ACHIEVING EFFICIENCY GAINS THROUGH HYDRAULIC FLUID SELECTION: LABORATORY PREDICTION AND FIELD EVALUATION

Ispitivanja završena na krilnim i klipnim pumpama srednjeg i visokog tlaka pokazala su da njihova djelotvornost ovisi o tlaku na ispustu i o viskoznosti ulja. Nedavno je ograničeno praktično ispitivanje provedeno na rovokopaču srednje veličine potvrdilo da se značajno povećanje djelotvornosti i radnog učinka, čak i kod umjerenih radnih temperatura, može postići zamjenom OEM preporučenih ulja s tzv. hidrauličkim uljem najveće djelotvornosti (MEHF). Da bismo razumjeli porijeklo poboljšanja djelotvornosti u praktičnom ispitivanju, opremili smo Eaton-Vickers V 104C pumpu instrumentima za bilježenje tlaka, temperature, brzine protoka i ulazne snage na vratilu pumpe. Test je proveden kod 69 i 138 bara i u temperaturnom području između 30 i 90 oC. Ispitivana hidraulička ulja uključivala su dva ulja iz praktičnog testa i ISO VG 46 HM ulje. Poboljšanje djelotvornosti postignuto na pumpnom ispitnom stolu u skladu je s onim koje je postignuto kod praktičnog ispitivanja, što taj test čini vrijednim alatom za procjenu potencijalne koristi od MEHF ulja u stvarnoj primjeni. Termodinamički modeli koji su prije utvrđeni mogu se koristiti za procjenu temperature uljnog toka istjecanja i stvarne temperature unutar pumpe.Studies completed in medium and high pressure vane and piston pumps showed that their efficiency depends on discharge pressure and on oil viscosity. Recently, a limited field test completed in a medium size excavator confirmed that significant gains in efficiency and productivity even under moderate operating temperatures could be achieved by substituting the OEM-recommended oil with a Maximum Efficiency Hydraulic Fluid (MEHF). To understand the origin of the efficiency gains observed in the field test, we instrumented an Eaton-Vickers V104C pump to record pressure, temperature, flow rate and power input at the pump shaft. Tests were completed at 69 and 138 bars and temperatures ranging between 30 and 90°C. Candidate hydraulic fluids included the two field test oils and an ISO VG 46 HM oil. The efficiency gains in the pump stand are consistent with those generated in the field test making the former a valuable tool to assess the potential benefits of MEHF oils in actual service. Thermodynamic models determined earlier can be used to estimate the temperature of the oil leakage stream and the actual oil temperature inside the pump

IMPACT OF FRESH AND SHEARED OIL VISCOSITY REQUIREMENTS ON THE FORMULATION OF HYDRAULIC FLUIDS

Već se godinama odabir hidrauličkih ulja obavlja na temelju ISO 3448 klasifikacije viskoznosti razvijene sredinom sedamdesetih godina, koja definira određeni broj diskontinuiranih gradacija viskoznosti na temelju minimalne i maksimalne kinematičke viskoznosti kod 40 °C. Aktivnošću ASTM-a 1997. godine uvedena je ASTM D 6080-97 klasifikacija koja uključuje nekoliko zahtjeva za viskoznošću svježeg ulja i ulja nakon smicanja. U posljednje vrijeme predložene su dvije nove postavke viskoznosti i ograničenje indeksa viskoznosti kod svježih ulja i ulja nakon smicanja kako bi se poboljšala učinkovitost opreme u usporedbi s konvencionalnim HM uljima. Definirana je maksimalna djelotvornost hidrauličke tekućine (MEHF) i National Fluid Power Association (NFPA) smjernice za odabir viskoznosti hidrauličkih tekućina. Svaki dodatni viskometrijski zahtjev za određivanje ISO gradacije viskoznosti uvodi nova ograničenja na kinematičku viskoznost i indeks viskoznosti kod formulacije. Korištenjem velikog broja mješavina temeljenih na poboljšivačima indeksa viskoznosti s različitom smičnom stabilnosti, ispitan je utjecaj ograničenja viskoznosti, uključen u MEHF i NFPA smjernice, na područje formulacije tri najčešće ISO gradacije viskoznosti. Utvrđeno je da stupanj preklapanja smjernica, takozvano "područje formulacije", ovisi o ISO gradaciji viskoznosti i smičnoj stabilnosti poboljšivača indeksa viskoznosti kojeg se razmatra. Ovaj rad pruža okvir za poboljšanu sposobnost odabira ciljeva formuliranja s obzirom na spomenute nove smjernice.For many years hydraulic oils were selected using the ISO 3448 viscosity classification. Developed in the mid-seventies, it defines a finite number of discontinuous grades based on a minimum and maximum viscosity at 40 °C. In 1997, efforts by ASTM resulted in the ASTM D 6080-97 classification that included several viscosity requirements on the fresh and sheared oil. More recently, two new sets of viscosity and VI limits on the fresh and sheared oil were proposed to provide improved equipment efficiency compared to conventional HM oils. These are the Maximum Efficiency Hydraulic Fluid definition (MEHF) and the National Fluid Power Association (NFPA) guidelines for hydraulic fluid viscosity selection. Any additional viscometric requirement to the ISO grade definition introduces new constraints on both the kinematic viscosity and VI of the formulation. Using a large number of blends based on VI Improvers having a different shear stability level, we investigated the impact of the viscosity constraints included in the MEHF and NFPA guidelines on the formulation windows of the three most common ISO grades. The degree to which the guidelines overlap, the so-called “formulation window” was found to depend on the ISO grade and shear stability of the VI Improver considered. This work provides a framework for an improved ability to select formulation targets considering these new guidelines

Exact asymptotics of the freezing transition of a logarithmically correlated random energy model

We consider a logarithmically correlated random energy model, namely a model for directed polymers on a Cayley tree, which was introduced by Derrida and Spohn. We prove asymptotic properties of a generating function of the partition function of the model by studying a discrete time analogy of the KPP-equation - thus translating Bramson's work on the KPP-equation into a discrete time case. We also discuss connections to extreme value statistics of a branching random walk and a rescaled multiplicative cascade measure beyond the critical point

Sampling distribution.

<p>Sampling was restricted to the periphery of the colony. Orange zone boundaries are marked on the ground for remote parameter assessment. Shaded clusters run from C1 (north-west) to C6 (south-east). Orange zone: extent of the colony at the peak of the breeding season.</p

First axis of principal component analysis as a summary habitat-quality index.

<p>White polygons: clusters C1 to C6.</p

Microsatellite analysis: multiplexing parameters and summary statistics.

<p>Microsatellite analysis: multiplexing parameters and summary statistics.</p

Ecological descriptors of breeding-site quality exhibit a strongly heterogeneous distribution across the colony.

<p>(A) Adult tick load, averaged for years 2005–2012. Contour lines: 0.02 steps. (B) 8-neighbour chick survival, averaged for years 2010–2012. Contour lines: 0.1 steps. (C) Site occupancy chronology, averaged for years 2006–2013. Ratio of brooding birds amongst 50 randomly selected breeders. Contour lines: 0.1 steps.</p

Individual inbreeding and nearest-neighbours-relatedness tend to have a clustered distribution throughout the colony.

<p>(A) Distribution of Ritland’s individual inbreeding coefficient along the sampling area. Shaded zones represent analysis clusters C1 to C6. Gray circles signal point displacement for representation purposes. (B) 2D-LSA scores (9 neighbours analysis). Red triangles represent individuals that are significantly more related to their 9 nearest neighbours than to random individuals.</p