Numerical and experimental investigation on heat transfer of multi-heat sources mounted on an array of printed circuit boards in a rectangular case

Conjugate heat transfer in an electronic module containing an array of printed circuit board assemblies (PCBAs) was experimentally and numerically investigated. Each PCBA was assembled with a matrix of rectangular heat sources (4 x 4 with 0.5 W each). It was inserted in parallel in an aluminum case by leaving two opposite opened ends to allow air to flow through. The experiment and simulation were carried out on three different cases based on module orientations and PCBA arrangement; horizontal orientation with PCBA facing upwards (CASE I) and downwards (CASE II), and vertical orientation (CASE III) under both natural and forced convection at an ambient temperature of 30 degrees C. The simulation was done by varying the number of PCBAs (N) from 5 to 7 sets, the distance (1) between PCBAs array and module wall from an original design of 10 to 20 mm by an increment step of 5 mm, and air velocity from 1 m/s to 4 m/s. The results showed that under natural convection the global maximum temperature increased slightly (from 64.9 degrees C to 65.9 C) as the number of PCBAs increased from 5 to 7 sets for the vertical orientation module (CASE III), while it increased significantly (from 97.9 C to 127.4 degrees C) for the horizontal orientation module (CASE I). When the number of boards in the module increased, the board that possessed the global maximum temperature would vary in board position in the module according to the module's orientation. However, the location of global maximum temperature on that board was still in the same region in the heat source matrix. By increasing the distance (1) between PCBA and the module wall, the heat transfer was enhanced. Under forced convection, it can be observed that the drawback of heat removal from the horizontal orientation module diminished under forced convection when air speed was sufficiently high. The global maximum temperature decreased with an increase in the air speed from 63.5 degrees C to 48.7 degrees C and from 64.7 degrees C to 48.8 degrees C for the six PCBAs of CASE III and CASE I, respectively. A comparison of the experimental and numerical results shows good agreement for both natural and forced convection.