Emme susturucu geometrisinin valf hareketleri ve basınç salınımları üzerindeki etkisinin incelenmesi
Investigation of the effect of suction muffler geometry on valve dynamics and pressure oscillations
- Tez No: 949145
- Danışmanlar: PROF. DR. SEYHAN ONBAŞIOĞLU
- Tez Türü: Doktora
- Konular: Makine Mühendisliği, Mechanical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2025
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Lisansüstü Eğitim Enstitüsü
- Ana Bilim Dalı: Makine Mühendisliği Ana Bilim Dalı
- Bilim Dalı: Makine Mühendisliği Bilim Dalı
- Sayfa Sayısı: 127
Özet
Tez kapsamında; pistonlu kompresörlerde emme hattı üzerinde yer alan susturucu geometrisinin verim parametrelerine, basınç salınımlarına ve valf hareketlerine olan etkisinin ortaya konulması amaçlanmıştır. Bu bağlamda, soğutkanın silindir hacmine girmeden önce geçtiği son kısım olan plenum borusunun çapı ve uzunluğu parametre olarak belirlenmiştir. Tezin ilk kısmında literatürde bulunan çalışmalar incelenmiştir. Literatür araştırması üç ana başlık altında incelenmiştir. İlk olarak susturucu geometrisinin performans parametrelerine etkisine yönelik çalışmalar irdelenmiştir. Ancak literatürde R600a soğutkanı ile buzdolabı kompresörleri gibi küçük boyutlu kompresörlerde gerçekleştirilen konuyu tüm yönleriyle ele alan kapsayıcı bir çalışmaya rastlanılamamıştır. Diğer iki başlıkta ise deneysel ve sayısal modelleme çalışmalarına ilişkin literatürde bulunan teknikler incelenmiştir. Tezin ikinci kısmında farklı geometrilere sahip susturucuların detaylı deneysel ölçümleri gerçekleştirilmiştir. Deneysel ölçümler kapsamında, silindir içerisine yerleştirilen basınç transdüseri ve krank üzerine yerleştirilen enkoder ile pV-indikatör diyagramları çıkarılmıştır. Böylelikle sıkıştırma işi hesaplanabilmiştir. Ayrıca emme plenumuna da basınç transdüseri yerleştirilerek basınç salınımları kayıt altına alınmıştır. Son olarak ise hem silindir hem de emme plenum basıncına bağlı olarak salınımlarını gerçekleştiren emme valfinin hareketlerini ölçmek için gerinim ölçer valfin bel bölgesine yerleştirilmiştir. Tüm deneysel çalışmalar kompresörün kontrollü şartlar altında çalışmasını sağlayan kalorimetre test düzeneği içerisinde gerçekleştirilmiş olup soğutma kapasitesi, güç tüketimi verileri ölçülmüştür. Elde edilen deney sonuçlarına ilişkin değerlendirmeler ve çıkarımlar paylaşılmıştır. Üçüncü bölümde ise sayısal modelleme çalışmalarına ağırlıklı olarak yer verilmiştir. Tez kapsamında kurulan sayısal modelde emme susturucusu ve egzoz hatlarında bir boyutlu akış kabulüyle modelleme gerçekleştirilmiştir. Akış patikası genel olarak hacim ve boru yaklaşımlarıyla modellenmiştir. Silindir hacmi ve susturucu hacimlerinde yığın (lumped) yaklaşımı kullanılmıştır. Emme ve egzoz valfleri için ise yay-kütle-sönümleyici yaklaşımı tercih edilmiştir. Deneysel çalışmalardan elde edilen katı yüzey sıcaklıkları sayısal modele girdi olarak verilmiş, katı yüzeyle ısı transferi hesaplamaları gerçekleştirilmiştir. Sayısal modelden elde edilen sonuçlar deneysel verilerle doğrulanmış ve sayısal modelin yetkinliği gösterilmiştir. Modelin doğrulanmasının ardından, deneysel çalışmada kullanılmış olan test noktaları genişletilerek daha detaylı incelemeler için sayısal sonuçlar elde edilmiştir. Bu sonuçlar ışığında yorumlamalar genişletilerek emme susturucu geometrisinin verim parametreleri üzerindeki etkileri detaylı bir şekilde irdelenmiştir.
Özet (Çeviri)
The energy consumption of household refrigerators constitutes a significant portion of residential electricity usage. Within refrigerators, the primary source of energy consumption is the compressor. Today, hermetic reciprocating compressors are widely used in conjunction with the refrigerant R600a. Considering that over two million refrigerators are sold annually in Turkey, the impact of compressors on energy consumption becomes more apparent. Therefore, improving compressor efficiency is one of the important research topics. In this context, the suction flow path within the compressor—an intersection of heat transfer, thermodynamics, fluid dynamics, and solid mechanics—has been examined in this dissertation. The main objective of this thesis is to investigate the effects of the suction muffler geometry, located along the suction line of reciprocating compressors, on performance parameters, pressure fluctuations, and valve motion. For this purpose, the diameter and length of the plenum pipe—the final section the refrigerant passes through before entering the cylinder—were defined as design parameters. The thesis is broadly structured into the following sections: a literature review, experimental investigations and the interpretation of their results, the development of a numerical model, the validation of this model with experimental data, and finally, extended analyses using the validated model. The literature review conducted in this study categorizes previous work into three main areas: numerical modelling, experimental studies, and research focused on muffler design. Particularly, it was observed that studies involving detailed parametric analyses of suction muffler geometry—specifically in compressors using R600a and having smaller internal geometries compared to other types—are limited. Therefore, a comprehensive evaluation of muffler geometry's impact on performance, under variables such as pressure pulsations, valve motion, and mass flow rate fluctuations, is expected to contribute meaningfully to the existing literature. Furthermore, existing numerical and experimental techniques were examined and utilized as references throughout this thesis. In the second part of the thesis, detailed experimental measurements were carried out using suction mufflers with different geometries. The diameter and length of the plenum pipe were varied, resulting in three different muffler designs referred to as types A, B, and C. When evaluated in terms of flow resistance, the resistance decreased progressively from type A to type C. In the experimental setup, pressure transducers placed inside the cylinder and an encoder mounted on the crankshaft were used to generate p-V indicator diagrams. The pressure transducer was calibrated for both hot and cold conditions using a pressure calibrator. The angular position data obtained from the encoder was converted to cylinder volume information using a kinematic equation based on the compressor's geometric properties. Encoder calibration was achieved by aligning the piston's top dead centre with the encoder's N-signal. This enabled the calculation of compression work as the area enclosed by the p-V diagram. Additionally, a pressure transducer was placed in the suction plenum to record pressure pulsations. The transducer was mounted at the exit of the plenum pipe, in line with the nominal flow direction, capturing the refrigerant's pressure just before it entered the cylinder. To measure the motion of the suction valve—affected by the pressures in both the cylinder and the plenum—a strain gauge was mounted on the central belt region of the valve. The strain gauge was calibrated by applying displacements to the point projected from the centre of the port on the valve, with corresponding calibration results recorded. All experimental tests were performed within a calorimeter test bench, which ensures the compressor operates under controlled conditions. Within this setup, cooling capacity and power consumption data were also measured. The calorimeter allowed precise control of evaporation and condensation pressures, superheating-subcooling values, and ambient temperatures. The p-V indicator diagram, plenum pressure measurements, and valve displacement recordings were all captured once steady-state conditions were achieved within the calorimeter. Experimental results indicated that the design of the suction muffler outlet pipe affected volumetric efficiency by up to 11% at 3000 rpm. At lower speeds, this effect was observed to decrease due to the reduction in mass flow rate. When transitioning from type A to type C muffler design, the normalized coefficient of performance was found to increase by 9.6% at 3000 rpm and by 2% at 1300 rpm. As compressor speed increases, pressure losses in both the suction and discharge phases increase the p-V diagram area, which in turn leads to a decrease in coefficient of performance. Furthermore, muffler design was observed to have a significant effect on both the opening and closing behavior of the suction valve and the pressure pulsations in the plenum. Fast Fourier Transform (FFT) analysis of suction valve displacement signals revealed that the outlet pipe design significantly influences the valve's operating frequency. As the geometry transitioned from type A to type C, the valve's frequency dropped from 384 Hz to 315 Hz. In contrast, compressor speed did not have a notable impact on the valve's operating frequency. To quantify the effect of valve motion on volumetric efficiency, time-based integrals of valve displacement were calculated and analysed in two categories: total and effective. It was observed that while mufflers with higher flow resistance led to higher total valve integrals, their effective valve integrals remained low. The third section of the thesis focused heavily on numerical modelling. A compressor model was developed using the GT-Suite® software and its component library. In the numerical model, one-dimensional flow assumptions were made for both the suction and discharge lines. The flow path was represented using pipe and volume elements. Lumped parameter modelling was applied for the cylinder and muffler volumes. For suction and discharge valves, a spring-mass-damper approach was used. Solid wall temperatures obtained from experiments were fed into the model to enable heat transfer calculations. Numerical results were first validated against experimental data. The maximum deviation between numerical and experimental results was calculated to be 4.8% for volumetric efficiency and 4.1% for normalized coefficient of performance. Valve motion and plenum pressure oscillations also showed good agreement between simulations and experiments. After validation, the numerical model was extended beyond the experimental test points for further analysis. First, while experimental studies considered four different speed values, the numerical model evaluated 36 different speeds at intervals of 100 rpm. Results showed that volumetric efficiency generally decreased with increasing compressor speed. This trend was further analysed using cylinder mass flow rate curves and valve motion data. Outlier points showing trends contrary to the general behaviour were examined in detail using mass flow rate, cylinder mass, and valve displacement curves to identify root causes. Increasing compressor speed shortens the suction phase. Although initial suction flow increases, the pressure drop caused by high-speed limits the time available for cylinder filling, which cannot be fully compensated. In the second part of the numerical study, two pipe diameters and lengths used in experiments were expanded to five lengths and six diameters. The results were analysed to evaluate how plenum pipe geometry influences performance metrics. Pressure loss in the plenum pipe was found to significantly affect volumetric efficiency, particularly at higher speeds where the time for pressure recovery becomes more critical. Based on 168 test points generated from the numerical model, a general linear model analysis showed that compressor speed accounted for approximately 75% of the variation in volumetric efficiency. The second most influential parameter was pipe diameter, contributing around 22%. The model's error margin was about 25%, which includes unquantifiable effects such as valve timing uncertainties.
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