Impact of fluid-mover characteristics on heat exchanger performance: A new reality-based analysis approach

The performance of convective heat transfer devices is necessarily linked to the characteristics of the participating fluid flow. The most common connection between the heat transfer and the fluid flow is by means of the Reynolds number. However, the Reynolds number provides very limited information about the nature of the fluid flow that is conveyed to the heat exchange device by the fluid mover. Other highly relevant features of the fluid presented to the inlet of the device include steadiness, uniformity, unidirectionality, and flow regime. These characteristics are highly dependent on the type of the participating fluid mover. In both the published heat transfer literature as well in traditional thermal design modalities, these and other fluid flow issues are virtually absent. Consequently, device-specific heat transfer results are presented without any reference to the fluid-mover and to the nature of the flow that it provides. The goal of the present research is to demonstrate that this traditional approach to heat transfer analysis and design may give rise to significant errors. It is demonstrated that the performance of a heat transfer device may be strongly impacted by the nature of the flow provided to it by the specific participating fluid mover. In such situations, the performance of the heat transfer device is actually the result of the performance of a system consisting of the device and the fluid mover. The conclusions set forth here are based on numerical simulations of a reality model which meticulously models an actual rotating fan and a multi-member fin array. A second model, designated as the baseline case, utilizes the best available literature model to obtain heat transfer results for comparison with those from the reality model. The baseline model follows the traditional approach of ignoring the actual attributes of the fan-delivered flow. It was found that the baseline model overestimates the heat transfer rate by almost a factor of two.