Working Fluid Research Articles

"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.

Research on performance of jet refrigeration cycle driven by waste heat of refrigerated vehicle

Nowadays, refrigerated food storage and transport vehicles are very common. However, with regard to the engine of vehicles, a significant amount of heat is discharged into the environment in the form of exhaust gas and jacket water. If the cooling system is used to convert this waste heat into cooling capacity, the thermal efficiency of the engine will be improved to a certain extent. Therefore, this paper uses two waste heat recovery jet refrigeration systems to recover heat from the exhaust gas and jacket water of the refrigerated vehicle. One is a conventional jet refrigeration system that uses only engine exhaust as the heat source, and the other is a system that adds a preheater upstream of the generator based on the conventional system, using engine jacket water to preheat the working fluid. This paper presents the results of comparing the impact of R141b/R123, R141b/R245fa, R142b/R134a, and R142b/R152a working fluids on system performance, and considers the effects of operating temperature and secondary flow pressure drop in the ejector receiving chamber on the system performance. The research results indicate that of the four selected working fluids, the R141b/R245fa (0.4/0.6) blend has the best overall performance. After the addition of a preheater, the system using R142b/R134a (0.6/0.4) hybrid working fluid achieves the maximum cooling capacity of 16.0994 kW and the maximum thermal efficiency of 5.45%, and the exergy loss in the generator is 1 kW lower than without the preheater.

Role of CO2-based mixtures in the organic Rankine cycle using LNG cold energy

Organic Rankine cycle (ORC) is an attractive method for recovery of liquefied natural gas (LNG). Zeotropic mixtures are optimal working fluids for improving the ORC power generation performance. In this study, eight CO2-based binary mixtures were selected as alternative working fluids for the utilization of medium-temperature LNG cold energy for ORC. The effect of CO2-based binary mixture on thermodynamic performance of ORC was presented and investigated. The genetic algorithm was applied to optimize the thermodynamic performance of ORC so as to determine the optimal working fluid among CO2-based binary mixtures. The results indicate that CO2-based binary mixtures significantly improve the thermodynamic performance of ORC in the recovery of LNG cold energy when compared with pure-CO2 ORC. There is a specific CO2 mass fraction that leads to the highest net power output of the ORC, and the mass fraction of CO2 increases with higher condensation temperatures (For CO2/Propane, the condensation temperatures are −55 °C, −40 °C, and −30 °C, and this CO2 mass fraction is 0.35, 0.65, and 0.8, respectively). Furthermore, the ORC using CO2/R134a exhibits the highest net power output at 13.50 kW among the eight alternative CO2-based binary mixtures.

Adicción al teléfono inteligente, inteligencia fluida y memoria operativa en estudiantes mexicanos

The purpose of this article was to determine the association of the level of smartphone addiction with working memory in university students and fluid intelligence in high school graduates. For this purpose, initial measurements were made with an adaptation of the smartphone addiction scale to measure the former, with complex scope tasks for working memory and with Raven’s progressive matrices for fluid intelligence. For this purpose, a descriptive and cross-sectional study was implemented in three groups of Mexican institutions that receive a public subsidy. The sample consisted of 154 participants in total: 65 high school and 89 university students. The average age of high school students was 15.9 years, while the average age of university students was 20.9 years. Of the participants in general, 23% perceived themselves to be addicted, with the most prevalent symptoms tolerance and withdrawal syndrome, and the least prevalent being disregard for the consequences. The results indicate that there was no association between perceived addiction and working memory capacity or fluid intelligence. These findings lead to the development of new studies to determine other harmful effects on the daily lives of Mexican adolescents and young adults.

Effect of trans-1,3,3,3-tetrafluoropropene on flammability of difluoromethane

At present, mixed working fluids have received increasing attention due to their excellent comprehensive performance. Among them, R1234ze(E) (trans-1,3,3,3-tetrafluoropropene) and the R32 (difluoromethane) with excellent thermal properties can form a safe and environmentally friendly new mixture through advantageous complementarity. In this paper, the flammability of the binary mixture R1234ze(E)/R32 mentioned above was studied. Firstly, the flammability limits and critical concentration inhibition ratio of R1234ze(E)/R32 were tested at different ratios. Then, based on density functional theory (DFT), the interaction mechanism between the two components in the mixture was analyzed. The results show that with the increase of R1234ze(E), the flammable limit range becomes narrower. In the early stage of the reaction between R1234ze(E)/R32, R32 preferentially breaks the bond to generate H and F radicals, but the reactions between R1234ze(E) and free radicals are dominant. CF3 radical is an important free radical for R1234ze(E) to inhibit the flammability of R32. The research results will have guiding significance for the internal interaction mechanism of the flammability of new binary mixtures and their safe applications.

Numerical study on the flow and heat transfer performance of SCO2/molten salt in Z-type printed circuit heat exchangers

The utilization of a PCHE in conjunction with a SCO2 Brayton cycle and molten salt thermal storage demonstrates a high efficiency. Investigating the flow and heat transfer characteristics of SCO2 and molten salt within a Z-type PCHE is essential. However, this particular aspect has not been explored by previous researches. This study employs a Z-type PCHE to analyze the heat transfer and flow characteristics of SCO2 and molten salt under different inlet temperatures, mass fluxes, and outlet pressures. Furthermore, the heat transfer efficiency of a Z-type PCHE is evaluated and compared to that of a conventional straight-type PCHE. The results indicate that the flow pattern of SCO2 exhibits periodic behavior due to the periodic bending structure of Z-type PCHE, while the flow of molten salt is minimally affected. Furthermore, different SCO2 conditions lead to divergent patterns in flow and heat transfer efficiency compared to molten salt. Z-type channels help alleviate the decline in heat transfer that typically happens in the inlet section of straight channels. Nu for a dual working fluid in a straight-type PCHE is only 1.1 times greater than that of a single working fluid. In Z-type PCHE configuration, the ratio of the dual working fluid to the single working fluid Nu is 1.4. The sensitivity of SCO2/molten salt dual working fluid to the heat exchanger structure is significant, with Z-type PCHE demonstrating superior heat transfer capabilities. The results outlined in this study offer the prospect of improving the design and deployment of Z-type PCHE in molten salt energy storage systems that operate within SCO2 Brayton cycle.

Experimental research on condensation flow and heat transfer characteristics of immiscible binary mixed vapors on different wettability wall surfaces

In the process of biomass gasification syngas waste heat recovery, water and organic compounds in the syngas will condense at the same time, resulting in immiscible condensates adhering to the wall, which can reduce the heat exchanger heat transfer efficiency and working life. Changing the wettability of the wall surface can affect the condensate flow state on the wall surface, thus affecting the condensation heat transfer performance. Water and organic cyclohexane were used as immiscible working fluids in this paper, the condensation flow and heat transfer characteristics of the mixed vapors on hydrophilic, super-hydrophilic, and super-hydrophobic wall surfaces were experimentally investigated. The results showed that cyclohexane in immiscible condensates existed as a liquid film on hydrophilic, super-hydrophilic, and super-hydrophobic wall surfaces, while the water existed in droplets on the hydrophilic and super-hydrophobic wall surfaces, and there were two forms of channels and droplets on the super-hydrophilic wall surface. The condensation heat transfer coefficient on the super-hydrophobic wall surface was higher than that on the hydrophilic wall surface and the super-hydrophilic wall surface, with a maximum of 34% higher than hydrophilic and 45% higher than super-hydrophilic, which was related to the smaller droplet departure diameter on the super-hydrophobic surface. In addition, the super-hydrophilic wall surface had better heat transfer performance than the hydrophilic wall surface only when the immiscible condensate was a "film-channel" flow pattern. The results can provide guidance for enhancing the condensation heat transfer of the water and organic compounds binary mixed vapors.

Complex Use of the Main Marine Diesel Engine High- and Low-Temperature Waste Heat in the Organic Rankine Cycle

The decarbonization problem of maritime transport and new restrictions on CO2 emissions (MARPOL Annex VI Chapter 4, COM (2021)562) have prompted the development and practical implementation of new decarbonization solutions. One of them, along with the use of renewable fuels, is the waste heat recovery of secondary heat sources from a ship’s main engine, whose energy potential reaches 45–55%. The organic Rankine cycle (ORC), which uses low-boiling organic working fluids, is considered one of the most promising and energy-efficient solutions for ship conditions. However, there remains uncertainty when choosing a rational cycle configuration, taking into account the energy consumption efficiency indicators of various low-temperature (cylinder cooling jacket and scavenging air cooling) and high-temperature (exhaust gas) secondary heat source combinations while the engine operates within the operational load range. It is also rational, especially at the initial stage, to evaluate possible constraints of ship technological systems for ORC implementation on the ship. The numerical investigation of these practical aspects of ORC applicability was conducted with widely used marine medium-speed diesel engines, such as the Wartsila 12V46F. Comprehensive waste heat recovery of all secondary heat sources in ORC provides a potential increase in the energy efficiency of the main engine by 13.5% to 21% in the engine load range of 100% to 25% of nominal power, while individual heat sources only achieve 3% to 8%. The average increase in energy efficiency over the operating cycle according to test cycles for the type approval engines ranges from 8% to 15% compared to 3% to 6.5%. From a practical implementation perspective, the most attractive potential for energy recovery is from the scavenging air cooling system, which, both separately (5% compared to 6.5% during the engine’s operating cycle) and in conjunction with other WHR sources, approaches the highest level of exhaust gas potential. The choice of a rational ORC structure for WHR composition allowed for achieving a waste heat recovery system energy efficiency coefficient of 15%. Based on the studied experimental and analytical relationships between the ORC (generated mechanical energy) energy performance (Pturb) and the technological constraints of shipboard systems (Gw), ranges for the use of secondary heat sources in diesel operational characteristic modes have been identified according to technological limits.

Organic Rankine Cycle (ORC) Systems: A fundamental Overview of Small-scale Applications Fuelled by Low-grade Heat Sources

Environmental issues shift energy production from conventional methods to new and more efficient alternatives. One of these alternatives is the use of organic Rankine cycles (ORC) in low-grade heat sources to generate both heat and power at small scales. Among different technologies available for this purpose, ORC-based systems seem to be the most suitable and promising option due to their simplicity and versatility. Thus, such systems have been investigated intensively. However, current studies often focus on only one aspect of these systems due to the massive research scale in this field. Therefore, this study aims to provide a fundamental and holistic overview to evaluate ORC-based low-heat sourced and small-scale applications from multiple perspectives. As a result, the basic operating principles and application areas of ORCs, selection and design criteria of their working fluids and all other system components, methods of improving their performance, and other thermodynamic cycles that can be ORC alternatives are examined in detail. The results of this study show that ORC applications can enable small-scale combined heat and power generation, while geothermal and solar energy sources have the potential to scale the size of such applications up to kW capacities. The results also showed that dry & isentropic fluids and vane & scroll expanders are the most suitable refrigerant and expander types, respectively, for small-scale ORC applications. Furthermore, the implications of all findings are critically discussed.

Understanding the thermodynamic effects of chemically reactive working fluids in the Stirling engine

The Stirling engine, renowned for its high theoretical efficiency, is capable of partaking an active role in the current energy transition. Given its closed-cycle operation, the choice of the working fluid is pivotal in designing the Stirling engine. Dinitrogen tetroxide N2O4 has been extensively investigated in the past, based on the ideal gas thermodynamic model, as a chemically reactive working fluid for Stirling cycles. This molecule reversibly and rapidly dissociates into nitrogen dioxide NO2–and recombines into N2O4–under the influence of thermodynamic transformations throughout the cycle, in accordance with chemical equilibrium. Addressing discrepancies in previous studies, this work aims at assessing a wide range of theoretical chemically reactive gases as working fluids in a Stirling cycle, employing the ideal gas mixture model. The behavior of each reactive fluid is examined throughout the cycle, and the thermodynamic performance is evaluated. Therefore, this work quantifies and analyzes the thermodynamic performance of a chemically reactive Stirling engine. Results indicate a slight increase in the net specific work output with certain reactive fluids, offering a thermal efficiency comparable to that of inert working fluids. In addition, it is emphasized that for chemically reactive working fluids, the isochoric heat exchange within the internal regenerator is incomplete due to chemical reactions, in contrast to the case of inert fluids. To address this, either a supplementary heat source, heat sink, or both are required during the isochoric processes. Furthermore, chemically reactive fluids in the Stirling engine induce irreversibility in the internal regenerator, stemming from heat exchange across a finite temperature difference, penalizing the thermal efficiency of the engine for the majority of reactive fluids studied.

Waste heat utilization using organic rankine cycle from a pressurized pulverized combined cycle power plant

Power plants release a massive amount of waste heat at very low temperatures. Posing a challenge for efficient conversion into useful work through conventional methods. By selecting appropriate working fluids, low-grade power cycles can solve this problem by converting waste heat to electricity. The present work dealt with waste heat utilization using the Organic Rankine Cycle (ORC) from a 400 MWe coal based supercritical Pressurized Pulverized Combined Cycle (PPCC). The working fluid for the ORC is the refrigerant R245fa. High-ash (HA) Indian coal and low-ash (LA) South African coal are used as fuel to assess the plant’s ability to produce electricity under ambient conditions in India. The simulation flowsheet program “Cycle-Tempo” models and simulates different plant layouts. The thermodynamic assessment unveiled that the standalone plant has energy and exergy efficiencies of 43.46% and 39.87% for HA & 45.42% and 43.84% for LA, respectively. According to this study, the proposed plant has energy and exergy efficiencies of 44.63% and 40.94% for HA & 46.69% and 45.07% for LA, respectively. Moreover, using ORC, the waste heat generates additional electricity of 9.38 MWe, with an energy efficiency of 12.92% and exergy efficiency of 34.63%.

Research on the Performance Characteristics of a Waste Heat Recovery Compound System for Series Hybrid Electric Vehicles

In this paper, a waste heat recovery compound system for series hybrid electric vehicles is established. The existing components of vehicle air conditioning are used in the organic Rankine cycle (ORC) to realize miniaturization. The waste heat recovery compound system is constructed using GT-SUITE, and the objective of the analysis is to increase the power output and engine thermal efficiency increase ratio (ETEIR). The effects of the expander speed, pump speed, working fluid mass flow rate, and working fluid type on the waste heat recovery compound system are analyzed. The simulation results show that the optimal schemes for the ORC system and compound system corresponding to the expander speed and pump speed are 1000 pm, 2500 rpm, 1200 rpm, and 2500 rpm, respectively. Compared with the ORC system, the maximum power output of the compound system with the same working fluid in three states (1500 rpm, 2500 rpm, and 3500 rpm) of the engine is increased by 21.67%, 24.05%, and 28.23%, respectively. Working fluid supplies of 0.4 kg/s, 0.4 kg/s, and 0.6 kg/s in the three engine states are also considered the best solutions. The working fluid R1234yf and R1234ze are the preferred choices for a waste heat recovery compound system, which have a high system power output and ETEIR and are environmentally friendly.

Comparative analysis of geothermal binary ORC systems: performance and environmental considerations for CO2 andwater as geofluids

This study considers the process simulation of geothermal binary Organic Rankine Cycle (ORC) systems which utilizes CO2 and water as geofluids for electricity generation. The simulation was performed using Hysys v11 software by using Peng Robinson’s fluid property package. Two dry working fluids including isopentane and n-pentane, were used. The effects of geofluid temperature and working fluid mass flowrate on power generation, as well as the maximum pressure of working fluids were evaluated. The result showed that power generation increases with higher geofluid temperature due to enhanced heat transfer. Isopentane outperformed n-pentane, attributed to its superior thermodynamic properties. CO2 showed better performance as geofluid than water highlighting its superiority, observed in the increased power generation. The unique characteristics of CO2 enable efficient heat transfer at lower temperatures, making it an environmentally friendly and effective choice. Contrarily, the use of water as a geofluid poses some implications for local ecosystems and water resources. From an environmental perspective, CO2 shows greater potential for reduced environmental impact, which aligns with the transition to cleaner energy sources. However, the economic considerations suggest a trade-off, as CO2 projects may entail higher upfront costs compared to water-based systems. Regulatory factors and economic feasibility, therefore, play a crucial role in the choice of geofluid for geothermal power generation.

A new heat transfer correlation based on flow patterns for hydrocarbon refrigerants condensation flow

To accurately predict heat transfer coefficients for hydrocarbon refrigerants condensation flow in heat exchangers is imperative for designing efficient systems. While various studies have proposed numerous correlations for predicting heat transfer coefficients, some of these correlations are based on fitted experimental data and are limited to predicting specific conditions. The prediction accuracy and capability for different working fluids remain to be evaluated. Currently, most researches mainly focus on pure working fluids, with relatively little attention given to mixed working fluids. In this study, six commonly used heat transfer correlations are evaluated and a new heat transfer correlation based on flow patterns is proposed. The research results indicate that the existing correlations have poor universality for predicting hydrocarbon refrigerants, and the prediction accuracy needs to be improved. The correlation developed in this study demonstrates good prediction performance for condensation heat transfer coefficients of 413 sets of hydrocarbon refrigerants, including methane, propane, ethane/propane, and methane/propane. The overall mean relative deviation (MRD) is −1.77%, and mean absolute relative deviation (MARD) is 8.12%. The correlation developed in this study can provide theoretical guidance for predicting condensation heat transfer coefficient for pure and mixed hydrocarbon refrigerants, aiding in the design of efficient heat exchangers.

Performance research of a solution cross-type absorption-resorption heat transformer using NH3/H2O work fluid

Absorption-resorption heat transformer (ARHT) can realize the efficient utilization of low-grade heat under lower operating pressure than traditional absorption heat transformer (AHT), but the application is limited by the low coefficient of performance (COP). In this paper, an ammonia-water solution cross-type absorption-resorption heat transformer is proposed to improve the performance. The rectifier can be eliminated because the component can be balanced with the adjustment of solution's mass flow rate between the absorber and resorber. A thermodynamic model is established to investigate the influences of different parameters on the coefficient of performance. The results reveal that: When the high/low pressure pair is 1.5/0.48 MPa and the temperatures of generator, absorber, resorber and desorber are 105 °C, 80 °C, 80 °C and 4 °C, the COP of the proposed system can reach 0.4049, which is 19 % higher than traditional ARHT, resulting in a corresponding gross temperature lift (GTL) is 25 °C. Besides, the proposed system has wider working temperature ranges than the traditional system. The advantages of the proposed system also include the lower optimal low-pressure values. Therefore, the ammonia-water solution cross-type absorption-resorption heat transformer is appropriate for working in larger pressure differences and makes waste heat recovery more economical and efficient.

Development status and research recommendations for thermal extraction technology in deep hot dry rock reservoirs

AbstractBased on a comprehensive review of domestic and foreign literature, this article discusses the technical difficulties and development status of enhanced geothermal system (EGS) concerning the thermal energy extraction of deep hot dry rock (HDR) reservoirs and proposes suggestions for the research focus of numerical simulation of HDR reservoir stimulation. Additionally, it summarizes the existing methods and mainstream working fluids for HDR reservoir stimulation. The article emphasizes the significance of factors such as well location, production well depth, artificial fracture orientation, and complexity in optimizing the thermal production efficiency of the EGS. Furthermore, this article delves into a detailed discussion on the influence of fracture spacing, fracture permeability, fracture length, fluid injection rate, and injected fluid temperature on the performance of the EGS. In light of the thermo‐hydro‐mechanical coupling challenges associated with high‐temperature reservoirs, it is suggested that future research efforts should focus on investigating the impact of thermo‐induced stresses on the stability of the artificial fracture network within the EGS during long‐term (>30 years) circulation of hot and cold fluids.

Risk factors associated with indicators of dehydration among migrant farmworkers

ObjectiveFarmworkers are at increased risk of adverse health outcomes related to occupational heat exposure and inadequate access to water, shade, or rest breaks. Presently, there is a dearth of studies examining the prevalence of dehydration and related factors in U.S. farmworkers. Our objectives were to characterize hydration status during typical workdays and to identify risk factors associated with increased dehydration in migrant farmworkers employed in Florida. MethodsUrine samples were collected and analyzed for urine specific gravity (USG) 2–3 times per person per day over five days in May 2021 and 2022. Data collection included demographic characteristics, wet-bulb-globe-temperature (WBGT), and information on working conditions (task type, duration, and crop units harvested), fluid intake, clothing worn, and heat safety behaviors. Multivariable mixed regression models were used to evaluate risk factors associated with change in USG levels (continuous) during a work shift. ResultsA total of 111 farmworkers participated in this study providing 1020 cumulative USG measurements, of which 96.8% of end-of-shift USG samples were above 1.020 indicating potential dehydration. In multivariable models, dehydration assessed using change in USG levels significantly declined with age (β = −0.078; 95%CI: 0.150, −0.006) but showed significant increase with body mass index (β = 0.016; 95%CI: 0.003, 0.028), WGBT (β = 0.054; 95%CI:0.044, 0.064), mean shift duration, and state of primary residence. We did not find significant associations of dehydration with type of clothing worn, intake of employer-provided water, or crop units harvested during a shift in this sample of farmworkers. ConclusionOur findings underscore the need for additional research to evaluate adverse outcomes related to dehydration and to better understand recovery patterns from chronic dehydration across workweeks and harvest seasons in migrant farmworkers.

Multi-objective optimization and benefit evaluation of heat pump system for tobacco drying using waste heat from data center

Tobacco drying is a highly energy-consuming process that requires a large amount of thermal energy. In this study, the waste heat from a data center is utilized to reduce fossil energy consumption in the tobacco drying process. A heat pump system is designed to address the issue of the waste heat temperature from the data center not meeting the required temperature for tobacco drying. Multi-objective optimization is performed with the goal of maximizing the specific moisture extraction rate and minimizing the specific investment cost, and seven hydrofluoroolefins are selected as the circulating working fluids. Coal-fired tobacco drying and Air Source Heat Pump Tobacco Drying (ASHPTD) are selected as comparison benchmarks to evaluate the energy efficiency and environmental benefits of the Data Center Waste Heat Tobacco Drying (DCWHTD) method in this study. The results indicate that R1234ze(Z) is the best working fluid. The specific moisture extraction rate of DCWHTD is improved by 36.69% and 20.21% compared to the coal-fired tobacco drying and ASHPTD, respectively, demonstrating enhanced energy efficiency. Although the specific investment cost of DCWHTD is higher compared with the coal-fired tobacco drying, it is 21.00% lower than that of ASHPTD. DCWHTD produces fewer emissions, the life-cycle carbon emissions are 26.93% and 16.80% lower than that of the coal-fired tobacco drying and ASHPTD, respectively. Furthermore, waste heat recovery improves the energy reuse efficiency of the data center by 64.92%. The tobacco drying method proposed in this study has better comprehensive performance and greater application potential.

A novel approach for designing efficient and sustainable cooling cycles with low global warming potential refrigerants

With the current legislation on the phase-out of 3rd generation refrigerants, new cooling cycles are expected to operate with 4th generation refrigerants, hence, the need for optimal system performance with these new working fluids. In this study, an innovative optimization approach was applied for the design of cooling cycles with 4th generation refrigerants based on integrating statistical analysis design of experiments (DoE) with molecular modeling using the polar soft-SAFT model. First, a detailed multi-criteria assessment was applied for the selection of 4th generation refrigerants in medium–low temperature applications. Results demonstrated the potentiality of trans-1,3,3,3-tetrafluoroprop-1-ene (R1234ze(E)) or cis-1,2,3,3,3-pentafluoroprop-1-ene (R1225ye(Z)) in terms of environmental, safety, and technical criteria in basic cooling cycles under specific operating conditions. Multi-objective optimization guided using statistical analysis tools were implemented to study potential enhancement in cooling cycle performance using these promising refrigerants in terms of energy and exergy efficiency. This included evaporator and condenser temperature, fluid choice, compression yield, superheating/subcooling degrees, and cycle type. The evaporation and condenser temperature, and the compressor efficiency are shown to monopolize more than three-quarters of the cumulative contribution on system efficiency for those operated with R1234ze(E) in advanced liquid-to-suction line heat exchangers (LL/SL-IHX). Further optimization through examining the effect of heat transfer phenomena assisted in determining optimal operating conditions for new systems operating with low GWP refrigerants, instilling annual cost savings of $1.59 K and reduction in CO2 emissions by 1.02 tCO2-eq compared to the baseline system.

Multi-objective optimization of the organic Rankine cycle cascade refrigeration cycle driven by sugar mills waste heat

The research on the recovery of low-grade thermal energy carried away by boiler flue gas is significant for sugar mills. This paper designs a waste heat recovery system based on sugar plant flue gas, integrating absorption refrigeration cycle and the organic Rankine cycle, and the effects of nine working fluids on the system are investigated. The aim is to realize the multi-form conversion of energy. The performance of the system is evaluated in terms of energy, exergy, and economic metrics. Multi-objective optimization is performed with the method of the NSGA-II genetic algorithm. The results show that Butane is the most suitable working fluid for ORC. The exergy efficiency of the system is 32.125% before optimisation, with an increased space cooling capacity of 15820.56 MW per year for the sugar mill. The exergy destruction analysis of the system reveals that the generator accounts for the highest proportion of exergy destruction (50.8%). The entire system shows the LCOE is as low as 0.0406$/kWh under the optimized condition. The optimized system can obtain an estimated annual electricity sales revenue of $136,300, and the sugar mill can save $308,600 in cooling costs. In addition, the payback period can be shortened to 5.79 years.