High Temperature Heat Source Research Articles

Advances in coupled use of renewable energy sources for performance enhancement of vapour compression heat pump: A systematic review of applications to buildings

Vapour compression heat pump provides efficient cooling and heating through the use of various renewable energy sources and plays a significant role in the energy conservation of modern buildings. Its performance enhancement gains increasing attention under the background of conventional energy and environmental crisis. Since the efficiency of a heat pump cycle is closely related to its thermal source condition, a stable high-temperature heat source or low-temperature cold source could benefit its heating or cooling efficiency a lot. Following this improvement strategy, significant progress has been made over the past years on the use of different renewable energy sources as coupled thermal sources of heat pumps. However, a specialised review that summarises relevant studies remains to be published. This paper aims at presenting operating mechanisms, characteristics, benefits, and limitations of different energy source coupling methods for heat pump performance enhancement towards its building application. The most concerning research on solar-assisted air source heat pumps, solar-assisted ground source heat pumps, and air-ground dual source heat pumps is emphasised. The existing thermal source coupling attempts under other renewable energy fields, such as waste heat, biomass, and water sources, are also summarised. Recommendations for further research and marketisation of such technologies are made based on detailed performance characterisation and comparison. The review is expected to benefit researchers in heat pumps and relevant applied energy fields to understand the challenges and opportunities in thermal source coupling technology and to promote its research and application development.

Nonlinear modeling and multi-scale influence characteristics analysis of organic Rankine cycle (ORC) system considering variable driving cycles

The reasonable construction of the organic Rankine cycle (ORC) system model under road conditions is the key to analyze, evaluate, and optimize the performance of the ORC system. However, due to the variability of high-temperature waste heat source and the strong coupling correlation of operating parameters, the operation characteristics of the ORC system show evident time-varying characteristics. Based on the coupling correlation and redundancy characteristics of the ORC system in complex environment, this paper presents a nonlinear modeling framework for the multi-scale influence analysis of the ORC system under road conditions. The nonlinear modeling framework can improve the prediction accuracy of ORC model by at least 68.36% and reduce the time cost by 53.37%. Based on the nonlinear model, the synergistic effects of multiple variables on ORC system performance at different scales are studied. The frequent fluctuation of vehicle speed enhances the coupling correlation of operating parameters, resulting in nonlinear, hysteretic dynamic characteristics of ORC thermal efficiency. The maximum thermal efficiency of ORC is only 3.28%. The nonlinear modeling framework proposed in this paper can provide a practical solution for constructing the intelligent analysis, design, and optimization models of ORC systems under complex road conditions.

Design and partial-load operation of a reversible Solid Oxide Cell system with molten salts thermal storage

The increasing penetration of renewable energy sources in the electricity mix requires efficient storage solutions on the seasonal scale. Reversible Solid Oxide Cell (rSOC) systems are receiving increased attention as viable options to fulfil this requirement. In this work, a MW-scale rSOC system capable of working over a large operating window is studied via modelling on Aspen Plus®. To ease the thermal integration, a molten salt thermal storage is coupled to the system, enabling heat recovery in fuel cell mode, which is then exploited for water evaporation in electrolysis mode. The rSOC stack is designed to operate exothermically in the electrolysis mode at nominal load. In both modalities, the air mass flow rate is regulated to control the stack temperature, while limiting the in-out gradients within 100°C. At nominal load, the system achieves an electrical efficiency of 52% in fuel cell mode and of 87% in electrolysis mode. The operation at low partial loads, due to the decrease of the air flow rate, requires an additional high-temperature heat source to guarantee the heat integration. In this regard, the adoption of an electrical resistance in electrolysis mode and a hydrogen-fed combustor in fuel cell mode are selected as viable solutions to amplify the operating range of the system. As a results, the system can be operated down to the 30% of the stack nominal power in both modalities, where the system achieves an electric efficiency of 44% and 80% in fuel cell and electrolysis mode, respectively.

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.

Investigation and multi-objective optimization of vehicle engine-organic Rankine cycle (ORC) combined system in different driving conditions

Organic Rankine cycle (ORC) can improve the fuel efficiency of internal combustion (IC) engine. However, the dynamic characteristics of ORC system in driving conditions are not only affected by variable high-temperature waste heat source, but also have strong coupling correlation between operating parameters and performance. Under the superimposed influence, the performance of vehicle engine-ORC combined system has obvious nonlinearity and uncertainty. This paper first constructs a vehicle engine-ORC combined system model for the driving conditions. Based on different driving cycles, the combined system is verified. The influence of ORC system on engine performance in driving conditions is evaluated. The synergetic influence laws of operation parameters in driving conditions is systematically analyzed. Based on vehicle engine-ORC combined system for driving conditions model, simulation model with different coupling units and multi-objective optimization algorithm, this paper proposes an integrated multi-objective optimization framework of combined system with complex driving conditions. The real-time optimization of integrated system performance in driving conditions is realized. The trade-off and uncertainty correlation between combined system performance in driving conditions are analyzed. Finally, the improvement of IC engine performance by ORC system in driving conditions is quantitatively evaluated. The nonlinear optimization framework proposed in this paper can provide a practical solution for the analysis, evaluation and real-time optimization of vehicle engine-ORC combined system performance in driving conditions.

Redox Cycles, Active Materials, and Reactors Applied to Water and Carbon Dioxide Splitting for Solar Thermochemical Fuel Production: A Review

The solar thermochemical two-step splitting of H2O and CO2 based on metal oxide compounds is a promising path for clean and efficient generation of hydrogen and renewable synthetic fuels. The two-step process is based on the endothermic solar thermal reduction of a metal oxide releasing O2 using a high-temperature concentrated solar heat source, followed by the exothermic oxidation of the reduced oxide with H2O and/or CO2 to generate pure H2 and/or CO. This pathway relates to one of the emerging and most promising processes for solar thermochemical fuel production encompassing green H2 and the recycling/valorization of anthropogenic greenhouse gas emissions. It represents an efficient route for solar energy conversion and storage into renewable and dispatchable fuels, by directly converting the whole solar spectrum using heat delivered by concentrating systems. This eliminates the need for photocatalysts or intermediate electricity production, thus bypassing the main limitations of the low-efficient photochemical and electrochemical routes currently seen as the main green methods for solar fuel production. In this context, among the relevant potential redox materials, thermochemical cycles based on volatile and non-volatile metal oxides are particularly attractive. Most redox pairs in two-step cycles proceed with a phase change (solid-to-gas or solid-to-liquid) during the reduction step, which can be avoided by using non-stoichiometric oxides (chiefly, spinel, fluorite, or perovskite-structured materials) through the creation of oxygen vacancies in the lattice. The oxygen sub-stoichiometry determines the oxygen exchange capacity, thus determining the fuel production output per mass of redox-active material. This paper provides an overview of the most advanced cycles involving ZnO/Zn, SnO2/SnO, Fe3O4/FeO, ferrites, ceria, and perovskites redox systems by focusing on their ability to perform H2O and CO2 splitting during two-step thermochemical cycles with high fuel production yields, rapid reaction rates, and performance stability. Furthermore, the possible routes for redox-active material integration and processing in various solar reactor technologies are also described.

An optical-mechanical integrated modeling method of solar dish concentrator system for optical performance analysis under service load

Solar dish concentrator system (SDC system) is an optical device that provides a high-temperature heat source for Stirling engine. However, due to its heavy structural and large windward area, it is easy to be deformed by self-weight or wind load during service, which leads to changes the mirror shape and receiver position of SDC system, thus deteriorating its optical performance. In order to predict and evaluate the optical performance and flux distribution of SDC system under service load, this paper proposes an optical-mechanical integrated modeling method considering the deformation of SDC system by combining the finite element method and ray-tracing method. It discretizes mirror surface into a large number of plane element, and directly establishes the optical model by its deformation information, which is suitable for any concentrator using mirrors. The modeling process is derived, including the optical model of concentrator under non-deformation and deformation, spatial position model and flux distribution model of the receiver, mirror shape error model. Finally, the modeling method is verified by examples and literature results, the flux distribution and mirror shape error calculated by this method are in good agreement with comparison results, and relative error ranges from 0.6% to 5.6%.

Innovative proposal of energy scheme based on biogas from digester for producing clean and sustainable electricity, cooling and heating: Proposal and multi-criteria optimization

It has long since been established that biomass energy may be utilized as a sustainable source to turn chemical energy into electricity, heating and cooling. It has lower emission, higher heat source temperature, available and flexible with many energy systems. In this study the chemical energy of the biomass is used to generate heating, cooling and power, via efficient hybrid ARC and steam rankine cycle based on digester. The system is actually have three main subsystems, the digester and externally fired gas turbine acts as the prime mover and upper cycle of the system. The exit hot gases then are used to heat up an steam rankine cycle the condenser of which is the generator of an ARC. The 3E analysis, and parametric study is conducted. The results indicate that have great effect on system performance. Also the results sighn posted that at its optimal position, the system emits 0.4797 kg of carbon dioxide per kilowatt-hour and has a cost rate of 683 dollars per hour. The most beneficial aspects of the system performance are the pressure ratio of 6.64 and the biomass flow rate of 4.77 kg per second. The system can generate 3375 kW of cooling energy if the temperature of the gas turbine intake is raised to 1450 K and the temperature differential between the pinch point and the gas turbine inlet is raised to 9 °C.

Newton trust-region methods with primary variable switching for simulating high temperature multiphase porous media flow

Coupling multiphase flow with energy transport due to high temperature heat sources introduces significant new challenges since boiling and condensation processes can lead to dry-out conditions with subsequent re-wetting. The transition between two-phase and single-phase behavior can require changes to the primary dependent variables adding discontinuities as well as extending constitutive nonlinear relations to extreme physical conditions. Practical simulations of large-scale engineered domains lead to Jacobian systems with a very large number of unknowns that must be solved efficiently using iterative methods in parallel on high-performance computers. Performance assessment of potential nuclear repositories, carbon sequestration sites and geothermal reservoirs can require numerous Monte-Carlo simulations to explore uncertainty in material properties, boundary conditions, and failure scenarios. Due to the numerical challenges, standard NR iteration may not converge over the range of required simulations and require more sophisticated optimization method like trust-region.We use the open-source simulator PFLOTRAN for the important practical problem of the safety assessment of future nuclear waste repositories in the U.S. DOE geologic disposal safety assessment Framework. The simulator applies the PETSc parallel framework and a backward Euler, finite volume discretization. We demonstrate failure of the conventional NR method and the success of trust-region modifications to Newton’s method for a series of test problems of increasing complexity. Trust-region methods essentially modify the Newton step size and direction under some circumstances where the standard NR iteration can cause the solution to diverge or oscillate. We show how the Newton Trust-Region method can be adapted for Primary Variable Switching (PVS) when the multiphase state changes due to boiling or condensation. The simulations with high-temperature heat sources which led to extreme nonlinear processes with many state changes in the domain did not converge with NR, but they do complete successfully with the trust-region methods modified for PVS. This implementation effectively decreased weeks of simulation time needing manual adjustments to complete a simulation down to a day. Furthermore, we show the strong scalability of the methods on a single node and multiple nodes in an HPC cluster.

Study on the Circulation Efficiency of Different Nonideal Gases

The thermodynamic properties of two kinds of representative non-ideal real gases van der Waals gas and Onnes gas are expounded and discussed by common thermodynamic methods, and the specific expressions of heat engine efficiency based on Carnot cycle, Stirling cycle and Otto cycle with these two real gases as working fluids are derived through theoretical derivation and calculation. On this basis, the variation rules of various thermal efficiency corresponding to heat engine with cycle parameters (such as high-temperature heat source temperature T1, low-temperature heat source temperature T2, the isovolumetric molar heat capacity of gas, initial volume V in the cycle process, gas volume expansion ratio r) are analyzed, and the general rules which are helpful to improve the efficiency of heat engine are found. This work will provide some theoretical reference for the optimal design of the actual operating conditions of the heat engine.

Enhancement of heat transfer during rubber pyrolysis process

Pyrolysis can transform the waste rubber into high value oil, gas and solid carbon, which is a green and environmental protection treatment method. However, due to the poor thermal conductivity of rubber and easy to bond to the reactor wall when heated, the heat transfer efficiency of rubber is low, which has seriously affected the industrialization process of waste rubber pyrolysis. In order to solve this problem, Internal Circulational Thermal Dispersion Technology (ICTDT) was proposed in this study. A certain number of spherical heat-conducting media made of alumina oxide was added into the rotary kiln, forming more high temperature heat source, making the heat transfer efficiency of the rubber in the rotary kiln greatly increase. Besides, the friction between heat-conducting media and the wall of rotary kiln or rubber inhibited the formation of the coking center, thus reducing coking production to a certain extent. The improvement of coking also improved the heat transfer efficiency of pyrolysis process. Through experiments and numerical simulations, the influence of diameter and filling rate of the heat-conducting media on the distribution of pyrolysis products and the temperature rise of the rotary kiln was analyzed, which is expected to provide a feasible method and scientific guidance for the industrialization of waste rubber pyrolysis.

Experimental investigation on an R290-based organic Rankine cycle utilizing cold energy of liquid nitrogen

Organic Rankine cycle (ORC) has been widely used to utilize low-grade waste heat from low, medium, and high-temperature heat sources. Meanwhile, the research of the ORC operates in the cryogenic temperature has also attracted much attention due to the increasing requirement of liquid natural gas (LNG). However, there is still a lack of experimental research on the cryogenic ORC. In this paper, the experimental study of a cryogenic ORC using a semi-hermetic scroll expander and propane (R290) has been investigated. Liquid nitrogen is used as the cryogenic cold source in this system while the circulation water is used to simulate the low-grade waste heat. The system performance of utilizing the cold energy of the liquid nitrogen and thermal energy of the circulation water has been investigated. First, the effects of the evaporation pressure and pressure drop on system performance are examined. Moreover, the system performance between the regenerative organic Rankine cycle (RORC) and basic organic Rankine cycle (BORC) has been compared. The experimental results indicate that evaporation pressure has a significant effect on system performance, and different optimum evaporation pressure will be obtained under different liquid nitrogen mass flow rates. The maximum electrical power 673.59 W, system thermal efficiency 6.78%, and cold energy utilization efficiency 12.32% can be obtained, while the evaporation pressure and liquid nitrogen mass flow rate are 1.36 MPa and 120 kg/h, respectively. What’s more, the results also indicate that the pressure drop exhibits a high sensitivity on system performance, and there is a clear linear proportional relationship between pressure drop and electrical power. Furthermore, the comparison results show that RORC has a better system performance than BORC. The experimental results provide design and optimal operation strategy for the cryogenic organic Rankine cycle.

Different cases study on the heating surface layout of a new 600 MWe coal-fired power plant coupled with CaO-based carbon capture system based on heat exchanger network

This work provides a practical engineering design on the new 600 MWe coal-fired power plant coupled with CaO-based carbon capture system. Three heating surface layout cases are proposed in order to realize the high temperature heat source of the new power plant to heat the feed water into the superheated steam (24.2 MPa, 566 °C). In addition, pipeline calculation and economic analysis for three cases are carried out. The results show that the heat exchange area of three cases increases, respectively by around 33.5%, 47.3% and 53.7% as comparing to the benchmark 600 MWe coal-fired power plant under the carbon capture efficiency of the coupled system is around 90%. In the pipeline design, the flue gas resistance of case 1 through heat exchange pipeline is about 0.74 MPa. The economic analysis shows that case 1 has a slight advantage as comparing to cases 2 and 3. The research provides a good direction for future research direction of the coal-fired power plant coupled with CaO-based carbon capture system.

Analysis of thermal runaway propagation characteristics of lithium-ion battery module under local high temperature

Lithium-ion batteries are increasingly used in the field of new energy vehicles. Thermal runaway is the biggest potential safety hazard. In order to achieve safer battery design, it is necessary to fully understand thermal runaway. In this research, the thermal abuse model of lithium-ion battery module is established. Temperature propagation characteristics of lithiumion battery pack under high temperature heat source is discussed and analyzed. The results show that there is consistency in the thermal runaway of lithium-ion battery at different surface heat source temperatures, and the thermal runaway of lithium-ion battery packs occurs at 453 K. The location of surface heat source only affects the distribution of temperature when thermal runaway occurs. The smaller the thermal conductivity of the battery spacer layer, the slower the temperature propagation when the battery is out of control.

Investigation to attain high power of a low-temperature difference Stirling engine

Since the Industrial Revolution, the mankind has achieved astonishing technological innovation and economic development. Recently, the environmental pollution and global warming caused by a large amount of consumption of fossil fuels have become apparent. From such a background the Sustainable Development Goals (SDGs), which include climate change measures, were adopted at the UN Summit in 2015. On the other hand, Japan's energy self-sufficiency rate is 11.8%, which is low among developed countries, and Japan is dependent on imports of most fossil fuels from other countries. Besides the Stirling engines is not necessarily require the combustion of fossil fuels and is therefore low polluting. From this point, the Stirling engines attracts, attention in recent years. But one of the problems preventing the practical use of the Stirling engine is that it is more difficult to miniaturize than a conventional internal combustion engine. Another disadvantage is that the output response is poor. In this study, we focused on the Stirling engine as an engine that uses renewable energy and designed and manufactured a Stirling engine that can be operated even when snow or ice is used as the low-temperature heat source. And, we use a room temperature as the high-temperature heat source. The aim of this research is to make effective use of low-temperature heat sources that have not been used until now.

Numerical investigation on comprehensive control system of cooling and heat insulation for high geothermal tunnel: A case study on the highway tunnel with the highest temperature in China

Solving the high temperature problem during the construction of high geothermal tunnel is of great significance to ensure the safety of workers, improve production efficiency and improve structural safety. Therefore, this paper innovatively establishes a high temperature comprehensive control system of high geothermal tunnel combining high-temperature treatment in tunnel and high-temperature heat source insulation. Based on the highway tunnel with the highest temperature in China—the Nige Tunnel, the temperature field in tunnel with various cooling measures under different surrounding rock temperatures and the temperature variation of lining structure with different thermal insulation methods and thicknesses are studied by numerical simulation. Furthermore, the selection standard of cooling measures, the laying method and the thickness of thermal insulation layer (TIL) are proposed. In the Nige Tunnel, the high temperature comprehensive control system and cooling measures are adopted based on on-site temperature monitoring, so that the temperature in the tunnel can meet the construction requirements and ensure the safety and efficiency of high geothermal tunnel construction.

Thermodynamic analysis of the superiority of the direct mass transfer design in the supercritical water gasification system

Supercritical water gasification (SCWG) is a promising clean technology for coal utilization due to high chemical reactivity and no tar emission. However, the wall-type heat exchange in the SCWG system demands a large heating surface area and an extreme high-temperature heat source. This paper puts forward an optimized design, namely direct mass transfer, in which the final product gas is partially recycled back into the gasification reactor to supplement the gasification agent and provide sensible heat energy. A whole system simulation was established to analyze the mass flow and exergy efficiency in the reference design and the optimized design. The process analysis shows that the optimized design has higher exergy efficiency (85.6%) than that (72.5%) of the reference design. In the optimized system, direct mass transfer significantly alters the mass flow and exergy flow, with less influent water (33.3%), less heat transfer rate (30.5%), and less oxygen consumption (51.5%). Furthermore, sensitivity analysis shows that increasing circulation ratio, feedstock concentration, and preheating temperature can reduce oxygen consumption and improve gas output and efficiency. The study indicates that direct mass transfer has the potential superiority to solve the challenge of heat integration and facilitate the application of the industrial-scale SCWG system.

System Design and Application of Supercritical and Transcritical CO2 Power Cycles: A Review

Improving energy efficiency and reducing carbon emissions are crucial for the technological advancement of power systems. Various carbon dioxide (CO2) power cycles have been proposed for various applications. For high-temperature heat sources, the CO2 power system is more efficient than the ultra-supercritical steam Rankine cycle. As a working fluid, CO2 exhibits environmentally friendly properties. CO2 can be used as an alternative to organic working fluids in small- and medium-sized power systems for low-grade heat sources. In this paper, the main configurations and performance characteristics of CO2 power systems are reviewed. Furthermore, recent system improvements of CO2 power cycles, including supercritical Brayton cycles and transcritical Rankine cycles, are presented. Applications of combined systems and their economic performance are discussed. Finally, the challenges and potential future developments of CO2 power cycles are discussed. CO2 power cycles have their advantages in various applications. As working fluids must exhibit environmentally-friendly properties, CO2 power cycles provide an alternative for power generation, especially for low-grade heat sources.

Existence of High Temperature Geothermal Resources in the Igneous Rock Regions of South China

Large areas of Yanshan period granites with high heat production values (3–10 μW/m3) and mantle plume around Hainan province co-exist in Igneous Rocks Regions of South China (IRRSC). Surface manifestations are mainly warm/hot springs with temperatures below 90 °C and no typical phenomenon of high temperature resources have been observed. The main objective of this paper is to discuss the existence of high temperature geothermal resources and their possible locations under this kind of geothermal and tectonic background by analysis of high temperature heat sources, borehole temperature measurement, and reservoir temperature estimation. Two possible partial melts of the magma chamber were detected as high temperature heat sources in the Southern Leizhou Peninsular and North Hainan Island at a depth of 8–15 km. Other low resistivity zones in the upper crust are more likely caused by fluid in the formations or faults but not high temperature heat sources. This was also verified by borehole temperature measurement in these two areas, with maximum formation temperatures of 211°C and 185°C found, respectively. Reservoir temperatures from fluid geothermometers show lower temperatures of between 110–160°C for typical geothermal fields over the IRRSC but not in the Southern Leizhou Peninsular and Northern Hainan Island. In all, high temperature geothermal resources may be found in the Southern Leizhou Peninsular and on Northern Hainan Island.

Drop-in fuels from sunlight and air.

Aviation and shipping currently contribute approximately 8% of total anthropogenic CO2 emissions, with growth in tourism and global trade projected to increase this contribution further1-3. Carbon-neutral transportation is feasible with electric motors powered by rechargeable batteries, but is challenging, if not impossible, for long-haul commercial travel, particularly air travel4. A promising solution are drop-in fuels (synthetic alternatives for petroleum-derived liquid hydrocarbon fuels such as kerosene, gasoline or diesel) made from H2O and CO2 by solar-driven processes5-7. Among the many possible approaches, the thermochemical path using concentrated solar radiation as the source of high-temperature process heat offers potentially high production rates and efficiencies8, and can deliver truly carbon-neutral fuels if the required CO2 is obtained directly from atmospheric air9. If H2O is also extracted from air10, feedstock sourcing and fuel production can be colocated in desert regions with high solar irradiation and limited access to water resources. While individual steps of such a scheme have been implemented, here we demonstrate the operation of the entire thermochemical solar fuel production chain, from H2O and CO2 captured directly from ambient air to the synthesis of drop-in transportation fuels (for example, methanol and kerosene), with a modular 5 kWthermal pilot-scale solar system operated under field conditions. We further identify the research and development efforts and discuss the economic viability and policies required to bring these solar fuels to market.