Automotive Heat Exchangers Research Articles

Forced air flow through a rectangular channel with 3D turbulence enhancers: visualization of flow structures by laser sheet scattering

In recent times, the design of heat transfer devices is strongly evolving due to both the diffusion of additive manufacturing techniques, that use a wide variety of materials, and Computational Fluid Dynamics (CFD) -based shape optimization techniques. Considering high-aspect ratio rectangular channels, that represent the geometry of heat transfer devices used, among other applications, for batteries cooling systems and compact automotive heat exchangers, the first step of a project towards the design of optimized turbulence enhancers is the validation of the CFD methodology. In particular, since it is important to have a fast-running 3D simulation with physical meaning, several techniques of increasing complexity and computational requirements and times are currently under scrutiny, and their validation is mainly carried out by experiments that measure both local and global heat transfer enhancement. In this context, flow visualization is a powerful tool to get insights of the physical mechanisms that generate convective heat transfer enhancement. In this paper, the setup of a laser sheet scattering method to visualize turbulent structures in a Plexiglas, 1:10 aspect-ratio, rectangular channel ribbed on one of the main surfaces is presented, and results on two different cutting planes are presented for 90° and V-down squared ribs for Re = 500.

Aerodynamic investigation of the turbulent flow past a louvered-fin-and-tube automotive heat exchanger

Turbulent flow past a radiator contributes to noise emission when interacting with a downstream cooling fan. This study examines turbulent flow characteristics downstream of a radiator, focusing on turbulence production, dissipation, non-homogeneity, and anisotropy. We assess turbulence models based on isotropy and homogeneity for noise prediction in real applications. Results show significant non-homogeneity due to the radiator grid’s wakes, extending downstream to a region where the fan would be located. Flow in this region trends toward isotropy, especially when considering a downstream circularly-holed wood panel mimicking the flow contraction caused by a fan casing. The radiator core’s fins and louvers break down vortical structures more than generating large eddies, as reported in studies involving heat exchangers with larger gaps between cooling pipes. The von Kármán turbulence model approximates the experimental spectrum, but caution is needed with rapid flow acceleration. This investigation enhances our understanding of turbulence characteristics in the vicinity of radiators with implications for noise spectrum prediction and modeling in such systems.

The Effect of Soaking Time on Mechanical Properties of Roll-Bonded AA3003 and AA4045 Used for Heat Exchangers

Due to the rising need for energy saving, high-performing automotive heat exchangers, demand has significantly grown in recent years. As a result, effective fin-tube heat exchangers are becoming more popular. These tubes are typically made by rolling flat strips of AA3003 aluminum alloys that have either one or both sides coated with AA4xxx alloys. The AA3003 type of alloy is typically used as the core, which is then covered in either AA4045 or AA4343, which melts during the brazing process to adhere the fins to the tubes. To maintain the optimal size and distribution of manganese (Mn)-containing precipitates, preheating parameters are carefully controlled. Then, longer soaking times or higher soaking temperatures result in larger precipitates, which cause the final product to exhibit poor mechanical properties. Therefore, it is crucial to optimize the different manufacturing steps, such as homogenization, soaking time, and brazing in order to achieve a high quality product. Studies on the impact of homogenization temperature and time on the microstructure of AA3xxx aluminum alloys have been conducted. However, there has been little research on the impact of soaking (reheating) time on AA3003 cladded alloys. Hence, the effects of isothermal soaking time on the microstructure and mechanical properties of AA3003 cladded with AA4045 alloy were investigated in this work. Optical microscopy (OM) and scanning electron microscopy (SEM) were used to characterize the microstructure and identify intermetallic phases. The final microstructure in terms of grain structure at various homogenization times was characterized by electron backscattered diffraction (EBSD). After the hot-rolling and cold-rolling of the as-received material, large particles of intermetallic (mainly in the form of Chinese script morphology consisting of Fe-Mn-Si) were broken into smaller particles with an increased Fe, Mn, and Si content, indicating the formation of an α-Al(Fe,Mn)Si phase. The α-Al(Mn,Fe)Si was found to be a dominant dispersoid precipitate in the modified AA3003 core. Coarsening of the Al(Mn,Fe)Si dispersoids at 505 °C was only observed at a 45 h homogenization time. The hardness trend with homogenization time was found to be similar to that after homogenization, cold working, and annealing, with exception of an increase in hardness in the latter possibly due to strain hardening (from cold-rolling).

Atomic-scale investigation of Si/Al interface in multilayer aluminum sheets using HRTEM and first-principle calculation

The atomic-scale structure and electronic structure of the interface between Si precipitates and the Al matrix in multi-layered aluminum sheets are investigated by combining high-resolution transmission electron microscopy (HRTEM) with first-principles calculation. The results show that Si needle precipitates and Guinier Preston (GP) zones occur during the natural aging process of the core material in automotive heat exchangers. In addition, Al(Fe,Mn)Si precipitate can serve as effective heterogeneous nucleation sites for the formation of high-density Si precipitates during aging. The charge density differences analysis shows that the formation of covalent bonds between interfacial Si and Al atoms is crucial to the interfacial bonding strength. These results provide important insights for future research efforts focused on the production of multilayer aluminum sheets with high-performance.

The factors of alloying elements on corrosion resistance of aluminum alloys

Corrosion resistance is a key property for aluminum alloys used in automotive heat exchangers. This study focuses on comparing two variations of post-brazed 3003-H24 aluminum alloys with 2-sided cladding 4045. One of them is the special developed for corrosion resistance. Another one is the generic and widely commercial used alloy. The specimens were prepared by heating in the brazing furnace at temperature of 600 °C for 5 min in order to let the clad material diffuse into the core layer to create the corrosion protection layer. This study compared the corrosion resistance of two alloys by the car maker’s Cyclic Condenser Corrosion test method (CCCT). The results indicate that the special developed alloy has better corrosion resistance than the generic alloy. According to the corrosion test result, further study was performed in order to explain potential factors that make the difference between two alloys. The results were discussed in terms of chemical composition, mechanical properties, microstructure and corrosion potential. It was observed that the difference of Fe content in the core layer of the alloys yields highly impact on the corrosion resistance.

Effect of Airflow Non-Uniformities on the Thermal Performance of Water–Air Heat Exchangers—Experimental Study and Analysis

The thermal performance of fin-and-tube heat exchangers (HX) is a crucial aspect in a multitude of applications and fields; several design and operational parameters influence this performance. This study focuses on the issue of flow maldistribution and its effect on the HX thermal performance. For this purpose, an experimental setup is designed and implemented to emulate the conditions under which an automotive heat exchanger operates in regard to the non-uniform upstream airflow velocity distribution over the HX surface. The setup allows obtaining various configurations of airflow velocity non-uniformity of some desired mean velocity and standard deviation. The experimental results reveal that a higher degree of non-uniformity (higher standard deviation of the velocity distribution) causes an increased deterioration of the HX thermal performance. For example, at a water flowrate of 200 L/h and a mean airflow velocity of 2 m/s, increasing the standard deviation from 0 to 2 m/s (i.e., moving from the lowest to highest degrees of non-uniformity) causes a total deterioration of 27% in the performance (3.78 to 2.75 kW, respectively), which can also be observed in the increased level of outlet water temperature (53.8 to 58.2 °C, respectively). The obtained results confirm the numerical results reported in the literature.

Numerical and experimental investigation of heavy-duty EGR cooler thermal performance

Exhaust Gas Recirculation (EGR) cooler is a crucial automotive heat exchanger that decreases the temperature of the recirculated exhaust gas fed to engine cylinders to reduce the NOx emissions. The high temperature gradients in the heat exchanger and its varying hot and cold operation makes it necessary to accurately determine the temperature distribution of the EGR cooler to evaluate vulnerability to various thermal failures. This study demonstrates a thermal assessment of EGR cooler using detailed CFD simulation methods developed and validated with comprehensive experimental design and measurements. The experimental data including detailed boiling detection is collected on a gas burner test bench for eight different working conditions of the EGR cooler with conditioned cooling with an average of 3% repeatability error. The detailed and highly resolved CFD model which includes the heat transfer enhancing features of the heat exchanger is validated at these working conditions and resulted in an average of 1% difference in temperature and maximum 5% difference in pressure drop values. The developed detailed CFD methodology reduces the amount of EGR performance and boiling tests significantly and enables assessment of the EGR cooler at engine assembly conditions which affects the hot gas distribution and resulting temperature gradients. Furthermore, the CFD methodology and its correlation with the experiment proved that a coupled CFD methodology can be used instead of the development tests for analytical sign-off purposes as long as the detailed heat exchanger design is included in the CFD model. • A detailed CFD model with all geometrical features was built as essential alternative to EGR cooler tests. • The detailed CFD model does not require any additional numerical approach for pressure drop or heat transfer. • Acoustic Emission sensor was utilized for the more precise assessment of boiling level. • CFD predictions were validated with experimental data by using acoustic emission sensor measurements. • Predicted temperature and pressure change were validated by experimental results with high accuracy.

Corrosion inhibition of AA6060 by silicate and phosphate in automotive organic additive technology coolants

Coolant corrosion inhibitors are paramount for the durability of automotive heat exchangers. The novel generation of “hybrid coolants” consists of inorganic inhibitors added to an OAT (Organic Additive Technology) backbone. This investigation appraises the corrosion inhibition provided by OAT, phosphate and silicate (separately and combined) on AA6060 exposed to antifreeze coolant at 75 °C. The effects of hard water cations and temperature are also discussed. Linear Polarization Resistance provided a time-resolved assessment of inhibition, and potentiodynamic polarisation extrapolated the corrosion behaviour to more severe scenarios. Supported by SEM-EDX analysis, schematic diagrams of the inhibition mechanisms were elaborated for the coolant systems.

CFD analysis of an anemometric sensor design for air flow measurement in a heat exchanger

This paper focuses on the issue of flow measurement in automotive heat exchangers. The measurement is complicated due to the limited space in the heat exchanger area and the non-uniform velocity profile. Therefore, only some measuring techniques can be used, which must be adapted to the specific conditions. The paper presents the initial stages of the development of a sensor for measuring the flow in a heat exchanger. These are CFD simulations used to determine the nature of the flow around the sensor and verify its effect on the flow field in its surrounding and on the entire heat exchanger. The results of these initial simulations are presented and discussed.

Corrosion Properties for Roll-Bonded Two-Layer AA4045/AA3003 for Heat Exchanger Application

During their service life, heat-exchangers are subjected to a variety of environments, including heating and cooling cycles, salt water environment on the surface, and mechanical loading. As a result, corrosion performance is critical, as perforation of the material could result in system failure. Corrosion behaviour of brazed roll-bonded aluminium sheet is significant since this is the most common mode of failure for automotive heat exchangers, especially with the trend toward lighter automotive parts. Furthermore, thermal treatments such as solution heat treatment, homogenization, and brazing alter the microstructure and, as a result, vary the corrosion behaviour. The effect of homogenization temperature and duration on the microstructure of AA-3xxx aluminium alloys has been studied, but more research is needed. The goal of this investigation was to see how different holding times during homogenization heat treatments affect corrosion behaviour. Accelerated laboratory corrosion tests are essential for ranking trial materials and ultimately qualifying an alloy for production. The corrosion behaviour of two-layer modified aluminium sheets (AA4045/3003 Modified) was examined in this research before and after brazing. The corrosion propagation was attributed to potential differences between the brazing sheet, creating a galvanically driven perforation of the core material by the diffusion zone after sea water acid accelerated testing (SWAAT) and electrochemical testing of the AA4045/3003 modified brazing sheet. Furthermore, a link between SWAAT and potentiodynamic polarization measurements has been established, suggesting that these electrochemical approaches could be used to replace or reinforce the SWAAT and so reduce the cost.

Estimation of energy efficiency factor for models of porous automotive heat exchangers

The present paper examines the effect of the geometry of an open cell foam material on pressure drop, heat flux, and energy efficiency. Models of highly porous media with disordered (DEM) and ordered (SC, FCC, BCC) structures with various porosities were created: ε = 0.85; ε = 0.9; ε = 0.95. The ANSYS Fluent (v. 19.2) software package was used to calculate the heat flux, pressure drop, and energy efficiency from the computational domain at different flow velocities of the gas and for different porosities of the medium. At the porosity value ε = 0.85, the highest pressure drop corresponds to the FCC cell packing, and at porosities ε = 0.9 and ε = 0.95 corresponds to the BCC cell packing. At flow rates of 0.01 m/s and 0.05 m/s, the heat flux value is approximately the same for all types of structures. At porosity of the media ε = 0.85 at velocities of 0.25-1.25 m/s, the value of heat flux and pressure drop is higher for FCC cell packing. At the porosity values ε = 0.9 and ε = 0.95, the BCC cell packaging shows a greater heat flux than the FCC structure. The lowest heat flux value corresponds to the SC structure. At the same time, the lowest pressure drop is also observed for SC cell packing, due to which this structure shows the highest values of the energy efficiency factor.

Analytical and experimental investigation on heat transfer and flow parameters of Multichannel louvered fin cross flow heat exchanger using iterative LMTD and ∊-NTU method

Automotive Heat exchangers plays vital role by ensuring human comfort in cabin by maintaining optimum temperature and maintains operating temperature of Internal Combustion(IC) engine within permissible limits. In this work, iteration based mathematical model to solve for analytical thermo-hydraulic performance estimation of a typical heat exchanger is adopted with Log Mean Temperature Difference (LMTD) method by incorporating the variation in properties of fluids during each iteration, since the overall thermal resistance ratio between targeted & calculated Heat Rejection Rate (HRR) has to be converged to unity to solve for the actual thermal performance of the heat exchanger. This condition ensures convergence and there is no deviation between the two adjacent iterations in terms of HRR value. Additionally, the above condition ensures that deviation between analytical value calculated by Effectiveness-NTU (∊-NTU) method and experimental data will be reduced significantly due to the proposed iterative LMTD approach adopted in this work. Along with iterative LMTD methodology, ∊-NTU method is adopted for last iteration to cross-verify the obtained value of the HRR for same operating conditions. In order to evaluate heat transfer coefficients for air and coolant side, standard correlations are used from well-established and validated literature data. For coolant side pressure drop calculations, network solution methodology is adopted where fluid flow behavior in each segment of heat exchanger is studied in detail and analytical relationships are used to predict net pressure drop in entire heat exchanger. In our mathematical model, louvered fin effects on heat transfer is taken into account by adopting colburn approach and the geometrical effects of internal fins on flow channels is also included. Experimental validations tests are carried out to compare with the analytical results of HRR, Coolant Side Pressure Drop (CSPD) and Air Side Pressure Drop (ASPD) across heat exchanger. A good agreement is found between experimental and analytical results which validates the accuracy of present mathematical model and methodology, the maximum deviation for HRC is 4% on higher side, for CSPD and ASPD it is 15.4%,8.7% on higher side respectively.

Numerical and analytical approach to study condensation for automotive heat exchangers

Heat exchanger (condenser, evaporator etc.) is one of the essential component in the automotive air conditioning system. In these heat exchanger the phase change phenomenon involves, which makes the calculation complicated. In this study, two different approaches are used to analyze the condensation phenomena inside the automotive condenser. The first approach, an analytical study based on empirical correlation is used to calculate the heat transfer and internal pressure drop of the condenser and it is validated with experimental results. In analytical approach, condenser is discretized into multiple segments and ε-NTU method is applied in each segment to calculate the heat transfer and internal pressure drop. In the second approach, Computational Fluid Dynamics (CFD) is used to analyze condensation phenomena inside the microchannel and it is compared with the analytical results. The maximum deviation of heat transfer and internal pressure drop (refrigerant side) for the analytical approach is found to be 8.3% & 9.4% respectively compared to experimental results. In CFD simulation, the condensation of refrigerant commenced from 125 mm in the first pass along the length of the tube (in the direction of refrigerant flow), while the same is begun from 128 mm in the case of analytical approach. Beside to that the dryness fraction across all the passes of the condenser is compared between these approaches.

Error-lumped inverse uncertainty quantification of automotive heat exchangers (HEXs) using large-scale database from system level tests

Error-lumped inverse uncertainty quantification of automotive heat exchangers (HEXs) using large-scale database from system level tests

Internal Corrosion of Warm Formed Aluminum Alloy Automotive Heat Exchangers

The objective of this study is to evaluate the effects of sheet temper, forming conditions, and the resultant post-braze microstructure on the corrosion behavior of Al alloy heat exchangers. Accelerated corrosion tests were performed by flowing a corrosive water solution through brazed heat exchanger samples fabricated from O and H24 temper sheet formed between room temperature and 250 °C. Sheet perforations within the brazed samples were found to be concentrated at the coolant channel inlets, due to crevice corrosion, or around other formed features within the coolant channel, which was attributed to erosion corrosion. A clear relationship between corrosion initiation sites and local microstructure was not observed in the accelerated test. Potentiodynamic polarization measurements were performed using the corrosive water solution and sheet samples pre-strained to 4 and 10% and subjected to a simulated brazing heat treatment. The average corrosion current density was the same for the two conditions, but liquid film migration occurred during brazing in the sample strained to 4%, resulting in localized corrosion and greater variability in the polarization measurements. It is concluded that warm forming does not impair the corrosion resistance of H24 temper sheet, but the corrosion resistance of brazed samples fabricated from O temper sheet is altered by warm forming.

Development of an Aluminum Brazing Sheet Product with Barrier Layer for High-Performance Automotive Heat Exchangers

Development of an Aluminum Brazing Sheet Product with Barrier Layer for High-Performance Automotive Heat Exchangers

К вопросу о возможности разработки средств и методов инструментального диагностирования теплообменников транспортной техники в эксплуатации

Heat exchangers are used to stabilize and maintain the temperature regime of various units and systems of cars. The technical condition of heat exchangers in operation is different and unstable. At a certain operating time interval, the technical condition of any of the heat exchangers can become limiting due to the influence of various kinds of operational factors. The article analyzes the possibility of improving the means and methods of diagnostic support of automobile heat exchangers in operation. In the design and manufacture of automotive heat exchangers, they are tested in specialized laboratories equipped with test stands characterized by high capital and operating costs. The use of these stands for diagnosing heat exchangers in operation is not applicable. Due to the limitations and imperfections of the known methods and means of diagnosing automobile heat exchangers in operation, an objective assessment of their current technical condition is difficult and requires the search for new, more advanced diagnostic options. The relevance of the topic of the article lies in the search for ways to improve the diagnostic support, adapted for a quantitative assessment of the technical condition of heat exchangers in operation. The aim of the work is to improve the method and means of diagnosing heat exchangers in operation on the basis of modernizing the design of the test bench for radiator modules. Potentially a possible upgrade option was chosen previously developed by the authors stand for testing modules of automobile radiators, which is distinguished by the effect of resource saving when obtaining the test result. Achievement of the goal requires updating the architecture of the structural elements of the stand, and the search for design and technological solutions that contribute to the achievement of the goal. The methodological research toolkit is based on dialectically interrelated methods: analysis of a problem situation and subsequent design and technological synthesis. Scientific novelty lies in the development of conditions for modernization, allowing to expand the functionality of the basic structure of the stand. The practical significance of the results lies in the choice of the direction of research, with a new set of technical proposals and conditions for achieving the goal of the work.

Measurement-based strategies for high-fidelity thermo-fluid dynamics simulation of an automotive heat exchanger

Measurement-based strategies for high-fidelity thermo-fluid dynamics simulation of an automotive heat exchanger

Effect of brazing parameters on fillet size and microstructure of cladded fin-microchannel tube joints

Abstract This work concerns the optimization of furnace brazing conditions for joining micro-multiport aluminum tubes and fins made with AA4343/AA3003/AA4343 brazing sheet in mini-assemblies mimicking the core of an automotive heat exchanger. Taguchi method was used for design of experiment, considering five process parameters with two levels of values. The aim was to maximize the fillet size of the brazed joints, which has an important influence on the thermal integrity and mechanical properties. Fillet length measurements of brazed joints were performed with a metallographic microscope. The statistical analysis allowed to obtain the optimum values of process parameters (peak temperature, residence time, heating rate, microchannel tube type and flux). At a 95% confidence level, the variability of fillet length is most significantly affected by the peak brazing temperature (77%), residence time (15%) and heating rate (7%). The predicted maximum fillet length was (152±11) µm, which was corroborated by confirmation trials. The microstructural analysis of tube−fin joints showed that variations in peak temperature and residence time affect only the size of the eutectic zone of fillet formed, but not the nature or composition of the constituent phases.

Performance assessment of the automotive heat exchanger with twisted tape for thermoelectric based waste heat recovery

Waste heat recovery in automobiles is a practical technique to reduce emissions and fuel consumption. The extent of waste heat recovery is directly proportional to the efficiency of the heat exchanger. However, the change in internal geometry has become a convenient method to extract the maximum heat from the exhaust heat exchanger while producing a minimum pressure drop. In the current study, the performance of the exhaust heat exchanger with twisted ribs has been studied for the six different operating points of the diesel engine. Three distinct geometric parameters of twisted tape i.e., pitch ratio, twist ratio, and tilt angle have been studied in detail. Experiments were repeated for various geometric parameters to arrive at the best specification of the twisted tape. The results show that the pitch ratio of 8, twist ratio of 4, and the tilt angle of 60° yield the highest power output. The results obtained were compared with the internal flat heat exchanger. It has been observed that the system equipped with a twisted rib produces more net power than the smooth surface system. Moreover, a comparison of fuel consumption with the commonly used alternator has been performed and the proposed system has the potential to improve the BSFC by 0.65%.