compression refrigeration systems. An ejector-based dual-evaporator refrigeration system (EDERS) is developed utilizing photovoltaic (PV) modules and a nano-refrigerant (NR) with 0.5 wt% of Al2O3. This novel arrangement combines four promising environmentally friendly technologies: dual-temperature cycle, ejector, PV panel, and NR. The comprehensive thermodynamic analysis and optimization of the proposed system, energetic and exergetic analysis methods are incorporated to evaluate the performance of nanoparticle (NP)-doped EDERS in this study. The results demonstrate that the use of Al2O3 NP compared with utilizing pure R134a EDERS notably improves performance under typical operating conditions. Specifically, the coefficient of performance (COP), volumetric cooling capacity, and exergy efficiency (ηex) are 7.14 %, 4.33 %, and 8.91 % higher, respectively. Moreover, the compressor power and total exergy destruction are 6.76 % and 9.94 % lower, respectively. Additionally, under the operating conditions considered in this study, the required PV area is reduced by 5.31 %–8.07 %, whereas the COP and ηex values improve by 5.64 %–8.39 % and 5.38 %–10.06 %, respectively. The study also finds that the COP and ηex values of (R600a + Al2O3) surpass those of (R134 + Al2O3), whereas the COP and ηex values of (R1234ze(E) + Al2O3) and (R1234yf + Al2O3) are smaller than those of (R134 + Al2O3). This suggests that the performance benefits of NPs may vary depending on the specific refrigerant used in the system. The results can be employed as a useful guide for the application of NRs to multi-evaporator refrigeration systems before setting up an experimental system.

Thermo-economic assessment of air conditioner utilizing direct evaporative cooling: A comprehensive analysis

As concerns regarding energy consumption and environmental impact continue to grow, the need for efficient and sustainable cooling technologies becomes increasingly significant. Among various alternatives, direct evaporative cooling (DEC) has emerged as a promising solution due to its energy-efficient operation and low environmental footprint. This paper aims to provide a comprehensive thermo-economic assessment of a 5.25 kW capacity split air conditioner (SAC) integrated with direct evaporative cooling, focusing on evaluating its performance, energy consumption, coefficient of performance(COP), and economic viability. A numerical model is developed to determine the reduction in the condenser inlet air temperature due to direct evaporative cooling. The ambient temperature (30–45 ⁰C), relative humidity (20–80 %), and evaporator temperature (3–12 ⁰C) are taken as the design variables. Box–Behnken design (BBD) technique of response surface methodology is applied for multi-objective optimization. The COP, total cost rate (TCR), and total exergy destruction (E˙D,t) are set as the objective functions. Cooling capacity, life period, operation time, interest rate, maintenance factor, and electricity cost are taken as constants. The thermoeconomic optimization evolved maximized COP enhancement of 68.94 %, and reduction in TCR and ED,t by 26.12 % and 57.23 %, respectively. The water consumption to energy saving ratio varies from 5.5 to 9.8 L/kWh for different months of the cooling season. The thermoeconomic performance and sustainability of DECSAC is observed to significantly improve compared to conventional SAC specifically in hot-dry climates. The simple payback of the proposed system ranges between 1.21 to 2.99 years depending upon the operating conditions.

A comprehensive study of a green hybrid multi-generation compressed air energy storage (CAES) system for sustainable cities: Energy, exergy, economic, exergoeconomic, and advanced exergy analysis

Coastal cities can generate electricity via wind and solar farms. However, the variable nature of these renewable sources makes power output fluctuate. Compressed air energy storage (CAES) is the best solution to address this issue. On the other hand, the challenge of providing potable water persists, even in coastal cities, despite the proximity to the sea. Therefore, reverse osmosis (RO) technology has been used to address this issue due to its reduced energy consumption and environmental impact. The waste heat from the CAES is recommended to increase the system's overall efficiency. In this regard, an innovative green hybrid multi-generation system based on a CAES is proposed. The organic Rankine cycle ORC and RO desalination system have been used in this system to recover waste heat and supply potable and domestic hot water. A comprehensive analysis of the proposed system includes energy, exergy, economic, exergoeconomic, and advanced exergy analyses. The findings indicate this system can produce 37.48 MWh of electricity, 19.42 kg/s of potable water, and 2.67 kg/s of domestic hot water. Furthermore, with a total profit of $ 24.54 M and a payback period of 3.3 years, this system's energy and exergy round trip efficiencies are 73.54 % and 55.01 %, respectively. According to the advanced exergy analysis of the system, 31.5 % of the total exergy destruction is avoidable.

Comprehensive energy, exergy, and economic analyses of a geothermal and flue gas-based dual-source power, hydrogen, and freshwater trigeneration system

Designing a ploy-generation system to produce various products is an effective method to improve the common power plant’s performance. Hence, the current investigation proposes a green poly-generation system driven by geothermal and flue gas. The proposed scheme consists of an organic Rankine cycle, proton exchange membrane electrolyzer, saline water desalination unit, and Allam cycle to produce power, hydrogen, and freshwater. The produced oxygen in the electrolyzer feeds the Allam cycle to perform an oxyfuel process to achieve zero CO2 emission. Per the 4E analysis, the system produces 27,720 kW net power, 931 kmol/h hydrogen, and 616.7 kmol/h freshwater. In this way, the energy and exergy efficiencies are obtained at about 16.87% and 51.65%. The total exergy destruction rate is estimated at about 78,926 kW, in which the organic Rankine cycle and its vapor generator have the highest portions among the different parts and equipment by about 69% and 18.87%. The sensitivity analysis indicates that by the CO2 recycle ratio of 60%, the highest energy and exergy efficiencies reach 19.3% and 54.33%. Furthermore, the unit cost of hydrogen and electricity productions are 0.07$/kWh and 7.24 $/GJ, which is a considerable reduction compared to similar methods.

Exergy and energy analysis of a hybrid natural Gas/Hydrogen liquefaction cycle combined with methanol production plant

This paper presents an innovative renewable multi-generation system designed to simultaneously produce various fuels, including biomass-based methanol, liquid hydrogen, and liquid natural gas. This system is part of a broader strategy aimed at streamlining different processes within a comprehensive plant, enabling the simultaneous production of multiple biomass-based fuels at a single location. The implementation of this system in regions where natural gas liquefaction plants coexist with abundant forest resources allows for the efficient production of all required fuels. In this process, a new configuration leverages to regenerate the waste heat of methanol synthesis process in the diffusion absorption refrigeration cycle integrated to the natural gas liquefaction process to maximize energy and exergy efficiencies. Additionally, three hydrogen liquefaction processes are evaluated to identify the most suitable option based on performance, efficiency, and power consumption. The investigations reveal that the combined mixed refrigerant cycle (CMRC) emerges as the ideal choice for hydrogen liquefaction process, characterized by lower power consumption and a higher coefficient of performance. The energy and exergy efficiencies of biomass gasification and methanol synthesis processes are 87.54% and 80.41%. The energetic coefficient of performance of the natural gas liquefaction process and CMRC is 0.9 and 0.2209. The specific power consumption of natural gas liquefaction process is 0.225 kWh/kgLNG, and the specific power consumption of CMRC is 5.462 kWh/kgLH2. The natural gas liquefaction process is responsible for the highest portion of the total exergy destruction, with 32%.

Analysis of an ejector-assisted flash tank vapor injection heat pump cycle with dual evaporators for dryer application

In this paper, an ejector-assisted flash tank vapor injection heat pump cycle with dual evaporators (EFVIC) for heat pump dryer applications is proposed based on a basic flash tank vapor injection heat pump cycle (FVIC). An ejector is introduced to recover the expansion work of the system, and a high temperature evaporator is added to utilize the ejector's entrainment ability to reduce the irreversible loss caused by lower temperature difference. The performance improvements of EFVIC are evaluated through energy analysis, exergy analysis and comparisons with FVIC. The results indicate that the volumetric heating capacity and heating coefficient of performance of EFVIC with R1234yf are improved by 66.99 % and 18.88 % compared with those of FVIC using R1234yf, respectively. In addition, the presented cycle achieves better exergy efficiency because the exergy destruction proportion of expansion valves in EFVIC is 75.98 % lower than that in FVIC. Furthermore, the compressor has the highest exergy destruction among all components for EFVIC, accounting for 33.22 % of the total exergy destruction, hence it has the greatest optimization potential. The advantages of the presented cycle performance reveal its energy saving characteristics and application potential in heat pump dryer.

Thermodynamic and economic evaluation of a CCHP system with biomass gasifier, Stirling engine, internal combustion engine and absorption chiller

This work proposes a combined cooling, heating and power (CCHP) system based on biomass gasification with an internal combustion engine (ICE), a Stirling engine and an absorption chiller. The energy and exergy efficiencies and economic performance of the CCHP are evaluated under different working conditions by thermodynamic model and net present value method. The Stirling engine recovers the high temperature potential of syngas during cooling process and improves the CCHP output power by 14 % along with ICE, while the thermal efficiency of ICE reaches 39 % at 5000 rpm. In this work, about half of the total exergy destruction comes from ICE rather than gasifier due to the utilization of Stirling engine as an additional mover to produce electricity. The recycling of weak solution in absorber is adopted in order to increase the COP (Coefficient of performance) of single-effect absorption chiller. The COP could be increased by 7 % and reach 76 % as half of the weak solution recycling to absorber. The electric efficiency and total CCHP efficiency of this system reach 37 % and more than 60 %, respectively. The payback period is estimated to be less than 6 years at an ICE rotational speed of over 4000 rpm and an operation time of more than 4000 h/year.