Thermal Modeling of Hybrid Storage Clusters

There is a lack of thermal models for storage clusters; most existing thermal models do not take into account the utilization of hard drives (HDDs) and solid state disks (SSDs). To address this problem, we build a thermal model for hybrid storage clusters that are comprised of HDDs and SSDs. We start this study by generating the thermal profiles of hard drives and solid state disks. The profiling results show that both HDDs and SSDs have profound impacts on temperatures of storage nodes in a cluster. Next, we build two types of hybrid storage clusters, namely, inter-node and intra-node hybrid storage clusters. We develop a model to estimate the cooling cost of a storage cluster equipped with hybrid storage nodes. The thermal model is validated against data acquired by temperature sensors. Experimental results show that, compared to the HDD-first strategy, the SSD-first strategy is an efficient approach to minimize negative thermal impacts of hybrid storage clusters.     

The Effect of Temperature on Tribological Properties of Chemically Modified Bio-Based Lubricant

Vegetable oil has several characteristics that provide advantages for use as lubricant. This includes a high viscosity index, high flash point, high biodegradability, and friction and wear reduction properties. However, vegetable oil has some disadvantages such as low oxidation stability and low thermal stability. The transesterification process of palm oil using trimethylolpropane (TMP) alcohol has been proven to reduce the oxidation stability of vegetable oil. However, little research has been carried out on the effect of TMP ester as a lubricant in term of friction and wear. Therefore, this study investigated the effect of temperature on the tribological properties of TMP ester using a four-ball machine. The load and speed of the sample were set at 40 kg and 1,200 rpm, respectively. Temperature was varied between 50 and 100°C. It was found that TMP ester improved the friction properties by around 15–20%. At low temperature, TMP esters have a higher coefficient of friction (COF) compared to paraffin oil. However, as the temperature increased higher than 80°C, paraffin oil had a highere COF value. This is because at high temperature, the lubricant filmed formed by fatty acids tends to be less stable and breaks down more easily.     

Tribological Study of a Tetrahedral Diamond-Like Carbon Coating under Vegetable Oil–Based Lubricated Condition

Maintaining a clean environment is the major concern of industries that produce fuel and lubricants for automotive applications. Thus, vegetable-based oils are being explored for the preparation of biobased lubricants because of their biodegradability and nontoxicity. Despite their low thermal stability, vegetable oils show better tribological characteristics than mineral oils. Nonetheless, the thermal stability of vegetable oils could be improved by transesterification. In this study, three vegetable-based oils (sunflower, palm, and coconut) were used to investigate the tribological properties of ta-C diamond-like carbon (DLC) coating under DLC–steel contact condition. A BICERI ball-on-a plate tribotesting machine was used to conduct experiments. During the experiment, test contacts of tribopairs lubricated with sunflower oil exhibited better tribological characteristics than those using coconut oil as a lubricant.     

Corrosion of Mild Steel by Urban River Water

The corrosion processes of mild steel immersed in river water were investigated. The reaction of the Bahlui River on common steel used in domestic and industrial installations was studied. The corrosion of mild steel is an extensive topic approached in different media, yet little information about river water as a corrosive has been reported. The experimental determinations were performed for short term immersion of four alloys in the laboratory. By using Tafel extrapolation and electrochemical impedance spectroscopy, the corrosion of the alloys was investigated. Scanning electron microscopy coupled with energy dispersive X-ray analysis and Fourier-transform infrared spectroscopy were employed to characterize the morphology of corrosion products and identify their phases. The corrosive activity of river water leads to the formation of inner compact and outer porous layers. The differences between corrosion products formed in the presence of underground and surface waters are described.     

CATALYTIC HYDROTREATMENT OF PETROLEUM RESIDUE

ABSTRACT

Iraqi reduced crude (350°C+) with a sulfur content of 4.3 wt% and a total metal content (Ni+V) of 141 WPPM was n-heptane deasphalted at specified conditions. The deasphalted oil (97.2 wt% of original residue) contains 4.1 wt% of sulfur and 103 ppm of metal. The original reduced crude and deasphalted oil were hydrotreated on a commercial Ni-Mo-alumina catalyst presulfided at specified conditions in a laboratory trickle-bed reactor. The reaction temperatures varied from 300 to 420°C with the liquid hourly space velocity (LHSV) ranging from 0.37 to 2.6 h^?1. Hydrogen pressure was kept constant throughout the experiments at 6.1 MPa, with a hydrogen/oil ratio of about 300 NLL^?1 (normal liters of hydrogen per liter of feedstock). Analysis for sulfur, nickel, vanadium and n-pentane asphaltenes were carried out for hydrotreated products from both the original residue and the deasphalted oil. The comparison of the results obtained for the hydrotreatment of deasphalted oil and original reduced crude indicates that the removal of sulfur, nickel and vanadium was higher for the deasphalted oil than those obtained for the non-deasphalted residue over the entire range of conversion. The exclusion of extremely high molecular weight asphaltenes by n-heptane deasphalting seems to improve the access of oil into catalyst pores resulting in higher desulfurization and conversion of the lower molecular weight asphaltenes. The sulfur content of n-pentane precipitated asphaltenes remained unchaneed with LHSV for various temperature for hydrotreated products produced from both deasphalted oil and original reduced crude.     

Frictional power loss in solid‐grease‐lubricated needle roller bearing

The use of solid grease as a lubricant, in comparison with standard grease or oil, is a pre‐requisite when needle roller bearings undergo a high‐speed oscillating motion and when access to the bearing is difficult for maintenance purposes. This paper examines the frictional power loss of a solid‐grease‐lubricated needle roller bearing. First set of measurement result reveals that the test bearing has higher frictional power loss as compared with other bearings with conventional lubrications, due to the high viscosity of the solid grease. Furthermore, measurements are compared with the Palmgren and SKF models. For improving these models, the parameters of the models are updated on the basis of the measurement data. A second set of measurement result shows that the use of oil (kept at higher temperature) in addition to solid grease significantly reduces the frictional power loss. The reduction is due to the decrease in operational viscosity of the solid grease. Copyright © 2012 John Wiley & Sons, Ltd.     

Concentration and Exposure Assessment of Mercury in Commercial Fish and Other Seafood Marketed in Oman

The results of this study present analytical data of the mercury levels in several fish and shellfish species to create awareness among individuals of the risks associated with consuming fish contaminated with mercury. Mercury concentrations varied from a mean of 0.02 mg/kg in Indian mackerel to 0.19 mg/kg in shark in both fresh and frozen fish, from 0.02 mg/kg in sardines to 0.18 mg/kg in skipjack tuna in canned fish, and from 0.02 mg/kg in Indian mackerel to 0.79 mg/kg in shark in dried fish. Shellfish contained a slightly higher amount of mercury than fresh or frozen fish with a mean of 0.09 mg/kg. Trophic position, followed by habitat, was the most important factors for variability in mercury concentrations in fish and shellfish. The maximum safe weekly intake (MSWI) values of mercury were significantly higher for herbivores than for carnivores. The MSWI value for total mercury in the case of consuming most (72%) fish species was more than 5 kg; however, the MSWI value was never more than 5 kg in most (66%) shellfish species. Risks were identified upon consumption of 120 g of dried shark when exceeding the provisional tolerable weekly intake threshold (1.6 μg/kg) for methylmercury. Therefore, fish‐eating populations should reduce the quantity of dried shark to efficiently diminish the exposure to mercury.