Heat Source Temperature Research Articles

A low-temperature driven organic Rankine cycle for waste heat recovery from a geothermal driven Kalina cycle: 4E analysis and optimization based on artificial intelligence

It has long been proven that geothermal energy may be used to generate electricity and heat sustainably. It emits less pollution, has a greater heat source temperature, and is compatible with a wide variety of energy systems. This research aims to use an ORC to utilize the excess energy of Kalina cycle systems (KCS) driven by a geothermal unit to generate clean, sustainable, and cost-effective low-temperature electricity. The most amazing feature of the Kalina cycle is that it gains more heat during heat addition in its evaporator owing to its significant thermo physical effects, as seen in Fig. 5. The system's extensive modeling is based on energy, exergy, and economic considerations. Additionally, optimization is carried out in order to get the lowest Levelized cost of power (product). The sensitivity analysis is used to determine the most effective parameters for system implementation. The results indicate that the unit cost of the product for the hybrid system is at its minimum amount of 0.04898. For the Kalina, the system is 0.5023, in which the effectiveness hybrid scheme will be 48.57%, and the effectiveness of the Kalina system will be 44.21%. The most exergy destruction occurs in the evaporator and then the Kalina cycle condenser because these components have the highest temperature difference. Finally, the AI-based genetic algorithm is implemented to find the best solution point in terms of LCOC using neural networks.

Thermo-economic-environmental optimization design of dual-loop organic Rankine cycle under fluctuating heat source temperature

Fluctuating heat source temperature leads to off-design operation of organic Rankine cycle systems, which is a challenge for its optimal design. For a dual-loop organic Rankine cycle, this study proposed a multi-objective optimization design framework, which integrates off-design optimization into design optimization to determine the optimal design point of the system under heat source temperature fluctuations. In the optimization design framework, we developed a multi-objective optimization model to maximize the exergy efficiency and annual CO2 emission reduction of the dual-loop organic Rankine cycle and minimize its payback period. Then, the effects of design heat source temperature Td,h on the lifetime performance of dual-loop organic Rankine cycle were investigated. To balance the conflict between different indexes, we proposed a comprehensive evaluation index based on the entropy method. The results show that the influence of actual heat source temperature on the performance of dual-loop organic Rankine cycle is greater than the Td,h. Compared with traditional research that ignore the off-design performance, the proposed design method can avoid 35.8% annual CO2 emission reduction overestimation and 58.7% payback period underestimation at Td,h of 573.1 K. In addition, the optimal Td,h is significantly influenced by the selected index. The optimal Td,h is 513.1 K for the dual-loop organic Rankine cycle to minimize its lifetime payback period. To maximize the comprehensive index, the optimal Td,h for the dual-loop organic Rankine cycle is 573.1 K, which is the temperature at 0.9 of the cumulative distribution curve of the heat source. The average exergy efficiency and annual CO2 emission reduction in the lifetime of the dual-loop organic Rankine cycle at the optimal Td,h of 573.1 K is 4.1% and 6.0% higher than that at the average Td,h of 529.1 K, respectively.

Parametric study and optimization of a novel geothermal-driven combined cooling, heating, and power (CCHP) system

To reduce energy-related costs, integrating cogeneration systems is one of the most apposite avenues. Herein, a combined cooling, heating, and power (CCHP) cogeneration system grounded on geothermal (GTh) energy heat recovery is introduced. Accordingly, the cogeneration system comprises three subsystems, namely, the Kalina cycle (KC), ejector refrigeration cycle (ERC), and organic Rankine cycle (ORC). A comprehensive program is developed to address energy, exergy, and exergoeconomic analyses. Also, the TOPSIS multi-objective optimization method is used to select the optimal parameters at four different GTh heat source temperatures with the objective parameters of Net output power, Total investment cost (Ztot), and exergy efficiency. Thermal efficiency, exergy efficiency, Ztot, total exergy destruction rate, net power production capacity, and cycle cooling capacity were gauged under optimal conditions with a GTh temperature of THS = 490 K at 23.04%, 26.55%, 45944.49 $/yr, 226 kW, 75.17 kW, and 111.6 kW. In addition, the parametric study indicated that the increase in GTh heat source temperature, ammonia concentration, and KC flow rate (m˙1) reduces the thermal efficiency and increases Ztot. Finally, the effective system parameters, including ΔTcon2 and evaporator temperature were optimized for the different configurations using the Pareto multi-objective method. The optimal point of ΔTcon2 at the GTh heat source temperatures 480, 490 and 495 K are 14.58, 14.38 and 14.58 K respectively. Likewise, the optimal points based on the evaporator temperature at the GTh heat source temperatures 480, 485, 490 and 495 are 287.4, 279.3, 279.3, and 279.3 K, respectively.

Thermo-economic feasibility analysis of trilateral-cycle power generators for waste heat recovery-to-power applications

The trilateral cycle (TLC), a promising alternative waste heat recovery-to-power cycle, is receiving increasing attention due to feats such as the high thermal match between the exergy of the heat source temperature profiles and its working fluid. Although the TLC has neither been broadly applied nor commercialised because of its thermo-economic feasibility considerations. This study examined the thermo-economic analysis of different TLC power generator configurations; i.e., the saturated subcritical simple (non-recuperative) and recuperative cycles using n-pentane as the working fluid for low-grade waste heat recovery-to-power generation. Based on the thermodynamic and economic analyses, the feasibility analysis models of the cycles were established using Aspen Plus, considering efficiency, cost, and expected operating and capacity factors. Furthermore, the capacity factor, specific investment cost (SIC), and payback period (PBP), among other, were used to evaluate the cycle design configurations and sizes. The SICs of the simple and recuperative TLCs were 3,683.88 $/kW and 4,220.41 $/kW, and their PBPs were 8.43 years and 8.55 years, respectively. The simple TLC had a lower investment ratio of 0.24 compared to an investment ratio of 0.28 for the recuperative TLC. These economic values suggest that the simple TLC is more cost-effective when compared with the recuperative TLC because the recuperation process does not recompense the associated cost, making it unattractive.

Graphene thermionic energy converter combined with an absorption heat transformer for electricity generation and thermal upgrading

To improve energy utilization by recycling waste heat, a novel hybrid system composed of a graphene-based thermionic energy converter (GTEC) and an absorption heat transformer (AHT) is presented, where the GTEC anode waste heat is absorbed by the AHT for thermal upgrading. Considering major irreversible losses, the mathematical expressions for the equivalent power density, energy efficiency and exergy efficiency of the hybrid system are derived using thermionic emission and nonequilibrium thermodynamic theory. The hybrid system's general performance characteristics are also discussed in detail. Additionally, according to numerical calculation, the hybrid system's maximum energy efficiency (MEE), maximum power density (MPOD), and maximum exergy efficiency are 54.53 %, 7.73 W/cm2 and 68.16 % respectively, at the high-temperature heat source temperature of 1500 K. The hybrid system MPOD and MEE have risen by 17.97 % and 17.96 %, respectively, and maximum exergy efficiency has increased by 17.97 % as compared to a single GTEC. Furthermore, the impacts of the high-temperature heat source temperature, the Fermi energy level of graphene, cathode work function, ambient temperature, heat transfer coefficients of AHT, and the temperature of heated space on the hybrid system are investigated in depth. This study provides a new avenue for waste heat utilization in GTEC.

Towards efficient continuous thermally regenerative electrochemical cycle: Model-based performance map and analysis

Continuous thermally regenerative electrochemical cycle (TREC), which could convert heat to power and realize the continuous power output, is a promising technology for low-grade heat harvesting. However, the mechanism elucidation and performance analysis of continuous TREC are still incomplete, which hinders its performance improvement and practical applications. In this study, a pseudo-two-dimensional flow and electrochemical coupled model for continuous TREC is developed to investigate its performance. Based on the model, the polarization mechanism is revealed, and the effects of operating parameters and physical properties of electrolytes on the cycle performance are analyzed in detail. The results indicate that the concentration polarization is the major contributor to the system overpotential, especially at low electrolyte flow velocities. Regarding operating parameters, although temperatures of heat source and heat sink and electrolyte flow velocity determine the power density, the heat recuperation efficiency shows a decisive effect on the efficiencies. With perfect recuperation, the thermal efficiency and exergy efficiency could reach 8.3 % and 57.5 %, respectively. Regarding physical properties of electrolytes, the electrolyte concentrations affect the power density by changing the limiting current density. In addition, the temperature coefficient significantly affects the power density at any electrolyte flow velocity, while the internal resistance does so only at high flow velocities. With a temperature difference of 50 °C, a high power density of 4.33 W m−2 is expected if the temperature coefficient is increased to 4.0 mV K−1 and the area specific resistance is reduced to 1.0 Ω cm2. Based on the results, beneficial recommendations are put forward for further optimizing the system configuration and screening electrolytes for continuous TREC.

Sensitivity analysis of avoidable and unavoidable exergy destructions in a parallel double‐effect LiBr–water absorption cooling system

AbstractA parametric study has been carried out based on advanced exergy assessment for a parallel double‐effect LiBr–water absorption chiller. The advanced exergy method provides the real potential of the equipment for improvement in the system by recognizing the avoidable irreversibilities. The sensitivity analysis of various parts of the exergy destruction (endogenous avoidable, endogenous unavoidable, exogenous avoidable, and exogenous unavoidable) in system components and the overall performance (coefficient of performance, exergy efficiency, and modified exergy efficiency) of the system has been done to identify the actual potential of different components of the system to improve the overall performance of the system relative to operational parameters. Operational parameters include the heat source temperature, heat sink temperature, and the difference between the absorption and condensation temperature. The results showed that by modifying and improving the performance of components, 18.5% of the total exergy destruction of the system could be reduced. The modified exergy efficiency reduces sharply (nearly 40%) with the rising heat sink temperature. The endogenous exergy destruction increases in all system components except the condenser and evaporator by the heat source temperature increase. With the increase in the heat sink temperature, the avoidable part of the total exergy destruction in the system increases due to the significant rise in the avoidable exogenous exergy destruction in the components, and the unavoidable endogenous exergy destruction decreases (more than 200%) in the absorber. Increasing the condensation temperature reduces the unavoidable endogenous exergy destruction in the components except for the low‐temperature heat exchanger.

Finite-Time Thermodynamic Modeling and Optimization of Short-Chain Hydrocarbon Polymerization-Catalyzed Synthetic Fuel Process.

The short-chain hydrocarbon polymerization-catalyzed synthetic fuel technology has great development potential in the fields of energy storage and renewable energy. Modeling and optimization of a short-chain hydrocarbon polymerization-catalyzed synthetic fuel process involving mixers, compressors, heat exchangers, reactors, and separators are performed through finite-time thermodynamics. Under the given conditions of the heat source temperature of the heat exchanger and the reactor, the optimal performance of the process is solved by taking the mole fraction of components, pressure, and molar flow as the optimization variables, and taking the minimum entropy generation rate (MEGR) of the process as the optimization objective. The results show that the entropy generation rate of the optimized reaction process is reduced by 48.81% compared to the reference process; among them, the component mole fraction is the most obvious optimization variable. The research results have certain theoretical guiding significance for the selection of the operation parameters of the short-chain hydrocarbon polymerization-catalyzed synthetic fuel process.

Experimental investigation on passive cooling, thermal storage and thermoelectric harvest with heat pipe-assisted PCM-embedded metal foam

With the progresses of intelligence and integration of electronic devices, the growing demand for electrical energy will inevitably give rise to the increase of exhausted heat which has potential threat to thermal safety of the devices. Confronted with above issues, this article proposes a thermal-energy management method based on heat pipe-assisted hybrid foam/paraffin phase change material (PCM) and thermoelectric power generator (TEG) for passive cooling, heat storage and energy harvest. The copper foam with high thermal conductivity and surface area is employed to enhance the heat transfer of paraffin. A heat pipe is added to transfer the heat from heat source to TEG's hot side to further regulate their temperatures. The experimental results indicate that heat-source temperature rapidly increases to 85°C by just using solitary metal foam. Comparatively, using foam/PCM composite reduces the heat-source temperature by 33.5°C at the cost of achieving only 1/10 of thermoelectrical power. The composite with higher porosity attains better thermal control during melting process and higher electrical power of 25 mW. Moreover, adding heat pipe could further reduce the heat-source temperature and regulate the thermoelectric energy output.

Experimental investigation on micro-ORC system operating with partial evaporation and two–phase expansion

This paper presents an experimental analysis conducted on a low-temperature micro-ORC energy system, to assess its performance operating with partial evaporation (PE-ORC). Temperatures of the heat source in the range between 40 °C and 75 °C have been tested, and for each value, the vapour quality at the expander inlet has been varied by regulating the feed-pump rotating speed. The thermodynamic state of the working fluid in two-phase conditions has been estimated by means of a thermal balance at the heat exchangers, using the measured values of temperature, pressure and flow rate.Detailed experimental results are provided, with special focus on the performance of evaporator, expander and feed-pump, highlighting the difference in their behaviour compared with the regular operation with dry expansion of the same micro-ORC system. Relevant improvements have been observed in the evaporator effectiveness, mainly due to the reduction of the pinch point temperature difference. Also, the volumetric and total efficiencies of the feed-pump are improved substantially. On the other hand, the net power output and the expander efficiency resulted penalized by the operation with partial evaporation. The maximum power output obtained was close to 1.2 kW, with heat source temperature equal to 75 °C and fluid quality close to 1. The power output is reduced, at constant temperature, by decreasing the vapour quality at the expander inlet.The results suggest that operating a small-scale ORC system with partial evaporation may lead to some improvements to the performance of the cycle, especially regarding the evaporator performance. Moreover, with values of fluid quality at the expander inlet between 0.8 and 1, the penalization on the expander performance, compared to the dry expansion mode, is limited. However, a proper redesign of the power plant for the specific purpose is required in order to make partial evaporation an effective solution. Specifically, the expander and pump geometry and control require to be optimized for the particular working conditions, the recuperator must be removed, and the evaporator should be designed for the optimal exploitation of the heat source.

Temperature control of a heat source using a loop heat pipe integrated with a thermoelectric converter

The paper presents the results of experimental studies of automatic temperature control of a heat source cooled by a loop heat pipe integrated with a thermoelectric converter. The power supply of the thermoelectric converter was regulated by a PID controller having feedback on the heat source temperature. The tests were carried out under conditions of varying the heat load value of the heat source from 10 to 320 W at the set points of the heat source temperature of 20, 40 and 60 °C, of the heat sink temperature from −10 to +30 °C and of the slope angles of 0° and +90°. It was shown that the control system makes it possible to control the heat source temperature with an accuracy of ±0.2 °C in the stationary mode and with a short-term deviation from the set value of no more than 2.5 °C with a sharp change in the heat load. Additional logical conditions were also tested, which were included in the controller program and ensured the operability of the loop heat pipe when starting from low heat loads and exiting the control mode at maximum heat loads.

Experiments of advanced centrifugal heat pump with supply temperature up to 100 °C using low-GWP refrigerant R1233zd(E)

High-temperature heat pumps (HTHPs) can play an extremely important role in reducing carbon emissions in industry heating. At the same time, heat pumps with low global warming potential (GWP) refrigerants need to be developed and promoted urgently, especially after the Kigali amendment entering into force. Therefore, a HTHP with low-GWP refrigerant R1233zd(E) was evaluated under 50 °C temperature lift conditions in this study. The advanced HTHP unit equipped with high-efficiency centrifugal compressor and enhanced heat exchangers was built to achieve the performance breakthrough. Control volume method of heat exchanger model was used in the simulation model of heat pump to optimize design of heat exchanger and heat transfer temperature difference from the perspective of the overall system. Experimental tests were conducted at working conditions of heat source temperature of 30–50 °C and output temperature of 60–100 °C. At the condition of 50 °C heat source and supplying 100 °C hot water, heating capacity of 381 kW and coefficient of performance (COP) of 3.67 were achieved, which is the highest efficiency in this condition among published lab-scale and prototype-scale units. The performance breakthrough of the heat pump improves the HTHP technology and promotes the applications in industrial process heating.

Experimental investigation of energy storage and reuse of recovered waste heat based on thermoelectric generation

Heat energy may be converted into electric energy via a thermoelectric generator (TEG). It is an effective method of recovering and utilizing low-grade energy. However, the output voltage of a TEG is typically too low for direct applications. A waste heat recovery system based on thermoelectric generation was developed to convert waste heat energy into electric energy for energy storage and to operate an LED car light. The variability of thermal-electrical conversion and energy distribution in different stages of the system, as well as the response characteristics of the LED car light under heating temperature fluctuations, are investigated experimentally. The performance of different energy storage components on the time-dependent output characteristics of the light is also analyzed. The results indicate that the energy storage elements can store the energy derived from waste heat, power an LED car light independently, and buffer the power fluctuations caused by the heat source's temperature variation. The energy distribution ratio differs for different energy storage components. Lithium batteries have a high energy density and can store more electricity. The cold start of the LED car light is quick, and the illumination time is longer, but it requires more time to obtain a full charge. The supercapacitor has a sluggish cold start but a high charge and discharge speed, reducing voltage fluctuations when the waste heat recovery system is turned on for a short period. In addition, the system may be utilized to power additional low-power devices.

Research on medium–low temperature geothermal power generation system

In order to make full use of the medium and low temperature geothermal resources and industrial waste heat resources, a power cycle system using ammonia–water mixed solution as the working fluid is proposed. The system can use medium and low temperature geothermal resources with a temperature of 350–450 K, and the basic circulating working fluid is ammonia aqueous solutions. Simulation calculations show that the Carnot cycle efficiency of the circulation system is 14.01%, and the theoretical cycle thermal efficiency of the circulation system is 10.28%. The article further analyzes the influence of steam turbine outlet pressure and heat source temperature on the thermal efficiency of the circulation system. This research provides a reference for the effective utilization of medium and low temperature waste heat resources.

Effect of cooling water flow on heat transfer performance of horizontal tube spray falling film evaporator in ORC system

Organic Rankine cycle (ORC) uses low-temperature heat source to realize thermoelectric conversion, which is an important way to realize the effective recovery and utilization of waste heat. Based on the horizontal tube spray falling film evaporator, an orc power generation system with R245fa as the circulating working medium is built to study the influence of the change of cooling water flow on the heat transfer performance of the evaporator. The results show that under the condition of constant heat source temperature, the evaporation pressure and condensation pressure first decrease and then increase with the increase of cooling water flow, while the total heat transfer coefficient outside the evaporator tube first increases and then decreases. When the cooling water flow is greater than 3100 L/h, it has little effect on the heat exchange system of the evaporator, and it is more appropriate to keep the cooling water flow at about 3100 L/h. By studying the influence of cooling water flow on the heat transfer performance of evaporator, an important experimental basis is provided for the design and optimization of ORC cooling system.

Design of ORC-RO system for utilizing waste heat from flue gases of coal-fired thermal power plant

Waste heat recovery is an efficient tool to reuse waste energy to provide useful energy products. This method addresses the practical solution for sustainable products, which reduces CO2 emissions. The organic Rankine cycle is the most desirable option for waste heat recovery systems as it operates with low heat source temperature, which is auspicious in designing flexible and compact systems. This paper aims to design an organic Rankine cycle coupled with reverse osmosis to drive RO system by utilizing waste heat from flue gases of the thermal power plant. The boiler feed (make-up) water has been treated using the RO system, and the concentrate from the RO system can be used to suppress coal fly ash. The recycling reverse osmosis system is designed according to the boiler feedwater input for achieving more than 80 % recovery. The RO feed water is pre-heated by condensing vapor from the ORC expander, which reduces the specific energy consumption of the RO system. Also, the flue gas characteristics are discussed, which can be utilized at above dew-point temperature to avoid corrosion. This concept design is developed for the 2 MW coal-fired thermal power plant.

Optimal structure design of supercritical CO2 power cycle for waste heat recovery: An improved intelligent synthesis method

When designing the system structure of the supercritical CO2 cycle (S-CO2), the optimal cycle structure may be missed by a priori specification of the up-bottom methods, such as the enumeration method and the superstructure method. The intelligent synthesis method, as a kind of bottom-up method, can break through this limitation. With the diverse compression process of the S-CO2 cycle for waste heat recovery (WHR), the elementary cycle in the original intelligent synthesis method has obvious limitations. Therefore, the novelty of this paper is to propose an improved intelligent synthesis method based on the original intelligent synthesis method. The proposed method improves the compression process of the elementary cycle with a dual compression process, which could be extended for the application of S-CO2 cycle structure design for WHR. Besides introducing the optimization results under different cooling conditions, the supercritical CO2 cycle system obtained by the enumeration method, the superstructure method, the original and the improved intelligent synthesis methods are compared and analyzed. The results show that when the heat source temperature is 400–600 °C, the net power output of the optimal system obtained by the improved intelligent synthesis method is increased by 12.29–14.70 % and 3.08–4.22 % compared with two typical S-CO2 cycle systems, by 0.36–1.88 % compared with the superstructure method and by 1.06–1.78 % compared with the original intelligent synthesis method, respectively.

Thermodynamic Analysis and Working Fluid Selection of a Novel Cogeneration System Based on a Regenerative Organic Flash Cycle

Recently proposed organic flash cycles maintain lower irreversibility in the evaporator than traditional organic Rankine cycles. This study presented a novel combined heat and power system that was based on a regenerative organic flash cycle, in order to improve thermal efficiency. Parametric analyses for the proposed combined heat and power system were carried out, using six working fluids, and performed with heat source temperatures and heat sink temperatures that ranged from 130 °C to 170 °C, and from 20 °C to 40 °C, respectively. The results showed that the preferable working fluid was altered, with a change in the operating condition. Isopentane, R1234ze(Z), R1233zd(E), and R245fa performed better at a cooling water temperature of 20 °C. The system that used R245fa showed more promising performance when the heat source temperatures were set to 150 °C and 160 °C. R365mfc was determined to be the best working fluid at a heat source temperature of 150 °C, and at cooling water temperatures of 30–40 °C. Finally, the analyses evaluated the year-round system performance on the basis of monthly ambient and water temperatures in Daegu, Korea, as the system’s parameters. Compared to the single regenerative organic flash cycle, the thermal efficiency of the novel system improved significantly, from 8.37 % to 32.80% in August, and to 74.34% in February.

Bottom-up assessment of industrial heat pump applications in U.S. Food manufacturing

Decarbonization of the industrial process heat supply through electrification could contribute significantly to climate change mitigation efforts. In the U.S. industry, thermal processes accounted for more than two-thirds of the total final energy demand in 2021. Cross-cutting electrification technologies like industrial heat pumps are suitable for the process heat supply to several industrial unit operations in a sustainable way while also improving overall energy efficiency. This study employs a bottom-up approach to investigate the techno-enviro-economic potentials of deploying high-temperature and steam-generating heat pumps in the major U.S. food manufacturing sectors in different timeframes. The results show that the annual technical potential energy and CO2 savings by electrifying process heat supply are 325 PJ (or approximately 20% of the total final energy demand in U.S. food manufacturing) and 31 MtCO2 (equivalent to the annual CO2 emissions from over 6 million cars in the U.S.) in 2050, respectively; however, these incur additional costs in each sector. Although there may be individual cost-effective opportunities for electrifying heat supply in specific industrial sites, the overall costs are estimated to be high in the food sectors due to the large disparity between electricity and natural gas prices and low heat source temperatures. To overcome the identified techno-economic barriers, comprehensive action plans for different stakeholders are needed. This study provides novel insights that should inform policymakers’ and executives’ decisions about the electrification of the current and future U.S. industrial heat supply in relevant industrial sectors.

Compressor operated sorption system for high temperature thermochemical energy storage using Mg based hydrides

Thermal energy storage based on sorption technology has been flourishing due to its high storage density, wide operating temperatures, and long-term storage. In this work, an innovative compressor operated sorption thermochemical energy storage (CSTES) system is proposed and investigated for high temperature (≥250 °C) thermal energy storage with a large heat upgradation. The system uses magnesium-based metal hydrides as energy storage material due to their high hydrogen absorption capacity and good reversibility. The proposed CSTES system stores energy in the temperature range between 228 and 587 °C with a maximum heat upgradation of 78 °C. The highest coefficient of performance and energy storage density of 0.91 and 1991.843 kJ/kg is obtained using Mg–Al–Ti and Mg–Al–Ni alloys, respectively. Variation of compression ratio and heat source temperature on the performance of the CSTES system is studied.