Nano-Additives to Improve Pumping Capacity

Project / Leader

1G.2 - Eric Loth (UIUC)

Title

Nano-Additives to Improve Pumping Capacity

Statement of Project Goals

The objective of this pump research with nano-scale additives is to investigate whether small concentrations (ppm quantities that do not affect viscosity) of nano-structured solid lubricants and high strength particles with high aspect ratio (nano-scale diameters but micro-scale lengths) can reduce internal leakage in pumping systems

Project's Role in Support of the Strategic Plan

This project directly supports the efficiency thrust. It supports the strategic plan by increasing the fundamental understanding of nano-additives in the context of oils, the critical fluid for hydraulic fluid power.  Furthermore, the additives are planned for use in Test Bed 1 (the excavator) and Test Bed 3 (HHPV) to improve overall system performance.

Description and Explanation of Research Approach

It is well known that additives in significant volume fractions can act like thickening agents to increase the overall viscosity of the fluid.  This can increase the performance of pumps in fluid power by reducing leakage in small gaps.  However, this increase in viscosity also increases the viscous losses in a manner similar to using a different hydraulic liquid.  In this project, it is hypothesized that nano-structured solid lubricants and high strength particles with high aspect ratio (nano-scale diameters but micro-scale lengths) may increase the effective viscosity of the fluid in regions with small gaps (on the order of the particle lengths) while not altering the viscosity in other regions.  This would allow a reduction in internal leakage and thus an increased volumetric flow rate of pump without sacrificing overall power requirements.  Research is required to investigate this potential mechanism.

To investigate nano-additives, high-aspect ratio graphite and multi-wall carbon nanotube additives were added in small amounts (<<1% by volume) to ethanol.  Based on detailed viscometer measurements with gaps on the order of 100 m, the additive concentration levels in ethanol were too small to have any change in viscosity. In order to blend ultrafine graphite particles (<1 micron) into ethanol, ethylcellulose was used as a dispersant with a concentration of 1% by weight. Carbon nanotube dispersion in ethanol was prepared by using a polyglycol acrylic dispersant with the same concentration as ethylcellulose. Pump efficiency measurements were conducted using a hydraulic loop driven by an external gear pump (1750 rpm).  The discharge pressure was manipulated by adjusting the pump's internal relief valve and a needle valve installed downstream of the pump.  Pressure rise, pump volumetric flow rate, and electric power were recorded and used to calculate overall efficiency. 

Figure 3: Efficiency as a function of differential pump pressure for graphite solutions.