High Temperature Heat Exchanger Research Articles

Heat transport by thermoacoustically generated steady flow

Conventional heat exchangers for thermoacoustic engines have limited heat transfer area and may not utilize heat effectively. A self-circulating heat exchanger proposed by Backhaus and Swift is a looped tube that connects a heat source and a high-temperature heat exchanger, a steady flow is generated in the looped tube due to a thermoacoustic spontaneous acoustic oscillation taking place in a thermoacoustic engine and heat is transported from the heat source to the high-temperature heat exchanger by the steady flow. The purpose of this study is to confirm the heat transport by the acoustically generated steady flow. A standing-wave thermoacoustic engine was constructed with a looped tube connected to the high-temperature side heat exchanger. The relationship between the ratio of the lengths of the thermoacoustic engine and the loop tube and the pressure amplitude was measured. The pressure amplitude became zero when the length of the loop tube was about one times the length of the thermoacoustic engine. Furthermore, the streaming flow was confirmed indirectly by measuring the temperature inside the loop tube. The temperature field of the loop tube implied to the generation of the acoustically generated steady flow.

The Calculation of Double Nonlinearity and Material Anisotropy Influence on the Temperature Distribution in the Cylinder Under High Temperature Heat Exchange

At the present stage of the development of technology, it is necessary to ensure the strength, reliability and durability of the structure that successfully functions under conditions of high-temperature heat exchange as maximum as possible. In this regard, graphite structural elements are widely used, and they are also applied for parts of space and aircraft, jet and rocket engines. The transversely isotropic graphite cylinder used in this work has a unique set of qualities that make it indispensable for problems in nuclear physics and power engineering; however, in the calculation of thermal engineering practice, it has not been studied enough, since it contains a large scatter of thermophysical characteristics for various grades of graphite. The aim of the study, including the basis of the developed method for solving boundary value problems of doubly nonlinear unsteady thermal conductivity, is to consider the effect of temperature dependences of the thermophysical characteristics of the material on temperature, zonal radiative-convective heat transfer and anisotropy on the distribution of temperature fields along the length, at the center and surface of a semi-infinite solid cylinder. The essence of this method is that the Goodman’s and Kirchhoff’s transformations are applied to the problem posed converted to a dimensionless form, then the relative temperature and functions from it, are expanded in the series of sines on the a priori interval, then the superposition principle is applied, after which the original setting is converted to a set of linearized problems with reduced thermophysical characteristics. Linear problems are solved by the method of integral transformations, which are summed up. The upper limit of the priori interval is determined from the condition that the relative temperature obtained from the solution of the problem Fo ® ¥ takes the value of the upper limit of the a priori interval. A large number of numerical calculations in the Matlab environment graphically show changes in the relative temperature on the axis and surface of the cylinder in a wide range of Fourier criteria. It is found that with an increase in the Fourier criterion, the character of heating changes qualitatively from the axis to the surface of the cylinder, both in terms of nonlinearities and anisotropy. For the case of double nonlinearity, the location of the temperature fields at different anisotropies in comparison with an isotropic material is shown graphically.

Optimal recovery of thermal energy in liquid air energy storage

The increasing share of renewables in energy systems requires energy storage technologies to handle intermittent energy sources and varying energy sinks. Liquid air energy storage (LAES) is a promising technology since it has a high energy density and is not geographically constrained. A relatively high round-trip efficiency (RTE) is obtained by using hot and cold energy recovery cycles in the LAES. In this work, seven cases related to different cold energy recovery cycles are optimized and compared for a standalone LAES system. Multi-component fluid cycles (MCFCs) and Organic Rankine Cycles (ORCs) are considered for the first time to be used as cold recovery cycles in the LAES. The optimal results show that the LAES system with dual MCFC has the best performance with an RTE of 62.4%. This RTE can be further increased to 64.7% by reducing the minimum temperature difference of high-temperature heat exchangers from 10 °C to 5 °C. Optimization results also indicate that ORCs used in the cold energy recovery system are not producing any work, and only phase change of the working fluid takes place, thus they should not be used. Finally, the exergy transfer effectiveness is applied to measure thermodynamic performance of the charging and discharging processes.

Thermodynamic Evaluation of a Direct Expansion Ground-Sourced Heat Pump with Horizontal Ground Heat Exchangers Using Advanced Exergy Analysis

This paper deals with the advanced exergetic analysis of a horizontal direct-expansion ground sourced CO2 heat pump operating in a transcritical cycle. The cycle is thermodynamically modeled in Engineering Equation Solver (EES) considering the pressure drops in both high and low temperature heat exchangers, and the system is to provide a fixed heating load. Conventional exergy analysis orderly suggests a compressor, expansion valve, gas cooler and ground heat exchanger to be considered for system improvement, while tracing exergy destruction of all components in detail demonstrates true improvement potential of each and all components and the system as a whole and offers a different order. Advanced exergy analysis points out that the compressor is directly and indirectly responsible for 56% of the overall exergy destruction generated in the cycle, confirming the detrimental role of this component in the system. The second influential component is recognized to be a ground heat exchanger accounting for 20% exergy destruction of the compressor as well as submitting 89% avoidability in its own exergy destruction, and expansion valve proves to be the last option for system improvement according to this analysis.

Thermal performance measurement of additive manufactured high-temperature compact heat exchangers

Due to increased distribution of high-temperature processes in energy and process plants, more efficient and compact high-temperature heat exchangers are being developed. The additive manufacturing allows the construction of compact sizes and application-specific requirements. To evaluate the thermal performance of these heat exchangers, experimental investigations are evident. This study presents a test rig for testing compact high-temperature heat exchangers as well as a first set of thermal performance data of an additively manufactured plate-fin heat exchanger. The test rig can provide a maximum fluid temperature of 900°C and a maximum mass flow rate of 0.8 kg/min. A steam unit can add steam to the fluid stream to evaluate the influence of gas radiation on the thermal performance. The capabilities of this test rig are being tested with the plate-fin heat exchanger, varying the mass flow rate between 0.2 - 0.52 kg/min at a hot and cold inlet temperature of 750°C and 250°C. The overall effectiveness of the heat exchanger is approx. 0.9.

Corrosion Behavior Research on Austenitic stainless steel in Dynamic Molten Salt

In order to identify the corrosion properties of three kinds of austenitic stainless steel used in solar power plant, experiments were conducted to test the weight loss after dynamic immersing in molten salt, the corrosion thickness rates per year was obtained, and the surface morphology by SEM and component of corrosive product by EDS were analyzed. The test result showed that the corrosion resistance of 316L and 347H are outstanding, much better than 304. The corrosion resistance order of the three material is 304 <316L< 347H. 304 and 316L can be considered as the candidate materials of low-temperature molten salt storage tank, and 347H can be used as the materials of high-temperature molten salt storage tank and molten salt heat exchanger.

Extrusion-based additive manufacturing of Ti3SiC2 and Cr2AlC MAX phases as candidates for high temperature heat exchangers

High Temperature Heat Exchangers (HTHXs) are used in many industrial processes and are likely to become key components in green power generation. For the development of HTHXs, novel designs and new materials need to be explored. Additive manufacturing (AM) opens many possibilities for novel designs. Extrusion-based AM in general, and composite extrusion modelling (CEM) in particular, offers the opportunity of using new binder systems, that cannot be employed in other AM techniques. MAX phases, due to their ceramic-metallic properties combination, are great candidates for HTHXs. In this work, the printability of Ti3SiC2 and Cr2AlC, through CEM with an innovative sustainable binder is explored. For this purpose, rheological properties of the feedstocks and the influence of the printing parameters are studied for each MAX phase feedstock. Microstructural analysis and final sample characterisation is performed, in order to determine the suitability of this technique to obtain near-net shape MAX phase parts.

Modeling of a high temperature heat exchanger to supply hydrogen required by fuel cells through reforming process

Hydrogen as a clean fuel and a new energy source can be produced by various methods. One of these common and economical methods of hydrogen production is hydrocarbon vapor modification. This research studies hydrogen production using a propane steam reforming process inside a high temperature heat exchanger. The application of this high temperature heat exchanger in the path of the power supply line is a fuel cell stack unit to supply the required hydrogen of the device. The heat exchanger consists of a set of cylindrical tubes housed inside a packed-bed called a reformer. The energy required to perform the reaction is supplied through these tubes in which high temperature gas is injected and the heat exchanger is insulated to prevent energy loss. The results show that at maximum temperature and velocity of hot gases, (900 K and 1.5 m s−1), complete consumption of propane can be observed before the outlet of the reformer. Also, in the mentioned conditions, the maximum hydrogen production (above 92%) is obtained. The best permeability under which the system can perform best is 1×10−9 m2.

(Plenary) Integrate to Extend the Reach of Solid Oxide Fuel Cells

Solid Oxide Fuel Cells (SOFCs) offer the potential for compelling thermo-economic value propositions in wide range of stationary and transportation applications through their potential for high conversion efficiency and their inherent fuel flexibility. Furthermore, many of the core SOFC materials, component, and system technologies have tremendous potential in electrolysis applications where fuels or chemicals could be produced using renewable electricity. However, to date, the wide-spread commercialization of SOFC/SOEC systems has been hampered by their high cost and durability challenges.Fortunately, high temperature solid oxide-based energy conversion systems are well suited for integration with thermal-mechanical energy conversion systems in configurations that offer the potential for significant cost and thermodynamic performance synergies. Specifically, their integration with gas turbines or internal combustion engines offers the potential for ultra-high (>70%) efficiency at an attractive manufacturing cost (<$1/W). In these hybrid systems, engines or turbines are used to convert stack waste exergy to additional useful work resulting in higher overall efficiency and lower power-specific cost (e.g., $/kW) compared to SOFC-only systems.Furthermore, in the case of SOFC and gas turbine hybrid systems, the SOFC stacks are typically located downstream of the gas turbine compressor and are at elevated pressure—enabling increased Nernst potential and decreased overpotentials and thereby higher power density at constant voltage. This benefit translates into a significant power-specific stack cost reduction. Additionally, the gas turbine compressor and recuperator may serve as the SOFC stack blower and recuperator—yielding further cost synergies via the elimination of duplicative balance of plant components.In 2017, ARPA-E launched the INTEGRATE program to develop hybrid system concepts and enabling component technologies that if realized would result in 100kW-scale distributed generation systems with >70% fuel to electricity conversion efficiencies and system manufacturing costs of <$1/W. In the initial two-year Phase I portion of the program, nine teams developed a suite of hybrid system concepts. Given these concepts, the teams then proceeded to develop 1) durable SOFC stacks that are capable of operating at high (~4 bar) pressure, 2) high temperature (>600 °C) and low-cost heat exchangers, and 3) innovative control system approaches. In 2019, three of the original nine teams were selected to design, build and demonstrate 100kW-scale systems by 2023.In the interest of focusing limited financial resources on foundational development risks, while avoiding the weight, volume, and fuel flexibility challenges associated with transportation applications and mitigating the financial risks associated with adopting new technologies at utility (e.g., >100MW) scale, natural gas fueled distributed generation (DG) systems were selected as the initial INTEGRATE application target. These DG systems would offer a fuel to electric power conversion efficiency that is roughly double that of the fossil fueled portion of the US electric grid. Furthermore, as renewable fuels such as hydrogen, ammonia, and bio- or electro- derived hydrocarbons (e.g., renewable natural gas or synthetic kerosene) become available, these systems would be capable of operating on them with relatively minor fuel processing system adjustments.Moving beyond stationary DG applications, SOFC hybrid systems can leverage their fuel flexibility in the pursuit of a decarbonized of long-distance transportation sector—if the systems can be made both light and small enough. To this end, ARPA-E recently launched three programs that have taken on the challenge of developing ultra-efficient, yet compact and light weight carbon-neutral electrified propulsion systems for commercial aviation.One of these programs is focused on carbon-neutral fuel to electric power conversion sub-systems—Range Extenders for Electric Aviation with Low Carbon and High Efficiency (REEACH). In the two-year Phase 1 of this program, six of nine selected teams will develop SOFC/gas turbine/battery hybrid systems that are fueled with renewable natural gas or synthetic kerosene. Phase 1 focuses on system conceptual design and fuel conversion component risk reduction, while full system design and prototype demonstration of a sub-scale fuel-to-electric power conversion device using a carbon-neutral liquid fuel is planned for Phase 2.If the REEACH-envisioned systems are successfully developed, they would enable economically attractive all-electric commercial aircraft up to a narrow body airframe with dramatically reduced (ideally zero) net carbon emissions. Furthermore, INTEGRATE/REEACH hybrid system technologies would also have attractive value propositions in maritime, rail, or heavy-duty vehicle applications.

Application of Ceramic Lattice Structures to Design Compact, High Temperature Heat Exchangers: Material and Architecture Selection.

In this work, we report the design of ceramic lattices produced via additive manufacturing (AM) used to improve the overall performances of compact, high temperature heat exchangers (HXs). The lattice architecture was designed using a Kelvin cell, which provided the best compromise among effective thermal conductivity, specific surface area, dispersion coefficient and pressure loss, compared to other cell geometries. A material selection was performed considering the specific composition of the fluids and the operating temperatures of the HX, and Silicon Carbide (SiC) was identified as promising materials for the application. The 3D printing of a polymeric template combined with the replica method was chosen as the best manufacturing approach to produce SiC lattices. The heat transfer behaviour of various lattice configurations, based on the Kelvin cell, was determined through computational fluid dynamics (CFD). The results are used to discuss the application of such structures to compact high temperature HXs.

Energetic, Exergetic, Economic and Environmental (4E) Assessment of a Residential Micro-CHP System: A Case Study

In this study, energetic, exergetic, economic and environmental (4E) assessment of a micro-cogeneration system implemented in a multi-family building with 137 flats in Konya is conducted. Although industrial CHP applications are prevalent in Turkey, the first residential use is reported and thoroughly analysed in this communication. Thermodynamic analyses showed that the micro-CHP system was capable of reaching 87% of cycle efficiency with 70 kWe of electrical and 115 kWt of thermal power, respectively. Moreover, II. Law analysis revealed inefficiencies across the system such that the high temperature heat exchanger had the lowest exergy efficiency of 63.7% which is the part requiring improvement. The economic analyses showed that the system could generate $22.10/month of economic return per flat and the payback period was found to be 5.48 years. Lastly, environmental analysis indicated that how environmentally friendly the CHP system is and argued that the system has prevented more CO2 emissions in winter than summer due to operating at full capacity. The findings support the potential and elucidate the specific conclusion for the practice of residential CHP applications in Turkey.

Design, Manufacturing, and Numerical Simulation of a Tube-in-tube High-temperature Heat Exchanger with Microstructures to Enhance Heat Transfer

Design, Manufacturing, and Numerical Simulation of a Tube-in-tube High-temperature Heat Exchanger with Microstructures to Enhance Heat Transfer

Optimal scheduling of flexible thermal power plants with lifetime enhancement under uncertainty

• The proposed method can limit equipment damage in different scenarios. • Damage can be reduced 40% with a revenue loss of less than 1%. • Different damage mechanisms in the equipment can be included in the method. • Variable uncertainty in power demand and price can be included. • Adequate selection of material design temperature reduces deterioration. Renewable energy sources have been the focal point to decarbonise the power sector. The large deployment of these intermittent power generation units requires mechanisms to balance the grid. Thermal power plants can provide this service by increasing the number of start-ups, shut-downs, and intraday ramps at the expense of higher deterioration in critical equipment, including high-pressure steam drums, turbine rotors and blades, and high-temperature heat exchangers and pipes. This work proposes a method to formulate the power generation scheduling of thermal power plants as a stochastic optimisation problem with limitations on the maximum damage in critical components. This method models the uncertainty associated with intermittent power generation from renewable sources with a scenario-tree whilst computing the deterioration of the equipment in each scenario to limit the maximum damage. Scheduling of a flexible natural gas combined cycle demonstrated how this methodology can reduce the deterioration of the superheating heat exchanger of the power plant with minimum detriment in power generation and revenue. Furthermore, the effect of the design temperature of the material on the total damage was analysed for a broad range of temperatures and operating profiles, showing how adequate selection of design temperature can reduce the deterioration of the equipment and enhance its lifetime.

Manufacturing of molten salt reactor heat exchangers using inner hole welding

ABSTRACT Inner hole welding was applied to weld UNS N10003 nickel-based alloy tubes (φ13.72*1.65 mm) to heat exchanger tubesheet in the Thorium Molten Salt Reactor for the first time. Welding defects were eliminated after the welding technology optimization after a great deal of trials and errors. And proper inner hole welding procedure and good butt joints were obtained. Welding procedure qualification shows that the strength of the welded joints at room temperature, 650°C and 700°C was higher than the qualified values of the base metal. After the confirmation of exact welding conditions on full-size mockup, the first batch of two heat exchangers of Thorium Molten Salt Reactor was fabricated by using inner hole welding technics in the world. The tube bundles containing 58 tubes (116 joints) were welded to tubesheet successfully. Penetration and radiation inspection revealed all the welds had no defects and were 100% qualified. Finally the completed unit passed 0.85 MPa hydrostatic testing. The successful development and application of inner hole welding process also establish a good foundation for the manufacture of high-temperature heat exchangers of other reactors besides Molten Salt Reactor.

Fast and stable approximation of laminar and turbulent flows in channels by Darcy’s Law

In the design of flow geometries consisting of channels such as high-temperature gas heat exchangers, a great number of design parameters can be chosen, why solving the turbulent Reynolds Averaged Navier-Stokes (RANS) equations by CFD coupled with other physics can become computational demanding. Therefore, we here propose a method for a significant reduction of computational resources and consequent high speed. This is done by using the less computational demanding Darcy’s Law (DL) to approximate the laminar and turbulent flows in channels with circular and arbitrary cross-sections. To obtain the right velocity profile, an artificial permeability variation across the cross-section of the channel is determined. This is obtained based on the analogy of the DL and Darcy–Weisbach equation (DW). Results demonstrate that the DL approximations predict velocities and pressures distributions from the laminar and turbulent flows in the channels with circular and arbitrary cross-sections very well. At the same time, the models with DL approximations reduce the runtime up to ~40 times as compared to RANS, and improve the stability and convergence of the model. Lastly, a cross-flow heat exchanger is studied as an application of the DL approximations.

Assessment of the strength reliability of high-temperature heat exchangers with long service life at the design stage

The article describes a method for assessing the strength reliability of high-temperature heat exchangers with service life of several tens of thousands of hours at the design stage, when there is not enough statistical data on the operating time of elements and material properties. The method shows, how to determine the missing coefficients of variation for calculating reliability and build the function of the probability of failure-free operation, considering the change of the properties of the structural material over time. The method of visualizing the distribution of zones, both satisfying and not satisfying reliability criteria at the nodes of any finite element model, is also described.

Technical and economical evaluation of a high-temperature air heater intended for integrated gasification combined cycle unit

In this paper the costs of creating a high-temperature air heater intended for the integrated gasification combined cycle unit developed by the authors are estimated and are compared with a steam boiler. The results can be used not only in the further development of the integrated gasification combined cycle plant under consideration, but also be interesting to specialists involved in the development of various high-temperature heat exchangers.

Thermal Stress and Deformation of Hollow Paddle-Shaft Components with Internal High Temperature Molten Salt Flow

Excessive thermal stress and deformation are important reasons causing disservice of high temperature heat exchangers. This paper presents thermal stress and expansion analysis of single-leaf type hollow paddle-shaft components with internal high temperature molten salt flow based on three-dimensional numerical simulations. The results show that the hollow paddles enhance the heat transfer and decrease the maximum thermal stress simultaneously with the expense of a much higher pressure drop than that of solid paddles. The cumulative von Mises stress distribution curve shows that the stress distribution of the component with hollow paddles is more uniform than that with solid paddles. The radial and axial deformations do not differ much for the components with hollow and solid paddles. A larger volume of the fluid space in the hollow paddles leads to stronger heat transfer, smaller maximum thermal stress, and more uniform stress distribution. The effects of the paddle height, the diameter and number of flow holes, the molten salt flow rate, and the material-side heat transfer coefficient are identified. The advantages of hollow paddle designs in both heat transfer and thermal stress (local and overall) performance are revealed. The work in this study can provide a reference for the design and optimization of hollow paddle heat exchangers with high temperature molten salt as working fluid.

Thermodynamic Optimization of a Geothermal Power Plant with a Genetic Algorithm in Two Stages

Due to the harmful effects and depletion of non-renewable energy resources, the major concerns are focused on using renewable energy resources. Among them, the geothermal energy has a high potential in volcano regions such as the Middle East. The optimization of an organic Rankine cycle with a geothermal heat source is investigated based on a genetic algorithm having two stages. In the first stage, the optimal variables are the depth of the well and the extraction flow rate of the geothermal fluid mass. The optimal value of the depth of the well, extraction mass flow rate, and the geothermal fluid temperature is found to be 2100 m, 15 kg/s, and 150 °C. In the second stage, the efficiency and output power of the power plant are optimized. To achieve maximum output power as well as cycle efficiency, the optimization variable is the maximum organic fluid pressure in the high-temperature heat exchanger. The optimum values of energy efficiency and cycle power production are equal to 0.433 MW and 14.1%, respectively.

Materials for High Temperature Heat Exchanger Applications: A Review

Materials for High Temperature Heat Exchanger Applications: A Review