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Effect of temperature, flow rate and contamination on hydraulic filtration

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The performance of a mechanical filter is an implicit function of many variables pertinent to fluid condition, flow variables, filter element condition and operational parameters. This paper presents the details and results of a parametric study that examined the effect of oil temperature, contamination level and flow rate on the performance of a hydraulic filter through laboratory experiments. A 5 μm rated commercial filter with glass fiber made element that had an effective surface area of 0.154 m2 through 57 pleats was used to filter VG32 hydraulic oil. The filtrate was supplied with the contaminant of ISO medium test dust at four gravimetric levels - 2, 5, 8 and 10 mg/L of oil. The tests were conducted at the flow rates of 40 and 120 L/min for different oil viscosities, corresponding to the temperatures of 30, 40, 50 and 60o C. As the temperature increases, the oil viscosity decreases due to weakened cohesive forces, which leads to increased filtration rates and hence more time to build the pressure, upstream of the element. On the other hand, the pressure on upstream of filter bed builds up at higher rate when the filtrate has higher level of contamination loading. An extensive investigation on the effect of flow variables and oil condition parameters on the pressure drop across the element would therefore give a better knowledge about filter element lifetime.
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... For this study, comprehensive laboratory tests have been made in order to produce filtration performance data relating the effect of flow rate, contaminant particle concentration, and fluid temperature to the pressure drop measured over the filter element. [9] In this paper, the laboratory test results will be analysed and mathematical correlation expressions will be derived from the experimental data giving estimates for the pressure drop over the filter as a function of the operating conditions and service time. While these mathematical correlation expressions represent the nearterm goal, the aim of the future research is to develop Internet-of-things (IoT) enabled, smart filtering connected to the overall computerized condition monitoring solution in the machine system, e.g., in a ship. ...
... The oil that was used was the standard ISO VG 32 hydraulic oil. [9] The different oil conditions considered for this study were the oil flow rate, temperature, and gravimetric contamination level. For adjusting the gravimetric contamination level, the fluid was subjected to ISO medium test dust (ISO12103-1-A3) at different rates resulting in four different contamination levels at 2 mg/l, 5 mg/l, 8 mg/l and 10 mg/l. ...
... For adjusting the gravimetric contamination level, the fluid was subjected to ISO medium test dust (ISO12103-1-A3) at different rates resulting in four different contamination levels at 2 mg/l, 5 mg/l, 8 mg/l and 10 mg/l. The flow rates were set to 40 l/min, 80 l/min and 120 l/min, and the fluid temperatures were adjusted to 30 °C, 40 °C, 50 °C, and 60 °C, [9]. Figure 1 illustrates the types of effect that the different oil conditions have on the pressure drop development over time. ...
Conference Paper
In fluid power systems, one of the most common causes of failure is contamination of the hydraulic fluid. Without filtering the fluid gets contaminated with harmful particles over time, which will cause excessive wear of components or even block motion of parts in flow control valves. In order to avoid machine downtime, it is important to monitor that adequate technical performance level of the fluid is maintained at all times. This study contributes to condition-based maintenance of hydraulic fluid filter units by establishing a correlation equation, based on comprehensive laboratory tests and incorporated in a simulation model, relating the pressure drop over the filter unit with the main variables describing the operating conditions of the fluid system as well as with filter operating time. The paper describes how the correlation equation and the simulation model was constructed. The results indicate that good correlation was obtained (R-square value 0.98) with the constructed equation between the physical variables and the temporal development of the pressure drop over the filter. The model can be used as a building block for a smart filter unit that can predict its lifetime.
... This resulted in 48 experiments in total. The experimental results, including the test bench description, was described in more detail in [7]. Figure 1 illustrates examples of the different experiments. ...
Conference Paper
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In hydraulic systems, the presence of foreign material in the system oil accounts for the majority of system troubles due to mechanical wear of components, sticking of different parts etc. Therefore, it is essential to maintain an adequate cleanliness level of the fluid at all times through filtration. Mechanical filters are used for this purpose, to separate solid particles from the system oil. As a hydraulic filter gets accumulated with dirt throughout its service life, the pressure drop over the filter element increases. This pressure drop is typically used for determining the lifetime of a filter element: once a predetermined pressure drop at certain flow conditions has been reached, the filter has accumulated enough dirt to require servicing or replacement. In this paper, a correlation model has been developed to describe the effects of flow and fluid properties on the dirt holding capacity and the service life duration of a hydraulic filter. For this purpose, extensive laboratory tests have been carried out in order to measure the pressure drop development of a filter unit at different oil flow rates, viscosities and gravimetric contamination levels. The work in this paper has been done as part of the initial research for investigating the effects of different flow and fluid parameters on hydraulic filtration. The aim of the overall research project is to develop an IoT-enabled smart filter unit that could predict its remaining lifetime, and estimate the condition of the system oil as well.
... The return flow to a hydraulic tank often brings the foreign matter of different physical and chemical properties. Although the solid contamination can be separated from the oil stream using a return line filter [4], the air bubbles however inevitably pass through the filter and enter the tank, and then the suction line [5]. Also, a sudden drop in oil pressure in the tank can lead to cavitation and increases the chance of bubbles in the tank [6]. ...
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In this work, a series of first-principle analytical expressions are derived to predict the instantaneous pressure drop and collection efficiency of pleated filters under dust loading condition. Both the depth and surface filtration regimes are formulated for filters with triangular and rectangular pleats. The analytical expressions derived in this paper can be used in the early stages of designing a pleated filter to circumvent the need for conducting CPU-intensive numerical calculations. The predictions of our analytical expressions are compared with those reported in previous studies and good agreement is observed.
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A modified Darcy's law. Theoretical and Computational Fluid Dynamics
  • S Gisinger
  • A Dörnbrack
  • J Schröttle
Gisinger, S., Dörnbrack, A. and Schröttle, J. A modified Darcy's law. Theoretical and Computational Fluid Dynamics, 2015, Vol.29, No.4, pp.343-347