Thermal management has become a key constraint 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. 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 scaling laws, and their efficiencies reduced. This paper investigates such deviations, and reduced efficiency, through experimental measurements of the performance of two geometrically-similar pumps of – a fully scaled pump of diameter 34.3mm, and a half scale version of the same construction. A facility for the measurement of bulk pressure-flow performance characteristics is described. Particle Image Velocimetry (PIV) measured velocity profiles were extracted at varying radii in the blade passages, and at varying angular positions in the volutes. The absolute, relative, radial and whirl velocity vectors were evaluated for each flow field at three operating points and compared with conventional pump theory. The data was plotted non-dimensionally to investigate points of similitude. Fluidic phenomena occurring in the impeller passage at both pressure and suction sides of the impeller blades are addressed. The theoretical velocity triangles occurring at the impeller tip are compared with the experimental data. The blade angle at inlet and discharge are found to have a large bearing on the poor pumping performance. The quantitative velocity characteristics are discussed in the context of efficiency degradation at decreasing Reynolds numbers.

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