Hierarchic modeling of heat transfer processes in heat exchangers

An alternate approach based on hierarchic modeling is proposed to simulate fluid and heat flow in heat exchangers. On the first level, the direct simulations have been performed for the geometry that is similar to a segment of the examined heat sink. Based on the obtained results, the Reynolds number dependencies of the scaling factors f and StPr^2/3 have been established. On the second level, the integral model of the whole heat sink has been built using the volume averaging technique (VAT). The averaging of the transport equations leads to a closure problem. The direct model Reynolds number dependencies f and StPr^2/3 have been used to calculate the local values of the drag coefficient and the heat transfer coefficient , which are needed in the integral model. The example calculations have been performed for 14 different pressure drops across the aluminum heat sink. The whole-section drag coefficient and Nusselt number have been calculated and compared with the experimental data [M. Rizzi, M. Canino, K. Hu, S. Jones, V. Travkin, I. Catton, Experimental investigation of pin fin heat sink effectiveness, in: Proc. of the 35th National Heat Transfer Conference Anaheim, California, 2001]. A good agreement between the modeling results and the experiment data has been reached with same discrepancies in the transitional regime. The constructed computational algorithm offers possibilities for geometry improvements and optimization, to achieve higher thermal effectiveness.     

Use of the microscopic parabolic heat conduction model in place of the macroscopic model validation criterion under harmonic boundary heating

Parabolic heat conduction models are considered. The validity of using a microscopic under harmonic fluctuating boundary heating source is investigated. It is found that using the microscopic parabolic heat conduction model is essential when . The phase-shift between the electron gas and solid lattice temperatures is found to be . This phase-shift reaches a fixed value of 1.5708 rad at very large values of . It is found that using the microscopic parabolic heat conduction model is essential when rad/s for most metallic layers regardless of their thickness.