S-shaped Fins Research Articles

Numerical study of crossed airfoil fins in a printed circuit heat exchanger

Airfoil fin is a new type of discontinuous fin that can provide better thermal–hydraulic performance than Zigzag fin and S-shaped fin when used in a printed circuit heat exchanger with supercritical CO2 as the working fluid. However, previous studies were limited to two-dimensional shape optimization of the airfoil fin and did not consider the shape adjustment in the height direction. In this study, we proposed a new fin consisting of crossed fins on the upper and lower heat exchanger plates to achieve shape change in the height direction. We compare the heat transfer and flow resistance of this new fin with the traditional airfoil fin using numerical simulation method. The results show that the crossed airfoil fin can generate longitudinal vortex that destroy the boundary layer of the heat transfer wall, improving the heat transfer performance. Under the multiple inlet Re number conditions studied in this paper, the heat exchanger with crossed airfoil fins has a 25.5%-30.8% higher Nu number than the traditional airfoil fins, and the thermal performance factor is increased by more than 10%. It concludes that significantly improves the thermal performance and has good engineering application value.

Study of thermal-hydraulics of a sinusoidal layered heat exchanger for MSR

Plate-type heat exchangers have been investigated as promising heat exchangers for molten salt reactors. It has been found that the heat transfer coefficient of complex channel geometries such that with S-shaped fins studied as printed circuit heat exchangers (PCHE) is generally very high. However, because there is a risk of blockage in the heat exchanger of the extremely small flow area for a molten salt reactor, a sinusoidal-shaped heat exchanger with a large flow area and a simpler shape has been selected. Thermal-hydraulic analyses of several types of flow channels have been performed using the FLUENT code. The turbulence model and the wall function selected in the present calculation were verified in advance by the experimental data. The calculated results were compared with the experimental results using the zigzag flow channels and experimental correlations. The computation results using FLUENT reproduce the empirical correlations previously obtained with smooth ducts for heat transfer and pressure drop. These comparisons also demonstrate that the turbulence model and the mesh of the computation in this study are appropriate. The proposed heat exchanger with a sinusoidal flow geometry is promising because the heat transfer coefficient is larger than that of the empirical correlation for a smooth duct and is almost the same as that of zigzag geometry. The heat transfer coefficient of the sinusoidal geometry is approximately twice as large as the Dittus and Boelter correlation. The friction factor is far below that of the zigzag geometry. In the case of a heat exchanger of this shape, it has been found from the extrapolation of the results of FLUENT that the number of channels required to remove heat of 175 MW is approximately 6000 sets of hot and cold channels. This result is also supported by a real-scale analysis using the RELAP5-3D code.

Feasibility Study of the CO2 Regenerator Parameters for Oxy-Fuel Combustion Power Cycle

The atmosphere carbon dioxide content grows subsequently due to anthropogenic factors. It may be considerably mitigated by the development of thermal power plants with near zero emissions. A promising way is the transition to the semi-closed oxy-fuel combustion power cycles with carbon dioxide and water vapor mixture as a working fluid. However, their wide implementation requires reduction of the metal consumption for the highly efficient regeneration system. This paper discloses the results of feasibility study for the regeneration system of the prospective oxy-fuel combustion power plant. The effect of operating parameters on the cycle energy efficiency, overall dimensions, and the cost of the regenerator was determined. Underheating increase in the regenerator by 1 °C leads to the net efficiency factor drop of the oxy-fuel combustion power cycle by 0.13% at average and increases fuel costs by 0.28%. Increase of pressure drop in the hot channel by 1% leads to efficiency drop by 0.14%. The optimum set of design and operating parameters of the feed heating system has been determined, which ensures the best technical and economic indicators of electrical power generation: the minimum cumulative costs are achieved when underheating in the regenerator is 20 °C and pressure drop in the hot channel is 4%, under the use of S-shaped fins channels.

Experimental study on heat transfer and pressure drop characteristics in a microchannel heat exchanger assembly with S-shaped fins

Experimental studies on the water-to-water heat transfer and flow resistance characteristics of a microchannel heat exchanger assembly with S-shaped fins were conducted using the high-temperature and high-pressure water open experimental loop at Shanghai Jiao Tong University. The effects of different Reynold numbers of both the hot and cold sides on the heat transfer and flow resistance characteristics were analyzed. Correlations for the Nu number and friction factor for both the hot and cold sides were gained based on the experimental data. The same Nusselt correlation was used for both the hot and cold sides, and the fitting results showed satisfactory accuracy, where the fitting error was within ±15%. The power-law scheme was used to fit the total friction factor correlations, and the fitting results showed a fitting error of ±15% and ±12% for the hot and the cold sides, respectively. The correlations proposed in this study can be used in the design of this type of heat exchanger.

Thermal hydraulic characteristics of trans-critical natural gas flowing through staggered S-shaped fin microchannel

As a newly-developed microchannel heat exchanger, printed circuit heat exchanger (PCHE) is employed as the primary LNG vaporizer in floating storage and re-gasification unit for high efficiency and compactness. In this paper, thermal–hydraulic characteristics of trans-critical NG through the improved staggered S-shaped fin channels were numerically investigated. Variation tendencies of fin performance under different operating pressures and a wide range of Reynolds numbers were analyzed. Sensitivity analyses on the effect of various thermophysical properties on heat transfer around pseudo-critical temperature revealed that heat transfer capacity were deeply affected by specific heat, and effects of thermal conductivity and viscosity could be canceled each other. Additionally, to further estimate forced convective heat transfer mechanism, common features of HTC and f factor distributions were analyzed and some reasonable criteria were also discussed. The results showed that except for a few data points across critical temperature affected by entrance effect, the peak HTC always appeared in the vicinity of the pseudo-critical points. Furthermore, the Bo of 10-5 and q+ of 5×10- 4 could be adopted to analyze buoyancy and flow acceleration influences qualitatively. The simulated results agreed with the predictions from Ngo Correlation within 16.32% and 12.36% errors respectively for HTC and f factors, which implied that though the drastic local changes of performance tendency could not be predicted well, suitable correlations were sufficiently accurate for engineering applications.

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.

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.

Thermal-aerodynamic performance measurement of air heat transfer fluid mechanics over S-shaped fins in shell-and-tube heat exchangers

Forced convection heat transfer of pure air fluid inside an open channel as a section of ashell-and-tube heat exchanger has been evaluated, numerically. S-shaped obstacles (or fins)have been used in the mentioned channel. Air flow inside the channel has been considered asa turbulence flow. Governing equations have been solved throughout computational finitevolume method. These equations have been analyzed using k-e model. The results have beendesigned based on geometry of S-shaped obstacles. Mentioned results have been shown inthe form of temperature profiles, and heat transfer distribution. This type of analysis is veryuseful in many industry and engineering related problem for getting good idea about thephysical model whenever the analytic solution is out of reach.

Multi-objective optimization of supercritical carbon dioxide recompression Brayton cycle considering printed circuit recuperator design

Supercritical carbon dioxide recompression Brayton cycle is well suited to a broad range of applications including nuclear and concentrated solar energy. As printed circuit recuperators are employed to optimize the thermal performance of the cycle, the recuperator optimal design is required with the objective of maximizing the cycle thermal efficiency and minimizing the total cycle cost. In this paper, a thermo-economic model of recompression Brayton cycle with the S-shaped fin printed circuit recuperator is developed to perform multi-objective optimization considering the recuperator design parameters (i.e. mass fluxes and enthalpy efficiencies of recuperators and recompression fraction). Nondominated sorting genetic algorithm is used to obtain Pareto frontier. The results show that compared to the mass fluxes, the enthalpy efficiencies of recuperators and recompression fraction play more important roles in the optimization. From the Pareto frontier, the optimum range of the cycle thermal efficiency is 0.4303–0.5380 and that of the total cycle cost is 7.468 M$–12.31 M$. As high cycle thermal efficiency is preferred, the high recompression fraction, high mass flux and high enthalpy efficiency of low temperature recuperator, low mass flux and high enthalpy efficiency of high temperature recuperator are required. In contrast, as low cycle cost is preferred, the opposite selections of design parameters are required.

An adaptive flow path regenerator used in supercritical carbon dioxide Brayton cycle

The supercritical CO2 recompression Brayton cycle is proposed to be used as a typical application in 4th generation reactors. In the cycle, the performance of the regenerator has a significant impact on the performance of the entire cycle. As the specific heat capacity and density of SCO2 change significantly with the temperature and pressure. Therefore, in this paper, a new adaptive flow path regenerator is proposed and designed in order to further improve the performance of the regenerator, in which the flow path sizes varied with the CO2 density when the CO2 flowing through the regenerator. Firstly, the heat transfer performance and hydraulic performance of the adaptive flow path regenerators are analyzed in detail by simulation, and it is verified in theory that the design of new adaptive regenerator is feasible. Then, a new adaptive flow path regenerator with S-shaped fins is manufactured by metal 3D printing technology and the performances of the new regenerator are tested by a SCO2 experimental platform. The experimental results are consistent with simulation results and show that the performances of the new regenerator are significantly improved: the pressure loss can be reduced up to 69%, the effectiveness can be increased by nearly 2%, and the compactness and heat transfer rate can be improved at the same time.

Optimization of fin arrangement and channel configuration in an airfoil fin PCHE for supercritical CO2 cycle

As a new type of discontinuous fin, airfoil fin (AFF) can bring a better thermal-hydraulic performance than Zigzag fin and S-shaped fin when applied to PCHE using supercritical CO2 as a working fluid. In this study, the effects of AFF arrangements on heat transfer and flow resistance are investigated. The results show that a sparser staggered arrangement of fins can lead to a better thermal-hydraulic performance in an AFF PCHE and the flow resistance plays a major role in determining the overall performance. It concludes that reducing the flow resistance needs to be considered first in the optimal design of a PCHE using supercritical CO2 as working fluid. Furthermore, a new fin structure (modified AFF) is proposed for flow resistance reduction and is proved to be better than the AFF.

Ｓ字型フィンを有するマイクロチャンネル熱交換器に関するＮｕｓｓｅｌｔ数相関式

An advanced microchannel heat exchanger (MCHE) with S-shaped fins can realize high heat transfer performance and reduced pressure drop performance. Simulation calculations by the three-dimensional computational fluid dynamics (3D-CFD) code were examined for a MCHE with S-shaped fins using carbon dioxide (CO2) as the working fluid in the wide range of inlet pressure and temperature conditions, which are from subcritical conditions to supercritical conditions. From the numerical results, a Nusselt number correlation was obtained using multivariable analysis. The standard deviation between the correlation and numerical results was 6.1%. A MCHE test piece with the same flow channel configuration as that for numerical simulation was manufactured, and experimental verification of the thermal-hydraulic performance of the test piece was examined. The heat transfer performance of the test piece was calculated using the Nusselt number correlation and was compared with experimental results. Numerical heat transfer performance showed good coincidence with a deviation of 2.5%. The conditions used in numerical simulation include the conditions of a recuperator and an intermediate heat exchanger of CO2 gas turbine cycle. Using the obtained Nusselt number correlation, designing these heat exchangers becomes easier.

Nusselt number correlations for a microchannel heat exchanger hot water supplier with S-shaped fins

Using 3D-CFD code, Nusselt number correlations for a microchannel heat exchanger (MCHE) with S-shaped fins used for hot water suppliers are obtained through numerical experiments and then validated. The supercritical carbon dioxide working fluid is assumed to operate around the pseudo-critical point, where fluid properties change radically. Calculations with 20 different temperatures are executed to produce Nusselt number correlations for each side. The fluid inlet temperature in each calculation is defined as 2 °C lower or higher than the constant wall temperature, respectively, for cold and hot side simulations. The small temperature difference of 2 °C is sufficiently small to regard thermal–hydraulic properties as constant. A new integrating method using the correlations to calculate the heat-transfer-performance is proposed. The resultant heat-transfer-performance is compared with that of another numerical result, which is reduced from large geometry and integration. The results agree within 3% error; the calculation accuracy of the method is confirmed. Experimental results with MCHE verify the correlations. The difference is approximately 5%. Using few computer resources, these Nusselt number correlations and the heat-transfer-performance calculation methods using correlation information are sufficiently accurate to evaluate heat exchangers.

Advanced Microchannel Heat Exchanger with S-shaped Fins

Fin shape effects on thermal-hydraulic characteristics were studied for a Microchannel Heat Exchanger (MCHE) with S-shaped fins using 3D-CFD and changing the fin parameters: fin angle, overlapping length, fin width, fin length, and edge roundness. The fin angle effect on the pressure drop is consistent with the equation obtained experimentally by Weisbach for a circular bent tube: the pressure drop in the S-shaped fin configuration results from bent flow. The overlap of fins with those located immediately downstream at the offset position provides a guide wing effect that reduces the pressure drop remarkably. The overlap was changed by changing the fin radial position and arc length. The pressure drop was minimized when the downstream fins are placed in the middle of the bent flow channels formed by the fins upstream, which differs from Ito's configuration obtained from experiments with a single bent duct. Regarding arc length, the pressure drop is minimized at the standard overlapping length, which was formed to have the longest arc without a change in channel width. Shorter arc lengths from the optimum value by 30 and 50%, respectively, give 2.4 and 4.6% decreases in the heat transfer rate and 17 and 13% increases in the pressure drop. Thinner fins show better thermal-hydraulic performance for fin widths of 0.2–0.8 mm. However, the pressure drop reduced by the longer fin and heat transfer rate was also reduced. Rounded fins with 0.1mm radius increased the pressure drop by about 30% compared with that of the fin designed with no roundness.

Advanced Microchannel Heat Exchanger with S-shaped Fins

Fin shape effects on thermal-hydraulic characteristics were studied for a Microchannel Heat Exchanger (MCHE) with S-shaped fins using 3D-CFD and changing the fin parameters: fin angle, overlapping length, fin width, fin length, and edge roundness. The fin angle effect on the pressure drop is consistent with the equation obtained experimentally by Weisbach for a circular bent tube: the pressure drop in the S-shaped fin configuration results from bent flow. The overlap of fins with those located immediately downstream at the offset position provides a guide wing effect that reduces the pressure drop remarkably. The overlap was changed by changing the fin radial position and arc length. The pressure drop was minimized when the downstream fins are placed in the middle of the bent flow channels formed by the fins upstream, which differs from Ito's configuration obtained from experiments with a single bent duct. Regarding arc length, the pressure drop is minimized at the standard overlapping length, which was formed to have the longest arc without a change in channel width. Shorter arc lengths from the optimum value by 30 and 50%, respectively, give 2.4 and 4.6% decreases in the heat transfer rate and 17 and 13% increases in the pressure drop. Thinner fins show better thermal-hydraulic performance for fin widths of 0.2–0.8 mm. However, the pressure drop reduced by the longer fin and heat transfer rate was also reduced. Rounded fins with 0.1mm radius increased the pressure drop by about 30% compared with that of the fin designed with no roundness.

Heat transfer and pressure drop correlations of microchannel heat exchangers with S-shaped and zigzag fins for carbon dioxide cycles

A new microchannel heat exchanger (MCHE) with S-shaped fins was developed using the three-dimensional computational fluid dynamics (3D CFD) FLUENT code. The MCHE provided 6–7 times lower pressure drop while maintaining heat-transfer performance that was almost equivalent to that of a conventional MCHE with zigzag fins. This study was done to confirm the simulation results of thermal-hydraulic performance using a supercritical carbon dioxide loop, and to propose empirical correlations of Nusselt numbers and pressure-drop factors for a new MCHE with S-shaped fins and a conventional one with zigzag fins. This study is also intended to confirm the independence of Pr obtained in the previous study by widely varying Pr from 0.75 to 2.2. Experimental results show that the pressure-drop factor of the MCHEs with S-shaped fins is 4–5 times less than that of MCHE with zigzag fins, although Nu is 24–34% less, depending on the Re within its range. The Nusselt number correlations are expressed, respectively as Nu S-shaped fins = 0.1740 Re 0.593 Pr 0.430 and Nu zigzag fins = 0.1696 Re 0.629 Pr 0.317 for the MCHE with S-shaped and zigzag fins, and their pressure-drop factors are given as f S-shaped fins = 0.4545 Re −0.340 and f zigzag fins = 0.1924 Re −0.091. The Nu correlation of the MCHE with S-shaped fins reproduces the experimental data of overall heat transfer coefficients with a standard deviation (1 sigma) of ±2.3%, although it is ±3.0% for the MCHE with zigzag fins. The calculated pressure drops obtained from pressure-drop factor correlations agree with the experimental data within a standard deviation of ±16.6% and ±13.5% for the MCHEs with S-shaped and zigzag fins, respectively.

New printed circuit heat exchanger with S-shaped fins for hot water supplier

A new PCHE with an S-shaped fin configuration was applied to a hot water supplier in which cold water of 7 °C is warmed to 90 °C through heat-exchange with supercritical CO 2 of 118 °C and 11.5 MPa pressure. The fin and plate configurations were determined using 3D CFD simulations for the CO 2 side and H 2O side and the thermal–hydraulic performance of hot water supplier was evaluated. Compared with a hot water supplier that is currently used in a residential heat pump, the new PCHE provides about 3.3 times less volume; and lower pressure drop by 37% in the CO 2 side and by 10 times in H 2O side.