Automotive cooling system component interactions
In the development of automotive cooling systems, cooling airflow rate predictions are generally based on cooling system component flow resistance characteristics obtained from tests of individual or "isolated" components. The assumption is that the flow resistance of a complete cooling package is equivalent to the sum of the flow resistance of the isolated components. It is shown in the current investigation that this assumption can lead to significant errors in calculations of the net flow resistance of the cooling package. Furthermore, it is demonstrated that the interaction between the fan and the surrounding components is the primary source of this discrepancy. Understanding how the fan interacts with the other cooling package components is the key to understanding component interactions.
Fan pressure jump evaluations based on thrust measurements taken while the fan is operating downstream of a heat exchanger(s) and upstream of the engine bay are shown to provide accurate installed fan performance evaluations. It is found that restriction of the swirl component upstream of the fan by a low resistance flow straightening device does not significantly affect fan performance. However, as the free flow area of the heat exchanger decreases (i.e., as the blockage increases), the fan performance is modified. The engine bay, a downstream obstruction in the direct path of the fan efflux, does not significantly affect fan performance.
An isolated heat exchanger mounted on a flowstand experiences an approximately uniform approach flow. In contrast, when mounted in a cooling package, the energy input from the fan and blockage at the comers of the fan shroud induces a less uniform flow which must always lead to higher heat exchanger pressure drops. Utilizing the fan thrust and plenum pressure measurements, the "installed" (i.e., mounted as part of the cooling package) heat exchanger pressure drop is readily evaluated and the results support the conclusion that interference effects lead to a higher heat exchanger pressure drop.