Numerical and Experimental Investigation of a Volumetric Resistance Blower Performance and Its Optimization for Portable Computing Device Applications

Abstract

In this paper, we present our results on a relatively new kind of blower called Volumetric Resistance Blower (VRB) for cooling of portable computing platforms like laptop computers. The VRB performance was modeled numerically and compared to traditional bladed blowers. The sources of noise, dominant in bladed blower are absent in case of VRB, because it uses a continuous porous disc instead of discrete blades. Thus, even though at iso-rpm, VRB yielded lower flow rate, its iso acoustic performance could be superior. Hence, further analysis was crucial to quantify the potential benefit. The acoustics experiments for bladed blower and VRB were conducted in a hemi-anechoic chamber in accordance with ECMA-74[1] and ECMA TR/99 [2] standards. Iso-acoustics pressure vs volume flow rate plot for both bladed blower and VRB are compared. VRB was found to have superior performance as compared to bladed blower. The volume flow rate at open flow condition for bladed blower and VRB are comparable, but as back pressure increased the flow rate yielded by VRB kept increasing and at stagnation condition, VRB showed around 79% higher static pressure. In the second part of the work, the experimentally validated numerical model for VRB was used for numerical optimization using a DOE approach and varying the geometrical parameters. Rotor distance (minimum distance from the axis of rotation of impeller to the cutwater surface) was found to be the most important parameter and an optimum value was found. A second DOE elucidated the optimal rotor hub center location in the 2-dimensional space inside the casing as when the rotor is tucked back into the casing as much as possible and when the rotor distance is above 20.15 mm. A partial P-Q curve is generated (up to 20 Pa) for optimal geometry configuration. Based on the numerical and experimental evidence, VRB is found to have the potential to replace traditional bladed design in portable computing devices. In addition, due to absence of blades, it creates lower tonal noise, giving a much more comfortable experience to the end user.