Hermetik kompresörlerde krank yatak tasarımının sürtünme kayıplarına etkisinin incelenmesi
An investigation of the effect of crank shaft bearing design on the frictional losses in hermetic reciprocating compressors
Yazar: AHMET BURAK TOP
Danışman: PROF. DR. SEYHAN UYGUR ONBAŞIOĞLU
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Makine Mühendisliği Ana Bilim Dalı / Isı-Akışkan Bilim Dalı
Derece: Yüksek Lisans, 2012
Konu: Makine Mühendisliği = Mechanical Engineering
Dizin: Kompresör = Compressor ; Krank mili = Crankshaft ; Sürtünme kaybı = Frictional loss ; Yataklar = Bearings

Özet:
Teknoloji konusunda ilerlemeler ve yenilikler her sektörde olduğu gibi beyaz eşya sektöründe de düzenli olarak takip edilmektedir. Ayrıca daha verimli, ucuz ve müşterinin ihtiyacı doğrultusunda yeni ürünlerin tasarlanıp sunulması için araştırma ve geliştirme çalışmaları artarak devam etmektedir. Sürdürülebilir rekabet açısından bu çalışmalar doğrultusunda buzdolabı üreticilerinin sürekli olarak yeni ürünler tasarlayıp üretmesi, mevcutlarını da sürekli iyileştirmesi ve geliştirmesi gerekmektedir.Beyaz eşya sektöründe özellikle de buzdolaplarında, soğutma sistemleri önemli bir yer tutmaktadır. Buzdolabı soğutma performansını belirleyen en önemli soğutma elemanı kompresördür. Kompresörün performansını etkileyen birçok unsurdan birisi de kompresör yataklarında oluşan sürtünme kayıplarıdır. Kompresör yataklarının tasarımı, kompresörün ömrünü önemli derecede etkilediği için çok dikkatle ele alınmalıdır. Yatak boyu, çapı, boşluğu, pürüzlülüğü, yağ viskozitesi, yağlama rejimi, yatak yükü ve kompresör devri yatak ömrünü belirleyen en önemli parametrelerdir. Yeni bir yatak tasarımında, yataklarda hidrodinamik yağlama filmi ile sürtünme kuvvetinin minimum değerinin olması gerekmektedir. Bu çalışmada ise yatak alanı ve yağ viskozitesinin yatak kayıplarına etkisi deneysel ve analitik olarak incelenmiştir.Tez çalışmasının ilk bölümünde, enerji maliyetlerine neden olan kompresör yataklarında oluşan toplam sürtünme kaybı iki farklı sistem tarafından ölçülmüş, sürtünme kayıpları belirli yataklar bazında ayrıştırılmakta, hidrodinamik ve karışım yağlama teorilerine göre yatak kayıpları analitik olarak hesaplanmıştır.Tezin ikinci bölümünde hermetik buzdolabı kompresörleri hakkında genel bilgi verilmiş ve kompresörde bulunan yatak bölgeleri gösterilmiştir.Üçüncü bölümde yataklarda sürtünme kaybını etkileyen parametreler ve genel olarak krank yatak tasarımı ve yatak kayıplarına yönelik literatür taraması sunulmuştur. Bu araştırmada önemli görülen noktalar ise: Literatürde kompresörün mekanik kaybını krankın yatak içerisindeki konumuna göre ifade eden, yatağın yük taşıma kapasitesinden krankın yatak içerisindeki konumunu gösteren teorik eşitlikler üzerinde değinilmiştir. Ayrıca krankın yatak içerisinde eş eksenli çalışma durumunu irdeleyen eşitlik sunularak milin eksantrik konumuna göre mekanik kaybın etkisi gösterilmiştir.Dördüncü bölümde mekanik kayıp değerlerini ölçmek için kullanılan sistemler, çalışma prensipleri ve deneysel sistemlerde kullanılan ölçüm elemanları ile kompresör mekanik kayıp ölçüm sonuçları sunulmuştur. Krank uzun muylu 2 yatak alanı azaltılmış ve basmalı yatak yüzeyine eksenel rulman eklenmiş tasarımlara ek olarak farklı yağ sıcaklıkları ve viskozitelerde kombinasyonlar yapılarak deneysel sonuçlar sunulmuştur.Beşinci bölümde MATLAB programında hazırlanan krank yatakları mekanik kayıplarını irdeleyen yarı analitik model sunulmaktadır. Model sonuçları kompresör çalışma şartlarına göre elde edilmiş olup model sonuçları ile deneysel sonuçlar karşılaştırılmıştır.Son bölümde elde edilen sonuçların özeti ile öneriler sunulmuştur. Teoride belirtilen viskozite değişimi ve yatak alanın azaltılmasının, mekanik kayıplara etkisi elde edilen sonuçlarla desteklenmiştir.

Abstract:
Every sector of industry as well as white good manufacturers have been following advances and innovations in technology on a regular basis. Moreover, research and development activities have been incresing to design and present new products that are more efficient, cheaper and in line with consumer needs. Refrigerator manufacturers have to design constantly and produce their products in accordance with these studies in terms of sustainable competition also they need to improve and develop existing products consistently.White goods industry especially refrigerators have an important place in cooling systems. The household compressor is the most important part of the cooling system in terms of refrigerators? cooling performance. One of the many factors which affects the compressor performance is the household compressor bearings frictional loss. Designing the compressor bearings have to be done precisely since it significantly effects the life of the compressor. Bearing lenght, diameter, clearance, roughness, oil viscosity, lubrication regime, bearing load and compressor speed are important parameters which determine the bearing life.Friction force of the bearings should be minimum and bearing's lubrication regime should be hydrodynamic condition simultaneously when a new compressor bearing design is needed. This study aims to investigate analytically and experimentally the effect of bearing surface area and oil viscousity which affect bearing?s frictional losses.The compressor bearings' total frictional loss which decreases the coefficient of performance is measured by the two different test systems. Moreover, the frictional loss is seperated on the basis of certain bearings. According to the theory of hydrodynamic and mixed lubrication, bearing losses are calculated analytically in the first part of this thesis.Development of the compressor and compressor history is described. Some special compressor types are given for refrigeration compressors. Compressor types and the hermetic reciprocating compressors? components are given for inside of the compressor vessel. The household compressor bearing have represented and positon of the crank shaft bearings are addressed in compressor CAD draft.General information about the hermetic refrigerator compressors is given and compressor housing parts are described in the second part of this thesis.At the third section, the parameters that affect the friction in the bearings are presented. Compressor housing lubrication regime types are explained and these lubrication types can be Hydrodynamic, Elasthohydrodynamic, Boundary and Mixed lubrication. Importance of the lubrication regime is explained. The compressor bearing is classifacted by radial and axial bearing which are determined with force direction. Moreover radial bearing mechanical loss calculation basics are given for simple fluid particle. Some important parameters for radial bearings are given for the position of the crankshaft in radial bearing. And also axial type of compressor bearing explaniton is presented. Some mechanical loss calculation basics are given for axial bearings. Furthermore viscosity and temperature relation is also described in this part.General literature review is given for crank bearing design and bearing losses. The radial bearings' equations are given in the literature in order to find the mechanical loss of the compressor as a function of the position of the crankshaft; where the position of the crank shaft is determined by the calculation of the load-carrying capacity. In addition, coaxial crank shaft bearings' mechanical loss is presented to make comparisons with the mechanical loss of an eccentrically revoluting crank shaft. Mechanical loss calculation for solid contact bearings is given. The minimum film thickness for the no contact design of the crank and bearing parts? is also given. Mechanical loss of the crankshaft bearing test rig is scanned for literature part. Crankshaft mechanical loss calculation is explained.The systems used to measure the mechanical losses, their working principles, measurement equipments that are used in mechanical loss mesaurement systems and mechanical loss values are presented in the fourth chapter. Different designs like reduced bearing surface area for crank long bearing 2, application of axial rolling bearing and different oil temperatures and viscousity combinations are also evaluated expermentally and the results are given in this chapter. Measurement System-2 experimental setup with the model results broadly consistent with the results of the measurement of mechanical loss, change in oil viscosity and bearing area are exactly the same trends of change in mechanical losses.Reduction of mechanical losses occurs in all the experimental results when the oil temperature is increased. However, the use of low-viscosity oil to improve the mechanical losses decrease the amount of the oil temperature is less than a high-viscosity state. The reason for this is to have declined as the bearing load carrying capacity of the bed closer to the shaft together with the fact that due to the turns. Acceleration and deceleration forces of inertia within the scope of the thesis in experimental studies with the test equipment used in the determination of the mechanical losses (Measurement System-1) with the separation of the electrical losses and the friction forces identify the experimental device (Measurement System-2) are used. In this study, the reduction of the radial and axial bearing areas with different temperatures and mechanical loss of the use of low-viscosity oil, examined the effects of film thickness values. The radial shortening of the length of bed reduction of bed space in the axial direction with the reduction of bed space has been added to the bearing. Oil temperature of 40 ° C and 60 ° C and 5 cSt and 10 cSt oil viscosity were examined.The fifth section, semi-analytical model is presented where the crank chaft loss is modeled with MATLAB program. Model results are obtained for different compressor working conditions and crank model results are compared with the experimental results. Model operating conditions are the same with the experimental conditions. Measurement System-2 experiment with the results of the model system results in degradation of the oil temperature decreased and the bearing. Bearing impact of using BY character is identical with the alteration of the mechanical loss. In general, the results of the measurement results of the model has a high value. Shortening the length of 5 mm with KUM 2 has been earning the mechanical losses. However, with the insertion of the mechanical loss of thrust bearings BY values provided more revenue. In general, the effect of lowering the temperature of the oil viscosity and the friction losses gain, the oil temperature is greater than the reduction of viscosity. All the model results with the mechanical effect of adding BY bearing consists of a reduction in losses. However, bearing high temperature or low-viscosity model that is lower than the value earned. This bearing, low viscosities depending on the situation in the area treated with high viscosity is less than the original mechanical loss, and thus added to the bearing of this region must be less than the yield of the high-viscosity state.Model results are same with measurment results. Reduction of mechanical losses takes place all model results when the oil temperature is increased. However, the oil temperature rise in the use of lower viscosity reduction of mechanical losses is less than the amount of high-viscosity state. This is because the load-carrying capacity of the bearings which have started to decline with the way the shaft turns closer to the bed due to being. At low temperatures, bearing the same axis are forced to work more. Viscosity ratio for all model results are compared with the mechanical loss ratio of these values are not the same and also the viscosity ratio is greater than the rate observed values of the mechanical loss. According to these results, do not return to a co-axially in the bearing shaft. The difference in viscosity increases, the difference between the rates is growing.The final section offers advice with a summary of the results obtained. In the study, according to the types of bearing designs with basic information about the crank bearings and crank bearings presented in literature for the reduction of the mechanical loss values with the hermetic compressor design modification made in the other deposits are offering the work. It is shown that viscousity change and reduction of bearing surface are affect the mechanical losses as predicted by the theory.Some parts of this results are given in the last part of this thesis. The inertia forces are not greater than compressive forces. Measurement System-2 results were more than Model results. Among the reasons for this measurement accuracy, the film thickness of BY is not fully measured in the Model. The model with the result of the measurement accuracy of 8.5 % consistent with the average results of System-2. The maximum difference is 22 %. Current arrangements measuring system-2 mechanical loss values obtained with the maximum gain of 52 % for 60 °C and 40 °C becomes 60%, the results of the model is 57 % for 60 °C and 40 °C becomes 60 %.This study thought to be useful as a continuation of the suggestions provided below:Mechanical loss of viscosity variation with axial bearing of BY added setting out more clearly the development of a model, the results will help clarify the imposition.Changes made installed case bearings the influence experimental investigation and mechanical lost and possible abrasions determination future studies is helpful.