The need for methods to predict temperatures of electronic packages is becoming more important as time to market decreases and the need to reduce engineering costs increases. Geometric parameters that are commonly found in a card cage computer design are duct height to package height ratio (H/B) and longitudinal to latitudinal spacing (L/D). The velocity of the air flowing through the card cage is also an important parameter. The purpose of this experimental research is to develop correlations that can be used to predict heat transfer coefficients and thus temperatures of electronic packages in a staggered array in the hydrodynamic and thermal entrance regions of a duct. The ten components in the array are mounted on one wall of the duct to simulate a printed circuit board in a card cage. Results are presented for three values of Reynolds number (20250, 50000 and 65000) for a range of H/B from 1 to 5 by increments of 2 while L/D is varied from 1 to 3 by increments of 0.5. Comparisons are made between upstream and downstream packages. It was determined that one correlation could be used to predict the Nusselt number for upstream heatsinks. This correlation is a function of Reynolds number and H/B. The results also indicate that three correlations are necessary to predict the Nusselt number of downstream heatsinks. When H/B = 1, the Nusselt number is only a function of Reynolds number; when H/B is greater than 1 and L/D is less than 2, the Nusselt number is dependent on Reynolds number, H/B and L/D; when H/B is greater than 1 and L/D is greater than or equal to 2, the Nusselt number is a function of Reynolds number and H/B.

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