| 1. |
- Arora, Sampann, et al.
(författare)
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A partitioned FSI methodology for analysis of sloshing-induced loads on a fuel tank structure
- 2020
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Ingår i: Proceedings of the 6th European Conference on Computational Mechanics: Solids, Structures and Coupled Problems, ECCM 2018 and 7th European Conference on Computational Fluid Dynamics, ECFD 2018. ; , s. 3037-3048
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Konferensbidrag (refereegranskat)abstract
- Liquid sloshing is a source of major concern in the structural design of containers. In fuel tanks of heavy duty trucks, with capacities of up to 900 litres, this phenomenon is capable of causing fuel to impact the container tank with high forces, and exposing the vulnerable parts of the tank to heavy dynamic loads. This highly non-linear and transient phenomenon is simulated here using the commercial Computational Fluid Dynamics (CFD) code STAR-CCM+. The two phase problem is solved using the VOF interface capturing approach. Owing to the thin walled structures of the fuel tank, it becomes important to account for the effects of Fluid-Structure Interaction (FSI). To this end, a partitioned FSI methodology is employed by coupling the CFD and Finite Element Analysis (FEA) solvers for this multi-physics problem. One-way and two-way coupled FSI methodologies are compared with experimental results. The one-way coupled simulations yield good agreement of wall deformations with the experiments for low filling levels. While the two-way coupled FSI analysis corroborates well with the experiments for all filling levels, its high computational costs render the one-way coupled methodology a promising tool to analyse sloshing for industrial applications. This coupling strategy could inform a fuel tank design suited to prevent structural damage due to sloshing, thus contributing towards its safety and longevity.
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| 2. |
- Båstedt, Peter, et al.
(författare)
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Subcooled Flow Boiling in High Power Density Internal Combustion Engines I: Thermal Survey Measurement Campaign
- 2022
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Ingår i: SAE International Journal of Engines. - : SAE International. - 1946-3944 .- 1946-3936. ; 16:1
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Tidskriftsartikel (refereegranskat)abstract
- Nucleate boiling occurs inadvertently in the coolant jacket of high power density internal combustion engines, especially in vicinity of regions experiencing high thermal loads. Occurrence of boiling can be beneficial and be an efficient way to improve heat transfer locally near hot spots, but excessive boiling can be detrimental to structural integrity of the engine. While most of the efforts to understand boiling have been focused on experiments in simplified geometries, this article presents results from thermal survey measurement on a production engine. The purpose of the measurement campaign is to understand the intensity and extent of nucleate boiling occurring in different parts of the engine coolant jacket. This is achieved by sweeping across different input parameters, such as engine operating load point, cooling system operating pressure, coolant flow rate, and coolant inlet temperature. Different boiling regimes are encountered in different parts of the coolant jacket. A wide database of local solid temperatures measured at several critical locations is obtained and these results are interpreted in line with the underlying physics of subcooled flow boiling. The database not only helps to understand the boiling phenomenon occurring in engine coolant jacket, but is also used to calibrate a numerical boiling model.
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| 3. |
- Vasudevan, Sudharsan, 1991, et al.
(författare)
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Comparative analysis of single and multiphase numerical frameworks for subcooled boiling flow in an internal combustion engine coolant jacket
- 2023
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Ingår i: Applied Thermal Engineering. - : Elsevier BV. - 1359-4311. ; 219
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Tidskriftsartikel (refereegranskat)abstract
- Computational analysis of nucleate boiling occurring in liquid cooled applications, such as internal combustion engines is often implemented within a single phase Computational Fluid Dynamics (CFD) framework, owing to low vapor fractions involved. With increase in specific power and the resulting higher thermal loads, accounting for the presence of the vapor phase using a multiphase framework is required in certain conditions, despite the higher computational costs. While detailed resolution of the liquid and vapor phases in nucleate boiling using a two fluid model is excessively computationally expensive, the homogeneous mixture multiphase framework is a good compromise between resolution and computational cost. In this article a numerical wall boiling model is implemented within both, a single phase and the mixture multiphase frameworks. Results from the two approaches are compared with measurements in a channel flow. The results from both approaches are in good agreement with experiments. The single phase approximation is valid when the vapor generation is low. The sensitivity of the results to the computational grid is also discussed in detail. Further, the two frameworks are used to simulate the heat transfer in the coolant jacket of a four-cylinder petrol engine. The results from the numerical simulations are compared with measurements. Both computational frameworks compare reasonably well with the measurements in terms of local metal temperature. However, the advantage of accounting for the vapor phase using the mixture multiphase framework is evident when the parameter related to vapor bubble interactions is analyzed in detail.
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| 4. |
- Vasudevan, Sudharsan, 1991, et al.
(författare)
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Improved estimation of subcooled flow boiling heat flux for automotive engine cooling applications
- 2019
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Ingår i: ASME-JSME-KSME 2019 8th Joint Fluids Engineering Conference, AJKFluids 2019. ; 3A-2019
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Konferensbidrag (refereegranskat)abstract
- Tapping the potential of subcooled flow boiling can be the key strategy for enhanced cooling of modern day internal combustion engines with high specific power. Accurate prediction of the boiling heat flux is a prerequisite for employing such strategy and to avoid stepping into the dangerous film boiling regime. The complexity involved in the boiling phenomena makes it difficult to develop a model that accounts for all the dominant mechanisms. However, boiling models available in literature provide a good estimate of the heat flux within their range of applicability. This work attempts to introduce a blending based on probability of bubble nucleation to blend two different models developed for different boiling regimes. Corroboration of results with experiments show improved estimation of boiling heat flux.
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| 5. |
- Vasudevan, Sudharsan, 1991, et al.
(författare)
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Numerical model to estimate subcooled flow boiling heat flux and to indicate vapor bubble interaction
- 2021
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Ingår i: International Journal of Heat and Mass Transfer. - : Elsevier BV. - 0017-9310. ; 170
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Tidskriftsartikel (refereegranskat)abstract
- There are numerous technical applications where hot components, with uneven temperature distribution, require cooling. In such applications, it is desired to provide efficient local cooling of the hot spots, while avoiding unnecessary over-cooling of the other regions. Such an approach, known as precision cooling, has several advantages. In addition to the fact that it reduces the effort for cooling, it limits the unintended heat lost to the cooling medium. In liquid cooled systems, such as Internal Combustion Engines (ICE), subcooled flow boiling offers immense potential for precision cooling. The primary challenges in extracting this potential are understanding the complexities in the subcooled flow boiling phenomenon and estimating the risk of encountering film boiling. The present study introduces a numerical model to estimate the wall heat flux in subcooled flow boiling and the model includes a mechanistic formulation to account for vapor bubble interaction. The formulation for vapor bubble interaction serves two purposes: (a) blends two well-established models in the literature, one in the isolated bubbles regime and other in the fully developed boiling regime, to estimate the wall heat flux; and (b) provides information to limit boiling in order to not encounter film boiling. The results from the new model are validated with two different experiments in the literature and the wall heat flux estimated by the model is in agreement with experimental results and responsive to different input parameters, such as bulk velocity, operating pressure and inlet subcooling. The new model requires only input of local flow quantities and hence implementation in Computational Fluid Dynamics (CFD) is straightforward.
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| 6. |
- Vasudevan, Sudharsan, 1991
(författare)
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Precision cooling for C02 reduction
- 2019
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Global climate is adversely affected by increasing emissions of carbon dioxide and other green-house gases. The road transport sector contributes significantly to these emissions. Irrespective of the source of energy– Internal Combustion Engines (ICEs) or electric motors, cooling is an important factor that affects the operating performance and more importantly, the efficiency. Efficient cooling positively impacts operating efficiency by reducing fuel consumption and thereby leads to reduced CO2 emissions. The high power density of modern day ICE causes excessive thermal loads to be exerted on the engine components. This reiterates the demand for efficient cooling. While the convectional cooling system grows in size, it also extracts more power from the engine output. It is, therefore, desired to provide efficient cooling of the hot spots, while avoiding over-cooling of the regions with low or moderate temperature. This method, known as precision cooling, improves local cooling and minimizes overall cooling. This in turn reduces the heat losses and thereby improves the thermodynamic efficiency of the ICE. Local boiling can be an efficient way to implement precision cooling. The heat transfer involving nucleating and collapsing vapor bubbles near the surface of a hot metal is known as nucleate boiling. This phenomenon can positively impact cooling, as a significant amount of heat is extracted from the hot metal for the evaporation of the coolant to its vapor phase. Thus, heat is efficiently transferred locally near the hot spot through the vapor bubbles. However, excessive boiling could be counter productive and can lead to formation of a thin vapor film with low thermal conductivity on the metal surface. This film reduces heat transfer, prevents cooling and can eventually lead to material breakdown. Hence, it is extremely important to use nucleate boiling without the risk of having film boiling. Therefore, accurate estimation of boiling heat flux is the first step towards utilizing the potential of nucleate boiling. The main focus of this work is on numerical models to estimate the wall boiling heat flux. Such numerical models can be used in conjunction with Computational Fluid Dynamics (CFD) to analyse the heat transfer inside an ICE coolant jacket. A semi-mechanistic boiling model, based on established existing models in literature, has been proposed. Experiments performed on simplified geometries, representative of the areas in the ICE where boiling can be encountered, are used for validating the new model. The results from the validation study show that boiling is affected by properties of the flow, fluid and the solid. In addition to an improvement in accuracy of predicting the boiling heat flux, the model also provides a conservative measure to limit boiling and ensure the adverse effects of excessive boiling are not encountered. Finally, the limitations in the current model are discussed along with a possible solution for improvement.
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| 7. |
- Vasudevan, Sudharsan, 1991
(författare)
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Subcooled boiling flow in liquid-cooled internal combustion engines
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Road transport sector contributes significantly to emission of carbon dioxide and other greenhouse gases, which negatively impact the global climate. Efficient management of energy, irrespective of the type of propulsion, has the potential to minimize fuel consumption and to reduce emission of greenhouse gases. This makes thermal (energy) management an indispensable part of automotive propulsion research and development. Cooling plays an important role in protecting the components from failure due to extreme thermal loads. An efficient cooling strategy, such as precision cooling, removes the excess heat precisely from the parts experiencing critical temperatures, without over cooling the component. The thesis focuses primarily on numerical methodologies to explore the potential of local nucleate boiling for efficient cooling of internal combustion engines. Nucleate boiling is a heat transfer phenomenon involving a phase change process, where the liquid coolant vaporizes in the form of bubbles close to the heated surface. Occurrence of nucleate boiling, locally in the vicinity of hot spots, offers a significant potential for efficient precision cooling, but at the risk of encountering film boiling. Film boiling is encountered as a consequence of excessive boiling which leads to coalescence and agglomeration of vapor bubbles, resulting in formation of a thin vapor film, next to the heated surface. On account of the low thermal conductivity of the vapor, film boiling prevents cooling and could potentially lead to material failure. Therefore, tapping the potential of controlled local nucleate boiling is a preferable approach. In the current work, a new semi-mechanistic wall boiling model is proposed that not only estimates the occurrence of boiling, but also the boiling heat flux and the extent of boiling. It is vital to know the extent of boiling in order to avoid, with sufficient margin, the risk of encountering film boiling. The proposed model is validated with results from channel flow experiments available in the literature. Further, the model is implemented in real engine simulations in both single phase and multiphase Computational Fluid Dynamics (CFD) frameworks. The model performance is evaluated by comparing the results of the simulations with relevant measurements. The model estimates the wall boiling heat flux with reasonably good accuracy and indicates the occurrence of excessive boiling with sufficient margin for industrial applications.
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| 8. |
- Vasudevan, Sudharsan, 1991, et al.
(författare)
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Subcooled Flow Boiling in High Power Density Internal Combustion Engines II: Numerical Modeling
- 2022
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Ingår i: SAE International Journal of Engines. - : SAE International. - 1946-3944 .- 1946-3936. ; 16:1
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Tidskriftsartikel (refereegranskat)abstract
- Results from a thermal survey measurement campaign on a four-cylinder Volvo engine was presented in Part I of this article. The focus was predominantly on heat transfer in the engine coolant jacket. This part presents numerical modeling focused specifically on the coolant flow and associated heat transfer in the coolant jacket using computational fluid dynamics (CFD), as a part of a high-resolution complete engine 3D conjugate heat transfer (CHT) model. With local nucleate boiling being an indispensable phenomenon in high power density engines, a dedicated boiling model is essential and is to be used in conjunction with CFD while analyzing heat transfer in the coolant jacket. This article validates a new boiling model with data obtained from the extensive thermal survey measurements, presented in Part I. The new model includes a parameter, based on vapor bubble interactions, that serves as an indication of the transition from beneficial nucleate boiling to high-risk transition and film boiling regimes. This parameter might be used to assess the robustness of new engine designs. The advantages and limitations of the new boiling model are presented and are discussed in detail.
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