LEE- Makina Mühendisliği Lisansüstü Programı
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ÖgeNumerical and experimental investigation of the effect of refrigerant mixtures on the refrigeration system(Fen Bilimleri Enstitüsü, 2020) Özsipahi, Mustafa ; Güneş, Hasan ; 620640 ; Makine MühendisliğiIncreasing energy costs urge not only developing but also developed countries to have new regulations on energy prevention and recovery. Several protocols have already applied to reduce global warming and ozone depletion potential. These protocols force producers and suppliers to work with less harmful refrigerants in the refrigeration and air conditioning sector. Besides using environment-friendly refrigerants, it is also demanded to increase the energy efficiency of such devices to compete with the rivals of the global market. Reciprocating compressors in the refrigeration systems such as refrigerators and freezers are the main components in the household appliances. Moreover, the largest part of the electric consumption related to refrigerators is caused by compressors. Due to the increasing demands on new refrigerants considering their efficiency and the regulations for the protection of the environment, the natural refrigerants or refrigerant blends are widely used. Within the study, the effect of refrigerant mixtures on the household refrigeration system is studied. In addition to the refrigerant mixtures, the optimum lubricant is investigated for the reciprocating compressors. In the first chapter, a brief introduction to the vapor compression refrigeration systems is given. Lubricants and compressors used in vapor compression refrigeration systems are mentioned and a comprehensive literature survey is presented in this chapter. In the second chapter, experimental studies are discussed. This chapter divided into two parts. In the first part, the effect of refrigerant mixtures on the household refrigeration is studied. In this context, in house refrigerant mixtures test stand is constructed. The performance evaluation of the three different refrigerant mixtures of R600a/R290 is compared with R600a. The performance results of the test stand are compared with calorimeter tests carried out by Arcelik A.S. and the results of both test stands are showed that increase in energy efficiency is possible by using R600a/R290 refrigerant mixture. In the second part, the lubrication system of the hermetic reciprocating compressor is investigated in detail. Oil management and lubrication mechanism in journal bearings may change drastically between compressor maximum and minimum speeds. Nevertheless, sufficient lubrication should be provided to the bearings and all moving parts to avoid any mechanical damage on the compressor. In this context, in house lubrication test bench is built using various instruments. Experiments are conducted to investigate the effect of viscosity and compressor speed on the oil mass flow rate of the compressor. In addition to the oil mass flow rate measurements, flow visualization is performed and flow patterns inside the compressor are given for start-up and steady-state operating conditions. In the third chapter, numerical investigations are presented in detail. This chapter is divided into two sections. Firstly, the numerical modeling of the lubrication system of a compact inverter compressor (CIC) is presented. In the numerical modeling, a finite volume-based ANSYS-FLUENT package is used to model two-phase (air-oil) flow inside the compressor using the Volume of Fluid Method (VoF) method. Transient behavior of the oil flow under laminar flow conditions is both simulated by imposing Sliding Mesh (SM) and the Moving Reference Frame (MRF) methods at various crankshaft speeds varying between 1200 and 4500 rpm. The measurements are used to compare/validate CFD results obtained from SM and MRF methods. Moreover, the start-up behavior of the compressor is studied and the instantaneous flow field is given for both methods. Advantage and disadvantage of the methods are mentioned in the study.