Particle image velocimetry is a well-established technique that Lubrizol has employed to visualise and quantify fluid flow. The hydraulic fluid is seeded with microscopic particles, and under laser illumination, the particle motion can be captured with high speed cameras.

This allows visualisation and quantification of undesirable flow behaviours. For instance, a fluid approaching a pipe bend has coherent and largely non-mixing streamlines that comprise the primary flow path. The fastest moving fluid is in the centre of the channel, whilst slower-moving fluid hugs the pipe walls.

As this fluid transits the bend, a secondary flow emerges with a vortex-like motion that mixes the streamlines (Figure 1). The fast-moving fluid is then combined with the slow-moving fluid causing a loss in momentum. This results in a pressure drop across the pipe bend leading to reduced hydraulic power.

As wasted energy typically manifests itself as heat, it is unsurprising that in addition to flow improvements a reduction in operating temperature is also observed (Figure 2). Sump temperatures can be lowered by up to 5 °C, which has practical benefits on fluid life and durability by limiting thermal stress. A reduced burden on energy intensive cooling systems further contributes to total system efficiency.

In addition to its unique energy-saving features, this new hydraulic fluid was carefully formulated to exceed the requirements of main-line hydraulic pump OEM specifications.

Retention of performance is assured by its exceptional shear stability. Unlike many conventional hydraulic fluids on the market,the energy-efficient fluid does not shear out-of-grade after industry standard shear testing. The robust additive technology extends fluid life, potentially leading to longer drain intervals.

Tightly controlled field trials were conducted to accurately compare Lubrizol’s energy-efficient hydraulic fluid against conventional multi-grade and mono-grade examples. In all cases, the formulations consisted of API Group II base oils, an anti-wear hydraulic fluid additive and a pour point depressant.

The comparative multi-grade fluid contained a poly(alkyl methacrylate) [PMA] viscosity modifier making it highly representative of many readily available multi-grade fluids. Crucially, and in contrast to several other studies, all the formulations were ISO viscosity grade 46 and met industry requirements for OEM hydraulic fluid specifications Parker Denison HF-0 and Eaton Brochure E-FDGN-TB002-E.

The real-world relevance of the field trials was ensured by comparing all fluids at equal viscosity and testing

Figure 1: An illustration of fluid flow and the energy depleting mixing motion induced in pipe bends. Continued on page 12 LUBE MAGAZINE NO.158 AUGUST 2020 11

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