Experimental modeling of the passive cooling limit of notebook computers

Rapid expansion of the portable computing market segment coupled with ever increasing power dissipation and severe battery power limitations are combining to bring new importance to the development of minimum-energy thermal solutions for notebook-type computers. Passive cooling provides a very attractive thermal management option for such systems. Determination of the amount of heat that can be passively dissipated from the outer surfaces of a notebook computer provides thermal designers with a well-defined performance target and a quantitative demarcation between actively and passively cooled equipment categories. Previous work has analytically and numerically estimated the passive cooling limit from the external surfaces of a 305×248 mm notebook and found that as much as 38.8 Watts could be dissipated. The current paper describes the experimental validation of the natural convection models, underpinning those results, and the apparatus used to obtain the necessary data. The measurement error and repeatability in this apparatus are also described. In addition to validating the isolated, isothermal natural convection models, experiments were conducted to explore "real world" behavior, such as 3-D flow effects and interactions between heat dissipating surfaces. The experimental results are used to refine the theoretical limits on passive cooling.