An experimental and theoretical investigation of the pumping performance of geometrically similar flow fields within miniature-scale centrifugal pumps

Thermal management has become a key point in the development of contemporary electronics systems. It is evident that heat fluxes are currently approaching the limits of conventional forced air cooling, and that liquid cooling technologies are now under consideration. Most recent research in liquid cooling has focused on primary heat removal, with relatively little attention paid to liquid pumping. As the space available to incorporate a pump is often limited, miniature-scale pumps are required. Because such pumps operate at low Reynolds numbers, their operation may deviate from that predicted from the conventional pump affinity laws, and their efficiencies reduced. This paper investigates such deviations, and reduced efficiency, through experimental measurements of the performance of three pumps of varying scale. The pumps were fabricated using transparent material to allow optical access for PIV measurements. A characterization facility is described, which allows measurement of bulk pressure-flow performance characteristics. The measurements demonstrate that variations in diameter, without changed pump height, cause deviation from the affinity laws, whilst the characteristics of pumps whose diameter and height are varied proportionately obey the affinity laws. Efficiency was seen to reduce significantly with Reynolds number. PIV measurements of flow in the pump blade passages are also presented, which show a clear increase in the absolute velocity vectors within the blade passage and conversely a decrease in fluid velocity directly after blade tip in the expanding volute of the pump. The paper concludes that pump scaling laws predict accurately the pump performance in downsizing a geometrically identical pump but fail to predict when all aspects of the pump are scaled except height. It is also concluded that there is a significant decrease in efficiency in pump performance at low Reynolds numbers.