Compact Plate-fin Heat Exchangers Research Articles

Heat Transfer and Pressure Drop in Plate Fin Heat Exchangers: A Numerical Approach

An apparatus for transferring thermal energy across an impermeable barrier between two or more fluids is a heat exchanger. The effective transmission of heat from a hot fluid to a cold fluid is its primary goal. The temperature differential between the two fluids directly affects this heat transfer. Using CFD study with FLUENT 2020 R1, the performance characteristics of the compact plate fin heat exchanger's improved surfaces are examined. The simulation of heat transfer and flow encompassed a variety of velocities including completely turbulent regions. The pressure, temperature, and velocity contours were taken from the Fluent simulations. To determine the heat exchanger's flow and heat transfer performance, numerical analysis has been done. Since boundary conditions are crucial to CFD, they have been carefully chosen. The flow field, heat transfer, thickness, and wavelength were all predicted using the software code for a range of air to water velocities. Three distinct wavelengths of numerical simulations for a plate-fin heat exchanger were used in the study (10, 20, and 30). There were changes to the fin thickness, entry locations, and air and water entry velocities. Solid Works and Ansys were used to create the geometry for the three-level fin models that were placed inside the heat exchanger, both with and without a cover. For determining the heat exchanger's geometry and fin isometry, three levels measuring 19.6 mm in height and 53.64 mm in width were constructed. The fins have a thickness of 0.2 to 0.4 mm. As the air and water velocities vary, so does the temperature inside the heat exchanger. Because the topmost layer is a warm stream's flow channel, the temperature rises there, whereas the opposite effect is seen close to the bottom layer. Convection heat transmission to the surroundings and conduction heat transfer through the heat exchanger's side plates are the causes of fluid temperature fluctuations in the depth direction.

Liquid Cooling Systems for Batteries of Electric Vertical Takeoff and Landing Aircraft

Batteries are the lynchpin of electric vertical takeoff and landing (eVTOL) aircraft, and the high discharge rates pose a critical challenge to the battery thermal management system (BTMS). This work presents a channeled liquid cooling technology-based BTMS for eVTOL aircraft. During the flight, the heat generated from the batteries is partly extracted by circulating liquid coolant within a wavy channel (WC) attached firmly to the battery cells. The heat is then transported into a plate-fin compact heat exchanger (HEX), where all the heat is dissipated into the atmosphere. We report sensitivity analyses of the HEX model to shed light on the impact of the relevant design parameters on the BTMS size, weight, and power. We also examine critical parameters of the coupled WC-HEX BTMS in a one-dimensional off-design analysis. We demonstrate that the liquid cooling system can maintain the battery operating temperature within acceptable levels with a mass of less than 20% of the battery pack mass. Battery degradation using the liquid cooling system is reduced by over three times compared to an air-cooled system for both tilt-wing and lift+cruise eVTOL aircraft.

Experimental investigation on condensation heat transfer coefficient and frictional pressure drop of low GWP refrigerant R1234yf on a wavy fin surface

Refrigerant R1234yf is an ideal substitute to replace R134a due to its lower value of global warming potential (GWP). The thermophysical properties of R1234yf are similar with R134a and thus it is considered as a potential replacement for R134a in thermal fluid systems. Further, it was noticed that there is a lack of analysis on the condensation of R1234yf in a brazed plate fin compact heat exchanger (CHE) employing wavy fins. In the present work, condensation heat transfer coefficient and frictional pressure drop of refrigerant R1234yf are investigated in a brazed plate fin compact heat exchanger with wavy fin surfaces. The test condenser with wavy fin surface was selected to examine the condensation heat transfer coefficient and frictional pressure drop using refrigerants R134a and R1234yf for varying mass flux and saturation temperatures. The present study also discusses the dependency of specific kinetic energy of refrigerant on frictional pressure drop. Further, using the experimental data of wavy fin surfaces, suitable correlations for the condensation heat transfer coefficient and frictional pressure drop of R1234yf were proposed. The present paper also reports the comparison made between refrigerants R134a and R1234yf. Comparison between R1234yf and R134a shows that condensation heat transfer coefficient and frictional pressure drop of R1234yf is 9–16 % and 10–17 %, respectively, lower than of R134a in the mass flux range 15–44 kg/m2s.

Enhanced Performance of Structurally Optimized Plate-Fin Heat Exchangers Through Numerical Modeling of Heat Transfer and Pressure Drop

This study aims to optimize the structure of compact Plate-Fin Heat Exchangers (PFHE) by incorporating corrugated fins and validating their improved performance through numerical modeling and simulation. The results provide valuable insights for refining application-specific design guidelines and enhancing the performance of PFHEs. Using Computational Fluid Dynamics (CFD), the PFHE geometry was created in SolidWorks and Ansys Fluent, with fins modeled in three layers inside the heat exchanger both with and without a cover. To investigate the fins' performance, flow field, and heat transfer, fin thickness, entry velocities, and locations of water and air were varied across three wavelengths (10, 20, and 30) during the numerical investigation. The analysis focused on the variations in pressure, temperature, and fluid velocity within the heat exchanger. Key findings include the observation that temperature distribution is influenced by the velocities of both water and air, with the upper layer experiencing a temperature increase due to the warm fluid stream, while the opposite effect is observed near the bottom layer. Furthermore, fluid temperature variation in the depth direction is attributed to conductive heat transfer through side plates and convective heat transfer to the surroundings. The outcomes of this study have the potential to reduce the pressure difference generated during heat exchange and increase the thermal efficiency of PFHEs.

Experimental and numerical investigation of additively manufactured novel compact plate-fin heat exchanger

Plate-fin heat exchanger (PFHX) is one of the vital compact heat exchangers due to its high heat transfer area per unit volume and promising potentials in industrial applications where dimensions and weight are limited. Additive manufacturing presents great potentials for fabricating novel compact heat exchangers. In this work, three types of compact heat exchangers including a PFHX with twisted fins, a PFHX with improved rectangular fins and a PFHX with conventional rectangular fins are manufactured using the laser powder bed fusion (LPBF) technology. The experimental tests together with numerical simulations are conducted to evaluate the thermal performance and pressure drop of the heat exchangers. The results show that PFHX with twisted fins exhibits superior thermal performance among the three heat exchangers, and the PFHX with improved rectangular fins has the highest experimental coefficient of performance (COP) and provides outstanding overall performance. Furthermore, the impact of LPBF accuracy on the performance of heat exchanger are discussed to provide guidance for future designs.

Heat transfer factor j and friction factor f correlations for offset strip fin and wavy fin of compact plate-fin heat-exchangers

A unique model of heat transfer factor "j" and friction factor "f" are developed for different types of fins, which are rectangular offset strip fin, rectangular wavy fin compact heat exchangers by considering the geometric variables such as plate space (Hp), fin pitch (Pf), hydraulic diameter (Dh), wave amplitude (Aa), fin length (λ), and Reynolds number (Re). The proposed j and f models provided 98% of experimental data points within ±20% and 82.3% of experimental data points within ±10% accuracy for OSF fins. Also, they provided 100% of Kays and London's experiential data points within ±5% accuracy for wavy fins. These proposed j and f models for a wide range (120–10000) of Reynolds number flows, including laminar and turbulent flows. j model provides maximum RMSPE 15% and 2% accuracy values for PFHE offset strip fins and wavy fin geometries, respectively. f model provides maximum RMSPE 17% and 3% accuracy values for PFHE offset strip fins and wavy fin geometries, respectively. Based on RMSPE and experimental data analysis, proposed j and f models were validated and better than existing models for offset strip fins and wavy fins.

Condensation heat transfer performance in multi-fluid compact heat exchangers with wavy and strip fins

The effect of different geometrical parameters of wavy and strip fins in a three-fluid plate-fin compact heat exchanger on the condensation heat transfer in the middle heat exchanger has been experimentally investigated. The three-fluid heat exchanger consisted of three heat exchangers with strip and wavy fins. In the examined system, the hot and cold fluids flowed through the adjacent heat exchangers (strip channels), while the middle heat exchanger (wavy channels) was occupied with a single-component two-phase flow (condensed vapor). The Nusselt number, the friction factor, the heat transfer surface contribution between the middle heat exchanger and each of the adjacent heat exchangers, and the thermal performance factor were calculated using the measured data at the inlets and outlets of the heat exchangers, and by using the thermal balance equations between the fluids passing through the heat exchangers. In the examined heat exchanger, the hot and cold flows had a cross-direction with the two-phase fluid flow. The two-phase Reynolds number, the vapor quality, and the heat transfer surface contribution of the middle heat exchanger with the adjacent heat exchangers were 50–4800, 0.1–0.67, and 0.19–0.7, respectively. The results show that the two-phase flow pattern in the wavy channels of the middle heat exchanger is stratified and wavy. According to the findings, a higher thermal performance factor is observed when the ratio of the wavy channel heat transfer surface to the heat transfer surface of the cold or hot flows is closer to 1. Also, with higher wave amplitude to wavelength ratios, lower pitch to height ratio of the fins, the lower wavelength to the fin length ratios, and lower fin pitch to wave amplitude ratios are obtained a higher thermal performance factor.

Paraffins as phase change material in a compact plate-fin heat exchanger - Part II: Validation of the “curve scale” hysteresis model for incomplete phase transitions

Technical-grade and mixed solid–liquid phase change materials (PCM’s), such as commercial paraffins, can show a complex non-isothermal phase transition behavior, possibly with hysteresis and supercooling, two-step transitions and asymmetric phase transition peaks. Phenomenological modeling approaches can use data-driven methods to derive phase transition models represented by enthalpy–temperature or apparent heat capacity–temperature curves. These curves are then linked with simulation models for heat transfer in thermal storages with PCM’s. If the phase change is significantly affected by hysteresis, different curves might be tracked either for heating or for cooling. This “curve track” modeling approach is straightforward and easy to implement. However, it shows a poor performance considering conditions with interrupted phase change, which are relevant for the partial charging and discharging operation of thermal storages. This contribution presents a novel so-called “curve scale” model. Its superior performance is proved for three commercial paraffins and experiments with 31 interrupted phase change scenarios.

Paraffins as phase change material in a compact plate-fin heat exchanger - Part I: Experimental analysis and modeling of complete phase transitions

Thermal energy storages with phase change materials (PCM’s) based on plate-fin and tube-fin (gas-to-liquid) heat exchanger (HEX) designs show a comparatively high heat transfer performance and compactness. High heat transfer rates allow for optimal storage designs and operation close to the PCM’s phase change temperature. However, industrial-grade solid–liquid PCM’s and mixtures usually show a non-isothermal phase change behavior over an extended temperature range, sometimes with multi-step transitions, hysteresis and supercooling. These complex phenomena depend on the physical dimensions of the PCM in the HEX and the operating conditions. They need to be verified for each particular application and cannot be neglected. This contribution presents an experimental and model-based analysis of the phase transition behavior of three commercial paraffins filled in compact plate-fin HEX’s. The results indicate that non-isothermal phenomena critically affect the storage temperatures. Their impact on the thermal performance can be studied using relatively simple numerical models.

Waste heat recovery in commercial gas-fired tumble dryers

Thermal drying is energy intensive due to the unavoidable thermodynamic constraint of supplying sufficient energy to evaporate the water (hfg > 2000 kJ kg−1). Textile dryers only use about half (∼55%) of the total input energy for drying. To reduce the wasted energy, exhaust gas recirculation and waste heat recovery using a recuperative heat exchanger are investigated numerically and experimentally. The two methods aim to recover energy from the exhaust stream typically at T < 55 °C for most of the drying period. Experiments are conducted on a commercial gas-fired tumble dryer. A theoretical model is developed to simulate and optimize the drying process. Recirculating the hot humid exhaust gases improves heat and mass transfer in the drum; however, the high humidity ratio of the recirculated air is not amenable to enhancing evaporation. An optimal recirculation ratio of 51% is found to reduce the specific moisture extraction ratio and drying time by 9% and 164 s, respectively. To avoid the rise in humidity associated with recirculation, a compact plate-fin heat exchanger is used to recuperatively preheat the air entering the combustor. Energy savings of ∼15% and reduction in drying time by 216 s over the baseline case are estimated. The predicted data demonstrate good agreement with experiments.

Characterization and Scaling of Forced Convective Swirl in Sinusoidal Wavy-Plate-Fin Cores of Compact Heat Exchangers

Abstract The characterization and scaling of the thermal-hydraulic performance in wavy plate-fin compact heat exchanger cores, based on the understanding of the physical phenomena and heat transfer enhancement mechanism is delineated. Experimental data are presented for forced convection in air (Pr = 0.71) with flow rates in the range 50 ≤ Re ≤ 4000. A variety of wavy-fin cores that span viable applications, with geometrical attributes described by the cross section aspect ratio α (ratio of fin spacing to height), fin corrugation aspect ratio γ (ratio of 2× corrugation amplitude to wave pitch), and fin spacing ratio ζ (ratio of fin spacing to wave pitch), are considered. To characterize and correlate the vortex-flow mixing in interfin spaces, a Swirl number Sw is introduced from the balance of viscous, inertial and centrifugal forces. It is shown that the laminar, transitional and turbulent flow regimes can be explicitly identified by this Swirl number. Based on the experimental results and extended analysis, new correlations for Fanning friction factor f and Colburn factor j are developed with Sw, α, γ, and ζ as scaling parameters. Requisite expressions are devised by a superposition of both enhancement components due to the corrugated surface area enlargement and induced swirl flow field, and they are combined to cover the laminar, transitional and turbulent regimes by the method of asymptotic matching. The resulting generalized correlations are further shown to predict all available experimental data for f and j factors to within ±20% and ±15%, respectively.

Integrative numerical modeling and thermodynamic optimal design of counter-flow plate-fin heat exchanger applying neural networks

In this study, an optimization technique combined with a Random Vector Functional Link (RVFL) network in the form of a surrogate-assisted approach was carried out for the optimal design of counter-flow plate-fin compact heat exchanger (PFHE) with offset-strip fins considering different mass flow rates. Computational Fluid Dynamics (CFD) simulations generated dataset for training and testing by RVFL network, reducing processing time and assuring PFHE accuracy when applied in many-objective optimization based on Non-Dominated Sorting Genetic Algorithm III (NSGA-III). Next, the NSGA-III was designed to achieve the maximum effectiveness, minimum volume, and pressure drop at the hot and cold sides in PFHE design. For experimental validation the Shear Stress Transport (SST) k-ω turbulence model was used to simulate the flow and heat transfer in PFHE showing 4.36% and 3.27% of error, respectively, to pressure drop and convective heat transfer coefficient measurements. The optimized results by NSGA-III indicated that the volume and effectiveness values are in agreement with the literature, decreasing approximately 55.4% and 72.3% of pressure drop at the hot and cold sides, respectively, which showed that the convective heat transfer was enhanced and the flow resistance was also significantly reduced.

Measurement of heat transfer coefficient and pressure drops in a compact heat exchanger with lance and offset fins for water based Al2O3 nano-fluids

Compact Heat Exchangers (CHEs) are widely used in various applications in thermal fluid-systems including aerospace due to their compactness and light weight coupled with high effectiveness. Among the different types of CHEs for Aircraft Environmental Control System (ECS) and Avionics cooling applications, a cross-flow CHE with Lance & Offset fin is of special interest because of their high heat rejection capability. In the present work, the heat transfer coefficient of water based Al2O3 nano-fluid (NF) flowing in a Compact Plate-fin Heat Exchanger having Lance & Offset fins is studied experimentally. As part of experimental investigation a test setup is designed and developed. Experiments are conducted in the range of mass flux from 50 to 350 kg/s m2 (100 ≤ Re ≤ 600) at room temperature as well as at higher temperatures up to 70 °C. In this study, Al2O3 volume concentration in water is varied from 0.255% to 0.51%. The variation of heat transfer coefficients and pressure drops of Al2O3 nano-fluid with respect to water are presented in graphical form for different mass fluxes. The heat transfer coefficient gets enhanced in low NF temperature regions (between 30 °C-45 °C) up to 25% for 1%NF and up to 35% for 2%NF, where as there is only a marginal improvement at higher operating temperatures (between 60 °C-75 °C). The uncertainty analysis is carried out for heat transfer coefficient based on sensors specification.

Kinetic model of a plate fin heat exchanger with catalytic coating as a steam reformer of methane, biogas, and dimethyl ether

The paper presents an analysis of a compact plate fin heat exchanger with catalytic coating. The unit is used to convert various fuels into hydrogen-rich gas, which is then fed into the anodic compartments of a solid oxide fuel cell (SOFC) stack. The study looks at the fuel processor for methane, biogas, and dimethyl ether (DME). In the first phase, the reaction kinetics model was based on data from the literature. This was followed by tuning and validation of the numerical model using data collected during an experimental campaign. Four values of the steam to carbon ratio (2.0, 2.5, 3.0, and 3.5) were used to analyze the performance of the heat exchanger, which was investigated in a temperature range of 500°C to 750°C. The experimental data are compared with predictions of the model implemented in Aspen HYSYS modeling software and discussed. It was found that the relative prediction error of the simulator does not exceed 3.5%.

Experimental study on the thermal hydraulic performance of plate-fin heat exchangers for cryogenic applications

Efficient and compact plate-fin heat exchangers are critical for large-scale helium liquefaction/refrigeration systems as they constitute major part in the cold box. This study experimentally explores the heat transfer and pressure drop behaviors of helium gas at low temperature in four types of plate-fin channels, namely offset-strip and perforated fins, with different geometrical parameters. A series of cryogenic experiments at approximately liquid nitrogen temperature are carried out to measure the Colburn j factors and Fanning friction f factors with a wide range of Reynolds number. Besides, to reveal the performance variations under different operating temperatures, comparative experiments respectively conducted at room temperature and liquid nitrogen temperature are implemented. The results show that in comparison with the performance data at room temperature, most of j factors are relatively smaller perhaps because the lower aluminum thermal conductivity and higher Prandtl Number at low temperature. Meanwhile, the f factors corresponding to cryogenic conditions exhibit slightly larger even though the core pressure drops show considerable reductions. In contrast to the calculated results from the frequently-used performance curves (Chen and Shen, 1993), the Root Mean Squared Errors of j and f values are correlated within 8.38% and 6.97% for one perforated fin core, 41.29% and 34.97% for three OSF cores, respectively. For OSFs, further comparisons with the previous empirical correlations from literatures are conducted to verify the accuracy of each correlation. Generally, most of the calculated results predict acceptably within the deviations of ±25% for the j factors, while the predicted results express relatively large deviations for the f factors. Therefore, it may be revealed that most of the existing correlations were not able to accurately predict the experimental data in consideration of the performance differences under realistic cryogenic operating conditions, which could have significant influences during the design process of cryogenic heat exchangers.

Numerical analysis of compact plate-fin heat exchangers for aerospace applications

PurposeThe purpose of this study is to find the thermo-hydraulic performances of compact heat exchangers (CHE’s), which are strongly depending upon the prediction of performance of various types of heat transfer surfaces such as offset strip fins, wavy fins, rectangular fins, triangular fins, triangular and rectangular perforated fins in terms of Colburn “j” and Fanning friction “f” factors.Design/methodology/approachNumerical methods play a major role for analysis of compact plate-fin heat exchangers, which are cost-effective and fast. This paper presents the on-going research and work carried out earlier for single-phase steady-state heat transfer and pressure drop analysis on CHE passages and fins. An analysis of a cross-flow plate-fin compact heat exchanger, accounting for the individual effects of two-dimensional longitudinal heat conduction through the exchanger wall, inlet fluid flow maldistribution and inlet temperature non-uniformity are carried out using a Finite Element Method (FEM).FindingsThe performance deterioration of high-efficiency cross-flow plate-fin compact heat exchangers have been reviewed with the combined effects of wall longitudinal heat conduction and inlet fluid flow/temperature non-uniformity using a dedicated FEM analysis. It is found that the performance deterioration is quite significant in some typical applications due to the effects of wall longitudinal heat conduction and inlet fluid flow non-uniformity on cross-flow plate-fin heat exchangers. A Computational Fluid Dynamics (CFD) program FLUENT has been used to predict the design data in terms of “j” and “f” factors for plate-fin heat exchanger fins. The suitable design data are generated using CFD analysis covering the laminar, transition and turbulent flow regimes for various types of fins.Originality/valueThe correlations for the friction factor “f” and Colburn factor “j” have been found to be good. The correlations can be used by the heat exchanger designers and can reduce the number of tests and modification of the prototype to a minimum for similar applications and types of fins.

Numerical Study of Compact Plate-Fin Heat Exchanger for Rotary-Vane Gas Refrigeration Machine

Plate-fin heat exchangers are widely used in refrigeration technique. They are popular because of their compactness and excellent heat transfer performance. Here we present a numerical model for the development, research and optimization of a plate-fin heat exchanger for a rotary-vane gas refrigeration machine. The method of analysis by graphic method of plate - fin heat exchanger is proposed. The model describes the effects of secondary parameters such as axial thermal conductivity through a metal matrix of the heat exchanger. The influence of geometric parameters and heat transfer coefficient is studied. Graphs of dependences of length, efficiency of a fin and pressure drop in a heat exchanger on the thickness of the fin and the number of fins per meter are obtained. To analyze the results of numerical simulation, the heat exchanger was designed in the Aspen HYSYS program. The simulation results show that the total deviation from the proposed numerical model is not more than 15%.

Experimental study of boiling heat transfer and flow characteristics in fin channels with variable cross section

The object of this work is to investigate the boiling heat transfer performance of transverse serrated fin (TSF) channel and triangle perforated fin (TPF) channel in compact plate-fin heat exchanger. A series of boiling heat transfer performance tests are carried out for volume flow rate range of 0.03–0.3m3/h and heat flux of 10–20kW/m2. The local and average heat transfer coefficient of TSF channel and TPF channel are examined. It indicates that both local and average boiling heat transfer coefficient of TSF channel was higher than that of TPF channel. The boiling heat transfer occurs in TSF channel at lower wall superheat. The growth rate of wall temperature significant declines significantly when heat flux is up to ONB point, which means the boiling heat transfer has happened. The rising rate of average boiling heat transfer coefficient have is smaller than that of the local boiling heat transfer coefficient hout.

Numerical and experimental investigations of transient behaviour of compact plate fin heat exchanger

In this paper, models for the transient simulation of a 2 stream plate fin heat exchanger (PFHE) with offset strip fins (OSF) have been formulated based on unsteady mass and energy conservation equations. The behaviour of a PFHE during start up, cool down and during a ramp change in the inlet temperature of one of the fluids have been studied with the help of these models. Initially, a simplified model considering constant helium properties is developed. This model is further evolved to take into account the temperature dependence of helium properties in the cryogenic temperature domain, along with axial heat conduction (AHC) and thermal capacity of the metal separating plate. Computer codes based on the models have been developed to simulate PFHE behaviour. Experiments at room temperature have been carried out for code validation. It has been found that the model based on constant helium properties is sufficient to predict behaviour of the heat exchanger under room temperature conditions.

Numerical studies on sizing/ rating of plate fin heat exchangers for a modified Claude cycle based helium liquefier/ refrigerator

Performance of modern helium refrigeration/ liquefaction systems depends significantly on the effectiveness of heat exchangers. Generally, compact plate fin heat exchangers (PFHE) having very high effectiveness (>0.95) are used in such systems. Apart from basic fluid film resistances, various secondary parameters influence the sizing/ rating of these heat exchangers. In the present paper, sizing calculations are performed, using in-house developed numerical models/ codes, for a set of high effectiveness PFHE for a modified Claude cycle based helium liquefier/ refrigerator operating in the refrigeration mode without liquid nitrogen (LN2) pre-cooling. The combined effects of secondary parameters like axial heat conduction through the heat exchanger metal matrix, parasitic heat in-leak from surroundings and variation in the fluid/ metal properties are taken care of in the sizing calculation. Numerical studies are carried out to predict the off-design performance of the PFHEs in the refrigeration mode with LN2 pre-cooling. Iterative process cycle calculations are also carried out to obtain the inlet/ exit state points of the heat exchangers.