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THE USE OF IRON IN PEAT WATER FOR FENTON PROCESS Mirna Apriani, Ali Masduqi REFERENCES Alaton, I.D., Gursoy, B.H., and Schmidt, J.E., (2008), “Advanced oxidation of acid and reactive dyes : Effect of Fenton treatmnent on aerobic, anoxic and anaerobic processes”, Dyes and pigments, Vol. 78, 117-130 Barchia, M.F., (2006), Gambut (Agroekosistem dan transformasi karbon), Gadjah Mada University Press, Yogyakarta, Indonesia Jiang, C., Pang, S., Ouyang, F., and Jiang, J., (2010), “A new insight into Fenton and Fenton-like processes for water treatment”, Journal of hazardous materials, Vol. 174, 813-817 Katsumata, K., Sada, M., Kaneco, S., Suzuki, T., Ohta, K., and Yobiko, Y., (2008), “Humic acid degradation in aqueous solution by the photofenton process”, Journal of chemical engineering, Vol. 137, 225-230 Matilainen, A., and Sillanpaa, M., (2010), “Review removal of natural organic matter from drinking water by advanced oxidation processes”, Chemosphere, Vol. 80, 351-365 Murray, A.C. and Parsons, S.A., (2004), “Removal of NOM from drinking water : Fenton’s and photo-Fenton’s processes”, Chemosphere, Vol. 54, 1017-1023 Parsons, S., (2004), Advanced oxidation processes for water and wastewater treatment, IWA publishing, London, UK Riduan, R., (2002), Penurunan kandungan organik pada air gambut menggunakan membran ultrafiltrasi dengan pre-treatment PAC (Powdered Activated Carbon), Master Thesis of Environmental Engineering, Institut Teknologi Sepuluh Nopember (ITS) Rohmatun, Roosmini, D., and Notodarmojo, S., (2 007), “Studi penurunan kandungan besi organic dalam air tanah dengan oksidasi H 2 O 2 –UV”, Proc.ITB Sains & Tek, Vol. 39 A, No. 1&2, 58-69 Sukandarrumidi, (1995), Batubara dan gambut, Gadjah Mada University Press, Yogyakarta, Indonesia Water Environment Federation (WEF), (2008), Manual of practice no. FD-3 : Industrial wastewater management, treatment and disposal, WEF press, USA Wu, Y., Zhou, S., Ye, X., Zhao, R., and Chen, D., (2011), “Oxidation and coagulation removal of humic acid using Fenton Process”, Colloids and surfaces A : Physicochemical and engineering aspects, Vol. 379, 151-156 AcademyPublish.org – Journal of Engineering and Technology Vol.2, No.2 38
TRIBOLOGY OF HIGH-SPEED MOVING MECHANICAL SYSTEMS FOR SPACECRAFTS: LUBRICATION SYSTEMS OF BALL BEARINGS K. Sathyan Tribology of High-Speed Moving Mechanical Systems for Spacecrafts: Lubrication Systems of Ball Bearings K Sathyan, krishnan.sathyan@gmail.com * Department of Mechanical Engineering Prince Mohammed Bin Fahd University, Po Box:1664, Al-Khobar- 31952, KSA Tel.: +966 38498532; +966 505181702 ABSTRACT The spacecraft attitude control system contains a number of moving mechanical systems (MMS). These include attitude error sen sors such as gyroscopes and actuators such as momentum wheels and reaction wheels. All these systems are designed to operate continuously till the end of the mission at varying speeds of several thousand rpm. The on-orbit performance of spacecrafts depends largely on the performance of the momentum/reaction wheels which, in turn, depend on the bearings used and its lubrication. The only component which undergoes wear in these systems are the ball bearings. Currently, the life cycle of spacecrafts are aimed to be around 20–30 years. However, the increases in size, complexity and life expectancy of spacecrafts demand advanced technologies especially in tribology and the development of more innovative lubrication systems for long-term operation. This part of the serial review presents an account of different types of lubrication systems commonly used in spacecraft highspeed moving mechanical systems. The features and working of active and passive lubrication systems are presented. The merits and demerits of each system are highlighted. Keywords: tribology, lubrication, momentum wheel, spacecraft, ball bearing INTRODUCTION It is well understood that no bearing can work indefinitely with the initial charge of lubricant given to it at the time of assembly. There will be progressive loss of lubricant from the bearing surface, and the rate is dependent on the operating conditions. In a spacecraft system bearing, it is not possible to provide lubricant in excess initially with a view to extending its life. To operate bearings with least frictional torque and torque variation, they have to work in the elastohydrodynamic lubrication ( EHL) regime. Therefore, bearings of high speed moving mechanical systems ( MMS) are centrifuged to remove the excess oil before assembling to the system. The bearing then contains the surface oil and the oil absorbed in the retainer pores. Thus, in order to achieve long mission life, supplementary lubrication is extremely important. The function of the supplementary lubrication system is to maintain right amount of lubricant at the bearing working surfaces to produce a thin film supporting the load. The thickness of the film should be sufficient to maintain the bearing in the EHL regime of lubrication. The ultimate aim of a spacecraft system designer is to minimize the size and weight of the system. Both these factors are critical in deciding the final weight and size of the spacecraft, which in turn influence the selection of launch vehicle. Therefore, optimum use of available space is appreciated. For this reason, the lubrication systems are enclosed either inside the bearing unit or inside the system enclosure. Currently, there are a number of different types of lubrication systems developed and used by different manufacturers for high speed MMS. However, according to the nature of operation, these lubrication systems used in high speed MMS can be broadly classified as passive lubrication systems and active lubrication systems. Various lubrication systems which come under these two categories are described in the following sections. PASSIVE LUBRICATION SYSTEMS The passive lubrication systems, also known as continuous lubrication system, supply lubricants continuously at a controlled rate irrespective of the requirement. In this class of systems, the lubricant is stored at ambient pressure in a lubricant reservoir located near the bearings. From the reservoir, the lubricant is fed continuously to the bearings at a predetermined rate. Most of these systems use centrifugal force due to the rotation of the bearing assembly to deliver the lubricant, while some use a transfer material such as cotton fiber that remains in touch with the bearing surface and lubricant in the reservoir. Passive type systems are simple in construction, but are difficult to control for the flow rate to the required level. Different techniques are used to control the flow rate in this type of lubricators. There are a number of designs of passive lubrication systems used today by different manufacturers of MMS for spacecrafts. The oozing flow lubricators (Kingsbury et al., 1999, Hashimoto, 2001, Jones et al., 1997, Singer, Gelotte, 1994), wick feed systems (Loewenthal et al., 1985), porous lubricant reservoirs (Sathyan, 2003), the centrifugal lubricators (Sathyan, 2003, Sathyan et al., 2008, Sathyan et al., 2010) etc., come under this classification. AcademyPublish.org – Journal of Engineering and Information Technology Vol.2, No.2 39
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