CONJUGATE HEAT-TRANSFER WITH BUOYANCY EFFECTS FROM MICRO CHIP SIZED REPEATED HEATERS

Laminar mixed convection heat transfer across five in-line microchip-s ized heaters, surface mounted on printed circuit board (PCB), was inve stigated by the weighted residual finite element method. The effects o f axial heat conduction within the PCB for both mixed convection and p ure forced convection are reported. The flow regime considered was 200 less than or equal to Re less than or equal to 800 and 0 less than or equal to Gr less than or equal to 58,000. Internal heat generation wa s included in the microchip-sized blocks in order to accurately model the thermal response to predict the maximum temperature rise. On the o uter PCB walls, convective heat transfer conditions were given. Thermo physical and transport properties based on materials used in the elect ronics industry, including orthotropic thermal conductivity in PCB, we re used. The flow and solid domains were solved simultaneously. A sens itivity study of PCB heat transfer coefficients, isotropic thermal con ductivity, thermal conductivity variations, and spacing effects was pe rformed. The mixed convection transient heating process was compared w ith the steady-state formulation to estimate the influence of flow osc illation in heat transfer. It was found that the maximum temperature r ise in the microchips predicted by pure forced convection was, at most , 10 percent higher than that predicted by mixed convection. The diffe rence in maximum temperature between the trailing and leading chips in the array was 30 percent.