Thermal Exergy Efficiency Research Articles

Performance Evaluation of CO2 + SiCl4 Binary Mixture in Recompression Brayton Cycle for Warm Climates

This work demonstrates the potential of CO2 + SiCl4 binary mixture as a working fluid for power generation cycle. Recompression Brayton cycle configuration is considered due to its proven record of high performance for medium- to high-temperature sources. The objective of this study is to assess the thermodynamic performance of a recompression Brayton cycle using a CO2 + SiCl4 binary mixture as a working fluid, particularly under warm climate conditions. The cycle is simulated using the Peng–Robinson equation of state in Aspen Hysys (v11) software, and the model is validated by comparing VLE data against experimental data from the literature. The analysis involves the assessment of cycle’s thermal efficiency and exergy efficiency under warm climatic conditions, with a minimum cycle temperature of 40 °C. The results demonstrate a notable improvement in the cycle’s thermodynamic performance with CO2 + SiCl4 binary mixture compared to pure CO2. A small concentration (5%) of SiCl4 in CO2 increases the thermal efficiency of the cycle from 41.7% to 43.4%. Moreover, irreversibility losses in the cooler and the heat recovery unit are significantly lower with the CO2 + SiCl4 binary mixture than with pure CO2. This improvement enhances the overall exergy efficiency of the cycle, increasing it from 62.1% to 70.2%. The primary reason for this enhancement is the substantial reduction in irreversibility losses in both the cooler and the HTR. This study reveals that when using a CO2 + SiCl4 mixture, the concentration must be optimized to avoid condensation in the compressor, which can cause physical damage to the compressor blades and other components, as well as increase power input. This issue arises from the higher glide temperature of the mixture at increased SiCl4 concentrations and the limited heat recovery from the cycle.

Solar air heater energy and exergy enhancement using a v-corrugated wire mesh absorber: An experimental comparison

In this paper, the energy and exergy performance of a double-pass solar air heater (SAH) using a novel model of a v-corrugated wire mesh absorber (CM-SAH) is investigated experimentally. The v-corrugated wires are adjacent to each other in one layer along the airflow direction to reduce the hydraulic resistance. Simultaneously, this arrangement increases the surface absorptance rate of solar radiation and expands the heat exchange area. To evaluate the performance of CM-SAH, a standard SAH having a v-corrugated absorber plate (CP-SAH) and the same configuration dimensions is compared with CM-SAH. The comparison is achieved under the same operating conditions and using different air mass flow rates of (0.01, 0.02, and 0.03 kg/s). The results show that the CM-SAH outperformed the CP-SAH in terms of thermal efficiency, exergy efficiency, and output air temperature. The maximum thermal efficiencies reach 87.3 % and 65.1 %, while the maximum exergy efficiencies reach 4.4 % and 3.4 %, for CM-SAH and CP-SAH, respectively. In addition, the thermal efficiency of CP-SAH decreased after midday while that of CM-SAH continuously increased.

Multi-objective optimization and life cycle assessment of mass-integrated combined heat and power system

As the effects of climate change become more widely recognized, technical innovation and green energy will promote the growth of combined heat and power systems. This study proposes a novel mass-integrated combined heat and power system and conducts energy analysis, exergy analysis, and techno-economic analysis for the system. The optimization strategy integrated polynomial regression and non-dominated sorting genetic algorithm III is established, with system thermal efficiency, exergy efficiency, and return on investment (ROI) as objective functions. The system's environmental consequences are then assessed throughout its life cycle using life cycle assessment (LCA) under ideal operating circumstances. The findings reveal that the waste heat recovery heat exchanger has the highest exergy destruction in the system, with a value of 674.61 kW. Furthermore, the intermediate heat exchanger 1 and intermediate heat exchanger 2 (IHX2) with lesser exergy efficiency have an exergy destruction of less than 32.00 kW. The IHX2 is the most expensive equipment in the system, costing $90,931.19, but it also provides the most potential for system improvement. The multi-objective optimization findings suggest that the thermal efficiency, exergy efficiency, and ROI for the system are 0.17, 0.97, and 0.30, respectively. The LCA demonstrates that the system has a negligible influence on global warming and ozone generation with corresponding LCA findings of less than 4.20. The construction and operation phases of the investigation system have the most significant environmental consequences. The correlation between the raw materials necessary for the construction of the equipment in the system and the reaction temperatures, conditions, and waste composition during the preparation of the working fluids is large, so it is necessary to take corresponding environmental protection measures during production and processing to reduce the system's environmental emissions from the source and promote ecologically sustainable development.

Integration and capacity optimization of molten-salt heat storage in coal-fired power plant with carbon capture system

Developing a new generation of economical, low-carbon, and flexible coal-fired power plants (CFPP) is crucial for achieving the low-carbon transformation of the energy industry. Deploying molten salt heat storage (MSHS) in the CFPP can effectively enhance its peak shaving capability and reduce the limitations of carbon capture on wide range operation of the plant. To this end, this paper proposes four integration schemes for MSHS into the power plant-carbon capture system. The thermal efficiencies, exergy efficiencies, and peak shaving capabilities of the entire plant under different integration schemes are evaluated and compared. The results indicate that the optimal integration scheme involves utilizing hot reheat steam to heat the cold molten salt and further provide heat for the carbon capture system during the heat charging process and utilizing hot molten salt to heat the outlet water of the feed water pump during the heat discharging process, which achieves the highest thermal efficiency of 38.00 % and exergy efficiency of 37.09 % across the entire cycle. A novel integrated design, scheduling, and control optimization (IDSCO) method is proposed to find the optimal capacity configuration of MSHS, in which the investment, maintenance, fuel, carbon emission, and long-timescale and short-timescale load tracking deviation penalty costs are fully considered. A design parameter-aware control system is developed based on a multi-parametric programming model predictive control approach to ensure a fair evaluation of closed-loop dynamic performance under different configuration capacities. The simulation results demonstrate that the deployment of MSHS can significantly enhance the flexibility of the power plant-carbon capture system and the proposed IDSCO approach can reduce 17.05 % of load tracking deviation penalty cost and 1.38 % of totalized cost compared to the conventional configuration approach. This paper effectively leverages the potential of MSHS in enhancing the operational flexibility of CFPP-PCC system, thereby providing useful guidance for future deployment of MSHS within CFPP-PCC system.

Experimental study on the performance of enhanced air-cooled photovoltaic thermal energy-supplied manure treatment technology

Implementing renewable energy technologies for manure treatment to reduce energy consumption and environmental damage is steadily becoming more prevalent. In this work, an air-cooled photovoltaic thermal (PV/T) device was enhanced and constructed to provide energy for bio-composting manure treatment. Experiments were conducted to analyze the performance data such as air supply temperature, energy and exergy efficiency, and mass flow rate. When calculating the mass flow rate of the PV/T-supplied manure treatment technology, factors such as exergy efficiency, and hot air temperature must be considered. The results of the study indicate that the thermal performance of the developed equipment is adequate for manure composting treatment. The thermal exergy efficiencies of the V2, V3, and V4 cases are approximately 1/3 greater than the thermal exergy efficiency of the V1 case, indicating a considerable change in thermal efficiency. The mass flow rate of 0.020 kg/s is determined to be a more suitable set value. Its total exergy efficiency can reach 46.79%, and the apparatus could heat up to 43.63 kg/m2 of compost to begin the bio-composting process. This study lays the groundwork for future research and deployment of PV/T-powered manure treatment devices.

Investigation of double-PCM based PV composite wall for power-generation and building insulation: Thermal characteristics and energy consumption prediction

The integration of phase change material (PCM) with building-integrated photovoltaic (BIPV) presents a compelling approach to enhance solar energy utilization and mitigate indoor thermal loads, contributing to energy-efficient and low-carbon building development. Traditional BIPV-PCM structures, however, struggle to balance PV efficiency and thermal insulation, particularly with varying PCM wall positions. To address this situation, this study introduces a novel double-PCM BIPV composite envelope (BIPV-dPCM). An experimentally validated dynamic heat transfer model was developed and used to perform a comparative simulation analysis with three reference systems to quantify the energy-saving potential of the BIPV-dPCM, focusing on PV output and wall insulation effectiveness metrics. Further dimensionless parametric analysis were carried out to investigate the systematic performance of the two PCMs at different relativities. In addition, the coupled working mechanism of the BIPV-dPCM system concerning the power generation performance and thermal insulation performance under transient variations is explored. It was found that the BIPV-dPCM showcases superior thermoelectric coupling performance compared to three alternative enclosures. Incorporating two PCMs significantly enhances electrical exergy efficiency by 11.66 % and thermal exergy efficiency by 1.54 %, surpassing other reference systems. The increase in PCM latent heat ratio has a limited effect on performance gain. Notably, as the PCM thickness ratio exceeds 1, the decline in P value decelerates, for every 0.5 increment in the g, the P value diminishes by merely 0.2 %. The ideal h is identified between 1 and 1.5, with 1.5 being optimal for energy conservation objectives. Additionally, the self-sufficiency coefficient (SSC) of the BIPV-dPCM remains robust, sustaining a range of 55 % to 65 % over prolonged periods. This study offers novel perspectives and serves as a design reference for optimizing building energy systems and enhancing cooling efficiencies in subtropical climates.

Economic and exergy transmission analysis of the gas-liquid type compressed CO2 energy storage system

Exergy transmission characteristic of the compressed CO2 energy storage system is significant to evaluate the system performance while little attention has been paid to this analytical method in the literature. A CO2 energy storage cycle configured with a gas holder as a low-pressure gas reservoir and a liquid tank as a high-pressure gas reservoir is studied comprehensively. The exergy transmission characteristics and the cost uncertain analysis are considered. Results demonstrated that the round trip efficiency and levelized cost of storage are 71.2 % and 0.1286 $/kWh under optimal design parameters, respectively. Keeping the charge/discharge duration ratio close to 1 has a positive effect on optimizing the economic performance of the system. With the general exergy model of the whole system configured for the charge and discharge process, the study uncovers the fluctuations in the pertinent proportional ratios and exergy transfer efficiency in relation to important parameters. Except for the turbomachinery isentropic efficiency, which impacts nearly all efficiencies, the variation of each parameter only governs the modification of the exergy transfer efficiency for a specific term or a pair of terms. Furthermore, the thermal exergy efficiency of the discharge process and intercooler has a maximum value as the cold-side temperature difference of the high-temperature cooler changes to 27 °C.

A parametric study of the exergetic, exergoeconomic, and exergoenvironmental performances of chlorine family thermochemical cycles for sustainable hydrogen production

Hydrogen plays a crucial role in global net-zero policies due to its numerous advantages and is widely regarded as a key future fuel. Clean and sustainable hydrogen production technologies are currently a focal point of research, with thermochemical methods showing promise in achieving environmentally friendly hydrogen. This study builds upon previous research conducted by the authors on thermochemical hydrogen production through chlorine family cycles. It conducts a thorough sensitivity analysis of various system variables that significantly impact the overall performance of these processes. The investigation assesses the performance of chlorine family thermochemical cycles from exergetic, exergoeconomic, and exergoenvironmental perspectives. Exergetic performance parameters include net thermal exergies and exergy efficiencies, exergoeconomic parameters encompass hourly levelized and total cost rates, and exergoenvironmental parameters involve exergoenvironmental factors and component-associated environmental impact rates. The system variables under consideration include ambient temperature, system lifetime, annual operating hours, and operation and maintenance cost factor. The analysis reveals that the system's lifetime notably influences both the exergoenvironmental factors and component-associated environmental impact rates (by about 80%). Meanwhile, its impact on both the hourly levelized (around 11.5%) and total cost rates (approximately 1.2%) is comparatively less significant. Similarly, ambient temperature has a marginal effect on the net thermal exergies and exergy efficiencies of the considered cycles.

Solar FPC performance enrichment with Al2O3 / SiO2 nanofluids and hybrid nanofluid

Sustainable energy harvesting plays a crucial role in advancing the goals outlined in the United Nations Sustainable Development Goals (SDGs). Solar flat plate collectors (FPC) are integral to sustainable energy harvesting, aligning closely with several Sustainable Development Goals (SDGs) particularly goals 7, 8, 9, 13 and 17. The heat transfer fluid is one of the most important inputs in the solar flat plate collector system. The improvement in the properties of heat transfer fluid significantly improves the collector efficiency. Though Nanofluid is one of the solutions, this investigation is motivated by the use of Al2O3 and SiO2 along Syltherm 800 in the form of nanofluids and hybrid nanofluid to improve the efficiency of FPC. The Syltherm 800 fluid (BF), Syltherm 800/Al2O3 nanofluid (ANF), Syltherm 800/SiO2 nanofluid (SNF), and Syltherm 800/Al2O3/SiO2 hybrid nanofluid (HNF) were tested and analysed to improve FPC performance. The results exemplified that using HNF improved the outlet temperature to the high of 126.9 °C, the average heat absorption of 4734.5 W, and the heat transfer coefficient (HTCO) of 166.3 W/m2K. The maximum average thermal efficiency and exergy efficiency of about 76.3%, and 49.8% respectively. Based on the experimental outcomes of the Syltherm 800/Al2O3/SiO2 hybrid nanofluid is recommended to improve the FPC thermal performances.

Thermodynamic, exergoeconomic evaluation and optimization of S–N2O/t-N2O nuclear power cycle for the construction of the lunar base

With the continuous development of deep space exploration, many planetary exploration schemes and development plans regard the construction of planetary bases as an essential goal, especially the exploration of the Moon. Supercritical and transcritical nitrous oxide (N2O) cycles are compact, low-cost, efficient, and lightweight for nuclear reactors to supply power to the bases on other planets. This paper presents the thermodynamic, exergoeconomic, and mass analyses of a combined cycle consisting of a supercritical N2O recompression Brayton cycle and a transcritical N2O cycle (S–N2O/t-N2O). It is shown that under the optimal conditions, the combined thermal efficiency and exergy efficiency are 45.52 % and 60.13 %, respectively. Based on the exergy analysis, the exergy destruction mainly occurs in the reactor and main compressor. A sensitivity study shows that the split ratio, pressure ratio in the supercritical N2O cycle, main compressor inlet pressure, turbine2 inlet temperature, and turbine2 inlet pressure have significant effects on the net output work, thermal efficiency, specific mass, and levelized cost of electricity. Furthermore, multi-objective optimizations are considered to obtain the Pareto frontier solutions for different multi-objectives, and the optimal design condition is found. These findings could improve the power cycle performance for the construction of the Lunar Base.

Performance Prediction and Optimization of Nanofluid-Based PV/T Using Numerical Simulation and Response Surface Methodology.

A numerical investigation was carried out in ANSYS Fluent® on a photovoltaic/thermal (PV/T) system with MXene/water nanofluid as heat transfer fluid (HTF). The interaction of different operating parameters (nanofluid mass fraction, mass flow rate, inlet temperature and incident radiation) on the output response of the system (thermal efficiency, electrical efficiency, thermal exergy efficiency, and electrical exergy efficiency) was studied using a predictive model generated using response surface methodology (RSM). The analysis of variance (ANOVA) method was used to evaluate the significance of input parameters affecting the energy and exergy efficiencies of the nanofluid-based PV/T system. The nanofluid mass flow rate was discovered to be having an impact on the thermal efficiency of the system. Electrical efficiency, thermal exergy efficiency, and electrical exergy efficiency were found to be greatly influenced by incident solar radiation. The percentage contribution of each factor on the output response was calculated. Input variables were optimized using the desirability function to maximize energy and exergy efficiency. The developed statistical model generated an optimum value for the mass flow rate (71.84 kgh-1), the mass fraction (0.2 wt%), incident radiation (581 Wm-2), and inlet temperature (20 °C). The highest overall energy and exergy efficiency predicted by the model were 81.67% and 18.6%, respectively.

Performance improvement of photovoltaic-thermal collector equipped with copper metal foam air channel

ABSTRACT Avoiding high temperatures in photovoltaic cells with appropriate cooling is necessary to increase their conversion efficiency. Passive cooling systems using metal foam in the air channel were investigated, but an overall assessment is necessary for its viable application. In this numerical study, the thermal, electrical, and exergy efficiencies, as well as the entropy generation of a PVT are analyzed in the presence of copper metal foam in the air channel. The investigation is performed using a CFD code based on the pressure-based finite volume method. The non-Darcy effects of the porous foam are taken into account. Validation of the numerical model is made by comparison of the numerical predictions with experimental results of the literature. The outcomes indicate that varying the porosity from 1 to 0.89 increases the thermal energy, electrical energy, and exergy efficiency from 44.50% to 67.01%, 10.64% to 11.54%, and 12.01% to 13.19%, respectively, while the entropy generation decreases from 1.3116 W/K to 1.2942 W/K. Furthermore, the optimum thickness of the cooling channel is determined (30 cm for 0.93 copper foam porosity).

Experimental investigation of humidification-dehumidification desalination system based on double-ends open evacuated tube solar air heater with inbuilt heat storage unit

The scarcity of freshwater has become an increasingly serious concern for society. The adoption of small-scale and decentralized desalination techniques presents a viable solution to the issue of water scarcity by overcoming the challenges inherent in large-scale desalination techniques. The solar-based humidification-dehumidification (SBH-DH) process is considered to be a very appropriate approach for small-scale desalination. However, the available SBH-DH system was only operational during sunshine hours. The current study involves the experimental investigation of a novel SBH-DH system that incorporates a solar air heater (4.687 m2) based on phase change material (PCM), a humidifier having cellulose as packing material, and a dehumidifier. The performance of the SBH-DH system with and without phase change material is compared using a parametric study. The use of PCM increases the operating time by 3 h. But the yield of the system with PCM does not change significantly in comparison to the system without PCM. Moreover, the cost of the obtained yield increased by 41.4 %. Additionally, the thermal energy and exergy efficiencies of the system with PCM are estimated at three distinct flow rates. The results reveal that a higher air flow rate leads to greater mean energy efficiency (36.2 %) and exergy efficiency (4.40 %).

Thermal entropy generation and exergy efficiency analysis of rGO/water nanofluid in a tube under turbulent regime using experimental and fully connected neural network

Analyzing entropy generation is one of the most effective methods for examining how well thermal systems operate. To determine the ideal operating conditions, numerous researchers have examined the entropy generation of thermal systems. In this work, the effects of concentrations of reduced graphene oxide (rGO) nanoparticles on the formation of entropy in water-rGO nanofluid flow through a circular pipe with a constant wall heat flux boundary condition in turbulent regimes are investigated experimentally. rGOs were prepared from Hummer's technique. Experiments are conducted at particle volumes from 0.5 % to 2.0 %, mass flow rates from 0.0333 kg/s to 0.25 kg/s, and Reynolds numbers from 1800 to 21,000, respectively. Later, estimated data points were anticipated with a convolutional neural network (CNN). The model was analyzed through several performances like root-mean-square-error (RMSE), mean-square-error (MSE), mean-absolute-percentage-error (MAE), and the coefficient of determination (R2). Results indicated, with used by 2.0 vol% of nanofluid, entropy generation-thermal is reduced to 39.24 %, entropy generation-frictional is higher by 16.92 %, entropy generation-total is decreased by 37.82 %, and second law efficiency is augmented to 34.17 % at Reynolds number of 13,705, against base fluid data. The correlation coefficient R2 evaluated from CNN for thermal entropy generation, frictional entropy generation, total entropy generation, and exergy efficiency are 0.99297, 0.99924, 0.9989, and 0.99273, respectively.

"3E" Analysis and Working Fluid Selection for a Cogeneration System for Geothermal Large Temperature Difference Utilization.

Widespread utilization of geothermal energy as a clean energy source can reduce the use of fossil fuels and thereby protect the environment. Previous combined heat and power (CHP) systems using low-temperature geothermal heat as a heat source have limited utilization of geothermal heat. In this study, a cogeneration system based on organic Rankine cycle (ORC) and absorption heat exchanger (AHE) is designed. We analyzed the thermal efficiency, exergy efficiency, and economics of the proposed system utilizing 85 °C low-temperature geothermal heat, and the optimal operating fluid for this system is discussed. The results show that the optimal working fluid for the proposed system is R245fa. Using R245fa as the working fluid, the proposed system can achieve an exergy efficiency of 61.39%, when the heat source outlet temperature can be as low as 23 °C, while the proposed system can achieve the lowest LCOE of 0.082 ($/kW ·h) when using R22 as the working fluid.

A Comprehensive Review of the Thermohydraulic Improvement Potentials in Solar Air Heaters through an Energy and Exergy Analysis

Supply disruptions, uncertainty, and unprecedented price rises of fossil fuels due to the recent pandemic and war have highlighted the importance of using renewable sources to meet energy demands. Solar air collectors (SACs) are major types of solar energy systems that can be utilized for space and water heating, drying, and thermal energy storage. Although there is sufficient documentation on the thermal analyses of SACs, no comprehensive reviews of the exergetic performance or qualitative insight on heat conversion are available. The primary objective of this article is to provide a comprehensive review on the optimum conditions at which the thermal performance of diverse types of solar air collectors is optimized. The effect of operating parameters such as temperature rise, flow rate, geometric parameters, solar radiation, and the Reynolds number on the thermal performance of SACs in terms of thermal hydraulic performance, energy, and exergy efficiencies has been reviewed adaptively. Beyond the operating parameters, a deep investigation is outlined to monitor fluid dynamics using analytical and computational fluid dynamics (CFDs) methodologies in the technology of SACs. In the third phase, thermodynamic irreversibility due to optical losses, thermal losses between absorber and environment, heat losses due to insulation, edge losses, and entropy generation are reported and discussed, which serve as the fundamental tools for optimization purposes.

Thermal Performance Analysis of an Indirect Solar Cooker Using a Graphene Oxide Nanofluid

Solar energy has become an energy source for a wide range of uses, including in solar cookers, due to its availability, cleanliness, environmental friendliness, and sustainability. In this study, an indirect solar cooker was investigated by measuring its thermal performance using a Graphene Oxide (GO) nanofluid. Water, GO (250 ppm)-water, and GO (500 ppm)-water were used as heat transfer fluids. The experimental set-up consisted of the cooking part and a solar collector, which are the two essential elements in indirect solar cookers. The cooking part was a wooden box solar cooker, and the parabolic trough solar collector was a polished stainless steel structure. The solar cooker was assessed using the stagnation test and load test as well as energy and exergy measurements. According to the test results, the averaged F1 was 0.1 for the base fluid water, 0.11 for GO (250 ppm)-water, and 0.13 for GO (500 ppm)-water. In addition, using a GO nanofluid instead of water in the solar cooker, the system’s thermal performance, energy, and exergy efficiency were improved. The use of the GO (250 ppm)-water and GO (500 ppm)-water nanofluids instead of water in the system improved the overall energy efficiency of the system by 3.3 and 4.2%. Moreover, using GO (500 ppm)-water allowed for achieving superior performance.

Design and optimization of a household photovoltaic/thermal collector with serpentine tube: Energy and exergy analysis

Hybrid photovoltaic/thermal (PV/T) collectors that simultaneously generate electricity and heat have promise for sustainable energy production. However, their performance depends strongly on four key design parameters. These are: panel aspect ratio, serpentine tube pitch, solar intensity, and coolant flow rate. This study optimized these design parameters for a household serpentine-tube PV/T collector using energy and exergy analysis to enhance electrical and thermal efficiencies. Response surface methodology was employed to model the complex relationships between these parameters and the electrical and thermal efficiency responses. Increasing the panel aspect ratio from 0.125 to 8 resulted in 1.99 and 12.10 % improvements for electrical and thermal energy efficiencies along with 1.99 and 26.36 % improvements for electrical and thermal exergy efficiencies. Larger serpentine pitch from 80 to 400 mm decreased all four efficiencies. Higher radiation intensity from 200 to 1000 W/m2 reduced electrical efficiency by 8.36 % but increased thermal efficiency 75.33 %. Increasing the coolant flow rate from 0.1 to 1.4 L/min raised thermal and electrical efficiencies by 167.8 % and 12.4 %, respectively. Single-objective optimization yielded maximum electrical and thermal energy efficiencies of 11.8 % and 63.2 %, while multi-objective optimization gave lower responses. The study provides new insights into design trade-offs between electrical and thermal performance using comprehensive modeling and optimization. The model and methodology can guide significant PV/T design improvements.

Thermo-enviroeconomic assessment of a solar dryer of two various commodities

The energy, environmental, and health issues necessitate the development of renewable energy-based food processing, especially solar drying. However, the low efficiency and high production costs of such systems are still challenges and have been widely considered. Accordingly, this work aimed to present a solar drying system for processing two various products: eggplant and grapes. In advance, three types of solar air heaters were tested and compared to select a proper one for the drying system: finned plate, evacuated tube, and modified evacuated tube solar air heaters. The findings indicated that the modified evacuated tube solar air heater had the highest thermal efficiency (67.92%), exergy efficiency (2.97%), and average temperature difference (27.48 °C). Then, this selected heater was employed in the proposed drying system. The considered parameters included dryer exit temperature, mass ratio, water removal rate, overall thermal efficiency, and cumulative drying exergy efficiency. Additionally, economic and environmental calculations were used to estimate the cost for each product, the payback period for each type, and CO2 reduction. As a result, the cost per kg of dried eggplant and grapes was 3.38 and 8.16 $/kg, saving 66.24 and 29.07%, respectively.

Thermal performance enhancement of novel integrated vapor compression and organic rankine cycle for electricity production: a full-condensing vs. desuperheating approach comparison in ultra-low-grade waste heat recovery

This paper presents the thermodynamic analysis, performance assessment and working fluid selection for a novel integrated vapor compression cycle and the organic Rankine cycle system, which recovers ultra-low-temperature waste heat (50 °C) rejected by the condenser of a vapor compression cycle (VCC). The study is conducted on a vapor compression system of a 35 kW cooling capacity, followed by the component sizing of the organic Rankine cycle (ORC) based on the available waste heat in the condenser of the refrigeration system. The effect of the operational parameters of the vapor compression cycle on the overall system performance are investigated. The system performance of the integrated system is estimated in terms of coefficient of performance, cycle thermal efficiency and exergy efficiency. The novel integrated systems has been analyzed thermodynamically for 36 pairs of pure refrigerants. Results show that the working fluid pair R600a/R141b with combined coefficient of performance (3.54), ORC thermal efficiency (3.05 %), electricity saving ratio (13.34 %) and total exergy destruction (6.94 kW) is the most suitable VCC/ORC working fluid pair in full condensing method. R407c-R141b is found to be the best working fluid pair in desuperheating method for the same integrated system. The performance analysis for full condensation and desuperheating methods are also investigated. The results indicate a 12.5 % improvement in the coefficient of performance of the integrated system using the full condensation method and a 2.5 % improvement using the desuperheating method compared to the standalone air conditioning system. Additionally, the sensitivity analysis results show that there exists optimum operating condition that maximize the system performance of the integrated system.