Offset Strip-fin Heat Exchanger Research Articles

Influence of polishing process on surface morphology and thermo-hydraulic performance of additively manufactured Gyroid-structured heat exchanger

As additive manufacturing technology overcomes fabricating obstacles, the Gyroid structure, characterized by its intricate topology, emerges as a promising heat exchanger configuration. Nonetheless, the substantial surface roughness intrinsic to additive manufacturing considerably constrains the practical deployment of Gyroid-structured heat exchangers. This study focuses on the post-treatment of a Gyroid-structured heat exchanger, manufactured by selective laser melting, employing abrasive jet polishing. It further investigates the influence of this process on surface morphology and thermo-hydraulic performance, utilizing characterization, experimental, and numerical methodologies. Surface characterization indicates that the polishing process markedly diminishes the distribution density of protrusion microstructures on the internal surface. Pre-polishing surface roughness results in an area expansion of 106–123%, which is reduced to 20–45% after polishing. Moreover, the coupling effect of concurrent reduction in wall thickness and surface roughness enables the polished prototype to attain a 40% decrease in differential pressure, while maintaining nearly identical heat transfer capacity. The overall performance evaluation criterion of the post-polishing prototype consistently surpasses the offset strip fin heat exchanger by 12.94–26.09%, within a Reynolds number range of 300–3000. This study introduces a validated technology for modifying the internal surface of additively manufactured heat exchangers, especially Gyroid-structured heat exchangers, thereby facilitating its practical utilization in cutting-edge fields.

Performance Analysis of a Compact Offset Strip Fin Heat Exchanger for Lubrication System in Aero Engine

Abstract As a typical fuel-oil heat exchanger, an offset strip fin heat exchanger (OSFHX) can ensure the efficient and stable operation of the aero engine lubrication system. The paper establishes 20 kinds of numerical models of OSFHX that are verified by experiments. The effects of different structural parameters on the performance of lubricating oil in OSFHX were systematically studied. Based on dimensional analysis, the prediction model which can describe the overall performance of the OSFHX is obtained. The results show that with the decrease of fin distance (s), fin length (l), fin height (h), fin thickness (t), and fin shape angle (α), the heat transfer performance of the OSFHX is enhanced and the resistance is increased. With the decrease of s and h, and the increase of t and α, the comprehensive performance of the OSFHX is enhanced. The OSFHX exhibits the optimal performance when l = 4 mm. α has the most significant effect on the comprehensive performance of the OSFHX, successively followed by h, s, t, and l. The average error of Colburn factor (j) and friction factor (f) prediction models is 4.09% and 5.31%, respectively, which can realize the theoretical calculation of the performance of the OSFHX for aviation.

Numerical study of heat transfer and fluid flow in the offset strip-fin heat exchanger: A fin-by-fin analysis

Heat transfer and fluid flow in the offset strip-fin heat exchanger are studied numerically, fin by fin. The impact of the offset strip-fin geometry on j/f performance is also evaluated. The mathematical model is validated against j- and f-factor correlations from the literature. The numerical analysis revealed that the offset strip-fin heat exchanger achieves best j/f performance in the laminar flow region (Redh < 700). At higher Reynolds numbers, the j/f factor deteriorates under the impact of flow recirculations, oscillatory wakes and the contribution of form drag. Compared to the continuous rectangular fin, the offset strip-fin increases the air-side heat transfer coefficient by 50% at Redh = 100 and by 120% at Redh = 4000 while the pressure drop increases by a factor of 3–5. Generally, the offset strip-fin achieves j/f performance between 0.20 and 0.30, with maximum values found in the laminar flow region (Redh 〈1000). Offset strip-fin geometries with reduced fin space and increased wall thickness strongly affect the form drag, which reduces the j/f performance, especially for Redh > 1000. The fin height weakly influences the performance, and the j/f factor is between 0.22 and 0.23 for a wide range of fin heights.

Thermo-hydraulic performance prediction for offset-strip fin heat exchangers using artificial neural networks

In this study, an artificial neural network (ANN) model was applied to predict the thermo-hydraulic performance of the offset-strip fin heat exchanger. The ANN model was used for predicting the thermo-hydraulic performance to improve the prediction accuracy and extend the applicable range compared to the results of using the empirical equations reported in previous studies. The main parameters of these empirical equations were fin height (0.134 < α < 0.997), fin length (0.012 < δ < 0.048), fin width (0.041 < γ < 0.121), and Reynolds number (120 < Re <104). In addition, the Fanning friction factor f and the Colburn factor j were considered as the outputs of the ANN model. The impact of the parameters on the thermo-hydraulic performance of the heat exchanger was quantitatively evaluated, and the prediction accuracy was improved over a wide range for the thermo-hydraulic performance generated by the ANN model. Thus, the results obtained using the ANN model agreed well with the experimental data over a wider range than possible for the previous empirical correlations, showing extremely high accuracy and validity of the ANN model in comparison to the empirical equations.

Multi-objective optimization of an offset strip fin heat exchanger for waste heat recovery in electric vehicles

To increase short driving range of electric vehicle, it is important to reduce power consumption of heat pump system. In this study, an offset strip fin heat exchanger with perpendicular flow is investigated to improve the performance of an electric vehicle heat pump using waste heat. The correlations of the Colburn and friction factor are developed using the experimental data. The simulation results are compared to the experimental results and are validated within temperature and pressure errors of 1.51% and 1.55%, respectively. A multi-objective optimization is performed to maximize the thermal–hydraulic performance of the offset strip fin heat exchanger with six independent design variables via the approximation-assisted optimization technique. The five optimal designs exhibit a 3.7% increase in the heat transfer rate and a 42.1% decrease in the pressure drop for the main simulation condition. Sensitivity analysis and parametric studies are conducted to analyze the effects of each design variable. The results reveal that the fin wrinkle angle, fin height, fin length, and fin spacing had a significant impact on the thermal–hydraulic performance of the offset strip fin heat exchanger.

Overall Pressure Loss and Heat Transfer Performance of Additively Manufactured Offset Strip Fins Used in Compact Heat Exchangers

Abstract Preliminary heat exchanger design relies heavily on correlations for overall heat transfer and pressure drop performance, particularly for heat transfer augmentation features such as fins. Extensive work has been performed by the research community to develop these correlations for the numerous designs. However, with the new technology of metal additive manufacturing and the resultant surface roughness, the traditional correlations and design considerations related to performance need to be adjusted. As a result, two metal additively manufactured offset strip fin heat exchanger geometries with different fin spacing are studied for heat transfer and pressure drop performance and compared with traditional correlations. Deviations between the additively manufactured geometries and previous correlations for smooth fins are found and are further amplified as the surface roughness-to-hydraulic diameter ratio is increased. Furthermore, the surface roughness from the additive process results in a constant friction factor behavior at high Reynolds numbers, which is unlike behavior observed for conventionally manufactured fins. Considerations for both the laminar and turbulent flow regimes are needed for correct performance prediction. A final offset strip fin geometry with a change in the fin spacing every third of the way through the flow path is tested. This study found that the orientation of fin spacing, wider spaced to tightly spaced or tightly spaced to wider spaced, did not have a significant effect on pressure drop or heat transfer. However, the study found a method for predicting the performance which will become important as additive manufacturing increases the complexity of heat exchanger designs.

Numerical investigation of heat transfer and pressure drop characteristics in an offset strip fin heat exchanger

This paper presents a numerical simulation to determine the air-side heat transfer and the pressure drop characteristics of a flat tube heat exchanger with offset strip fin. The effects of the fin bending ratio such as 29%, 36%, 44%, 50%, and the fin spacing such as 2.10 mm, 2.35 mm, 2.60 mm on the performance of the heat exchanger are studied by using a commercial CFD software. The air having constant viscosity, thermal conductivity, and density enters the heat exchanger at 298 K and the wall temperature of the strip fins is considered as constant at 314 K. Variations of the heat transfer coefficient and the pressure drop in the airside are presented with respect to the frontal air velocity while Colburn j-factor and the friction factor f are presented with respect to the airside Reynolds number ranging from 200 to 1200. Finally, the thermal-hydraulic performance of all investigated cases is compared by using the volume goodness factor, j/f 1/3. The results show that the air-side heat transfer coefficient and the pressure drop increase when the frontal air velocity ascends. The air-side heat transfer coefficient decreases with the increase of fin spacing. The fin bending ratio does not have a significant effect on the pressure drop in the considered fin spacing. Both the Colburn j-factor and friction factor reduce with the increment of Reynolds number and fin spacing.

Improved heat transfer and friction correlations of aluminum offset-strip fin heat exchangers for helium cryogenic applications

• Improved performance correlations of cryogenic helium through OSFs were proposed. • Comparative thermal–hydraulic performance at different temperatures were studied. • Accuracy and robustness of the correlations’ prediction ability were validated. • Sensitivity of Re , Pr and η f on j values in laminar and turbulent regions was analyzed. • Correlations were qualified for OSF performance prediction in helium refrigerators. Aluminum plate-fin heat exchangers (PFHEs) with offset-strip fins (OSFs) are widely used in modern helium liquefaction/refrigeration systems characterized by enhanced heat transfer abilities and high compactness. This study numerically and experimentally investigated the thermal–hydraulic characteristics of cryogenic helium gas flowing through various OSF channels. Through the comparative tests conducted by well-validated numerical model as well as the contrast experiments respectively at room and nitrogen liquefaction temperatures, the results indicated that the OSF performance was not only affected by fin geometrical structures, but also deeply influenced by additional effect factors under actual cryogenic operating conditions. Based on the orthogonal table with 0.077 ⩽ α ⩽ 1.103 , 0.008 ⩽ δ ⩽ 0.15 and 0.029 ⩽ γ ⩽ 0.333 , the heat transfer and pressure drop performance of OSFs was systematically studied at a wide range of Re number ( 200 ⩽ Re ⩽ 12000 ) in three common refrigeration stages (300 K @ 12 bar, 77 K @ 6 bar and 20 K @ 2 bar). To improve the prediction accuracy of the correlations at low temperatures, the non-dimensional Pr Number and iteratively-solved fin efficiency η f that considering the thermophysical property variations of fluid and metal were introduced in the correlations of Colburn j and Fanning friction f factors. Compared with the experimental data, the proposed model had strong robustness of prediction ability, with the predicted errors of 11.33% and 22.49% respectively for j and f factors. Additionally, the effect of Pr number and η f occupied different weights in the j factors from laminar to turbulent flow. The sensitivity of the heat transfer performance with respect to each condition parameter was also discussed. Different from the most of the existing correlations derived from the fitted data based on common steam-to-air tests, the proposed correlations were more qualified for predicting the thermal–hydraulic performance of OSF channels in PFHEs through the cool-down process in helium refrigerators.

Thermal-hydraulic performance of TiO2-water nanofluids in an offset strip fin heat exchanger

The flow and heat transfer characteristics of the TiO2-water nanofluid assuming as a single-phase in the rectangular offset strip fin structure for different Reynolds number (500-1000) and TiO2 nanoparticle volume concentration values (0-4%) were investigated numerically under 3-D, steady-state, and laminar flow conditions. Simulations were also performed for 1% and 4% nanoparticle volume concentrations of Al2O3-water nanofluid, and the results were compared with those of TiO2-water nanofluid. Results show that when the TiO2-water nanofluid is used, the heat transfer rate, heat transfer coefficient, and Nusselt number increase with increasing both Reynolds number and nanoparticle volume concentration, and parallel to these, both pressure loss, and pumping power increase. Considering the values of the performance evaluation criteria number, it is clear that the use of TiO2-water nanofluid in offset strip fin structure at all Reynolds numbers examined between 1-4% volume concentration values is quite advantageous. It is observed that TiO2-water nanofluid is much superior to Al2O3-water considering the performance evaluation criteria number. When the Reynolds number is 1000 and the volume concentration value of the TiO2 nanoparticle is 4%, the performance evaluation criteria number value is found to be 1.19, that is, there is a 19% increase compared to water. It is considered that the results of this study can be used as important data on the design of automobile radiators, air-conditioning, and defense.

Optimum Design, Heat Transfer and Performance Analysis for Thermoelectric Energy Recovery from the Engine Exhaust System

Thermoelectric waste heat recovery can improve the thermal efficiency of internal combustion engines and reduce CO2 emissions. In this study, a mathematical optimization using a genetic algorithm method is applied to obtain the optimal fin parameters of a rectangular offset-strip fin heat exchanger, used with an automotive thermoelectric generator (TEG) system. Three fin parameters are considered (fin spacing, fin thickness and fin height). Their effect on the exhaust pumping power, the exhaust heat transfer coefficient and the system performance is explored. The main goal is to maximize the net power output of the system. Results show that fin spacing has the most significant effect on the system performance. Moreover, when fin spacing is reduced below 0.5 mm, a negative net power output is obtained. By comparing the performance of stainless-steel (SS) and copper heat exchangers, it was found that the SS heat exchanger requires smaller fin spacing and fin height, which induces a higher pressure drop. TEGs with higher maximum operating temperature will allow further utilization of the exhaust heat, without a decline in performance due to overheating. Finally, a maximum net power output of 553.3 W is achieved using the copper heat exchanger and commercial bismuth-telluride (Bi2Te3) thermoelectric modules.

A correlation for heat transfer and flow friction characteristics of the offset strip fin heat exchanger

The correlation for heat transfer and flow friction characteristics of fins is the basis for the optimization of heat exchangers, and it is of great importance to develop generally accurate formulas. To study the hydrodynamics and heat transfer characteristics of offset strip fins, Fluent is adopted to conduct the numerical simulation. Based on the calculation results of empirical correlations, the fluid constitutive model under different Reynolds numbers is determined in order to ensure the prediction efficiency and accuracy of offset strip fins. Good agreements are obtained between the numerical simulation and the Manglik & Bergles correlation, which verifies the validity and reliability of the numerical simulation method. Due to the fact that the traditional empirical formula is not able to cover the general specifications of Chinese domestic offset strip fins, the correlation of flow and heat transfer characteristics is improved based on the numerical simulation results and the industrial standard (Aluminum plate-fin heat exchanger NB/T 47006-2009). By coupling the Manglik & Bergles equation with the ALEX equation, a new relational expression of offset strip fins is proposed.

Transient analysis of an FHR coupled to a helium Brayton power cycle

The Fluoride salt-cooled High-temperature Reactor (FHR) features a passive decay heat removal system and a high-efficiency Brayton cycle for electricity generation. It typically employs an intermediate loop, consisting of an intermediate heat exchanger (IHX) and a secondary heat exchanger (SHX), to couple the primary system with the power conversion unit (PCU). In this study, a preliminary dynamic system model is developed to simulate transient characteristics of a prototypic 20-MWth Fluoride salt-cooled High-temperature Test Reactor (FHTR). The model consists of a series of differential conservation equations that are numerically solved using the MATLAB platform. For the reactor, a point neutron kinetics model is adopted. For the IHX and SHX, a fluted tube heat exchanger and an offset strip-fin heat exchanger are selected, respectively. Detailed geometric parameters of each component in the FHTR are determined based on the FHTR nominal steady-state operating conditions. Three initiating events are simulated in this study, including a positive reactivity insertion, a step increase in the mass flow rate of the PCU helium flow, and a step increase in the PCU helium inlet temperature to the SHX. The simulation results show that the reactor has inherent safety features for those three simulated scenarios. It is observed that the increase in the temperatures of the fuel pebbles and primary coolant is mitigated by the decrease in the reactor power due to negative temperature feedbacks. The results also indicate that the intermediate loop with the two heat exchangers plays a significant role in the transient progression of the integral reactor system.

Comparative analysis of compact heat exchangers for application as the intermediate heat exchanger for advanced nuclear reactors

A comparative evaluation of alternative compact heat exchanger designs for use as the intermediate heat exchanger in advanced nuclear reactor systems is presented in this article. Candidate heat exchangers investigated included the Printed circuit heat exchanger (PCHE) and offset strip-fin heat exchanger (OSFHE). Both these heat exchangers offer high surface area to volume ratio (a measure of compactness [m2/m3]), high thermal effectiveness, and overall low pressure drop. Helium–helium heat exchanger designs for different heat exchanger types were developed for a 600MW thermal advanced nuclear reactor. The wavy channel PCHE with a 15° pitch angle was found to offer optimum combination of heat transfer coefficient, compactness and pressure drop as compared to other alternatives. The principles of the comparative analysis presented here will be useful for heat exchanger evaluations in other applications as well.

Thermo-hydraulic behavior of ice slurry in an offset strip-fin plate heat exchanger

Ice slurry is a promising alternative to conventional single-phase coolants in indirect refrigeration systems. In this paper, an experimental analysis of an offset strip-fin heat exchanger operating with ice slurry as working fluid is presented. The pressure drop and thermal performance have been determined. In order to obtain the partial thermal resistance in the ice slurry side an empirical correlation for the secondary fluid side was determined by applying the Wilson plot method in a set of tests performed previously. An empirical correlation in terms of the Colburn j-factor to describe the thermal behavior of the heat exchanger with ice slurry was obtained. On the other hand, the direct pressure drop measurements operating with different flow rates and ice fractions are shown and compared with values obtained with single-phase fluids. Pressure drop instabilities have been observed for flow rates lower than the nominal value provided by the manufacturer.

Single phase pressure drop and two-phase distribution in an offset strip fin compact heat exchanger

Experiments have been conducted in a compact heat exchanger with two-phase inlet conditions and vertical upflow in order to study the flow behavior. The test section consists of an offset strip fin heat exchanger with a rectangular cross-section (dimensions: 1 m × 1 m × 7.13 mm). The distributor was designed to optimize two-phase flow distribution. In a preliminary step, pressure drop of single phase flow in offset strip fins is needed to assess the quality of the distribution in the single phase case. For that, pressure drop of single phase flow has been measured in the experimental loop. Pressure drop has also been analysed numerically via CFD simulations. For low Reynolds numbers, numerical results show good agreement with experimental measurements. In a second step, the two-phase flow distribution at the outlet was characterized using air and water as working fluids and for different operating conditions. This characterization consists of the measurement of gas and liquid flow rates in different zones evenly distributed at the outlet. We observed that high air flow rates led to a more homogenous distribution.

Analysis of heat transfer and pressure drop characteristics in an offset strip fin heat exchanger

A steady-state three-dimensional numerical model was used to study the heat transfer and pressure drop characteristics of an offset strip fin heat exchanger. Water was the heat transfer medium, and the Reynolds number Re dh ranged from 10 to 3500. Variations in the Fanning friction factor f and the Colburn heat transfer factor j relative to Re dh were observed. General correlations for the f and j factors were derived, and these could be used to analyze fluid flow and heat transfer characteristics of offset strip fins in the laminar, transition, and turbulent regions. Finally, three performance criteria ( j/ f, j/ f 1/3, and JF) were adopted, and the best performance criteria for the cases Pr = 7 and Pr = 50 were chosen to be JF and j/ f 1/3, respectively.

The Parametric Study of an Innovative Offset Strip-Fin Heat Exchanger

Offset strip-fin heat exchangers have numerous applications throughout various industries because they can provide a large amount of heat transfer area in a small volume. The widespread use of the offset strip-fin design has ensured that there are numerous dimensional variations and shown that changes in dimensional parameters affect performance. It is then important to understand how the geometry of an offset strip-fin heat exchanger can affect its performance. Therefore, an investigation into the parametric effects on the global performance of an innovative high-temperature offset strip-fin heat exchanger was numerically performed in this study, where the numerical solution was obtained through a finite-volume method. Computations were carried out for each of the heat exchanger’s geometrical parameters: fin thickness (t), fin length (l), channel height (H), spanwise pitch (px), and the newly introduced gap parameter (g). Also, the effects of rounding the fins leading and trailing edges were investigated, while the heat exchanger’s volume, mass flow rates, and inlet temperatures were kept constant. The results are presented in the form of pressure drops and heat transfer rates, and the coefficient of performance parameter shows that fins with rounded leading and trailing edges outperform fins with rectangular edges.

An Experimental Study of the Friction Factor and Mass Transfer Performance of an Offset-Strip Fin Array at Very High Reynolds Numbers

Thermal-hydraulic performance data for offset-strip fin arrays are readily available in the range Re&lt;10,000. However, in emerging applications in automotive and aerospace systems, where fan power is not a constraint and compactness is important, it may be desirable to operate offset-strip fin heat exchangers at very high Reynolds numbers. In this paper, friction factor and mass transfer performance of an offset-strip fin array at Reynolds numbers between 10,000 and 120,000 are characterized. A scale-model, eight-column fin array is used in pressure drop and naphthalene sublimation experiments, and the data are compared to predictions of performance given by available analytical models and extrapolations of the best available correlations. The friction factor data follow the correlation-predicted trend of decreasing monotonically as the Reynolds number is increased to 20,000. However, at higher Reynolds numbers, the friction factor increases as the Reynolds number increases and local maxima are observed in the data. Over the range investigated, the modified Colburn j factor decreases monotonically as the Reynolds number increases. For Reynolds numbers in the range 10,000&lt;Re&lt;120,000, well beyond that covered by state-of-the-art correlations, both the friction factor and Colburn j factor are roughly twice that predicted by extrapolating the best available correlations. The higher-than-predicted Colburn j factor at very high Reynolds numbers is encouraging for the use of offset-strip fin heat exchangers in emerging applications where compactness is of high importance.

A numerical investigation of heat transfer enhancement in offset strip fin heat exchangers in self‐sustained oscillatory flows

Numerical analysis of the instantaneous flow and heat transfer has been carried out for offset strip fin geometries in self‐sustained oscillatory flow. The analysis is based on the two‐dimensional solution of the governing equations of the fluid flow and heat transfer with the aid of appropriate computational fluid dynamics methods. Unsteady calculations have been carried out. The obtained time‐dependent results are compared with previous numerical and experimental results in terms of mean values, as well as oscillation characteristics. The mechanisms of heat transfer enhancement are discussed and it has been shown that the fluctuating temperature and velocity second moments exhibit non‐zero values over the fins. The creation processes of the temperature and velocity fluctuations have been studied and the dissimilarity between these has been proved.

Computation of the availability destroyed in offset strip-fin heat exchangers

Computation of the availability destroyed in offset strip-fin heat exchangers