Diffusion Bonded Heat Exchangers Research Articles

The Versatile Loop Facility: A New Infrastructure for Testing Components and Systems of Lead Fast Reactor Technology

There has recently been growing interest in the development of innovative nuclear technologies that offer greater sustainability and cost effectiveness of electricity production. One of the most promising options is the lead fast reactor (LFR) technology. Lead stands out for its favorable neutron properties, allowing a hard neutron spectrum core as well as good shielding, heat transfer, and radioisotope retention capabilities. As lead has a boiling point in excess of 1700°C and does not react exothermically with either air or water, it also allows for the design of a low-pressure reactor block without an intermediate cooling circuit, which is used in other advanced reactor technologies for protecting against the interaction between primary and power conversion system coolants. The deployment of a new fleet of fast reactors is conditional on the control/prevention of the corrosion and erosion effects of the coolant against the structural materials, the systematic characterization of the interaction phenomena between the coolant and fuel and water, and the experimental qualification of innovative systems and components. To support LFR technology development, the UK Department for Business, Energy & Industrial Strategy has recently allocated 10 M£ to a team composed of Westinghouse Electric Company LLC, the Ansaldo Nuclear Group, the Italian National Agency for New Technologies, Energy and Sustainable Economic Development, the University of Manchester, and other organizations for the design, construction, and first operation of a network of eight test infrastructures widespread in the United Kingdom to address the LFR’s highest priority research and development needs. One of the experimental rigs is the Versatile Loop Facility (VLF) currently under construction at the Ansaldo Nuclear Group’s workshop in Wolverhampton, United Kingdom. The plant consists of a lead loop operable up to 650°C and equipped with a 500-kW electric fuel bundle simulator (resembling the Westinghouse LFR bundle) and a hybrid microchannel-type diffusion-bonded heat exchanger (which simulates the primary heat exchanger adopted in the Westinghouse LFR design). The heat removal is delegated to a supercritical water-cooling loop having a design pressure of 330 bar and maximum operating temperatures up to 620°C. In this paper we present the design of the VLF with specific details about its prototypical components and an insight into the construction and installation phases currently underway.

Thermal hydraulic characteristics of liquid sodium and supercritical CO2 in a diffusion bonded heat exchanger

Compact heat exchangers are being examined for use in advanced, high-temperature nuclear or concentrated solar power plants to improve thermal efficiencies and reduce capital costs. At the time of this work, no experimental investigation of liquid sodium in the popular diffusion-bonded heat exchanger design had been performed. This paper describes the thermal-hydraulic and overall operations performance observed during testing of a 316/L stainless steel “zig-zag” microchannel heat exchanger operating between a (0.5 kg/s) sodium loop and a (0.3 kg/s) recuperated supercritical CO2 system with outlet conditions up to 550 °C at 16 MPa. Observed pressure drop is presented in the form of an effective friction factor correlation which aligns closely with recent experimental data. The thermal performance of this heat exchanger, measured by its overall conductance under various flow conditions, was decomposed to examine the independent convection behaviors of both the CO2 and sodium streams. These results are presented in the form of Nusselt correlations fitted to the experimental data. The sodium heat transfer correlation aligns closely with the widely accepted Lubarsky-Kaufman correlation, while the CO2 heat transfer correlation lies between previous correlations developed by computational and experimental methods. This was the first long-duration use of sodium in a microchannels (∼ 1.8 mm hydraulic diameter) heat exchanger. The use of an oxide control system enabled trouble-free operation of the heat exchanger for over 150 h of high-temperature operation. This first-of-a-kind demonstration using liquid sodium and supercritical carbon dioxide shows great promise for further application of this technology in advanced nuclear or solar power plants.

Pressure drop and heat transfer characteristics of nitrate salt and supercritical CO2 in a diffusion-bonded heat exchanger

A lab-scale 316/L stainless steel diffusion-bonded heat exchanger was examined within a coupled high-temperature test facility consisting of an atmospheric-pressure nitrate salt loop and a supercritical carbon dioxide (sCO2) loop operating between 10 and 16 MPa. Pressure loss measurements collected for flow rates up to 0.55 kg/s of Solar Salt and up to 0.6 kg/s of carbon dioxide were used to generate friction factor correlations for the respective circular and semicircular zig-zag flow passages. Heat transfer measurements were also performed over a wide range of conditions to produce Nusselt correlations for the CO2 and nitrate salt geometries. The Nusselt number is deduced from a heat transfer resistance network and overall conductance measurements collected across the operating envelope of the coupled sCO2 – nitrate salt test facility. The CO2 side correlation showed excellent agreement with existing correlations in the literature. The salt side, having nearly circular channels with a different zig-zag angle and hydraulic diameter, yielded a new correlation applicable to the laminar flow regime. To examine the similitude of the friction correlations, pressure drop testing with water was performed on both sides of the component as well. Finally, results from non-destructive examination are discussed to provide insights regarding inspection methods and draining performance of high-temperature liquids in compact heat exchangers.

Thermal Hydraulic Characteristics of Liquid Sodium and Supercritical Co2 in a Diffusion Bonded Heat Exchanger

Thermal Hydraulic Characteristics of Liquid Sodium and Supercritical Co2 in a Diffusion Bonded Heat Exchanger

Heat transfer investigation of a 90° zigzag channel diffusion-bonded heat exchanger

Abstract Supercritical CO2 (S-CO2) Brayton cycle components are subject to high pressure and temperature conditions, which are intrinsic to the operation cycle. Among the equipment used for these applications, diffusion-bonded heat exchangers are receiving more attention to be used as pre-coolers on the cycle, due to their robustness and capability of operating at the demanded conditions. Currently, limited research focused on the influence of the pre-cooler’s cold-side fluid, water, on the thermal performance of the diffusion-bonded heat exchangers. In the present study, a novel zigzag channel for the diffusion-bonded heat exchangers with square cross-section was manufactured and experimentally investigated in a water-water configuration. During the experiments, the Reynolds number of the hot and the cold sides varied from 1529 to 8313 and from 1299 to 6618, respectively, covering laminar to turbulent flow regimes. A new heat transfer correlation is proposed based on dimensionless Reynolds and Prandtl numbers, covering a large Reynolds number range not yet experimentally investigated for the water. In the laminar regime, the current geometry increases the Nusselt number up to 4.1 times when compared to a straight channel. For the complete Reynolds number range evaluated, from 1299 to 8313, the average enhancement of a diffusion bonded heat exchanger with the proposed geometry compared to a straight channel one is of 2.2 times. Therefore, the current zigzag design proposed in this study provided a significant advantage in terms of heat transfer performance.

Experimental investigation of thermal-hydraulic performance of discontinuous fin printed circuit heat exchangers for supercritical CO2 power cycles

The supercritical carbon dioxide (sCO2) Brayton cycles have the potential to attain higher cycle efficiencies than the conventional steam Rankine cycles. Using compact diffusion-bonded heat exchangers for thermal recuperation in sCO2 Brayton cycles can lead to cost-effective, simple, and compact cycle footprint. This study focuses on the experimental thermal-hydraulic performance evaluation of a set of chemically etched discontinuous offset rectangular and airfoil fin surface patterns for use in diffusion bonded heat exchangers. Local and average heat transfer coefficients and pressure drops were measured for a wide range of operating conditions relevant to the sCO2 Brayton cycles. Empirical correlations for the friction factor and the Nusselt number are proposed based on the experimental data. The friction factor correlations were able to reproduce the experimentally measured pressure drops with a standard deviation of ±13.5% and ±14.7% for the discontinuous offset rectangular and airfoil fins respectively. Nusselt number correlations were able to reproduce the experimental Nusselt numbers with standard deviation of ±15.4% and ±8% for the discontinuous offset rectangular and airfoil fins respectively.

A study on diffusion bonding performance of inconel 617 heat exchanger

This paper proposes diffusion bonding characteristics of a heat exchanger whose material is Inconel. In order to respond to high temperature and pressure operating conditions, the diffusion bonding technology and Inconel 617 material were applied to the heat exchanger. However, it is difficult to estimate how well the diffusion-bonded Inconel heat exchanger is made. In this paper, the bonding performance for the diffusion-bonded heat exchanger was examined and analyzed. The analysis with measuring thermal and mechanical properties such as thermal diffusivity and tensile strength were conducted and parametric studies about bonding temperature and pressing force were carried out. The bonding condition of 1200°C, 50 ton was found to be suitable for this heat exchanger. Through thermal resistance model, impurity management with 10μm level would be expected to be necessary. Besides pressure-resistant test, the deformation in the stacking direction of the plates was found to be important observation element. The heat exchanger was tested for evaluating its capability where the performance showed 10 kW for capacity and 0.7 for effectiveness at 1.5 kg/min. From the results, we were able to establish the base technology for the manufacture of Inconel 617 heat exchanger through the application of the diffusion bonding.

인코넬 617을 이용한 고온고압용 미세채널 열교환기의 확산접합 공정에 관한 연구

Abstract Recently, the heat exchangers are requiring higher performance and reliability since they are being used under theoperating condition of high temperature and pressure. To satisfy these requirements, we need special materials and bondingtechnology. This study presents a manufacturing technology for high temperature and high pressure micro channel heat exchanger using Inconel 617. The bonding performance for diffusion bonded heat exchanger was examined and analyzed. The analysis were conducted by measuring thermal and mechanical properties such as thermal diffusivity and tensile strength,and parametric studies about bonding temperature and pressing force were also carried out. The results provided insight for bonding evaluation and the bonding condition of 1200 ℃ , and 50 tons was found to be suitable for this heat exchanger.From the results, we were able to establish the base technology for the manufacturing of Inconel 617 heat exchanger throughthe application of the diffusion bonding.

Fabrication and design aspects of high-temperature compact diffusion bonded heat exchangers

Abstract The Very High Temperature Reactor (VHTR) using gas-cooled reactor technology is anticipated to be the reactor type for the Next Generation Nuclear Plant (NGNP). In this reactor concept with an indirect power cycle system, a high-temperature and high integrity Intermediate Heat Exchanger (IHX) with high effectiveness is required to efficiently transfer the core thermal output to a secondary fluid for electricity generation, hydrogen production, and/or industrial process heat applications. At present, there is no proven IHX concept for VHTRs. The current Technology Readiness Level (TRL) status issued by NGNP to all components associated with the IHX for reduced nominal reactor outlet temperatures of 750–800 °C is 3 on a 1–10 scale, with 10 indicating complete technological maturity. Among the various potential IHX concepts available, diffusion bonded heat exchangers (henceforth called printed circuit heat exchangers, or PCHEs) appear promising for NGNP applications. The design and fabrication of this key component of NGNP with Alloy 617, a candidate high-temperature structural material for NGNP applications, are the primary focus of this paper. In the current study, diffusion bonding of Alloy 617 has been demonstrated, although the optimum diffusion bonding process parameters to engineer a quasi interface-free joint are yet to be determined. The PCHE fabrication related processes, i.e., photochemical etching and diffusion bonding are discussed for Alloy 617 plates. In addition, the authors’ experiences with these non-conventional machining and joining techniques are discussed. Two PCHEs are fabricated using Alloy 617 plates and are being experimentally investigated for their thermal-hydraulic performance in a High-Temperature Helium Facility (HTHF). The HTHF is primarily of Alloy 800H construction and is designed to facilitate experiments at temperatures and pressures up to 800 °C and 3 MPa, respectively. Furthermore, some preliminary microstructural and mechanical property characterization studies of representative diffusion bonded Alloy 617 specimens are presented. The characterization studies are restricted and less severe from an NGNP perspective but provide sufficient confidence to ensure safe operation of the heat exchangers in the HTHF. The test results are used to determine the design operating conditions for the PCHEs fabricated.

Heat Transfer of Supercritical Carbon Dioxide in Printed Circuit Heat Exchanger Geometries

The increasing importance of improving efficiency and reducing capital costs has led to significant work studying advanced Brayton cycles for high temperature energy conversion. Using compact, highly efficient, diffusion-bonded heat exchangers for the recuperators has been a noteworthy improvement in the design of advanced carbon dioxide Brayton cycles. These heat exchangers will operate near the pseudocritical point of carbon dioxide, making use of the drastic variation of the thermophysical properties. This paper focuses on the experimental measurements of heat transfer under cooling conditions, as well as pressure drop characteristics within a prototypic printed circuit heat exchanger. Studies utilize type-316 stainless steel, nine channel, semi-circular test section, and supercritical carbon dioxide serves as the working fluid throughout all experiments. The test section channels have a hydraulic diameter of 1.16 mm and a length of 0.5 m. The mini-channels are fabricated using current chemical etching technology, emulating techniques used in current diffusion-bonded printed circuit heat exchanger manufacturing. Local heat transfer values were determined using measured wall temperatures and heat fluxes over a large set of experimental parameters that varied system pressure, inlet temperature, and mass flux. Experimentally determined heat transfer coefficients and pressure drop data are compared to correlations and earlier data available in literature. Modeling predictions using the computational fluid dynamics (CFD) package FLUENT are included to supplement experimental data. All nine channels were modeled using known inlet conditions and measured wall temperatures as boundary conditions. The CFD results show excellent agreement in total heat removal for the near pseudocritical region, as well as regions where carbon dioxide is a high or low density fluid.

Experimental Investigations on Sodium Plugging in Narrow Flow Channels

A series of experiments was performed to investigate the potential for plugging of narrow flow channels of sodium by impurities (e.g., oxides). In the first phase of the experiments, clean sodium was circulated through the test sections simulating flow channels in a compact diffusion-bonded heat exchanger such as a printed circuit heat exchanger. The primary objective was to see if small channels whose cross sections are semicircles of 2, 4, and 6 mm in diameter are usable in liquid sodium applications where sodium purity is carefully controlled. It was concluded that the 2-mm channels, the smallest of the three, could be used in clean sodium systems at temperatures even as low as 100 to 110°C without plugging. In the second phase, sodium oxide was added to the loop, and the oxygen concentration in the liquid sodium was controlled by means of varying the cold-trap temperature. Intentional plugging was induced by creating a cold spot in the test sections, and the subsequent plugging behavior was observed. It was found that plugging in the 2-mm test section was initiated by lowering the cold spot temperature below the cold-trap temperature by 10 to 30°C. Unplugging of the plugged channels was accomplished by heating the affected test section.