The present work considers Transient electrothermal simulation of sub-micrometer silicon device and electron-phonon interactions in electrical and thermal fields. A coupled thermal and electrical model is developed for a silicon n+ − n − n+ structure consisting of the hydrodynamic equations for electron transport and energy conservation equations for phonon. The results indicate that, for one electric field the lattice temperature gradient has significant effect on the magnitude of electric current. The Transient phonon temperature affects the device performance due to the change of mobility and gradient temperature of electron. At an external voltage of 0.1 V, calculations show that an increase in the junction boundary temperature by 100°C, cause increasing the drain current by 16% at 3 picosecond and decreases it by 17% up to steady state condition.

In the boundary element formulation of heat conduction, the heat source effect imposes an additional domain integral term on the system of integral equations. With this term, an important advantage of the boundary element method as a boundary-only formulation will be lost. This paper presents an accurate method for the evaluation of heat source domain integrals, with no need of domain discretization. Transformation of the domain integral into the corresponding boundary integral is carried out using Green's theorem. Both time-dependent and time-independent fundamental solutions are considered. The methodology can be implemented in general and for similar situations. Numerical examples will be presented to demonstrate the accuracy and efficiency of the presented method.

Transient natural convection in a square cavity is studied numerically. Before the onset of heat transfer, the temperature is uniform throughout the cavity. Then the side walls are heated and cooled by +Delta T and -Delta T,respectively. The top and bottom walls are insulated. The problem is formulated by the unsteady 2-D differential equations. In this study, Ra ranged from 10(-1) to 10(10) with Pr fixed at 0.71. The differential equations are solved by a control-volume-based finite difference method. With the unsteady formulation, the results are presented for the Transient and steady states. It is found that, at higher Pa, the heat transfer coefficient has an oscillatory behavior as it approaches the steady solution Isotherms are also examined at different times.

In the present study, Computational Fluid dynamics is used for heat transfer studies in the dimple, and flat plate heat exchangers. By employing water as a working medium (fluid), the same and different flow analyses were numerically studied. SOLID WORKS 2018 software was used for the study. The study primarily investigated the effect of the flow rate of hot fluid on the overall heat transfer coefficient. The study also analyzed the influence of hot fluid’, s Reynolds number on cold fluid’, s Nusselt number. It was observed that an increase in the mass flow rate of the hot fluid from 0. 016 to 0. 067 kg/s resulted in an increase in the heat transfer coefficient from 65 to 298 W/(m2. K) for the dimple plate heat exchanger (DPHE). Meanwhile, an increase in the Reynolds number of the hot fluid (from 200 to 1000), induced an increase in the Nusselt number of the cold fluid from 1. 9 to 8. 7 for DPHE. A correlation was developed to calculate the Nusselt number for the same flow analysis of the flat plate heat exchanger (FPHE). The study also compared the performance of the DPHE with that of the FPHE. The results of the same flow analysis indicated that the DPHE exhibited a Nusselt number value 39% greater than the FPHE at the highest mass flow rate of 0. 067 kg/s, while in different flow analysis, the DPHE demonstrated a Nusselt number value 41% greater than the FPHE at the highest mass flow rate of 0. 067 kg/s.