Conjugate Heat Transfer With Buoyancy Effects From Micro-Chip Sized Repeated Heaters

Laminar mixed convection heat transfer across five in-line microchipsized heaters, surface mounted on printed circuit board (PCB), was investigated by the weighted residual finite element method. The effects of axial heat conduction within the PCB for both mixed convection and pure forced convection are reported. The flow regime considered was 200 ≤ Re ≤ 800 and 0 ≤ Gr ≤ 58,000. Internal heat generation was included in the microchip-sized blocks in order to accurately model the thermal response to predict the maximum temperature rise. On the outer PCB walls, convective heat transfer conditions were given. Thermophysical and transport properties based on materials used in the electronics industry, including orthotropic thermal conductivity in PCB, were used. The flow and solid domains were solved simultaneously. A sensitivity study of PCB heat transfer coefficients, isotropic thermal conductivity, thermal conductivity variations, and spacing effects was performed. The mixed convection transient heating process was compared with the steady-state formulation to estimate the influence of flow oscillation in heat transfer. It was found that the maximum temperature rise in the microchips predicted by pure forced convection was, at most, 10 percent higher than that predicted by mixed convection. The difference in maximum temperature between the trailing and leading chips in the array was 30 percent.