Analisa Perubahan Temperature Lube Oil Dan Flow Rate Demineralized Water Terhadap Effectiveness Lube Oil Cooler

Rokhim, Muhammad Taufiqur (2024) Analisa Perubahan Temperature Lube Oil Dan Flow Rate Demineralized Water Terhadap Effectiveness Lube Oil Cooler. Other thesis, Institut Teknologi Sepuluh Nopember.

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Abstract

Lube oil cooler merupakan heat exchanger yang berfungsi mendinginkan temperature oli sehingga kekentalannya terjaga optimal. Oli digunakan sebagai pelumas agar bearing dan shaft BFW Pump dapat berputar dengan mulus dan vibrasi rendah sehingga menjaga keandalan tinggi. Idealnya, temperature cooling water tetap tanpa perubahan agar tidak terjadi perubahan cooling capabilities guna mencapai heat duty. Namun, setelah 25 tahun beroperasi terjadi kenaikan temperature air laut sebesar 0,024°C/tahun akibat pemanasan global sehingga menaikkan temperature cooling water berupa demineralized water yang berasal dari proses desalinasi air laut dari desain 35℃ menjadi aktual 35,5℃. Selain itu, pasca overhaul pada turn around pabrik 1A November 2023 akan dinaikkan rate BFW Pump dari flow rate 370 m^3⁄h dengan speed 3884 rpm (normal 100%) menjadi 407 m^3⁄h dengan speed 4272 rpm (rated 110%). Kenaikan rate ini akan mengakibatkan kenaikan temperature lube oil keluaran bearing pompa dan turbin atau lube oil inlet lube oil cooler secara eksponensial dari aktual 51℃ menjadi 54,44℃. Pada tugas akhir ini dilakukan evaluasi effectiveness dengan metode number of transfer unit (NTU). Untuk memperoleh nilai NTU, penulis melakukan perhitungan overall heat transfer coefficient dengan menghitung semua thermal resistance salah satunya adalah koefisien konveksi lube oil dan demineralized water dengan nilai Nusselt number. Untuk memperoleh nilai Nusselt number dilakukan perhitungan Reynold number. Selain itu, penulis juga menghitung pressure drop dan kebutuhan pumping power untuk melihat losses yang terjadi. Perhitungan secara teoritis ini dilakukan untuk validasi perhitungan software HTRI XChanger Suite. Variasi temperature lube oil inlet dari 51°C hingga 54,44°C dan flow rate demineralized water 60 L/Min hingga 160 L/Min digunakan sebagai bahan perhitungan dan analisa untuk mendapatkan nilai penurunan kinematic viscosity lube oil serta pendinginan terbaik lube oil cooler. Kenaikan temperature lube oil rata – rata 1,25℃ atau 2,55% akan menurunkan kinematic viscosity sebesar 6,46% dengan batas 10%. Pada temperature lube oil inlet 54,44℃ kinematic viscosity turun sebesar 15,84% sehingga perlu dilakukan penambahan aliran pendinginan flow rate demineralized water guna menurunkan temperature lube oil outlet agar kinematic viscosity dapat meningkat mendekati desain. Pendinginan terbaik adalah flow rate demineralized water 60 L/Min pada temperature lube oil inlet 53°C (rate 105%) dengan penurunan kinematic viscosity 9,9% dan effectiveness 0,3872. Selain itu, flow rate demineralized water 95 L/Min pada temperature lube oil inlet 54,44°C (rate 110%) dengan penurunan kinematic viscosity 14,81% dan effectiveness 0,4095. Menaikkan rate mencapai 110% tidak direkomendasikan karena penurunan kinematic viscosity di luar batas penurunan 10%. Apabila tetap dilakukan, usia bearing akan semakin pendek akibat keausan meningkat. Hal ini terjadi karena penurunan kinematic viscosity berarti berkurangnya kemampuan redam gesek lube oil terhadap bearing.
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Lube oil cooler is a heat exchanger that functions to cool lube oil temperature, ensuring its viscosity maintained at an optimal level. The oil serves as a lubricant to allow smooth rotation of BFW Pump and Steam Turbine bearings and shaft with low vibrations, thus ensuring high reliability. Ideally, the cooling water temperature remains unchanged to maintain consistent cooling capabilities to achieve the required heat duty. However, after 25 years of operation, there has been an increase in seawater temperature by 0,024°C annually due to global warming, leading to a rise in the cooling water, which is demineralized water from the seawater desalination process from design 35℃ to actual 35,5℃. Furthermore, after overhaul during plant turnaround in November 2023 BFW Pump's flow rate will be increased from 370 m^3⁄h at a speed of 3884 rpm (normal 100%) to 407 m^3⁄h at a speed of 4272 rpm (rated 110%). This increasing flow rate will result in an exponential rise of lube oil temperature at the pump and turbine bearing outlets or the lube oil cooler inlet, from the actual 51℃ to 54,44℃. In this final project, an evaluation of effectiveness is carried out using Number of Transfer Unit (NTU) method. To obtain the NTU value, the author calculates the overall heat transfer coefficient by considering all thermal resistances, including convective coefficients of lube oil and demineralized water with Nusselt number values. Reynolds number calculations are performed to determine the Nusselt number. Additionally, the author calculates pressure drop and pumping power requirements to assess the losses. Theoretical calculations are conducted to validate the HTRI XChanger Suite software calculations. Variations in lube oil inlet temperatures from 51°C to 54,44°C and demineralized water flow rate from 60 L/Min to 160 L/Min are used for calculations and analysis to obtain the kinematic viscosity reduction of lube oil and the best cooling for the lube oil cooler. An average temperature increases of 1,25℃ or 2,55% will decrease kinematic viscosity by 6,46%, still within the acceptable limit of 10%. At a lube oil inlet temperature of 54,44℃, kinematic viscosity decreases by 15,84%, requiring an increase in the demineralized water flow rate to lower the lube oil outlet temperature and approach the design viscosity. The optimal cooling is achieved with a demineralized water flow rate of 60 L/Min at lube oil inlet temperature 53°C (rate 105%), resulting in a kinematic viscosity decrease of 9,9% and an effectiveness of 0,3872. Additionally, demineralized water flow rate of 95 L/Min at lube oil inlet temperature 54,44°C (rate 110%) resulting in a kinematic viscosity decrease of 14,81% and an effectiveness of 0,4095. Increasing the rate to 110% is not recommended due to a kinematic viscosity decrease beyond the 10% limit, which could lead to increased wear and shortened bearing lifespan. This is because a decrease in kinematic viscosity implies a reduced ability of the lube oil to dampen friction on the bearing.

Item Type:	Thesis (Other)
Uncontrolled Keywords:	Lube Oil Cooler, Effectiveness, HTRI XChanger Suite. Lube Oil Cooler, Effectiveness, HTRI XChanger Suite.
Subjects:	T Technology > TJ Mechanical engineering and machinery T Technology > TJ Mechanical engineering and machinery > TJ1077 Lubrication and lubricants. T Technology > TJ Mechanical engineering and machinery > TJ263 Heat exchangers
Divisions:	Faculty of Industrial Technology and Systems Engineering (INDSYS) > Mechanical Engineering > 21201-(S1) Undergraduate Thesis
Depositing User:	Muhammad Taufiqur Rokhim
Date Deposited:	15 Feb 2024 06:12
Last Modified:	15 Feb 2024 06:12
URI:	http://repository.its.ac.id/id/eprint/107142

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