Abstract
In recent years, CO2 emission constraint has been strengthened worldwide in order to fight global warming, and it is believed that the demand for compact and energysaving car will be increasing year after year. On the other hand, larger interior space of vehicle and lower noise level are demanded to assure passenger comfort, so that it is getting more and more important for the HVAC to be space-saving, energy-saving and low noise type.
Therefore, we have developed the new type of compact high-efficiency blower fan for the compact HVAC. Because of the requirements that the blower fan to be not only small size but energy-saving and low noise efficient, we started this development by modifications for basic blower fan internal air flow system of existing products. Generally, Sirocco fan, which is compact and able to supply high pressure, is often adopted for blower to be used for car airconditioner. Previously, some studies (1-4) reported that flow loss and fluid noise were mostly generated at the areas in between fan blades, yet those generation systems were still not completely clarified.
This paper includes following important results concerning the newly developed blower fan.
First, basic analysis of Sirocco fan airflow mechanism was conducted to apprehend fundamental causes of total pressure loss and fluid noise generation. Especially for the flow visualization between rotating blades, we newly created "Image derotator devise". This device makes it possible to visualize the airflow movement between rotating blades with temporal continuity. Using this innovative device, we investigated how the flow condition between blades changes as the fan rotates inside the scroll casing, as a result it is found that flow loss and fluid noise were caused by next three factors.
A. The separation at the blade leading edge
B. Inhomogeneity by the influence of the separation at the suction department
C. The rapid change of the flow between blades while the blades pass the nose of the scroll casing. This especially causes the broad band noise.
Next, on the basis of those investigations, we succeeded to establish the technology of airflow homogenization at the areas between blades so that we did productization of the compact high efficiency blower fan.
Finally, As for the compact high-efficiency blower fan which applied the technology of airflow homogenization, the blower volume decreased by 30%, the power consumption decreased by 15% and the specific noise level reduced by 1dB(A) comparing the conventional blower fan. Thus, substantial improvement in the blower fan was achieved and this technology will be applied to the next generation blower fan.
This is a report how we achieved the project.
Keywords: Air Conditioning / HVAC, Blower Fan, Flow visualization, Fluid noise, Fan efficiency