High Temperature Heat Transfer Research Articles

Predicting thermophysical properties of molten salts in the MgCl2-NaCl-KCl-LiCl system with a shell-model potential

Ternary eutectic salts composed of MgCl2, NaCl, and KCl, referred to as MNK salts, have recently emerged as promising candidates as high-temperature heat transfer fluids and thermal energy storage media. In this study, we performed classical molecular dynamics (MD) simulations to predict the densities, specific heat capacities, viscosities, and ionic self-diffusivities for MNK salts over a wide temperature range. The impact of LiCl additive on their thermophysical properties was also investigated. To capture the electronic polarization of Cl anions by neighboring cations, we developed a novel shell-model potential using the force-matching method and a dataset of ab initio calculated interatomic forces. Our extensive MD simulations predict structure and properties for pure salts and binary/ternary salt mixtures in the MgCl2-NaCl-KCl-LiCl system in overall good agreement with available experimental and theoretical data, which corroborates the accuracy and reliability of our developed potential.

Turbulent flow and heat transfer in a new type of internally torsion-ribbed helical tube

Adding inserts is an effective technique to enhance heat transfer in tubes. In this paper, a new internally torsion-ribbed helical tube is designed to enhance the heat transfer capability and improve the temperature uniformity inside the pipe by adding torsional ribs inside the tube. The flow and heat transfer characteristics of high-temperature heat transfer oil in a straight tube, a common helical tube, and a new internally torsion-ribbed helical tube are numerically compared. The results show that the presence of internally torsional ribs can effectively strengthen the fluid perturbation inside the tube and further weaken the boundary layer, thus improving the heat transfer effect. Moreover, the convergence of strong vortices in the fluid is weakened by 29.3 % to 41.2 %. The comprehensive heat transfer factor (PEC) of the internally torsion-ribbed helical tube is between 1.1 and 1.2, which is 11.1 % to 12.0 % higher than that of the common helical tube, and the temperature uniformity TU = 0.18 % is 72.3 % better than that of the common helical tube. These data show that the new helical tube has excellent performance in strengthening heat transfer and preventing carbon deposition and coking caused by high local temperature of high-temperature heat transfer oil.

An improved laser flash method for thermal conductivity measurement of molten salts

Thermal conductivity measurement of high-temperature heat transfer fluids provides a crucial basis for designing utility-scale thermal systems. Molten salts are promising heat transfer and thermal storage fluids in high-temperature thermal energy storage systems, while the molten salt thermal conductivity obtained in existing studies exhibits large deviations due to the high experimental complexity and unstandardized test procedures. In this work, we improve the conventional laser flash analysis method by proposing a theoretical heat transfer model for multi-layer heat conduction and providing a near-optimal molten salt container design. With water as a test sample, the relative error of thermal conductivity measurement using the improved method is 6.3%. The thermal conductivity of Solar Salt from 250 to 400 ​°C, and of Hitec Salt from 160 to 250 ​°C are measured and compared with the previous work. Both results show that the thermal conductivity increases with the temperature rising. This work will promote the technology standardization for accurately acquiring the thermal conductivity of molten salts or other similar high-temperature heat transfer fluids.

Experimental and Numerical Investigation of Effect of Inclination on sCO2 Heat Transfer in a Circular Pipe

Abstract Supercritical carbon dioxide (sCO2) can be utilized as a working fluid in various thermal systems including large-scale power cycles; portable power production units, centralized coolant systems, and standalone cooling devices. However, the lack of accurate prediction tools such as heat transfer coefficient correlations and insufficient research studies about the mechanisms controlling heat transfer processes are hindering its practical realization for key energy and cooling systems. The overall objective of this study is to extend fundamental knowledge about heat transfer and fluid dynamic processes in conduits pertinent to sCO2 with an emphasis on flow direction and inclination effects. This paper presents the study on effects of gravity, buoyancy on sCO2 flow at temperatures near and away from the pseudo-critical temperature. The experimental setup consists of a high temperature and pressure sCO2 heat transfer loop and flow testing facility. Recently, researched sCO2 heat exchangers can have tubes oriented at different angles such as 45 deg or 90 deg to horizontal. For optimized design of efficient and cost-effective turbomachinery components utilizing sCO2 as the heat transfer fluid, an understanding of convective heat transfer inside a tube/pipe is equally as important as external heat transfer. This paper presents an experimental and numerical study on sCO2 heat transfer at various inclinations with angles ranging from 0 deg (horizontal) to 90 deg (vertical) along with upward and downward flow direction with different inlet temperatures. Thermocouple-based temperature measurement is utilized at multiple locations within the test section axially and circumferentially to study the temperature distributions on the tube surface. Computational fluid dynamics (CFD) simulations have been performed using ANSYS Fluent to complement experimental data. The CFD and experiment have been analyzed against the well-known Gnielinski Nusselt number correlation.

Geothermal Power Generation: Harnessing Electrical Energy Through The Organic Rankine Cycle (ORC) System

The research employs a thermodynamic simulation method using an Engineering Equation Solver (EES), relying on theoretical calculations. This method is integrated into a geothermal power plant, precisely focusing on geothermal source temperatures of approximately 95ºC. The investigation centers on the heat transfer process within a high-temperature heat transfer fluid from geothermal sources, conveying stored heat to the Organic Rankine Cycle (ORC) evaporator. Three specific working fluids, R134a, R11, and R22, examine working fluid selection for ORC at 95ºC. The results highlight the R11 organic fluid as an optimal compromise, excelling in two crucial criteria. Firstly, R11 exhibits the highest net mechanical power, = 34.81 kW compared to alternative fluids. Secondly, it boasts the best energetic efficiency of the cycle, registering = 16.01%, outperforming both R134a ( = 13.17%) and R22 ( = 12.64%). In summary, this study conducts a focused analysis of the energy aspects of an Organic Rankine Cycle (ORC) for electricity production using geothermal sources and organic fluids. Operating at a geothermal source temperature of 95ºC with a water flow rate of 80 lt/s and environmental conditions at 20ºC, the parametric study emphasizes the superiority of the R11 organic fluid. R11 emerges as the optimal choice, demonstrating the highest net mechanical power and superior energetic efficiency compared to alternative fluids, thereby contributing valuable insights to advancing sustainable and efficient energy technologies.

Numerical and experimental characterization of high-temperature heat transfer in a ceramic foam with dual-scale porosity

In this paper, we compare numerical predictions and measurements of the high-temperature apparent thermal conductivity of an insulating alumina foam with dual-scale porosity: the foam contains ▪-sized cells and also ▪-sized pores in the highly scattering foam skeleton. Simulations of the apparent thermal conductivity are performed on tomography-reconstructed foams, with a three-part multi-scale approach to account for the dual-scale porosity. The effective phonon thermal conductivity of the foam is first computed using a finite element homogenization technique. The spectral and temperature-dependent effective radiative properties of the foam are next computed through an improved Monte Carlo ray-tracing approach, with foam skeleton scattering modeled using a physical-optics-based approach. The apparent thermal conductivity of the foam is then simulated by resolving the coupled conductive-radiative heat transfer through a semi-infinite homogeneous slab. The simulated high-temperature apparent thermal conductivity is found to be in good agreement with experimental data up to ▪, obtained by parallel hot wire measurements coupled with an improved quadrupolar model for low-density insulating materials. The large influence of scattering at the cell-skeleton interface is shown through a numerical parametric study. It is also shown that the Rosseland conductivity calculated directly from the simulated spectral radiative properties provides a good estimation of radiative heat transfer for optical thicknesses exceeding 30.

Exploring Cr and molten salt interfacial interactions for molten salt applications.

Molten salts play an important role in various energy-related applications such as high-temperature heat transfer fluids and reaction media. However, the extreme molten salt environment causes the degradation of materials, raising safety and sustainability challenges. A fundamental understanding of material-molten salt interfacial evolution is needed. This work studies the transformation of metallic Cr in molten 50/50 mol% KCl-MgCl2via multi-modal in situ synchrotron X-ray nano-tomography, diffraction and spectroscopy combined with density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations. Notably, in addition to the dissolution of Cr in the molten salt to form porous structures, a δ-A15 Cr phase was found to gradually form as a result of the metal-salt interaction. This phase change of Cr is associated with a change in the coordination environment of Cr at the interface. DFT and AIMD simulations provide a basis for understanding the enhanced stability of δ-A15 Cr vs. bcc Cr, by revealing their competitive phase thermodynamics at elevated temperatures and probing the interfacial behavior of the molten salt at relevant facets. This study provides critical insights into the morphological and chemical evolution of metal-molten salt interfaces. The combination of multimodal synchrotron analysis and atomic simulation also offers an opportunity to explore a broader range of systems critical to energy applications.

Experimental and numerical investigation on the cold harvest of composite phase change materials for building energy conservation

This paper investigates the cold energy storage of a horizontal shell-tube latent heat thermal energy storage (LHTES) unit for the cold harvest during night time. An experimental apparatus containing a horizontal circular tube with circumferential heating/cooling was designed and developed. Paraffin based phase change material (PCM) with a melting temperature of 27 °C was adopted as the cold harvest media. To improve the heat transfer rate, multi-walled carbon nanotubes (MWCNTs) were mixed with the paraffin to form a composite PCM with high thermal conductivity. A corresponding model of the composite PCM was developed and verified against the experimental data. Numerical simulations were performed for different boundary temperatures and concentrations of MWCNTs. The results show that when the heat transfer temperature difference is 20 °C, 0.05 wt% nanoparticles increase the melting rate of PCMs. When the heat transfer temperature difference was 40 °C, 0.10 wt% nanoparticles significantly affect the PCM melting rate. For low or high temperature (heat transfer temperature difference of 10 °C and 80 °C), the addition of nanoparticles is not conducive to improving the melting rate.

Development of Rotary Solar Receiver and Solar Simulator Facility for Concentrated Solar Power Applications

A prototype rotary solar receiver and a solar simulator facility have been designed, built and commissioned by Odqa Renewable Energy Technologies in conjunction with The Oxford Thermofluids Institute, University of Oxford for the validation of concentrated solar power technologies. The key features of the rotary solar thermal receiver include the rotating absorber surface which incorporates a high temperature heat transfer design. The innovative design also includes a compact solar power inlet aperture for very high incident heat flux to reduce the radiant heat loss from the high temperature surface. Air is used as the heat transfer fluid as this has system integration advantages over other types of heat transfer media, such as CO2, steam, molten salt, or solid particles. A 30kWe Xenon-arc lamp high heat flux incident light has also been developed to enable experimental validation of the solar receiver technologies. The Xenon-arc lamp array consists of three lamps combined with a custom designed, 5-degree-of-freedom focusing mechanism to achieve precise focus and maximise the heat flux. The receiver has successfully produced working fluid temperatures reaching 1200°C, demonstrating the concept viability for high temperature processes.

Improving the Heat Transfer Performance of the Tower Molten Salt Solar Receiver With the Novel Folded Flow Tubes

Abstract The molten salt has been widely used in concentrated solar power generation as an effective high-temperature heat transfer and heat storage working fluid. However, due to the concentrating characteristic of the tower receiver, the solar flux distribution of the molten salt receiver is extremely non-uniform, and thus the circumferential non-uniform heat flux has a prominent effect on the heat transfer performance and reliability of the traditional solar molten salt receiver tube (TRT). In this contribution, in order to solve above problems, we propose some novel folded flow tubes (NFTs), which add a partition in the tube and seal the top with end cap so that the inflow and outflow of the fluid can only proceed from the same cross section. Then, we apply the binary nitrate (solar salt) as a heat transfer fluid, which is a mixture of 60% sodium nitrate and 40% potassium nitrate. First, we analyze some effects such as flow parameters, structure, and heat flux loading direction on the convective heat transfer performance of the NFTs. The results show that the circumferential temperature difference of NFTs is about 17–92 K lower than that of TRT, and the molten salt temperature distribution is more uniform accordingly. Moreover, the heat transfer coefficient is increased about 88.37–122.85%, which can provide a guidance for the structural optimization of practical solar molten salt receivers to improve the heat transfer performance and reliability.

In-situ thermophysical measurement of flowing molten chloride salt using modulated photothermal radiometry

Molten salts are leading candidates for high-temperature heat transfer fluids (HTFs) for thermal energy storage and conversion systems in concentrated solar power (CSP) and nuclear energy power plants. The ability to probe molten salt thermal transport properties in both stationary and flowing status is important for the evaluation of their heat transfer performance under realistic operational conditions, including the temperature range and potential degradation due to corrosion and contamination. However, accurate thermal transport properties are usually challenging to obtain even for stagnant molten salts due to different sources of errors from convection, radiation, and corrosion, let alone at flowing status. To the best of authors’ knowledge, there is no available in-situ technique for measuring flowing molten salt thermal conductivity. Here, we report the first in-situ flowing molten salt thermal conductivity measurement using modulated photothermal radiometry (MPR). We could successfully perform the first in-situ thermal conductivity measurement of flowing molten NaCl-KCl-MgCl2 in the typical operating temperature (520 and 580 °C) with flow velocities ranging from around 0.3 to 1.0 m s−1. The relative change of the molten salt thermal conductivity was measured. Gnielinski’s correlation was also used to estimate the heat transfer coefficient h of the flowing NaCl-KCl-MgCl2 in the given experimental condition. The work showed the potential of the MPR technique serving as an in-situ diagnostics tool to evaluate the heat transfer performance of flowing molten salts and other high-temperature HTFs.

The design and test of the electrical insulation break for the EAST Divertor primary heat transfer system

Experimental Advanced Superconducting Tokamak (EAST) is one of the important steady-state divertor Tokamak physical experiment platforms in the world. The main functions of the high-temperature and high-pressure Divertor Primary Heat Transfer System (DIV PHTS) are to provide high-pressure cooling water for the divertor to remove the heat load deposited on the divertor under the plasma operation mode and to provide high-temperature nitrogen gas for the divertor system to achieve vacuum condition during the baking mode. The stability and reliable operation of the DIV PHTS play an important role in the EAST tokamak plasma physics experiment. The high-temperature and high-voltage electrical insulation break are one of the important components of the system. The main function of the Electrical Insulation Break (EIB) is to break the closed circuit of the heat transfer system to avoid eddy current during plasma discharge affecting the magnetic field distribution characteristics of the tokamak. On the other way, it also needs to meet the requirement, there is no leak of the cooling water and nitrogen gas during cooling and baking operation mode. This paper proposes the design of an electrical insulating break (EIB) to meet the design requirements of EAST tokamak at first. Then the electric field analysis is carried out by using a finite element model to evaluate its electrical insulation characteristics. And the sealing structural characteristics are verified by applying the finite element method under two design modes. Finally, the sealing test result under the high-temperature baking and high-pressure cooling modes are presented to validate the design.

An evaluation model for fire resistance heat transfer of multi-layer floor assembly structure of rail vehicles

The high-temperature heat transfer performance of rail vehicle floor assembly is an important parameter to study whether the vehicle can resist external fire. The traditional method cannot measure the heat transfer parameters of the aluminum profile sprayed with fireproof paint in the floor assembly. This paper proposes a model for calculating the equivalent density and specific heat capacity of aluminum profiles after the fire. The equivalent density and specific heat capacity can be obtained by using this calculation method. A deep neural network method was used to predict the thermal conductivity of the component, which was 0.6 W / (m·K), combined with the 30-minute fire resistance test data of aluminum profiles with fireproof paint. Using the obtained thermal physical parameters, the finite element calculation and test were carried out for the floor assembly with 5 mm, 10 mm and 15 mm three kinds of thickness heat-insulating cotton. It is found that the calculated prediction results are close to the test results and have a strong correlation. Pearson correlation coefficients of three kinds of heat-insulating cotton with different thickness are 0.964, 0.98 and 0.978 respectively. After obtaining the thermal physical parameters, the finite element model can effectively predict the back fire surface temperature of multi-layer floor assembly and guide vehicle floor design. In this paper, a calculation model for fire resistance heat transfer of the floor assembly of rail vehicles is proposed, which is of great significance for accurate and rapid design of the floor assembly of rail vehicles.

What is the long-term demand for liquid hydrocarbon fuels and feedstocks?

Liquid hydrocarbons made from crude oil serve many functions: (1) a dense, easy-to-store, easy-to-transport energy source, (2) a method for daily-to-seasonal energy storage, (3) a chemical feedstock, (4) a chemical reducing agent and (5) a method to enhance high-temperature heat transfer in many furnaces and industrial processes. Liquid hydrocarbons can be produced and used without increasing atmospheric carbon dioxide levels if made from non-fossil feedstocks such as carbon dioxide or biomass. Understanding future liquid hydrocarbon demand is the starting point in assessing the viability of such options. Our assessment is that U.S. demand for liquid hydrocarbons is unlikely to go below the equivalent of 10 million barrels per day of crude oil but could be as high as 20 million barrels per day. The costs to replace liquid hydrocarbons increases rapidly at lower liquid hydrocarbon consumption rates. Hydrocarbon biofuels from cellulosic feedstocks can meet such demands if produced with large external inputs of heat and hydrogen. Options based on more limited feedstocks (starches, plant oils, sugars, etc.) can’t meet such demands.

High-temperature heat transfer simulation and optimization of quartz fiber-aerogel composite multilayer 3D fabric

Quartz fabrics, which have excellent mechanical properties and high temperature resistance abilities, had been widely applicated in aerospace, military, and other thermal insulation fields. However, single-layer quartz fabric has poor thermal insulation performance, which is unfavorable to the high temperature application of this material. In order to improve the thermal insulation effect of quartz fiber fabric, silica aerogel materials with outstanding thermal insulation performance were introduced to the fabrication of quartz fabrics. Thermal insulation properties of quartz fiber and mechanical properties of silica aerogel were improved by a 3D braiding technique. Firstly, a 3D-fabric structure of quartz fiber-aerogel multilayer composite was designed. Silica aerogel and quartz yarn were woven into 3D composite fabric by textile technique. Through 3D braiding technique, silica aerogels were protected by quartz yarns while enhancing their mechanical properties. The thermal insulation performance and high temperature erosion resistance of the fiber-aerogel fabric are improved. Secondly, to explore the influence of the internal structure of the 3D fiber-aerogel composite fabric, a full-scale 3D simulation model for the heat transfer performance of fiber-aerogel multilayer composite was established. The thermal insulation performance of the composite fabric at 700 °C was predicted. Finally, the temperature of different positions inside the fabric in different environments (300 °C, 400 °C, 500 °C, 600 °C, 700 °C) was tested. It has been proved that introducing aerogel materials to the quartz fabric could reduce the surface temperature by about 60%.

UNITY: Kyoto Fusioneering’s Unique Integrated Testing Facility for Fusion Power Generation

One of the major research and development challenges on the critical path to achieving a fusion pilot plant is demonstrating the viability of power production from fusion. In August 2022, Kyoto Fusioneering launched the construction of the world’s first integrated testing facility for fusion power generation. The primary testing loop of the facility will initially adopt PbLi, with the prospect of adding an additional molten salt loop, with dimensions of around 5 × 5 × 3 m with a coolant inventory of approximately 100 L. To be completed in 2025, this facility will demonstrate (1) heat extraction from a mock-up blanket, (2) high-temperature heat transfer and exchange, (3) electricity generation from blanket heat, and (4) hydrogen isotope extraction under commercially relevant conditions—to be completed in time for the first-generation demonstration fusion plants. This facility is named UNITY, standing for Unique Integrated Testing facilitY to symbolize the integration of all critical components.

Mathematical modeling of rocks plasma disintegration process at borehole reaming

The mathematical model of thermal disintegration of rocks during the reaming of boreholes, which takes into account the compatibility of the thermogas dynamic problem for a high-temperature heat transfer agent and the thermal problem for the rock heated by this heat transfer agent, has been developed. The mathematical model is based on the laws of conservation of mass, quantity of motion and energy and takes into account the dependences for determining the thermal stresses and the temperature of brittle fracture of rocks. As a result of solving the equations of the mathematical model, the temperature distribution in the rock mass (magnetite quartzite) during heating in the process of borehole plasma reaming and productivity of the borehole plasma reaming process are obtained. Calculated and experimentally determined productivity of the process of plasma reaming of the borehole were compared.

The design and construction of divertor primary heat transfer system for EAST Tokamak

The Experimental Advanced Superconducting Tokamak (EAST) had been under major upgrading from 2020 to 2021 in China. In this campaign of major upgrading, the new lower tungsten divertor is successfully installed to achieve the targets of long pulse and high β H-mode plasma operation. High temperature and high pressure Divertor primary heat transfer system (DIV PHTS) is also developed to remove the plasma deposition heat load on the Divertor. This paper presents a description of the design and construction of DIV PHTS for EAST Tokamak. Starting from the requirements specified in the Technical Specifications of DIV PHTS, the process to meet the Divertor cooling and baking requirement is designed and validated by the supported thermal-hydraulic analysis. Then, the piping stress analysis under different types of load combinations is performed to verify the structural design requirements. General layout design is also performed based on the component requirement and the allocated space in the EAST Tokamak hall. Finally, the procurement and test of the system main equipment is also given.

Control strategy effect on storage performance for packed-bed thermal energy storage

Energy storage will play an essential role by complementing renewable energy sources, which are central to the decarbonization of the power sector. Sensible thermal energy storage (TES) system through heating materials with high-temperature heat transfer fluid (HTF) is the simplest and most inexpensive TES technology. However, the inherent disadvantage of thermocline degradation makes the packed-bed TES system has several negative consequences. In the present study, a passive thermocline control (TCC) method with a high ratio of height-diameter and an active TCC method by setting an ending charging temperature were proposed. The results showed that the heat transfer between air and solid thermal storage materials was enhanced because of the fast airflow and the long airflow passage of the TES system with the passive TCC method. The utilization factors were about 75%, and thermal energy efficiencies were about 78%–80% under different interval times between charging and discharging. Combined with the active TCC method, the stable discharging duration was 6%–19% longer than just using the passive TCC method.

Analysis of Coolant Purification Strategies for Tritium Control in DEMO Water Primary Coolant

A major objective of the European fusion program is the design of the DEMOnstration power plant named DEMO. Up to now, most fusion experiments have been dedicated to a plasma physics investigation while, in DEMO-oriented activities, large attention is devoted also to other systems necessary to produce tritium and to convert the fusion power to electricity. The blanket region, responsible for tritium breeding, is characterized by high tritium concentrations, high temperature, and large heat transfer metallic surfaces in which tritium can permeate. Therefore, the problem of tritium permeation and the resulting tritium content in the primary coolant are of great relevance for DEMO. For the pre-conceptual design of the Water-Cooled Lead–Lithium variant, the tritium permeation rate from blanket into coolant was assessed and possible mitigation strategies were suggested. Starting from a review of the CANDU tritium experience, a preliminary assessment of the maximum tritium concentration target in the DEMO primary coolant was performed and different strategies (off-line, on-line, and hybrid) for the water coolant purification system coupled with the DEMO operating scenario were analyzed. The intent is to identify suitable solutions to reduce the tritium concentration inside the water coolant, having in mind the complexity of a water detritiation process.