Browsing by Subject "Thermal modeling"

Now showing 1 - 6 of 6

A numerical study of the thermal processes relevant to infrared solder reflow
(1990) Bhandari, Ravi Kumar, 1947-; Bergman, T. L.
A numerical model has been developed to predict the transient thermal response of a card assembly subjected to heating conditions found in the infrared solder reflow process. Predictions are compared to analytical solutions and experimental results to validate the model. Additional simulations give insight to important transport mechanisms and suggest the level of sophistication needed to model the infrared solder reflow process. A PCB populated with an array of nine modules is simulated with radiative heating supplied from above and below. The center module's thermal response and the temperature differences across the board and leads are reported. The card assembly geometry is varied to investigate the effects of shading. These simulations are repeated with the use of two simple radiative analyses, which assume minimum and maximum shading effects, respectively. The detailed radiative analysis predictions exhibited the important effects of shading. As shading is increased by increasing the modules' heights, the increased module surface area counteracts the decreased module-to-panel heater view factor and the module's thermal response and temperature differences across the board and leads are relatively unchanged. As shading is increased by decreasing the intermodule spacing, a slower module thermal response causes a greater temperature difference across the board and leads. In contrast, these thermal characteristics were not shown in the predictions of the simple analysis models
An advanced hydraulic-thermal model for drilling & control of geothermal wells
(2021-05-07) Fallah, AmirHossein; Chen, Dongmei, Ph. D.; Bahadur, Vaibhav; Wang, Yaguo; Karimi Vajargah, Ali
Geothermal energy is considered a promising source of green energy production and is more reliable than its clean energy competitors. To generate geothermal energy at a global scale, access to deep geothermal resources with temperatures of 200+ ℃ is necessary. Current drilling technology expertise in the field of oil & gas such as managed pressure drilling (MPD) is currently used to drill challenging extended reach drilling (ERD) and high-pressure high temperature (HPHT) wells under extreme conditions. Applying these technologies to drill geothermal wells enables access to high-temperature resources and globally scalable energy generation. However due to the complexities associated with HPHT conditions and extended lateral sections, efficient drilling and reliable well control during the drilling and operation of geothermal wells is challenging and requires a comprehensive understanding of downhole conditions in real-time. Sophisticated hydraulic modeling is required to accurately capture the complex physics of multiphase wellbore flow. In this dissertation, an integrated hydraulic and thermal model is developed based on a drift-flux modeling (DFM) approach applied to the conservation equations of the multiphase flow in wellbores. A semi-implicit numerical scheme is used to solve the transient governing equations, allowing the use of small time-steps to simulate automated drilling and well control operations in real-time. To apply the model to the wide range of scenarios observed in drilling and operation of DCLG wells, various sub-models are developed and integrated that simulate complex phenomena such as gas solubility and break-out, cuttings settling and bed blockage, rock formation cooling, temperature-dependent fluid properties, pressure waves and automated MPD choke control, etc. The developed modeling approach is applied to various scenarios during the drilling and operation of deep CLGS (DCLGS) wells. The following applications are explored in this work: (1) Reservoir influx detection and automated gas kick control under HPHT conditions, which is governed by liquid-gas multiphase flow; (2) Hole cleaning and cuttings transport modeling in horizontal wells, which is governed by liquid-solid multiphase flow; and (3) Operation and performance analysis of DCLGS wells with barefoot lateral sections, which is governed by liquid single-phase flow.
Feedback control of gas metal arc braze-welding using thermal signals
(2011-08) Shah, Sanjiv Edlagan; Howell, John R.; Seepersad, Carolyn; Taleff, Eric M.; Ezekoye, Ofodike A.; Prime, Michael B.
In serial manufacturing processes, localized energy sources (e.g. plasma cutters, arc welders or water jets) induce material geometry transformations that yield a desired product. Simple parameter control of these energy sources does not necessarily ensure an optimal or successful part because of disturbances in the manufacturing process (material and temperature variations, etc). Currently, control in manufacturing is based on statistical process control where large databases for the manufacturing of a fixed process are available and have been compiled over several manufacturing runs. In the absence of a statistical database, and with the increased need for improved monitoring and throughput, there is need for active process control in manufacturing. In this work, Gas Metal Arc Braze-Welding (GMABW) will serve as a test-bed for the implementation of model predictive control (MPC) for a serial manufacturing process. This dissertation investigates the integration of real time modeling of the temperature field with control algorithms to control the evolving temperature field in the ix braze-welded base metal. Fundamental problems involving MPC that are addressed are modeling techniques to calculate temperature fields with reduced computational requirements and control algorithms that utilize the thermal models directly to inform the controller. The dissertation first outlines and compares analytical and computational thermal models and comparison with experimental data are obtained. A thermal model based on a metamodeling approach is used as the plant model for a classical control system and control parameters are found. Various techniques for dealing with signal noise encountered during experimentation are investigated. A proportional controller is implemented in the experimental setup that applies feedback control of the braze –welding process using thermal signals. A novel approach to MPC is explored by using a metamodel as the plant model for the braze-welding process and having the temperature trajectory dictated by the metamodel in the steady state region of the weld. Lastly, future work and extensions of this research are outlined.
Hybrid neural net and physics based model of a lithium ion battery
(2011-05) Refai, Rehan; Chen, Dongmei, Ph. D.; Fernandez, Benito R.
Lithium ion batteries have become one of the most popular types of battery in consumer electronics as well as aerospace and automotive applications. The efficient use of Li-ion batteries in automotive applications requires well designed battery management systems. Low order Li-ion battery models that are fast and accurate are key to well- designed BMS. The control oriented low order physics based model developed previously cannot predict the temperature and predicts inaccurate voltage dynamics. This thesis focuses on two things: (1) the development of a thermal component to the isothermal model and (2) the development of a hybrid neural net and physics based battery model that corrects the output of the physics based model. A simple first law based thermal component to predict the temperature model is implemented. The thermal model offers a reasonable approximation of the temperature dynamics of the battery discharge over a wide operating range, for both a well-ventilated battery as well as an insulated battery. The model gives an accurate prediction of temperature at higher SOC, but the accuracy drops sharply at lower SOCs. This possibly is due to a local heat generation term that dominates heat generation at lower SOCs. A neural net based modeling approach is used to compensate for the lack of knowledge of material parameters of the battery cell in the existing physics based model. This model implements a neural net that corrects the voltage output of the model and adds a temperature prediction sub-network. Given the knowledge of the physics of the battery, sparse neural nets are used. Multiple types of standalone neural nets as well as hybrid neural net and physics based battery models are developed and tested to determine the appropriate configuration for optimal performance. The prediction of the neural nets in ventilated, insulated and stressed conditions was compared to the actual outputs of the batteries. The modeling approach presented here is able to accurately predict voltage output of the battery for multiple current profiles. The temperature prediction of the neural nets in the case of the ventilated batteries was harder to predict since the environment of the battery was not controlled. The temperature predictions in the insulated cases were quite accurate. The neural nets are trained, tested and validated using test data from a 4.4Ah Boston Power lithium ion battery cell.
Thermal modeling for calculation of formation temperatures for deep water wells with chemical heat source
(2015-12) Incedalip, Oguz; Oort, Eric van; Espinoza, David Nicolas
Drilling through depleted zones is becoming more common as the resources are exhausted and the fields mature. To be able to access deeper sections of the reservoirs, it is essential to drill through depleted zones effectively. This need brings around the challenges including severe lost circulation and poor zonal isolation. Artificially strengthening the wellbore is of crucial importance in order to achieve successful drilling as well as cementing for deep water wells. Altering the thermal stresses results in increased tangential stresses in the vicinity of the wellbore and therefore increases the fracture gradient. Thermal stresses can be increased through a controlled exothermic chemical reaction of certain salts which are coated via pharmaceutical techniques to delay the reaction until the carrier fluid transports the materials to the target zone. This approach with its innovative method surpasses other methods like downhole heaters as it is more practically feasible. The technique has a great potential to decrease mud losses, hence to decrease non-productive cost and time. In this study a computational thermal model is developed in order to calculate the temperature distribution of the formation as well as the annular and tubular fluids for given heat generation rates. The numerical model which uses finite volume techniques is developed for an axisymmetric cylindrical geometry including the drilling fluid, casing, annulus, and formation for transient heat transfer including a time and location dependent heat generation source. The results are analyzed in comparison to one analytical solution as well as a commercial software package, Drill Bench, in order to verify the accuracy of the model for scenarios with no heat generation, since modelling of heat generation is not available for the other approaches. Some parameters of the model such as the heat transfer coefficient are calibrated in order to achieve the best agreement between different analyses. Heat generation rates are obtained for different chemical compounds tested in insulated calorimeter experiments. The results of different heat generation rates for different heat generation durations as well other problem parameters such as circulation rate are investigated. In addition, thermal stress calculations based on the temperature increase are also presented.
Thermal modelling of the infrared solder reflow process
(1992) Eftychiou, Marios A., 1964-; Bergman, T.L.
A numerical model has been developed to predict the transient thermal response of a typical card assembly during infrared solder reflow. The model solves the transient, two-dimensional, laminar, compressible, and variable-property Navier-Stokes and energy equations which are coupled with the two-dimensional conduction and differential diffuse-gray radiation exchange equations. To validate the model, algorithm predictions are compared with published benchmark solutions. A base case geometry and operating conditions are defined and parametric investigations of the reflow process are performed to determine the important transport mechanisms and quantify the sensitivity of the process to uncertainties in convective and radiative conditions. The response of a typical card under reflow conditions is also presented. Predictions show that, for the case considered here, radiation is the dominant mode of heat transfer. The mixed convection heat transfer rates, although smaller than the radiative heating rates, affect the soldering process