G. Bognár | Searcharxiv

arXiv2023

Analytical investigation of time-dependent two-dimensional non-Newtonian boundary layer equations

In this study, five different time-dependent incompressible non-Newtonian boundary layer models in two dimensions are investigated, including external magnetic field effects. The power law, the Casson fluid, the Oldroyd-B model, the Walter fluid B model and the Williamson fluid are analyzed. For the first two models, analytical results are given for the velocity and pressure distributions, which can be expressed by different types of hypergeometric functions. Depending on the parameters involved in the analytical solutions of the nonlinear ordinary differential equation obtained by the similarity transformation, a very wide range of solution types is presented.

physics.flu-dyn↗

arXiv2021

Self-similar analysis of the time-dependent compressible and incompressible boundary layers including heat conduction

We investigate the incompressible and compressible heat conducting boundary layer with applying the two-dimensional self-similar Ansatz. Analytic solutions can be found for the incompressible case which can be expressed with special functions. The parameter dependencies are studied and discussed in details. In the last part of our study we present the ordinary differential equation (ODE) system which is obtained for compressible boundary layers.

physics.flu-dyn↗

arXiv2007

Contactless Thermal Characterization Method of PCB-s Using Different IR Sensor Arrays

In this paper the methodology and the results of a quasi real-time thermal characterization tool and method for the temperature mapping of circuits and boards based on sensing the infrared radiation will be introduced. With the proposed method the IR radiation-distribution of boards from the close proximity of the sensor card is monitored in quasi real-time. The proposed method is enabling in situ IR measurement among operating cards of a system e.g. in a rack, enabling the immediate detection of potential hot spots in the system. . The elevated temperature encountered in different packaged electronic devices, like digital processors, high power amplifier, high power switches, etc., demands the application of careful temperature-aware design methodologies and the electro-thermal simulations of PCBs. The results of different electro-thermal simulations and modeling in most of the cases give good approximating results and consider the coupled effects of the real surroundings of these cards and other dissipation elements in an operating system. However the simulation time may take hours, and different systems, different surroundings should be simulated again and again. In our expectation, by using contactless temperature measurement procedure the heat distribution and the places of high dissipation elements on an operating PCB board (PCI or AGP cards in a rack-house of a PC) can be measured and localized in a dense rack system, where only a thin measuring board can be inserted between the cards during operation.

cond-mat.mtrl-sci↗