Browsing by Subject "Automobiles -- Motors -- Cooling systems"
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Item Automotive cooling system component interactions(Texas Tech University, 2001-05) Walter, John D.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.Item Ram pressure correlations for aspirated cylinders(Texas Tech University, 2004-05) Scholz, Zachary JamesDesign of automobile cooling systems involves tradeoffs in the sizing of grille openings to provide adequate cooling airflow and the tendency to reduce grille opening size to decrease vehicle cooling drag and produce aesthetically pleasing designs. Air that enters the cooling system of an automobile is driven by two major sources, the freestream dynamic pressure resulting from the forward motion of the vehicle and the internal vacuum created by the underhood fan. The flow fields associated with both sources must be considered when assessing the cooling performance of a new automobile design. The current investigation focuses on characterizing the external or dynamic pressure induced flow through a parameter known as the ram coefficient. The investigation utilized an aspirated cylinder in cross-flow as an idealized representation of an automobile front end with grille openings. The pressure distribution on the upstream side of the cylinder model includes a stagnation point and a significant surface pressure gradient similar to those of an actual automobile front end fascia. Various sized openings machined into the side of the cylinder model simulated the grille openings in an automobile. A flexible hose connecting one end of the cylinder to a shop vacuum provided a simulation of the cooling air flow induced by a radiator fan. The primary advantage of the cylinder model is a dramatic reduction in the number of experimental influences on the ram coefficient. The elimination of the various underhood components simplifies the investigation process down to the most basic components, yielding accurate, repeatable results. Primary results are that the cylinder does provide a useful representation of automobile front end. These results verify the general trends seen in previous full scale model tests. Additionally, it was found that ram coefficients for single openings are determined by opening size and location relative to the external surface pressure distribution. It was also found that ram coefficients for combinations of openings can be predicted from knowledge of the performance characteristics of the individual openings.