Heat Exchanger Core Research Articles

Development of additively manufactured cryogenic heat exchangers for hydrogen-electric aircraft propulsion

Storage of liquid hydrogen at low pressures and temperatures is advantageous in terms of overall system weight compared to high-pressure gas storage at room temperature [1]. The weight penalty for insulation of cryogenic media is typically outperforming the combined weight and volume penalty of high-pressure storage [2] [3]. For aviation applications, where light-weight and compact design is key, it is, therefore, preferred to store the propellant as liquid. In the context of hydrogen, this implies storage of the liquid between 20K and 30K, depending on tank pressure. As the fuel cell, which converts chemical energy to electrical energy, requires the hydrogen to be provided at temperatures well above the freezing level of water, hydrogen extracted from the tank must be thermally conditioned, to comply with applicable requirements [4] [5].In the presented work, a liquid hydrogen and fuel cell based electrical propulsion system for aircraft is developed, which incorporates several novel technologies and non-trivial operating conditions [6]. One major focus is the utilization of additive manufacturing enabling advanced geometric designs to enhance performance and reduce weight. However, the influence of hydrogen and cryogenic operating conditions on thermal and mechanical properties of additively manufactured materials must be assessed and accounted for in the design process.The underlying architecture of the investigated hydrogen-electric aircraft powertrain incorporates several heat exchangers with different purposes. One of the heat exchangers is tasked with transfer of heat from a liquid coolant cycle to the gaseous hydrogen in order to rise its temperature to the working level of the fuel cell (>300K). The design of the heat exchanger is based on empirical formulae for cylindrical tube bundles (pins), which enhance heat transfer on the gas side. Alternating flow planes of gaseous hydrogen and liquid coolant media are stacked to reach a number of units, which generate the desired heat transfer rates and keep the pressure loss due to friction below the defined limit. The particular arrangement of rows, columns, pin diameter or distances between individual pins is optimized to arrive at the minimum structural mass, while satisfying heat transfer and pressure drop requirements. Boundaries for this parameter optimization may originate from manufacturing limitations, like the minimum thickness of fine structures impacting the reliability of the manufacturing process. Therefore, accompanying manufacturing tests are required, to feed the optimizer with meaningful limits.After the initial optimization, computational fluid dynamics (CFD) analysis confirms the performance of the entire heat exchanger, including the intake and outflow manifold. Lastly, the lower limits of wall thicknesses may be defined by either the manufacturability in the 3d-printer or the differential pressure across the wall causing material stress. Therefore, mechanical analysis is performed, to confirm that the manufacturing limit is the actual driving limit for the minimum wall thickness.Comparison of results of the analytical method with CFD show very good agreement with deviations of average media temperature at the heat exchanger exit of less than 3% for relevant conditions. The pressure drop results deviate predictably in the order of 50%, which can be accounted for with a correction factor. CFD analysis of the entire heat exchanger shows good agreement of the flow properties in the heat exchanger core, but also demonstrate that the intake (from pipe flow into heat exchanger core) and outflow plena can contribute significantly to the overall pressure drop, depending on flow conditions and geometry.This presentation summarizes the entire development process of a heat exchanger starting with the requirements derivation based on a system analysis, via the initial design optimization based on empirical coupled thermal and fluid mechanical formulae to CFD and mechanical strength analysis of the detailed design. Close attention is paid on the additional degrees of freedom and restrictions in design gained by additive manufacturing as well as the impact of the manufacturing method on material properties especially in the context of cryogenic hydrogen.

Demonstration of a multi-channel fluidized bed particle–supercritical carbon dioxide heat exchanger for concentrating solar applications

High-temperature thermal energy storage in oxide particles at temperatures above 600°C can couple concentrated solar energy with high-efficiency thermal power cycles to provide dispatchable solar-driven electricity. Challenges remain in developing cost-effective primary heat exchangers, which require expensive alloys, to extract the high-temperature thermal energy from the particles to power cycle fluids, such as supercritical CO2 (sCO2) in recuperated Brayton cycles. To explore one pathway for cost-effective, high-temperature particle heat exchangers, the current study demonstrates a shell-and-plate, particle–sCO2 heat exchanger with narrow-channel fluidized beds coupled with micro-channel sCO2 flows in the heat exchanger walls. This study evaluates the feasibility of multiple parallel, narrow-channel fluidized beds in shell-and-plate particle–sCO2 HXs, to achieve high bed-wall heat fluxes at elevated temperatures. A reduced-order model simulates the narrow-channel, fluidized-bed particle–sCO2 heat exchanger to design the fluidized bed geometry, in terms of depth, height, and number of channels,for a nominal 40-kWth heat exchanger at particle and sCO2 inlet temperatures up to 600°C and 400°C respectively. The resulting shell-and-plate heat exchanger design operates with bubbling fluidization of the downward-flowing oxide particles to enhance bed-wall heat transfer. The heat exchanger core is fabricated with etched sCO2 micro-channels in thin wall plates that are diffusion bonded to spacer frames to form the shell-and-plate structure with 12 parallel, fluidized bed channels, 10.4 mm deep. The heat exchanger is tested at the National Solar Thermal Test Facility at Sandia National Laboratories with CARBOBEAD HSP particles at design particle flow rates of 0.20 kg s−1 and inlet temperatures up to 525°C. Results show that fluidization across multiple parallel channel beds can maintain uniform particle inventory with a common freeboard zone above the heat exchanger core. Bubbling fluidization improves particle–wall heat transfer coefficients but also increases axial dispersion of particle thermal energy, which lowers the log-mean temperature difference such that total heat transfer remains relatively constant to within ±10% over a broad range of fluidization gas velocities. The axial dispersion required particle and sCO2 flow rates to be increased by 25% over model-designed conditions to achieve the targeted 40 kWth, which indicates the importance of incorporating axial dispersion into heat exchanger design models and of deploying bed structures to suppress it. This study demonstrates the feasibility and preferred fluidizing gas conditions for particle heat exchangers for releasing high-temperature thermal energy storage systems.

Optimization method for compact heat exchanger cores with circular channels

Optimization method for compact heat exchanger cores with circular channels

Analysis of the Sum Minimization Possibilities of Heat Exchanger Core Masses in Internal Combustion Engine Cooling Systems

Rational designs for cooling systems (CS) of internal combustion engines are formulated in the form of a series of circulation circuits. The engine is integrated into a circuit with the highest and unregulated flow of internal circuit coolant (ICC). All heat exchangers are placed in circulation circuits with relatively reduced and adjustable ICC flow rates. While the circuits are usually interconnected, they can also be designed to operate independently. This CS scheme enables the achievement of the minimum possible value of the sum of masses of exchanger cores, denoted as MΣ. The reduction in MΣ is achieved through the regulation of ICC flow in a closed circulation loop involving two heat exchangers. The variations in MΣ based on the circuit parameters have been thoroughly investigated. The reduction in MΣ can also be applicable to more intricate systems. A decrease in MΣ, under identical initial CS parameters, may occur in different magnitudes, depending on the specific features of the CS scheme and the operating conditions of the heat exchangers within it. Cooling systems, constructed with the same initial parameters and comprising multiple circulation circuits that meet all criteria for rational design, may exhibit diverse configurations. Examples of such systems are explored, and the minimum values of MΣ are calculated for each. It has been determined that the disparity in the minimum values of MΣ for such systems, while maintaining equal efficiency, can exceed 30%. The selection of the optimal CS scheme is contingent not only on achieving the minimum possible value of MΣ but also on various other factors.

Numerical Study on Fracture Behavior of Printed Circuit Heat Exchanger Core Based on Elasto-Plastic Phase Field Method

Abstract Printed circuit heat exchanger (PCHE) is a type of compact heat exchanger with high thermal efficiency, more compact, and suitable for high pressure and high temperature conditions. The safety assessment of PCHE is very important, especially for PCHE core. Because PHCE core is different from the PCHE headers which are typical pressure vessel components. However, there is no standard design method to ensure the structural integrity for PCHE core. Some failure modes of PCHE core are studied in recent years, but seldom researches have been conducted concerning the fracture behavior of PCHE core. In addition, the phase field method for fracture has developed rapidly in recent years with its advantages in predicting crack initiation, bifurcation, and merging. In this work, the fracture behavior of PCHE core with and without defects is investigated based on elasto-plastic phase field method. The model parameter of Ni-based Alloy for elasto-plastic phase field method is first calibrated by comparing the numerical results with tensile test data of diffusion-bonded PHCE core specimen. Then, the influence of loading directions, defect locations, and defect sizes on the fracture behavior of PCHE core with semicircular and semicircular-rectangular channels are analyzed. Some conclusions are discussed.

Prediction of Heat Transfer for Compact Tube Heat Exchanger Based on Porous Models

Abstract A prediction method for temperature distributions in compact heat exchangers was developed by modeling the microchannel as porous medium. The study is focused on the mathematical formulas and solution methods for convective heat transfer of heat core. The governing parameters include Reynolds number, longitudinal pitch, transverse pitch, Nusselt number, inertial resistance factor, and effective heat transfer coefficient. First, the correlation mechanisms and laws between the key parameters’ effects and heat transfer were revealed and explained. The results show that the temperature/pressure/velocity contours obtained from the porous-media model are consistent with those of the tube-matrix. When the longitudinal pitch has little effect on flow characteristics and Reynolds number, porous-media model and Zukauskas-correlation are consistent. Transverse pitch has significant effects on the flow characteristics and the Reynolds number. The heat transfer performance and Nusselt numbers obtained from tube-matrix, porous-media model, and Zukauskas-correlation decrease as the transverse pitch increases. Under different pitch conditions, the Nusselt number obtained by Zukauskas-correlation is larger than that of the porous-media model, which is larger than that of the tube-matrix. Second, the simplified model and fast calculation method were developed. Tube bundles of the heat exchanger core were modeled as micro-channels and theoretically as fluid-saturated porous structures. Results show the heat transfer performance predicted by the micro-channels, tube-matrix, and porous-media model is consistent under the same boundary conditions. These results are consistent with the experiment. In addition, the computing cost and time required for the porous-media and micro-channels model is relatively reduced. Especially for the micro-channels model, the calculating time is less than one-tenth of the original. Compared with the time-consuming numerical method, the new analytical solution has the advantages of cost and speed.

Experimental study of a heat recovery ventilator preheated by a Building Integrated Photovoltaic system in a cold climate

The use of heat recovery ventilators (HRVs) in cold climate housing is becoming increasingly common, to provide outside air to the occupied space while recovering heat from the exhausted air. However, frosting of the heat exchanger core impedes HRV operation in cold climate conditions. Strategies for defrosting the core include recirculating the exhaust airstream while stopping the supply of the outside air during the defrost cycle. Preheating the air using heating coils is also used, but its application is limited by the increased energy use of the preheater. This study aims to investigate the impact of a building integrated photovoltaic/thermal (BIPV/T) system on the HRV thermal performance by using it to preheat the outside air. In this experimental study, measurements of a heat recovery ventilator preheated by the BIPV/T system are carried out in a test cell of the Future Buildings Laboratory (FBL) at Concordia University in Montreal, Canada. The results are compared to a HRV without BIPV/T preheating. The relative humidity, temperature and airflow rate of the fresh air and exhaust airstreams are monitored at the inlet and outlet of the HRV. The experiments are conducted during two weeks from January 26th, 2023 to February 08th, 2023. The change of the sensible heat recovery effectiveness ∈ sens of the HRV, outside air outlet temperature T 2 from the HRV and outside air flow rate, ṁ1 and exhaust air flow rate ṁ4 are determined. The primary experimental results indicate that preheating the outside air by the BIPV/T system before entering the HRV can help to increase the outside air outlet temperature T 2 by up to 2.7°C at an outdoor temperature of -25 °C, and the sensible heat recovery effectiveness ∈ sens , outside air flow rate, ṁ1 (23L/s) and exhaust air flow rate ṁ4 (43L/s) of the HRV are kept constant at the same level with preheating by BIPV/T on the HRV at -5 °C to -25 °C of outdoor temperature.

Discretized and experimental investigation of thermo-hydraulic behavior in a compact heat exchanger manufactured via SLM process

The demand for a better understanding of the fluid thermal and hydrodynamic behavior along the heat exchanger makes it necessary to develop a discretized analysis. The temperature and pressure distributions from the local analysis allow the obtaining of mechanical and thermal stress fields, making the method advantageous in comparison to the conventional global analysis. This work developed a local thermo-hydraulic model for a compact heat exchanger manufactured via Selective Laser Melting (SLM) process. The cross-flow heat exchanger core, produced with American Iron and Steel Institute (AISI) 316L, has 100 mm height, 100 mm width, 100 mm length, and a 2 mm channel diameter. The local steady-state models were compared with experimental data. The experiments were performed with water on both sides, using different temperatures for the hot side, and Reynolds numbers ranging from 1748 to 12247. The local analytical models have a good agreement, with 14% average errors for the thermal and hydrodynamic models. Besides, the impacts of channel diameter and surface roughness in the pressure drop were studied.

Design and optimization of intermediate heat exchanger for lead-bismuth cooled fast reactor coupled with supercritical carbon dioxide Brayton cycle

Printed circuit heat exchanger has become a new choice for the intermediate heat exchanger of the lead/lead–bismuth cooled fast reactor coupled with supercritical carbon dioxide nuclear power system because of its large heat transfer area density, high power density and ability to work at high temperature and high pressure. In this study, the channel dimensions of the intermediate heat exchanger were optimized to improve its thermal–hydraulic performance. An in-house code for the thermal–hydraulic design of printed circuit heat exchanger with lead–bismuth and supercritical carbon dioxide as working fluid was built. The relationship between the cold side pressure drop of intermediate heat exchanger and cycle efficiency of the nuclear power system is revealed. The power density and pressure drop of the cold side are selected as two optimization objectives, and the multi-objective optimization process is conducted with the non-dominated sorting genetic algorithms II. The optimal design results of the intermediate heat exchanger are obtained with Pareto-front method. The Pareto-front shows that when the heat exchange density increases, the pressure loss of the cold side also increases, but more quickly than the former. Finally, considering the design limitations, the intermediate heat exchanger core design scheme is selected by the auxiliary function which considering both capital cost and operating cost.

Numerical and experimental performance investigation of a heat exchanger designed using topologically optimized fins

Topology optimization for thermal-fluid problems has been successfully used to improve performance of small structures used for heat transfer. Optimization of full heat exchangers, due to analysis method limitations and computational costs, has not been able to produce manufacturable designs complex enough to satisfy heat exchanger specifications. The goal of this study is determining if a practical heat exchanger design can be obtained by the use of topology optimization. By considering a plate-fin heat exchanger, topology optimization is used to obtain a locally optimized fin pattern which is extended to form a heat exchanger core. A modification of the Number of transfer units method is presented to deal with the unique topology obtained by optimization and evaluate the performance of the exchanger. The performance, when compared to traditional serrated fin designs, show that optimization improvements extend beyond the optimized region onto the entire exchanger. The results show that the optimized design is an improvement outside optimization flow parameters. However, the limitations in 3D printer technology result in slight deviation of experiment results compared to the analysis, and prevent the manufacturing of designs with comparable total performance values to heat exchangers manufactured through traditional methods. • Design procedure obtains a heat exchanger core by localized topology optimization. • NTU method is modified to evaluate results of topology optimization. • Modified NTU, CFD and experimental evaluations are in good agreement with each other. • Performance improvements are maintained outside optimization flow parameters.

Structural stress analysis of hybrid heat exchangers in the S-CO2 power cycle for marine waste heat recovery

Due to its high thermodynamic efficiency and small equipment size, the S-CO2 Brayton power cycle is a leading candidate for ship waste heat utilization. The hybrid heat exchanger formed by diffusion bonding of fins and etched plates can be used for heat exchange between the high temperature flue gas and the high pressure S-CO2. However, the law of structural strength is not clear for the hybrid heat exchanger. It is critical to carry out structural stress analysis. In this study, to assess the structural strength of the hybrid heat exchanger, the FEM was used and compared with a currently used method from ASME codes. The results show that the thermal stress caused by the temperature gradient is independent of the absolute temperature value. The change in the supercritical carbon pressure in the etched channel affects the mechanical stress more than the exhaust gas in the fin channel. Under design conditions, thermal stress and mechanical stress are equally important to the total stress of the hybrid heat exchanger. Moreover, the total stress is not a simple numerical superposition of thermal stress and mechanical stress but instead indicates a complex effect. From the FEM results, the etched channel exit that withstands a higher pressure load is the weakest point in the hybrid heat exchanger core. The FEM is a more comprehensive means for structural assessment than the ASME codes. This research can provide guidance for structural stress analysis of hybrid heat exchangers

Design of an Additively Manufactured Recuperator With 800 °C Inlet Temperature for sCO2 Power Cycle Application

Abstract Recuperators with design temperatures at and above 800 °C can further increase the thermal efficiency of supercritical CO2 power cycles by enabling higher turbine exhaust temperatures. Mar-M247 is a well-suited nickel-based superalloy for high temperature service due to its high creep strength that prevents excessive material thickness being required for pressure containment. Additive manufacturing using a high-speed laser-directed energy deposition (L-DED) process presents a promising solution, with build trials demonstrating the ability to produce nonconventional flow channels for enhanced heat transfer. A design process is presented that includes aerothermal and mechanical evaluation to maximize performance within the constraints of the manufacturing process. A 2-D heat transfer network and pressure drop code allows prediction of flow distribution and its effect on overall thermal performance. Established literature correlations, along with CFD simulation, inform the prediction of heat transfer coefficients and friction factors for the flowpaths and enhancement features in the heat exchanger core. Mechanical evaluation using finite element analysis (FEA) modeling with the intent of the ASME Boiler & Pressure Vessel Code (BPVC) Section VIII, Div. 2 assesses the operational safety of the design. The detailed design features annular finned passages that take advantage of helical flow paths to distribute the flow from separated headers to shared heat transfer surfaces. Performance predictions for the recuperator at a 50 kW scale provide insights into the feasibility of the additively manufactured (AM) process to produce recuperators on a commercial scale that extend existing operating envelopes.

Numerical study of the effect of flow nonuniformities on the low-pressure side of a Cooled Cooling Air heat exchanger

The Cooled Cooling Air (CCA) heat exchanger is a precooler that cools the bleed air from the compressor stages and is located inside the bypass duct of the aeroengine. Nonuniform flows enter the core of the heat exchanger because the cold side is the off-take from the fan flow, compromising its aerothermal performance. These aspects has been disregarded in the literature until now. In this study, the aerothermal performance of a CCA heat exchanger with flow nonuniformities on its Low-Pressure (LP) side is investigated. Three-wire meshes were designed using correlations from the literature, showing three off-design cases, namely, Cases 1, 2, and 3. The porous media and dual cell heat exchanger models were used in numerical simulations for the baseline and off-design cases. Experiments were performed at hot and cold conditions to validate the numerical simulations under actual gas turbine operating conditions. It has been found that heat transfer rate increases in Case 1 and 2 by 1.0% and 1.5%, as the flow non-uniformity is symmetric with respect to XZ plane. In contrast, in Case 3, the heat transfer rate reduces by 4.2% because the flow non-uniformity is asymmetric with respect to XZ plane, inducing cross-flows immediately upstream of the heat exchanger core. • Aerothermal performance with flow nonuniformities along LP side was investigated. • The porous media and dual cell heat exchanger models were used. • Experiments were performed under actual gas turbine operating conditions. • The overall heat transfer rates were improved by 1.0% and 1.5% in Cases 1 and 2. • The overall heat transfer rate declined by 4.2% in Case 3.

Design of a Compact Dry Cooler With an Aluminum Heat Exchanger Core for a Supercritical CO2 Power Cycle Is Evaluated for a Concentrating Solar Power Application

Abstract As the supercritical CO2 power cycle develops and the component technologies mature, there is still a need to reduce the associated capital and operating costs to maintain a competitive levelized cost of electricity (LCOE) in order to enter the market. When considering concentrating solar power (CSP) coupled with an sCO2 power block and sensible thermal storage, the technology presents a clean source for utility-scale power generation to support baseload or peak-load electrical demand. However, the LCOE of the technology is still considered higher than the competing technologies and should be reduced to better compete in the market; 2030 targets for dispatchable solar plants are 5¢/kWh for baseload CSP and 10¢/kWh for peaker plants, as set by the United States Department of Energy. In response to this need, this study is targeting improvements in the power cycle precooler to reduce power block contribution to LCOE. This study considers a dry cooler, as CSP plants are sensitive to water consumption because many installations are slated for remote or arid locations where solar irradiance is very high, but water is scarce. Furthermore, the power block footprint for an sCO2 system is quite compact, especially as compared to a steam cycle. Therefore, there is interest in installing a more compact dry cooler that is proportional to the reduced footprint sCO2 power block, while conventional dry coolers are an order of magnitude larger. The competing goals of size, performance, and cost were considered in this study to develop a compact dry cooler that can easily be packaged with the power block, significantly reducing the installation and transport cost compared to the current state of the art, while maintaining or improving upon the heat transfer performance and impact on plant LCOE. This paper details the high-level findings of a large dry cooler sensitivity study for design point selection, design of the compact dry cooler, expected year-round performance for the dry cooler and the power cycle, and the predicted LCOE for a 30-year plant life. It was found that an aluminum heat exchanger core can be suitably designed to meet the pressure and temperature requirements for a precooler in an sCO2 recompression Brayton cycle. The dry cooler assembly was found to have improved heat transfer performance, allowing for increased cycle efficiencies and a reduced plant LCOE. When coupled with a centrifugal blower and compact transition duct, the dry cooler assembly was able to reduce the installation footprint by over 50%.

Novel thermosyphon-assisted setup for determining heat exchanger thermal characteristics

To be used in the market, thermal and friction characteristics of newly launched heat exchangers must be acknowledged, usually by experimental methods. Steady-state Kays and London is considered the classical experimental technique. In this setup, one of the heat exchanger streams is usually vapor, to provide controlled known heat transfer and temperature conditions, while the other stream is subjected to different flow rates, for the determination of the equipment thermal and pressure drop behaviors. Large expensive industrial boilers are usually used, resulting in difficulties in stabilizing and controlling vapor temperatures. In the present work, a new experimental setup, based on the above-mentioned technique, is proposed for determining the heat transfer characteristics of compact heat exchangers. The boiler vapor flow is substituted by the working fluid (water in vapor state) of a two-phase thermosyphon. Being smaller and much more flexible, this technology allows for easy control of the vapor temperature, while providing uniform temperature distribution along one of the heat exchanger streams, which is difficult to obtain with the classical procedure. In the proposed apparatus, the “known side” of the heat exchanger takes the role of the condenser of the thermosyphon. Two well-known heat exchanger cores, composed by circular and square cross section channels, were used to validate the proposed arrangement, considering the ranges: 2200 < Re < 8000 and 850 < Re < 2800, respectively. The wall temperatures were tested in the range 120 °C to 220 °C with a precision of ± 0.5 °C in steady-state. In addition, the resulting Nusselt number (Nu) and the Fanning friction factor (f) data were compared with consolidate literature correlations showing an average discrepancy of 15% for both geometries and parameters. Therefore, the use of thermosyphons results in smaller, simpler and more precise test benches to be used for the evaluation of heat exchangers, as it provides the desired constant wall temperature conditions for the characterization of core geometries, substituting, with advantages, the use of large and expensive steam boilers.

Structural analysis of compact heat exchanger samples fabricated by additive manufacturing

Compact heat exchangers are extensively employed in the industry due to their flexibility, geometric configuration characteristics, and the low ratio between heat transfer area by volume. Usually, these heat exchangers are exposed to high thermal and pressure gradients, which can cause structural failures during the operation. A new fabrication method employing additive manufacturing was evaluated to produce that equipment in this context. Twelve samples of 316L stainless steel that simulated a heat exchanger geometry were fabricated in two machines. A test rig was constructed for hydrostatic tests to evaluate their structural integrity through strain gauges. Some samples were submitted to pressures up to 700 bar without any leakage. The results show that printing orientation is crucial to the process, which influences material properties and, consequently, the von Mises stress observed. Properties on vertical orientation present lower stress levels. The influence of heat treatment was also verified, showing that machining processes locally alter mechanical properties. In parallel, a numerical study was developed for structural evaluation. It was observed that the pressurization of the distribution chamber strongly influences the stress of prototype channels. The high-stress region does not surpass the material yield strength for the test pressure. Furthermore, any deformation on the experimental prototype was not observed, indicating that the geometric characteristics guarantee a structural integer of the heat exchanger core. It is highlighted that the numerical results proved a good adherence to experimental results.

Design and modeling of a multiscale porous ceramic heat exchanger for high temperature applications with ultrahigh power density

The efficiency of a heat engine can be significantly improved by operating in a high-temperature and high-pressure environment, which is crucial for a wide range of applications such as hybrid and electric aviation as well as power generation. However, such extreme operating conditions pose severe challenges to the heat exchanger design. Although recently developed superalloys and ceramics can survive high-temperature and high-pressure loads, using these materials in a traditional heat exchanger design requires high cost and yields low power density. In this work, we propose an ultrahigh power density ceramic heat exchanger for high-temperature applications enabled by a multiscale porous design. By optimizing the design of centimeter-scale macrochannels and microchannels, significant improvement to both heat transfer and structural strength is predicted, with a negligible pressure drop penalty (< 1%). Based on finite element simulations, an optimized heat exchanger core design is expected to achieve power densities of 717 MW/m3 and 300 kW/kg, which indicates more than 2.5× enhancement in thermal performance compared to printed-circuit heat exchanger design. Furthermore, the heat exchanger design features low material costs and scalable fabrication, enabling highly customizable applications in aerospace and terrestrial power generation.

Numerical investigation of heat transfer and flow resistance characteristics of interpenetrated flying-wing finned tubes

In the present study, three possible interpenetration modes named vertical insertion, horizontally staggered shift, and streamwise staggered shift are proposed to improve the compactness of the flying-wing finned tube heat exchanger. Also, the effects of these modes on heat transfer and flow resistance characteristics of the finned tubes are numerically analyzed in the Reynolds number range of 1500–3000. It was found that a large vertically embedded depth (Lv), which in the present study has a maximum value of 3.4 mm, creates an acute-angled slit in the fin gradual contraction region. This slit weakens the convective heat transfer. However, the flow resistance characteristic is improved to a certain extent with increasing Lv. It was also found that the monotonous characteristic curves obtain a local inflection point in the range of 2.35–3.05 mm of Lv. An equivalent insertion coefficient is proposed to simplify the comparison of heat transfer rate (Φ). When the envelope size of the heat exchanger core, finned tube number, and pressure drop (Δp) are fixed, the overall thermal-hydraulic characteristics (Φ versus Δp) of the interpenetrated flying-wing finned tube heat exchanger are most significantly improved with Lv equal to 2.7 mm by 6.5% on average. Finally, two interpenetration correction factors are proposed to quantify the effect of interpenetration on the thermal-hydraulic characteristics.

Optimization Method for Compact Heat Exchanger Cores Produced by Additive Manufacturing

Optimization Method for Compact Heat Exchanger Cores Produced by Additive Manufacturing

4 E’s (Energy, Exergy, Economic, Environmental) performance analysis of air heat exchanger equipped with various twisted turbulator inserts utilizing ternary hybrid nanofluids

Advancement in technologies needs a critical heat removal technique for better exergo-economic performance of compact air heat exchangers. The passive technique is used for heat transfer improvement with various turbulators inserts TTI, PTTI, and DTTI in plain tube air heat exchanger. This paper investigates the exergo-economic sustainable performance of heat exchanger devices assisted with water-based different tripartite hybrid nanofluids under various geometrical turbulator inserts modifications. Simulation is proceeded for tripartite hybrid nanofluids of mainly six various compositions based on the nanoparticles morphology variant and three different turbulators inserts at the core of plain tubes heat exchanger. The four E’s (Exergy, Energy, Economic, and Environmental) aspects with sustainability analysis of the device are studied with operating parameters. Results revealed that only nanofluid would not be useful for energy enhancement, while turbulator inserts with THNF result in a significant improvement in the thermohydraulic performance of the device. The device inserts with DTTI in plain tubes using THNF 6 results in the highest26% overall heat transfer coefficient, 2.94% exergy efficiency, 5.04% performance index, and higher sustainability index at low Reynolds number, meanwhile turbulator inserts yield to highest 91.94% operating cost and equivalent CO2emissions. DTTI with THNF 6 is preferred as working fluid as PEC ranges highest 1.42–2.35, and THNF 2 working fluid should be least preferred due to its high operating cost.