For reliability and thermal management of power devices, the most frequently used technique is to employ heatsinks. In this work, a new configuration of offset strip fin heatsink based on using the concept of curvy fins and U-turn is proposed with the aim of improving the heat transfer performance. With this aim, a three-dimensional model of heatsink with Silicon Insulated-Gate Bipolar Transistors (IGBTs) and diodes, solder, Direct Bonded Copper (DBC) substrate, baseplate and thermal grease is developed. Richardson’s extrapolation is used for increasing the accuracy of the numerical simulations and to validate the simulations. To study the effectiveness of the new offset design, results are compared with conventional offset strip fin heatsink. Results show that in aspects of design of heatsinks (including heat transfer coefficient, maximum chip temperature and thermal resistance), the new introduced model has advantages compared to the conventional offset strip fin design. These enhancements are caused by the combination of the longer coolant passage in the heatsink associated with generation of disturbance and recirculation areas along the curvy fins, creation of centrifugal forces in the U-turn, and periodic breaking up boundary layers. Also, it is shown that due to narrower passage and back-and-forth route, the new introduced design can handle the hot spots better than conventional design.
Pulsed jets in various configurations have shown potential for improving transport phenomena. In this study, a system of confined laminar two-dimensional pulsed impinging streams of air is simulated numerically by solving the governing conservation equations using the control volume method. The key parameters examined in this study are as follows: frequency and amplitude of pulsation, mean jet Reynolds number and phase difference between the nozzle exit velocity profiles. The effects of these parameters are computed and discussed comprehensively. Temperature is used as a passive tracer to quantify the degree of mixing in the system. Results show that flow pulsation has significant effects on the flow field, vortex formation and secondary structures, which are generated. These vortex structures influence the thermal shear layer and improve the mixing behavior. A better mixing index is observed as a result of the formation of larger vortices due to increased amplitude of the pulsation velocity amplitude. In the range of parameters tested, the frequency of the pulsation is found to have negligible effect on the mixing behavior of the system. Also, it is observed that by introducing a phase difference between the two jet velocity profiles, the stagnation point oscillates between the two jets and, in general, the system with phase differences shows better mixing behavior.
The motion and drying characteristics of a single particle in a novel two-dimensional pulsed opposing jet contactor (POJC) are modeled and discussed. Hot air is used as the drying medium. To simulate particle drying, the gas phase and dispersed phase conservation equations are considered in the Eulerian reference frame and the Lagrangian reference frame, respectively. The RNG turbulence model is used to determine the turbulent characteristics of the gas phase. The particle motion is described by the BBO (Basset-Boussinesq-Oseen) equation. The effects of the key parameters, such as the jet Reynolds number, amplitude of pulsation, frequency of pulsation, particle diameter, location of release of particle from one jet as well as velocity profile on residence time (RT) and particle penetration depth (PN) into the opposite jet, are examined. Results show that POJC has strong potential for particulate heat transfer as well as drying; it can improve evaporation rate relative to the corresponding steady OJC by up to 30% as a result of increased residence time in the impingement zone within the parameter ranges simulated.
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