Değişken kapasiteli hermetik kompresörlerde termodinamik ve mekanik verimin iyileştirilmesi
Improvement of thermodynamic and mechanical efficiency in variable capacity hermetic compressors
Yazar: FURKAN AHMET TOK
Danışman: PROF. DR. HASAN GÜNEŞ
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Makine Mühendisliği Ana Bilim Dalı / Isı-Akışkan Bilim Dalı
Derece: Yüksek Lisans, 2015
Konu: Enerji = Energy ; Makine Mühendisliği = Mechanical Engineering ; Mühendislik Bilimleri = Engineering Sciences

Özet:
Son yıllarda buzdolabı enerji verimliliği ve ayrıca kullanıcıya sağladığı artı avantajlar açısından değişken kapasiteli kompresör (VCC) kullanımı hızla artmaktadır. Özellikle dünya genelinde bulunan kompresör üreticileri son dönemde ürünlerinin çoğunda değişken kapasiteli kompresör kullanmaya başlamıştır.Üreticiler gelecek dönemde de ürünlerinin tamamında değişken kapasiteli kompresör kullanılacağı söylemini pazarda reklam aracı olarak kullanmaktadırlar. Son yıllarda Arçelik A.Ş. tarafından üretilen buzdolaplarında da değişken kapasiteli hermetik kompresör kullanımı artmıştır. Çok yakın gelecekte bu sayının daha da artması planlanmaktadır. Ayrıca daha verimli, ucuz ve müşterinin ihtiyacı doğrultusunda yeni ürünlerin tasarlanıp sunulması için araştırma ve geliştirme çalışmaları artarak devam etmektedir. Sürdürülebilir rekabet açısından Arge çalışmaları doğrultusunda üreticilerin değişken kapasiteli inverter kompresör tasarımında iyileştirmeye açık alanları belirlemesi, iyileştirme çalışmaları ile verimlilik düzeyinin yukarı çekilmesi için sürekli olarak çalışmalar gerçekleştirmesi gerekmektedir.
Bu tez çalışmasında mevcut değişken kapasiteli kompresör tasarımındaki termodinamik ve mekanik kayıpların detaylı incelenmesi, kompresör performans ölçümleri ve benchmark kompresör inceleme çalışmaları gerçekleştirilmiştir. Ayrıca COP iyileştirme çalışmaları kapsamında gerçekleştirilen aktiviteler anlatılarak prototipleme çalışması yapılmış ve performans testleri gerçekleştirilerek elde edilen sonuçlar incelenmiştir.
Tez çalışmasının ilk bölümünde, buhar sıkıştırmalı soğutma çevrimi,değişken devirli hermetik buzdolabı kompresörleri ve çalışma prensibi hakkında genel bilgi verilmiştir. 
Tezin ikinci bölümünde, genel olarak mekanik verim, termodinamik verim, performans tahmini ve piston gaz kaçakları hakkında literatür araştırmasına yer verilmiştir.
Tezin üçüncü bölümünde baseline durumda bulunan değişken devirli hermetik kompresörlerde deneysel olarak yapılan kalorimetre performans ölçümleri, ses gücü düzeyi(SGD) ölçümleri, pV testleri , mekanik kayıp ölçümleri, yağ sıcaklık ölçümü ve piston gaz kaçakları test sonuçları incelenerek termodinamik ve mekanik verim incelenmiştir. Ölçümler hem ARÇELİK hemde benchmark kompresörler üzerinde gerçekleştirilmiş ve birbiriyle karşılaştırılmıştır. Detaylı pV ölçümleri ve mekanik kayıp ölçümleri gerçekleştirilmiştir. Performansın iyileştirilmesine yönelik önemli tespitlerde bulunulmuştur.
Dördüncü bölümde değişken kapasiteli bir hermetik kompresörde gerçekleştirilen COP iyileştirme çalışmaları anlatılmıştır. Hazırlanan prototipler hakkında bilgi verilerek deneysel olarak elde edilen ölçüm sonuçları paylaşılmış ve performans artışları incelenmiştir.
Dördüncü bölümde değişken devirli bir hermetik kompresörde gerçekleştirilen COP iyileştirme çalışmaları anlatılarak, deneysel olarak elde edilen ölçüm sonuçları paylaşılmıştır.
Beşinci bölümde inceleme çalışmaları ve SEK/COP iyileştirme çalışmaları sonrası elde edilen sonuçlar özetlenerek elde edilen verim ve COP artışı yorumlanmış ve öneriler sunulmuştur.

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 increasing to design and present new products that aremore efficient, cheaper and in line with consumer needs.
In recent years, environmental concerns and energy consumption become more important. Therefore, the use of variable capacity compressor is rapidly increasing in terms of refrigerator energy efficiency and also plus benefits provided to users. Especially worldwide compressor manufacturers recently began using variable capacity compressors in most of their products. Producers will use the discourse that they will use variable capacity compressors in all of their products as an advertisement tool in the future stage as well. Refrigerators manufactured by the Arçelik in recent years has increased the use of variable capacity hermetic compressors. Very near future  it is planned to further increase this number. In addition, it continues to increase research and development efforts for more efficient, cheap and designed in accordance with the needs of customers for the provision of new products.As part of research and development works producers should continuously execute projects for determining the open areas (opportunities) for improving the design of variable capacity hermetic compressors and increase the level of productivity with the improvement work in terms of sustainable competition.  
In this thesis, detailed examination of the thermodynamic and mechanical losses in the variable capacity compressor design, compressor performance measurements and benchmark compressor investigations were carried out Furthermore, the actvities carried out under the COP improvement studies were explained and the results obtained from these improvements were examined. Also high efficiency prototype were made and declared.
General information about the vapor-compression refrigeration cycle and the variable capacity hermetic refrigerator compressors is given and working principle of compressorsare described in the first part of this thesis. Also literature studies about performance estimation of hermetic reciprocating compressors,mechanical and thermodynamic efficiency are summarized. Additionaly there are some articles about detailed thermodynamic characterization of hermetic reciprocating compressors and thermal analysis. Most of the studies are focused on performance estimation and they are related with compressor efficiency. In these articles there are some models to estimate compressor efficiency and help to determine design parameters.
In the secondpart of this thesis, several experimental studies are presented. These studies begin with calorimeter measurements to determine performance of compressors. Cooling cycle is controlled and performance parameters like cooling capacity, input power and coefficient of performance (COP) can be specified in calorimeter devices. These measurements were done for ASHRAE working conditions (Evoporation fixed at 0.624 bar and -23.3 °C, condensation fixed at 7.61 bar and 54.4 °C) and some household refrigeration conditions (Evoporation fixed at -25 °C, condensation fixed 35 °C). The results were obtained from calorimeter and calculated. We analyzed and compared the results of each compressors.
After these performance tests,detailed temperature measurements were carried out on a compressor model 89 at different operating speeds. These measurements were obtained during the calorimeter tests. While we were measuring temperatures, 20 thermocouples were used on different components and different areas on compressor shell. 6 critical point were determined along the flow line and average temperature values were calculated for the results. Also average oil temperature and average motor temperature were determined for 4 different working speeds.
Another experimental study was measurement of sound level power. Measurements were performed on variable capacity refrigeration compressor at household rerigeration conditions (Evoporation fixed at -25 °C, condensation fixed 35 °C). During the test, compressor worked on several different speeds in a special designed acoustic room in Arçelik. These measurements is very useful to determine the positions and levels of flow-induced noises in flow line.
After these sound tests, mechanical loss tests were performed on variable capacity refrigeration compressor. For the measurements, mechanical loss test system were used. The objective of this measurement was to investigate mechanical losses at different working speeds and different oil temperatures. Calculation parameters and working principle of system were described. Arçelik and benchmark compressor were adapted to system and measured. After that, the results are explained and compared according to oil temperature change.According to results, when oil tempreature is increased, mechanical losses decreaseat more than 1600 rpm speed because of viscosity change depend on temperature. Also when oil tempreature is decreased, mechanical losses begin to increase at less than 1600 rpm speed because of viscosity change depend on temperature. Mixed lubrication situation was spotted at lower level speeds.
Also compressor motor efficiency tests were desrcribed in second part. Two different compressors were used to measure motor efficiency. These are Arçelik and Embraco compressor motors. To get solo performance of compressor motors, motor measurements were done in variable speeds. With these measurements motor torque, power and efficiency according to the speed are determined for cold and hot conditions. Hot and cold tests were done between 1200 rpm to 3000 rpm for Arçelik compressor's motor. Motor efficiency was measured for 5 different speeds. The increase of efficiency was seen until 2000 rpm in cold and hot condition tests respectively. The most efficient working speed were determined at 3000 rpm (%93).These efficiencies were investigated beetwen 25N cm to 30 Ncm. Also efficiencies were really close in variable speeds from 1200 rpm  to 2000 rpm.
Then hot and cold tests were done between 1200 rpm to 3000 rpm for Embraco compressor's motor. Motor efficiency was measured for 3 different speeds. The most efficient working speed were determined at 3000 rpm (%92).These efficiencies were investigated beetwen 25N cm to 30 Ncm. Also efficiencies were really close for both compressors 3000 rpm speed.
After motor efficiency tests, pV measurements were carried out for Arçelik and Embraco compressors at different working speeds. The objective of this measurement is to obtain pressure-volume diagram for the compressors during working cycle. This pV diagrams help to determine thermodynamic losses in suction and discharge stages. So according to measurements that we performed, pV diagrams were created for both compressors. Then these diagrams were investigated and compression works were obtained. After these results, distribution of power losses were determined for different working speeds. Also pie-chart graphics of every compressor losses(mechanical loss, electrical loss, thermodyamic loss) were created to comment about what is the good advantage to improve compressor.
Finally, piston gas leakage measurements of compressor are presented. These measurements were performed on calorimeter device with ASHRAE working condition. To investigate how much gas is leaking between piston and cylinder, special measurement system was prepared and integrated with calorimeter device. Also some techical changes were made on suction line in compressor by adaptating the line to direct suction. Rubber bellows has been used to do this. After the preparation process, measurements were carried out at 4 different speeds (1200-1600-2000-3000 rpm). Also oil viscosity was changed for every different speeds. According to results, increased piston gas leakage was determined depending on the speed reduction. Also oil viscosity change effect is presented. It was determined that when oil viscosity is decreasing, gas leakages increase or when oil viscosity is increasing, gas leakages decrease.
In the third part of this thesis, COP improvement works carried out in a variable capacity copmressor are described. These improvements comprise mechanical and thermodynamic improvement studies.In mechanical section, oil viscosity change is investigated in variable speed compressor by measuring performance changes of compressor in calorimeter device. According to results, we determined compressor COP level is increasing at high speed levels when we use low viscosity oil otherwise compressor COP level is increasing at low speed levels when we use high viscosity oil. This situation is result from mechanical loss changes by oil viscosity. In thermodynamic section, improvement works was described which was related with components. The objective of these improvements is mostly about increasing volumetric efficiency.
Finally, some of these mechanical and termodynamic improvements were performed on some variable capacity compressors and prototypes were prepared. Then perfoemance tests is done. The measurement results shared which was obtained experimentallyand performance improvements have been examined by giving information about the prototypes were prepared. The results were examined and compared with compressor's baseline performance results. After these studies, we obtained the most efficiency variable capacity compressor with 2,04 W/W COP result at 2000 and 2200 rpm.
The final section offers advice with a summary of the results obtained from all experimental studies which was performed on several variable capacity compressors.