Automotive Heat Exchangers Research Articles

Reduction of Liquid Clad Formation Due to Solid State Diffusion in Clad Brazing Sheet

Warm forming operations have shown promise in expanding automotive heat exchanger designs by increasing forming limits of clad brazing sheet. The impact of isothermal holds below the clad melting temperature on subsequent brazeability has not previously been studied in detail. The effect of these holds on brazeability, as measured by the clad thickness loss due to solid state diffusion of Si out of the clad layer prior to clad melting, was assessed through parallel DSC and optical microscopy measurements, as well as through the use of a previously developed model. EPMA measurements were also performed to support the other measures. Overall, the same trends were predicted by DSC, microscopy, and the theoretical model; however, the DSC predictions were unable to accurately predict remaining clad thickness prior to melting, even after correcting the data for clad–core interactions. Microscopy measurements showed very good agreement with the model predictions, although there were slight discrepancies at short hold times due to the inability of the model to account for clad loss during heating to the brazing temperature. Further microscopy measurements showed that when the heating rate is set below a critical value, there is a reduction in the clad thickness from the as-received condition.

Constitutive modelling of aluminium alloy sheet at warm forming temperatures

The formability of aluminium alloy sheet can be greatly improved by warm forming. However predicting constitutive behaviour under warm forming conditions is a challenge for aluminium alloys due to strong, coupled temperature- and rate-sensitivity. In this work, uniaxial tensile characterization of 0.5 mm thick fully annealed aluminium alloy brazing sheet, widely used in the fabrication of automotive heat exchanger components, is performed at various temperatures (25 to 250 °C) and strain rates (0.002 and 0.02 s-1). In order to capture the observed rate- and temperature-dependent work hardening behaviour, a phenomenological extended-Nadai model and the physically based (i) Bergstrom and (ii) Nes models are considered and compared. It is demonstrated that the Nes model is able to accurately describe the flow stress of AA3003 sheet at different temperatures, strain rates and instantaneous strain rate jumps.

Extrusion of AA 3003 micro condenser tube with multi-hole and thin wall section using porthole die

Recent interest in condenser tubes for an automotive heat exchanger is linked to developing a tube with high strength to allow the minimization of the wall thickness and the multi-hole of the cross section. These goals can be achieved by using alternative materials and strengthening the design of the tube’s cross-section. However, the design of the tube’s cross-section indicates that the gains from it are limited due to the mechanical properties of the materials such as yield and tensile strength. To overcome this problem, AA 3003 has recently been used for the condenser tubes. However, it has the disadvantage of low extruability compared with AA 1100. This study was designed to develop AA 3003 condenser tube using a porthole extrusion die and was specially focused on comparing material flows of the AA 3000 and AA 1000 during extrusion. Estimations were carried out using FE simulations of the hot extrusion process. After the FE simulations, the validity of the results was verified by the extrusion experiments of AA 3003 condenser tube. Also, the welding strength of the extruded tube was estimated by surface nano-hardness of the welding line using nano-indentation test.

Mechanical and microstructural behavior of brazed aluminum / stainless steel mixed joints

There is a requirement to combine different materials such as aluminum and stainless steel in industrial applications like automotive heat exchangers. Brazing offers the possibility to reduce the joining temperature in comparison to welding due to the lower liquidus temperature of the fillers. In the present work, the mechanical and microstructural behavior of aluminum / stainless steel mixed joints is investigated. The specimens are produced by induction brazing using an AlSi10filler and a non-corrosive flux. To evaluate the mechanical properties of the joints, tensile tests at elevated temperatures are carried out. Additionally, long-term thermal exposure experiments are done in order to investigate the changes in the microstructure.

Parametric Analysis of Heat Exchanger Thermal Performance in Complex Geometries—Effect of Air Velocity and Water Flow Distributions

The thermal performance of automotive heat exchangers is greatly affected by the relationship that binds the nonuniformities in flow velocity and the distribution of upstream temperatures. Consequently, an in-house two-dimensional code is established to evaluate the thermal performance based on known parameters, namely, distribution of upstream velocity of an air–liquid heat exchanger, the flow rate of heat exchanger liquid, and the inlet air and liquid temperatures. A parametric research study is then performed to confirm the relation between the thermal performance of the heat exchanger and these different parameters. It was observed that nonuniformities in air velocity and water flow distributions decrease the thermal performance of a heat exchanger by up to 33 and 42%, respectively.

Experimental and simulation study on the air side thermal hydraulic performance of automotive heat exchangers

Flat tube heat exchangers with louvered fins were applied in order to meet the performance requirements and compactness in automotive air conditioning systems. Experimental and simulation study focusing on the air side thermal hydraulic performance of automotive heat exchangers were performed in this article. Test results showed that the heat capacity of a condenser with 5.4 mm height louvered fins can be 3.0%–8.6% higher than the 8 mm fin height condenser of the same size. Automotive evaporator can have 9.3% volume reduction by using short louvered fins while retain the same cooling capacity. Distributed parameter models were developed for automotive heat exchangers and effectiveness NTU method was used to calculate the heat capacity. The models were validated by comparing the results to those calculated via Coil Designer 3.6. Verification has been done for several well-known correlations used for the calculation of thermal hydraulic performance of wet and dry louvered surfaces. The correlations were evaluated by comparing calculations with test data of 24 different specimens under typical automotive heat exchanger working conditions. It was concluded that the existing correlations can give satisfactory predictions for heat capacity of condensers and evaporators, and air side pressure loss of condenser. However, further study on the friction characteristic of wet louvered fins is still needed.

Electrochemical Investigation of the Corrosion Behavior and Galvanic Compatibility Between Microchannel Tubes and Fins of an Aluminum Automotive Condenser

The condenser of air-conditioning unit for automotive application is an aluminum heat exchanger with three main components: the headers, microchannel tubes and fins. It is normally installed in the neighborhood of the front grill, so it is subjected to external corrosion. Of main concern is the possibility of tube perforation, leading to coolant leaking. One way to improve the corrosion resistance of the condenser is to protect the outside of the microchannel tubes with a sprayed zinc coating. The standard test for corrosion of automotive heat exchangers is saltwater acetic acid test (SWAAT) which is intended to reproduce lifetime performance. With the aim of satisfying recent demands in the industry for higher SWAAT performance, a condenser prototype was developed in this study using flat tubes made with a 1000 series alloy spray-coated with zinc and fins made with 3003 series alloy with a double clad of 4343 alloy. The condenser prototype was brazed in a controlled atmosphere industrial furnace, using the Nocolok® flux brazing process. External corrosion was simulated by immersion, in SWAAT solution, of small samples cut from the tube/fin panel, taking care to seal the ends of the tubes with epoxy resin. Results of potentiodynamic polarization and electrochemical impedance spectroscopy were compared to those for individual components (uncouple tube and fin) and indicated that the electrochemical behavior is dominated by the fins. The pitting corrosion resistance of the condenser is afforded by the zinc diffusion layer on the tubes and this effect was investigated with cross-sectional corrosion potential profiles and potentiodynamic determination of the pitting potential. Galvanic compatibility between the tube and fins was evaluated with zero resistance ammetry (ZRA) and showed that there is an evolution in galvanic corrosion as zinc in the diffusion layer gets depleted. Furthermore, the localized corrosion behavior at the tube-fin joint was investigated with scanning electrochemical microscopy (SECM) and scanning vibrating electrode (SVET).

Development of Al-Mn-Cu-Mg Brazing Sheet Core Alloys for Automotive Heat Exchanger Units for Service at High Temperatures

Development of Al-Mn-Cu-Mg Brazing Sheet Core Alloys for Automotive Heat Exchanger Units for Service at High Temperatures

Tensile failure of thin aluminium sheet observed by in-situ EBSD

Tensile tests on two similar 75-μm-thick aluminium sheet materials were carried out inside a scanning electron microscope equipped with an electron backscatter detector. The materials were subjected to simulated brazing prior to the test because this type of material is used for fins in automotive heat exchangers. Grain sizes were large relative to sheet thickness and ND-rotated cube and P texture components dominated the recrystallization textures; their volume fractions differed strongly in the two different materials, though. Strains over the microscope image fields were determined from positions of constituent particles or from grain sizes; the two methods gave consistent results. Grains with high Schmid factors accumulated significantly more deformation than grains with low Schmid factors. Cracks nucleated in high-Schmid factor grains, or in groups of such grains, at the specimen edges. When only low-Schmid factor grains were present at the specimen edges, the crack nucleated inside the specimen. The subsequent crack growth was intragranular and occurred at approximately 90° relative to the load direction.

1020 小型インタークーラの乱れ構造制御と感温液晶による対流熱伝達計測

Recently, heat transfer enhancement in an automotive heat exchanger becomes one of key technologies. Then, a flow in tube of heat exchanger has a low Re number. For heat transfer enhancement, the saliences are designed on the inner surface of tube. Saliences promote turbulent flow and mixing effect, at low Re number, even though a turbulent flow is vanished by viscous effect. The saliences which promotes continuous turbulence is needed. For this reason, we have carried out a flow visualization experiment. Temperature contour has been visualized with liquid crystal thermometry. And, 3D particle tracking velocimetry has also conducted for visualization of turbulent generation. So, heat transfer performance has been evaluated with the experimental results.

G0501102 車載用小型熱交換器内の低速域における対流熱伝達係数の計測

G0501102 車載用小型熱交換器内の低速域における対流熱伝達係数の計測

Use of a Soluble Anode in Electrodeposition of Thick Bismuth Telluride Layers

Integration of thermoelectric devices within an automotive heat exchanger could enable conversion of lost heat into electrical energy, contributing to improved total output from the engine. For this purpose, synthesis of thick bismuth telluride (Bi2Te3) films is required. Bismuth telluride has been produced by an electrochemical method in nitric acid with a sacrificial bismuth telluride anode as the source of cations. The binary layer grows on the working electrode while the counter-electrode, a Bi2Te3 disk obtained by high frequency melting, is oxidized to BiIII and TeIV. This process leads to auto-regeneration of the solution without modification of its composition. The thickness of films deposited by use of the Bi2Te3 anode was approximately 10 times that without. To demonstrate the utility of a soluble anode in electrochemical deposition, we report characterization of the composition and morphology of the films obtained under different experimental conditions. Perfectly dense and regular Bi2Te3 films (∼400 μm) with low internal stress and uniform composition across the cross-section were prepared. Their thermoelectric properties were assessed.

Design for Six Sigma (DFSS) for Optimization of Automotive Heat Exchanger and Underhood Air Temperature

Design for Six Sigma (DFSS) for Optimization of Automotive Heat Exchanger and Underhood Air Temperature

Tensile, Fatigue, and Creep Properties of Aluminum Heat Exchanger Tube Alloys for Temperatures from 293 K to 573 K (20 °C to 300 °C)

Abstract Since automotive heat exchangers are operated at varying temperatures and under varying pressures, both static and dynamic mechanical properties should be known at different temperatures. Tubes are the most critical part of the most heat exchangers made from aluminum brazing sheet. We present tensile test, stress amplitude-fatigue life, and creep–rupture data of six AA3XXX series tube alloys after simulated brazing for temperatures ranging from 293 K to 573 K (20 °C to 300 °C). While correlations between several mechanical properties are strong, ranking of alloys according to one property cannot be safely deduced from the known ranking according to another property. The relative reduction in creep strength with increasing temperature is very similar for all six alloys, but the general trends are also strong with respect to tensile and fatigue properties; an exception is one alloy that exhibits strong Mg-Si precipitation activity during fatigue testing at elevated temperatures. Interrupted fatigue tests indicated that the crack growth time is negligible compared to the crack initiation time. Fatigue lifetimes are reduced by creep processes for temperatures above approximately 423 K (150 °C). When mechanical properties were measured at several temperatures, interpolation to other temperatures within the same temperature range was possible in most cases, using simple and well-established equations.

Thermo-mechanical fatigue design of automotive heat exchangers

Automotive heat exchangers are manufactured using brazed thin aluminium tubes and are submitted to pressure pulses, thermal shocks and corrosion. Thermal shocks induce low cycle thermo-mechanical fatigue that leads to failure after several thousand cycles. We propose a thermo-mechanical fatigue design approach for automotive heat exchangers based on the experimental identification of the thermal history during the thermal shock by infrared thermography, the identification of the cyclic elasto-plastic behaviour of the brazed aluminium tubes and the development of a multiaxial lifetime criteria. A finite element simulation of the cyclic thermo-mechanical response in the critical area of the heat exchanger and the use of a multiaxial energy based lifetime criteria lead to the prediction of the heat exchanger’s life.

3527/4343 알루미늄 클래드재의 인장 및 침식특성에 미치는 미세조직 제어의 영향

Aluminum clad sheets for brazing materials in the automotive heat exchangers are required to exhibit both high strength and excellent erosion resistance. In this study, the effects of microstructural changes on the property of clad sheets due to thermomechanical treatment were investigated. The clad sheets were fabricated by roll bonding of twin-roll-cast AA3527 and AA4343 alloys followed by cold rolling down to a thickness of 0.22mm. Partial or full annealing was conducted at the final thickness in order to improved the erosion resistance while keeping the proper strength. Since full annealing was achieved for a temperature of <TEX>$400^{\circ}C$</TEX>, annealing treatments were performed at 360, 380, and <TEX>$400^{\circ}C$</TEX>, respectively. The tensile strength of 3527/4343 clad material was found to be inversely proportional to the annealing temperature before the brazing heat treatment. After this latter treatment, however, the tensile strength of the clad material was about 195~200MPa regardless of the annealing temperature. The erosion depth ratio of the clad annealed at <TEX>$400^{\circ}C$</TEX> was 8.8% (the lowest), while that of the clad annealed at <TEX>$380^{\circ}C$</TEX> was 17% (the highest). The effect of annealing temperature on the tensile and erosion properties of 3527/4343 aluminum clad sheets was elucidated by means of microstructural analyses.

3D CFD Simulation of Thermal Hydraulic Performances on Louvered Fin Automotive Heat Exchangers

This study deals with Computational Fluid Dynamics (CFD) studies of the interactions between the air flow and louvered fins which equipped the automotive heat exchangers. 3D numerical simulation results are obtained by using the ANSYS Fluent 13.0 code and compared to experimental data. The paper studies the effect of louver angle and louver pitch geometrical parameters, on overall thermal hydraulic performances of louvered fins. The comparison between CFD simulations and experimental data show that established 3-D CFD model gives a good agreement. The validation agrees, with about 7% of deviation respectively of friction and Colburn factors to experimental results. As first, it is found that the louver angle has a strong influence on the heat transfer rate. Then, louver angle and louver pitch variation of the louvers and their effects on thermal hydraulic performances are studied. In addition to this study, it is shown that the second half of the fin takes has a significant contribution on pressure drop increase without any increase in heat transfer. Keywords—CFD simulations, automotive heat exchanger, performances.

Effect of Engine Operating Conditions and Coolant Temperature on the Physical and Chemical Properties of Deposits From an Automotive Exhaust Gas Recirculation Cooler

The effect of engine operating conditions on exhaust gas recirculation (EGR) cooler fouling was studied using a 6.4 L V-8 common rail turbodiesel engine. An experimental setup, which included a custom-made shell and tube heat exchanger (EGR cooler) with six surrogate tubes, was designed to control flow variables independently. The engine was operated at 2150 rpm, 203 Nm and 1400 rpm, 81 Nm, representing medium and low load conditions, respectively, and the coolant to the heat exchanger was circulated at 85 °C and 40 °C. Heat exchanger effectiveness and pressure drop was monitored throughout the tests. Deposits from the EGR cooler were collected every 1.5 h for a total of 9 h, and their microstructure was analyzed using a scanning electron microscope while their chemical composition was analyzed using a pyrolysis GC-MS apparatus, and the elemental weight percentages were obtained using a CHN analyzer. The results of these analyses showed that the effectiveness of the EGR cooler drops rapidly initially and asymptotes in a few hours. The medium load condition had a higher effectiveness loss due to a greater accumulation of deposits inside the EGR cooler, mostly due to increased thermophoresis, and produced smaller and coarse particles. The low load condition had lower effectiveness loss but produced bigger particles mostly due to excess hydrocarbons. Coolant temperature played a significant role in altering the deposit microstructure and in increasing the amount of condensed hydrocarbons. More deposits were produced for the cold coolant condition, indicating that lower coolant temperature promotes greater hydrocarbon condensation and thermophoresis. These results indicate the complex nature of fouling in automotive heat exchangers.

Effect of cooling rate during solidification on corrosion resistance of aluminum alloy fin stock for automotive heat exchangers

The effect of cooling rate during solidification on corrosion resistance of aluminum alloy fin stock for automotive heat exchangers has been investigated. Constituent particles become much finer and denser with increasing of cooling rate, but, the area function of secondary phase particle did not change. Corrosion rate did not change with becoming finer and denser of secondary phase particle in Al–0.7mass%Fe–1.5mass%Zn alloy, because, Al3Fe particles themselves worked as a cathode. On the other hand, corrosion rate increased in the cases of Al–1.0mass%Mn–0.4mass%Fe–1.5mass%Zn alloy, because, matrix/Al6 (Mn, Fe) interface acts as a more active cathode than particles themselves.

A closer look at the internal corrosion test for automotive heat exchangers: the OY water test

AbstractNowadays, automotive heat exchangers are mainly made from aluminum. Over the last few decades, the development of aluminum brazing sheet has been mainly focused on the improvement of the external corrosion resistance. Recently, the interest of the heat exchanger manufacturers has also moved toward the assessment of the internal corrosion resistance. Accelerated tests are used to simulate in‐service conditions. These tests are crucial as they provide information to predict the material and product performance. Various internal corrosion tests have been developed, the so‐called ‘OY water tests’. Among all companies, the testing parameters can be varied in terms of ion concentrations or pH. Although the OY water tests are constantly being improved, there is so far no common internal corrosion standard as existing for external corrosion assessment. The present work aims at providing better understanding corrosion mechanisms encountered in the OY water media. The role of various elements present in the solution, cupric, chloride, sulfate ions, has been determined. These parameters were assessed via immersion testing. In order to get better understanding of the corrosion mechanism, electrochemical analysis combined with SEM characterization was carried out. The electrochemical analysis enables the understanding of the thermodynamics and kinetics of the corrosion process while immersion tests are performed to quantify the level of corrosion and follow the surface evolution over time. Copyright © 2010 John Wiley &amp; Sons, Ltd.