Airfoil Fins Research Articles

Experimental study on heat transfer performance of sCO2 near pseudo‐critical point in airfoil‐fin PCHE from viewpoint of average thermal‐resistance ratio

The printed circuit heat exchanger (PCHE) is one of the leading heat exchanger candidates in the supercritical carbon dioxide Brayton cycle, which has high efficiency and compactness. In the present paper, a novel type of PCHE with airfoil fins was proposed and tested. The effect of the thermal resistance variation on the heat transfer performance near the pseudo-critical point was analyzed. Meanwhile, a non-dimensional factor defined as the ratio of bulk temperature to the pseudo-critical temperature was applied to evaluate the heat transfer performance. The results indicate that the variation of the heat transfer performance can be attributed to the different average thermal-resistance ratios, where a larger the average thermal-resistance ratio corresponds to a better heat transfer performance. When the non-dimensional factor is around 1.03, the heat exchanger exhibits the highest heat transfer performance. In this regard, a working condition analysis method based on the non-dimensional factor and the average thermal-resistance ratio is suggested. Finally, a modified heat transfer correlation considering the non-dimensional working parameters near the pseudo-critical point is obtained.

Numerical study of thermal-hydraulic performance of sCO2-molten salt printed circuit heat exchanger with discontinuous fins channel

Printed circuit heat exchanger (PCHE) is an essential part of supercritical CO2 (sCO2) Brayton cycle in the 3rd generation of concentrating solar power plant. Molten salt and sCO2 as the heat transfer fluid in PCHE, it is of great significance to improve its thermal and hydraulic performance. To reach this goal, two new discontinuous fin channels of PCHE were designed and their thermal-hydraulic performance was studied by numerical simulation. The results show that the second discontinuous fins channel with the best comprehensive thermal-hydraulic performance for sCO2, which has the Colburn j factor improvement by 2.1-4.6% and the Fanning friction factor f reduction by 3.8-6.4% compared with that of the airfoil fins; While the third discontinuous fins channel has the best hydraulic performance for both the heat transfer medium of molten salt and sCO2, among which the pressure drop per unit length and f have the largest reduction by 0.05-24.7% and 5.91-19.1% for sCO2, and by 25.62-29.39% and 1.35-2.4% for molten salt. As a result, the second and third discontinuous fins channel of PCHE are proposed to sCO2 and molten salt, respectively, which can contribute to design the PCHE for the 3rd generation of solar thermal power generation.

Parametric Study on Thermo-Hydraulic Performance of NACA Airfoil Fin PCHEs Channels

In this work, a discontinuous airfoil fin printed circuit heat exchanger (PCHE) was used as a recuperator in a micro gas turbine system. The effects of the airfoil fin geometry parameters (arc height, maximum arc height position, and airfoil thickness) and the airfoil fin arrangements (horizontal and vertical spacings) on the PCHE channel’s thermo-hydraulic performance were extensively examined by a numerical parametric study. The flow features, local heat transfer coefficient, and wall shear stress were examined in detail to obtain an enhanced heat transfer mechanism for a better PCHE design. The results show that the heat transfer and flow resistance were mainly increased at the airfoil leading edge owing to a flow jet, whereas the airfoil trailing edge had little effect on the thermo-hydraulic performance. The airfoil thickness was the most significant while the arc height and the vertical spacing were moderately significant to the performance. Moreover, only the airfoil thickness had a significant effect on the PCHE compactness. Based on a comprehensive investigation, two solutions NACA-6230 and -3220 were selected owing to their better thermal performance and smaller pressure drop, respectively, with horizontal spacings of 2 mm and vertical spacings of 2 or 3 mm.

The Effect of Flow Channel Geometry on Thermomechanical Performance of Printed Circuit Heat Exchanger (PCHE)

Abstract The carbon-free energy systems such as nuclear can benefit from compact and highly efficient heat exchanger technologies. The plate-type compact heat exchangers such as the printed circuit heat exchanger (PCHE) holds promise to fulfill these requirements. This work presents the thermal-hydraulic and structural analysis of PCHE for molten salt applications with thermal energy storage. In this study, three distinct types of geometry are chosen for the analysis, i.e., the zigzag channel type, the airfoil fin type, and the slotted fin type. For the working fluid, FLiBe (Li2BeF4) and solar salt (60% NaNO3 and 40% KNO3) are chosen for hot side and cold side, respectively. Titanium grade 5 is chosen as the structural material. The study is conducted by computational fluid dynamics (CFD) and finite element method (FEM) analysis. The thermomechanical behavior including pressure drop, fluid temperature, velocity profile, stress, and deformation of the flow channel were considered in this work. From the results, the zigzag channel geometry gives the best thermal hydraulic performance in terms of heat transfer and pressure drop. The structural analysis shows that the stress intensity has an exponential growth with power generation level with zigzag channel geometry being the highest out of three geometries. Overall, the zigzag channel PCHE is still the most suitable geometry for this application. Zigzag channel geometry should be substituted with an alternative geometry at a high-power application having both airfoil-fin and slotted-fin geometry at relatively identical stress intensity.

Thermo-Hydraulic performance of printed circuit heat exchanger as precooler in supercritical CO2 Brayton cycle

The Printed Circuit Heat Exchanger (PCHE) is one of the potential precooler candidates to be employed in the supercritical carbon dioxide (S-CO2) Brayton cycle with its high compactness, high efficiency and high endurance to extreme condition. Since the S-CO2 precooler operates in the condition close to the pseudo-critical region, it is of importance understanding the performance differences among different types of PCHE with the dramatical change of thermal-physical properties. Thus, in this study the effect of three channel configurations with zigzag, wavy and airfoil fin channel on heat transfer and flow resistance under precooler condition are investigated with numerical method. Based on the local analysis, it is found that the zigzag channel PCHE presents the better heat transfer performance compared to wavy and airfoil fin channel, and differences are increased as the temperature approaches the pseudo-critical region. Meanwhile, the airfoil fin channel shows the lower friction factor with only 6.12% and 41.31% of the zigzag and wavy channel, respectively. Furthermore, comprehensive performances are compared through the methods of entropy number, JF factor (ratio of Colburn j to friction factor) and Q/(ṁ∙ΔP) (ratio of heat exchange to pressure drop and mass flow). Based on the results, it is recommended for the airfoil channel to be adopted near the pseudo-critical region due to its larger surface area and smoother structural design.

Numerical investigation on the thermal-hydraulic performance of supercritical CO2 in a modified airfoil fins heat exchanger

The numerical studies on the modified airfoil fins channel using supercritical CO2 as working fluid showed that front-dense and rear-sparse (FDRS) and front-sparse and rear-dense (FSRD) distributions of fins could enhance heat transfer by improving the distribution uniformity of temperature difference in channel. The match of local dense distribution of fins with the region near pseudocritical point could obtain better overall thermal performance in the modified airfoil fins heat exchanger. The differences of thermal-hydraulic performance among channels with uniform, FDRS and FSRD distributions of fins could be explained with field synergy principle. The FSRD distribution of fins is the optimum scheme in the three distributions of the modified airfoil fins channel, because its comprehensive performance is 23–29 % higher than that of the uniform distribution of fins and 2–7.6 % higher than that of the FDRS distribution of fins. The present work provides insights into the mechanisms of supercritical CO2 heat transfer characteristics as well as practical guidance on the design and optimisation of relevant components.

Three-dimensional shape optimization of fins in a printed circuit recuperator using S-CO2 as the heat-transfer fluid

Printed circuit heat exchangers (PCHEs) are among the most promising candidates for recuperators in the S-CO2 Brayton cycle owing to their high-pressure resistance and high compactness, where the fins are usually installed in channels to improve the thermal-hydraulic performance. The fin shape optimizations have been performed in several previous studies for enhancing the heat transfer and reducing the pressure drop. However, most of them are limited to two-dimensional optimization where the shape variation along the height direction was ignored. In the present study, three-dimensional fin shape optimizations are performed for the PCHE recuperators using S-CO2 as heat transfer fluid to further improve the thermal-hydraulic performance. The heat transfer and pressure drop characteristics in channels with optimized fins are comprehensively evaluated by comparing against conventional cylindrical fins and airfoil fins. The results indicate that the optimized three-dimensional fins feature variable cross-sections along the height direction. Such three-dimensional fins can significantly diminish the impact area of fluid, which is conducive to reducing the local flow resistance caused by high-velocity gradient and consequently improving the comprehensive heat transfer performance. Under the typical working condition studied in this paper, the heat transfer capacity in hot channels of recuperators with the optimized three-dimensional fins is 21.2% greater than the cylindrical fins, and 17.3% greater than the airfoil fins when the identical pressure drop is fixed; while the heat transfer capacity in cold channels with the optimized three-dimensional fins is 24.3% greater than the cylindrical fins, and 29.3% greater than the airfoil fins. In addition, the robustness analysis indicates that the optimized three-dimensional fins can yield more excellent thermal-hydraulic performance than conventional cylindrical fins and airfoil fins over a wide range of working conditions.

Topology optimization of an airfoil fin microchannel heat exchanger using artificial intelligence

High-performance microchannel heat exchangers are needed to supply heat for power conversion for nuclear microreactors. An airfoil fin microchannel design, constructed of Alloy 617 with helium as the working fluid, is analyzed and optimized using a design of experiments with artificial intelligence techniques. The use of airfoil fins offers the potential to reduce pressure drop across the heat exchanger, as compared to other types of channel configurations. A framework for topology optimization of airfoil fin printed circuit heat exchangers (PCHEs) has been developed that can be readily extended to different fin sizes and shapes, as well as different inlet and operating conditions, materials of construction, and working fluids. An optimization procedure is developed that employs computational fluid dynamics for a set of design points identified using Latin hypercube sampling. Computational fluid dynamics is used to analyze a simplified two-channel configuration where five design parameters are varied – inlet angle, fin scale, extent of staggering, transverse and longitudinal pitches. Two methods (a 5D polynomial and a regression neural network) are compared for generating surrogate models and the resulting response surface approximation is input to a genetic algorithm that is used to identify a set of optimal parameters. The optimal geometries are found across six channel Reynolds numbers ranging from 1000 to 5000, since inlet conditions affect flow through the heat exchanger. A set of optimal designs that maximizes heat transfer and minimizes pressure drop is identified, and a thermal stress analysis is performed on the optimal design. Correlations for the Nusselt number and Darcy friction factor are developed that can be useful for thermal hydraulic analyses using system codes. Thermal stresses are analyzed and a brief discussion of the status of code cases of PCHEs for nuclear applications is given. Testing and thermomechanical modeling is needed to facilitate future code compliance of PCHEs for high pressure and high temperature applications.

Multi-objective optimal design of NACA airfoil fin PCHE recuperator for micro-gas turbine systems

• An AF-PCHE was first employed as a micro gas turbine recuperator. • Heat transfer, pressure drop and compactness are multi-objective studied. • A comprehensive optimal solution is obtained for recuperator design. In this study, an airfoil fin printed circuit heat exchanger (PCHE) was first employed as a micro gas turbine recuperator for extended-range electric vehicles. Optimal heat transfer rate, pressure drop, and compactness are important requirements for a PCHE to serve as a recuperator; therefore, in this study, a multi-objective optimal design was proposed using the aforementioned three targets. The considered factors included three airfoil fin structure parameters (arc height, maximum arc height position, and airfoil thickness), two airfoil fin arrangement parameters (horizontal and vertical spacings), and the velocity inlet condition, for both cold and hot sides. A series of 53 numerical tests were designed using the central composite surface method. And the numerical work was performed by the realizable k - ε model with the maximum validation error is less than ± 5%. Moreover, regression formulas for the three targets were established based on the results of the 53 numerical tests, using the high-determine factors. The maximum arc height position was found to be an insignificant factor; thus, it was neglected in the regression formulas. The Pareto fronts for the cold and hot sides were obtained based on nondominated sorting genetic algorithm II; decision-making could be achieved on the Pareto front, according to the design requirements. A comprehensive optimal solution was recommended for the recuperator PCHE with an overall heat transfer rate of 181.29 W/m 2 /K, a total pressure drop of 26.63 kPa/m, and compactness of 8.5 kw/m 2 .

Role of beryllium oxide on the thermal efficiency of microchannel heat exchanger with an optimum fin structure

High-efficiency microchannel heat exchangers (MHEs) can remarkably meet the thermal requirements in many areas of technology. Several active and passive techniques can improve the efficiency of heat exchangers; the improvement enables engineering processes to decrease operational costs through waste heat reduction. In the present article, two different passive techniques are applied to improve the heat transfer efficiency of a counter-flow heat exchanger. To do this, four various microchannels with airfoil fins, circular fins, trapezoidal fins, and triangular fins are designed. First, the temperature distribution and effectiveness for each microchannel are calculated and compared with each other. Results of the comparison showed that the optimum structure belongs to the microchannel with trapezoidal fins. Second, BeO ceramic is utilized as the microchannel heat exchanger's material. At a given mass flow rate of 30.5 kg/h, the superior thermal features of BeO lead to more uniform temperature distribution, and also it makes an improvement of 219% in the effectiveness of MHE with trapezoidal fins compared to alumina-made MHE with simple channels.

Design and Optimization of a New Heterogeneous Pche with Molten Salt Zigzag Passage and Sco2 Airfoil Fin Passage

Design and Optimization of a New Heterogeneous Pche with Molten Salt Zigzag Passage and Sco2 Airfoil Fin Passage

Optimal Design of Airfoil Fin Microchannel Heat Exchanger for the S-Co2 Brayton Cycle of Generation IV Nuclear Reactors

Optimal Design of Airfoil Fin Microchannel Heat Exchanger for the S-Co2 Brayton Cycle of Generation IV Nuclear Reactors

Optimization method of a novel airfoil fin heat exchanger based on the entransy dissipation theory

<p indent=0mm>The structure of the novel airfoil fin heat exchanger was optimized by the synergistic enhancement method based on the entransy matching performance, and two types of nonuniform fin distribution structures were proposed. The heat transfer and flow performance of various airfoil fin distribution structures were numerically studied by using supercritical CO₂ as the working medium under constant heat flux boundary conditions. The results showed that considering the extremely uneven distribution of heat transfer parameters arising from the drastic changes in the physical properties of supercritical fluid, the distribution of novel airfoil fins was changed under the condition that the total heat transfer area remained constant. The matching performance between the entransy of fluid and that of the wall heat flux was improved, and the distribution uniformity of the local entransy dissipation rate in the channel was improved. Hence, the total entransy dissipation rate in the channel was reduced, and the heat transfer performance was improved. The numerical studies under the boundary condition of variable heat flux in the two-fluid coupled heat transfer process showed that the distribution mode of the novel airfoil fins changed according to the distribution characteristics of heat transfer parameters in the two-fluid coupled heat exchanger. Under the condition that the total heat transfer area remained constant, the distribution matching of the entransy of hot and cold fluid also improved, so that the local entransy dissipation rate was more uniform in the heat transfer area, and the entransy dissipation rate was reduced. The entransy distribution-matching principle provides a new idea and method for the structural optimization and improvement of heat exchangers, which has important theoretical and engineering significance.

Effects of Fin Arrangements on Thermal Hydraulic Performance of Supercritical Nitrogen in Printed Circuit Heat Exchanger

The printed circuit heat exchanger (PCHE) with discontinuous fins is a novel type of compact and highly efficient plate heat exchanger, which has superior thermal hydraulic performance. The morphology and characteristics of the flow channel greatly affect the performance of the PCHE. The discontinuous airfoil fins are used in PCHE channel design because they can affect the flow and heat transfer by increasing the heat transfer area and the disturbance in the channel. In this paper, the effects of different staggered distance (Ls) and transverse distance (Lv) of airfoil fin arrangements on the heat transfer and flow of supercritical nitrogen in the PCHE are numerically simulated using ANSYS Fluent. Simulation results and subsequent analysis show that the appropriate decrease in Ls and reduction in Lv between the two rows of fins can improve the convective heat transfer of the PCHE. A fully staggered arrangement of fins (Ls = 1.2) and an appropriate increase in the Lv can mitigate pressure drop. The comprehensive performance of different channel geometries is compared by the performance evaluation criteria (PEC) in this study. It is shown that considering flow resistance and heat transfer, the comprehensive heat transfer performance can be enhanced by properly increasing the staggered distance and the vertical distance between fins. When Ls = 1.2 mm and Lv = 1.25 mm, the PEC value of the staggered channel is the highest, which is 11.6% higher than that of the parallel channel on average.

Experimental and numerical investigations of thermal-hydraulic characteristics in a novel airfoil fin heat exchanger

A novel airfoil fin (AFF) Printed Circuit Heat Exchanger (PCHE) with a 100 kW class heat transfer capacity was experimentally tested as a cooler in a supercritical CO2 system. Numerical analysis was also conducted to have an insight into the flow and heat transfer mechanism in the AFF channels. The results showed that the novel AFF structure has superior hydraulic performance as the pressure drop in the AFF PCHE is only about 1/6 of that in the zigzag channel PCHE with a comparative heat transfer rate. In comparison with the mass flow rate and operating pressure, the inlet temperature has relatively insignificant effect on the heat transfer rate and pressure drop in the AFF heat exchanger. The broadening of the fin has no obvious improvement in heat transfer coefficient but increases the friction factor massively, and thereby resulting in worse comprehensive performance in the fin channel. At smaller temperature and mass flow rate, the periodic fluctuations of the heat transfer coefficient and comprehensive performance criterion could be weakened significantly. In addition, the determinant effect of the effective thermal conductivity in the viscous sublayer and buffer layer on local heat transfer coefficient is also validated in AFF channels.

Experimental and numerical studies on novel airfoil fins heat exchanger in flue gas heat recovery system

• The novel airfoil fins heat exchanger was studied experimentally and numerically. • The novel airfoil fins channel has the best thermal–hydraulic performance. • The enhancement mechanism could be explained with field synergy principle. • Thermal-hydraulic correlations of novel airfoil heat exchanger were proposed. To improve the performance of waste heat recovery, a novel airfoil fins heat exchanger was applied to flue gas waste heat recovery. Two groups of experimental conditions were installed to test the heat effectiveness of the novel airfoil fins heat exchanger. The results showed that the heat effectiveness of the novel airfoil fins heat exchanger could reach more than 96%, which is higher than the conventional heat exchanger. The thermal–hydraulic performances of the novel airfoil channel, NACA 0020 airfoil channel and zigzag channel were investigated with the first and second laws of thermodynamics, which showed that the novel airfoil channel has the best comprehensive thermal–hydraulic performance among the three channels. The correlations of Nusselt number and friction factor of the novel airfoil fins heat exchanger were proposed for flue gas, whose maximum deviations were within ±5.0% and ±7.1%, respectively. The present work could provide guidance for the application of the novel airfoil fins heat exchanger in waste heat recovery.

Thermal-hydraulic performance of compressed humid air flowing in a recuperator

A novel heat exchanger unit structure was adopted to improve the thermal–hydraulic performance of compressed humid air and high-temperature flue-gas in a megawatt (MW) grade humid air turbine (HAT) cycle. Staggered airfoil fin channels and rectangular straight fin channels were projected for the compressed humid air and flue-gas, respectively. A three-dimensional model of the heat exchanger unit structure was built to simulate the heat transfer and flow of flue-gas and compressed humid air under different moisture content, mass flow-rate, and inlet temperature of humid air. The thermal–hydraulic performances of staggered airfoil channels were contrasted with that of straight and zigzag channels. The results showed that the airfoil channel has the best comprehensive thermal–hydraulic performance. Heat transfer and friction factor correlations were proposed to predict thermal–hydraulic performances of the compressed humid air flowing in the airfoil channel. The effects of moisture content on the heat transfer and flow characteristics were quantitatively described using correlations. The moisture content of the humid air is the main influence factor on heat transfer performance. In present study, the results and correlations can provide guidance for the design and application of recuperator structures with airfoil fins for the MW grade HAT cycle.

Design and Assessment of Lead–sCO2 Intermediate Heat Exchanger for LFRs

Lead–sCO2 intermediate heat exchanger (IHX) was designed for lead-cooled fast reactor (LFR). The reactor coolant is lead and flowing through a circular straight channel, meanwhile, sCO2 is heated through 5 channels with different geometries were investigated respectively, including straight channel, zigzag 52° channel, S-shaped fins, offset rectangular fins, and airfoil fins. Considering the thermal-hydraulics characteristics, mechanical structure, corrosion, and flow blockage in the IHX designs, the performance, total cost, and power density of several heat exchanger designs were evaluated and compared. Finally, a printed circuit heat exchanger (PCHE) design using the circular straight (lead) - offset rectangular fins (sCO2) channels was proposed. The straight and S-shaped channels for sCO2 flow were recommended as alternative designs under certain circumstances. However, S-shaped fins and zigzag channels will dramatically increase the cost while straight and airfoil channels will greatly increase the volume.

Investigation of the flow and heat transfer characteristics of helium gas in printed circuit heat exchangers with asymmetrical airfoil fins

This work presents a numerical investigation on the flow and heat transfer performance of printed circuit heat exchangers with asymmetrical airfoil fins, and the influence of the arrangements, attack angles, horizontal spacings, and staggered spacings of fins are studied. Then an orthogonal experiment is designed to optimize the comprehensive performance of these printed circuit heat exchangers. Finally, empirical correlations of Nusselt number and friction factor for these heat exchangers with the inlet Reynolds number ranging from 2000 to 10,000 are proposed based on our numerical results. The results show that the printed circuit heat exchangers with a consistent layout of fins show better comprehensive performance than those with a reverse layout. The comprehensive performance of these printed circuit heat exchangers with asymmetrical airfoil fins increases as the horizontal fin spacing and fin attack angle decrease. The staggered spacing has little influence on the comprehensive performance of printed circuit heat exchangers. In the present work, the printed circuit heat exchanger with the values of the normalized horizontal spacing, staggered spacing, and attack angles of 4, 1.0, and 1.269, respectively, exhibits the best comprehensive performances.

Comparative study on the thermal-hydraulic performance of a shell and plate particle-SCO2 moving packed bed heat exchanger with various channel configurations

This article proposes a predictive static model to evaluate the thermal-hydraulic performance of a shell and plate particle-SCO2 moving packed bed heat exchanger, with consideration of pressure drop, radiation and property variations. The results reveal that convection resistance on the SCO2 straight channel side occupies a large part of total thermal resistance in most design and off-design cases. A three-dimensional model inheriting conclusions from the static model is raised, which demonstrates that extremely short entrance region in the x-y plane hinders the overall heat transfer behavior of the SCO2 straight channel. Deservedly, suppressions of the development of thermal layers in the y direction will contribute to improving the thermal-hydraulic performance of the shell and plate particle-SCO2 moving packed bed heat exchanger. Four different fin configurations on SCO2 channel side are presented, analyzed and compared via the static model at the design-point case. Offset rectangular fins configuration behaves the best heat transfer enhancement in total heat transfer rate and overall heat transfer coefficient when compared with the original channel, followed by zigzag fins configuration, offset airfoil fins configuration and s-shaped fins configuration. Zigzag fins-modified channel expresses the worst hydraulic behavior, of which the pressure drop is nearly four times that of original straight channel. The pressure drop of channel with s-shaped fins nearly equals to that of the unmodified channel. Introduction of fins on SCO2 channel side reduces the ratio of convection resistance as a result of apparently increased SCO2 convection coefficients.