Jet akışlı sistemlerde darbeli akışın yüzey temizleme performansına etkisinin incelenmesi
Investigation of the effect of pulsed flow on surface cleaning performance in jet flow systems
Yazar: MUTLU ELMAS
Danışman: PROF. DR. SEYHAN ONBAŞIOĞLU
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Makine Mühendisliği Ana Bilim Dalı / Isı-Akışkan Bilim Dalı
Derece: Yüksek Lisans, 2020
Konu: Makine Mühendisliği = Mechanical Engineering

Özet:
Ev tipi yıkayıcılarda temizleme işlemi müşteri memnuniyeti açısından büyük bir önem taşımaktadır. Bununla birlikte yıkayıcılarda temizleme performansına etki eden 4 ana parametre bulunmaktadır. Bunlar kimyasal etki, sıcaklık etkisi, mekanik etki ve zaman etkisidir. Bu parametrelerden birinde gerçekleştirilecek iyileşme diğer parametreler üzerinde değişiklik yapılmasına olanak tanır. Örneğin mekanik etkinin iyileştirilmesi ile termal etki düşürülebilir, enerji kazancı sağlanabilir.
Ev tipi yıkayıcılarda temizleme işlemi bir yıkama çözeltisinin kirli yüzeylere püskürtülmesiyle gerçekleşmektedir. Bu püskürtme işlemi bir jet akışı ile sağlanmaktadır. Jet akışı yüzeye ulaştığında sahip olduğu hızdan dolayı yüzeyde kayma gerilmesi oluşmaktadır. Oluşan kayma gerilmesi yardımıyla kirin kendi içerisindeki bağlar ve kir ile yüzey arasındaki bağlar kopartılarak kir yüzeyden uzaklaştırılmakta ve yüzey temizlenmektedir. Yıkayıcılarda bir pompa yardımıyla pervanelere su iletilmesiyle gerçeleşen bu jet akışı daimi akış olarak kabul edilmektedir.
Burada gerçekleştirilen yüksek lisans kapsamındaki çalışmalarda temizleme işlemine etki eden parametrelerden biri olan mekanik etki incelenmektedir. Yıkayıcılardaki pervane üzerinde bulunan nozullar yardımıyla gerçekleşen jet akışı buradaki çalışmalarda tek bir nozul geometrisi için simüle edilerek darbeli akışın yüzey temizleme performansı üzerindeki etkisi incelenmekte ve daimi akışla karşılaştırılmaktadır.
Yüksek lisans tez çalışması kapsamında seçilen konu ile ilgili çalışmaya başlama nedeni ve amacı belirtilerek bir giriş yapılmıştır. Bu çalışmalar kapsamında kir yapısı, yüzey kir ilişkisi, yüzey temizleme, jet akışının yapısı, darbeli akış konularında literatür araştırması yapılmıştır. Bu literatür araştırması özet haline getirilerek tezde sunulmuştur. Bununla birlikte endüstride kullanılan darbeli akış oluşturma yöntemleri ve ev tipi yıkayıcı kapsamında yapılan patent başvuruları incelenmiştir. Bu çalışmalar kapsamında tezde jet akışlı sistemlerde darbeli akışın farklı parametreler altında yüzey temizleme performansına etkisinin incelenmesine odaklanılmaya karar verilmiştir.
Literatür araştırmasının yanında kayma gerilmesinin zamana bağlı modellenebilmesi için teorik çalışmalar gerçekleştirilmiştir. Bu çalışmalar ışığında literatürde daha önce mevcut olan çarpan jetlerde zamandan bağımsız olarak elde edilebilen kayma gerilmesi formülasyonu darbeli akışın en önemli parametrelerinden biri olan frekans etkisini de içererek zamana bağlı olarak modellenmiştir. 
Literatür araştırması ve teorik çalışmalara ek olarak darbeli akışın yüzey temizleme performansı üzerindeki etkisinin incelenmesi amacıyla ev tipi yıkayıcılardaki pervaneler üzerinde bulunan tek bir nozulu simüle edecek bir deney düzeneği tasarımı gerçekleştirilerek deneysel çalışmalar yapılmıştır. Deney düzeneği kapalı bir hacim içerisinde yıkama sıvısının belirli bir süre içerisinde sirküle edilebileceği şekilde tasarlanmıştır. Deneysel çalışmalar kapsamında tek bir nozuldan kirli bir yüzeye yıkama çözeltisi belirlenen darbeli akış ve normal jet akışı parametrelerine uygun olarak püskürtülerek yüzeyin temizlenme performansı incelenmiştir.
Tüm çalışmaların sonunda deneysel çalışmaların sonuçları grafik haline getirilmiş, bu grafikler literatürden bulunan benzer çalışmaların sonuçlarıyla karşılaştırılarak yorumlanmıştır. Bu yorumlara ek olarak da çalışmalar ve sonuçlar ile ilgili değerlendirmeler ve öneriler paylaşılarak tez çalışması sonlandırılmıştır.

Abstract:
Washing which means cleaning process in domestic washers is very significant for customer satisfaction. There are 4 main parameters which affect the cleaning performance in domestic washers. These are chemical effect, thermal effect, mechanical effect and time. Improvement one of them make the cleaning more efficient and also allows changes to the other parameters. For example, with the improvement of mechanical efficiency, a reduction can be achieved in subjects such as energy consumption, wated water and time. However, increasing chemical effect, thermal effect and time have also some disadvantages. For instance, increasing chemical effect means more detergent and more waste water, increasing thermal efect means more energy consumption. Thus, for these reasons the motivation of this master thesis is improving mechanical effect.
In domestic washers, cleaning is done by spraying a washing solution to dirty loads. Spraying is performed by circulation system. This system includes closed cabin, sump, radial pump, pipe line and propeller. This spraying process is provided by a jet flow. This jet flow occurs with the delivery of water to the propellers by pump in washers cabin. Then, water comes out from the nozzles on the propeller with a velocity which provides shear stress neccessary to remove dirt from the loads. The characteristic curve of the pump which means work condition as flow rate and pressure, nozzle design affect the shear stress created by jet flow. This jet flow in domestic washers is considered as a steady flow. In steady flow, In a steady flow, the properties of the flow are time-independent and are considered to be constant.
In this master thesis the mechanical effect which is one of the parameters of affecting the cleaning process, is examined. The jet flow that occurs with the nozzles on the propeller in the domestic washers is examined in the studies here to simulate a single nozzle geometry, and the effect of the pulsed flow on the surface cleaning performance is compared to the steady flow.
Master thesis studies are started with an introduction has been made by specifying the reason, purpose of the work and brief information about domestic washers. Within the scope of these studies, a literature search started with cleaning process. After that the dirt structure and  surface dirt relationship was examined. In addition to these the jet flow structure was investigated detailly. Parameter of jet flow, jet flow regions, the effect of the conditions to the jet flow was explained detailly. Latly, the main subject of this master thesis as pulsed flow was examined. Pulsed flow types, parameters were explained. These literature researches is summarized and presented in the thesis. In addition to this, pulse flow methods used in industry as adding new components like pumps, structural design and algorithm are examined. Furthermore, the patent applications of domestic washer the companies about pulsed flow generation methods are searched. Lastly, the literature searced is completed and it was decided to focus on the study of the effect of pulsed flow on surface cleaning performance under different parameters in impinging jets.
In addition to the literature research, theoretical studies are carried out for modelling the shear stress based on time. In past studies, there is a formula for shear stress for impinging jets. However, this formulations are only about steady flow. The shear stress formulation for impinging jets is independent from the time in the impinging jets In theoretical studies, it is aimed to modeled the shear stress for impinging jets depending on time means frequency, which is one of the most important parameters of the pulsed flow. The absence of a study in the literature where frequency was added directly to the shear stress formulation increases the importance of modeling based on time. For this purpose, previous pulsed flow modeling studies the literature were examined and adapted for the conditions for this thesis. Two different methods were investigated and the more suitable for domestic washers are chosen. Then, our modeling was realized by adapting the conditions in the thesis.
In next studies  to examine the effect of pulsed flow on surface cleaning performance, experimental studies were carried out by designing a single nozzle on the propellers in domestic washers to simulate a single nozzle. The test setup is designed so that the washing liquid can be circulated within in a closed cabin was designed as transparent rectangle and created with plexiglass materieal. For the circulation system, radial pump which can work at different speeds, pipe line, a nozzle, water tank, heater, surface and surface holder were used. Moreoever, a solenoid valve was also used to create pulsed flow. In order to adjust the opening and closing times of the solenoid valve for setting the frequency of the pulses timer was connected to the circulation system. Ceramic plate is used as a surface and spinach is used as a dirt. Within the scope of experimental studies, the cleaning performance of the surface was investigated by spraying the washing solution from a single nozzle to a dirty surface in accordance with the determined pulsed flow and normal jet flow parameters. For different types of parameters were determined as flow rate, frequency, nozzle to surface distance and surface angle. In detail, 3 different flow rates, 3 different frequencies, 2 different nozzle to surface distances and 2 different surface angles are examined. Standard water for domestic washers was used as a cleaning solution and no chemical was added. The temperature of the water was kept constant as 35°C. Although there were 3 different frequencies, the total cleaning time was also kept constant for all experiments. Initially, 72 experiments were performed for 36 different scenarios, with the decision to make the experiments in 2 replicates. The cleaning performance was determined by comparing dirt on the plate before cleaning and dirt on the plate after cleaning. The dirt before and after cleaning on the plate were evaluated by image processing by using algorithm in Python. The results of the experimental studies were analyzed. In Minitab, the graphics of the parameter and their effects on the cleaning performance were created. The result and graphics were interpreted by proving the similar studies found in the literature. Additional experimental works were planned for not initially interpreted results of the effect of frequency. Thus, a total of 90 tests were performed with adding 18 extra experiments.
Finally, the thesis study was ended by sharing the interpretation of the result graphics. Evaluations about the results were made. The results were compared considering similarities and differences with previos studies. It was interpreted where these differences and similarities might originated. It is explained in this section what the interpretations of the graphics are based on, what is expected in the studies and what is obtained. In order to further enlighten the studies on this subject, the question of which studies can be done additionally was asked. Thus, suggestions were made for additional studies that could be done. At the end of all these, all the studies carried out within the scope of the master thesis were evaluated and the thesis was completed.